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Sphingosine 1-phosphate (S1P) is one of the lipid mediators involved in diverse physiological functions. S1P circulates in blood and lymph bound to carrier proteins. Three S1P carrier proteins have been reported, albumin, apolipoprotein M (ApoM) and apolipoprotein A4 (ApoA4). The carrier-bound S1P exerts its functions via specific S1P receptors (S1PR1-5) on target cells. Previous studies showed several differences in physiological functions between albumin-bound S1P and ApoM-bound S1P. However, molecular mechanisms underlying the carrier-dependent differences have not been clarified. In addition, ApoA4 is a recently identified S1P carrier protein, and its functional differences from albumin and ApoM have not been addressed. Here, we compared the three carrier proteins in the processes of S1P degradation, release from S1P-producing cells and receptor activation. ApoM retained S1P more stable than albumin and ApoA4 in the cell culture medium when compared in the equimolar amounts. ApoM facilitated theS1P release from endothelial cells most efficiently. Furthermore, ApoM-bound S1P showed a tendency to induce prolonged activation of Akt via S1PR1 and S1PR3. These results suggest that the carrier-dependent functional differences of S1P are partly ascribed to the differences in the S1P stability, S1P-releasing efficiency and signaling duration. [ABSTRACT FROM AUTHOR]

Intratumoral hypoxia is associated with tumor progression and therapeutic resistance. The VHL tumor suppressor gene was identified in 1993, and later studies revealed that the gene product pVHL interacts with other proteins to form the VBC complex. The VBC complex functions as an E3 ubiquitin ligase and regulates the abundance of the α‐subunit of the transcription factor hypoxia‐inducible factor (HIF). Hypoxia‐inducible factor regulates thousands of genes required for cells to adapt and survive in hypoxic conditions, and thus pVHL plays a major role in oxygen‐sensing pathways. Patients with von Hippel–Lindau (VHL) disease, harboring a germline mutation of the VHL gene, develop renal cell carcinomas and a series of tumors showing hypervascular phenotypes. The extensive findings that have clarified the function of VHL have contributed to the development of novel first‐in‐human drugs, including belzutifan, a HIF‐2α inhibitor. The 2019 Nobel Prize in Physiology or Medicine was awarded to Dr. William G. Kaelin Jr., Dr. Peter J. Ratcliffe, and Dr. Gregg L. Semenza as researchers contributing to clarifying the mechanism of the oxygen‐sensing pathway of cells. The first report of VHL disease was in 1894, meaning the development of a specific drug for this disease took almost 125 years. In this article, we describe how researchers and clinician scientists successfully clarified the function of VHL and achieved a preclinical proof of concept to apply for clinical trials, key requirements for drug development. [ABSTRACT FROM AUTHOR]

GDE4 and GDE7 are membrane-bound enzymes that exhibit lysophospholipase D activities. We found that GDE7 produced not only lysophosphatidic acid (LPA) but also cyclic phosphatidic acid (cPA) from lysophospholipids by a transphosphatidylation reaction. In contrast, GDE4 produced only LPA. The analysis of substrate specificity showed that 1-alkyl-lysophosphospholipids were preferred substrates for both enzymes rather than 1-alkyl-lysophospholipids and 1-alkenyl-lysophospholipids. Among the various lysophospholipids with different polar head groups that were tested, lysophosphatidylglycerol and lysophosphatidylserine were preferred substrates for GDE4 and GDE7, respectively. The detailed analysis of the dependency of the enzyme activities of GDE4 and GDE7 on divalent cations suggested multiple divalent cations were bound in the active sites of both enzymes. Taken together, these results suggest the possibility that GDE7 functions as a cPA-producing enzyme in the body. [ABSTRACT FROM AUTHOR]

