ABSTRACT
Autophagy, an evolutionarily conserved process by which components of the cell are degraded in lysosomes, may facilitate survival of cancer cells under stress conditions. 8-Azaguanine (8-AG), an inhibitor of purine nucleotide biosynthesis, shows antineoplastic activity in multiple tumor cells. However, chemoresistance has restricted its development as an anticancer agent, and the mechanism of 8-AG resistance is not fully understood. We report here that 8-AG induces a protective autophagy to eliminate its cytotoxicity, and inhibition of autophagy increases cellular sensitivity of cancer cells to 8-AG treatment. Using HepG2 or SMMC-7721 hepatic cancer cell lines, we found that 8-AG inhibited cell viability and induced intrinsic apoptosis, accompanied by the up-regulation of the pro-apoptotic protein BimS, one of Bim (also known as BCL-2-like protein 11, BCL2L11) isoforms. Furthermore, 8-AG treatment enhanced the autophagy flux by promoting the dephosphorylation and activation of Unc-51-like autophagy activating kinase 1 (ULK1) via Akt/mTORC1 (mammalian target of rapamycin complex 1) signaling inhibition. Depletion of autophagy-related gene 7 (ATG7) markedly enhanced the level of BimS, and promoted cell death in response to 8-AG. 8-AG in combination with autophagy inhibitor chloroquine (CQ) or bafilomycin A1 (Baf A1) promoted the 8-AG-induced apoptosis in hepatic cancer cells. Altogether, these findings suggest that autophagy promotes chemoresistance of cancer cells for 8-AG, and blocking autophagy increases cellular sensitivity of cancer cells to 8-AG treatment.
ABSTRACT
Objective Studies are rarely reported on the correlation of the Toll-like receptor (TLR) gene polymorphisms with fungal infection in the Chinese Han population. This study aims to explore the association between TLR gene polymorphisms and pulmonary candida infection (PCI) and candida colonization (CC) in patients with chronic obstructive pulmonary disease (COPD) in the Guizhou Han population. Methods Using the polymerase chain reaction-direct sequencing (PCR-SBT) method, we genotyped six single nucleotide polymorphisms (SNP) of the TLR1, TLR2 and TLR4 genes in 344 Guizhou Han patients with COPD, including 80 cases complicated by PCI (the PCI group), 103 cases complicated by CC (the CC group), and 161 negative controls. We analyzed the correlation of the SNPs with PCI and CC in the COPD patients in different genetic models with the SNPstats online software, measured the levels of IL-6, IL-8, IL-1β and TNF-α proteins in the plasma of the patients by ELISA, and assessed the functional consequences of these polymorphisms. Results The polymorphisms of rs5743611, rs5743708, rs4986790 and rs4986791 were found in none of the patients. The genotype frequency of rs4833095 was significantly different between the PCI and control groups in the codominant, dominant and overdominant models (P < 0.05), with the dominant model as the best genetic pattern. No statistically significant difference was observed either in the rs4833095 genotype frequency between the CC and control groups (P > 0.05) or in the rs5743618 genotype frequency between any two groups (P > 0.05). In the PCI group, the T allele of the rs4833095 polymorphism significantly decreased the levels of IL-6, IL-8 and IL-1β in the plasma (P < 0.05), and that of TNF-α as well, though with no statistically significant difference (P > 0.05). Conclusion The rs4833095 polymorphism of the TLR1 gene is associated with PCI in COPD patients. The T allele of rs4833095 may affect the function of TLR1, decrease the levels of IL-6, IL-8 and IL-1β proteins in the plasma. Neither rs4833095 nor rs5743618 gene polymorphism is correlated with the susceptibility to candida colonization.