Colorectal Cancer, ATR

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Expand Collapse Colorectal Cancer  - General Description Colorectal Cancer (CRC) is cancer that initiates in the colon or rectum-the lower part of the digestive system in the body. During digestion, food moves through the stomach and small intestine into the colon. The colon absorbs water and nutrients from food, and stores waste matter (stool) that moves from the colon through the rectum before leaving the body.

Most CRC's and rectal cancers are adenocarcinomas, meaning that they originate in cells that make and release mucus and other fluids. CRC often begins as a growth called a polyp, which may form on the inner wall of the colon or rectum. Over time, some polyps become cancerous. This highlights the importance of colonoscopy screening to find and remove polyps before they become cancerous.

CRC is the fourth most common type of cancer diagnosed in the U.S. Deaths from CRC have decreased with the use of colonoscopies and fecal occult blood tests, which check for blood in the stool. Disparities in survival have been observed between African American and other populations. This may be due to factors such as access to colonoscopy screening, or to other factors not yet identified.

Because of its prevalence, scientists have studied CRC extensively, even creating models of how cancer develops using CRC as an example. There are also families with a very high incidence of CRC occurrence. When these families were studied, certain conditions that create instability in the whole genome were identified that predispose people to CRC. These include what is called the Chromosomal Instability pathway (CIN), as well as MicroSatellite Instability pathway (MSI). These can also occur as spontaneous (uninherited) conditions in some patients. Between 6-10% of CRC's are found to have MSI. Some CRC tumors have been found to have a lot of mutations, or as physicians call it, a "very high mutational load". Some also express a ligand called PD-L1.

These are now recognized features of some CRC's, and immunological treatments may be recommended in these cases. MGH has one of the most extensive Immuno-oncology clinical trials portfolios of any US hospital. Testing for features such as CIN, MSI, a high mutational burden, and the expression of PD-L1 can be conducted at the MGH genetics laboratory, as well as at other large academic centers. Genetic instability such as CIN or MSI lead to the activation of oncogenes such as KRAS, and the inactivation of tumor suppressors such as PTEN, both of which promote tumor growth.

Other genetic alterations in how the DNA in cells is organized have been found to contribute to CRC in families and individuals. These are called epigenetic changes. Normal DNA has methyl groups added in specific regions that regulate gene expression. When the genes that suppress growth-called tumor suppressors-are methylated abnormally, this prevents the production of tumor suppressor proteins important in controlling or stopping cell growth. When tumor suppressor genes are missing, unregulated growth occurs, contributing to the development of cancer. Some tumor suppressor proteins that are frequently inactivated in CRC are APC, TP53, or loss of one arm of chromosome 18 that contains a tumor suppressor.

The study of families with a high prevalence of CRC have lead scientists to discover genetic changes that contribute to the development of CRC in sporadic cases occurring in patients. Mutations in the genes encoding the following proteins have now been associated with subsets of CRC; ALK, AKT, APC, beta-catenin, BRCA1 and BRCA2, BRAF, EGFR, ERBB2 (HER2), ERBB3 (HER3), IDH2, KRAS, MET, NRAS, PI3K, ROS, PTEN, SMO,TP53, TRK 1, 2 and 3, and others that are still being identified. Information on these specific genes is available on this website if you select the gene you want to know more about.

Distinct familial syndromes of CRC such as Lynch syndrome have been studied in patients, leading to the identification of other mechanisms contributing to the development of cancer. Before a cell can divide into two daughter cells, DNA has to be replicated so both daughter cells will have a full complement of chromosomes. DNA replication requires an enzyme called DNA Polymerase. DNA Polymerase occasionally makes errors while it is replicating DNA. Cells therefore have a "proof-reading" process that detects mistakes when they occur during DNA replication. DNA Polymerase mistakes mean that incorrect nucleotides have been incorporated into the DNA, causing mutations. Mistakes in the DNA sequence are repaired in a process called mismatch repair (MMR).
MMR involves a complex of multiple proteins. In Lynch syndrome, one or more of the proteins involved in MMR is mutated, and the mistakes in the DNA do not get corrected. Mutations in MMR proteins are not only found in familial cases of CRC, but also in patients with sporadic (non-inherited) CRC. Defects in MMR also contribute to microsatellite instability (MIS), described above. The accumulation of these mutations can lead to cancer.