Metformin is one of the most widely used therapeutics for type 2 diabetes mellitus and also has anticancer and antiaging properties. However, it is known to induce metformin-associated lactic acidosis (MALA), a severe medical condition with poor prognosis, especially in individuals with renal dysfunction. Inhibition of prolyl hydroxylase (PHD) is known to activate the transcription factor hypoxiainducible factor (HIF) that increases lactate efflux as a result of enhanced glycolysis, but it also enhances gluconeogenesis from lactate in the liver that contributes to reducing circulating lactate levels. Here, we investigated the outcome of pharmaceutical inhibition of PHD in mice with MALA induced through the administration of metformin per os and an intraperitoneal injection of lactic acid. We found that the PHD inhibitors significantly increased the expression levels of genes involved in gluconeogenesis in the liver and the kidney and significantly improved the survival of mice with MALA. Furthermore, the PHD inhibitor also improved the rate of survival of MALA induced in mice with chronic kidney disease (CKD). Thus, PHD represents a new therapeutic target for MALA, which is a critical complication of metformin therapy. [ABSTRACT FROM AUTHOR]

Loss of prolyl hydroxylase 2 (PHD2) activates the hypoxia-inducible factor-dependent hypoxic response, including anaerobic glycolysis, which causes large amounts of lactate to be released from cells into the circulation. We found that Phd2-null mouse embryonic fibroblasts (MEFs) produced more lactate than wild-type MEFs, as expected, whereas systemic inactivation of PHD2 in mice did not cause hyperlacticacidemia. This unexpected observation led us to hypothesize that the hypoxic response activated in the liver enhances the Cori cycle, a lactate-glucose carbon recycling system between muscle and liver, and thereby decreases circulating lactate. Consistent with this hypothesis, blood lactate levels measured after a treadmill or lactate tolerance test were significantly lower in Phd2-liver-specific knockout (Phd2-LKO) mice than in control mice. An in vivo 13C-labeled lactate incorporation assay revealed that the livers of Phd2-LKO mice produce significantly more glucose derived from 13C-labeled lactate than control mice, suggesting that blockade of PHD2 in the liver ameliorates lactic acidosis by activating gluconeogenesis from lactate. Phd2-LKO mice were resistant to lactic acidosis induced by injection of a lethal dose of lactate, displaying a significant elongation of survival. Moreover, oral administration of a PHD inhibitor improved survival in an endotoxin shock mice model. These data suggest that PHD2 is a potentially novel drug target for the treatment of lactic acidosis, which is a serious and often fatal complication observed in some critically ill patients. [ABSTRACT FROM AUTHOR]

Aberrations in epigenetic processes, such as histone methylation, can cause cancer. Retinoblastoma binding protein 2 (RBP2; also called JARID1A or KDM5A) can demethylate tri- and dimethylated lysine 4 in histone H3, which are epigenetic marks for transcription- ally active chromatin, whereas the multiple endocrine neoplasia type 1 (MEN1) tumor suppressor promotes H3K4 methylation. Previous studies suggested that inhibition of RBP2 contributed to tumor suppression by the retinoblastoma protein (pRB). Here, we show that genetic ablation of Rbp2 decreases tumor formation and prolongs survival in Rb1+/- mice and Menl-defective mice. These studies link RBP2 histone demethylase activity to tumorigenesis and nominate RBP2 as a potential target for cancer therapy. [ABSTRACT FROM AUTHOR]

Hypoxia-inducible factor (HIF), consisting of a labile α subunit and a stable β subunit, is a master regulator of hypoxia-responsive mRNAs. HIF α undergoes oxygen-dependent prolyl hydroxylation, which marks it for polyubiquitination by a complex containing the von Hippel-Lindau protein (pVHL). Among the three Phd family members, Phd2 appears to be the primary HIF prolyl hydroxylase. Phd3 is induced by HIF and, based on findings from in vitro studies, may participate in a HIF-regulatory feedback loop. Here, we report that Phd3 loss exacerbates the HIF activation, hepatic steatosis, dilated cardiomyopathy, and premature mortality observed in mice lacking Phd2 alone and produces a closer phenocopy of the changes seen in mice lacking pVHL than the loss of Phd2 alone. Importantly, the degree to which Phd3 can compensate for Phd2 loss and the degree to which the combined loss of Phd2 and Phd3 resembles pVHL loss appear to differ for different HIF-responsive genes and in different tissues. These findings highlight that the responses of different HIF target genes to changes in prolyl hydroxylase activity differ, quantitatively and qualitatively, in vivo and have implications for the development of paralog-specific prolyl hydroxylase inhibitors as therapeutic agents. [ABSTRACT FROM AUTHOR]

