Increased Expression of the Very Low-Density Lipoprotein Receptor Mediates Lipid Accumulation in Clear-Cell Renal Cell Carcinoma

Abstract

Clear-cell renal cell carcinoma (RCC) is, in most cases, caused by loss of function of the tumor suppressor gene von Hippel–Lindau, resulting in constitutive activation of hypoxia-inducible factor (HIF)-1α and expression of hypoxia-induced genes in normoxic conditions. Clear-cell RCC cells are characterized histologically by accumulation of cholesterol, mainly in its ester form. The origin of the increased cholesterol remains unclear, but it is likely explained by an HIF-1α-driven imbalance between cholesterol uptake and excretion. Here, we showed that expression of the very low-density lipoprotein receptor (VLDL-R) was significantly increased in clear-cell RCC human biopsies compared with normal kidney tissue. Partial knockdown of HIF-1α in clear-cell RCC cells significantly reduced the VLDL-R expression, and knockdown of either HIF-1α or VLDL-R reduced the increased lipid accumulation observed in these cells. We also showed increased uptake of fluorescently labeled lipoproteins in clear-cell RCC cells, which was significantly reduced by knockdown of HIF-1α or VLDL-R. Taken together, our results support the concept that the pathological increase of HIF-1α in clear-cell RCC cells upregulates VLDL-R, which mediates increased uptake and accumulation of lipids. These results explain the morphological characteristics of clear-cell RCC, and open up novel possibilities for detection and treatment of clear-cell RCC.

Lipidomic differentiation between human kidney tumors and surrounding normal tissues using HILIC-HPLC/ESI–MS and multivariate data analysis

“…Numerical values of mean concentrations and their standard deviations are listed in Table S4. Decreased levels of PE, SM and LPC in kidney tumor tissues in comparison with surrounding normal tissues are in agreement with previous reports [18,23].…”

“…Lipidomic analysis of RCC tissues and normal kidney tissues was performed using HPLC/MS [18], where significantly increased levels of cholesteryl esters (CE) and triacylglycerols (TG) and decreased levels of phosphatidylethanolamines (PE) and sphingomyelins (SM) in tumor tissues were reported. Mass spectrometry imaging using matrix-assisted laser desorption/ionization or desorption electrospray ionization was used for the relative comparison of tumor and surrounding normal tissues [19][20][21][22].…”

Regulation of Cancer Cell Metabolism by Hypoxia

“…It has been demonstrated that HIF-1 directly binds to the promoter of the VLDL receptor (VLDLR). Furthermore, silencing of HIF-1α has been demonstrated to lead to a decrease in VLDLR and a subsequent decrease in LDL and VLDL uptake in response to hypoxia [160,161]. These effects of HIF-1 on VLDLR regulation help explain the higher levels of cholesterol observed in clear-cell RCC [161].…”

“…Furthermore, silencing of HIF-1α has been demonstrated to lead to a decrease in VLDLR and a subsequent decrease in LDL and VLDL uptake in response to hypoxia [160,161]. These effects of HIF-1 on VLDLR regulation help explain the higher levels of cholesterol observed in clear-cell RCC [161]. Lipoprotein receptor-related protein 1 (LRP1), which is also involved in the internalization of LDL, has also been shown to be a direct target of HIF-1 in vascular smooth muscle cells.…”

Constitutive Expression of HIF-α Plays a Major Role in Generation of Clear-cell Phenotype in Human Primary and Metastatic Renal Carcinoma

“…The tumor cells exhibit a characteristic histological feature of clear cytoplasm because of the large amount of lipid accumulation in the cytoplasm. 2 This lipid consists principally of cholesterol esters. Glycogenesis is also regulated by HIF-1α .…”