Differential regulation of hypoxia-inducible factor-1 through receptor tyrosine kinase transactivation in vascular smooth muscle cells

Cd stabilizes HIF-1α under normoxic conditions via lysine-63-linked ubiquitination and induces ER stress and cell proliferation

Cadmium, a carcinogenic and toxic substance released into the environment, has emerged as a potent activator of lysine-63 ubiquitination, and lysine-63 is a crucial regulator of signal transduction pathways. Although critical, very little information is currently available about how the activation of lysine 63 ubiquitination by Cd might contribute to cancers and inflammatory diseases. The present study provides the first evidence that Cd stabilizes hypoxia-inducible factor-1-alpha, a transcription factor, under normoxic conditions via lysine 63 ubiquitination. Cd induces the accumulation of lysine 63 polyubiquitinated proteins. Importantly, Cd-induced ubiquitination does not prevent oxidative damage or proteasome impairment. Instead, we demonstrated that Cd activates lysine 63 ubiquitination and amplifies its accumulation by overloading the capacity of the autophagy pathway, thus promoting endoplasmic reticulum stress and cell death. At the molecular level, Cd-induced lysine 63 polyubiquitination is correlated with the stabilization of hypoxia-inducible factor-1-alpha, which translocates into the nucleus and promotes the expression of oncogenes such as interleukin 8 and vascular endothelial growth factor. Strikingly, prolonged cell exposure to high Cd concentrations induces increased lysine-63 polyubiquitination, which promotes aggresome formation, thus preventing this protein from interacting with its downstream nuclear targets. Our results showed that Cd is an activator of K63-linked ubiquitination that stabilizes and promotes the accumulation of HIF-1α, which blocks autophagy, thus resulting in endoplasmic reticulum stress. In addition, a small amount of HIF-1α was observed in the nucleus. We therefore propose that the aberrant activation of lysine 63 polyubiquitination by the carcinogen Cd could promote cell proliferation and inflammation at low levels, while high levels lead to cell death.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43188-024-00266-9.

The role of EGFR in vascular AT1R signaling: From cellular mechanisms to systemic relevance

The epidermal growth factor receptor (EGFR) belongs to the ErbB-family of receptor tyrosine kinases that are of importance in oncology. During the last years, substantial evidence accumulated for a crucial role of EGFR concerning the action of the angiotensin II type 1 receptor (AT1R) in blood vessels, resulting form AT1R-induced EGFR transactivation. This transactivation occurs through the release of membrane-anchored EGFR-ligands, cytosolic tyrosine kinases, heterocomplex formation or enhanced ligand expression. AT1R-EGFR crosstalk amplifies the signaling response and enhances the biological effects of angiotensin II. Downstream signaling cascades include ERK1/2 and p38 MAPK, PLCγ and STAT. AT1R-induced EGFR activation contributes to vascular remodeling and hypertrophy via e.g. smooth muscle cell proliferation, migration and extracellular matrix production. EGFR transactivation results in increased vessel wall thickness and reduced vascular compliance. AT1R and EGFR signaling pathways are also implicated the induction of vascular inflammation. Again, EGFR transactivation exacerbates the effects, leading to endothelial dysfunction that contributes to vascular inflammation, dysfunction and remodeling. Dysregulation of the AT1R-EGFR axis has been implicated in the pathogenesis of various cardiovascular diseases and inhibition or prevention of EGFR signaling can attenuate part of the detrimental impact of enhanced renin-angiotensin-system (RAAS) activity, highlighting the importance of EGFR for the adverse consequences of AT1R activation. In summary, EGFR plays a critical role in vascular AT1R action, enhancing signaling, promoting remodeling, contributing to inflammation, and participating in the pathogenesis of cardiovascular diseases. Understanding the interplay between AT1R and EGFR will foster the development of effective therapeutic strategies of RAAS-induced disorders.

Allicin, an Emerging Treatment for Pulmonary Arterial Hypertension: An Experimental Study

We assessed whether allicin, through its antihypertensive and antioxidant effects, relieves vascular remodeling, endothelial function, and oxidative stress (OS), thereby improving experimental pulmonary arterial hypertension (PAH). Allicin (16 mg/kg) was administered to rats with PAH (monocrotaline 60 mg/kg). Allicin encouraged body weight gain and survival rate, and medial wall thickness and the right ventricle (RV) hypertrophy were prevented. Also, angiotensin II concentrations in the lung (0.37 ± 0.01 vs. 0.47 ± 0.06 pmoles/mL, allicin and control, respectively) and plasma (0.57 ± 0.05 vs. 0.75 ± 0.064, allicin and control respectively) and the expressions of angiotensin-converting enzyme II and angiotensin II type 1 receptor in lung tissue were maintained at normal control levels with allicin. In PAH rats treated with allicin, nitric oxide (NO) (31.72 ± 1.22 and 51.4 ± 3.45 pmoles/mL), tetrahydrobiopterin (8.43 ± 0.33 and 10.14 ± 0.70 pmoles/mL), cyclic guanosine monophosphate (5.54 ± 0.42 and 5.64 ± 0.73 pmoles/mL), and Ang-(1-7) (0.88 ± 0.23 and 0.83 ± 0.056 pmoles/mL) concentrations increased in lung tissue and plasma, respectively. In contrast, dihydrobiopterin increase was prevented in both lung tissue and plasma (5.75 ± 0.3 and 5.64 ± 0.73 pmoles/mL); meanwhile, phosphodiesterase-5 was maintained at normal levels in lung tissue. OS in PAH was prevented with allicin through the increased expression of Nrf2 in the lung. Allicin prevented the lung response to hypoxia, preventing the overexpression of HIF-1α and VEGF. Allicin attenuated the vascular remodeling and RV hypertrophy in PAH through its effects on NO-dependent vasodilation, modulation of RAS, and amelioration of OS. Also, these effects could be associated with the modulation of HIF-1α and improved lung oxygenation. The global effects of allicin contribute to preventing endothelial dysfunction, remodeling of the pulmonary arteries, and RV hypertrophy, preventing heart failure, thus favoring survival. Although human studies are needed, the data suggest that, alone or in combination therapy, allicin may be an alternative in treating PAH if we consider that, similarly to current treatments, it improves lung vasodilation and increase survival. Allicin may be considered an option when there is a lack of efficacy, and where drug intolerance is observed, to enhance the efficacy of drugs, or when more than one pathogenic mechanism must be addressed.