Germline von Hippel–Lindau tumour suppressor gene (VHL) mutations cause renal cell carcinomas, haemangioblastomas and phaeochromocytomas in humans. Mutations in VHL also occur in sporadic renal cell carcinomas. The protein encoded by VHL, VHL, is part of the ubiquitin ligase that downregulates the heterodimeric transcription factor Hif under well-oxygenated conditions. Here we show that acute VHL inactivation causes a senescent-like phenotype in vitro and in vivo. This phenotype was independent of p53 and Hif but dependent on the retinoblastoma protein (Rb) and the SWI2/SNF2 chromatin remodeller p400. Rb activation occurred through a decrease in Skp2 messenger RNA, which resulted in the upregulation of p27 in a Hif-independent fashion. Our results suggest that senescence induced by VHL inactivation is a tumour-suppressive mechanism that must be overcome to develop VHL-associated neoplasias. [ABSTRACT FROM AUTHOR]

The involvement of tissue ischemia in obesity-induced kidney injury remains to be elucidated. Compared with low fat diet (LFD)-mice, high fat diet (HFD)-fed mice became obese with tubular enlargement, glomerulomegaly and peritubular capillary rarefaction, and exhibited both tubular and glomerular damages. In HFD-fed mice, despite the increase in renal pimonidazole-positive areas, the expressions of the hypoxia-responsive genes such as Prolyl-hydroxylase PHD2, a dominant oxygen sensor, and VEGFA were unchanged indicating impaired hypoxic response. Tamoxifen inducible proximal tubules (PT)-specific Phd2 knockout (Phd2-cKO) mice and their littermate control mice (Control) were created and fed HFD or LFD. Control mice on HFD (Control HFD) exhibited renal damages and renal ischemia with impaired hypoxic response compared with those on LFD. After tamoxifen treatment, HFD-fed knockout mice (Phd2-cKO HFD) had increased peritubular capillaries and the increased expressions of hypoxia responsive genes compared to Control HFD mice. Phd2-cKO HFD also exhibited the mitigation of tubular damages, albuminuria and glomerulomegaly. In human PT cells, the increased expressions of hypoxia-inducible genes in hypoxic condition were attenuated by free fatty acids. Thus, aberrant hypoxic responses due to dysfunction of PHD2 caused both glomerular and tubular damages in HFD-induced obese mice. Phd2-inactivation provides a novel strategy against obesity-induced kidney injury. [ABSTRACT FROM AUTHOR]

Clear cell carcinoma of the kidney is a major cause of mortality in patients with von Hippel-Lindau (VHL) disease, which is caused by germ line mutations that inactivate the VHL tumor suppressor gene. Biallelic VHL inactivation, due to mutations or hypermethylation, is also common in sporadic clear cell renal carcinomas. The VHL gene product, pVHL, is part of a ubiquitin ligase complex that targets the alpha subunits of the heterodimeric transcription factor hypoxia-inducible factor (HIF) for destruction under well-oxygenated conditions. All VHL mutations linked to classical VHL disease compromise this pVHL function although some missense mutations result in a low risk of kidney cancer (type 2A VHL disease) while others result in a high risk (type 2B VHL disease). We found that type 2A mutants were less defective than type 2B mutants when reintroduced into VHL-/- renal carcinoma cells with respect to HIF regulation. A stabilized version of HIF2 promoted tumor growth by VHL-/- cells engineered to produce type 2A mutants, while knock-down of HIF2 in cells producing type 2B mutants had the opposite effect. Therefore, quantitative differences with respect to HIF deregulation are sufficient to account for the differential risks of kidney cancer linked to VHL mutations. [ABSTRACT FROM AUTHOR]