Maintenance of telomere length is predicted to be essential for bypass of senescence and crisis checkpoints in cancer cells. The impact of telomere dysfunction on tumorigenesis was assessed in successive generations of mice doubly null for the telomerase RNA (mTR) and the INK4a tumor suppressor genes. Significant reductions in tumor formation in vivo and oncogenic potential in vitro were observed in late generations of telomerase deficiency, coincident with severe telomere shortening and associated dysfunction. Reintroduction of mTR into cells significantly restored the oncogenic potential, indicating telomerase activation is a cooperating event in the malignant transformation of cells containing critically short telomeres. The results described here demonstrate that loss of telomere function in a cancer-prone mouse model possessing intact DNA damage responses impairs, but does not prevent, tumor formation.

The nature of the molecules underlying the radioresistance phenotype of laryngeal cancer cells remains to be established. We initially generated radioresistant laryngeal cancer cell lines from human HEp-2 cells with fractionated radiation. These RR-HEp-2 cells and isolated clones displayed more radioresistant and anti-apoptotic phenotypes than parental HEp-2 cells after radiation. Characteristics of RR-Hep-2 cell lines were confirmed by upregulation of radioresistance-related genes, such as epidermal growth factor receptor, Hsp90, and Bcl-xl. Subsequently, we examined proteome changes between HEp-2 and RR-HEp-2 cells and identified 16 proteins showing significantly altered expression levels. Interestingly, protein expression of chloride intracellular channel 1 (CLIC1) was markedly suppressed in RR-HEp-2 cells, compared with non-irradiated control cells. Suppression of CLIC1 with an indanyloxyacetic acid-94 or small interfering RNA led to radioresistance in HEp-2 cells by suppressing the radiation-induced cellular ROS level. However, ectopic overexpression of CLIC1 induced radiosensitivity in RR-HEp-2 cells via induction of ROS level after radiation, suggesting that the protein acts as a positive regulator of ROS production. Our results collectively indicate that suppression of CLIC1 contributes to acquisition of the radioresistance phenotype of laryngeal cancer cells via inhibition of ROS production, implying that this protein is an important candidate molecule for radiotherapy in radioresistant laryngeal cancer cells.

The low efficiency of conventional therapies in achieving long-term survival of patients with lung cancer calls for development of novel treatment options. Although several genes have been investigated for their antitumor activities through gene delivery, problems surrounding the methods used, such as efficiency, specificity, and toxicity, hinder application of such therapies in clinical settings.

The gradual loss of telomeric DNA can contribute to replicative senescence and thus, having longer telomeric DNA is generally considered to provide a longer lifespan. Maintenance and stabilization of telomeric DNA is assisted by binding of multiple DNA-binding proteins, including those involved in double strand break (DSB) repair. We reasoned that declining DSB repair capacity and increased telomere shortening in aged individuals may be associated with decreased expression of DSB repair proteins capable of telomere binding. Our data presented here show that among the DSB repair proteins tested, only the expression of Ku70 and Mre11 showed statistically significant age-dependent changes in human lymphocytes. Furthermore, we found that expressions of Ku70 and Mre11 are statistically correlated, which indicate that the function of Ku70 and Mre11 may be related. All the other DSB repair proteins tested, Sir2, TRF1 and Ku80, did not show any significant differences upon aging. In line with these data, people who live in the regional community (longevity group), which was found to have statistically longer average life span than the rest area, shows higher level of Ku70 expression than those living in the neighboring control community. Taken together, our data show, for the first time, that Ku70 and Mre11 may represent new biomarkers for aging and further suggest that maintenance of higher expression of Ku70 and Mre11 may be responsible for keeping longer life span observed in the longevity group.

Although much is known about interleukin (IL)-1␤ and its role as a key mediator of cartilage destruction in osteoarthritis, only limited information is available on IL-1␤ signaling in chondrocyte dedifferentiation. Here, we have characterized the molecular mechanisms leading to the dedifferentiation of primary cultured articular chondrocytes by IL-1␤ treatment. IL-1␤ or lipopolysaccharide, but not phorbol 12-myristate 13-acetate, retinoic acid, or epidermal growth factor, induced nicotinamide phosphoribosyltransferase (NAMPT) expression, showing the association of inflammatory cytokines with NAMPT regulation. SIRT1, in turn, was activated NAMPT-dependently, without any alteration in the expression level. Activation or inhibition of SIRT1 oppositevely regulates IL-1␤-mediated chondrocyte dedifferentiation, suggesting this protein as a key regulator of chondrocytes phenotype. SIRT1 activation promotes induction of ERK and p38 kinase activities, but not JNK, in response to IL-1␤. Subsequently, ERK and p38 kinase activated by SIRT1 also induce SIRT1 activation, forming a positive feedback loop to sustain downstream signaling of these kinases. Moreover, we found that the SIRT1-ERK complex, but not SIRT1-p38, is engaged in IL-1␤-induced chondrocyte dedifferentiation via a Sox-9-mediated mechanism. JNK is activated by IL-1␤ and modulates dedifferentiation of chondrocytes, but this pathway is independent on NAMPT-SIRT1 signaling. Based on these findings, we propose that IL-1␤ induces dedifferentiation of articular chondrocytes by up-regulation of SIRT1 activity enhanced by both NAMPT and ERK signaling.