Metabolic regulation of the proteasome under hypoxia by Poldip2 controls fibrotic signaling in vascular smooth muscle cells

The polymerase delta interacting protein 2 (Poldip2) is a nuclear-encoded mitochondrial protein required for oxidative metabolism. Under hypoxia, Poldip2 expression is repressed by an unknown mechanism. Therefore, low levels of Poldip2 are required to maintain glycolytic metabolism. The Cellular Communication Network Factor 2 (CCN2, Connective tissue growth factor, CTGF) is a profibrogenic molecule highly expressed in cancer and vascular inflammation in advanced atherosclerosis. Because CCN2 is upregulated under hypoxia and is associated with glycolytic metabolism, we hypothesize that Poldip2 downregulation is responsible for the upregulation of profibrotic signaling under hypoxia. Here, we report that Poldip2 is repressed under hypoxia by a mechanism that requires the activation of the enhancer of zeste homolog 2 repressive complex (EZH2) downstream from the Cyclin-Dependent Kinase 2 (CDK2). Importantly, we found that Poldip2 repression is required for CCN2 expression downstream of metabolic inhibition of the ubiquitin-proteasome system (UPS)-dependent stabilization of the serum response factor. Pharmacological or gene expression inhibition of CDK2 under hypoxia reverses Poldip2 downregulation, the inhibition of the UPS, and the expression of CCN2, collagen, and fibronectin. Thus, our findings connect cell cycle regulation and proteasome activity to mitochondrial function and fibrotic responses under hypoxia.

Tailoring therapies to counter the divergent immune landscapes of breast cancer

Breast cancer remains a significant clinical concern affecting millions of women worldwide. Immunotherapy is a rapidly growing drug class that has revolutionized cancer treatment but remains marginally successful in breast cancer. The success of immunotherapy is dependent on the baseline immune responses as well as removing the brakes off pre-existing anti-tumor immunity. In this review, we summarize the different types of immune microenvironment observed in breast cancer as well as provide approaches to target these different immune subtypes. Such approaches have demonstrated pre-clinical success and are currently under clinical evaluation. The impact of combination of these approaches with already approved chemotherapies and immunotherapies may improve patient outcome and survival.

Effects of blood oxygen saturation on pulmonary artery remodeling in an in vitro perfusion circuit model

Background

Patients with transposition of the great arteries are likely to survive surgery despite severe pulmonary artery hypertension. However, the underlying mechanisms remain largely unknown. The present study aimed to test the hypothesis that high blood oxygen saturation may protect the pulmonary artery from remodeling.

Methods

An in vitro pulmonary artery perfusion model was successfully performed by connecting rabbit pulmonary artery to a closed perfusion circuit. Twenty-five rabbits were divided randomly into 5 groups according to exposure conditions: Normal Control (NC) group (unperfused normal pulmonary artery), High Saturation (HS) group (oxygen saturation range: 90–100%), Medium Saturation (MS) group (oxygen saturation: 65–75%); Low Saturation (LS) group (oxygen saturation: 40–50%), and anti-hypoxia inducible factor-1α (anti-HIF-1α) group (oxygen saturation range: 40–50%, and LW6, which is a novel HIF-1α inhibitor; was added). By staining and optical microscopy examination, pathological morphology was analyzed, and the protein expression levels of HIF-1α, angiotensin-II (Ang-II), endothelin-1 (ET-1), Rho-associated protein kinase-1 (Rock-1), and matrix metallopeptidase-2 (MMP-2) were determined by Western blotting.

Results

The amounts of elastin, muscle, and collagen and the protein levels of ET-1, HIF-1α, Rock-1, and MMP-2, increased significantly with decreased oxygen saturation in the perfusion circuit. A significant improvement in pathological morphology was observed in the anti-HIF1α group. The expression of HIF-1α, ET-1, Ang-II, Rock-1, and MMP-2 in the anti-HIF1α group was also significantly lower than that in the LS group.

Conclusions

In the closed perfusion model, high blood oxygen saturation alleviated pulmonary vascular structural remodeling. Similar beneficial effects were observed when inhibiting the HIF-1α protein, suggesting a key role for HIF-1α in pulmonary artery remodeling.

Selective HIF-1 Regulation under Nonhypoxic Conditions by the p42/p44 MAP Kinase Inhibitor PD184161

Hypoxia-inducible factor-1 (HIF-1) is a key gene regulator for cellular adaptation to low oxygen. In addition to hypoxia, several nonhypoxic stimuli, including hormones and growth factors, are essential for cell-specific HIF-1 regulation. Our studies have highlighted angiotensin II (AngII), a vasoactive hormone, as a potent HIF-1 activator in vascular smooth muscle cells (VSMC). AngII increases HIF-1 transcriptional activity by modulating specific signaling pathways. In VSMC, p42/p44 mitogen-activated protein kinase (MAPK) pathway activation is essential for HIF-1-mediated transcription during AngII treatment. The present study shows that PD184161, a potent MEK1/2 inhibitor, is an HIF-1 blocker in Ang II-treated VSMC. Unlike PD98059, a widely-used MEK1/2 inhibitor, we found that PD184161 blocked AngII-driven HIF-1α protein induction in a dose-dependent manner. Interestingly, the effect of PD184161 was specific to nonhypoxic activators, since HIF-1α induction by hypoxia (1% O2) was unaffected under similar conditions. VSMC treatment with MG132, a proteasome inhibitor, indicated that PD184161 influenced HIF-1α protein stability. PD184161 also increased HIF-1α binding to von Hippel-Lindau tumor suppressor protein, an E3 ligase component and an indication of HIF-1α hydroxylation. Finally, we show that PD184161 blocked mitochondrial ROS (mtROS) production and cellular ATP levels, at the same time enhancing ascorbate availability in AngII-treated VSMC. Taken together, our study indicates that, independently of p42/p44 MAPK activation, PD184161 blocks mtROS generation by AngII, leading to re-establishment of cellular ascorbate levels, increased VHL binding, and decreased HIF-1α stability. Therefore, this study reveals a previously unsuspected role for PD184161 as an HIF-1 inhibitor in VSMC under nonhypoxic conditions.

A tumoural angiogenic gateway blocker, Benzophenone-1B represses the HIF-1α nuclear translocation and its target gene activation against neoplastic progression

Hypoxia is an important module in all solid tumours to promote angiogenesis, invasion and metastasis. Stabilization and subsequent nuclear localization of HIF-1α subunits result in the activation of tumour promoting target genes such as VEGF, MMPs, Flt-1, Ang-1 etc. which plays a pivotal role in adaptation of tumour cells to hypoxia. Increased HIF-α and its nuclear translocation have been correlated with pronounced angiogenesis, aggressive tumour growth and poor patient prognosis leading to current interest in HIF-1α as an anticancer drug target. Benzophenone-1B ([4-(1H-benzimidazol-2-ylmethoxy)-3,5-dimethylphenyl]-(4-methoxyphenyl) methanone, or BP-1B) is a new antineoplastic agent with potential angiopreventive effects. Current investigation reports the cellular biochemical modulation underlying BP-1B cytotoxic/antiangiogenic effects. Experimental evidences postulate that BP-1B exhibits the tumour specific cytotoxic actions against various cancer types with prolonged action. Moreover BP-1B efficiently counteracts endothelial cell capillary formation in in-vitro, in-vivo non-tumour and tumour angiogenic systems. Molecular signaling studies reveal that BP-1B arrests nuclear translocation of HIF-1α devoid of p42/44 pathway under CoCl₂ induced hypoxic conditions in various cancer cells thereby leading to abrogated HIF-1α dependent activation of VEGF-A, Flt-1, MMP-2, MMP -9 and Ang-1 angiogenic factors resulting in retarded cell migration and invasions. The in-vitro results were reproducible in the reliable in-vivo solid tumour model. Taken together, we conclude that BP-1B impairs angiogenesis by blocking nuclear localization of HIF-1α which can be translated into a potent HIF-1α inhibitor.

