Absence of the Birt–Hogg–Dubé gene product is associated with increased hypoxia-inducible factor transcriptional activity and a loss of metabolic flexibility

Abstract

Under conditions of reduced tissue oxygenation, hypoxiainducible factor (HIF) controls many processes, including angiogenesis and cellular metabolism, and also influences cell proliferation and survival decisions. HIF is centrally involved in tumour growth in inherited diseases that give rise to renal cell carcinoma (RCC), such as Von HippelLindau syndrome and tuberous sclerosis complex. In this study, we examined whether HIF is involved in tumour formation of RCC in Birt-Hogg-Dube´syndrome. For this, we analysed a Birt-Hogg-Dube´patient-derived renal tumour cell line (UOK257) that is devoid of the BirtHogg-Dube´protein (BHD) and observed high levels of HIF activity. Knockdown of BHD expression also caused a threefold activation of HIF, which was not as a consequence of more HIF1a or HIF2a protein. Transcription of HIF target genes VEGF, BNIP3 and CCND1 was also increased. We found nuclear localization of HIF1a and increased expression of VEGF, BNIP3 and GLUT1 in a chromophobe carcinoma from a Birt-HoggDube´patient. Our data also reveal that UOK257 cells have high lactate dehydrogenase, pyruvate kinase and 3-hydroxyacyl-CoA dehydrogenase activity. We observed increased expression of pyruvate dehydrogenase kinase 1 (a HIF gene target), which in turn leads to increased phosphorylation and inhibition of pyruvate dehydrogenase. Together with increased protein levels of GLUT1, our data reveal that UOK257 cells favour glycolytic rather than lipid metabolism (a cancer phenomenon termed the 'Warburg effect'). UOK257 cells also possessed a higher expression level of the L-lactate influx monocarboxylate transporter 1 and consequently utilized L-lactate as a metabolic fuel. As a result of their higher dependency on glycolysis, we were able to selectively inhibit the growth of these UOK257 cells by treatment with 2-deoxyglucose. This work suggests that targeting glycolytic metabolism may be used therapeutically to treat Birt-Hogg-Dube´-associated renal lesions.

Folliculin directs the formation of a Rab34–RILP complex to control the nutrient‐dependent dynamic distribution of lysosomes

“…This may be due to the complete long‐term loss of full‐length FLCN in these cells when compared to acute depletion, their tissue origin or metabolic adaptions acquired during tumourigenesis and clonal selection 47. It is notable that UOK257 cells do not show large deficiencies in mTORC1 activity 33.…”

The tumor suppressor folliculin regulates AMPK-dependent metabolic transformation

“…We reported recently that loss of the tumor suppressor FLCN leads to increased HIF transcriptional activity and a higher glycolytic rate in human kidney cancer cells, which is a recurrent characteristic of cancer metabolic adaptation referred to as the Warburg effect (5,6). HIF-α protein levels are regulated by oxygen-dependent prolyl hydroxylation, sequential VHL binding, and degradation of HIF-α via the proteasome (7).…”

Chronic AMPK activation via loss of FLCN induces functional beige adipose tissue through PGC-1α/ERRα

“…FLCN has no significant sequence homology with any known protein and is highly conserved across species, suggesting an important biological role, as illustrated by the embryonic lethality of Flcn homozygous disruption in mice (Baba et al 2008;Chen et al 2008;Hudon et al 2010). FLCN functions as a repressor of the master energy sensor AMP-activated protein kinase (AMPK) via FLCN-interacting protein (FNIP) (Baba et al 2006(Baba et al , 2008Behrends et al 2010;Preston et al 2011;Possik et al 2014;Yan et al 2014).…”

“…We reported previously that ablation of FLCN expression or loss of FLCN binding to AMPK induces chronic AMPK pathway hyperactivation in nematodes and various cellular contexts, leading to increased energy reserves, enhanced metabolic and osmotic stress resistance, and metabolic transformation (Preston et al 2011;Possik et al 2014;Yan et al 2014). This hyperactivation of AMPK induces the expression of PGC-1α in muscle cells, mouse embryonic fibroblasts (MEFs), and cancer cells, which triggers mitochondrial biogenesis and promotes transcriptional regulation of nuclear-encoded mitochondrial genes (Jäger et al 2007;Yan et al 2014).…”