Reciprocal positive regulation of hypoxia-inducible factor 1alpha and insulin-like growth factor 2.

Hypoxia-inducible factor 1 (HIF-1) activates transcription of genes encoding glucose transporters, glycolytic enzymes, vascular endothelial growth factor, and other proteins involved in O2 homeostasis and tumor progression. The expression and transcriptional activity of the HIF-1alpha subunit is regulated by the cellular O2 concentration. We demonstrate that insulin, insulin-like growth factor (IGF)-1, and IGF-2 induce expression of HIF-1alpha, which is required for expression of genes encoding IGF-2, IGF-binding protein (IGFBP)-2 and IGFBP-3. These data provide a novel mechanism by which HIF-1alpha overexpression may occur in tumor cells and contribute to an autocrine growth factor loop.

Modulation of hypoxia-inducible factor 1alpha expression by the epidermal growth factor/phosphatidylinositol 3-kinase/PTEN/AKT/FRAP pathway in human prostate cancer cells: implications for tumor angiogenesis and therapeutics.

Dysregulated signal transduction from receptor tyrosine kinases to phosphatidylinositol 3-kinase (PI3K), AKT (protein kinase B), and its effector FKBP-rapamycin-associated protein (FRAP) occurs via autocrine stimulation or inactivation of the tumor suppressor PTEN in many cancers. Here we demonstrate that in human prostate cancer cells, basal-, growth factor-, and mitogen-induced expression of hypoxia-inducible factor 1 (HIF-1) alpha, the regulated subunit of the transcription factor HIF-1, is blocked by LY294002 and rapamycin, inhibitors of PI3K and FRAP, respectively. HIF-1-dependent gene transcription is blocked by dominant-negative AKT or PI3K and by wild-type PTEN, whereas transcription is stimulated by constitutively active AKT or dominant-negative PTEN. LY294002 and rapamycin also inhibit growth factor- and mitogen-induced secretion of vascular endothelial growth factor, the product of a known HIF-1 target gene, thus linking the PI3K/PTEN/AKT/FRAP pathway, HIF-1, and tumor angiogenesis. These data indicate that pharmacological agents that target PI3K, AKT, or FRAP in tumor cells inhibit HIF-1alpha expression and that such inhibition may contribute to therapeutic efficacy.

Oncogenic levels of mitogen-activated protein kinase (MAPK) signaling of the dinucleotide KRAS2 mutations G12F and GG12-13VC.

We previously reported the occurrence of novel dinucleotide mutations of the K-RAS gene (KRAS2) in 2% of pancreatic tumors sampled, but it remained unknown whether these were functional mutations that convert the proto-oncogene to an oncogene, or unselected mutations that might inactivate protein function. In the current study, the functionality of these rare mutations was quantitated via a mitogen-activated protein kinase (MAPK) pathway-specific transactivational reporter system. Pathway activation by dinucleotide mutant proteins was comparable to that of the common G12V mutant K-Ras protein. Current allele-specific technologies often employed to detect K-RAS mutations in clinical tumor samples produce false results when dinucleotide mutations are present. Therefore, it is advisable to consider dinucleotide KRAS2 mutants in the strategic design of mutational screens used to assay clinical tumor samples. Hum Mutat 18:357, 2001.

'The metabolism of tumours': 70 years later.

Otto Warburg's classic treatise on the reprogramming of tumour metabolism from oxidative to glycolytic metabolism was published in London in 1930. Although the Warburg effect is one of the most universal characteristics of solid tumours, the molecular basis for this phenomenon has only recently been elucidated by studies indicating that increased expression of genes encoding glucose transporters and glycolytic enzymes in tumour cells is mediated by the transcription factors c-MYC and HIF-1. Whereas c-myc is a direct target for oncogenic mutations, expression of hypoxia-inducible factor 1 (HIF-1) is indirectly up-regulated via gain-of-function mutations in oncogenes and loss-of-function mutations in tumour suppressor genes that result increased HIF-1alpha protein expression and/or increased HIF-1 transcriptional activity in a cell-type-specific manner. As a result of genetic alterations and intratumoral hypoxia, HIF-1alpha is overexpressed in the majority of common human cancers relative to the surrounding normal tissue. In human breast cancer and brain tumours, HIF-1alpha overexpression is strongly correlated with tumour grade and vascularity.

Hypoxia, HIF-1, and the pathophysiology of common human diseases.

Hypoxia plays a fundamental role in the pathophysiology of common causes of mortality, including ischemic heart disease, stroke, cancer, chronic lung disease, and congestive heart failure. In these disease states, hypoxia induces changes in gene expression in target organs that either fail to result in adequate adaptation or directly contribute to disease pathogenesis. Hypoxia-inducible factor 1 (HIF-1) is a transcriptional activator that is expressed in response to cellular hypoxia and mediates multiple cellular and systemic homeostatic responses to hypoxia. Recent studies have provided evidence that important pathophysiological responses to hypoxia in pulmonary hypertension, myocardial ischemia, and cancer are mediated by HIF-1. Pharmacologic and gene therapy strategies designed to modulate HIF-1 activity may represent a novel and effective therapeutic approach to these common disorders.

Telomere dysfunction increases mutation rate and genomic instability.

The increased tumor incidence in telomerase null mice suggests that telomere dysfunction induces genetic instability. To test this directly, we examined mutation rate in the absence of telomerase in S. cerevisiae. The mutation rate in the CAN1 gene increased 10- to 100-fold in est1Delta strains as telomeres became dysfunctional. This increased mutation rate resulted from an increased frequency of terminal deletions. Chromosome fusions were recovered from est1Delta strains, suggesting that the terminal deletions may occur by a breakage-fusion-bridge type mechanism. At one locus, chromosomes with terminal deletions gained a new telomere through a Rad52p-dependent, Rad51p-independent process consistent with break-induced replication. At a second locus, more complicated rearrangements involving multiple chromosomes were seen. These data suggest that telomerase can inhibit chromosomal instability.