Regulation of cancer cell metabolism by hypoxia-inducible factor 1.

The induction of hypoxia-inducible factor 1 (HIF-1) activity, either as a result of intratumoral hypoxia or loss-of-function mutations in the VHL gene, leads to a dramatic reprogramming of cancer cell metabolism involving increased glucose transport into the cell, increased conversion of glucose to pyruvate, and a concomitant decrease in mitochondrial metabolism and mitochondrial mass. Blocking these adaptive metabolic responses to hypoxia leads to cell death due to toxic levels of reactive oxygen species. Targeting HIF-1 or metabolic enzymes encoded by HIF-1 target genes may represent a novel therapeutic approach to cancer.

Does loss of CD151 expression promote the metastasis of hypoxic colon cancer cells?

Intratumoral hypoxia increases invasion and metastasis through multiple mechanisms, including changes in gene expression that are mediated by hypoxia-inducible factor 1. In hypoxic colon cancer cells, hypoxia-inducible factor 1 inhibits the expression of CD151, a cell surface molecule that normally tethers epithelial cells to the basement membrane, which may promote metastasis.

Small molecule activation of adaptive gene expression: tilorone or its analogs are novel potent activators of hypoxia inducible factor-1 that provide prophylaxis against stroke and spinal cord injury.

A major challenge for neurological therapeutics is the development of small molecule drugs that can activate a panoply of downstream pathways without toxicity. Over the past decade our group has shown that a family of enzymes that regulate posttranscriptional and transcriptional adaptive responses to hypoxia are viable targets for neuronal protection and repair. The family is a group of iron, oxygen, and 2-oxoglutarate-dependent dioxygenases, known as the HIF prolyl 4-hydroxylases (HIF PHDs).

Tumor metabolism: cancer cells give and take lactate.

Tumors contain well-oxygenated (aerobic) and poorly oxygenated (hypoxic) regions, which were thought to utilize glucose for oxidative and glycolytic metabolism, respectively. In this issue of the JCI, Sonveaux et al. show that human cancer cells cultured under hypoxic conditions convert glucose to lactate and extrude it, whereas aerobic cancer cells take up lactate via monocarboxylate transporter 1 (MCT1) and utilize it for oxidative phosphorylation (see the related article beginning on page 3930).

Digoxin and other cardiac glycosides inhibit HIF-1alpha synthesis and block tumor growth.

A library of drugs that are in clinical trials or use was screened for inhibitors of hypoxia-inducible factor 1 (HIF-1). Twenty drugs inhibited HIF-1-dependent gene transcription by >88% at a concentration of 0.4 microM.

Transcriptional responses to intermittent hypoxia.

Recurrent apneas are characterized by transient repetitive cessations of breathing (two breaths duration or longer) resulting in periodic decreases in arterial blood PO2 or chronic intermittent hypoxia (IH). Patients with recurrent apneas and experimental animals exposed to chronic IH exhibit cardio-respiratory morbidities. The purpose of this article is to highlight the current information on the transcriptional mechanisms associated with chronic IH.

Induction of HIF-1alpha expression by intermittent hypoxia: involvement of NADPH oxidase, Ca2+ signaling, prolyl hydroxylases, and mTOR.

Sleep-disordered breathing with recurrent apnea (periodic cessation of breathing) results in chronic intermittent hypoxia (IH), which leads to cardiovascular and respiratory pathology. Molecular mechanisms underlying IH-evoked cardio-respiratory co-morbidities have not been delineated. Mice with heterozygous deficiency of hypoxia-inducible factor 1alpha (HIF-1alpha) do not develop cardio-respiratory responses to chronic IH.

Hypoxia-induced resistance to anticancer drugs is associated with decreased senescence and requires hypoxia-inducible factor-1 activity.

Hypoxia in solid tumors is associated with the development of chemoresistance. Although many studies have focused on the effect of hypoxia on drug-induced apoptosis, the effect of nonapoptotic pathways on hypoxia-induced drug resistance has not been previously investigated. Here, we determined the effects of hypoxia on multiple forms of drug-induced death in human MDA-MB-231 breast carcinoma cells.

The expanding universe of hypoxia.

Reduced oxygen availability (hypoxia) is sensed and transduced into changes in the activity or expression of cellular macromolecules. These responses impact on virtually all areas of biology and medicine. In this meeting report, we summarize major developments in the field that were presented at the 2008 Keystone Symposium on Cellular, Physiological, and Pathogenic Responses to Hypoxia.

Hypoxia-inducible factor 1 and cancer pathogenesis.

Hypoxia-inducible factor 1 (HIF-1) is a transcriptional activator that mediates adaptive responses to hypoxia. HIF-1 activity is increased in the majority of human cancers as a result of genetic alterations and intratumoral hypoxia. HIF-1 activates the transcription of genes that increase O(2) availability by stimulating angiogenesis or that reprogram cellular metabolism to adapt to reduced O(2) availability.

Age-dependent impairment of HIF-1alpha expression in diabetic mice: Correction with electroporation-facilitated gene therapy increases wound healing, angiogenesis, and circulating angiogenic cells.

