The goal of this research is to identify,clone,and characterize TSGs located on chromosomes 3p and 8p that are involved in the origin or development of major human malignancies: carcinomas of the lung, breast,kidney, and prostate.Our accomplishments this year are:(1) the novel pVHL target genes identified by us last year,namely,the carbonic anhydrases, CA9 and CA12 were further analyzed.We showed that the CA9 and CA12 genes are overexpressed in many tumor types due to the loss of VHL or other mechanisms and are involved in the control of the extracellular pH of the miliew surrounding the cells and thus create a microenvironment conducive to tumor growth and spread.Based on these finding Dr. E. Oldfield and a group of surgeons at the NIH Clinical Center initiated a prospective, non-randomized study of the effect of acetazolamide, a strong inhibitor of CAs, in patients with brain hemangioblastomas associated with brain tissue edema and cysts.Future work will focus on the role of carbonic anhydrases and othes genes in the regulation of tumor pH and its potential impact on cancer growth.(2) The 3p21.3 TSG:A subset of 19 genes were found within the deleted overlap region of ~370-kb. This region was further subdivided by a nesting 200-kb breast cancer homozygous deletion into two gene sets: 8 genes lying in the proximal ~120-kb segment and 11 genes lying in the distal ~250-kb segment. The 19 genes were analyzed extensively by computational methods and were tested by manual methods for loss of expression and mutations in lung cancers to identify candidate TSGs from within this group. Several genes showed loss-of-expression or reduced mRNA levels in non-small cell lung cancer (NSCLC) (CACNA2D2/ (a2d-2), SEMA3B (formerly SEMA(V),) BLU, RASSF1/A (formerly 123F2), and HYAL1) or small cell lung cancer (SCLC) (SEMA3B, BLU, RASSF1/A (formerly 123F2), and HYAL1) cell lines. We found six of the genes to have 2 or more amino acid sequence altering mutations including: BLU, NPRL2/Gene21, FUS1, HYAL1, FUS2, and SEMA3B. However, none of the 19 genes tested for mutation showed a frequent (>10%) mutation rate in lung cancer samples. This led us to exclude several of the genes in the region as classical tumor suppressors for sporadic lung cancer. On the other hand, the putative lung cancer TSG in this location may either be inactivated by tumor acquired promoter hypermethylation or belong to the novel class of haploinsufficient genes which predispose to cancer in a hemizygous (+/-) state but do not show a second mutation in the remaining wild type allele in the tumor. Functional testing of the critical genes by gene transfer and gene disruption strategies is under way and will permit the identification of the putative lung cancer TSG(s), LUCA. (3) The 3p12 TSG:Cytogenetic deletions and LOH at human 3p12 are a consistent feature of lung cancer specimens and suggest the presence of a tumor suppressor gene(s) (TSG) at this location. Only one gene (DUTT1, Deleted in U Twenty Twenty) was so far cloned from the overlapping region deleted in several lung and breast cancer cell lines (U2020, NCI H2198, HCC38). DUTT1 is the human ortholog of the fly gene ROBO that has homology to NCAM proteins. Extensive analyses of DUTT1 in lung cancer did not reveal any mutations, suggesting another gene(s) at this location could be associated with lung cancer initiation and/or development. We discovered in the overlapping critical region a new small (~230kb), nested homozygous deletion in the SCLC cell line GLC20. This deletion has been PCR-characterized using several polymorphic markers. P1 library screening produced three overlapping clones that cover the whole region and flanks. These clones were used to define by fiber-FISH the location and size of the deletion. Recently several BAC clones covering this region were sequenced by the MIT genome sequencing center providing a genomic tool to discover in silico the resident genes. Several genes represented by EST clusters were detected in the deletion and are being isolated. Subsequent mutation and functional studies will identify the potential 3p12 lung cancer TSG.
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