Abstract 425: GPD1L participates in glycerol-3-phosphate biogenesis and promotes tumor initiation and invasion in hepatocellular carcinoma
Authors: Yu Tiffany Ching-Yun , Zhao Luqing , Tian Lu , Kam Charles Shing , Lee Joyce Man-Fong , Ho Daniel Wai-Hung , Chan Lo-Kong , Tsui Yu-Man , Sze Karen Man-Fong , Ng Irene Oi-Lin 
Published: March 2024

Abstract
Background: Metabolic reprogramming in hepatocellular carcinoma (HCC) has received rising interest. However, current studies often focus on fatty acid de novo synthesis or oxidation, but less on glycerolipids metabolism. Interestingly, in HCC, we observed frequent dysregulation in enzymes responsible for glycerol-3-phosphate shuttle, which potentially links glycolysis and glycerolipids metabolism. Hence, we aimed to identify the functional significance of glycerol-3-phosphate dehydrogenase 1 like (GPD1L), an enzyme for the shuttle, and its regulation of expression in HCC.
Methods: We utilized transcriptomic analysis of clinical HCC samples to validate the frequent overexpression of GPD1L in tumor cells and examined its association with clinicopathological features. In vitro and in vivo assays were performed to explore the functional significance of GPD1L in HCC initiation and progression. Furthermore, with targeted metabolomics analysis, we investigated the role of GPD1L in glycerol-3-phosphate shuttle in HCC. We also performed promoter study to understand the transcriptional regulation on GPD1L expression.
Results: Among GPD family members, GPD1L was consistently upregulated at mRNA level in clinical HCC samples in The Cancer Genome Atlas-Liver Hepatocellular Carcinoma (TCGA-LIHC) (N=50) and our in-house RNA-sequencing cohorts (N=41), and in a separate independent in-house cohort as examined by RT-qPCR (N=80). GPD1L overexpression was associated with increased tumor invasiveness (p=0.008) and poorer overall survival (p=0.0017) in HCC patients. Functionally, knockdown of GPD1L suppressed HCC migration (fold change ≤ 0.43) and invasion (fold change ≤ 0.40). GPD1L knockdown also inhibited tumor initiation abilities, as shown by reduced colony (fold change ≤ 0.37) and sphere formation (fold change ≤ 0.41) in vitro, and lower stem cell frequency (p=1.96e-9) in vivo. Furthermore, GPD1L knockdown enhanced sensitivity of HCC cells to chemotherapeutic drugs, sorafenib and doxorubicin. Metabolically, GPD1L facilitated synthesis of glycerolipids precursor, glycerol-3-phosphate (G3P) from glycolysis intermediate dihydroxyacetone phosphate (DHAP) in HCC. Lastly, with chromatin-immunoprecipitation and Luciferase reporter assays, we demonstrated ELF1 bound to GPD1L promoter directly to enhance the gene transcription, while knockdown of ELF1 suppressed GPD1L mRNA and protein expression.
Conclusion: Our study demonstrated the overexpression of the glycolysis-related gene, GPD1L, in HCC. GPD1L promoted tumor initiation, invasion and chemoresistance, and in turn might lead to worse clinical outcome. Metabolically, it was responsible for DHAP-to-G3P conversion in HCC and might serve as a linkage between glycolysis and glycerolipid metabolism. Our results also identified the novel role of ELF1 as the transcriptional activator of GPD1L in HCC.
Citation Format: Tiffany Ching-Yun Yu, Luqing Zhao, Lu Tian, Charles Shing Kam, Joyce Man-Fong Lee, Daniel Wai-Hung Ho, Lo-Kong Chan, Yu-Man Tsui, Karen Man-Fong Sze, Irene Oi-Lin Ng. GPD1L participates in glycerol-3-phosphate biogenesis and promotes tumor initiation and invasion in hepatocellular carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 425.