Ras-Regulated Hypophosphorylation of the Retinoblastoma Protein Mediates Neuronal Differentiation in PC12 Cells |
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Authors: | &dagger HongZhen Li,&Dagger Hiroshi Kawasaki,&Dagger Eisuke Nishida,Seisuke Hattori, Shun Nakamura |
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Affiliation: | Division of Biochemistry and Cellular Biology, National Institute of Neuroscience, and; Department of Molecular Cellular Oncology and Microbiology, Faculty of Dentistry, Tokyo Medical and Dental University, Tokyo;and; Institute for Virus Research, Kyoto University, Kyoto, Japan |
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Abstract: | Abstract: To investigate the role of the retinoblastoma protein pRB in neuronal differentiation, we have measured the accumulation of hypophosphorylated pRB in PC12 cells stimulated by nerve growth factor (NGF). NGF induced the accumulation of hypophosphorylated pRB within 30 min and the level peaked after 12 h. Viral Kiras, cyclic AMP (cAMP), and 12- O -tetradecanoylphorbol 13-acetate (TPA) also induced the hypophosphorylation of pRB, but epidermal growth factor and interleukin-6 did not. The extent of hypophosphorylation of pRB correlated well with the capacity of these factors to stimulate neurite outgrowth. The constitutively activated Ras induced persistent shift of the phosphorylation state of pRB toward hypophosphorylation. A dominant negative form of cHa-Ras suppressed significantly induction of the hypophosphorylation of pRB by NGF, but not by cAMP. Taken together, these results suggest that the hypophosphorylation of pRB triggered by NGF is mediated by a Ras-dependent pathway. Furthermore, microinjection of a monoclonal antibody specific for the hypophosphorylated form of pRB blocked the neurite outgrowth initiated by NGF. These results suggest a crucial role of pRB in withdrawal of cells from the cell cycle and in neuronal differentiation of PC12 cells. |
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Keywords: | Ras Retinoblastoma protein Hypophosphorylation PC12 cells Nerve growth factor Neuronal differentiation |
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