DOWN-REGULATION OF CONNEXIN32 PROTEIN AND GAP-JUNCTIONAL INTERCELLULAR COMMUNICATION BY CYTOKINE-MEDIATED ACUTE-PHASE RESPONSE IN IMMORTALIZED MOUSE HEPATOCYTES

In the present study, we have analyzed the direct effects of cytokines , which mediate the acute-phase response in liver, on connexin express ion and gap-junctional intercellular communication in immortalized MHS V12 mouse hepatocytes. When these cells were stimulated for 24 h with interleukin 1 and interleukin 6, the amount of connexin26 (Cx26) mRNA increased together with beta-fibrinogen mRNA, as expected for this pos itive acute-phase gene. In contrast, connexin32 (Cx32) mRNA expression was not affected under these conditions. Indirect immunfluorescence r evealed a drastic decrease in Cx32 signals, whereas slightly more Cx26 signals were found. Stronger stimulation with interleukin 1 and tumor necrosis factor alpha gave a dose-dependent increase in steady state levels of Cx26 and beta-fibrinogen mRNA, but no further change in Cx32 mRNA level was seen. However, when Cx32 protein was analyzed on immun oblots, we found a 5-fold decrease in expression even at low cytokine doses that did not affect Cx32 mRNA expression. Under these conditions , cell to cell transfer of Lucifer yellow, microinjected into immortal ized hepatocytes, was decreased by 70%, suggesting that intercellular communication through Cx32 channels was partially inhibited earlier th an other genetic alterations characteristic of the acute-phase respons e. Thus, the major hepatic gap junction protein was largely downregula ted at the beginning of the experimental inflammatory reaction, but ab out 30% of gap-junctional intercellular communication was maintained. This suggests that, during the acute-phase response, the second hepati c Cx26 protein may compensate in part for the downregulation of the Cx 32 protein.