Abstract
In this study we explored the pattern of protein kinase C (PKC) isozyme selectivity of the bryostatins, a unique class of PKC activators that induce only a subset of the typical phorbol ester responses and antagonize those phorbol ester-mediated responses that they themselves fail to induce. The binding properties of individual recombinant PKC isozymes that had been expressed in insect cells, isolated, and reconstituted in Triton X-100/phosphatidylserine mixed micelles were determined. [3H]Bryostatin 1 showed lower affinity for PKC-beta 1 and -gamma, compared with PKC-alpha, -delta, -epsilon, and -eta. This pattern contrasts with that observed for other PKC ligands. These latter assays were conducted with isozymes reconstituted in phosphatidylserine, conditions that unfortunately do not permit quantitation of bryostatin 1 binding under equilibrium conditions. Using delta 19,20-bryostatin 10 and delta 19,20-isobryostatin 10, we could distinguish the respective roles of ligand and lipid in the pattern of selectivity. When isozymes were reconstituted in phosphatidylserine vesicles, delta 19,20-bryostatin 10 and delta 19,20-isobryostatin 10 showed similar affinities for PKC-alpha and -gamma, similarly to the phorbol esters. However, in the mixed micellar system, PKC-gamma showed a significantly lower binding affinity, as had been observed for bryostatin 1. These results suggest that the unique pattern of biological responses to the bryostatins does not represent a unique pattern of isotype recognition. Furthermore, the lipid environment of PKC plays an important role in determining the binding selectivity for individual isozymes.
MolPharm articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|