Abstract
SPROUTY-2 (SPRY2) regulates receptor tyrosine kinase signalling and therefore cell growth and differentiation. In this study, we show that SPRY2 expression in colon cancer cells is inhibited by the active vitamin D metabolite 1alpha,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) through E-cadherin-dependent and -independent mechanisms. In turn, SPRY2 represses both basal and 1,25(OH)(2)D(3)-induced E-cadherin expression. In line with this, SPRY2 induces ZEB1 RNA and protein, but not that of other epithelial-to-mesenchymal transition inducers that repress the CDH1/E-cadherin promoter. Consistently, SPRY2 and E-cadherin protein levels inversely correlate in colon cancer cell lines and xenografted tumours. Moreover, SPRY2 knockdown by small hairpin RNA increases CDH1/E-cadherin expression and, reciprocally, CDH1/E-cadherin knockdown increases that of SPRY2. In colon cancer patients, SPRY2 is upregulated in undifferentiated high-grade tumours and at the invasive front of low-grade carcinomas. Quantification of protein expression in 34 tumours confirmed an inverse correlation between SPRY2 and E-cadherin. Our data demonstrate a tumourigenic action of SPRY2 that is based on the repression of E-cadherin, probably by the induction of ZEB1, and a reciprocal regulation of SPRY2 and E-cadherin that dictates cell phenotype. We propose SPRY2 as a candidate novel marker for high-grade tumours and a target of therapeutic intervention in colon cancer.