Mitochondrial ROS regulation of proliferating cells

Once thought of exclusively as damaging molecules, reactive oxygen species (ROS) are becoming increasingly appreciated for the role they play in cellular signaling through redox biology. Notably, mitochondria are a major source of ROS within a cell (mROS). Mounting evidence now clearly shows that mROS are critical for intracellular redox signaling by which they contribute to a plethora of cellular processes such as proliferation. mROS are essential for physiological cell proliferation, particularly by the regulation of hypoxia inducible factors (HIFs) under hypoxia. mROS are also vital mediators of growth factor signaling cascades such as angiotensin II (Ang II) and T-cell receptor (TCR) signaling. Pathological proliferative diseases such as cancer utilize mROS to their advantage, aberrantly activating growth factor signaling cascades and perpetuating angiogenesis under hypoxia. This review discusses how mROS positively regulate mitogenic cellular signaling through redox biology, which is critical for both physiological and pathological proliferation.

Hypoxia-inducible factor-1 plays a role in phosphate-induced vascular smooth muscle cell calcification

Medial vascular calcification is a common complication of chronic kidney disease (CKD). Although elevated inorganic phosphate stimulates vascular smooth muscle cell (VSMC) osteogenic transdifferentiation and calcification, the mechanisms involved in their calcification during CKD are not fully defined. Because hypoxic gene activation is linked to CKD and stimulates bone cell osteogenic differentiation, we used in vivo and in vitro rodent models to define the role of hypoxic signaling during elevated inorganic phosphate-induced VSMC calcification. Cell mineralization studies showed that elevated inorganic phosphate rapidly induced VSMC calcification. Hypoxia strongly enhanced elevated inorganic phosphate-induced VSMC calcification and osteogenic transdifferentiation, as seen by osteogenic marker expression. Hypoxia-inducible factor-1 (HIF-1), the key hypoxic transcription factor, was essential for enhanced VSMC calcification. Targeting HIF-1 expression in murine VSMC blocked calcification in hypoxia with elevated inorganic phosphate while HIF-1 activators, including clinically used FG-4592/Roxadustat, recreated a procalcifying environment. Elevated inorganic phosphate rapidly activated HIF-1, even in normal oxygenation; an effect mediated by HIF-1α subunit stabilization. Thus, hypoxia synergizes with elevated inorganic phosphate to enhance VSMC osteogenic transdifferentiation. Our work identifies HIF-1 as an early CKD-related pathological event, prospective marker, and potential target against vascular calcification in CKD-relevant conditions.

Expression and Function of the Epidermal Growth Factor Receptor in Physiology and Disease

The epidermal growth factor receptor (EGFR) is the prototypical member of a family of membrane-associated intrinsic tyrosine kinase receptors, the ErbB family. EGFR is activated by multiple ligands, including EGF, transforming growth factor (TGF)-α, HB-EGF, betacellulin, amphiregulin, epiregulin, and epigen. EGFR is expressed in multiple organs and plays important roles in proliferation, survival, and differentiation in both development and normal physiology, as well as in pathophysiological conditions. In addition, EGFR transactivation underlies some important biologic consequences in response to many G protein-coupled receptor (GPCR) agonists. Aberrant EGFR activation is a significant factor in development and progression of multiple cancers, which has led to development of mechanism-based therapies with specific receptor antibodies and tyrosine kinase inhibitors. This review highlights the current knowledge about mechanisms and roles of EGFR in physiology and disease.

Methylation-dependent regulation of hypoxia inducible factor-1 alpha gene expression by the transcription factor Kaiso

Low oxygen tension (hypoxia) is a common characteristic of solid tumors and strongly correlates with poor prognosis and resistance to treatment. In response to hypoxia, cells initiate a cascade of transcriptional events regulated by the hypoxia inducible factor-1 (HIF-1) heterodimer. Since the oxygen-sensitive HIF-1α subunit is stabilized during hypoxia, it functions as the regulatory subunit of the protein. To date, while the mechanisms governing HIF-1α protein stabilization and function have been well studied, those governing HIF1A gene expression are not fully understood. However, recent studies have suggested that methylation of a HIF-1 binding site in the HIF1A promoter prevents its autoregulation. Here we report that the POZ-ZF transcription factor Kaiso modulates HIF1A gene expression by binding to the methylated HIF1A promoter in a region proximal to the autoregulatory HIF-1 binding site. Interestingly, Kaiso's regulation of HIF1A occurs primarily during hypoxia, which is consistent with the finding that Kaiso protein levels peak after 4 h of hypoxic incubation and return to normoxic levels after 24 h. Our data thus support a role for Kaiso in fine-tuning HIF1A gene expression after extended periods of hypoxia.

High Glucose Up-regulates ADAM17 through HIF-1α in Mesangial Cells

We previously showed that ADAM17 mediates high glucose-induced matrix production by kidney mesangial cells. ADAM17 expression is increased in diabetic kidneys, suggesting that its up-regulation may augment high glucose profibrotic responses. We thus studied the effects of high glucose on ADAM17 gene regulation. Primary rat mesangial cells were treated with high glucose (30 mm) or mannitol as osmotic control. High glucose dose-dependently increased ADAM17 promoter activity, transcript, and protein levels. This correlated with augmented ADAM17 activity after 24 h versus 1 h of high glucose. We tested involvement of transcription factors shown in other settings to regulate ADAM17 transcription. Promoter activation was not affected by NF-κB or Sp1 inhibitors, but was blocked by hypoxia-inducible factor-1α (HIF-1α) inhibition or down-regulation. This also prevented ADAM17 transcript and protein increases. HIF-1α activation by high glucose was shown by its increased nuclear translocation and activation of the HIF-responsive hypoxia-response element (HRE)-luciferase reporter construct. Assessment of ADAM17 promoter deletion constructs coupled with mutation analysis and ChIP studies identified HIF-1α binding to its consensus element at -607 as critical for the high glucose response. Finally, inhibitors of epidermal growth factor receptor (EGFR) and downstream PI3K/Akt, or ADAM17 itself, prevented high glucose-induced HIF-1α activation and ADAM17 up-regulation. Thus, high glucose induces ADAM17 transcriptional up-regulation in mesangial cells, which is associated with augmentation of its activity. This is mediated by HIF-1α and requires EGFR/ADAM17 signaling, demonstrating the potentiation by ADAM17 of its own up-regulation. ADAM17 inhibition thus provides a potential novel therapeutic strategy for the treatment of diabetic nephropathy.

