Biochemical effects of inherited MMR gene mutations and diet on colon cancer risk

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http://urn.fi/URN:ISBN:978-951-51-0223-2
Titel: Biochemical effects of inherited MMR gene mutations and diet on colon cancer risk
Författare: Dermadi Bebek, Denis
Medarbetare: Helsingfors universitet, bio- och miljövetenskapliga fakulteten, biovetenskapliga institutionen
Utgivare: Helsingin yliopisto
Datum: 2014-10-31
Språk: en
Tillhör serie: URN:ISSN:2342-317X
Permanenta länken (URI): http://urn.fi/URN:ISBN:978-951-51-0223-2
http://hdl.handle.net/10138/136151
Nivå: Doktorsavhandling (sammanläggning)
Abstrakt: Colorectal cancer (CRC) is one of the leading causes of death in developed countries. Although, a small fraction of cancers are caused by inherited genetic predisposition most of the CRCs are sporadic. In CRC, cancer risk is associated with lifestyle factors and aging. Even in dominantly inherited CRC predisposition such as in Lynch syndrome (LS), which is linked to germline mu- tations in the mismatch repair (MMR) genes MLH1, MSH2, MSH6 and PMS2, cancer develops as a result of accumulation of genetic and epigenetic changes. After diagnosing an LS family, to be able to offer contiguous pre-symptomatic surveillance and predictive gene counseling to mutation carriers in a family, the pathogenicity assessment of a mutation is needed. Dependent on the type and the site of a germline mutation, inherited cancer risk may vary from high to low and especially in the latter case cancer risk may be strongly affected by lifestyle factors such as diet. Epidemiological studies on humans and previous studies on mice have shown that especially a Western-style diet (WD) may predispose colon mucosa to CRC. However, the mechanisms, which mediate the effects of diet on tumorigenesis are largely unknown. Since both genetic and lifestyle factors have been shown to predispose to cancer, this the- sis analyzed biochemical defects caused by inherited MMR gene mutations and Western diet exposure. Different MMR gene mutations may compromise MMR function through various biochemical defects. Here, we studied 18 inherited non-truncating mutations in MSH2, the second most frequently mutated gene among Lynch syndrome patients. We assessed protein stability, DNA binding, and ATP mediated DNA release abilities of the MSH2 variants. The majority of variants in the amino terminal region including the connector and lever domains p.V161D, p.G162R, p.G164R, p.L173P, p.L187P, p.C333Y, p.D603N) affected protein stabil- ity. Variations in the ATPase domain (p.A636P, p.G674A, p.C697F, p.I745-I746del, p.E749K) totally abolished either mismatch binding or release. Four protein variants (p.T33P, p.A272 V, p.G322D, p.V923E) expressed slightly reduced mismatch binding and/or release efficiencies compared to wild-type (WT) MSH2 protein, while two variants (p.N127S, p.A834T) were in- distinguishable from WT. To define the effects of Western-style diet, we analyzed protein expression changes in histolog- ically normal colon mucosa of wild type (Mlh1+/+) and CRC predisposed mice (Mlh1+/-) after a long-term feeding experiment with WD and AIN-93G control diet. Using network analysis and data mining we also determined which of the affected proteins might be putative play- ers in early CRC development. Our results pinpoint changes in a complex protein interaction network involved in ATP synthesis coupled proton transport, oxidoreduction coenzyme and nicotinamide nucleotide metabolic processes, which are important in the generation of reactive oxygen species (ROS) and cellular protection against ROS toxicity. Additionally, we detected SELENBP1 and LGALS4, which are implied in neoplastic processes. Our studies show that mutations in the MMR gene affect the biochemistry of MMR, can have an effect on the phenotype of the mutation carriers and in the latest study suggest that the high sensitivity to Western diet may be linked to haplo-insufficiency caused by a loss of function mutation in the Mlh1+/- mice.Colorectal cancer (CRC) is one of the leading causes of death in developed countries. Although, a small fraction of cancers are caused by inherited genetic predisposition most of the CRCs are sporadic. In CRC, cancer risk is associated with lifestyle factors and aging. Even in dominantly inherited CRC predisposition such as in Lynch syndrome (LS), which is linked to germline mu- tations in the mismatch repair (MMR) genes MLH1, MSH2, MSH6 and PMS2, cancer develops as a result of accumulation of genetic and epigenetic changes. After diagnosing an LS family, to be able to offer contiguous pre-symptomatic surveillance and predictive gene counseling to mutation carriers in a family, the pathogenicity assessment of a mutation is needed. Dependent on the type and the site of a germline mutation, inherited cancer risk may vary from high to low and especially in the latter case cancer risk may be strongly affected by lifestyle factors such as diet. Epidemiological studies on humans and previous studies on mice have shown that especially a Western-style diet (WD) may predispose colon mucosa to CRC. However, the mechanisms, which mediate the effects of diet on tumorigenesis are largely unknown. Since both genetic and lifestyle factors have been shown to predispose to cancer, this the- sis analyzed biochemical defects caused by inherited MMR gene mutations and Western diet exposure. Different MMR gene mutations may compromise MMR function through various biochemical defects. Here, we studied 18 inherited non-truncating mutations in MSH2, the second most frequently mutated gene among Lynch syndrome patients. We assessed protein stability, DNA binding, and ATP mediated DNA release abilities of the MSH2 variants. The majority of variants in the amino terminal region including the connector and lever domains p.V161D, p.G162R, p.G164R, p.L173P, p.L187P, p.C333Y, p.D603N) affected protein stabil- ity. Variations in the ATPase domain (p.A636P, p.G674A, p.C697F, p.I745-I746del, p.E749K) totally abolished either mismatch binding or release. Four protein variants (p.T33P, p.A272 V, p.G322D, p.V923E) expressed slightly reduced mismatch binding and/or release efficiencies compared to wild-type (WT) MSH2 protein, while two variants (p.N127S, p.A834T) were in- distinguishable from WT. To define the effects of Western-style diet, we analyzed protein expression changes in histolog- ically normal colon mucosa of wild type (Mlh1+/+) and CRC predisposed mice (Mlh1+/-) after a long-term feeding experiment with WD and AIN-93G control diet. Using network analysis and data mining we also determined which of the affected proteins might be putative play- ers in early CRC development. Our results pinpoint changes in a complex protein interaction network involved in ATP synthesis coupled proton transport, oxidoreduction coenzyme and nicotinamide nucleotide metabolic processes, which are important in the generation of reactive oxygen species (ROS) and cellular protection against ROS toxicity. Additionally, we detected SELENBP1 and LGALS4, which are implied in neoplastic processes. Our studies show that mutations in the MMR gene affect the biochemistry of MMR, can have an effect on the phenotype of the mutation carriers and in the latest study suggest that the high sensitivity to Western diet may be linked to haplo-insufficiency caused by a loss of function mutation in the Mlh1+/- mice.
Subject: genetics
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