Radiotherapy is increasingly used in the treatment of joint diseases, but limited information is available on the effects of radiation on cartilage. Here, we characterize the molecular mechanisms leading to cellular senescence in irradiated primary cultured articular chondrocytes. Ionizing radiation (IR) causes activation of ERK, in turn generating intracellular reactive oxygen species (ROS) with induction of senescence-associated beta-galactosidase (SA-beta-gal) activity. ROS activate p38 kinase, which further promotes ROS generation, forming a positive feedback loop to sustain ROS-p38 kinase signaling. The ROS inhibitors, nordihydroguaiaretic acid and GSH, suppress phosphorylation of p38 and cell numbers positive for SA-beta-gal following irradiation. Moreover, inhibition of the ERK and p38 kinase pathways leads to blockage of IR-induced SA-beta-gal activity via reduction of ROS generation. Although JNK is activated by ROS, this pathway is not associated with cellular senescence of chondrocytes. Interestingly, IR triggers down-regulation of SIRT1 protein expression but not the transcript level, indicative of post-transcriptional cleavage of the protein. SIRT1 degradation is markedly blocked by SB203589 or MG132 after IR treatment, suggesting that cleavage occurs as a result of binding with p38 kinase, followed by processing via the 26 S proteasomal degradation pathway. Overexpression or activation of SIRT1 significantly reduces the IR-induced senescence phenotype, whereas inhibition of SIRT1 activity induces senescence. Based on these findings, we propose that IR induces cellular senescence of articular chondrocytes by negative post-translational regulation of SIRT1 via ROS-dependent p38 kinase activation.

Glioblastoma, the most common primary brain tumor in adults, is an incurable malignancy with poor short-term survival and is typically treated with radiotherapy along with temozolomide. While the development of tumor-treating fields (TTFields), electric fields with alternating low and intermediate intensity has facilitated glioblastoma treatment, clinical outcomes of TTFields are reportedly inconsistent. However, combinatorial administration of chemotherapy with TTFields has proven effective for glioblastoma patients. Sorafenib, an anti-proliferative and apoptogenic agent, is used as first-line treatment for glioblastoma. This study aimed to investigate the effect of sorafenib on TTFields-induced anti-tumor and anti-angiogenesis responses in glioblastoma cells in vitro and in vivo. Sorafenib sensitized glioblastoma cells to TTFields, as evident from significantly decreased post-TTFields cell viability (p < 0.05), and combinatorial treatment with sorafenib and TTFields accelerated apoptosis via reactive oxygen species (ROS) generation, as evident from Poly (ADP-ribose) polymerase (PARP) cleavage. Furthermore, use of sorafenib plus TTFields increased autophagy, as evident from LC3 upregulation and autophagic vacuole formation. Cell cycle markers accumulated, and cells underwent a G2/M arrest, with an increased G0/G1 cell ratio. In addition, the combinatorial treatment significantly inhibited tumor cell motility and invasiveness, and angiogenesis. Our results suggest that combination therapy with sorafenib and TTFields is slightly better than each individual therapy and could potentially be used to treat glioblastoma in clinic, which requires further studies.

Although much is known about interleukin (IL)-1β and its role as a key mediator of cartilage destruction in osteoarthritis, only limited information is available on IL-1β signaling in chondrocyte dedifferentiation. Here, we have characterized the molecular mechanisms leading to the dedifferentiation of primary cultured articular chondrocytes by IL-1β treatment. IL-1β 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-1β-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-1β. 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-1β-induced chondrocyte dedifferentiation via a Sox-9-mediated mechanism. JNK is activated by IL-1β and modulates dedifferentiation of chondrocytes, but this pathway is independent on NAMPT-SIRT1 signaling. Based on these findings, we propose that IL-1β induces dedifferentiation of articular chondrocytes by up-regulation of SIRT1 activity enhanced by both NAMPT and ERK signaling.

Glioblastoma is frequently associated with TP53 mutation, which is linked to a worse prognosis and response to conventional treatments (chemoradiotherapy). Therefore, targeting TP53 is a promising strategy to overcome this poor therapeutic response. Tumor-treating fields (TTFields) are a recently approved treatment for newly diagnosed glioblastoma, which involves direct application of low-intensity, intermediate-frequency alternating electric fields to the tumor, thereby offering a local tumor-killing effect. However, the influence of TP53 mutation status on the effectiveness of TTFields is controversial. Here, we identified the key gene signatures and pathways associated with TTFields in four glioblastoma cell lines varying in TP53 mutation status using gene profiling and functional annotation. Overall, genes associated with the cell cycle, cell death, and immune response were significantly altered by TTFields regardless of TP53 status. TTFields appeared to exert enhanced anti-cancer effects by altering the immune system in the inflammatory environment and regulating cell cycle- and cell death-related genes, but the precise genes influenced vary according to TP53 status. These results should facilitate detailed mechanistic studies on the molecular basis of TTFields to further develop this modality as combination therapy, which can improve the therapeutic effect and minimize side effects of chemoradiotherapy.