The importance of accurately replicating DNA following various types of mistakes or damage is reflected in the multiple pathways cells have for correcting or repairing broken DNA. Actual breaks in the DNA strands can happen due to exposure to radiation or other DNA damaging agents. In the case of the occurrence of breaks in DNA, there are also mechanisms for detecting these breaks. Double strand breaks (DSB's) in the DNA can be repaired via several mechanisms, including Non-Homologous End Joining (NHEJ) or Homologous Repair (HR). Many proteins are involved in DSB repair. Mutations in any of the many proteins involved in either of these repair pathways (see BRCA1 and BRCA2 genes) lead to damaged DNA, which results in DNA that is incorrectly replicated, causing mutations that contribute to the development of cancer. DNA repair machinery in the cell is important in keeping the genome stable and accurate.

Testing for the mutations and genomic conditions that contribute to the development or progression of CRC is available at MGH in the sophisticated CLIA certified genomic testing lab, and in other large Centers and some private testing companies used by physicians. Validated treatments, Immune therpies, as well as clinical trials investigating improved targeted and immunologic therapies are available to patients at MGH.

NIH/NCI Cancer Website www.cancer.gov 2017

Colorectal Cancer (CRC) is cancer that initiates in the colon or rectum-the lower part of the digestive system in the body. During digestion, food moves through the stomach and small intestine into the colon. The colon absorbs water and nutrients from food, and stores waste matter (stool) that moves from the colon through the rectum before leaving the body.

Most CRC's and rectal cancers are adenocarcinomas, meaning that they originate in cells that make and release mucus and other fluids. CRC often begins as a growth called a polyp, which may form on the inner wall of the colon or rectum. Over time, some polyps become cancerous. This highlights the importance of colonoscopy screening to find and remove polyps before they become cancerous.

CRC is the fourth most common type of cancer diagnosed in the U.S. Deaths from CRC have decreased with the use of colonoscopies and fecal occult blood tests, which check for blood in the stool. Disparities in survival have been observed between African American and other populations. This may be due to factors such as access to colonoscopy screening, or to other factors not yet identified.

Because of its prevalence, scientists have studied CRC extensively, even creating models of how cancer develops using CRC as an example. There are also families with a very high incidence of CRC occurrence. When these families were studied, certain conditions that create instability in the whole genome were identified that predispose people to CRC. These include what is called the Chromosomal Instability pathway (CIN), as well as MicroSatellite Instability pathway (MSI). These can also occur as spontaneous (uninherited) conditions in some patients. Between 6-10% of CRC's are found to have MSI. Some CRC tumors have been found to have a lot of mutations, or as physicians call it, a "very high mutational load". Some also express a ligand called PD-L1.

These are now recognized features of some CRC's, and immunological treatments may be recommended in these cases. MGH has one of the most extensive Immuno-oncology clinical trials portfolios of any US hospital. Testing for features such as CIN, MSI, a high mutational burden, and the expression of PD-L1 can be conducted at the MGH genetics laboratory, as well as at other large academic centers. Genetic instability such as CIN or MSI lead to the activation of oncogenes such as KRAS, and the inactivation of tumor suppressors such as PTEN, both of which promote tumor growth.

Other genetic alterations in how the DNA in cells is organized have been found to contribute to CRC in families and individuals. These are called epigenetic changes. Normal DNA has methyl groups added in specific regions that regulate gene expression. When the genes that suppress growth-called tumor suppressors-are methylated abnormally, this prevents the production of tumor suppressor proteins important in controlling or stopping cell growth. When tumor suppressor genes are missing, unregulated growth occurs, contributing to the development of cancer. Some tumor suppressor proteins that are frequently inactivated in CRC are APC, TP53, or loss of one arm of chromosome 18 that contains a tumor suppressor.

The study of families with a high prevalence of CRC have lead scientists to discover genetic changes that contribute to the development of CRC in sporadic cases occurring in patients. Mutations in the genes encoding the following proteins have now been associated with subsets of CRC; ALK, AKT, APC, beta-catenin, BRCA1 and BRCA2, BRAF, EGFR, ERBB2 (HER2), ERBB3 (HER3), IDH2, KRAS, MET, NRAS, PI3K, ROS, PTEN, SMO,TP53, TRK 1, 2 and 3, and others that are still being identified. Information on these specific genes is available on this website if you select the gene you want to know more about.