Wound healing is impaired in elderly patients with diabetes mellitus. We hypothesized that age-dependent impairment of cutaneous wound healing in db/db diabetic mice: (a) would correlate with reduced expression of the transcription factor hypoxia-inducible factor 1alpha (HIF-1alpha) as well as its downstream target genes; and (b) could be overcome by HIF-1alpha replacement therapy. Wound closure, angiogenesis, and mRNA expression in excisional skin wounds were analyzed and circulating angiogenic cells (CACs) were quantified in db/db mice that were untreated or received electroporation-facilitated HIF-1alpha gene therapy.

Macrophage migration inhibitory factor activates hypoxia-inducible factor in a p53-dependent manner.

Background: Macrophage migration inhibitory factor (MIF) is not only a cytokine which has a critical role in several inflammatory conditions but also has endocrine and enzymatic functions. MIF is identified as an intracellular signaling molecule and is implicated in the process of tumor progression, and also strongly enhances neovascularization. Overexpression of MIF has been observed in tumors from various organs.

O2 sensing: only skin deep?

The transcription factor HIF-1 mediates adaptive responses to hypoxia, and its activity is negatively regulated by O2-dependent binding of the von Hippel-Lindau (VHL) protein. In this issue, Boutin et al. (2008) use conditional knockout mice to demonstrate that sensing of O2 by keratinocytes in the epidermis leads to alterations in cutaneous blood flow that affect the production of the hormone erythropoietin, thereby modulating red blood cell production and the O2-carrying capacity of blood.

Mitochondrial autophagy: life and breath of the cell.

Homeostatic responses to reduced O(2) availability are regulated by the transcriptional activator hypoxia-inducible factor 1 (HIF-1) in all metazoan species. An essential adaptation to sustained hypoxia is an active repression of mitochondrial respiration. In mouse embryo fibroblasts, HIF-1 induces expression of BNIP3, which triggers selective mitochondrial autophagy.

LPS induces hypoxia-inducible factor 1 activation in macrophage-differentiated cells in a reactive oxygen species-dependent manner.

A prominent feature of various inflamed and diseased tissue is the presence of low oxygen tension (hypoxia). Effector cells of the innate immune system must maintain their viability and physiologic functions in a hypoxic microenvironment. Monocytes circulating in the bloodstream differentiate into macrophages.

Endothelin-1 mediates hypoxia-induced inhibition of voltage-gated K+ channel expression in pulmonary arterial myocytes.

Prolonged exposure to decreased oxygen tension causes contraction and proliferation of pulmonary arterial smooth muscle cells (PASMCs) and pulmonary hypertension. Hypoxia-induced inhibition of voltage-gated K(+) (K(v)) channels may contribute to the development of pulmonary hypertension by increasing intracellular calcium concentration ([Ca(2+)](i)). The peptide endothelin-1 (ET-1) has been implicated in the development of pulmonary hypertension and acutely decreases K(v) channel activity.

n-Propyl gallate activates hypoxia-inducible factor 1 by modulating intracellular oxygen-sensing systems.

HIF-1 (hypoxia-inducible factor 1) is a master regulator of cellular adaptive responses to hypoxia. The expression and transcriptional activity of the HIF-1alpha subunit is stringently controlled by intracellular oxygen tension through the action of prolyl and asparaginyl hydroxylases. In the present study we demonstrate that PG (n-propyl gallate) activates HIF-1 and expression of its downstream target genes under normoxic conditions in cultured cells and in mice.

Complete loss of ischaemic preconditioning-induced cardioprotection in mice with partial deficiency of HIF-1 alpha.

Aims: We investigated whether hypoxia-inducible factor 1 alpha (HIF-1 alpha) plays a role in the acute phase of ischaemic preconditioning (IPC).

Methods And Results: Hearts from wild-type (WT) mice and mice heterozygous for a null allele at the locus encoding HIF-1 alpha (HET) were subjected to IPC (10-min ischaemia/5 min reperfusion, or two cycles of 5 min ischaemia/5 min reperfusion), followed by 30 min ischaemia and reperfusion. Left ventricular-developed pressure, heart rate, and coronary flow rate were measured continuously.

Analysis of hypoxia-inducible factor 1alpha expression and its effects on invasion and metastasis.

Hypoxia-inducible factor 1 (HIF-1) plays an important role in human cancer cell invasion and metastasis. As a result, overexpression of the HIF-1alpha subunit in biopsy specimens is associated with increased patient mortality in several common cancers, including breast adenocarcinoma and oropharyngeal squamous cell carcinoma. Here, we describe methods for immunohistochemical detection of HIF-1alpha in tumor biopsy sections and ex vivo assays for analyzing the effects of hypoxia and HIF-1 on cancer cell invasiveness and cell-cell adhesion.

Calcineurin promotes hypoxia-inducible factor 1alpha expression by dephosphorylating RACK1 and blocking RACK1 dimerization.

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-1alpha and HIF-1beta subunits.