Lack of growth inhibition or enhancement of gap junctional intercellular communication and connexin43 expression by beta-carotene in murine lung epithelial cells in vitro

The carotenoid, beta-carotene, has been examined in human trials as a possible lung cancer chemopreventive agent, but initial results indicate that the compound is ineffective. Here we have considered whether beta-carotene could enhance gap junctional intercellular communication (GJIC) and affect the growth of lung epithelial cells, since these effects may be involved in the carotenoid's chemopreventive actions. In accordance with its lack of lung cancer chemopreventive activity, beta-carotene (1-10 mu M; 1-5 days treatment durations) did not affect GJIC, gap junction protein (connexin43; Cx43) expression, or growth in vitro of non-transformed (C10) or neoplastic (E9 and 82-132) murine lung epithelial cells. beta-Carotene enhanced GJIC and Cx43 expression and reduced the growth of C3H10T1/2 murine fibroblasts, however. These data indicate that the effects of beta-carotene on GJIC and growth are cell-specific which may partly explain why the carotenoid is an ineffective lung cancer chemopreventive agent.