Distinct familial syndromes of CRC such as Lynch syndrome have been studied in patients, leading to the identification of other mechanisms contributing to the development of cancer. Before a cell can divide into two daughter cells, DNA has to be replicated so both daughter cells will have a full complement of chromosomes. DNA replication requires an enzyme called DNA Polymerase. DNA Polymerase occasionally makes errors while it is replicating DNA. Cells therefore have a "proof-reading" process that detects mistakes when they occur during DNA replication. DNA Polymerase mistakes mean that incorrect nucleotides have been incorporated into the DNA, causing mutations. Mistakes in the DNA sequence are repaired in a process called mismatch repair (MMR).
MMR involves a complex of multiple proteins. In Lynch syndrome, one or more of the proteins involved in MMR is mutated, and the mistakes in the DNA do not get corrected. Mutations in MMR proteins are not only found in familial cases of CRC, but also in patients with sporadic (non-inherited) CRC. Defects in MMR also contribute to microsatellite instability (MIS), described above. The accumulation of these mutations can lead to cancer.

The importance of accurately replicating DNA following various types of mistakes or damage is reflected in the multiple pathways cells have for correcting or repairing broken DNA. Actual breaks in the DNA strands can happen due to exposure to radiation or other DNA damaging agents. In the case of the occurrence of breaks in DNA, there are also mechanisms for detecting these breaks. Double strand breaks (DSB's) in the DNA can be repaired via several mechanisms, including Non-Homologous End Joining (NHEJ) or Homologous Repair (HR). Many proteins are involved in DSB repair. Mutations in any of the many proteins involved in either of these repair pathways (see BRCA1 and BRCA2 genes) lead to damaged DNA, which results in DNA that is incorrectly replicated, causing mutations that contribute to the development of cancer. DNA repair machinery in the cell is important in keeping the genome stable and accurate.

Testing for the mutations and genomic conditions that contribute to the development or progression of CRC is available at MGH in the sophisticated CLIA certified genomic testing lab, and in other large Centers and some private testing companies used by physicians. Validated treatments, Immune therpies, as well as clinical trials investigating improved targeted and immunologic therapies are available to patients at MGH.

NIH/NCI Cancer Website www.cancer.gov 2017

Colorectal Cancer (CRC) is cancer that initiates in the colon or rectum-the lower part of the digestive system in the body. During digestion, food moves through the stomach and small intestine into the colon. The colon absorbs water and nutrients from food, and stores waste matter (stool) that moves from the colon through the rectum before leaving the body.

Most CRC's and rectal cancers are adenocarcinomas, meaning that they originate in cells that make and release mucus and other fluids. CRC often begins as a growth called a polyp, which may form on the inner wall of the colon or rectum. Over time, some polyps become cancerous. This highlights the importance of colonoscopy screening to find and remove polyps before they become cancerous.

CRC is the fourth most common type of cancer diagnosed in the U.S. Deaths from CRC have decreased with the use of colonoscopies and fecal occult blood tests, which check for blood in the stool. Disparities in survival have been observed between African American and other populations. This may be due to factors such as access to colonoscopy screening, or to other factors not yet identified.

Because of its prevalence, scientists have studied CRC extensively, even creating models of how cancer develops using CRC as an example. There are also families with a very high incidence of CRC occurrence. When these families were studied, certain conditions that create instability in the whole genome were identified that predispose people to CRC. These include what is called the Chromosomal Instability pathway (CIN), as well as MicroSatellite Instability pathway (MSI). These can also occur as spontaneous (uninherited) conditions in some patients. Between 6-10% of CRC's are found to have MSI. Some CRC tumors have been found to have a lot of mutations, or as physicians call it, a "very high mutational load". Some also express a ligand called PD-L1.

These are now recognized features of some CRC's, and immunological treatments may be recommended in these cases. MGH has one of the most extensive Immuno-oncology clinical trials portfolios of any US hospital. Testing for features such as CIN, MSI, a high mutational burden, and the expression of PD-L1 can be conducted at the MGH genetics laboratory, as well as at other large academic centers. Genetic instability such as CIN or MSI lead to the activation of oncogenes such as KRAS, and the inactivation of tumor suppressors such as PTEN, both of which promote tumor growth.

Other genetic alterations in how the DNA in cells is organized have been found to contribute to CRC in families and individuals. These are called epigenetic changes. Normal DNA has methyl groups added in specific regions that regulate gene expression. When the genes that suppress growth-called tumor suppressors-are methylated abnormally, this prevents the production of tumor suppressor proteins important in controlling or stopping cell growth. When tumor suppressor genes are missing, unregulated growth occurs, contributing to the development of cancer. Some tumor suppressor proteins that are frequently inactivated in CRC are APC, TP53, or loss of one arm of chromosome 18 that contains a tumor suppressor.

