ABSTRACT
Western blotting of autophagic markers LC3Ⅱ and p62 are widely used for estimating autophagic activity. To compare the regulation of various autophagy modulators on LC3Ⅱ and p62,HEK293 cells were treated separately with mTOR-dependent autophagy activator rapamycin or -independent autophagy activators trehalose, and autophagy inhibitors including 3-methyladenine (3-MA),bafilomycin A1 or E64d and pepstatin A that inhi-bited the initiation of autophagy,the fusion of autophagosome and lysosome,and the activities of lysosomal enzymes accordingly,and then LC3Ⅱ and p62 levels were assessed. Western blot results demonstrated that rapam-ycin enhanced the conversion of LC3I to LC3Ⅱ,promoted the degradation of p62 simultaneously,while trehalose merely increased the expression of LC3Ⅱ with no influence on the p62 level. Moreover,inhibition of autophagy commonly led to accumulation of LC3Ⅱ as well as blockage of p62 degradation in a concentration- and time-dependent manner. These results indicate that obvious differences exist in the regulation of LC3Ⅱ and p62 by various modulators although both are autophagic markers.
ABSTRACT
The tumor multidrug resistance reversal effect of NPB304, a novel taxane, was studied. MTT assay was used to determine the IC50 of chemotherapy drugs. Western blotting assay was applied to analyze the expression of P-glycoprotein (P-gp). The effect of compounds on the P-gp function and P-gp ATPase activity was determined by rhodamine 123 (Rh123) accumulation assay and analysis kit, respectively. Molecular docking was employed to predict the binding force between compounds and P-gp. Transmembrane transport of NPB304 was analyzed using MDCK II and MDR1-MDCK II cell model. NPB304 displayed multidrug resistance reversal effect on KBV cells and MCF-7/paclitaxel cells, NPB304 collaborative with P-glycoprotein (P-gp) inhibitors verapamil enhanced the reversal activity, specifically, 10 μmol x L(-1) verapamil in combination with paclitaxel reversed resistance by 56.5-fold, while combined with NPB304 increased the reversal fold; NPB304 synergistically increased Rh123 accumulation in the resistant cells when combined with verapamil, and NPB304 at 0-1 μmol x L(-1) enhanced the ATPase activity activated by verapamil was observed. NPB304 existed the hydrophobic interactions with the TM regions of P-gp, and the binding force between NPB304 and the A chain of the TM region was stronger. P-gp ATPase activity assay demonstrated NPB304 at lower concentrations (0-1.5 μmol x L(-1)) could activate the P-gp ATPase, playing a role on inhibition of P-gp function. However, NPB304 did not have an obvious feature of P-gp substrate. NPB304 exerted itself and synergy with verapamil activity on reversing tumor resistance via inhibiting the P-gp function.