Physical and functional evidence in support of candidate chromosome 3p tumour suppressor genes implicated in epithelial ovarian cancer

Epithelial ovarian cancer (EOC) is difficult to detect in early stage disease, resulting in a high mortality rate. The molecular events underlying EOC development remain largely unknown. Chromosome 3 exhibits frequent deletions and rearrangements in EOC by cytogenetic analysis. In addition, loss of heterozygosity (LOH) mapping of matched ovarian tumour and constitutional DNA samples exhibits specific regions of chromosome 3 loss involving distinct regions: 3p25-p26, 3p24 and a region proximal to 3p14. Thus, chromosome 3p loss points to the location of tumour suppressor genes (TSG) implicated in tumourigenesis, based on Knudson's 'two-hit' model and the paradigm of the classical TSG. The dissertation hypothesis states at least one TSG implicated in EOC is located on chromosome 3p. A novel complementation approach based on the transfer of normal chromosome 3 fragments into OV-90, a tumourigenic EOC cell line harbouring LOH of the 3p arm, was used to generate functional evidence for chromosome 3p TSGs. Three hybrids exhibited complete suppression of tumourigenic potential based on the inability to form colonies in soft agarose, spheroids in cell culture, and tumours in nude mice xenograft models. While all hybrids had acquired various chromosome 3 regions, they all shared in common a 3p12-pcen interval, suggesting at least one common gene may have affected the suppression of tumourigenicity in the OV-90-derived hybrids. Twelve known/hypothetical genes mapping to 3p12-pcen region were characterized based on gene expression and mutation analysis following a classical model for TSG inactivation. To establish the relevance to EOC, gene expression of candidates was investigated in primary cultures of normal ovarian surface epithelial cells and both malignant serous and benign serous tumour samples. The gene expression and genetic analysis identified seven TSG candidates, none of which appeared to be mutated or transcriptionally silenced based on classical mechanisms of TSG inactivation in OV-90, thus suppression of tumourigenicity may have resulted from the functional complementation of one more haploinsufficient 3p12-pcen genes. Several genes (GBE1, VGLL3, ZNF654 ) appeared underexpressed in malignant tumours and these findings suggest the intriguing possibility that more than one 3p12-pcen gene was involved in the suppression of tumourigenicity in OV-90, and by extension, EOC