GABPA-activated TGFBR2 transcription inhibits aggressiveness but is epigenetically erased by oncometabolites in renal cell carcinoma

Abstract

Background: The ETS transcription factor GABPA has long been thought of as an oncogenic factor and recently suggested as a target for cancer therapy due to its critical effect on telomerase activation, but the role of GABPA in clear cell renal cell carcinoma (ccRCC) is unclear. In addition, ccRCC is characterized by metabolic reprograming with aberrant accumulation of L-2-hydroxyglurate (L-2HG), an oncometabolite that has been shown to promote ccRCC development and progression by inducing DNA methylation, however, its downstream effectors remain poorly defined.

Methods: siRNAs and expression vectors were used to manipulate the expression of GABPA and other factors and to determine cellular/molecular and phenotypic alterations. RNA sequencing and ChIP assays were performed to identify GABPA target genes. A human ccRCC xenograft model in mice was used to evaluate the effect of GABPA overexpression on in vivo tumorigenesis and metastasis. ccRCC cells were incubated with L-2-HG to analyze GABPA expression and methylation. We carried out immunohistochemistry on patient specimens and TCGA dataset analyses to assess the effect of GABPA on ccRCC survival.

Results: GABPA depletion, although inhibiting telomerase expression, robustly enhanced proliferation, invasion and stemness of ccRCC cells, whereas GABPA overexpression exhibited opposite effects, strongly inhibiting in vivo metastasis and carcinogenesis. TGFBR2 was identified as the GABPA target gene through which GABPA governed the TGFβ signaling to dictate ccRCC phenotypes. GABPA and TGFBR2 phenocopies each other in ccRCC cells. Higher GABPA or TGFBR2 expression predicted longer survival in patients with ccRCC. Incubation of ccRCC cells with L-2-HG mimics GABPA-knockdown-mediated phenotypic alterations. L-2-HG silenced the expression of GABPA in ccRCC cells by increasing its methylation.

Conclusions: GABPA acts as a tumor suppressor by stimulating TGFBR2 expression and TGFβ signaling, while L-2-HG epigenetically inhibits GABPA expression, disrupting the GABPA-TGFβ loop to drive ccRCC aggressiveness. These results exemplify how oncometabolites erase tumor suppressive function for cancer development/progression. Restoring GABPA expression using DNA methylation inhibitors or other approaches, rather than targeting it, may be a novel strategy for ccRCC therapy.

Keywords: GABPA; L-2-HG; Oncometabolite; TGFBR2; ccRCC.