| Cisplatin is one of the most widely used chemotherapy agents for cancer. Its cytotoxicity has been linked to the production of covalent intra- and inter-strand crosslinks on DNA. The exact molecular mechanism of how cisplatin mediates its toxicity, however, has not been well established. Our work demonstrates that DNA-PK signaling plays a significant role in cell death following treatment with cisplatin. This discovery was first realized when cells mutant or knocked out for the DNA-PK component, Ku80, were found to exhibit resistance to cisplatin compared to their isogenic wild type counterparts. Further work demonstrated that cells mutant for the catalytic subunit of DNA-PK (DNA-PKcs) were also resistant to cisplatin compared to a complemented subclone. This differential response to cisplatin is dependent upon high cell density at time of exposure. The density dependent effect requires intercellular communication through gap junctions as blockade of gap junction intercellular communication (GJIC) either through chemical inhibitors, use of cell lines deficient in GJIC, or RNAi mediated silencing of the Connexin43 gene, all result in resistance to cisplatin. We also show that Ku80 wild type cells can decrease the survival of Ku80 knockout cells in mixed cell populations treated with cisplatin. The intercellular transmission of this cytotoxic signal does not occur in the absence of GJIC. These results place the Ku/DNA-PKcs complex in a cisplatin induced cell death signaling pathway dependent upon intercellular communication through gap junctions. |
