Induction of rat WT1 gene expression correlates with human chromosome 11p11.2-p12-mediated suppression of tumorigenicity in rat liver epithelial tumor cell lines

We have previously identified and mapped a locus within human chromosome 11 p11.2-p12 that suppresses the tumorigenic potential of some rat liver tumor cell lines. In the present study, possible molecular mechanisms of human 1 1p11.2-p12-mediated liver tumor suppression were investigated by examining gene expression patterns in suppressed and non-suppressed microcell hybrid (MCH) cell lines. The parental rat liver tumor cell lines (GN6TF and GP7TB) express moderate levels of p53 mRNA and protein, overexpress mRNAs for c-H -ras, c-myc, and TGF alpha, and do not express detectable levels of WT1 mRN A or protein. Suppression of tumorigenicity by human chromosome 11p11.2-p12 was not accompanied by significant alterations in the levels of expression of p53, c-myc, or TGF alpha. Expression of c-H-ras was decreased significa ntly in both suppressed and non-suppressed MCH cell lines, suggesting that down-regulation of c-H-ras is not directly responsible for tumor suppressio n. In contrast, the level of expression of WT1 correlated precisely with tu mor suppression in this model system. All suppressed MCH cell lines express ed WT1 mRNA and protein at levels comparable to that of untransformed rat l iver epithelial cells (WB-F344), whereas only trace WT1 mRNA and protein we re detected in 3 non-suppressed MCH cell line. PCR analysis demonstrated th at two suppressed MCH cell lines do not carry the human WT1 gene, indicatin g that WT1 expression in these lines originates from the rat locus. Further more, RT-PCR analysis showed that each of the four known splice variants of the WT1 mRNA are expressed in these suppressed MCH cell lines, recapitulat ing the expression pattern observed in the untransformed rat liver epitheli al cells. Re-expression of tumorigenicity by suppressed MCH cell lines was accompanied by the coordinate loss of human chromosome 11p11.2-p12 and of W T1 gene expression, suggesting that one or more human 11p11.2-p12 genes are required for sustained expression of WT1 in these cell lines. Together, th ese results suggest that the molecular mechanism governing human chromosome 11p11.2-p12-mediated liver tumor suppression may involve induction of rat WT1 gene expression under the direct or indirect transcriptional regulation of a genetic locus (or loci) on human 11p11.2-p12.