RESUMO
LCPTP (leucocyte-phosphotyrosine phosphatase) is a 42kDa protein tyrosine phosphatase expressed predominantly in haematopoietic cells which has been implicated in the early stages of the T cell receptor signalling pathway. The substrates of LCPTP have been shown to include MAP kinase family members, but it remains unclear whether LCPTP is found in stable constitutive association with these enzymes, or associates transiently during dephosphorylation. Here we report on LCPTP/MAP kinase interactions in CD3-stimulated Jurkat T cells. Pull-downs from Jurkat T cells using a recombinant GST-LCPTP substrate-trap protein, but not wild-type LCPTP show a clear specific association with both ERK1 and ERK2. In Jurkat cells overexpressing LCPTP, a small fraction of cell ERK1 can be immunoprecipitated in stable association with LCPTP. However, in both unstimulated and anti-CD3 antibody stimulated Jurkat T cells, we were unable to demonstrate any constitutive interaction between endogenous LCPTP and any MAP kinase family members. We propose that both ERK1 and ERK2 interact transiently with LCPTP as substrates for the phosphatase rather than as constitutive protein partners.