Role of epidermal growth factor receptor and endoplasmic reticulum stress in vascular remodeling induced by angiotensin II

The mechanisms by which angiotensin II (AngII) elevates blood pressure and enhances end-organ damage seem to be distinct. However, the signal transduction cascade by which AngII specifically mediates vascular remodeling such as medial hypertrophy and perivascular fibrosis remains incomplete. We have previously shown that AngII-induced epidermal growth factor receptor (EGFR) transactivation is mediated by disintegrin and metalloproteinase domain 17 (ADAM17), and that this signaling is required for vascular smooth muscle cell hypertrophy but not for contractile signaling in response to AngII. Recent studies have implicated endoplasmic reticulum (ER) stress in hypertension. Interestingly, EGFR is capable of inducing ER stress. The aim of this study was to test the hypothesis that activation of EGFR and ER stress are critical components required for vascular remodeling but not hypertension induced by AngII. Mice were infused with AngII for 2 weeks with or without treatment of EGFR inhibitor, erlotinib, or ER chaperone, 4-phenylbutyrate. AngII infusion induced vascular medial hypertrophy in the heart, kidney and aorta, and perivascular fibrosis in heart and kidney, cardiac hypertrophy, and hypertension. Treatment with erlotinib as well as 4-phenylbutyrate attenuated vascular remodeling and cardiac hypertrophy but not hypertension. In addition, AngII infusion enhanced ADAM17 expression, EGFR activation, and ER/oxidative stress in the vasculature, which were diminished in both erlotinib-treated and 4-phenylbutyrate-treated mice. ADAM17 induction and EGFR activation by AngII in vascular cells were also prevented by inhibition of EGFR or ER stress. In conclusion, AngII induces vascular remodeling by EGFR activation and ER stress via a signaling mechanism involving ADAM17 induction independent of hypertension.

Role of nitric oxide in the maintenance of pluripotency and regulation of the hypoxia response in stem cells

Stem cell pluripotency and differentiation are global processes regulated by several pathways that have been studied intensively over recent years. Nitric oxide (NO) is an important molecule that affects gene expression at the level of transcription and translation and regulates cell survival and proliferation in diverse cell types. In embryonic stem cells NO has a dual role, controlling differentiation and survival, but the molecular mechanisms by which it modulates these functions are not completely defined. NO is a physiological regulator of cell respiration through the inhibition of cytochrome c oxidase. Many researchers have been examining the role that NO plays in other aspects of metabolism such as the cellular bioenergetics state, the hypoxia response and the relationship of these areas to stem cell stemness.

Vascular induction of a disintegrin and metalloprotease 17 by angiotensin II through hypoxia inducible factor 1α

BACKGROUND

A disintegrin and metalloprotease 17 (ADAM17) is a membrane-spanning metalloprotease overexpressed in various cardiovascular diseases such as hypertension and atherosclerosis. However, little is known regarding the regulation of ADAM17 expression in the cardiovascular system. Here, we test our hypothesis that angiotensin II induces ADAM17 expression in the vasculature.

METHODS

Cultured vascular smooth muscle cells were stimulated with 100 nM angiotensin II. Mice were infused with 1 μg/kg/minute angiotensin II for 2 weeks. ADAM17 expression was evaluated by a promoter-reporter construct, quantitative polymerase chain reaction, immunoblotting, and immunohistochemistry.

RESULTS

In vascular smooth muscle cells, angiotensin II increased ADAM17 protein expression, mRNA, and promoter activity. We determined that the angiotensin II response involves hypoxia inducible factor 1α and a hypoxia responsive element. In angiotensin II-infused mice, marked induction of ADAM17 and hypoxia inducible factor 1α was seen in vasculatures in heart and kidney, as well as in aortae, by immunohistochemistry.

CONCLUSIONS

Angiotensin II induces ADAM17 expression in the vasculatures through a hypoxia inducible factor 1α-dependent transcriptional upregulation, potentially contributing to end-organ damage in the cardiovascular system.

Sirtuin 3 deficiency is associated with inhibited mitochondrial function and pulmonary arterial hypertension in rodents and humans

Suppression of mitochondrial function promoting proliferation and apoptosis suppression has been described in the pulmonary arteries and extrapulmonary tissues in pulmonary arterial hypertension (PAH), but the cause of this metabolic remodeling is unknown. Mice lacking sirtuin 3 (SIRT3), a mitochondrial deacetylase, have increased acetylation and inhibition of many mitochondrial enzymes and complexes, suppressing mitochondrial function. Sirt3KO mice develop spontaneous PAH, exhibiting previously described molecular features of PAH pulmonary artery smooth muscle cells (PASMC). In human PAH PASMC and rats with PAH, SIRT3 is downregulated, and its normalization with adenovirus gene therapy reverses the disease phenotype. A loss-of-function SIRT3 polymorphism, linked to metabolic syndrome, is associated with PAH in an unbiased cohort of 162 patients and controls. If confirmed in large patient cohorts, these findings may facilitate biomarker and therapeutic discovery programs in PAH.

Vasotrophic regulation of age-dependent hypoxic cerebrovascular remodeling

Hypoxia can induce functional and structural vascular remodeling by changing the expression of trophic factors to promote homeostasis. While most experimental approaches have been focused on functional remodeling, structural remodeling can reflect changes in the abundance and organization of vascular proteins that determine functional remodeling. Better understanding of age-dependent hypoxic macrovascular remodeling processes of the cerebral vasculature and its clinical implications require knowledge of the vasotrophic factors that influence arterial structure and function. Hypoxia can affect the expression of transcription factors, classical receptor tyrosine kinase factors, non-classical G-protein coupled factors, catecholamines, and purines. Hypoxia's remodeling effects can be mediated by Hypoxia Inducible Factor (HIF) upregulation in most vascular beds, but alterations in the expression of growth factors can also be independent of HIF. PPARγ is another transcription factor involved in hypoxic remodeling. Expression of classical receptor tyrosine kinase ligands, including vascular endothelial growth factor, platelet derived growth factor, fibroblast growth factor and angiopoietins, can be altered by hypoxia which can act simultaneously to affect remodeling. Tyrosine kinase-independent factors, such as transforming growth factor, nitric oxide, endothelin, angiotensin II, catecholamines, and purines also participate in the remodeling process. This adaptation to hypoxic stress can fundamentally change with age, resulting in different responses between fetuses and adults. Overall, these mechanisms integrate to assure that blood flow and metabolic demand are closely matched in all vascular beds and emphasize the view that the vascular wall is a highly dynamic and heterogeneous tissue with multiple cell types undergoing regular phenotypic transformation.