The study of families with a high prevalence of CRC have lead scientists to discover genetic changes that contribute to the development of CRC in sporadic cases occurring in patients. Mutations in the genes encoding the following proteins have now been associated with subsets of CRC; ALK, AKT, APC, beta-catenin, BRCA1 and BRCA2, BRAF, EGFR, ERBB2 (HER2), ERBB3 (HER3), IDH2, KRAS, MET, NRAS, PI3K, ROS, PTEN, SMO,TP53, TRK 1, 2 and 3, and others that are still being identified. Information on these specific genes is available on this website if you select the gene you want to know more about.

Distinct familial syndromes of CRC such as Lynch syndrome have been studied in patients, leading to the identification of other mechanisms contributing to the development of cancer. Before a cell can divide into two daughter cells, DNA has to be replicated so both daughter cells will have a full complement of chromosomes. DNA replication requires an enzyme called DNA Polymerase. DNA Polymerase occasionally makes errors while it is replicating DNA. Cells therefore have a "proof-reading" process that detects mistakes when they occur during DNA replication. DNA Polymerase mistakes mean that incorrect nucleotides have been incorporated into the DNA, causing mutations. Mistakes in the DNA sequence are repaired in a process called mismatch repair (MMR).
MMR involves a complex of multiple proteins. In Lynch syndrome, one or more of the proteins involved in MMR is mutated, and the mistakes in the DNA do not get corrected. Mutations in MMR proteins are not only found in familial cases of CRC, but also in patients with sporadic (non-inherited) CRC. Defects in MMR also contribute to microsatellite instability (MIS), described above. The accumulation of these mutations can lead to cancer.

The importance of accurately replicating DNA following various types of mistakes or damage is reflected in the multiple pathways cells have for correcting or repairing broken DNA. Actual breaks in the DNA strands can happen due to exposure to radiation or other DNA damaging agents. In the case of the occurrence of breaks in DNA, there are also mechanisms for detecting these breaks. Double strand breaks (DSB's) in the DNA can be repaired via several mechanisms, including Non-Homologous End Joining (NHEJ) or Homologous Repair (HR). Many proteins are involved in DSB repair. Mutations in any of the many proteins involved in either of these repair pathways (see BRCA1 and BRCA2 genes) lead to damaged DNA, which results in DNA that is incorrectly replicated, causing mutations that contribute to the development of cancer. DNA repair machinery in the cell is important in keeping the genome stable and accurate.

Testing for the mutations and genomic conditions that contribute to the development or progression of CRC is available at MGH in the sophisticated CLIA certified genomic testing lab, and in other large Centers and some private testing companies used by physicians. Validated treatments, Immune therpies, as well as clinical trials investigating improved targeted and immunologic therapies are available to patients at MGH.

NIH/NCI Cancer Website www.cancer.gov 2017

Colorectal Cancer (CRC) is cancer that initiates in the colon or rectum-the lower part of the digestive system in the body. During digestion, food moves through the stomach and small intestine into the colon. The colon absorbs water and nutrients from food, and stores waste matter (stool) that moves from the colon through the rectum before leaving the body.

Most CRC's and rectal cancers are adenocarcinomas, meaning that they originate in cells that make and release mucus and other fluids. CRC often begins as a growth called a polyp, which may form on the inner wall of the colon or rectum. Over time, some polyps become cancerous. This highlights the importance of colonoscopy screening to find and remove polyps before they become cancerous.

CRC is the fourth most common type of cancer diagnosed in the U.S. Deaths from CRC have decreased with the use of colonoscopies and fecal occult blood tests, which check for blood in the stool. Disparities in survival have been observed between African American and other populations. This may be due to factors such as access to colonoscopy screening, or to other factors not yet identified.

Because of its prevalence, scientists have studied CRC extensively, even creating models of how cancer develops using CRC as an example. There are also families with a very high incidence of CRC occurrence. When these families were studied, certain conditions that create instability in the whole genome were identified that predispose people to CRC. These include what is called the Chromosomal Instability pathway (CIN), as well as MicroSatellite Instability pathway (MSI). These can also occur as spontaneous (uninherited) conditions in some patients. Between 6-10% of CRC's are found to have MSI. Some CRC tumors have been found to have a lot of mutations, or as physicians call it, a "very high mutational load". Some also express a ligand called PD-L1.

These are now recognized features of some CRC's, and immunological treatments may be recommended in these cases. MGH has one of the most extensive Immuno-oncology clinical trials portfolios of any US hospital. Testing for features such as CIN, MSI, a high mutational burden, and the expression of PD-L1 can be conducted at the MGH genetics laboratory, as well as at other large academic centers. Genetic instability such as CIN or MSI lead to the activation of oncogenes such as KRAS, and the inactivation of tumor suppressors such as PTEN, both of which promote tumor growth.

