[TP53BP2/ASPP2 inhibits autophagy of HepG2 cells by activating mTOR pathway in a p53-independent manner].

Objective To study the regulative effect of tumor protein p53 binding protein 2/p53 apoptosis-stimulating protein 2 (TP53BP2/ASPP2) on the autophagy of HepG2 human hepatoma cells and its mechanism. Methods The expression of ASPP2 was up-regulated or down-regulated by HepG2 cells infected with adenovirus and lentivirus. HepG2 cells were cultured in medium without fetal bovine serum for 24 hours. Western blotting was used to detect the expression of microtubule-associated protein 1 light chain 3 (LC3), beclin1, P62, autophagy-related gene 5 (ATG5), ATG7, and mammalian target of rapamycin (mTOR) pathway-associated protein mTOR, phospho-mTOR (p-mTOR), eukaryotic transcription initiation factor 4E binding protein 1 (4EBP1), phospho-4EBP1 (p-4EBP1), ribosomal protein S6, phospho-S6 (p-S6), ribosomal S6 kinase B1 (RPS6KB1/p70S6K), phospho-p70S6K (p-p70S6K). Fluorescence microscopy was used to detect the green fluorescent protein-microtubule-associated protein 1 light chain 3 (GFP-LC3) fusion protein expressed by the cells. At the same time, the Hep3B cells without p53 expression were infected with lentivirus, and the levels of ASPP2 in the cells were knocked down. Western blotting was performed to detect the expression of ASPP2 and mTOR pathway-associated protein mTOR, p-mTOR, 4EBP1, p-4EBP1, S6, p-S6, RPS6KB1/p70S6K, p-p70S6K. Results When the expression of ASPP2 was up-regulated, the mTOR complex 1 (mTORC1) pathway was activated, and the expression of autophagy-related proteins and the number of autophagosomes were reduced. After the expression of ASPP2 was down-regulated, the mTORC1 pathway was inhibited, and the expression level of autophagy-related proteins and the number of autophagosomes increased. In Hep3B cells with p53 expression silence, the mTORC1 pathway was still inhibited when ASPP2 wasdown-regulated. Conclusion ASPP2 inhibits the autophagy of HepG2 cells by activating mTOR pathway in a p53-independent manner.

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