GSE125885
Natural WNT signaling variant potently synergizes with Cdkn2ab loss in skin carcinogenesis.
Cancer predisposing allelic variants have shown to be notoriously difficult to identify by conventional GWA studies. Searching for preferential co-occurrence with defined somatically acquired oncogenic lesions can significantly contribute to the identification of such alleles1. We here show that a natural Wnt-7b allelic variant in the mouse, which is not associated with increased tumour susceptibility, strongly synergizes with loss of the Cdkn2ab tumour suppressor locus in cancer development. Previously, we reported that Cdkn2ab-/- mice, generated from 129P2 ES cells develop skin carcinomas 2. The incidence of these carcinomas dropped gradually in the course of backcrossing to the FVB/N background suggesting that one or more 129P2 alleles cooperate with Cdkn2ab deficiency in skin carcinogenesis. Here we show that this skin cancer phenotype is linked to a 20Mb region of 129P2 chromosome 15 harboring the Wnt7b and Pdgfb genes. Both Wnt7b and Pdgfb are preferentially expressed from the 129P2 allele in skin carcinomas and derived cell lines. ChIPseq analysis showed enrichment of H3K27-Ac, a mark for active enhancers, in the 5' region of the Wnt7b 129P2 gene. Moreover, the Wnt7b 129P2 allele appeared sufficient to cause in vitro transformation and anchorage-independent growth of Cdkn2ab deficient cell lines. Further we show that Wnt7b contributes to transformation through Cdk6 activation. Our observations imply that normally occurring variations in Wnt expression can elicit transformation of cells upon Cdkn2ab locus loss and point to a critical role of the Cdkn2ab locus in keeping the oncogenic potential of physiological levels of Wnt signaling in check. Consequently, it will be worthwhile to explore whether human tumours that show loss of CDKN2ab are associated with distinct allelic variants causing enhanced WNT signaling. Overall design: ChIPseq for H3K27ac was performed in Cdkn2ab mutant FVB/129P2 backcross cells.