No abstract

The widespread environmental pollutant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a potent toxicant that causes significant neurotoxicity. However, the biological events that participate in this process remain largely elusive. In the present study, we demonstrated that TCDD exposure triggered apparent premature senescence in rat pheochromocytoma (PC12) and human neuroblastoma SH-SY5Y cells. Senescence-associated β-galactosidase (SA-β-Gal) assay revealed that TCDD induced senescence in PC12 neuronal cells at doses as low as 10 nM. TCDD led to F-actin reorganization and the appearance of an alternative senescence marker, γ-H2AX foci, both of which are important features of cellular senescence. In addition, TCDD exposure altered the expression of senescence marker proteins, such as p16, p21 and p-Rb, in both dose- and time-dependent manners. Furthermore, we demonstrated that TCDD promotes mitochondrial dysfunction and the accumulation of cellular reactive oxygen species (ROS) in PC12 cells, leading to the activation of signaling pathways that are involved in ROS metabolism and senescence. TCDD-induced ROS generation promoted significant oxidative DNA damage and lipid peroxidation. Notably, treatment with the ROS scavenger N-acetylcysteine (NAC) markedly attenuated TCDD-induced ROS production, cellular oxidative damage and neuronal senescence. Moreover, we found that TCDD induced a similar ROS-mediated senescence response in human neuroblastoma SH-SY5Y cells. In sum, these results demonstrate for the first time that TCDD induces premature senescence in neuronal cells by promoting intracellular ROS production, supporting the idea that accelerating the onset of neuronal senescence may be an important mechanism underlying TCDD-induced neurotoxic effects.

No abstract

Objective. Rab27b is reported to correlate with cancer development and progression. However, the association between Rab27b expression and the clinical characteristics of colorectal cancer (CRC) is barely investigated. Methods. One-step quantitative reverse transcription-polymerase chain reaction (qPCR) test with 18 fresh-frozen CRC samples and immunohistochemistry (IHC) analysis in 113 CRC cases were performed to explore the relationship between Rab27b expression and the clinicopathological features of CRC. Cox regression and Kaplan-Meier survival analyses were executed to evaluate the prognosis of CRC. Results. The results demonstrated that the expression levels of Rab27b mRNA and protein were significantly higher in CRC tissues than that in matched noncancerous tissues (P < 0.05). Rab27b protein expression in CRC was statistically correlated with serum CEA level (P = 0.004), lymph node metastasis (P = 0.001), distant metastasis (P = 0.009), and TNM stage (P = 0.001). Cox multifactor analysis and Kaplan-Meier method suggested that higher Rab27b protein expression (P = 0.041) and tumor differentiation (P = 0.001) were significantly associated with the overall survival of CRC patients. Conclusions. The data indicated that higher expression of Rab27b was observed in CRC tissues and Rab27b may be identified as a useful predictor of metastasis and prognosis for CRC.