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 activates 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 loss of a key transport site, the Na-K-Cl cotransporter). The effects of bryostatin 1 on these parameters are unknown. Methods. Cl secretion and barrier function of T84 human intestinal epithelia were assessed as cyclic adenosine monophosphate- stimulated short-circuit current and transepithelial resistance, respectively. Na-K-Cl cotransporter function and mRNA expression were assayed by ⁸⁶Rb uptake and Northern analysis. Results. Bryostatin 1 reduced Cl secretion, Na-K-Cl cotransport, and cotransporter mRNA expression. Unlike phorbol esters, these effects were largely transient. In contrast to phorbol esters, bryostatin 1 did not decrease barrier function. Conclusions. Bryostatin 1 transiently inhibits Na-K-Cl cotransport and Cl secretion, possibly through a PKC isoform also targeted by phorbol esters. Unlike phorbol esters, bryostatin 1 does not impair barrier function. The data imply that bryostatin 1 and phorbol esters differentially affect a PKC isoform involved in junctional regulation, and that epithelial transport and barrier function may be regulated by distinct PKC isoforms.