Tissue-specific alternative splicing analysis reveals the diversity of chromosome 18 transcriptome.

The Chromosome-centric Human Proteome Project (C-HPP) is aimed to identify the variety of protein products and transcripts of the number of chromosomes. The Russian part of C-HPP is devoted to the study of the human chromosome 18. Using widely accepted Tophat and SpliceGrapher, a tool for accurate splice sites and alternative mRNA isoforms prediction, we performed the extensive mining of the splice variants of chromosome 18 transcripts and encoded protein products in liver, brain, lung, kidney, blood, testis, derma, and skeletal muscles. About 6.1 billion of the reads represented by 450 billion of the bases have been analyzed. The relative frequencies of splice events as well as gene expression profiles in normal tissues are evaluated. Using ExPASy PROSITE, the novel features and possible functional sites of previously unknown splice variants were highlighted. A set of unique proteotypic peptides enabling the identification of novel alternative protein species using mass-spectrometry is constructed. The revealed data will be integrated into the gene-centric knowledgebase of the Russian part of C-HPP available at http://kb18.ru and http://www.splicing.zz.mu/.

High mutability of the tumor suppressor genes RASSF1 and RBSP3 (CTDSPL) in cancer.

BACKGROUND: Many different genetic alterations are observed in cancer cells. Individual cancer genes display point mutations such as base changes, insertions and deletions that initiate and promote cancer growth and spread. Somatic hypermutation is a powerful mechanism for generation of different mutations. It was shown previously that somatic hypermutability of proto-oncogenes can induce development of lymphomas. METHODOLOGY/PRINCIPAL FINDINGS: We found an exceptionally high incidence of single-base mutations in the tumor suppressor genes RASSF1 and RBSP3 (CTDSPL) both located in 3p21.3 regions, LUCA and AP20 respectively. These regions contain clusters of tumor suppressor genes involved in multiple cancer types such as lung, kidney, breast, cervical, head and neck, nasopharyngeal, prostate and other carcinomas. Altogether in 144 sequenced RASSF1A clones (exons 1-2), 129 mutations were detected (mutation frequency, MF = 0.23 per 100 bp) and in 98 clones of exons 3-5 we found 146 mutations (MF = 0.29). In 85 sequenced RBSP3 clones, 89 mutations were found (MF = 0.10). The mutations were not cytidine-specific, as would be expected from alterations generated by AID/APOBEC family enzymes, and appeared de novo during cell proliferation. They diminished the ability of corresponding transgenes to suppress cell and tumor growth implying a loss of function. These high levels of somatic mutations were found both in cancer biopsies and cancer cell lines. CONCLUSIONS/SIGNIFICANCE: This is the first report of high frequencies of somatic mutations in RASSF1 and RBSP3 in different cancers suggesting it may underlay the mutator phenotype of cancer. Somatic hypermutations in tumor suppressor genes involved in major human malignancies offer a novel insight in cancer development, progression and spread.