Other genetic alterations in how the DNA in cells is organized have been found to contribute to CRC in families and individuals. These are called epigenetic changes. Normal DNA has methyl groups added in specific regions that regulate gene expression. When the genes that suppress growth-called tumor suppressors-are methylated abnormally, this prevents the production of tumor suppressor proteins important in controlling or stopping cell growth. When tumor suppressor genes are missing, unregulated growth occurs, contributing to the development of cancer. Some tumor suppressor proteins that are frequently inactivated in CRC are APC, TP53, or loss of one arm of chromosome 18 that contains a tumor suppressor.

The study of families with a high prevalence of CRC have lead scientists to discover genetic changes that contribute to the development of CRC in sporadic cases occurring in patients. Mutations in the genes encoding the following proteins have now been associated with subsets of CRC; ALK, AKT, APC, beta-catenin, BRCA1 and BRCA2, BRAF, EGFR, ERBB2 (HER2), ERBB3 (HER3), IDH2, KRAS, MET, NRAS, PI3K, ROS, PTEN, SMO,TP53, TRK 1, 2 and 3, and others that are still being identified. Information on these specific genes is available on this website if you select the gene you want to know more about.

Distinct familial syndromes of CRC such as Lynch syndrome have been studied in patients, leading to the identification of other mechanisms contributing to the development of cancer. Before a cell can divide into two daughter cells, DNA has to be replicated so both daughter cells will have a full complement of chromosomes. DNA replication requires an enzyme called DNA Polymerase. DNA Polymerase occasionally makes errors while it is replicating DNA. Cells therefore have a "proof-reading" process that detects mistakes when they occur during DNA replication. DNA Polymerase mistakes mean that incorrect nucleotides have been incorporated into the DNA, causing mutations. Mistakes in the DNA sequence are repaired in a process called mismatch repair (MMR).
MMR involves a complex of multiple proteins. In Lynch syndrome, one or more of the proteins involved in MMR is mutated, and the mistakes in the DNA do not get corrected. Mutations in MMR proteins are not only found in familial cases of CRC, but also in patients with sporadic (non-inherited) CRC. Defects in MMR also contribute to microsatellite instability (MIS), described above. The accumulation of these mutations can lead to cancer.

The importance of accurately replicating DNA following various types of mistakes or damage is reflected in the multiple pathways cells have for correcting or repairing broken DNA. Actual breaks in the DNA strands can happen due to exposure to radiation or other DNA damaging agents. In the case of the occurrence of breaks in DNA, there are also mechanisms for detecting these breaks. Double strand breaks (DSB's) in the DNA can be repaired via several mechanisms, including Non-Homologous End Joining (NHEJ) or Homologous Repair (HR). Many proteins are involved in DSB repair. Mutations in any of the many proteins involved in either of these repair pathways (see BRCA1 and BRCA2 genes) lead to damaged DNA, which results in DNA that is incorrectly replicated, causing mutations that contribute to the development of cancer. DNA repair machinery in the cell is important in keeping the genome stable and accurate.

Testing for the mutations and genomic conditions that contribute to the development or progression of CRC is available at MGH in the sophisticated CLIA certified genomic testing lab, and in other large Centers and some private testing companies used by physicians. Validated treatments, Immune therpies, as well as clinical trials investigating improved targeted and immunologic therapies are available to patients at MGH.

NIH/NCI Cancer Website www.cancer.gov 2017

PubMed ID's
2188735, 23897299, 20965415
Expand Collapse ATR  - General Description
CLICK IMAGE FOR MORE INFORMATION
The protein encoded by ATR is a serine/threonine kinase and DNA damage sensor, activating cell cycle checkpoint signaling and causing a pause in the cell cycle following DNA replication stress or damage. The activated protein can phosphorylate and activate several important proteins that are involved in the inhibition of DNA replication and cell division, which are critical for DNA repair.

The maintenance of intact, correctly sequenced DNA is vital to the life of a cell. If there are mistakes made in replicating DNA before cell division, subsequent daughter cells will have inaccurate or damaged DNA, and may either die or carry mutations that can contribute to the development of cancer. For this reason, cells have evolved multiple pathways to repair mistakes in-or damage to- DNA. The specific repair pathway used by the cell depends on the type of DNA damage that has occurred. The types of DNA repair that we are focusing on relate directly to cancer. These involve a break in BOTH strands of DNA, which can be the result of ionizing radiation or other DNA damaging agents. This type of DNA damage is called Double Strand Breaks (DSB's). There are two main pathways used by cells to repair DSB's in DNA, one is Homologous Recombination (HR), the other is Non-Homologous End Joining (NHEJ). This page of our website focuses on the HR pathway (there is a separate web page for NHEJ repair if you select PKcs from the gene list when you sign on to this page).

