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 important means of regulating cell growth and the malignant potential of tumors. This study examined the effect of hexamethylene bisacetamide (HMBA), a hybrid polar compound and a potent differentiation inducer, on GJIC in cultured primary human peritoneal mesothelial cells. The redistribution of fluorescence after photobleaching was used to detect GJIC. After the incubation of confluent cell cultures with 3 or 6 mM HMBA for 3 and 6 days, GJIC was significantly increased in a concentration-dependent manner compared with cultures without HMBA. Western blotting showed that connexin 43 (Cx43), the major functional protein of gap junctions in peritoneal mesothelial cells, was present in unphosphorylated and phosphorylated forms in control cell cultures. The addition of HMBA to cultures induced a significant increase of total Cx43 protein because of an increase of the phosphorylated forms. Immunofluorescence studies showed that HMBA increased the intensity of fluorescence for Cx43 at cell membrane borders. Quantitative reverse transcription and PCR analysis revealed that the addition of HMBA to cultures resulted in the concentration-dependent up-regulation of mRNA for Cx43. These results indicate that HMBA induces the enhancement of GJIC in peritoneal mesothelial cells through both the up-regulation of Cx43 messages and an increase of post-translational phosphorylation. HMBA may contribute to the maintenance of cellular homeostasis through the up-regulation of GJIC.