Background/Aims The identification of factors that lead to CD8+ T cell dysfunction within the tumor microenvironment (TME) holds great promise for the development of innovative immunotherapies. However, the mechanisms underlying the exhausted phenotype of CD8+ T cells infiltrating early-stage hepatocellular carcinoma (HCC) tumors remain unclear.
Methods Single-cell RNA sequencing was performed using a murine HCC model. Flow cytometry and additional experimental approaches were employed to investigate the mechanisms of CD8+ T cell exhaustion.
Results CD8+ T cells infiltrating early-stage HCC exhibited a functionally exhausted phenotype, which escalated with HCC progression. At early stages of HCC, the TME was characterized by significant iron accumulation. Moreover, tumor-infiltrating CD8+ T cells in murine HCC exhibited higher levels of intracellular ferrous iron compared to splenic CD8+ T. This excessive iron led to increased lipid peroxide levels and impaired the effector function of CD8+ T cells. Mechanistically, CD36 upregulated the iron uptake protein transferrin receptor 1 (TfR1) by mediating the activation of oxidized low-density lipoprotein (oxLDL)-p38-CEBPB axis. Depletion of CD36 in CD8+ T cells inhibited the upregulation of TfR1 and the increase of iron levels. Furthermore, constitutively activated nuclear factor erythroid 2-related factor 2 (NRF2) effectively suppressed lipid peroxidation, thereby preserving the effector functions of intratumoral CD8+ T cells and ultimately inhibiting tumor growth.
Conclusions Our findings reveal a previously unidentified mechanism mediated by CD36 that regulates the progressive dysfunction of CD8+ T cells in early HCC TME and provide a potential novel therapeutic approach to restore T cell function.
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Background/Aims Ubiquitination is widely involved in the progression of hepatocellular carcinoma (HCC) by regulating various cellular processes. However, systematic strategies for screening core ubiquitin-related genes, clarifying their functions and mechanisms, and ultimately developing potential therapeutics for patients with HCC are still lacking.
Methods Cox and LASSO regression analyses were performed to construct a ubiquitin-related gene prediction model for HCC. Loss- and gain-of-function studies, transcriptomic and metabolomics analysis were used to explore the function and mechanism of UBE2S on HCC cell glycolysis and growth.
Results Based on 1,423 ubiquitin-related genes, a four-gene signature was successfully constructed to evaluate the prognosis of patients with HCC. UBE2S was identified in this signature with the potential to predict the survival of patients with HCC. E2F2 transcriptionally upregulated UBE2S expression by directly binding to its promoter. UBE2S positively regulated glycolysis in a HIF-1α-dependent manner, thus promoting the proliferation of HCC cells. Mechanistically, UBE2S enhanced K11-linkage polyubiquitination at lysine residues 171 and 196 of VHL independent of E3 ligase, thereby indirectly stabilizing HIF-1α protein levels by mediating the degradation of VHL by the proteasome. In particular, the combination of cephalomannine, a small molecule compound that inhibits the expression of UBE2S, and PX-478, an inhibitor of HIF-1α, significantly improved the anti-tumor efficacy.
Conclusions UBE2S is identified as a key biomarker in HCC among the thousands of ubiquitin-related genes and promotes glycolysis by E3 enzyme-independent ubiquitination, thus serving as a therapeutic target for the treatment of HCC.
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