Many proteins are involved in the complex HR pathway to repair DSB's in DNA. There is a graphic above that depicts the HR pathway (if you click on the graphic, it will enlarge and become a bit easier to follow). While complicated, the DSB at the top right of the graphic is acted upon by a series of proteins in the circle of steps shown that ultimately lead to the complete and accurate repair of the DSB in the DNA.

Some of the proteins involved in the HR DSB repair pathway are MRE11, NBS1, RAD50. These three proteins make up the MRN complex. This complex detects DSB's in the DNA. Once the DSB is found by the MRN complex, the MRN complex functions with BRCA1 and CtIP to resect the DSB’s to form single stranded DNA “tails”. Meanwhile, DSB's also activate the ATM protein, which in turn acts upon CHK2 to activate it, as well as directly activating the tumor suppressor TP53. TP53 can cause cell cycle delay, giving the cell time to repair DNA breaks or mistakes before the cell cycle leading to division resumes. In the next step, RPA binds to the single stranded DNA "tails" that have been created by BRCA1 and CtIP in conjunction with the MRN. The binding of RPA activates another protein called ATR. ATR has many important functions, including activating CHK1, which can cause cell cycle delay giving cells time to repair DNA. ATR also regulates BRCA1 which recruits a bound group of proteins including PALB2/BRCA2/RAD51. In the next step, RAD51 displaces the RPA that is on the single stranded DNA, with the involvement of BRCA2/PALB2 and RAD51c. BRCA1/BARD1 helps RAD51 coated single stranded DNA invade double stranded DNA with homologous sequences to form a DNA repair loop. With the help of DNA polymerases, the repair loop creates the opportunity to use the intact homologous DNA as a template to correctly repair DSB’s. Enzymes called ligases reconnect the ends of the DNA, leading to complete and accurate repair of the DSB in DNA.

After studying familial cancer syndromes, germline or inherited BRCA1 and BRCA2 were identified a while ago as proteins that when altered by mutation, cause certain cancers. Some BRCA1 and BRCA2 genes become mutated somatically, meaning in a non-inherited way. When either gene is mutated, the resulting protein cannot perform its role in DNA repair correctly. This turns out to be true for other proteins in the HR pathway as well. Recently, scientists have found mutations in many of the other genes that encode the proteins involved in the HR pathway. Mutations in HR pathway members include MRE11, NBS1, RAD50, ATM, CHK2, BRCA1, PALB2, RAD51, BRCA2, BARD1, and RAD51c (these are depicted in red in the above graphic). This remarkable number of mutations in proteins involved in the DNA repair pathway found in cancer highlights how important the HR DSB DNA repair pathway is in cells. The mutations in HR pathway proteins result in proteins that do not function properly in their role in DNA repair. Without proper function of the proteins involved in DNA repair, DNA mistakes or breaks are not properly repaired, and the damaged DNA contributes to the development of cancer.

ATR is only rarely mutated in cancer, however, the frequent mutations in ATM result in cells that are completely reliant on the ATR pathway to repair DSB's in the DNA. This has therapeutic implications for treatment of tumors that have mutations in the HR DNA repair pathway.

Testing for mutations in the many genes/proteins involved in DNA repair discussed above is available in the MGH genetics lab. Treatment as well as clinical trials studying new drugs that target defects in these proteins-including ATR- are available at the MGH Cancer Center.

The protein encoded by ATR is a serine/threonine kinase and DNA damage sensor, activating cell cycle checkpoint signaling and causing a pause in the cell cycle following DNA replication stress or damage. The activated protein can phosphorylate and activate several important proteins that are involved in the inhibition of DNA replication and cell division, which are critical for DNA repair.

The maintenance of intact, correctly sequenced DNA is vital to the life of a cell. If there are mistakes made in replicating DNA before cell division, subsequent daughter cells will have inaccurate or damaged DNA, and may either die or carry mutations that can contribute to the development of cancer. For this reason, cells have evolved multiple pathways to repair mistakes in-or damage to- DNA. The specific repair pathway used by the cell depends on the type of DNA damage that has occurred. The types of DNA repair that we are focusing on relate directly to cancer. These involve a break in BOTH strands of DNA, which can be the result of ionizing radiation or other DNA damaging agents. This type of DNA damage is called Double Strand Breaks (DSB's). There are two main pathways used by cells to repair DSB's in DNA, one is Homologous Recombination (HR), the other is Non-Homologous End Joining (NHEJ). This page of our website focuses on the HR pathway (there is a separate web page for NHEJ repair if you select PKcs from the gene list when you sign on to this page).

