phosphothreonine and Precursor-Cell-Lymphoblastic-Leukemia-Lymphoma

CD10/neutral endopeptidase 24.11 (NEP) regulates peptidemediated proliferation of lymphoid progenitors and certain epithelial cells and is itself regulated by cellular proliferation. To further characterize mechanisms by which cell-surface signaling might regulate CD10/NEP expression, we determined whether CD10/NEP was phosphorylated and whether the enzyme co-associated with additional cellular phosphoproteins. The CD10/NEP cytoplasmic tall contains two consensus recognition sequences for casein kinase II (CKII), a serine and threonine kinase that increases in activity following peptide signaling. In standard in vitro kinase assays, CKII phosphorylated full-length recombinant CD10/NEP but did not phosphorylate a truncated CD10/NEP protein that lacked the transmembrane region and cytoplasmic tail. To determine whether CD10/NEP might interact with additional cellular phosphoproteins, in vitro kinase assays were performed on CD10/NEP immune complexes from Nalm-6 cells. Three additional tyrosine phosphoproteins of approximately 40 kD, approximately 58 kD, and approximately 75 kD were identified in the CD10/NEP immunoprecipitates. The approximately 56-kD CD10/NEP-associated phosphoprotein was immunoprecipitated with an anti-lyn antibody confirming its identity as the lyn src-related kinase. Taken together, these data indicate that CD10/NEP is itself phosphorylated by CKII and that CD10/NEP co-associates with additional tyrosine phosphoproteins including lyn.

Topics: Animals; Casein Kinase II; CHO Cells; Cricetinae; Cricetulus; DNA, Complementary; Humans; Macromolecular Substances; Neoplasm Proteins; Neprilysin; Phosphoproteins; Phosphorylation; Phosphoserine; Phosphothreonine; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Protein Processing, Post-Translational; Protein Serine-Threonine Kinases; Recombinant Fusion Proteins; src-Family Kinases; Tumor Cells, Cultured