Paradoxical effects of T-cadherin on squamous cell carcinoma : up- and down-regulation increase xenograft growth by distinct mechanisms

Mechanisms underlying cutaneous squamous cell carcinoma (SCC) tumour growth and invasion are incompletely understood. Our previous pathological and in vitro studies suggest that cell surface glycoprotein T-cadherin (T-cad) might be a controlling determinant of the behaviour of SCC. Here we used a murine xenograft model to determine whether T-cad modulates SCC tumour progression in vivo. Silencing or up-regulation of T-cad in A431 (shTcad or Tcad(+) , respectively) both resulted in increased tumour expansion in vivo. To explain this unanticipated outcome, we focused on proliferation, apoptosis and angiogenesis/lymphangiogenesis, which are important determinants of the progression of solid tumours in vivo. shTcad exhibited enhanced proliferation potential in vitro and in vivo, and their signalling response to EGF was characterized by a higher Erk1/2:p38MAPK activity ratio, which has been correlated with more aggressive tumour growth. T-cad over-expression did not affect proliferation but staining for cleaved caspase 3 revealed a minimal occurrence of extensive apoptosis in Tcad(+) tumours. Immunofluoresence staining of xenograft sections revealed increased intra-tumoural total microvessel (CD31(+)) and lymphatic vessel (LYVE-1(+)) densities in Tcad(+) tumours. shTcad tumours exhibited decreased microvessel and lymphatic densities. Tcad(+) expressed higher levels of transcripts for VEGF-A, VEGF-C and VEGF-D in vitro and in vivo. Culture supernatants collected from Tcad(+) enhanced sprout outgrowth from spheroids composed of either microvascular or lymphatic endothelial cells, and these in vitro angiogenic and lymphangiogenic responses were abrogated by inclusion of neutralizing VEGF antibodies. We conclude that T-cad can exert pleiotropic effects on SCC progression; up- or down-regulation of T-cad can promote SCC tumour expansion in vivo but through distinct mechanisms, namely enhancement of angio/lymphangiogenic potential or enhancement of proliferation capacit