Connexin43 increases the sensitivity of prostate cancer cells to TNF-induced apoptosis

To examine the effects of increased expression of connexin43 (Cx43) upon cell viability and response to cytotoxic agents, we expressed Cx43 in LNCaP and PC3 prostate cancer cells by infection with a recombinant adenovirus (Ad-Cx43). Infection with Ad-Cx43 led to the formation of Cx43-containing gap junction plaques at appositional membranes and increased Lucifer Yellow transfer in LNCaP cells, but not in PC3 cells. The increased intercellular communication was blocked by co-infection with an adenovirus containing a dominant-negative Cx43 (Ad-Cx43DN). Infection of LNCaP (but not PC3) cells with Ad-Cx43 greatly increased their sensitivity to killing by tumor necrosis factor (TNF), anti-Fas antibodies, and TRAIL as quantified using an MTS assay. The TNF-induced cell death was dependent on cell density, and it was associated with increased annexin V staining, an increased proportion of sub-G1 cells, and activation of caspase 8. The TNF-induced effects on Ad-Cx43-infected LNCaP cells were blocked by co-infection with Ad-Cx43DN or by pre-incubation with neutralizing antibodies directed against TNF receptor 1. These results demonstrate that TNF induces apoptosis in LNCaP cells by signaling through TNF receptor 1 and that expression of functional Cx43 gap junction channels increases their sensitivity to TNF.