Analysis of protein tyrosine phosphorylation signal, which regulates synaptic function.

SHPS-1(SHP底物-1)是免疫球蛋白超家族膜蛋白的一员。SHPS-1的细胞质区域含有酪氨酸残基，酪氨酸残基被磷酸化，并与细胞质蛋白酪氨酸磷酸酶SHP-2结合。SHPS-1在大脑中高度表达，被认为在中枢神经系统中具有调节酪氨酸磷酸化信号的重要功能。SHPS-1的胞外区与其生理配体CD47特异性地相互作用。CD47也是一种免疫球蛋白超家族膜蛋白。CD47和SHPS-1之间的这种相互作用构成了一个细胞间通信系统(CD47-SHPS-1系统)。在本研究中，我们利用原代培养的海马神经元分析了这两个分子的表达模式，我们发现SHPS-1和CD47以不同的方式定位，前者主要分布在轴突上，后者主要分布在树突上。这些结果表明，CD47-SHPS-1系统在树突和轴突之间的相互作用部位起着定向细胞间信号系统的作用。我们还研究了CD47-SHPS-1系统在培养神经元中的功能。我们发现CD47的强制表达促进了神经突起的形成。我们还发现，含有SHPS-1胞外区的Fc融合蛋白可以诱导这些神经元形成丝状基座。此外，外源性表达的SHPS-1和CD47明显聚集在轴突和树突的扩大接触部位，每个轴突和树突都来自单独转染的神经元。我们的研究结果提示CD47-SHPS-1系统调节接触部位神经元的形态变化，从而调节神经元网络的形成。我们计划进一步研究CD47-SHPS-1系统在神经功能调节中的生理重要性。

SHPS-1 (SHP substrate-1) is a member of immunoglobulin superfamily membrane proteins. Cytoplasmic region of SHPS-1 contains tyrosine residues, which are phosphorylated and binds to a cytplasmic protein tyrosine phosphatase, SHP-2. SHPS-1 is highly expressed in the brain, and thought to have an important function to regulate tyrosine phosphorylation signal in the central nervous system. Extracellular region of SHPS-1 specifically interacts with its physiological ligand, CD47. CD47 is also an immunoglobulin superfamily membrane protein. This interaction between CD47 and SHPS-1 constitutes an intercellular communication system (the CD47-SHPS-1 system). In this research, we analyzed expression patterns of these two molecules by using primary cultured hippocampal neurons, and we found that SHPS-1 and CD47 were localized in a different manner; the former was predominantly on axons and the latter on dendrites, respectively. These results suggest that the CD47-SHPS-1 system acts as a directional intercellular signaling system at the interaction sites between dendrites and axons. We have also investigated the function of the CD47-SHPS-1 system in cultured neurons. We found that forced expression of CD47 promoted neurite formation. We also found that an Fc fusion protein containing the extracellular region of SHPS-1 induced filopodium formation in these neurons. Furthermore, exogenously expressed SHPS-1 and CD47 were markedly accumulated at the enlarged contact sites of axon and dendrite, each of which was derived from neurons transfected separately. All our findings suggest the CD47-SHPS-1 system regulates morphological change of neurons at their contact site, thereby regulates neuronal network formation. We are planning to further investigate the physiological importance of the CD47-SHPS-1 system in the regulation of neuronal function.