The prolyl isomerase Pin1 regulates hypoxia-inducible transcription factor (HIF) activity

Hypoxia-inducible transcription factor-1 (HIF-1) plays a decisive role in cell survival and adaptation to hypoxic stress by controlling the expression of genes involved in oxygen homeostasis. HIF-1 activity is fine-tuned through specific post-translational modifications of its essential HIF-1α subunit. Among these modifications, phosphorylation is important for HIF-1 transcriptional activity. Studies have shown that the mitogen-activated protein kinases, p42/p44 MAPKs, directly phosphorylate HIF-1α and increase HIF-1-mediated transcription. Pin1, a peptidyl-prolyl cis/trans isomerase, targets a number of proteins containing a phosphorylated Ser/Thr-Pro motif. Pin1 isomerization causes a change in target protein conformation which can modify their activity. Here, we identify Pin1 as an important HIF-1α partner. Immunoprecipitation and pull-down studies show that Pin1 interacts with HIF-1α. We demonstrate that the interaction between Pin1 and HIF-1α is regulated through p42/p44 MAPK pathway activation. By performing proteolysis studies, our results indicate that Pin1 catalytic activity generates a conformational change in HIF-1α. Finally, our work shows that Pin1 is required for gene-specific HIF-1 transcriptional activity. Our results indicate that the prolyl isomerase Pin1 regulates HIF-1 transcriptional activity by interacting with HIF-1α and promoting conformational changes in a p42/p44 MAPK phosphorylation-dependent manner.

Transcriptional repression of hypoxia-inducible factor-1 (HIF-1) by the protein arginine methyltransferase PRMT1

Hypoxia-inducible factors (HIF) are essential for the adaptive response of cells to low-oxygen conditions. Transcription of HIF-α subunits and HIF activity are repressed by the arginine methyltransferase PRMT1. Therefore PRMT1 is a novel regulator of hypoxic cell responses.

Hypoxia-inducible factors (HIF-1 and HIF-2) are essential mediators for the adaptive transcriptional response of cells and tissues to low-oxygen conditions. Under hypoxia or when cells are treated with various nonhypoxic stimuli, the active HIF-α subunits are mainly regulated through increased protein stabilization. For HIF-1α, it is clear that further transcriptional, translational, and posttranslational regulations are important for complete HIF-1 activity. Novel evidence links hypoxia and HIF-1 to arginine methylation, an important protein modification. These studies suggest that arginine methyltransferases may be important for hypoxic responses. Protein arginine methyltransferase 1 (PRMT1), the predominant arginine methyltransferase, can act as a transcriptional activator or repressor by modifying a diverse set of substrates. In this work, we show that PRMT1 is a repressor of both HIF-1 and HIF-2. The cellular depletion of PRMT1 by small interference RNA targeting leads to increased HIF transcriptional activity. This activation is the result of enhanced HIF-α subunit transcription, which allows increased HIF-α subunit availability. We provide evidence that PRMT1-dependent HIF-1α regulation is mediated through the activities of both specificity protein 1 (Sp1) and Sp3, two transcription factors known to control HIF-1α expression. This study therefore identifies PRMT1 as a novel regulator of HIF-1– and HIF-2–mediated responses.

Suboptimal maternal nutrition during early fetal kidney development specifically promotes renal lipid accumulation following juvenile obesity in the offspring

Reduced maternal food intake between early-to-mid gestation results in tissue-specific adaptations in the offspring following juvenile-onset obesity that are indicative of insulin resistance. The aim of the present study was to establish the extent to which renal ectopic lipid accumulation, as opposed to other markers of renal stress, such as iron deposition and apoptosis, is enhanced in obese offspring born to mothers nutrient restricted (NR) throughout early fetal kidney development. Pregnant sheep were fed either 100% (control) or NR (i.e. fed 50% of their total metabolisable energy requirement from 30-80 days gestation and 100% at all other times). At weaning, offspring were made obese and, at approximately 1 year, kidneys were sampled. Triglyceride content, HIF-1α gene expression and the protein abundance of the outer-membrane transporter voltage-dependent anion-selective channel protein (VDAC)-I on the kidney cortex were increased in obese offspring born to NR mothers compared with those born to controls, which exhibited increased iron accumulation within the tubular epithelial cells and increased gene expression of the death receptor Fas. In conclusion, suboptimal maternal nutrition coincident with early fetal kidney development results in enhanced renal lipid deposition following juvenile obesity and could accelerate the onset of the adverse metabolic, rather than cardiovascular, symptoms accompanying the metabolic syndrome.

Sphingosine-1-Phosphate as a Regulator of Hypoxia-Induced Factor-1α in Thyroid Follicular Carcinoma Cells

Sphingosine-1-phosphate (S1P) is a bioactive lipid, which regulates several cancer-related processes including migration and angiogenesis. We have previously shown S1P to induce migration of follicular ML-1 thyroid cancer cells. Hypoxia-induced factor-1 (HIF-1) is an oxygen-sensitive transcription factor, which adapts cells to hypoxic conditions through increased survival, motility and angiogenesis. Due to these properties and its increased expression in response to intratumoral hypoxia, HIF-1 is considered a significant regulator of tumor biology. We found S1P to increase expression of the regulatory HIF-1α subunit in normoxic ML-1 cells. S1P also increased HIF-1 activity and expression of HIF-1 target genes. Importantly, inhibition or knockdown of HIF-1α attenuated the S1P-induced migration of ML-1 cells. S1P-induced HIF-1α expression was mediated by S1P receptor 3 (S1P₃), G_i proteins and their downstream effectors MEK, PI3K, mTOR and PKCβI. Half-life measurements with cycloheximide indicated that S1P treatment stabilized the HIF-1α protein. On the other hand, S1P activated translational regulators eIF-4E and p70S6K, which are known to control HIF-1α synthesis. In conclusion, we have identified S1P as a non-hypoxic regulator of HIF-1 activity in thyroid cancer cells, studied the signaling involved in S1P-induced HIF-1α expression and shown S1P-induced migration to be mediated by HIF-1.

Epigenetic regulation of CD34 and HIF1A expression during the differentiation of human mast cells

Mast cells differentiate from circulating pluripotent hematopoietic progenitors. During this differentiation, the progenitor cells are exposed to changes in oxygen availability. HIF1A is the major sensor of oxygen concentration in mammalian cells. We investigated the expression of HIF1A during the in vitro differentiation of peripheral blood-derived progenitors into human mast cells. In a series of experiments, we determined the changes in CD34 expression, selected mast cell markers, and HIF1A in human mast cell cultures. While the expression of CD34 dramatically decreased, the expression of mast cell-specific genes, including FCER1A, MS4A2, TPSB2, and CMA1, steadily increased. HIF1A expression similarly increased during mast cell differentiation, reaching its maximum level at five weeks of culture. The analysis of the promoter methylation status showed decreasing levels of methylation at the HIF1A promoter, increasing levels of methylation at the CD34 promoter, and no significant changes in other genes. In silico analysis of the promoter regions of these genes revealed large CpG islands in close proximity to the HIF1A and CD34 transcription initiation sites, but not in other investigated genes. In conclusion, in vitro mast cell differentiation was associated with decreased CD34 expression and increased HIF1A expression. These changes were paralleled with changes in the methylation status of the respective promoters, suggesting that DNA methylation-dependent epigenetic regulation mediates the gene expression changes involved in maintaining the phenotype of hematopoietic stem cells and mature mast cells. Therefore, the baseline expression of HIF1A is epigenetically regulated in a cell type- and differentiation stage-specific fashion.

