Publications

Gaseous messengers in oxygen sensing

Hypoxia-inducible factor 1α: Essential role in cardiovascular development and physiology

Cyclin-dependent kinases regulate lysosomal degradation of hypoxia-inducible factor 1α to promote cell-cycle progression

Significance Hypoxia-inducible factor 1α (HIF-1α) is required for adaptive changes to low oxygen levels, which include a reduced rate of cell division. However, many cell types continue to proliferate under hypoxic conditions. Here, we show that cyclin-dependent kinases 1 and 2 physically and functionally interact with HIF-1α, inhibiting and promoting its degradation by lysosomes, respectively. Cancer cells that proliferate under hypoxia failed to do so when treated with lysosome inhibitors. Our studies reveal that HIF-1α levels are coupled to phases of the cell cycle through lysosomal degradation and identify a novel role for the lysosome as a regulator of cell-cycle progression under hypoxic conditions.

A compendium of proteins that interact with HIF-1α

Epigenetic regulation of redox state mediates persistent cardiorespiratory abnormalities after long‐term intermittent hypoxia

Key points The effects of short‐term (ST; 10 days) and long‐term (LT; 30 days) intermittent hypoxia (IH) on blood pressure (BP), breathing and carotid body (CB) chemosensory reflex were examined in adult rats. ST‐ and LT‐IH treated rats exhibited hypertension, irregular breathing with apnoea and augmented the CB chemosensory reflex, with all these responses becoming normalized during recovery from ST‐ but not from LT‐IH. The persistent cardiorespiratory responses to LT‐IH were associated with elevated reactive oxygen species (ROS) levels in the CB and adrenal medulla, which were a result of DNA methylation‐dependent suppression of genes encoding anti‐oxidant enzymes (AOEs). Treating rats with decitabine either during LT‐IH or during recovery from LT‐IH prevented DNA methylation of AOE genes, normalized the expression of AOE genes and ROS levels, reversed the heightened CB chemosensory reflex and hypertension, and also stabilized breathing. Abstract Rodents exposed to chronic intermittent hypoxia (IH), simulating blood O 2 saturation profiles during obstructive sleep apnoea (OSA), have been shown to exhibit a heightened carotid body (CB) chemosensory reflex and hypertension. CB chemosensory reflex activation also results in unstable breathing with apnoeas. However, the effect of chronic IH on breathing is not known. In the present study, we examined the effects of chronic IH on breathing along with blood pressure (BP) and assessed whether the autonomic responses are normalized after recovery from chronic IH. Studies were performed on adult, male, Sprague–Dawley rats exposed to either short‐term (ST; 10 days) or long‐term (LT, 30 days) IH. Rats exposed to either ST‐ or LT‐IH exhibited hypertension, irregular breathing with apnoeas, an augmented CB chemosensory reflex as indicated by elevated CB neural activity and plasma catecholamine levels, and elevated reactive oxygen species (ROS) levels in the CB and adrenal medulla (AM). All these effects were normalized after recovery from ST‐IH but not from LT‐IH. Analysis of the molecular mechanisms underlying the persistent effects of LT‐IH revealed increased DNA methylation of genes encoding anti‐oxidant enzymes (AOEs). Treatment with decitabine, a DNA methylation inhibitor, either during LT‐IH or during recovery from LT‐IH, prevented DNA methylation, normalized the expression of AOE genes, ROS levels, CB chemosensory reflex and BP, and also stabilized breathing. These results suggest that persistent cardiorespiratory abnormalities caused by LT‐IH are mediated by epigenetic re‐programming of the redox state in the CB chemosensory reflex pathway.

Dynamic regulation of stem cell specification and maintenance by hypoxia-inducible factors

Pathways for Oxygen Regulation and Homeostasis

In this Viewpoint, 2016 Lasker Award winners William Kaelin, Peter Ratcliffe, and Gregg Semenza discuss their discovery of pathways by which humans and other multicellular organisms sense and respond to changes in oxygen availability.

Transcription Factors and Huinan Disease

Abstract Several general principles have emerged from the study of human transcription factors. First, germline mutations in genes encoding transcription factors result in malformation syndromes in which the development of multiple body structures is affected. Second, somatic mutations involving many of the same genes contribute to tumorigenesis. Third, transcriptional regulatory mechanisms demonstrate remarkable evolutionary conservation. Fourth, prenatal development and postnatal physiology are unified by the demonstration that a single transription factor can control the proliferation of progenitor cells during development and the expression within the differentiated cells of gene products that participate in specific physiologic responses. Transcription Factors and Human Disease presents the basic science of transcriptional regulation and then describes inherited human diseases attributable to mutations in DNA sequences encoding transcription factors or their cognate binding sites. The involvement of transcription factors in somatic cell genetic diseases (cancer) and epigenetic disease (teratogenesis) is briefly discussed. The effect of specific mutations on transcription factor activity and the relationship between transcriptional dysregulation, dominant or recessive inheritance patterns, and disease pathogenesis are also explored. This book thus provides a direct connection between molecular defects in transcriptional regulation and human pathophysiology.

