Transfection of rhabdomyosarcoma cells with connexin43 induces myogenic differentiation.

Normal cell physiological processes rely heavily on cues from the extracellular environment to coordinate the proper functioning of cellular activities. The intercellular communication that takes place through gap junctions in neighboring cells has been implicated in growth control and embryonic differentiation. Indeed, many tumorigenic cells induced to overexpress gap junction proteins exhibit increased differentiation and decreased cell proliferation. Although absent in mature skeletal muscle, studies have demonstrated that gap junctions are present during the early stages of myogenesis, indicating their possible role in muscle development. In our present study, we have attempted to induce a more differentiated phenotype in communication-deficient rhabdomyosarcoma cells. These tumorigenic human cells were transfected with cDNA encoding the gap junction protein connexin43 (Cx43) such that clones of varying expression were isolated. Intercellular communication as measured with dye passage assays was directly proportional to the level of Cx43 expressed, and in those cells expressing Cx43 at high levels, a marked increase in cell membrane fusion and myosin expression was observed. Furthermore, clones expressing Cx43 at high levels exhibited a significant reduction in growth rate when grown under nonadhesive conditions, an indication that their tumorigenicity had been reduced. This apparent increase in myogenic differentiation lends further evidence to the possible role of gap junctional coupling during developmental processes.