Differential effects of formoterol on thrombin- and PDGF-induced proliferation of human pulmonary arterial vascular smooth muscle cells

Background

Increased pulmonary arterial vascular smooth muscle (PAVSM) cell proliferation is a key pathophysiological component of pulmonary vascular remodeling in pulmonary arterial hypertension (PH). The long-acting β₂-adrenergic receptor (β₂AR) agonist formoterol, a racemate comprised of (R,R)- and (S,S)-enantiomers, is commonly used as a vasodilator in chronic obstructive pulmonary disease (COPD). PH, a common complication of COPD, increases patients’ morbidity and reduces survival. Recent studies demonstrate that formoterol has anti-proliferative effects on airway smooth muscle cells and bronchial fibroblasts. The effects of formoterol and its enantiomers on PAVSM cell proliferation are not determined. The goals of this study were to examine effects of racemic formoterol and its enantiomers on PAVSM cell proliferation as it relates to COPD-associated PH.

Methods

Basal, thrombin-, PDGF- and chronic hypoxia-induced proliferation of primary human PAVSM cells was examined by DNA synthesis analysis using BrdU incorporation assay. ERK1/2, mTORC1 and mTORC2 activation were determined by phosphorylation levels of ERK1/2, ribosomal protein S6 and S473-Akt using immunoblot analysis.

Results

We found that (R,R) and racemic formoterol inhibited basal, thrombin- and chronic hypoxia-induced proliferation of human PAVSM cells while (S,S) formoterol had lesser inhibitory effect. The β₂AR blocker propranolol abrogated the growth inhibitory effect of formoterol. (R,R), but not (S,S) formoterol attenuated basal, thrombin- and chronic hypoxia-induced ERK1/2 phosphorylation, but had little effect on Akt and S6 phosphorylation levels. Formoterol and its enantiomers did not significantly affect PDGF-induced DNA synthesis and PDGF-dependent ERK1/2, S473-Akt and S6 phosphorylation in human PAVSM cells.

Conclusions

Formoterol inhibits basal, thrombin-, and chronic hypoxia-, but not PDGF-induced human PAVSM cell proliferation and ERK1/2, but has little effect on mTORC1 and mTORC2 signaling. Anti-proliferative effects of formoterol depend predominantly on its (R,R) enantiomer and require the binding with β₂AR. These data suggest that (R,R) formoterol may be considered as potential adjuvant therapy to inhibit PAVSM cell proliferation in COPD-associated PH.

Hypoxia-inducible factor-1α mediates TGF-β-induced PAI-1 production in alveolar macrophages in pulmonary fibrosis

Hypoxia-inducible factor-1α (HIF-1α), a transcription factor that functions as a master regulator of oxygen homeostasis, has been implicated in fibrinogenesis. Here, we explore the role of HIF-1α in transforming growth factor-β (TGF-β) signaling by examining the effects of TGF-β(1) on the expression of plasminogen activator inhibitor-1 (PAI-1). Immunohistochemistry of lung tissue from a mouse bleomycin (BLM)-induced pulmonary fibrosis model revealed that expression of HIF-1α and PAI-1 was predominantly induced in alveolar macrophages. Real-time RT-PCR and ELISA analysis showed that PAI-1 mRNA and activated PAI-1 protein level were strongly induced 7 days after BLM instillation. Stimulation of cultured mouse alveolar macrophages (MH-S cells) with TGF-β(1) induced PAI-1 production, which was associated with HIF-1α protein accumulation. This accumulation of HIF-1α protein was inhibited by SB431542 (type I TGF-β receptor/ALK receptor inhibitor) but not by PD98059 (MEK1 inhibitor) and SB203580 (p38 MAP kinase inhibitor). Expression of prolyl-hydroxylase domain (PHD)-2, which is essential for HIF-1α degradation, was inhibited by TGF-β(1), and this decrease was abolished by SB431542. TGF-β(1) induction of PAI-1 mRNA and its protein expression were significantly attenuated by HIF-1α silencing. Transcriptome analysis by cDNA microarray of MH-S cells after HIF-1α silencing uncovered several pro-fibrotic genes whose regulation by TGF-β(1) required HIF-1α, including platelet-derived growth factor-A. Taken together, these findings expand our concept of the role of HIF-1α in pulmonary fibrosis in mediating the effects of TGF-β(1) on the expression of the pro-fibrotic genes in activated alveolar macrophages.

The conflicting effects of maternal nutrient restriction and early-life obesity on renal health

Epidemiological and animal studies have demonstrated that early-life nutrition alters the metabolic responses and generates structural changes in complex tissues, such as the kidneys, which may lead to a reduction in the offspring lifespan. Independently, obesity induces a spontaneous low-grade chronic inflammatory response by modulating several of the major metabolic pathways that ultimately compromise long-term renal health. However, the combined effects of maternal nutrition and early-life obesity in the development of renal diseases are far from conclusive. Previous results, using the ovine model, demonstrated that the combination of a reduction in fetal nutrition and juvenile obesity induced a series of adaptations associated with severe metabolic syndrome in the heart and adipose tissue. Surprisingly, exposure to an obesogenic environment in the kidney of those offspring produced an apparent reduction in glomerulosclerosis in relation to age- and weight-matched controls. However, this reduction in cellular apoptosis was accompanied by a rise in glomerular filtration rate and blood pressure of equal intensity when compared with obese controls. The intention of this review is to explain the adaptive responses observed in this model, based on insights into the mechanism of renal fetal programming, and their potential interactions with some of the metabolic changes produced by obesity.

Hypoxia stimulates the expression of macrophage migration inhibitory factor in human vascular smooth muscle cells via HIF-1alpha dependent pathway

Background

Hypoxia plays an important role in vascular remodeling and directly affects vascular smooth muscle cells (VSMC) functions. Macrophage migration inhibitory factor (MIF) is a well known proinflammatory factor, and recent evidence suggests an important role of MIF in the progression of atherosclerosis and restenosis. However, the potential link between hypoxia and MIF in VSMC has not been investigated. The current study was designed to test whether hypoxia could regulate MIF expression in human VSMC. The effect of modulating MIF expression on hypoxia-induced VSMC proliferation and migration was also investigated at the same time.

Results

Expression of MIF mRNA and protein was up-regulated as early as 2 hours in cultured human VSMCs after exposed to moderate hypoxia condition (3% O₂). The up-regulation of MIF expression appears to be dependent on hypoxia-inducible transcription factor-1α(HIF-1α) since knockdown of HIF-1α inhibits the hypoxia induction of MIF gene and protein expression. The hypoxia induced expression of MIF was attenuated by antioxidant treatment as well as by inhibition of extracellular signal-regulated kinase (ERK). Under moderate hypoxia conditions (3% O₂), both cell proliferation and cell migration were increased in VSMC cells. Blocking the MIF by specific small interference RNA to MIF (MIF-shRNA) resulted in the suppression of proliferation and migration of VSMCs.

Conclusion

Our results demonstrated that in VSMCs, hypoxia increased MIF gene expression and protein production. The hypoxia-induced HIF-1α activation, reactive oxygen species (ROS) generation and ERK activation might be involved in this response. Both MIF and HIF-1α mediated the hypoxia response of vascular smooth muscle cells, including cell migration and proliferation.

