Gab1 mediates neurite outgrowth DNA synthesis, and survival in PC12 cells

The Gab1-docking protein has been shown to regulate phosphatidylinositol 3- kinase PI3K activity and potentiate nerve growth factor (NGF)-induced survi val in PC12 cells. Here, we investigated the potential of Gab1 to induce-ne urite outgrowth and DNA synthesis, two other important aspects of NGF-induc ed neuronal differentiation of PC12 cells and NGF independent survival. We generated a recombinant adenovirus encoding hemagglutinin (HA)-epitope-tagg ed Gab1 and expressed this protein in PC12 cells. HA-Gab1 was constitutivel y tyrosine-phosphorylated in PC12 cells and induced the phosphorylation of Akt/protein kinase B and p44/42 mitogen-activated protein kinase. HA-Gab1-s timulated a 10-fold increase in neurite outgrowth in the absence of NGF and a 5-fold increase in NGF-induced neurite outgrowth, HA-Gab1 also stimulate d DNA synthesis and caused NGF-independent survival in PC12 cells. Finally, we found that HA-Gab1-induced neuritogenesis was completely suppressed by pharmacological inhibition of mitogen-activated protein kinase kinase (MEK) activity and 50% suppressed by inhibition of PI3K activity. In contrast, H A-Gab1-stimulated cell survival was efficiently suppressed only by inhibiti on of both PI3K and MEK activities. These results indicate that Gab1 is cap able of mediating differentiation, DNA synthesis, and cell survival and use s both PI3K and MEK signaling pathways to achieve its effects.