Preliminary Study On The Regulation Mechanism Of PBX3 In Hepatoma Cells

Cancer stem cells(CSCs)play an important role in the development of tumors,and hence are important targets for cancer therapy.Previous studies have confirmed that pre-leukemia transcription factor 3(PBX3)plays an important role in maintaining the characteristics of liver cancer stem cells.Upon further studying the role of PBX3 in hepatocellular carcinomas,we found that PBX3 is an extremely unstable protein with a short half-life.Unstable proteins are believed to be susceptible to degradation by the ubiquitin-proteasome system(UPS).However,when we treated hepatoma cells with the proteasome inhibitor MG132,we found that the levels of PBX3 protein and m RNA were significantly downregulated,suggesting that PBX3 protein is not degraded by the ubiquitin-proteasome system.Our study aims to investigate the mechanism of MG132 regulation of PBX3.We observed that the levels of let-7c,mi R-200 b,mi R-222 and mi R-424 were upregulated when hepatoma cells were treated with MG132,and that this increase negatively correlated with the levels of PBX3.Using the mi RWalk algorithm,previous studies have predicted that these mi RNAs target the PBX3 gene.Thus,we investigated the mechanism by which the proteasome inhibitor MG132 regulates these mi RNAs.It has been reported that Argonaute2 protein is an important component of the RNA-induced silencing complex(RISC),it can regulate the levels of certain mi RNAs.Consequently,we also investigated whether the proteasome inhibitor regulates related mi RNAs by stabilizing Argonaute2.Using co-infection,co-immunoprecipitation(Co-IP)and western blot assays,we found that MG132 stabilizes the expression of the Argonuate2 protein by inhibiting its degradation via the ubiquitin-proteasome pathway.In summary,the PBX3 protein,which is closely related to the stemness of hepatoma cells,does not undergo degradation by the ubiquitin-proteasome system.However,the proteasome inhibitor MG132 can upregulate mi RNAs(let-7c,mi R-200 b,mi R-222 and mi R-424)by stabilizing Argonaute2,thereby inhibiting the expression of PBX3.