Hypoxia-inducible factor-1 activation in nonhypoxic conditions: the essential role of mitochondrial-derived reactive oxygen species

Hypoxia-inducible factor-1 (HIF-1) is a key transcription factor for responses to low oxygen. Different nonhypoxic stimuli, including hormones and growth factors, are also important HIF-1 activators in the vasculature. Angiotensin II (Ang II), the main effecter hormone in the renin-angiotensin system, is a potent HIF-1 activator in vascular smooth muscle cells (VSMCs). HIF-1 activation by Ang II involves intricate mechanisms of HIF-1α transcription, translation, and protein stabilization. Additionally, the generation of reactive oxygen species (ROS) is essential for HIF-1 activation during Ang II treatment. However, the role of the different VSMC ROS generators in HIF-1 activation by Ang II remains unclear. This work aims at elucidating this question. Surprisingly, repression of NADPH oxidase-generated ROS, using Vas2870, a specific inhibitor or a p22(phox) siRNA had no significant effect on HIF-1 accumulation by Ang II. In contrast, repression of mitochondrial-generated ROS, by complex III inhibition, by Rieske Fe-S protein siRNA, or by the mitochondrial-targeted antioxidant SkQ1, strikingly blocked HIF-1 accumulation. Furthermore, inhibition of mitochondrial-generated ROS abolished HIF-1α protein stability, HIF-1-dependent transcription and VSMC migration by Ang II. A large number of studies implicate NADPH oxidase-generated ROS in Ang II-mediated signaling pathways in VSMCs. However, our work points to mitochondrial-generated ROS as essential intermediates for HIF-1 activation in nonhypoxic conditions.

AMP-activated protein kinase inhibits IGF-I signaling and protein synthesis in vascular smooth muscle cells via stimulation of insulin receptor substrate 1 S794 and tuberous sclerosis 2 S1345 phosphorylation

AMP-activated protein kinase (AMPK) inhibits IGF-I actions, but the mechanism by which AMPK functions is undefined. This study identified signaling events that were induced by AMPK that mediated inhibition of IGF-I-stimulated phosphoinosotide-3-kinase (PI3K) pathway activation. The AMPK activator metformin stimulated AMPK Thr172 phosphorylation and inhibited IGF-I-stimulated phosphorylation of Akt/tuberous sclerosis 2 (TSC2)/mammalian target of rapamycin (mTOR)/p70S6 kinase (p70S6K). Expression of constitutively active forms of AMPK suppressed IGF-I-stimulated activation of Akt/TSC2/mTOR/p70S6K and protein synthesis, whereas AMPK knockdown resulted in enhanced responses to IGF-I. To determine the mechanism by which AMPK inhibited IGF-I signaling, the role of insulin receptor substrate-1 (IRS-1) was examined. Both metformin and constitutively activated AMPK enhanced phosphorylation of IRS-1 Ser794, which led to decreased IRS-1 tyrosine phosphorylation and recruitment of the p85 subunit of PI3K. Overexpression of IRS-1 S794A was associated with increased IGF-I-stimulated IRS-1 tyrosine phosphorylation, p85 association, and protein synthesis. To determine whether other signaling molecules mediated the effect of AMPK, TSC2 function was examined. Cells overexpressing TSC2/S1345A (the site of AMPK phosphorylation) were less responsive to metformin-induced inhibition of p70S6 kinase. These findings are relevant to whole animal physiology because administration of metformin to mice resulted in inhibition of IGF-I-stimulated phosphorylation of Akt/mTOR/p70S6K. In conclusion, AMPK functions to inhibit IGF-I-stimulated PI3K pathway activation through stimulation of IRS-1 serine 794 phosphorylation. Because IGF-I is an important stimulant of the anabolic response, this effect of AMPK could account for part of its inhibitory effect on protein synthesis, thus allowing more efficient energy use by other cellular processes.

Role of insulin-like growth factor 1 receptor and c-Src in endothelin-1- and angiotensin II-induced PKB phosphorylation, and hypertrophic and proliferative responses in vascular smooth muscle cellsThis article is one of a selection of papers published in a special issue on Advances in Cardiovascular Research

Endothelin-1 (ET-1) and angiotensin II (Ang II) are vasoactive peptides believed to contribute to the pathogenesis of vascular abnormalities such as hypertension, atherosclerosis, hypertrophy, and restenosis. The concept of transactivation of growth factor receptors, such as epidermal growth factor receptor (EGFR), in triggering vasoactive peptide-induced signaling events has gained much recognition during the past several years. We have demonstrated that insulin-like growth factor type 1 receptor (IGF-1R) plays a role in transducing the effect of H2O2, leading to protein kinase B (PKB) phosphorylation. Since vasoactive peptides elicit their responses through generation of reactive oxygen species, including H2O2, we investigated whether IGF-1R transactivation plays a similar role in ET-1- and Ang II-induced PKB phosphorylation and hypertrophic responses in vascular smooth muscle cells (VSMC). AG1024, a specific inhibitor of IGF-1R protein tyrosine kinase (PTK), attenuated both ET-1- and Ang II-induced PKB phosphorylation in a dose-dependent manner. ET-1 and Ang II treatment also induced the phosphorylation of tyrosine residues in the autophosphorylation sites of IGF-1R, which were blocked by AG1024. In addition, both ET-1 and Ang II evoked tyrosine phosphorylation of c-Src, a nonreceptor PTK, whereas pharmacological inhibition of c-Src PTK activity by PP2, a specific inhibitor of Src-family tyrosine kinase, significantly reduced PKB phosphorylation as well as tyrosine phosphorylation of IGF-1R induced by the 2 vasoactive peptides. Furthermore, protein and DNA synthesis enhanced by ET-1 and Ang II were attenuated by AG1024 and PP2. In conclusion, these data suggest that IGF-1R PTK and c-Src PTK play a critical role in mediating PKB phosphorylation as well as hypertrophic and proliferative responses induced by ET-1 and Ang II in A10 VSMC.

TGFbeta-induced GRK2 expression attenuates AngII-regulated vascular smooth muscle cell proliferation and migration

Through diametric actions, the transforming growth factor beta (TGFbeta) and Angiotensin II (AngII) play important roles in regulating various biological responses such as cell proliferation and migration. Signaling initiated by TGFbeta and AngII occurs through two structurally and functionally distinct receptor super families,the serine/threonine kinase and G protein-coupled receptors (GPCRs). Previously, we identified the Gprotein-coupled receptor kinase-2 (GRK2), a key regulatory factor in the desensitization of GPCRs, as a direct downstream target of the TGFbeta signaling cascade. GRK2 acts through a negative feed-back loop mechanism to terminate TGFbeta-induced smad signaling. To investigate the impact of TGFbeta-induced GRK2 expression on GPCR signaling, we examined its effect on AngII signaling in vascular smooth muscle cells (VSMCs). In this study, we show that activation of the TGFbeta signaling cascade in VSMCs results in increased GRK2 expression levels, which consequently inhibits AngII-induced ERK phosphorylation and antagonizes AngII-induced VSMC proliferation and migration. Moreover, the inhibitory effect of TGFbeta on AngII signaling occurs at the Mek-Erk interface and is abrogated when an anti-sense oligonucleotide directed against GRK2 is used. Thus,we conclude that TGFbeta signaling antagonizes AngII-induced VSMC proliferation and migration through the inhibition of ERK phosphorylation and that GRK2 is a key factor mediating the cross-talk between these two receptor super families.

