Transfection of C6 glioma cells with connexin32: the effects of expression of a nonendogenous gap junction protein.

C6 glioma cells do not express the gap junction protein connexin32 or its corresponding mRNA. Very low levels of connexin43 protein and mRNA, as well as weak intercellular coupling, have been detected. Studies investigating the role of gap junctions in cell proliferation and tumorigenesis have shown that C6 cells transfected with connexin43 have increased levels of intercellular coupling and reduced cell growth (D. Zhu et al., Proc. Natl. Acad. Sci. USA, 88:1883-1887, 1991). To determine whether this growth inhibition is observed with other connexins, a full-length cDNA for connexin32 was used to transfect C6 cells. A number of transfected clones, expressing various levels of connexin32 mRNA, were obtained. Further analysis of several of these clones has shown that they have a corresponding increase in both the amount of connexin32 immunoreactivity and intercellular coupling. Thus, transfection of the C6 glioma cell line with connexin32, a gene which is normally expressed in the rat brain but not in C6 cells, produces both a functional mRNA and protein. Growth of the transfected clones was reduced in vivo. In vitro, growth of the various clones was not correlated to either levels of connexin32 expression or intercellular coupling. This is in contrast to findings in the previous study, in which cell growth was reduced in response to connexin43 expression both in vivo and in vitro in the transfected cells. These clones provide a unique system to study the role of gap junctions in cell proliferation and other tumor characteristics.