CD45 protein-tyrosine phosphatase is specifically associated with a 116-kDa tyrosine-phosphorylated glycoprotein

CD45 is a protein-tyrosine phosphatase expressed on all cells of hematopoietic origin. In an attempt to further characterize CD45 function, we set out to identify molecule(s) that specifically associate with CD45. A 116-kDa protein was detected in immunoprecipitates from CD45+ cells but not CD45- cells. The association between CD45 and this 116-kDa protein can be reconstituted by mixing lysates from CD45- cell lines with purified CD45. p116 appears to associate with CD45 through the external, transmembrane, or membrane-proximal region of CD45 since p116 is associated with a mutant form of CD45 possessing a truncated cytoplasmic domain. The association of p116 with CD45 is not isoform-specific as p116 associates equally well with various CD45 isoforms. We have determined that p116 is a tyrosine-phosphorylated glycoprotein and that it is associated with CD45 in all hematopoietic cells examined. Because of its broad distribution, it is possible that identification of p116 will provide additional insight into the function of CD45 in lymphoid as well as non-lymphoid hematopoietic cells.