(2R)-[(4-Biphenylylsulfonyl)amino]-N-hydroxy-3-phenylpropionamide (BiPS), a matrix metalloprotease inhibitor, is a novel and potent activator of hypoxia-inducible factors

Hypoxia-inducible factors (HIFs) are unstable heterodimeric transcription factors and decisive elements for the transcriptional regulation of genes important in the adaptation to low-oxygen conditions. Hypoxia is the ubiquitous inducer of HIFs, stabilizing the alpha-subunit and permitting the formation of a functional HIF complex. Here, we identify (2R)-[(4-biphenylylsulfonyl)amino]-N-hydroxy-3-phenylpropionamide (BiPS), a commercially available metalloprotease-2 and -9 inhibitor, as a rapid and potent inducer of HIFs. We show that in different cell lines, BiPS induces the HIF-alpha subunit by inhibiting its degradation through stabilization of its labile oxygen-dependent degradation domain. This is achieved through the inhibition of HIF-1alpha hydroxylation. The HIF-1 complex, formed after BiPS treatment, is capable of DNA binding and activation of HIF target genes, including the expression of vascular endothelial growth factor. Because novel HIF activators have generated considerable interest in the possible treatment of different ischemic diseases, we believe that BiPS and derivative molecules could have strong therapeutic potential.

Nitric oxide donor, (+/-)-S-nitroso-N-acetylpenicillamine, stabilizes transactive hypoxia-inducible factor-1alpha by inhibiting von Hippel-Lindau recruitment and asparagine hydroxylation

We have confirmed that the NO donor (+/-)-S-nitroso-N-acetylpenicillamine (SNAP) stabilizes the transactive form of hypoxia-inducible factor-1alpha (HIF-1alpha), leading to the induction of HIF-1alpha target genes such as vascular endothelial growth factor and carbonic anhydrase 9. Activation of HIF-1alpha should require inhibition of the dual system that keeps it inactive. One is ubiquitination, which is triggered by hydroxylation of HIF-1alpha-proline and the subsequent binding of E3 ubiquitin ligase, the von Hippel Lindau (VHL) protein. The other is hydroxylation of HIF-1alpha-asparagine, which reduces the affinity of HIF-1alpha for its coactivator, cAMP responsive element binding protein/p300. We examined the effects of the NO donor SNAP on proline and asparagine hydroxylation of HIF-1alpha peptides by measuring the activities of the corresponding enzymes, HIF-1alpha-specific proline hydroxylase 2 (PHD2) and the HIF-1alpha-specific asparagine hydroxylase, designated factor inhibiting HIF-1alpha (FIH-1), respectively. We found that the SNAP did not prevent PHD2 from hydroxylating the proline of HIF-1alpha. Instead, it blocked the interaction between VHL and the proline-hydroxylated HIF-1alpha, but only when the reducing agents Fe(II) and vitamin C were limiting. The fact that the absence of cysteine 520 of HIF-1alpha abolishes its responsiveness to SNAP suggests that this residue mediates the inhibition by SNAP of the interaction between VHL and HIF-1alpha, presumably by S-nitrosylation of HIF-1alpha. Un-like PHD2, asparagine hydroxylation by FIH-1 was directly inhibited by SNAP, but again only when reducing agents were limiting. Substitution of cysteine 800 of HIF-1alpha with alanine failed to reverse the inhibitory effects of SNAP on asparagine hydroxylation, implying that FIH-1, not its substrate HIF-1alpha, is inhibited by SNAP.

Increased static pressure promotes migration of vascular smooth muscle cells: involvement of the Rho-kinase pathway

Vascular smooth muscle cell (VSMC) migration plays a pivotal role in the pathogenesis of arteriosclerosis, under influences of various mechanical factors. Thus, we examined whether static pressure promotes VSMC migration and if so, whether Rho-kinase is involved. Rat VSMCs were cultured on chambers coated on fibronectin, vitronectin, laminin, or type IV collagen, under pressure-free conditions and at 90 and 180 mm Hg. In monolayer-wounding assay, VSMC migration was significantly increased after 72 hours at 180 mm Hg on both fibronectin (11.3 +/- 3.4-fold vs. pressure-free conditions) and vitronectin (10.6 +/- 0.7-fold; both P < 0.05). In Boyden chamber assay, the VSMC migration was again significantly increased at 180 mm Hg on both fibronectin (4.0 +/- 0.5-fold) and vitronectin (5.0 +/- 0.8-fold; both P < 0.05). Neutralizing antibodies against beta1-, beta3- and beta5-integrins, all of which play an important role in cell migration, significantly inhibited the pressure-promoted VSMC migration. Static pressure also significantly increased Rho-kinase activity in VSMC, as evaluated by the extent of phosphorylation of its downstream substrate, ezrin-radixin-moesin. Fasudil, a selective Rho-kinase inhibitor, significantly suppressed the pressure-promoted VSMC migration with reduced Rho-kinase activity. These results indicate that increased static pressure promotes VSMC migration through the integrin/Rho-kinase signaling, suggesting the therapeutic importance of this mechanism for the treatment of hypertensive vascular diseases.

Hypoxia-inducible factor-1alpha stabilization in nonhypoxic conditions: role of oxidation and intracellular ascorbate depletion

Hypoxia-inducible factor-1 (HIF-1) is a decisive element for the transcriptional regulation of many genes induced under low oxygen conditions. Under normal oxygen conditions, HIF-1alpha, the active subunit of HIF-1, is hydroxylated on proline residues by specific HIF prolyl-hydroxylases, leading to ubiquitination and degradation by the proteasome. In hypoxia, hydroxylation and ubiquitination are blocked and HIF-1alpha accumulates in cells. Recent studies have shown that in normal oxygen conditions G-protein-coupled receptor agonists, including angiotensin (Ang) II and thrombin, potently induce and activate HIF-1 in vascular smooth muscle cells. The current study identifies HIF-1alpha protein stabilization as a key mechanism for HIF-1 induction by Ang II. We show that hydroxylation on proline 402 is altered by Ang II, decreasing pVHL binding to HIF-1alpha and allowing HIF-1alpha protein to escape subsequent ubiquitination and degradation mechanisms. We show that HIF-1alpha stability is mediated through the Ang II-mediated generation of hydrogen peroxide and a subsequent decrease in ascorbate levels, leading to decreased HIF prolyl-hydroxylase activity and HIF-1alpha stabilization. These findings identify novel and intricate signaling mechanisms involved in HIF-1 complex activation and will lead to the elucidation of the importance of HIF-1 in different Ang II-related cell responses.