Up-regulation of gap junctional intercellular communication by hexamethylene bisacetamide in cultured human peritoneal mesothelial cells

Gap junctional intercellular communication (GJIC) is believed to be an impo rtant means of regulating cell growth and the malignant potential of tumors . This study examined the effect of hexamethylene bisacetamide (HMBA), a hy brid polar compound and a potent differentiation inducer, on GJIC in cultur ed primary human peritoneal mesothelial cells. The redistribution of fluore scence after photobleaching was used to detect GJIC. After the incubation o f confluent cell cultures with 3 or 6 mM HMBA for 3 and 6 days, GJIC was si gnificantly increased in a concentration-dependent manner compared with cul tures without HMBA. Western blotting showed that connexin 43 (Cx43), the ma jor functional protein of gap junctions in peritoneal mesothelial cells, wa s present in unphosphorylated and phosphorylated forms in control cell cult ures. The addition of HMBA to cultures induced a significant increase of to tal Cx43 protein because of an increase of the phosphorylated forms. Immuno fluorescence studies showed that HMBA increased the intensity of fluorescen ce for Cx43 at cell membrane borders. Quantitative reverse transcription an d PCR analysis revealed that the addition of HMBA to cultures resulted in t he concentration-dependent up-regulation of mRNA for Cx43. These results in dicate that HMBA induces the enhancement of GJIC in peritoneal mesothelial cells through both the up-regulation of Cx43 messages and an increase of po st-translational phosphorylation. HMBA may contribute to the maintenance of cellular homeostasis through the up-regulation of GJIC.