Regulation of MAP Kinases by LC-PTP in hematopoietic cells

促分裂原活化蛋白激酶（MAPK）通过磷酸酶对调节性Tyr和Thr残基的去磷酸化而失活。最近我们发现，包括ERK在内的哺乳动物MAPKs被酪氨酸特异性磷酸酶（如LC-PTP、PTPBR 7和STEP）去磷酸化和失活。在这些磷酸酶中，LC-PTP主要在造血细胞中表达，因此，它可能参与淋巴细胞中MAPK的新型调节系统。首先，我们发现LC-PTP和MAPK形成复合物。然后，我们确定了LC-PTP中的结合位点，LC-PTP磷酸酶结构域外的一段短的氨基酸对于MAPK结合活性是必需的并且足够。对ERK和p38 MAPK的结合位点也进行了鉴定。果蝇sevenmaker（sem）突变体是由MAPK中的一个天冬氨酸残基点突变引起的功能获得性突变体，相应的突变被引入哺乳动物的ERK和p38 MAPK中。野生型MAPKs而非这些sem MAPKs与LC-PTP相关，表明残基在相关性中起关键作用。更重要的是，MAPK对LC-PTP的抑制有抵抗力，并且在体内表现出高活性，因此MAPK与磷酸酶的结合是其调控的关键。这些MAPKs可能是研究磷酸酶生理功能的有用探针。

Mitogen-activated protein kinases (MAPKs) are inactivated through dephosphorylation of regulatory Tyr and Thr residues by phosphatases. Recently we have found that mammalian MAPKs including ERK are dephosphorylated and inactivated by tyrosine-specific phosphatases, such as LC-PTP, PTPBR7, and STEP.Among these phosphatases, LC-PTP is predominantly expressed in hematopoietic cells and thus, it might be involved in the novel regulation system of MAPK in lymphocytes.First, we found the complex formation of LC-PTP and MAPK.Then, we identified the binding site in LC-PTP.A short stretch of amino acids outside the phosphatase domain of LC-PTP is essential and enough for the MAPK binding activity. It is also essential for the MAPK inhibition.The binding site in ERK and p38 MAPK was also identified. Drosophila sevenmaker (sem) mutant is a gain-of-function mutant that is caused by a point mutation of an Asp residue in MAPK.The corresponding mutation was introduced into mammalian ERK and p38 MAPKs. Wild type MAPKs but not these sem MAPKs associated with LC-PTP, indicating that the residue was critically involved in the association. More importantly, sem MAPKs were resistant to the suppression by LC-PTP and hyperactive in vivo.Thus, the association of MAPK with phosphatases is crucial for its regulation. The sem MAPKs might be useful probes to elucidate the physiological function of the phosphatases.