Data from Hypoxia Selectively Enhances Integrin α<sub>5</sub>β<sub>1</sub> Receptor Expression in Breast Cancer to Promote Metastasis

<div>Abstract<p>Metastasis is the leading cause of breast cancer mortality. Previous studies have implicated hypoxia-induced changes in the composition and stiffness of the extracellular matrix (ECM) in the metastatic process. Therefore, the contribution of potential ECM-binding receptors in this process was explored. Using a bioinformatics approach, the expression of all integrin receptor subunits, in two independent breast cancer patient datasets, were analyzed to determine whether integrin status correlates with a validated hypoxia-inducible gene signature. Subsequently, a large panel of breast cancer cell lines was used to validate that hypoxia induces the expression of integrins that bind to collagen (ITGA1, ITGA11, ITGB1) and fibronectin (ITGA5, ITGB1). Hypoxia-inducible factors (HIF-1 and HIF-2) are directly required for ITGA5 induction under hypoxic conditions, which leads to enhanced migration and invasion of single cells within a multicellular 3D tumor spheroid but did not affect migration in a 2D microenvironment. ITGB1 expression requires HIF-1α, but not HIF-2α, for hypoxic induction in breast cancer cells. ITGA5 (α<sub>5</sub> subunit) is required for metastasis to lymph nodes and lungs in breast cancer models, and high ITGA5 expression in clinical biopsies is associated with an increased risk of mortality.</p><p><b>Implications:</b> These results reveal that targeting ITGA5 using inhibitors that are currently under consideration in clinical trials may be beneficial for patients with hypoxic tumors. <i>Mol Cancer Res; 15(6); 723–34. ©2017 AACR</i>.</p></div>

Molecular cytogenetic characterization of a subtle interstitial del(3)(p25.3p26.2) in a patient with deletion 3p syndrome

Abstract Deletion 3p syndrome is associated with characteristic facial features, growth failure, and mental retardation. Typically, individuals with deletion 3p syndrome have terminal deletions that result in loss of material from 3p25 to 3pter. We present a child with a clinical phenotype consistent with deletion 3p syndrome (ptosis, microcephaly, growth retardation, and developmental delay) and a subtle interstitial deletion in the distal portion of the short arm of chromosome 3, del(3)(p25.3p26.2). Fluorescence in situ hybridization (FISH) studies using 3p subtelomeric probes confirmed the terminal region of chromosome 3 was present. Sequence tagged sites (STS)‐linked BAC clones mapping to chromosomal region 3p25‐p26 were used to characterize the interstitial deletion by FISH. The results indicate the deletion is within a region of approximately 4.5 Mb between STS markers D3S3630 and D3S1304. This interstitial deletion lies within all previously reported terminal deletions in deletion 3p syndrome individuals, and represents the smallest reported deletion associated with deletion 3p syndrome. Characterization of the deletion may help identify genes important to growth and development that contribute to the deletion 3p syndrome phenotype when present in a hemizygous state. © 2002 Wiley‐Liss, Inc.

Role of Hypoxia-Inducible Factor 1  in Gastric Cancer Cell Growth, Angiogenesis, and Vessel Maturation

Inhibition of HIF-1alpha activity impairs gastric tumor growth, angiogenesis, and vessel maturation.

Enrichment of breast cancer stem cells following cytotoxic chemotherapy is mediated by hypoxia-inducible factors

Abstract Breast cancers (BCs) that do not express the estrogen or progesterone receptor or human epidermal growth factor receptor 2 are known as triple negative breast cancers (TNBCs). Women with TNBC receive non-targeted chemotherapy with a durable response rate of less than 20%. BC stem cells (BCSCs) are a small subpopulation of BC cells that are characterized by the capacity for infinite self-renewal; are the only BC cells capable of forming a secondary (recurrent or metastatic) BC; and must be eliminated in order to eradicate BC. Hypoxia-inducible factors (HIFs) activate hundreds of genes in TNBCs and HIF-1α expression in the diagnostic tumor biopsy is associated with patient mortality. In this paper, we report that treatment of TNBC cells with cytotoxic chemotherapy increased HIF-1α and HIF-2α protein levels and HIF target gene expression. Chemotherapy also increased the percentage of BCSCs through pathways involving interleukin-6 (IL-6), IL-8, and multidrug resistance 1. HIF inhibitors blocked increased BCSC specification in response to cytotoxic chemotherapy and combination therapy led to tumor eradication. Increased HIF target gene expression in BC biopsies was correlated with increased mortality, especially in those patients treated with chemotherapy alone. Our results suggest that HIF-dependent BCSC enrichment provides a molecular and cellular basis for the high incidence of relapse in women with TNBC.

