VHL-Mediated Regulation of CHCHD4 and Mitochondrial Function.

Thomas Briston,Basma Greef,Patrick H Maxwell,Yuen-Li Chung,Luke W Thomas,Gyorgy Szabadkai,Mark Turmaine,Margaret Ashcroft,Saiful E Syafruddin,Sakari Vanharanta,Cinzia Esposito,Jenna M Stephen,Lucas A Maddalena

doi:10.3389/fonc.2018.00388

Abstract

Dysregulated mitochondrial function is associated with the pathology of a wide range of diseases including renal disease and cancer. Thus, investigating regulators of mitochondrial function is of particular interest. Previous work has shown that the von Hippel-Lindau tumor suppressor protein (pVHL) regulates mitochondrial biogenesis and respiratory chain function. pVHL is best known as an E3-ubiquitin ligase for the α-subunit of the hypoxia inducible factor (HIF) family of dimeric transcription factors. In normoxia, pVHL recognizes and binds hydroxylated HIF-α (HIF-1α and HIF-2α), targeting it for ubiquitination and proteasomal degradation. In this way, HIF transcriptional activity is tightly controlled at the level of HIF-α protein stability. At least 80% of clear cell renal carcinomas exhibit inactivation of the VHL gene, which leads to HIF-α protein stabilization and constitutive HIF activation. Constitutive HIF activation in renal carcinoma drives tumor progression and metastasis. Reconstitution of wild-type VHL protein (pVHL) in pVHL-defective renal carcinoma cells not only suppresses HIF activation and tumor growth, but also enhances mitochondrial respiratory chain function via mechanisms that are not fully elucidated. Here, we show that pVHL regulates mitochondrial function when re-expressed in pVHL-defective 786O and RCC10 renal carcinoma cells distinct from its regulation of HIF-α. Expression of CHCHD4, a key component of the disulphide relay system (DRS) involved in mitochondrial protein import within the intermembrane space (IMS) was elevated by pVHL re-expression alongside enhanced expression of respiratory chain subunits of complex I (NDUFB10) and complex IV (mtCO-2 and COX IV). These changes correlated with increased oxygen consumption rate (OCR) and dynamic changes in glucose and glutamine metabolism. Knockdown of HIF-2α also led to increased OCR, and elevated expression of CHCHD4, NDUFB10, and COXIV in 786O cells. Expression of pVHL mutant proteins (R200W, N78S, D126N, and S183L) that constitutively stabilize HIF-α but differentially promote glycolytic metabolism, were also found to differentially promote the pVHL-mediated mitochondrial phenotype. Parallel changes in mitochondrial morphology and the mitochondrial network were observed. Our study reveals a new role for pVHL in regulating CHCHD4 and mitochondrial function in renal carcinoma cells.

Highlights

Dysregulated mitochondrial function is associated with a broad range of diseases including renal disease [1] and cancer [2]
We show that pVHL increases the expression of CHCHD4, respiratory chain subunits known to be CHCHD4 substrates [28, 29] and promotes changes in mitochondrial morphology when re-expressed in pVHLdefective renal carcinoma cells
Consistent with Hervouet et al [21], we found that pVHL re-expression enhanced the basal expression of respiratory chain subunits of both nuclear and mitochondrial genetic origin, including the complex IV (CIV) subunits mtCO-2 and COX IV (Figure 1A)

Summary

Introduction

Dysregulated mitochondrial function is associated with a broad range of diseases including renal disease [1] and cancer [2]. Mitochondria are involved in regulating a broad range of cellular activities. Mitochondria communicate with the oxygen-sensing machinery and are involved in regulating the cellular response to hypoxia [5]. Hypoxia and increased HIF activation occurs in most cancers, leading to the upregulation of a range of genes involved in diverse cellular processes including metabolism and cell survival [6, 7]. Targeting of HIF-α protein for degradation is achieved through hydroxylation of conserved proline residues, catalyzed by the oxygen-sensing dioxygenases, prolyl hydroxylase domain (PHD) enzymes [7,8,9]. PVHL forms the substrate recognition and catalytic component of an E3-ligase complex which functions to polyubiquitinate HIF-α subunits, targeting them for degradation by the 26S proteasome [8, 11, 12] Recognition of the hydroxylated residues in HIF-α subunits is under the control of the von Hippel-Lindau (pVHL) tumor suppressor protein [10,11,12]. pVHL forms the substrate recognition and catalytic component of an E3-ligase complex which functions to polyubiquitinate HIF-α subunits, targeting them for degradation by the 26S proteasome [8, 11, 12]

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Results

Conclusion