In the present study, we have analyzed the direct effects of
cytokines, which mediate the
acute-phase response in liver, on
connexin expression and gap-junctional intercellular communication in immortalized MHSV12 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 positive acute-phase gene. In contrast, connexin32 (Cx32)
mRNA expression was not affected under these conditions. Indirect immunfluorescence revealed 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 immunoblots, 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 immortalized hepatocytes, was decreased by 70%, suggesting that intercellular communication through Cx32 channels was partially inhibited earlier than other genetic alterations characteristic of the
acute-phase response. Thus, the major hepatic
gap junction protein was largely downregulated at the beginning of the experimental inflammatory reaction, but about 30% of gap-junctional intercellular communication was maintained. This suggests that, during the
acute-phase response, the second hepatic Cx26
protein may compensate in part for the downregulation of the
Cx32 protein.