Mutant telomerase RNAs induce DNA damage and apoptosis via the TRF2‐ATM pathway in telomerase‐overexpressing primary fibroblasts

Abstract

Mutant template human telomerase RNAs (MT-hTers) have been shown to induce apoptosis in various cancer cells with high telomerase activity. However, the mechanism by which MT-hTers inhibit the growth of cancer cells and their effects on normal cells remain unknown. To determine the effects of MT-hTers on normal cells, MT-hTer-47A and -AU5 were introduced into IMR90 lung fibroblasts, which have low telomerase levels. Growth of IMR90 cells after MT-hTers infection was not significantly impaired; however, similar treatments in telomerase-overexpressing IMR90 [IMR90 wild-type (WT)hTERT] cells inhibited cell proliferation and induced apoptosis. Confocal microscopy showed that MT-hTers induced DNA damage foci (i.e. 53BP1 and γ-H2AX) in IMR90 WThTERT cells. Microarray analysis revealed that GADD45γ was significantly elevated in MT-hTer-treated IMR90 WThTERT cells. MT-hTers also induced ATM phosphorylation at Ser1981 in IMR90 WThTERT cells, and western blot analysis revealed high levels of phosphorylated p53 after the down-regulation of cellular TRF2 expression in MT-hTer-treated IMR90 WThTERT cells. Taken together, we have shown that MT-hTers induce double-stranded DNA break-like damages in telomerase positive IMR90 WThTERT cells after phosphorylation of ATM and p53 via suppression of TRF2, which may eventually lead to apoptosis via elevation of GADD45γ.

Telomere and Telomerase Therapeutics in Cancer

“…Incidentally, these telomeric aberrations induced phenotypic changes (e.g., extremely large, irregular cell and nuclear shapes) and senescence, ostensibly because telomere-binding proteins could no longer effectively bind the altered telomeric sequences [ 153 ]. When extended to mammalian systems, similarly altered TERC templates introduce by lentiviral infection into cancer cells induced foci of DNA damage at telomeres and characteristic “anaphase bridges” caused by telomeric fusions, and ultimately led to cancer cell apoptosis and decreased proliferation in vitro and in xenograft models [ 154 , 155 , 156 , 157 , 158 ]. These effects of mutant TERC were augmented by concurrent depletion of wild-type TERC [ 154 , 158 ].…”

Telomere biology: Rationale for diagnostics and therapeutics in cancer

“…Thus TERRA could serve as a marker for screening ALT cancers, and possibly also as a target for ALT cancers 40 protection of telomeres during their replication provides a therapeutic window. Also, antiproliferative effects of telomere uncapping strategies appear to be restricted to cancer cells, suggesting that the telomere cap may differ in cancer cells versus normal cells [45][46][47][48] . Deregulated expression of shelterin proteins has been reported in some human tumors, and Pot1 was found to be mutated in chronic lymphocytic leukemia (CLL) [49][50][51] , suggesting that the telomere cap in cancer cells may be different than in normal cells and that it may be possible to specifically target telomere function in cancer cells.…”

Effect of therapies-mediated modulation of telomere and/or telomerase on cancer cells radiosensitivity

“…Telomere RNA (TER) structure contains certain conserve elements such as template region, the pseudoknot, the trans-activating domain and the domains required to ensure in-vivo stability, meaning that TER contains the essential elements for telomerase activity, assembly, localization and stability of RNA. Apart from the telomerase activity of telomerase, telomerase and telomerase component have an alternative functions in cell life such as telomerase nuclease activity because the length of the final products depends on the template region of telomerase RNA [ 68 ], transferase activity via stimulation of certain small molecules [ 69 , 70 ], mitochondrial function activity via implication of hTERT in replication and repair of mtDNA [ 71 ], DNA damage activity [ 72 ] and regulation of gene activity [ 73 – 75 ]. According to the relationship between telomerase and telomere and their roles in cell function and life, dysfunction of telomere and /or telomerase can lead to dysfunction of a cell (disease).…”