Cellular redistribution of protein tyrosine phosphatases LAR and PTP sigma by inducible proteolytic processing
Cellular redistribution of protein tyrosine phosphatases LAR and PTP sigma by inducible proteolytic processing
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DOI：
10.1083/jcb.138.3.681
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发表时间：
1997-08-11
影响因子：
7.8
通讯作者：
Ullrich, A
中科院分区：
文献类型：
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作者：
Aicher, B;Lerch, MM;Ullrich, A
大多数受体样蛋白酪氨酸磷酸酶(PTPase)与其胞外区的细胞黏附分子具有高度的同源性。我们研究了受体样PTPase LAR和PTP sigma的加工功能意义。PTP sigma的生物合成和细胞内加工类似于相关的PTPase LAR，并以两个亚单位复合体的形式在细胞表面表达，LAR和PTP sigma在钙离子载体A23187或佛波酯TPA处理后都经历了进一步的蛋白质降解，TPA诱导293细胞的LAR加工确实需要PKCα的过表达。诱导的蛋白降解导致两个PTPase的胞外区脱落，这与鉴定氨基酸Pro(821)和Ile(822)之间的PTP sigma裂解位点是一致的。共聚焦显微镜研究发现，这两种PTPase的亚细胞定位均优先于黏附连接和桥粒，与此一致，我们在体外发现，蛋白球蛋白和β-连环蛋白与LAR的胞内结构域直接相关。综上所述，这些数据表明LAR和PTP sigma参与了细胞接触的调节，与钙粘素/连环蛋白家族的细胞黏附分子协同作用，在胞外结构域加工和脱落后，这两个PTPase的催化活性部分被内化并重新分布到远离细胞接触的位置，这表明了一种调节这些PTPase的活性和靶标特异性的机制。钙撤退导致细胞接触中断，也导致内化，但与先前的蛋白水解性裂解和胞外区脱落无关，我们得出结论，LAR和PTP sigma的亚细胞定位至少受两种独立机制调节，一种需要它们的胞外区存在，另一种涉及完整的细胞-细胞接触的存在。
Most receptor-like protein tyrosine phosphatases (PTPases) display a high degree of homology with cell adhesion molecules in their extracellular domains. We studied the functional significance of processing for the receptor-like PTPases LAR and PTP sigma. PTP sigma biosynthesis and intracellular processing resembled that of the related PTPase LAR and was expressed on the cell surface as a two-subunit complex, Both LAR and PTP sigma underwent further proteolytical processing upon treatment of cells with either calcium ionophore A23187 or phorbol ester TPA, Induction of LAR processing by TPA in 293 cells did require overexpression of PKC alpha. Induced proteolysis resulted in shedding of the extracellular domains of both PTPases, This was in agreement with the identification of a specific PTP sigma cleavage site between amino acids Pro(821) and Ile(822). Confocal microscopy studies identified adherens junctions and desmosomes as the preferential subcellular localization for both PTPases matching that of plakoglobin, Consistent with this observation, we found direct association of plakoglobin and beta-catenin with the intracellular domain of LAR in vitro. Taken together, these data suggested an involvement of LAR and PTP sigma in the regulation of cell contacts in concert with cell adhesion molecules of the cadherin/catenin family, After processing and shedding of the extracellular domain, the catalytically active intracellular portions of both PTPases were internalized and redistributed away from the sites of cell-cell contact, suggesting a mechanism that regulates the activity and target specificity of these PTPases. Calcium withdrawal, which led to cell contact disruption, also resulted in internalization but was not associated with prior proteolytic cleavage and shedding of the extracellular domain, We conclude that the subcellular localization of LAR and PTP sigma is regulated by at least two independent mechanisms, one of which requires the presence of their extracellular domains and one of which involves the presence of intact cell-cell contacts.