Connexin43 pseudogene in breast cancer cells offers a novel therapeutic target

Connexin43 (Cx43) is often deregulated in breast cancer tissue compared with normal adjacent tissue. Stable reexpression of Cx43 in cancer slows growth and renders the cells more sensitive to cytotoxic chemotherapeutics. Pseudogenes are often considered nonfunctional copies of DNA. The Cx43 pseudogene (Psi Cx43) possesses all the features of an expressed gene and is exclusively transcribed in breast cancer cell lines and not in normal cells. Psi Cx43 can be translated in vivo, and its protein exhibits growth-suppressive behavior similar to Cx43. We showed that Psi Cx43 binds to the polyribosomes in breast cancer cells and that exogenous expression of Psi Cx43 induces translational inhibition of Cx43. Furthermore, (Psi Cx43 is translated and binds more efficiently to the translational machinery than does Cx43 in an in vitro system. Following knockdown of Psi Cx43 in breast cancer cells, we observed an increase in Cx43 RNA and protein. This results in increased cellular sensitivity to cytotoxic chemotherapy. Our results show that Psi Cx43 acts as a posttranscriptional regulator of Cx43 in breast cancer cells, and that this represents an example of the regulation of genes by pseudogenes with potential therapeutic implications in cancer. [Mol Cancer Ther 2009;8(4):786-93]