BBOX1 restrains TBK1-mTORC1 oncogenic signaling in clear cell renal cell carcinoma

Clear cell renal cell carcinoma (ccRCC) is a metabolic disease that is believed to arise from renal proximal convoluted tubule (PCT) epithelial cells. However, the signaling events leading to ccRCC development are not completely understood. Here, we report that a carnitine synthesis enzyme predominantly expressed in PCT cells, γ-butyrobetaine hydroxylase 1 (BBOX1), is a novel ccRCC tumor suppressor. BBOX1 expression is lost in transformed primary renal epithelial cells and ccRCC patient tumors. Restoring BBOX1 expression in ccRCC tumor cells suppresses cell viability in physiological conditions as well as tumor growth and metastasis in xenograft models. Conversely, BBOX1 inhibition increases ccRCC tumor growth. To dissect the mechanism, we performed mass spectrometry analysis of BBOX1 interacting proteins and identified TANK-binding kinase 1 (TBK1). Binding was abrogated by introducing a mutation in BBOX1 that rendered the enzyme inactive. Mechanistically, BBOX1 loss leads to TBK1-dependent mTORC1 activation and increased glycolysis. Thus, the BBOX1-TBK1 axis represents a novel mechanism of dysregulated metabolic signaling offering potential new therapeutic strategies to target ccRCC.