Roles of ShcB/ShcC Docking Proteins in Neural Stem Cells and Neuronal Tumors

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ShoC is a family member of Shc docking proteins, which contain a unique PTB-CH1-SH2 modular organization and conduct as substrates of various receptor tyrosine kinases. Recently, we showed that hyperphosphorylated ShcC detected in some of neuroblastorna cell lines, such as NB-39-nu cells, is associated with constitutively activated anaplastic lymphoma kinase (ALK) caused by the gene amplification. The ALK gene amplification was also detected in about 10% of primary human neuroblastomas. Suppression of ALK expression in NB-39-nu cells by siRNA resulted in decreased phosphorylation level of ShcC, inactivation of MAPKIAkt pathway and cell apoptosis suggesting that ALK tyrosine kinase is dominating survival signal of this neuroblastoma line. To investigate the roles of hyperphosphorylated ShcC in neuroblastoma cell lines, we established NB-39-nu cell lines which overexpress wildtype or mutant ShcC proteins. It was demonstrated that cell-survival and differentiation, cell-motility were markedly impaired in the NB-39-nu cells expressing the 3YF mutant of ShcC which blocks ShcC-Grb2 pathway by the dominant-negative fassion. At the same time, activation level of MAPK and Akt was severely suppressed in these cells. On the other hand, cells overexpressing ShcC as well as the 3YF mutant showed decreased transforming ability, such as anchorage independency and in vivo tumorigenicity that might suggest ShcC-specific negative effects. Loss of persistent phosphorylation of pl3OCas in suspension cell culture was observed in both ShcC overexpressing cells and 3YF cells. These results suggest ShcC might negatively regulate an alternative pathway such as the Src family kinase (SFK)-p130cas pathway in addition to the authentic MAPK and Akt pathways.