Alternative lengthening of telomeres in hTERT-inhibited laryngeal cancer cells.

In most human malignancies, telomere homeostasis is maintained by the reactivation of telomerase. While inhibiting telomerase provides a novel approach to the treatment of many cancers, telomere maintenance can occur in the absence of telomerase activity by the alternative lengthening of telomeres (ALT) mechanism. Therefore, it must be determined if inhibiting telomerase selects for cancer cells that activate ALT. Here, we report that Hep-2 cells that survived anti-telomerase treatments showed sustained proliferation in culture with down-regulated human telomerase reverse transcriptase (hTERT) expression and significantly enhanced levels of ALT-specific promyelocytic leukemia (PML) bodies. Analysis of the telomere lengthening kinetics also demonstrated elevated telomeric sister-chromatid exchange (T-SCE) in surviving Hep-2 cells, consistent with their long and heterogeneous telomeres. Similar to ALT cells, the surviving cells showed evidence of ALT telomere homeostasis. Furthermore, proteomic analysis identified several proteins differentially expressed between the untreated Hep-2 cells and surviving cells that may provide new insight for understanding these two telomere maintenance mechanisms. Thus, the findings in this study may help to improve telomerase-based therapy for cancer.