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 BDNFpromoted 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.

Functional analysis of SIRPα in the growth cone

“…Interestingly the kinetics of SIRP␣ phosphorylation in GCPs were much faster than those reported elsewhere (Tsuda et al, 1998;Oh et al, 1999;Ohnishi et al, 1999;Maile and Clemmons, 2002a). Data suggest that the initial step of SHP-2 binding to phosphorylated SIRP␣ also serves to activate its phosphatase activity (Ohnishi et al, 1996), which is necessary for the role of SHP-2 in growth factoractivated signal transduction (Kharitonenkov et al, 1997;Araki et al, 2000;Maile and Clemmons, 2002a). In particular, SHP-2 is important for PI 3-kinase activation (Hakak et al, 2000;Wu et al, 2001;Zhang et al, 2002), and PI 3-kinase is necessary for axonal growth (Laurino et al, 2005).…”

“…There are data to suggest that, in neurons, SIRP␣ may be involved in the regulation of survival, neurite outgrowth and/or synapse formation and maintenance (Chuang and Lagenaur, 1990;Comu et al, 1997;Sano et al, 1997;Jiang et al, 1999;Araki et al, 2000;Mi et al, 2000).…”

The tyrosine phosphatase SHP‐2 regulates differentiation and apoptosis of individual primary T lymphocytes

“…1A-D). The first dominant-negative isoform is the commonly used C>S mutant ("SHP-2 C>S") [18,30], which inhibits the catalytic activity but retains its function as an adapter-like molecule (Fig. 1B, leftmost).…”

A role for SHPS-1/SIRPα1 in IL-1β- and TNFα-dependent signaling

“…SHPS-1 has four YXX (L/V/I) motifs in the cytoplasmic region those serve as binding sites for SHP-1/2 . In cells overexpressing wild type SHPS-1, both insulin-dependent activation of MAPK and BDNF-promoted neuronal survival via the PI3K-Akt pathway (Araki et al, 2000) were enhanced, whereas overexpression of mutant SHPS-1 lacking SHP-2 binding sites inhibited the MAPK activation by LPA . In contrast, overexpression of SIRPa1/SHPS-1 in NIH3T3 cells inhibited DNA synthesis and activation of MAPK by epidermal growth factor (EGF) and insulin or PI3K by EGFR (Kharitonenkov et al, 1997;Wu et al, 2000).…”

“…Although various types of stimuli appear to activate the tyrosine phosphorylation of SHPS-1, how receptor signaling links with SHPS-1 signaling is not yet clarified Araki et al, 2000;Takeda et al, 1998;Kharitonenkov et al, 1997;Wu et al, 2000). To address this important question, we investigated the interaction between IL-1 receptor signaling and SHPS-1 in Balb3T3 cells and Balb3T3 overexpressing the ECTM mutant.…”