No abstract

Metabolic reprogramming and immune escape play a major role in tumorigenesis. Increasing number of studies have shown that reprogramming of glutamine metabolism is a putative determinant of the anti-tumor immune response in the tumor microenvironment (TME). Usually, the predatory uptake of glutamine by tumor cells in the TME results in the limited utilization of glutamine by immune cells and affects the anti-tumor immune response. The cell-programmed glutamine partitioning also affects the anti-tumor immune response. However, the reprogramming of glutamine metabolism in tumors modulates immune escape by regulating tumor PD-L1 expression. Likewise, the reprogramming of glutamine metabolism in the immune cells also affects their immune function. Additionally, different types of glutamine metabolism inhibitors extensively regulate the immune cells in the TME while suppressing tumor cell proliferation. Herein, we discuss how metabolic reprogramming of tumor and immune cells regulates anti-tumor immune responses, as well as functional changes in different immune cells in the context of targeting tumor glutamine metabolism, which can better explain the potential of targeting glutamine metabolism in combination with immunotherapy for cancer.

Angiotensin-converting enzyme 2 (ACE2) protects against hypoxic pulmonary hypertension (HPH) by inhibiting the proliferation and migration of pulmonary artery smooth muscle cells (PASMCs). Under hypoxia, the hypoxia-inducible factor 1α (HIF-1α) inhibits ACE2 indirectly; however, the underlying mechanism is unclear. In the present study, we found that exposure to chronic hypoxia stimulated microRNA (miRNA) let-7b expression in rat lung via a HIF-1α-dependent pathway. Let-7b downregulated ACE2 expression by directly targeting the coding sequence of ACE2. Our in vitro and in vivo results revealed that let-7b contributed to the pathogenesis of HPH by inducing PASMCs proliferation and migration. Let-7b knockout mitigated right ventricle hypertrophy and pulmonary vessel remodeling in HPH by restoring ACE2 expression. Overall, we demonstrated that HIF-1α inhibited ACE2 expression via the HIF-1α-let-7b-ACE2 axis, which contributed to the pathogenesis of HPH by stimulating PASMCs proliferation and migration. Since let-7b knockout alleviated the development of HPH, let-7b may serve as a potential clinical target for the treatment of HPH.

Programmed death receptor-ligand 1 (PD-L1) plays a crucial role in immune evasion by tumour cells. Most tumour cells exhibit energy dependency and acquire energy from glycolysis. However, the relationship between glucose metabolism and PD-L1 expression remains unclear. In this study, changes in PD-L1 expression in renal carcinoma cells were evaluated during glucose deficiency and recovery, and PD-L1 could inversely regulate glycolysis. In addition, the possible signalling pathways activated by a low level of glucose to regulate PD-L1 were tested experimentally. The results showed that glucose deficiency could upregulate PD-L1 expression in two renal cancer cell lines, 786-O and OS-RC-2. Although the native levels of PD-L1 differed in the two cell lines, the upregulated PD-L1 expression was repristinated after glucose recovery. Moreover, epidermal growth factor receptor (EGFR) expression was upregulated in both cell lines with glucose deficiency. The use of an EGFR inhibitor reversed the upregulation of PD-L1 expression induced by glucose deficiency and inhibited the phosphorylation of extracellular regulated protein kinases 1 and 2 (ERK1/2). EGFR activated by epidermal growth factor (EGF) induced PD-L1 expression and ERK1/2 phosphorylation. Furthermore, an ERK1/2 inhibitor inhibited the phosphorylation of c-Jun and decreased the elevated PD-L1 expression induced by glucose deficiency. In addition, this study also showed that 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFK-2/FBPase 3 or PFKFB3) mediated upregulation of the level of glycolysis to improve the adverse environment through PD-L1 induction. Therefore, glucose metabolism can regulate the expression of PD-L1 through the EGFR/ERK/c-Jun pathway in renal cancer, and elevated PD-L1 can also regulate glycolysis by improving the expression of PFKFB3. The findings of this study could provide a new multiple target treatment for renal cell carcinoma (RCC) therapy.