[en] A telomere is a region of repetitive DNA at the end of chromosomes. They protect a cell's chromosomes from fusing with each other or rearranging and so cells are normally destroyed when their telomeres are consumed. Most normal somatic cells lose telomeric repeats after each cell division. Telomeric shortening in humans can induce replicative senescence which blocks cell division. This mechanism appears to prevent genomic instability by limiting the number of cell divisions. Telomerase is an attractive molecular target, since its activity has been found in more than 85% of human cancers. Combination therapy with chemotherapeutic agent is superior to single in overall response rate and progression free survival. In this study, we showed that telomerase null cells are more hypersensitive by paclitaxel treatment than at wild type cells

[en] Research highlights: → In our present manuscript, we have clearly showed an interesting but problematic obstacle of a radiosensitization strategy based on telomerase inhibition by showing that: Clonal population unresponsive to this radiosensitization occasionally arise. → The telomere length of unsensitized clones was reduced, as was that of most sensitized clones. → The unsensitized clones did not show chromosome end fusion which was noted in all sensitized clones. → P53 status is not associated with the occurrence of unsensitized clone. → Telomere end capping in unsensitized clone is operative even under telomerase deficiency. -- Abstract: A combination of a radiotherapeutic regimen with telomerase inhibition is valuable when tumor cells are to be sensitized to radiation. Here, we describe cell clones unresponsive to radiosensitization after telomere shortening. After extensive division of individual transformed clones of mTERC^-/- cells, about 22% of clones were unresponsive to radiosensitization even though telomerase action was inhibited. The telomere lengths of unsensitized mTERC^-/- clones were reduced, as were those of most sensitized clones. However, the unsensitized clones did not exhibit chromosomal end-to-end fusion to the extent noted in all sensitized clones. Thus, a defense mechanism preventing telomere erosion is operative even when telomeres become shorter under conditions of telomerase deficiency, and results in unresponsiveness to the radiosensitization generally mediated by telomere shortening.

[en] Highlights: • NANOG contributes to stabilization of HDAC1 protein through AKT signaling pathway. • NANOG-AKT axis leads to phosphor-dependent inactivation of CHFR, which is an E3 ligase for HDAC1 protein. • HDAC1 confers immune-resistance, drug-resistance and stem-like phenotype through its catalytic activity. • AKT inhibition disrupts HDAC1-mediated multi-resistance and stem-like phenotype. Cancer immunoediting enriches NANOG expression in tumor cells, resulting in multi-drug resistance and stem-like phenotypes. We previously demonstrated that these NANOG-associated phenotypes are promoted through HDAC1 transcriptional upregulation. In this study, we identified that NANOG also contributes to the stabilization of HDAC1 protein through the AKT signaling pathway. NANOG-AKT axis leads to phosphor-dependent inactivation of CHFR, an E3 ligase for HDAC1 protein, and thereby inhibiting the ubiquitin-mediated degradation of HDAC1. Furthermore, AKT inhibition disrupts HDAC1 WT-mediated phenotypes but had no effect on the phenotypes mediated by HDAC1 FM, a mutant that is unable to interact with CHFR. Critically, we applied a catalytic dead mutant, HDAC1-H141A, to uncover that HDAC1 confers immune-resistance, drug-resistance and stem-like phenotype in tumor cells through its catalytic activity. Collectively, our results establish a firm molecular link in immune-edited tumor cells among NANOG, AKT, CHFR, and HDAC1, identifying HDAC1 as a molecular target in controlling NANOGHIGH immune-refractory cancer.

