Schraven B, Schoenhaut D, Bruyns E, Koretzky G, Eckerskorn C, Wallich R, Kirchgessner H, Sakorafas P, Labkovsky B, Ratnofsky S
Department of Applied Immunology, Deutsches Krebsforschungszentrum, Heidelberg, Federal Republic of Germany.
J Biol Chem. 1994 Nov 18;269(46):29102-11.
CD45, a leukocyte-specific protein tyrosine phosphatase involved in signal transduction, has previously been shown to associate with a 32-kDa phosphoprotein in human T-lymphocytes and T-lymphoma cell lines. The 32-kDa protein was purified and its coding cDNA cloned. Since expression of the protein was found to be restricted to B- and T-lymphocytes it was termed LPAP (lymphocyte phosphatase-associated phosphoprotein). LPAP exists in two differentially phosphorylated forms in resting human T-lymphocytes c, both of which undergo alterations during T-lymphocyte activation. Analysis of LPAP protein and mRNA expression in CD45-deficient mutant T-cell lines suggests that LPAP protein is subjected to degradation in the absence of its binding partner, CD45. Stable expression of LPAP protein seems to require particular portions of CD45 distinct from the phosphatase domains. In pervanadate-treated human T-lymphocytes LPAP undergoes phosphorylation on tyrosine residues in vivo. Since tyrosine phosphorylation of LPAP is undetectable in T-lymphocytes expressing enzymatically active CD45, these data suggest that LPAP likely represents a novel substrate for CD45.
CD45是一种参与信号转导的白细胞特异性蛋白酪氨酸磷酸酶，此前已证明它与人T淋巴细胞和T淋巴瘤细胞系中的一种32 kDa磷蛋白相关联。纯化了该32 kDa蛋白并克隆了其编码cDNA。由于发现该蛋白的表达仅限于B淋巴细胞和T淋巴细胞，因此将其命名为LPAP（淋巴细胞磷酸酶相关磷蛋白）。LPAP在静息人T淋巴细胞中以两种不同磷酸化形式存在，在T淋巴细胞激活过程中两者都会发生变化。对CD45缺陷型突变T细胞系中LPAP蛋白和mRNA表达的分析表明，在没有其结合伴侣CD45的情况下，LPAP蛋白会被降解。LPAP蛋白的稳定表达似乎需要CD45中与磷酸酶结构域不同的特定部分。在过钒酸盐处理的人T淋巴细胞中，LPAP在体内酪氨酸残基上发生磷酸化。由于在表达具有酶活性的CD45的T淋巴细胞中未检测到LPAP的酪氨酸磷酸化，这些数据表明LPAP可能是CD45的一种新底物。
