Characterization of the 50 kDa Protein Phosphorylated in Concanavalin A-Stimulated Mouse T Cells

抄録

Concanavalin A (Con A) stimulated the phosphorylation of a protein with a molecular mass of 50 kDa and an approximate pI of 4.7 (p 50) in mouse spleen T cells. The phosphorylation of p 50 was also stimulated by a protein kinase C activator, phorbol myristate acetate (PMA), but not by a calcium ionophore, A 23187. This phosphorylation of p 50 was limited to serine and threonine residues in both Con A- and PMA-stimulated T cells. Purification and protein sequence analysis of p 50 enabled us to identify it as a lymphocyte-specific putative Ca²⁺-binding protein (LSP-1). These results suggest that p 50 may have some function, which is regulated through serine/threonine phosphorylation and the intracellular Ca²⁺ concentration, downstream of the phosphoinositide signaling system in the T cell activation cascade.