A Molecular Mechanism of Retinoblastoma Protein (pRB) in Neuronal Differentiation of PC12 Cells

Abstract

In order to investigate the molecular mechanism of the retinoblastoma protein, pRB, in neuronal differentiation, the accumulation of the hypophosphorylated pRB in PC12 cells stimulated by nerve growth factor (NGF) was measured by the western blotting method. NGF induced the accumulation of the hypophosphorylated pRB in 30 min. and maximized the level at 12h. Viral Ki-ras constitutively induced hypophosphorylation of pRB. A dominant negative form of c-Ha-ras suppressed the induction of the hypophosphorylation of pRB by NGF, but not by CAMP. This result is consistent with the idea that NGF induces hypophosphorylation of pRB through the Ras signaling pathway. The reduction of cdk2 activity caused by increment of p21 inhibitor may be a mechanism for hypophosphorylation of pRB. Furthermore, microinjection of a monoclonal antibody for the hypophosphorylated pRB blocked the neurite outgrowth initiated by NGF. It was also found that Hsc 71 interacted with hypophosphorylated pRB in vitro as well as in vivo in neuronal PC12 cells stimulated by NGF. These results suggested the dual role of pRB in the withdrawal of cells from the cell cycle and neuronal differentiation in PC12 cells.