USP22 promotes hypoxia-induced hepatocellular carcinoma stemness by a HIF1α/USP22 positive feedback loop upon TP53 inactivation

Objective We aimed to elucidate the mutual regulation mechanism of ubiquitin-specific protease 22 (USP22) and hypoxia inducible factor-1 alpha (HIF1 alpha), and the mechanism they promote the stemness of hepatocellular carcinoma (HCC) cells under hypoxic conditions. Design Cell counting, migration, self-renewal ability, chemoresistance and expression of stemness genes were established to detect the stemness of HCC cells. Immunoprecipitation, ubiquitination assay and chromatin immunoprecipitation assay were used to elucidate the mutual regulation mechanism of USP22 and HIF1 alpha. HCC patient samples and The Cancer Genome Atlas data were used to demonstrate the clinical significance. In vivo USP22-targeting experiment was performed in mice bearing HCC. Results USP22 promotes hypoxia-induced HCC stemness and glycolysis by deubiquitinating and stabilising HIF1 alpha. As direct target genes of HIF1 alpha, USP22 and TP53 can be transcriptionally upregulated by HIF1 alpha under hypoxic conditions. In TP53 wild-type HCC cells, HIF1 alpha induced TP53-mediated inhibition of HIF1 alpha-induced USP22 upregulation. In TP53-mutant HCC cells, USP22 and HIF1 alpha formed a positive feedback loop and promote the stemness of HCC. HCC patients with a loss-of-function mutation at TP53 and high USP22 and/or HIF1 alpha expression tend to have a worse prognosis. The USP22-targeting lipopolyplexes caused high tumour inhibition and high sorafenib sensitivity in mice bearing HCC. Conclusion USP22 promotes hypoxia-induced HCC stemness by a HIF1 alpha/USP22 positive feedback loop on TP53 inactivation. USP22 is a promising target for the HCC therapy.