Because HOX genes are important not only in development, but are also aberrantly expressed in many human malignancies35, we investigated whether HoxC5 itself might influence the expression of hTERT. Indeed, we found that lentivirus-mediated overexpression of HoxC5, but not GFP, resulted in significantly reduced hTERT mRNA levels, reduced telomerase activity, and gradual telomere shortening in multiple cancer cell lines, including HeLa, PC-3, U-251 and BT549 cells (Fig. 3b–d). Here, HOXC5 is linked to cancer.