Heterogeneity in the electrophoretic mobility of CD5 molecules after phorbol ester stimulation

As judged by Western blot analysis, phorbol 12-myristate 13-acetate (PMA) and phorbol 12,13-dibutyrate (PDBU) induce the rapid and dose-dependent appearance of slower mobility CD5 molecular forms from peripheral blood mononuclear cell (PBMC) and thymus cell lysates. This phenomenon was inhibited by staurosporine, suggesting that it can be mediated by PKC activation. Furthermore, under our experimental conditions, neither Concanavalin A, nor Phytohaemagglutinin P or the calcium ionophore A23187 were able to reproduce the phorbol ester-induced changes in the CD5 electrophoretic mobility. When immunoprecipitated from phorbol ester-stimulated P32 labelled PBMC lysates, the slower mobility of CD5 molecules was associated to important phosphorylation. This special electrophoretic behaviour after phorbol ester-stimulation makes CD5 different from other lymphocyte surface glycoproteins and may have important implications in the elucidation of the biological role of this molecule as discussed below.