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

Integrated genomic characterization of oesophageal carcinoma

Oesophageal cancers are prominent worldwide; however, there are few targeted therapies and survival rates for these cancers remain dismal. Here we performed a comprehensive molecular analysis of 164 carcinomas of the oesophagus derived from Western and Eastern populations. Beyond known histopathological and epidemiologic distinctions, molecular features differentiated oesophageal squamous cell carcinomas from oesophageal adenocarcinomas. Oesophageal squamous cell carcinomas resembled squamous carcinomas of other organs more than they did oesophageal adenocarcinomas. Our analyses identified three molecular subclasses of oesophageal squamous cell carcinomas, but none showed evidence for an aetiological role of human papillomavirus. Squamous cell carcinomas showed frequent genomic amplifications of CCND1 and SOX2 and/or TP63, whereas ERBB2, VEGFA and GATA4 and GATA6 were more commonly amplified in adenocarcinomas. Oesophageal adenocarcinomas strongly resembled the chromosomally unstable variant of gastric adenocarcinoma, suggesting that these cancers could be considered a single disease entity. However, some molecular features, including DNA hypermethylation, occurred disproportionally in oesophageal adenocarcinomas. These data provide a framework to facilitate more rational categorization of these tumours and a foundation for new therapies.ope

TSLC1 is a tumor suppressor gene associated with metastasis in nasopharyngeal carcinoma

In up to 87% of nasopharyngeal carcinoma (NPC) clinical tumor specimens, there was either down-regulation or loss of TSLC1 gene expression. Using a tissue microarray and immunohistochemical staining, the frequency of down-regulated or loss of expression of TSLC1 in metastatic lymph node NPC was 83% and the frequency of loss of expression of TSLC1 was 35%, which was significantly higher than that in primary NPC (12%). To examine the possible growth-suppressive activity of TSLC1 in NPC, three NPC cell lines, HONE1, HNE1, and CNE2, were transfected with the wild-type TSLC1 gene cloned into the pCR3.1 expression vector; a reduction of colony formation ability was observed for all three cell lines. A tetracycline-inducible expression vector, pETE-Bsd, was also used to obtain stable transfectants of TSLC1. There was a dramatic difference between colony formation ability in the presence or absence of doxycycline when the gene is shut off or expressed, respectively, with the tetracycline-inducible system. Tumorigenicity assay results show that the activation of TSLC1 suppresses tumor formation in nude mice and functional inactivation of this gene is observed in all the tumors derived from tumorigenic transfectants. Further studies indicate that expression of TSLC1 inhibits HONE1 cell growth in vitro by arresting cells in G 0-G 1 phase in normal culture conditions, whereas in the absence of serum, TSLC1 induced apoptosis. These findings suggest that TSLC1 is a tumor suppressor gene in NPC, which is significantly associated with lymph node metastases. ©2006 American Association for Cancer Research.link_to_subscribed_fulltex

THY1 is a candidate tumour suppressor gene with decreased expression in metastatic nasopharyngeal carcinoma

Using oligonucleotide microarray analysis, THY1, mapping close to a previously defined 11q22-23 nasopharyngeal carcinoma (NPC) critical region was identified as showing consistent downregulated expression in the tumour segregants, as compared to their parental tumour-suppressing microcell hybrids (MCHs). Gene expression and protein analyses show that THY1 was not expressed in the NPC HONE1 recipient cells, tumour segregants, and other NPC cell lines; THY1 was exclusively expressed in the non-tumourigenic MCHs. The mechanism of THY1 gene inactivation in these cell lines was attributed to hypermethylation. Clinical study showed that in 65\% of NPC specimens there was either downregulation or loss of THY1 gene expression. Using a tissue microarray and immunohistochemical staining, 44\% of the NPC cases showed downregulated expression of THY1 and 9\% lost THY1 expression. The frequency of THY1 downregulated expression in lymph node metastatic NPC was 63\%, which was significantly higher than in the primary tumour (33\%). After transfection of THY1 gene into HONE1 cells, a dramatic reduction of colony formation ability was observed. These findings suggest that THY1 is a good candidate tumour suppressor gene in NPC, which is significantly associated with lymph node metastases

Chromosomal localization of seven HSA3q13→q23 NotI linking clones on chicken microchromosomes: orthology of GGA14 and GGA15 to a gene-rich region of HSA3

Double-color fluorescence in situ hybridization was performed on chicken chromosomes using seven unique clones from the human chromosome 3-specific NotI linking libraries. Six of them (NL1-097, NL2-092, NL2-230, NLM-007, NLM-118, and NLM-196) were located on the same chicken microchromosome and NL1-290 on another. Two chicken microchromosome GGA15-specific BAC clones, JE024F14 containing the IGVPS gene and JE020G17 containing the ALDH1A1 gene, were cytogenetically mapped to the same microchromosome that carried the six NotI linking clones, allowing identification of this chromosome as GGA15. Two GGA14-specific clones, JE027C23 and JE014E08 containing the HBA gene cluster, were co-localized on the same microchromosome as NL1-290, suggesting that this chromosome was GGA14. The results indicated that the human chromosomal region HSA3q13-->q23 is likely to be orthologous to GGA15 and GGA14. The breakpoint of evolutionary conservation of human and chicken chromosomes was detected on HSA3q13.3-->q23 between NL1-290, on the one hand, and six other NotI clones, on the other hand. Considering the available chicken-human comparative mapping data, another breakpoint appears to exist between the above NotI loci and four other genes, TFRC, EIF4A2, SKIL and DHX36 located on HSA3q24-->qter and GGA9. Based on human sequences within the NotI clones, localization of the six new chicken coding sequences orthologous to the human/rodent genes was suggested to be on GGA15 and one on GGA14. Microchromosomal location of seven NotI clones from the HSA3q21 T-band region can be considered as evidence in support of our hypothesis about the functional analogy of mammalian T-bands and avian microchromosomes