EFFECTS OF BRYOSTATIN-1, A NOVEL ANTICANCER AGENT, ON INTESTINAL TRANSPORT AND BARRIER FUNCTION - ROLE OF PROTEIN-KINASE-C

Background. Bryostatin 1 is a novel chemotherapeutic agent that activa tes specific members of the protein kinase C (PKC) family in a complex pattern overlapping with, but distinct from, that of tumor-promoting phorbol esters. Phorbol esters profoundly alter epithelial phenotype, abolishing both barrier function and Cl secretion (the latter due to l oss of a key transport site, the Na-K-Cl cotransporter). The effects o f bryostatin 1 on these parameters are unknown. Methods. Cl secretion and barrier function of T84 human intestinal epithelia were assessed a s cyclic adenosine monophosphate-stimulated short-circuit current and transepithelial resistance, respectively. Na-K-Cl cotransporter functi on and mRNA expression were assayed by Rb-86 uptake and Northern analy sis. Results. Bryostatin 1 reduced Cl secretion, Na-K-Cl cotransport, and cotransporter mRNA expression. Unlike phorbol esters, these effect s were largely transient. In contrast to phorbol esters, bryostatin 1 did not decrease barrier function. Conclusions. Bryostatin 1 transient ly inhibits Na-K-Cl cotransport and Cl secretion, possibly through a P KC isoform also targeted by phorbol esters. Unlike phorbol esters, bry ostatin 1 does not impair barrier function. The data imply that bryost atin 1 and phorbol esters differentially affect a PKC isoform involved in junctional regulation, and that epithelial transport and barrier f unction may be regulated by distinct PKC isoforms.