Selective Killing of Hypoxia-Inducible Factor-1–Active Cells Improves Survival in a Mouse Model of Invasive and Metastatic Pancreatic Cancer

Abstract Purpose: Pancreatic cancer is characterized by intratumoral hypoxia, early and aggressive local invasion, and metastatic potential. Hypoxia-inducible factor-1 (HIF-1) is the major transcriptional activator of hypoxia-responsive genes and intratumoral hypoxia is associated with increased risk of metastasis. However, the behavior of the cells having HIF-1 activity during the malignant progression in pancreatic cancer has not been tested. Experimental Design: We orthotopically transplanted pancreatic cancer cells stably transfected with a HIF-1–dependent luciferase reporter gene and monitored HIF-1 activity in vivo in control and POP33-treated mice. POP33 is a novel prodrug, which has potential to increase caspase-3 activity and induce apoptosis in HIF-1–active/hypoxic cells. Results: In vivo optical imaging showed that HIF-1 activity proceeded along with local invasion, the peritoneal dissemination, and the liver metastasis. HIF-1–active hypoxic cells were selectively eradicated by POP33. Moreover, selective killing of HIF-1–active hypoxic cells significantly suppressed malignant progression, resulting in a significant improvement in survival rate. Conclusions: These results show that HIF-1–active cells constitute a large proportion of invading and metastatic cells and suggest that eradication of these cells may improve the outcome in advanced pancreatic cancer, a condition for which no effective therapy currently exists.

Data Supplement from Decreased Expression of Cystathionine β-Synthase Promotes Glioma Tumorigenesis

<p>Supplementary Table S1. Primer sequences used for qPCR.</p>

Hypoxia-inducible Factor 1 (HIF-1) Promotes Extracellular Matrix Remodeling under Hypoxic Conditions by Inducing P4HA1, P4HA2, and PLOD2 Expression in Fibroblasts

Extracellular matrix (ECM) composition, organization, and compliance provide both architectural and chemical cues that modulate tissue structure and function. ECM produced by stromal fibroblasts plays a key role in breast cancer invasion and metastasis, which are also stimulated by intratumoral hypoxia. Here, we demonstrate that hypoxia-inducible factor 1 (HIF-1) is a critical regulator of ECM remodeling by fibroblasts under hypoxic conditions. HIF-1 activates expression of genes encoding collagen prolyl (P4HA1 and P4HA2) and lysyl (PLOD2) hydroxylases. P4HA1 and P4HA2 are required for collagen deposition, whereas PLOD2 is required for ECM stiffening and collagen fiber alignment. Together P4HA1, P4HA2, and PLOD2 mediate remodeling of ECM composition, alignment, and mechanical properties in response to hypoxia. HIF-1-dependent ECM remodeling by hypoxic fibroblasts induces changes in breast cancer cell morphology, adhesion, and motility that promote invasion and metastasis.

Calcineurin Promotes Hypoxia-inducible Factor 1 Expression by Dephosphorylating RACK1 and Blocking

Oxygen homeostasis represents an essential organizing principle of metazoan evolution and biology. Hypoxia-inducible factor 1 (HIF-1) is a master regulator of transcriptional responses to changes in O2 concentration. HIF-1 is a heterodimer of HIF-1 and HIF-1 subunits. O2-dependent degradation of the HIF-1 subunit is mediated by prolyl hydroxylase, von HippelLindau protein (VHL)/Elongin-C E3 ubiquitin ligase, and the proteasome. O2-independent degradation of HIF-1 is regulated by the competition of RACK1 and HSP90 for binding to HIF-1. RACK1 binding results in the recruitment of the Elongin-C E3 ubiquitin ligase, leading to VHL-independent ubiquitination and degradation of HIF-1. In this report, we show that calcineurin inhibits the ubiquitination and proteasomal degradation of HIF-1. Calcineurin is a serine/threonine phosphatase that is activated by calcium and calmodulin. The phosphatase activity of calcineurin is required for its regulation of HIF-1. RACK1 binds to the catalytic domain of calcineurin and is required for HIF-1 degradation induced by the calcineurin inhibitor cyclosporine A. Elongin-C and HIF-1 each bind to RACK1 and dimerization of RACK1 is required to recruit Elongin-C to HIF1. Phosphorylation of RACK1 promotes its dimerization and dephosphorylation by calcineurin inhibits dimerization. Serine 146 within the dimerization domain is phosphorylated and mutation of serine 146 impairs RACK1 dimerization and HIF-1 degradation. These results indicate that intracellular calcium levels can regulate HIF-1 expression by modulating calcineurin activity and RACK1 dimerization.

Metabolic Regulation of Hematopoietic Stem Cells in the Hypoxic Niche

Transient Hypoglycemic Episodes Increase Hypoxia Inducible Factor-1α Nuclear Accumulation and Enhances the Angiogenic Response in Diabetic Eye Disease