An RNA-RNA crosstalk network involving HMGB1 and RICTOR facilitates hepatocellular carcinoma tumorigenesis by promoting glutamine metabolism and impedes immunotherapy by PD-L1+ exosomes activity

Hepatocellular carcinoma(HCC)is the global leading cause of cancer-related deaths due to the deficiency of targets for precision therapy.A new modality of epigenetic regulation has emerged involving RNA-RNA crosstalk networks where two or more competing endogenous RNAs(ceRNAs)bind to the same microRNAs.However,the contribution of such mechanisms in HCC has not been well studied.Herein,potential HMGB1-driven RNA-RNA crosstalk networks were evaluated at different HCC stages,identifying the mT0RC2 component RICTOR as a potential HMGB1 ceRNA in HBV^(+)early stage HCC.Indeed,elevated HMGB1 mRNA was found to promote the expressio n of RICTOR mRNA through competitively bin ding with the miR-200 family,especially miR-429.Functio nal assays emplo ying overexpressi on or in terference strategies dem on strated that the HMGB1 and RICTOR 3zuntra nslated regions(UTR)epigenetically promoted the malignant proliferation,self-renewal,and tumorigenesis in HCC cells.Intriguingly,in terference agai nst HMGB1 and RICTOR in HCC cells promoted a stron ger an ti-PD-L1 immuno therapy resp on se,which appeared to associate with the production of PD-L1^(+)exosomes.Mechanistically,the HMGB1-driven RNA-RNA crosstalk network facilitated HCC cell glutamine metabolism via dual mechanisms,activating a positive feedback loop involving mT0RC2-AKT-C-MYC to upregulate glutamine synthetase(GS)expression,and inducing mTORCI signaling to derepress SIRT4 on glutamate dehydrogenase(GDH).Meanwhile,this crosstalk network could impede the efficacy of immunotherapy through mTORCI-P70S6K dependent PD-L1 production and PD-L1^(+)exosomes activity.In conclusion,our study highlights the non-coding regulatory role of HMGB1 with implicatio ns for RNA-based therapeutic targeting together with a predictio n of an ti-PD-L1 immuno therapy in HCC.