BIT/SHPS‐1 Enhances Brain‐Derived Neurotrophic Factor‐Promoted Neuronal Survival in Cultured Cerebral Cortical Neurons

Abstract: Brain‐derived neurotrophic factor (BDNF) activates a variety of signaling molecules to exert various functions in the nervous system, including neuronal differentiation, survival, and regulation of synaptic plasticity. Previously, we have suggested that BIT/SHPS‐1 (brain immunoglobulin‐like molecule with tyrosine‐based activation motifs/SHP substrate 1) is a substrate of Shp‐2 and is involved in BDNF signaling in cultured cerebral cortical neurons. To elucidate the biological function of BIT/SHPS‐1 in cultured cerebral cortical neurons in connection with its role in BDNF signaling, we generated recombinant adenovirus vectors expressing the wild type of rat BIT/SHPS‐1 and its 4F mutant in which all tyrosine residues in the cytoplasmic domain of BIT/SHPS‐1 were replaced with phenylalanine. Overexpression of wild‐type BIT/SHPS‐1, but not the 4F mutant, in cultured cerebral cortical neurons induced tyrosine phosphorylation of BIT/SHPS‐1 itself and an association of Shp‐2 with BIT/SHPS‐1 even without addition of BDNF. We found that BDNF‐promoted survival of cultured cerebral cortical neurons was enhanced by expression of the wild type and also 4F mutant, indicating that this enhancement by BIT/SHPS‐1 does not depend on its tyrosine phosphorylation. BDNF‐induced activation of mitogen‐activated protein kinase was not altered by the expression of these proteins. In contrast, BDNF‐induced activation of Akt was enhanced in neurons expressing wild‐type or 4F mutant BIT/SHPS‐1. In addition, LY294002, a specific inhibitor of phosphatidylinositol 3‐kinase, blocked the enhancement of BDNF‐promoted neuronal survival in both neurons expressing wild‐type and 4F mutant BIT/SHPS‐1. These results indicate that BIT/SHPS‐1 contributes to BDNF‐promoted survival of cultured cerebral cortical neurons, and that its effect depends on the phosphatidylinositol 3‐kinase‐Akt pathway. Our results suggest that a novel action of BIT/SHPS‐1 does not occur through tyrosine phosphorylation of BIT/SHPS‐1 in cultured cerebral cortical neurons.