Rapid Inhibition of Cancer Cell Growth Induced by Lentiviral Delivery and Expression of Mutant-Template Telomerase RNA and Anti-telomerase Short-Interfering RNA

Abstract

In human cancers, telomeres are commonly maintained by elevated levels of the ribonucleoprotein enzyme telomerase, which contains an intrinsic templating RNA moiety (human telomerase RNA; hTER) and the core protein (human telomerase reverse transcriptase). We developed a lentiviral system for efficient overexpression of mutant-template human telomerase RNA (MT-hTer) to add mutant DNA to telomeres in cancer cells. We show that such MT-hTer overexpression rapidly inhibits cell growth and induces apoptosis in telomerase-positive precancerous or cancer cells but not in telomerase-negative cells. These rapid effects occurred independent of wild-type p53 and telomere length. Tumor growth and progression were significantly decreased in xenografts of human tumor cells overexpressing MT-hTers. Expression of a hairpin short-interfering RNA that specifically targeted the endogenous wild-type hTER template region, but spared the MT-hTers, also caused p53-independent cell growth inhibition and apoptosis, and when coexpressed with MT-hTer, synergistically killed cancer cells. Hence, anti-wild-type-hTER short-interfering RNA and MT-hTers may act through distinct pathways and, particularly in combination, represent a promising approach to anticancer therapies.

Mutated telomeres sensitize tumor cells to anticancer drugs independently of telomere shortening and mechanisms of telomere maintenance

“…These effects are most likely owing to the inability of telomeric proteins to bind to the mutated repeats and do not require telomere shortening (Marusic et al, 1997;Kim et al, 2001). However, unless the mutant hTR is highly overexpressed or the endogenous hTR is absent (Guiducci et al, 2001;Li et al, 2004), the endogenous telomerase complex adds wild-type sequences to mutant ones, partially restoring telomere function and mitigating the deleterious effects of the mutant telomerase. Hence, the expression of mutant template RNAs may only be partially effective in inducing cell death of telomerase-positive cancer cells and human tumors.…”

Telomeres and telomerase: their mechanisms of action and the effects of altering their functions

“…In human cancer cells, telomere uncapping is caused by expression of a telomerase RNA with a mutant template [25]. In these cells, DNA damage foci can be seen clearly forming at the telomeres themselves, the DNA damage protein p21 is induced, and apoptosis increases.…”

Elevated Bmi-1 expression is associated with dysplastic cell transformation during oral carcinogenesis and is required for cancer cell replication and survival

“…Actively proliferating BaP-T cells were infected with LV-GFP or LV-Bmi-1i vectors. For comparison, we also infected the cells with LV-hTERTi, targeting the cellular telomerase activity, which demonstrated effective anticancer activity (Li et al, 2004). The cells were maintained in culture for 10 days post-infection, and the total numbers of the infected cells were determined.…”