Salmonella enhance chemosensitivity in tumor through connexin 43 upregulation.

The use of preferentially replicating bacteria as oncolytic agents is one of the innovative approaches for the treatment of cancer. The capability of Salmonella to disperse within tumors and hence to delay tumor growth was augmented when combined with chemotherapy. This work is warranted to elucidate the underlying mechanism of antitumor effects by the combination therapy of Salmonella and cisplatin. The presence of functional gap junctions is highly relevant for the success of chemotherapy. Following Salmonella treatment, dose- and time-dependent upregulation of connexin 43 (Cx43) expressions were observed. Moreover, Salmonella significantly enhanced gap intercellular communication (GJIC), as revealed by the fluorescent dye scrape loading assay. To study the pathway underlying these Salmonella-induced effects, we found that Salmonella induced a significant increase in mitogen-activated protein kinases (MAPK) signaling pathways. The Salmonella-induced upregulation of Cx43 was prevented by treatment of cells with the phosphorylated p38 inhibitor, but not phosphorylated extracellular signal-regulated kinase (pERK) inhibitor or phosphorylated c-jun N terminal kinase (pJNK) inhibitor. Specific knockdown of Cx43 had an inhibitory effect on GJIC and resulted in a reduction of cell death after Salmonella and cisplatin treatment. Our results suggest that accumulation of Salmonella in tumor sites leads to increase Cx43 gap junction communication and enhances the combination of Salmonella and cisplatin therapeutic effects.