A model for intracellular translocation of protein kinase C involving synergism between Ca2+ and phorbol esters

Abstract

The activation of protein kinase C by diacylglycerol and by tumour promoters has implicated this enzyme in transmembrane signalling and in the regulation of the cell cycle. In vitro studies revealed that catalytic activity requires the presence of calcium and phospholipids with a preference for phosphatidylserine. Diacylglycerol and tumour promoters such as phorbol esters bind to the enzyme, leading to its activation while sharply increasing its affinity for Ca2+ and phospholipid. Addition of diacylglycerol analogues or phorbol esters to intact cells results in the phosphorylation of specific polypeptides. Several cellular processes, including hormone and neurotransmitter release and receptor down-regulation, are modulated by the activation of protein kinase C, while phorbol ester-induced stimulation of the enzyme in whole cells has been associated with its translocation from the cytoplasm to the plasma membrane. Moreover, the use of Ca2+ ionophores has revealed an apparent synergism between Ca2+ mobilization and protein kinase C activation. This synergism has recently also been found to apply to receptor down-regulation (ref. 23 and accompanying paper). Here we describe a reconstitution system in which intracellular translocation of protein kinase C and the synergism between Ca2+ and enzyme activators can be studied. The results suggest a rationale for concomitant Ca2+ mobilization and diacylglycerol formation in response to some hormones, neurotransmitters and growth factors.

Amyloid beta peptide directly inhibits PKC activation

“…We addressed this question by using B103 cells that do not express endogenous APP or Ah. It is well established that PKC, when phosphorylated, translocates to the membrane and that PKC in the membrane fraction represents the activated state (Kraft and Anderson, 1983;Kraft et al, 1982;Wolf et al, 1985). Results showed that exogenously added Ah lowers membrane translocation of PKC.…”

“…Because activated PKC is known to translocate to the cell membrane (Kraft and Anderson, 1983;Kraft et al, 1982;Wolf et al, 1985), the above results predicted that membrane translocation of PKC would be attenuated by Ah. We investigated this possibility by measuring subcellular distribution of PKCa and PKCq in B103 cells by Western blotting.…”

Prostratin Antagonizes HIV Latency by Activating NF-κB

“…To characterize the profile of PKC isoforms induced by prostratin, we prepared cytoplasmic and membrane fractions from J-Lat 6.3 cells treated with prostratin, TNF-␣, or PMA and analyzed which PKC isoforms were induced to translocate from the cytoplasm to the membrane. Such translocation serves as an early marker of PKC activation (25). Prostratin induced rapid translocation of PKC-and -␤ from the cytoplasm to the membrane fraction, with similar efficiency to PMA (Fig.…”

Polyamines enhance calcium mobilization in fMet‐Leu‐Phe‐stimulated phagocytes

“…Activation of PKC in the PMN is preceded by its Ca'+-dependent translocation from the cytosol to the plasma membrane, which can be monitored by changes in [%l]phorbol 12,13-dibutyrate (PDBu) binding to membrane-associated PKC in intact pbagocytes [5,6]. A model for synergistic stimulation of PMNs has been proposed in which increased cytosolic Ca?+ causes reversible association of PKC with the plasma membrane, thereby priming the enzyme for activation by diacylglycerol or phorbol esters [7].…”