Histone modifications and DNA double-strand break repair after exposure to ionizing radiations

Significant associations between X-ray repair cross-complementing group 3 genetic polymorphisms and thyroid cancer risk

Polymorphisms in X-ray cross-complementing group 3 (XRCC3) are proposed to be associated with cancer susceptibility, but previous studies on the associations between XRCC3 polymorphisms and thyroid cancer are controversial. We performed a systemic review and meta-analysis to investigate the associations of XRCC3 polymorphisms with thyroid cancer risk. We used odds ratio (OR) with 95 % confidence interval (95%CI) to assess the associations. For XRCC3 C241T polymorphism, meta-analysis of total eligible studies showed that there was no association between XRCC3 C241T polymorphism and thyroid cancer risk, but subgroup analysis in Caucasians showed that there was a significant association between XRCC3 C241T polymorphism and thyroid cancer risk (T versus C: OR = 1.30, 95%CI 1.05-1.62, P = 0.01; TT versus CC: OR = 1.74, 95%CI 1.13-2.70, P = 0.01; TT versus

CC/CT

OR = 1.74, 95%CI 1.16-2.60, P = 0.007). For XRCC3 A17893G polymorphism, meta-analysis of total eligible studies showed that there was an obvious association between XRCC3 A17893G polymorphism and thyroid cancer risk (GG versus AA/AG: OR = 0.57, 95%CI 0.35-0.93, P = 0.02), but subgroup analysis by ethnicity only identify the significant association in Asians. In summary, the meta-analysis suggests that there are significant associations of XRCC3 polymorphisms with thyroid cancer risk. Besides, more studies with large sample sizes are needed to further assess the associations above.

γH2AX foci formation in the absence of DNA damage: mitotic H2AX phosphorylation is mediated by the DNA-PKcs/CHK2 pathway

Phosphorylated H2AX is considered to be a biomarker for DNA double-strand breaks (DSB), but recent evidence suggests that γH2AX does not always indicate the presence of DSB. Here we demonstrate the bimodal dynamic of H2AX phosphorylation induced by ionizing radiation, with the second peak appearing when G2/M arrest is induced. An increased level of γH2AX occurred in mitotic cells, and this increase was attenuated by DNA-PKcs inactivation or Chk2 depletion, but not by ATM inhibition. The phosphorylation-mimic CHK2-T68D abrogated the attenuation of mitotic γH2AX induced by DNA-PKcs inactivation. Thus, the DNA-PKcs/CHK2 pathway mediates the mitotic phosphorylation of H2AX in the absence of DNA damage.

The role of inflammatory pathways in cancer-associated cachexia and radiation resistance

Dysregulated inflammatory responses are key contributors to a multitude of chronic ailments, including cancer. Evidence indicates that disease progression in cancer is dependent on the complex interaction between the tumor and the host microenvironment. Most recently, the inflammatory response has been suggested to be critical, as both the tumor and microenvironment compartments produce cytokines that act on numerous target sites, where they foster a complex cascade of biologic outcomes. Patients with cancer-associated cachexia (CAC) suffer from a dramatic loss of skeletal muscle and adipose tissue, ultimately precluding them from many forms of therapeutic intervention, including radiotherapy. The cytokines that have been linked to the promotion of the cachectic response may also participate in radiation resistance. The major changes at the cytokine level are, in part, due to transcriptional regulatory alterations possibly due to epigenetic modifications. Herein we discuss the role of inflammatory pathways in CAC and examine the potential link between cachexia induction and radiation resistance.