Regulation of MAP Kinases by LC-PTP in hematopoietic cells

丝裂原活化蛋白激酶（MAPKs）通过磷酸酶对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mapk被酪氨酸特异性磷酸酶（如LC-PTP、PTPBR7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，它可能参与了淋巴细胞中MAPK的新调控系统。首先，我们发现LC-PTP和MAPK的复合物形成。然后，我们确定了LC-PTP的结合位点。LC-PTP的磷酸酶结构域外的一小段氨基酸对于MAPK的结合活性是必需的和足够的。它也是抑制MAPK的必要条件。ERK和p38 MAPK的结合位点也被确定。果蝇7 - maker （sem）突变体是由MAPK中一个Asp残基的点突变引起的功能获得突变体。将相应的突变引入哺乳动物ERK和p38 MAPKs中。野生型的mapk，而不是这些与LC-PTP相关的mapk，表明该残基在关联中起关键作用。更重要的是，sem MAPKs抵抗LC-PTP的抑制，并且在体内过度活跃。因此，MAPK与磷酸酶的关联对其调控至关重要。sem MAPKs可能是阐明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.