Abstract

Background: Tumor microenvironment(TME) reflects the intertwined crosstalk between cancer cells and tumor-infiltrating immune cells, affecting the efficiency of immunotherapy. Metabolic reprogramming, one of the major hallmarks of hepatocellular carcinoma(HCC), is unclear in the aspect of reshaping TME. In this study, we report the vital role of SLC1A5, the major glutamine transporter of tumor cells, in HCC progression and the formation of immunosuppressive TME.

Methods: TCGA-LIHC cohort was obtained to analyze the expression level of SLC1A5 and its correlation with overall survival(OS) and SLC1A5 expression was further detected in our HCC cohort(metastatic vs non-metastatic patients) by qRT-PCR. The functions of SLC1A5 on HCC were investigated by gain-of-function and loss-of-function assays both in vitro and in vivo. Flow cytometry analysis, bioinformatics analysis, co-immunoprecipitation, qRT-PCR, Western blotting, and Oil Red O staining were performed to explore the mechanisms of SLC1A5 on HCC progression.

Results: We found that the expression of SLC1A5 was significantly upregulated in HCC compared with non-tumor tissues among 2 cohorts. Metastatic patients in our cohort markedly upregulated SLC1A5 in the tumor than in the paired non-tumor tissues, while the paired specimens of non-metastatic patients presented identical levels of SLC1A5 expression. And high expression of SLC1A5 predicted poor OS. SLC1A5 overexpression potentiated cellular proliferation and migration, whereas its knock-down significantly attenuated them both in vitro and in vivo. Besides, SLC1A5-overexpression enhanced the infiltration of Tregs, drove CD8⁺ T cells exhaustion and macrophage M2 polarization. Mechanistically, we found that SLC1A5 directly binds to lipid synthesis enzymes that engage in fatty acid elongation. SLC1A5 knockdown not only reduced lipid droplets but also decreased the expression of lipid synthesis and elongation-related genes, which is associated with poor survival. Finally, blocking SLC1A5 by GPNA effectively inhibits tumor growth and reduces Tregs infiltration.

Conclusion: Our results reveal that SLC1A5 plays a pivotal role in the development of HCC by directly interacting with lipid metabolic enzymes to facilitate tumor cell proliferation and migration, thereby constructing an immunosuppressive TME. Hence, SLC1A5 may serve as a novel prognostic biomarker and therapeutic target in HCC, and SLC1A5 blockade holds the promise to counteract immunotherapy resistance.