Am J Physiol Cell Physiol Journal of Applied Physiology
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Am J Physiol Cell Physiol 281: C1211-C1222, 2001;
0363-6143/01 $5.00
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Vol. 281, Issue 4, C1211-C1222, October 2001

Gap junction assembly: PTX-sensitive G proteins regulate the distribution of connexin43 within cells

Paul D. Lampe1, Qiu Qiu2, Rita A. Meyer2, Erica M. TenBroek2, Timothy F. Walseth3, Todd A. Starich2, Haiying L. Grunenwald2, and Ross G. Johnson2

1 Fred Hutchinson Cancer Research Center, Seattle, Washington 98109; and 2 Departments of Genetics, Cell Biology, and Development, and 3 Pharmacology, University of Minnesota, St. Paul, Minnesota 55108

Cells expressing connexin43 are able to upregulate gap junction (GJ) communication by enhancing the assembly of new GJs, apparently through increased connexin trafficking. Because G proteins are known to regulate different aspects of protein trafficking, we examined the effects of pertussis toxin (PTX; a specific inhibitor of certain G proteins) on GJ assembly. Dissociated Novikoff hepatoma cells were reaggregated for 60 min to form nascent junctions. PTX inhibited GJ assembly, as indicated by a reduction in dye transfer. Electron microscopy also revealed a 60% decrease in the number of GJ channels per cell interface. Importantly, PTX blocked the twofold enhancement in GJ assembly found in the presence of low-density lipoprotein. Two Gialpha proteins (Gialpha 2 and Gialpha 3), which have been implicated in the control of membrane trafficking, reacted with PTX in ADP-ribosylation studies. PTX and/or the trafficking inhibitors, brefeldin A and monensin, inhibited GJ assembly to comparable degrees. In addition, assays for GJ hemichannels demonstrated reduced plasma membrane levels of connexin43 following PTX treatment. These results suggest that PTX-sensitive G proteins regulate connexin43 trafficking, and, as a result of inhibition with PTX, the number of plasma membrane hemichannels available for GJ assembly is reduced.

gap junctions; pertussis toxin; protein trafficking; connexin


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