GPX8 regulates clear cell renal cell carcinoma tumorigenesis through promoting lipogenesis by NNMT

Abstract

Background Clear cell renal cell carcinoma (ccRCC), with its hallmark phenotype of high cytosolic lipid content, is considered a metabolic cancer. Despite the implication of this lipid-rich phenotype in ccRCC tumorigenesis, the roles and regulators of de novo lipid synthesis (DNL) in ccRCC remain largely unexplained. Methods Our bioinformatic screening focused on ccRCC-lipid phenotypes identified glutathione peroxidase 8 (GPX8), as a clinically relevant upstream regulator of DNL. GPX8 genetic silencing was performed with CRISPR-Cas9 or shRNA in ccRCC cell lines to dissect its roles. Untargeted metabolomics, RNA-seq analyses, and other biochemical assays (e.g., lipid droplets staining, fatty acid uptake, cell proliferation, xenograft, etc.) were carried out to investigate the GPX8’s involvement in lipid metabolism and tumorigenesis in ccRCC. The lipid metabolic function of GPX8 and its downstream were also measured by isotope-tracing-based DNL flux measurement. Results GPX8 knockout or downregulation substantially reduced lipid droplet levels (independent of lipid uptake), fatty acid de novo synthesis, triglyceride esterification in vitro, and tumor growth in vivo. The downstream regulator was identified as nicotinamide N-methyltransferase (NNMT): its knockdown phenocopied, and its expression rescued, GPX8 silencing both in vitro and in vivo. Mechanically, GPX8 regulated NNMT via IL6-STAT3 signaling, and blocking this axis suppressed ccRCC survival by activating AMPK. Notably, neither the GPX8-NNMT axis nor the DNL flux was affected by the von Hippel Lindau (VHL) status, the conventional regulator of ccRCC high lipid content. Conclusions Taken together, our findings unravel the roles of the VHL-independent GPX8-NNMT axis in ccRCC lipid metabolism as related to the phenotypes and growth of ccRCC, which may be targeted for therapeutic purposes. Graphical abstract

GPX8 regulates pan-apoptosis in gliomas to promote microglial migration and mediate immunotherapy responses

“…By stimulating the Wnt signaling pathway, GPX8 is transcriptionally controlled by FOXC1 and aids in the proliferation of gastric cancer cells( 39 ). Through encouraging lipogenesis by NNMT, GPX8 controls the development of clear cell renal cell carcinoma tumors( 40 ). However, when it comes to its involvement in cancer, particularly glioblastoma, there is limited information available.…”

Glycerol 3-phosphate dehydrogenases (1 and 2) in cancer and other diseases

“…Interestingly, a decreased GPD1 level was also found in serum samples of TNBC patients, suggesting the possible use of GPD1 as a diagnostic biomarker 135 . In kidney cancer, overexpression of GPD1 downregulated various lipid synthesis genes, leading to a decrease in lipid droplets 17 , the enrichment of which is a characteristic and cancer-requiring feature of ccRCC 136 – 138 . In addition to these lipid metabolic changes, decreased cell proliferation, migration, and invasion, as well as the inhibition of xenografted tumor growth, were also observed, consistent with the correlation between high GPD1 protein levels and better ccRCC patient survival.…”

Recent Advances in the Management of Clear Cell Renal Cell Carcinoma: Novel Biomarkers and Targeted Therapies

“…Notably, due to enhanced differential expression between RCC subtypes and healthy tissue detected through several techniques such as immunohistochemistry, ELISA and proteomic analysis, NNMT has been proposed as a biomarker for the diagnosis of the main RCC subtypes, in combination with other markers [ 166 , 167 , 168 ]. Furthermore, several in vitro studies reported that NNMT downregulation was associated with a decreased proliferation and invasiveness in ccRCC cells [ 166 , 169 , 170 , 171 , 172 ]. In the light of these observations, the enzyme seems to be a promising diagnostic and prognostic biomarker, which could be also utilized as a therapeutic target due to the large number of NNMT inhibitors available and currently tested for cancer treatment [ 173 , 174 , 175 , 176 , 177 , 178 ].…”