DIFFERENTIAL REGULATION OF CONNEXIN43 AND CONNEXIN37 IN ENDOTHELIAL-CELLS BY CELL-DENSITY, GROWTH, AND TGF-BETA-1

We studied the growth-related ex pression of the gap junction proteins connexin43 (Cx43) and connexin37 (Cx37) to characterize mechanisms of their differential regulation in cultured bovine aortic endothelial c ells. During growth to confluency, Cx43 mRNA levels were high in subco nfluent cells and decreased at confluency; Cx37 mRNA was weakly detect able until the cultures became confluent, when Cx37 levels became simi lar to those of Cx43. Immunoprecipitation, immunoblots, and immunostai ning demonstrated that Cx43 synthesis and content paralleled the chang es in mRNA levels. These data suggested regulation of connexin express ion related to growth status or cell density. We tested this hypothesi s by inhibiting growth with transforming growth factor-beta 1 (TGF-bet a 1). TGF-beta 1 treatment caused an upregulation of Cx43 synthesis, c ontent, and apparent half-life and an upregulation of mRNA, independen t of changes in cell density. Increases in Cx43 synthesis preceded inc reases in mRNA, suggesting both translational and transcriptional regu lation, whereas the increased half-life suggested posttranslational re gulation, as well. Immunostaining revealed the development of intense vesicular staining in the treated cells, which may explain the increas ed half-life. TGF-beta 1 treatment also suppressed the upregulation of Cx37 expression. These alterations in connexin expression may have im plications for endothelial communication under conditions of elevated vascular TGF-beta 1 concentrations such as in wound healing.