Medizinische Universität Graz Austria/Österreich - Forschungsportal - Medical University of Graz
Gewählte Publikation:
Schulz, E.
Discovering SEMA4A as a novel colorectal cancer predisposition gene
PhD-Studium (Doctor of Philosophy); Humanmedizin; [ Dissertation ] Graz Medical University; 2015. pp.96.
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- Autor*innen der Med Uni Graz:
- Schulz Eduard
- Betreuer*innen:
- Sill Heinz
- Zebisch Armin
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- Abstract:
- Background: Patients with familial colorectal cancer type X (FCRCX) fulfill clinical criteria of hereditary non-polyposis colorectal cancer (HNPCC) but lack detectable germline mutations in known cancer predisposition genes. This thesis aimed at elucidating the genetic background of this syndrome. Methods: In a large Austrian pedigree with FCRCX, linkage analysis, whole exome sequencing and Sanger re-sequencing was used for culprit mutation identification. All coding regions of the culprit gene were then screened in 53 FCRCX patients from Austria, Germany and the USA by direct sequencing and genotype frequencies were compared with 1138 Austrian non-cancer controls genotyped by 5'-exonuclease assay. To search for co-operating mutations, targeted deep sequencing of colorectal cancers (CRCs) from culprit variant carriers was performed. HCT 116 cells were transfected with wild-type and mutant cDNAs using Lipofectamine and effects on signaling pathways were examined by immunoblotting and on proliferation by 7-AAD/BrdU flow cytometric analysis. Results: The new p.Val78Met (c.232G>A) variant in SEMA4A was identified in the Austrian pedigree as a potential culprit mutation segregating with all CRCs and being associated with extracolorectal neoplasms. Screening of FCRCX patients led to the identification of two further variants (heterozygous p.Gly484Ala; homozygous p.Ser326Phe) and the SNP p.Pro682Ser in six of 48 (12.5%) German and Austrian individuals, respectively. Pro682Ser was highly associated with the FCRCX phenotype (prevalence of heterozygotes in controls 2.1% [24/1138], P=0.0009) and showed an increased risk for CRC (OR 6.79, 95% CI 2.63 to 17.52). Somatically acquired mutations in known CRC genes were identified in TP53, APC, KRAS and PIK3CA, respectively, as possible cooperating events in CRCs of SEMA4A V78M carriers. Compared with wild-type protein, SEMA4A V78M mutant demonstrated significantly higher activation of the mitogenic pathways MAPK/Erk and PI3K/Akt and increased proliferation in SEMA4A deficient HCT 116. Conclusion: Germline variants in SEMA4A predispose to FCRCX.