[en] Highlights: ► SIRT1 serves to retain GAPDH in the cytosol, preventing GAPDH nuclear translocation. ► When SIRT1 is depleted, GAPDH translocation occurs even in the absence of stress. ► Upon irradiation, SIRT1 interacts with GAPDH. ► SIRT1 prevents irradiation-induced nuclear translocation of GAPDH. ► SIRT1 presence rather than activity is essential for inhibiting GAPDH translocation. -- Abstract: Upon apoptotic stimulation, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a cytosolic enzyme normally active in glycolysis, translocates into the nucleus and activates an apoptotic cascade therein. In the present work, we show that SIRT1 prevents nuclear translocation of GAPDH via interaction with GAPDH. SIRT1 depletion triggered nuclear translocation of cytosolic GAPDH even in the absence of apoptotic stress. Such translocation was not, however, observed when SIRT1 enzymatic activity was inhibited, indicating that SIRT1 protein per se, rather than the deacetylase activity of the protein, is required to inhibit GAPDH translocation. Upon irradiation, SIRT1 prevented irradiation-induced nuclear translocation of GAPDH, accompanied by interaction of SIRT1 and GAPDH. Thus, SIRT1 functions to retain GAPDH in the cytosol, protecting the enzyme from nuclear translocation via interaction with these two proteins. This serves as a mechanism whereby SIRT1 regulates cell survival upon induction of apoptotic stress by means that include irradiation.

[en] Research highlights: → Paclitaxel serves as a stimulator of chromosomal fusion in cells in which telomeres are dysfunctional. → Typical fusions involve p-arms, but paclitaxel-induced fusions occur between both q- and p-arms. → Paclitaxel-stimulated fusions in cells in which telomeres are dysfunctional evoke prolonged G2/M cell cycle arrest and delay multinucleation. → Upon telomere erosion, paclitaxel promotes chromosomal instability and subsequent apoptosis. → Chromosomal fusion enhances paclitaxel chemosensitivity under telomere dysfunction. -- Abstract: The anticancer effect of paclitaxel is attributable principally to irreversible promotion of microtubule stabilization and is hampered upon development of chemoresistance by tumor cells. Telomere shortening, and eventual telomere erosion, evoke chromosomal instability, resulting in particular cellular responses. Using telomerase-deficient cells derived from mTREC-/-p53-/- mice, here we show that, upon telomere erosion, paclitaxel propagates chromosomal instability by stimulating chromosomal end-to-end fusions and delaying the development of multinucleation. The end-to-end fusions involve both the p- and q-arms in cells in which telomeres are dysfunctional. Paclitaxel-induced chromosomal fusions were accompanied by prolonged G2/M cell cycle arrest, delayed multinucleation, and apoptosis. Telomere dysfunctional cells with mutlinucleation eventually underwent apoptosis. Thus, as telomere erosion proceeds, paclitaxel stimulates chromosomal fusion and instability, and both apoptosis and chemosensitization eventually develop.

[en] Highlights: ► Under conditions of telomere erosion, cells become extremely sensitive to H₂O₂. ► Chromosomal regions adjacent to telomeres are cleaved by H₂O₂ under such conditions. ► H₂O₂ thus causes multichromosomal fusions and generation of small chromosomal fragments. ► N-acetylcysteine prevents H₂O₂-induced chromosomal aberrations. -- Abstract: During genotoxic stress, reactive oxygen species hydrogen peroxide (H₂O₂) is a prime mediator of the DNA damage response. Telomeres function both to assist in DNA damage repair and to inhibit chromosomal end-to-end fusion. Here, we show that telomere dysfunction renders cells susceptible to H₂O₂, via generation of multichromosomal fusion and chromosomal fragments. H₂O₂ caused formation of multichromosomal end-to-end fusions involving more than three chromosomes, preferentially when telomeres were erosive. Interestingly, extensive chromosomal fragmentation (yielding small-sized fragments) occurred only in cells exhibiting such multichromosomal fusions. Telomeres were absent from fusion points, being rather present in the small fragments, indicating that H₂O₂ cleaves chromosomal regions adjacent to telomeres. Restoration of telomere function or addition of the antioxidant N-acetylcysteine prevented development of chromosomal aberrations and rescued the observed hypersensitivity to H₂O₂. Thus, chromosomal regions adjacent to telomeres become sensitive to reactive oxygen species hydrogen peroxide when telomeres are dysfunctional, and are cleaved to produce multichromosomal fusions and small chromosomal fragments bearing the telomeres.