Abstract 4795: Metabolic vulnerability by UQCRH methylation in clear cell renal cell carcinoma
Authors: Luo Yanting , Bengtsson Louise Medina , Lu Xin 
Published: September 2020

Background: UQCRH, subunit 6 of complex III in the electron transport chain of the mitochondria, is a hinge protein that stabilizes cytochrome c-c1 complex formation. UQCRH is the top-ranked gene by inverse correlation between DNA methylation and gene expression in clear cell renal carcinoma (ccRCC) in the Cancer Genome Atlas and Broad Institute Cancer Cell Line Encyclopedia databases. In the clinic, ccRCC patients with low UQCRH expression exhibit higher tumor stage and grade. While its downregulation is correlated with worse tumor prognosis, little is known about the mechanism through which UQCRH is involved in cancer progression. We propose that hypermethylation-induced downregulation of UQCRH inhibits complex III activity, thus lowering the efficiency of oxidative phosphorylation and shifting the metabolic balance of the cell toward aerobic glycolysis, which contributes to tumor proliferation.

Methods: Two ccRCC cell lines were used, KMRC-2 and 786-O. We measured UQCRH and mRNA expression levels and identified which cell lines exhibited UQCRH downregulation. We used the global demethylation agent Decitabine (Dacogen) to test whether methylation of the UQCRH gene was present in the low-UQCRH cell line. UQCRH overexpression and knockout sublines were created for high and low-UQCRH cell lines, respectively. We characterized the metabolic preferences of the sublines and original cell lines and measured tumor proliferation in vitro and in vivo. We also studied the effect of ketogenic diet on cell proliferation in vitro.

Results: While 786-O expressed normal levels of UQCRH, KMRC-2 expressed low levels of UQCRH, but its UQCRH expression was rescued by increasing concentrations of Decitabine. Sublines with low UQCRH, whether by hypermethylation or knockout, had higher extracellular acidification rate compared to their high-UQCRH counterparts. Although no significant difference was detected in cell proliferation in vitro, low-UQCRH tumors grew faster in vivo. Ketogenic diet experiments indicated that high UQCRH expression was positively correlated with more efficient beta-hydroxybutyrate metabolism and cellular proliferation. Beta-hydroxybutyrate was toxic to low-UQCRH sublines.

Conclusion: Hypermethylation induced UQCRH downregulation in KMRC-2. Cells with lower UQCRH levels exhibited weaker mitochondrial membrane potential and were more reliant on aerobic glycolysis. While this metabolic reprogramming did not affect proliferation in vitro, low-UQCRH tumors grew faster in vivo. The metabolic shift also represents a vulnerability that could be targeted in the development of therapies to hinder tumor progression. The ketogenic diet showed promise as such a strategy.

Citation Format: Yanting Luo, Louise Medina Bengtsson, Xin Lu. Metabolic vulnerability by UQCRH methylation in clear cell renal cell carcinoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4795.