Long Noncoding RNA UCA1 Promotes Glutamine-Driven Anaplerosis of Bladder Cancer by Interacting With hnRNP I/L to Upregulate GPT2 Expression

Abstract

Background: Glutamine-driven anaplerosis maintains the tricarboxylic acid (TCA) cycle by replenishing its carbon source of intermediates with the glutamine-derived carbons in cancer cells. Long noncoding RNA urothelial cancer associated 1 (UCA1), initially identified in bladder cancer, is associated with multiple cellular processes, including metabolic reprogramming. However, its characteristics in the anaplerosis context of bladder cancer (BLCA) remains elusive. Methods: The mechanism of UCA1 bound to and facilitated the combination of hnRNP I/L to the promoter of GPT2 gene was investigated by RNA pulldown, qRT-PCR, western blot, dual luciferase reporter assays, immunohistochemical staining, chromatin immunoprecipitation and chromatin isolation by RNA purification. Metabolomics analysis and metabolic flux analysis were conducted to assess the effects of UCA1, hnRNP I/L, and GPT2 on metabolic reprogramming of BLCA.Results: We identified UCA1 as a binding partner of heterogeneous nuclear ribonucleoproteins (hnRNPs) I and L, RNA-binding proteins with no previously known role in metabolic reprogramming. UCA1 and hnRNP I/L profoundly affected glycolysis, TCA cycle, glutaminolysis, and viability of BLCA cells. Importantly, UCA1 specifically bound to and facilitated the combination of hnRNP I/L to the promoter of glutamic pyruvate transaminase 2 (GPT2) gene, resulting in upregulated expression of GPT2 and enhanced glutamine-derived carbons in the TCA cycle. We also systematically confirmed the influence of UCA1, hnRNP I/L, and GPT2 on metabolism and proliferation via glutamine-driven anaplerosis in BLCA cells. Conclusions: Our study reveals the critical mechanism by which UCA1 forms a functional UCA1-hnRNP I/L complex that upregulates GPT2 expression to promote glutamine-driven TCA cycle anaplerosis, providing novel evidence that lncRNA regulates metabolic reprogramming in tumor cells.