The catalytic domain of protein kinase Cδ confers protection from down-regulation induced by bryostatin 1

Bryostatin 1 (Bryo) has been shown to induce biphasic dose-response curves for down-regulating protein kinase C delta (PKC delta) as well as for protecting PKC delta from down-regulation induced by phorbol 12-myristate 13-acetate (PMA). To identify regions within PKC delta that confer these responses to Bryo, we utilized reciprocal PKC alpha and PKC delta chimeras (PKC alpha/delta and PKC delta/alpha) constructed by exchanging the regulatory and catalytic domains of these PKCs, These chimeras and wild-type PKC alpha/alpha and PKC delta/delta constructed in the same way were stably expressed in NIH 3T3 fibroblasts. Twenty-four h of treatment with Bryo induced a biphasic dose-response curve for down-regulating both wild-type PKC delta/delta and the PKC alpha/delta chimera. In contrast, Bryo led to a nearly complete down-regulation of both PKC alpha/alpha and PKC delta/alpha and also produced a faster mobility form of these species on SDS-polyacrylamide gel electrophoresis, The nature of both the regulatory and, to a lesser extent, the catalytic domains affected the potency of Bryo to down-regulate the chimeric PKC proteins as well as to protect PKC alpha/delta and PKC delta/delta from down-regulation. Bryo at high concentrations also inhibited the down-regulation of PKC delta/delta and PKC alpha/delta induced by 1 mu M PMA when co-applied, The portion of PKC protected by Bryo from down-regulation by either Bryo or PMA was localized in the particulate fraction of the cells. We conclude that the catalytic domain of PKC delta confers protection from down-regulation induced by Bryo or Bryo plus PMA, suggesting that this domain contains the isotype-specific determinants involved in the unique effect of Bryo on PKC delta.