HER2 (neu) signaling increases the rate of hypoxia-inducible factor 1alpha (HIF-1alpha) synthesis: novel mechanism for HIF-1-mediated vascular endothelial growth factor expression.
Hypoxia-inducible factor 1 (HIF-1) is a transcriptional activator composed of HIF-1alpha and HIF-1beta subunits. Several dozen HIF-1 targets are known, including the gene encoding vascular endothelial growth factor (VEGF). Under hypoxic conditions, HIF-1alpha expression increases as a result of decreased ubiquitination and degradation. The tumor suppressors VHL (von Hippel-Lindau protein) and p53 target HIF-1alpha for ubiquitination such that their inactivation in tumor cells increases the half-life of HIF-1alpha. Increased phosphatidylinositol 3-kinase (PI3K) and AKT or decreased PTEN activity in prostate cancer cells also increases HIF-1alpha expression by an undefined mechanism. In breast cancer, increased activity of the HER2 (also known as neu) receptor tyrosine kinase is associated with increased tumor grade, chemotherapy resistance, and decreased patient survival. HER2 has also been implicated as an inducer of VEGF expression. Here we demonstrate that HER2 signaling induced by overexpression in mouse 3T3 cells or heregulin stimulation of human MCF-7 breast cancer cells results in increased HIF-1alpha protein and VEGF mRNA expression that is dependent upon activity of PI3K, AKT (also known as protein kinase B), and the downstream kinase FRAP (FKBP-rapamycin-associated protein). In contrast to other inducers of HIF-1 expression, heregulin stimulation does not affect the half-life of HIF-1alpha but instead stimulates HIF-1alpha synthesis in a rapamycin-dependent manner. The 5'-untranslated region of HIF-1alpha mRNA directs heregulin-inducible expression of a heterologous protein. These data provide a molecular basis for VEGF induction and tumor angiogenesis by heregulin-HER2 signaling and establish a novel mechanism for the regulation of HIF-1alpha expression.
Laughner
E
E
Institute of Genetic Medicine, Departments of Pediatrics and Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21287-3914, USA.
Taghavi
P
P
Chiles
K
K
Mahon
P C
PC
Semenza
G L
GL
D016475:3T3 Cells; D000818:Animals; D064007:Ataxia Telangiectasia Mutated Proteins; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000378:metabolism; D015687:Cell Hypoxia; D004268:DNA-Binding Proteins / Q000096:biosynthesis*; D016228:Endothelial Growth Factors / Q000235:genetics*; D005260:Female; D015870:Gene Expression; D006801:Humans; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D008222:Lymphokines / Q000235:genetics*; D008297:Male; D051379:Mice; D020890:Neuregulin-1 / Q000494:pharmacology; D009687:Nuclear Proteins / Q000096:biosynthesis*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012334:RNA, Neoplasm / Q000235:genetics / Q000378:metabolism; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D014157:Transcription Factors; D014407:Tumor Cells, Cultured; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors
D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D016228:Endothelial Growth Factors; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D008222:Lymphokines; D020890:Neuregulin-1; D009687:Nuclear Proteins; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D018719:Erb-b2 Receptor Tyrosine Kinases; D014157:Transcription Factors; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; C497442:HIF1A protein, human; C497443:Hif1a protein, mouse; C576897:Atr protein, mouse; C494918:AKT1 protein, human; C576597:ATR protein, human