Many proteins are involved in the complex HR pathway to repair DSB's in DNA. There is a graphic above that depicts the HR pathway (if you click on the graphic, it will enlarge and become a bit easier to follow). While complicated, the DSB at the top right of the graphic is acted upon by a series of proteins in the circle of steps shown that ultimately lead to the complete and accurate repair of the DSB in the DNA.

Some of the proteins involved in the HR DSB repair pathway are MRE11, NBS1, RAD50. These three proteins make up the MRN complex. This complex detects DSB's in the DNA. Once the DSB is found by the MRN complex, the MRN complex functions with BRCA1 and CtIP to resect the DSB’s to form single stranded DNA “tails”. Meanwhile, DSB's also activate the ATM protein, which in turn acts upon CHK2 to activate it, as well as directly activating the tumor suppressor TP53. TP53 can cause cell cycle delay, giving the cell time to repair DNA breaks or mistakes before the cell cycle leading to division resumes. In the next step, RPA binds to the single stranded DNA "tails" that have been created by BRCA1 and CtIP in conjunction with the MRN. The binding of RPA activates another protein called ATR. ATR has many important functions, including activating CHK1, which can cause cell cycle delay giving cells time to repair DNA. ATR also regulates BRCA1 which recruits a bound group of proteins including PALB2/BRCA2/RAD51. In the next step, RAD51 displaces the RPA that is on the single stranded DNA, with the involvement of BRCA2/PALB2 and RAD51c. BRCA1/BARD1 helps RAD51 coated single stranded DNA invade double stranded DNA with homologous sequences to form a DNA repair loop. With the help of DNA polymerases, the repair loop creates the opportunity to use the intact homologous DNA as a template to correctly repair DSB’s. Enzymes called ligases reconnect the ends of the DNA, leading to complete and accurate repair of the DSB in DNA.

After studying familial cancer syndromes, germline or inherited BRCA1 and BRCA2 were identified a while ago as proteins that when altered by mutation, cause certain cancers. Some BRCA1 and BRCA2 genes become mutated somatically, meaning in a non-inherited way. When either gene is mutated, the resulting protein cannot perform its role in DNA repair correctly. This turns out to be true for other proteins in the HR pathway as well. Recently, scientists have found mutations in many of the other genes that encode the proteins involved in the HR pathway. Mutations in HR pathway members include MRE11, NBS1, RAD50, ATM, CHK2, BRCA1, PALB2, RAD51, BRCA2, BARD1, and RAD51c (these are depicted in red in the above graphic). This remarkable number of mutations in proteins involved in the DNA repair pathway found in cancer highlights how important the HR DSB DNA repair pathway is in cells. The mutations in HR pathway proteins result in proteins that do not function properly in their role in DNA repair. Without proper function of the proteins involved in DNA repair, DNA mistakes or breaks are not properly repaired, and the damaged DNA contributes to the development of cancer.

ATR is only rarely mutated in cancer, however, the frequent mutations in ATM result in cells that are completely reliant on the ATR pathway to repair DSB's in the DNA. This has therapeutic implications for treatment of tumors that have mutations in the HR DNA repair pathway.

Testing for mutations in the many genes/proteins involved in DNA repair discussed above is available in the MGH genetics lab. Treatment as well as clinical trials studying new drugs that target defects in these proteins-including ATR- are available at the MGH Cancer Center.



PubMed ID's
27617969, 24003211, PMC2988877
Expand Collapse ATR  in Colorectal Cancer
Alterations in the gene encoding ATR are not found in colorectal cancers. ATR is an important protein in the DNA repair pathway. ATR controls a signaling pathway in the cell by activating CHK1, which causes a delay in the cell cycle (see graphic above). Without this delay, cells would not have time to repair broken or damaged DNA. The accumulation of damaged DNA in the cell can lead to cancer.

ATR has become an important protein to inhibit with drugs in cancer. Cancer cells often have genetic alterations in other proteins in the DNA repair pathway (see red proteins in graphic above). If the ATM protein is mutated and unable to cause cell cycle arrest for DNA repair, then ATR is the only option for cancer cells to use to delay the cell cycle and repair DNA. Drugs targeting ATR block this pathway, leaving cancer cells no way to pause the cell cycle to achieve DNA repair. The tumor cells die as the result of accumulated damaged or broken DNA.

