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Replication error deficient (RER+) colorectal cancers are a distinct subset of colorectal cancers, characterized by inactivation of the DNA mismatch repair system. These cancers are typically pseudodiploid, accumulate mutations in repetitive sequences as a result of their mismatch repair deficiency, and have distinct pathologies. Regulatory sequences controlling all aspects of mRNA processing, especially including message stability, are found in the 3'UTR sequence of most genes. The relevant sequences are typically A/U-rich elements or U repeats. Microarray analysis of 14 RER+ (deficient) and 16 RER- (proficient) colorectal cancer cell lines confirms a striking difference in expression profiles. Analysis of the incidence of mononucleotide repeat sequences in the 3'UTRs, 5'UTRs, and coding sequences of those genes most differentially expressed in RER+ versus RER- cell lines has shown that much of this differential expression can be explained by the occurrence of a massive enrichment of genes with 3'UTR T repeats longer than 11 base pairs in the most differentially expressed genes. This enrichment was confirmed by analysis of two published consensus sets of RER differentially expressed probesets for a large number of primary colorectal cancers. Sequence analysis of the 3'UTRs of a selection of the most differentially expressed genes shows that they all contain deletions in these repeats in all RER+ cell lines studied. These data strongly imply that deregulation of mRNA stability through accumulation of mutations in repetitive regulatory 3'UTR sequences underlies the striking difference in expression profiles between RER+ and RER- colorectal cancers. doi/ 10.1073/pnas.1015604107

De novo point mutations arise predominantly in the male germline and increase in frequency with age, but it has not previously been possible to locate specific, identifiable mutations directly within the seminiferous tubules of human testes. Using microdissection of tubules exhibiting altered expression of the spermatogonial markers MAGEA4, FGFR3, and phospho-AKT, whole genome amplification, and DNA sequencing, we establish an in situ strategy for discovery and analysis of pathogenic de novo mutations. In 14 testes from men aged 39-90 y, we identified 11 distinct gain-of-function mutations in five genes (fibroblast growth factor receptors FGFR2 and FGFR3, tyrosine phosphatase PTPN11, and RAS oncogene homologs HRAS and KRAS) from 16 of 22 tubules analyzed; all mutations have known associationswith severe diseases, ranging from congenital or perinatal lethal disorders to somatically acquired cancers. These results support proposed selfish selection of spermatogonial mutations affecting growth factor receptor-RAS signaling, highlight its prevalence in older men, and enable direct visualization of the microscopic anatomy of elongated mutant clones. [ABSTRACT FROM AUTHOR]

The RAS proto-oncogene Harvey rat sarcoma viral oncogene homolog (HRAS) encodes a small GTPase that transduces signals from cell surface receptors to intracellular effectors to control cellular behavior. Although somatic HRAS mutations have been described in many cancers, germline mutations cause Costello syndrome (CS), a congenital disorder associated with predisposition to malignancy. Based on the epidemiology of CS and the occurrence of HRAS mutations in spermatocytic seminoma, we proposed that activating HRAS mutations become enriched in sperm through a process akin to tumorigenesis, termed selfish spermatogonial selection. To test this hypothesis, we quantified the levels, in blood and sperm samples, of HRAS mutations at the p.G12 codon and compared the results to changes at the p.A11 codon, at which activating mutations do not occur. The data strongly support the role of selection in determining HRAS mutation levels in sperm, and hence the occurrence of CS, but we also found differences from the mutation pattern in tumorigenesis. First, the relative prevalence of mutations in sperm correlates weakly with their in vitro activating properties and occurrence in cancers. Second, specific tandem base substitutions (predominantly GC>TT/AA) occur in sperm but not in cancers; genomewide analysis showed that this same mutation is also overrepresented in constitutional pathogenic and polymorphic variants, suggesting a heightened vulnerability to these mutations in the germline. We developed a statistical model to show how both intrinsic mutation rate and selfish selection contribute to the mutational burden borne by the paternal germline. [ABSTRACT FROM AUTHOR]