CD10 NEUTRAL ENDOPEPTIDASE-24.11 IS PHOSPHORYLATED BY CASEIN KINASE-II AND COASSOCIATES WITH OTHER PHOSPHOPROTEINS INCLUDING THE LYN SRC-RELATED KINASE/

CD10/neutral endopeptidase 24.11 (NEP) regulates peptide-mediated prol iferation of lymphoid progenitors and certain epithelial cells and is itself regulated by cellular proliferation. To further characterize me chanisms by which cell-surface signaling might regulate CD10/MEP expre ssion, we determined whether CD10/NEP was phosphorylated and whether t he enzyme co-associated with additional cellular phosphoproteins. The CD10/NEP cytoplasmic tail contains two consensus recognition sequences for casein kinase II (CKII), a serine and threonine kinase that incre ases in activity following peptide signaling. In standard in vitro kin ase assays, CKII phosphorylated full-length recombinant CD10/NEP but d id not phosphorylate a truncated CD10/NEP protein that lacked the tran smembrane region and cytoplasmic tail. To determine whether CD10/NEP m ight interact with additional cellular phosphoproteins, in vitro kinas e assays were performed on CD10/NEP immune complexes from Nalm-6 cells . Three additional tyrosine phosphoproteins of similar to 40 kD, simil ar to 56 kD, and similar to 75 kD were identified in the CD10/NEP immu noprecipitates. The similar to 56-kD CD10/NEP-associated phosphoprotei n was immunoprecipitated with an anti-lyn antibody confirming its iden tity as the lyn src-related kinase. Taken together, these data indicat e that CD10/NEP is itself phosphorylated by CKII and that CD10/NEP co- associates with additional tyrosine phosphoproteins including lyn. (C) 1996 by The American Society of Hematology.