Alterations in the gene encoding ATR are not found in colorectal cancers. ATR is an important protein in the DNA repair pathway. ATR controls a signaling pathway in the cell by activating CHK1, which causes a delay in the cell cycle (see graphic above). Without this delay, cells would not have time to repair broken or damaged DNA. The accumulation of damaged DNA in the cell can lead to cancer.

ATR has become an important protein to inhibit with drugs in cancer. Cancer cells often have genetic alterations in other proteins in the DNA repair pathway (see red proteins in graphic above). If the ATM protein is mutated and unable to cause cell cycle arrest for DNA repair, then ATR is the only option for cancer cells to use to delay the cell cycle and repair DNA. Drugs targeting ATR block this pathway, leaving cancer cells no way to pause the cell cycle to achieve DNA repair. The tumor cells die as the result of accumulated damaged or broken DNA.

Expand Collapse No mutation selected
The mutation of a gene provides clinicians with a very detailed look at your cancer. Knowing this information could change the course of your care. To learn how you can find out more about genetic testing please visit http://www.massgeneral.org/cancer/news/faq.aspx or contact the Cancer Center.
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Protocol # Title Location Status Match
NCT03192345 A First-in-human Study of the Safety, Pharmacokinetics, Pharmacodynamics and Anti-tumor Activity of SAR439459 Monotherapy and Combination of SAR439459 and REGN2810 in Patients With Advanced Solid Tumors A First-in-human Study of the Safety, Pharmacokinetics, Pharmacodynamics and Anti-tumor Activity of SAR439459 Monotherapy and Combination of SAR439459 and REGN2810 in Patients With Advanced Solid Tumors MGH Open D
NCT02715284 A Phase 1 Dose Escalation and Cohort Expansion Study of TSR-042, an Anti-PD-1 Monoclonal Antibody, in Patients With Advanced Solid Tumors A Phase 1 Dose Escalation and Cohort Expansion Study of TSR-042, an Anti-PD-1 Monoclonal Antibody, in Patients With Advanced Solid Tumors MGH Open D
NCT02817633 A Phase 1 Study of TSR-022, an Anti-TIM-3 Monoclonal Antibody, in Patients With Advanced Solid Tumors A Phase 1 Study of TSR-022, an Anti-TIM-3 Monoclonal Antibody, in Patients With Advanced Solid Tumors MGH Open D
NCT03144804 A Phase 2 Study of Lamivudine in Patients With p53 Mutant Metastatic Colorectal Cancer A Phase 2 Study of Lamivudine in Patients With p53 Mutant Metastatic Colorectal Cancer MGH Open D
NCT01714739 A Study of an Anti-KIR Antibody Lirilumab in Combination With an Anti-PD1 Antibody Nivolumab and Nivolumab Plus an Anti-CTLA-4 Ipilimumab Antibody in Patients With Advanced Solid Tumors A Study of an Anti-KIR Antibody Lirilumab in Combination With an Anti-PD1 Antibody Nivolumab and Nivolumab Plus an Anti-CTLA-4 Ipilimumab Antibody in Patients With Advanced Solid Tumors MGH Open D
NCT02880371 A Study of ARRY-382 in Combination With Pembrolizumab for the Treatment of Patients With Advanced Solid Tumors A Study of ARRY-382 in Combination With Pembrolizumab for the Treatment of Patients With Advanced Solid Tumors MGH Open D
NCT02467361 A Study of BBI608 Administered in Combination With Immune Checkpoint Inhibitors in Adult Patients With Advanced Cancers A Study of BBI608 Administered in Combination With Immune Checkpoint Inhibitors in Adult Patients With Advanced Cancers MGH Open D
NCT01351103 A Study of LGK974 in Patients With Malignancies Dependent on Wnt Ligands A Study of LGK974 in Patients With Malignancies Dependent on Wnt Ligands MGH Open D
NCT02857270 A Study of LY3214996 Administered Alone or in Combination With Other Agents in Participants With Advanced/Metastatic Cancer A Study of LY3214996 Administered Alone or in Combination With Other Agents in Participants With Advanced/Metastatic Cancer MGH Open D
NCT02327169 A Study of MLN2480 in Combination With MLN0128 or Alisertib, or Paclitaxel, or Cetuximab, or Irinotecan in Adult Participants With Advanced Nonhematologic Malignancies A Study of MLN2480 in Combination With MLN0128 or Alisertib, or Paclitaxel, or Cetuximab, or Irinotecan in Adult Participants With Advanced Nonhematologic Malignancies MGH Open D
Trial Status: Showing Results: 1-10 of 38 Per Page:
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