Murine colonic mucosa hyperproliferation. II. PKC-beta activation and cPKC-mediated cellular CFTR overexpression

In the companion article (Umar S, Scott J, Sellin JH, Dubinsky WP, and Morr is AP, Am J Physiol Gastrointest Liver Physiol 278: 753-764, 2000), we have shown that transmissible murine colonic hyperplasia (TMCH) increased cellu lar cystic fibrosis transmembrane conductance regulator (CFTR) mRNA and pro tein expression, relocalized CFTR within colonocytes, and enhanced mucosal cAMP-dependent Cl- secretion. We show here that these changes were dependen t on elevated cellular levels of membrane-bound Ca2+- and diacylglycerol-se nsitive protein kinase C (PKC) activity (12-fold), induced by selective (3- to 4-fold) rises in conventional PKC (cPKC) isoform expression and membran e translocation. Three cPKC isoforms were detected in isolated crypts: alph a, beta 1, and beta 2. cPKC-beta 1 rises preceded and those of cPKC-alpha a nd cPKC-beta 2 paralleled cellular hyperproliferation and its effects on CF TR expression and cAMP-dependent Cl- current secretion. Only cPKC-beta 1 an d cPKC-beta 2 were membrane translocated during TMCH. Furthermore, only cPK C-beta 1 trafficked to the nucleus, whereas cPKC-beta 2 remained partitione d among cytosolic, membrane, and cytoskeletal subcellular fractions. Modest increases in novel PKC-epsilon (nPKC-epsilon) expression and subcellular m embrane partitioning were recorded during TMCH, but no changes were seen fo r PKC-delta or -eta. No nPKC isoform nuclear partitioning was detected. The orally bioactive cPKC inhibitor Re-32-0432 reversed both TMCH and elevated cellular CFTR mRNA levels, whereas a pharmacologically inert analog (Ro-31 -6045) failed to inhibit either response. On the basis of these facts, we p resent a new hypothesis whereby PKC-dependent cellular proliferation promot es endogenous cellular CFTR levels. PKC-beta 1 was identified as a candidat e regulatory PKC isoform.