Association of phosphatidylinositol 3‐kinase with the photo‐oncogene product Cbl upon CD38 ligation by a specific monoclonal antibody in THP‐1 cells

Abstract

We reported that ecto‐NAD⁺ glycohydrolase activity induced upon differentiation of HL‐60 cells with retinoic acid is localized on the extracellular domain of CD38 and that CD38 ligation by a specific monoclonal antibody, HB‐7, is followed by rapid tyrosine phosphorylation of cellular proteins including a proto‐oncogene product, Cbl. In the present study, we investigated intracellular signaling linked to the HB‐7‐induced Cbl phosphorylation in dibutyryl cAMP‐treated THP‐1 cells. The 85‐kDa regulatory subunit (p85) of phosphatidylinositol (PI) 3‐kinase was immunoprecipitated with anti‐Cbl antibody in a manner dependent on the tyrosine phosphorylation of Cbl. PI 3‐kinase activity was also observed in the immunoprecipitated fractions containing tyrosine‐phosphorylated Cbl. The phosphorylated form of Cbl, which had been separated from the CD38‐stimulated cells, was capable of directly binding to a recombinant p85 fused to glutathione S‐transferase. Thus, the direct association of tyrosine‐phosphorylated Cbl with PI 3‐kinase, possibly leading to the kinase activation, appeared to be involved in intracellular signaling caused by the CD38 ligation.