BIT/SHPS-1 Promotes Antiapoptotic Effect of BDNF on Low Potassium-Induced Cell Death of Cultured Cerebellar Granule Neurons

Brain immunoglobulin-like molecule with tyrosine-based activation motifs/SHP substrate 1 (BIT/SHPS-1) is a neuronal adhesion molecule that is highly expressed in cerebellar granule neurons (CGNs); however its function in CGNs remains unclear. Our previous studies indicated that BIT/SHPS-1 is able to modulate the antiapoptotic effect of brain-derived neurotrophic factor (BDNF) on CNS neurons by cell type-specific mechanisms. In this article, we have studied the role of BIT/SHPS-1 in the antiapoptotic function of BDNF on low potassium (LK)-induced cell death of cultured CGNs which is an in vitro model system of neuronal apoptosis during brain development. Cultured rat CGNs were transduced with wild-type rat BIT/SHPS-1 (BIT/SHPS-1_WT), its 4F-mutant (BIT/SHPS-1_4F, in which all cytoplasmic tyrosine residues were substituted with phenylalanine), or nuclear localization signal-attached beta-galactosidase (NLS-LacZ, as control)-expressing adenoviruses. Expression of BIT/SHPS-1_WT and BIT/SHPS-1_4F alone did not affect steady-state cell viability. Tyrosine phosphorylation of BIT/SHPS-1 was only detected in BIT/SHPS-1_WT-expressing cultures in the presence and the absence of BDNF. When subjected to LK in the presence of BDNF, BIT/SHPS-1_WT- and BIT/SHPS-1_4F-expressing cultures showed a significant resistance to cell death, while the control virus-transfected culture did not. In addition, a phosphatidylinositol 3-kinase (PI3-K) inhibitor, LY294002, attenuated the antiapoptotic effect of BDNF on BIT/SHPS-1_WT-, and BIT/SHPS-1_4F-expressing cultures. These results demonstrated that in both tyrosine phosphorylation-independent and PI3-K-dependent manners, BIT/SHPS-1 promotes the antiapoptotic effect of BDNF on the LK-induced cell death of CGNs.