BIOCHEMICAL-ANALYSIS OF THE CD45-P56(LCK) COMPLEX IN JURKAT T-CELLS LACKING EXPRESSION OF LYMPHOCYTE PHOSPHATASE-ASSOCIATED PHOSPHOPROTEIN

In human and mouse lymphocytes the protein tyrosine phosphatase CD45, a key molecule involved in T cell activation, non-covalently associate s with the tyrosine kinase p56(lck) and lymphocyte phosphatase-associa ted phosphoprotein (LPAP), a 32 kDa phosphoprotein of unknown function . In order to gain insight into the function of LPAP we have generated an LPAP-deficient Jurkat variant by means of antisense strategies, An alysis of the CD45-p58(lck) molecular complex in this cell line reveal ed that loss of LPAP does not alter the expression or the enzymatic ac tivity of CD45 or p56(lck), In addition, the association between CD45 and p56(lck) is not affected in LPAP-deficient T cells, These data sug gest that LPAP does not regulate the enzymatic activity of CD45 or p56 (lck) and is not required for the association between these two protei ns. In order to identify polypeptides that preferentially associate wi th LPAP we established a Jurkat variant expressing a chimeric receptor which was composed of the extracellular portion of the human HLA-A2.1 molecule and the full-length LPAP protein, Comparative two-dimensiona l analysis of CD45 and HLA-AZ immunoprecipitates obtained from these c ells following metabolic labeling resulted in the identification of a 43 kDa protein that preferentially associates with LPAP under mild det ergent conditions.