Publications

Culturing cardiac precursors on a surface with the rigidity of heart tissue increases the yield of endothelial cells.

Intermittent hypoxia (IH) is the hallmark manifestation of sleep disordered breathing (SDB) with recurrent apnea. A large body of clinical evidence suggests that SDB patients are at increased risk to develop Type II diabetes. However, molecular mechanism(s) underlying the effects of IH on pancreatic beta cell function have not been established. Hypoxia‐inducible factor 1 (HIF‐1) mediates many of the systemic and cellular responses to IH. Mice with partial deficiency of HIF‐1α ( Hif1a +/‐ ) exhibit a remarkable absence of IH‐induced hypertension and breathing abnormalities, suggesting that activation of HIF‐1 contributes to the autonomic morbidities associated with IH. In the present study, we tested the role of HIF‐1α in IH‐induced pancreatic beta cell dysfunction. Experiments were performed on male littermate wild type (WT) and Hif1a +/‐ mice exposed to either 30 days of IH or normoxia. HIF‐1α levels were elevated in pancreatic islets from IH‐exposed WT mice but not in Hif1a +/‐ littermates. IH‐exposed WT mice exhibited elevated fasting plasma insulin levels and impaired glucose stimulated insulin secretion, but these effects were either absent or attenuated in IH‐ exposed Hif1a +/‐ mice. Furthermore, IH augmented basal insulin secretion and this effect was prevented by treating islets from WT mice with either digoxin or YC‐1, which blocked HIF‐1α accumulation. These results suggest that HIF‐1 mediates IH‐induced pancreatic beta cell dysfunction. Supported by NIH‐HL‐090554

Significance In proliferative diabetic retinopathy (PDR), the most vision-threatening sequela of diabetic eye disease, retinal ischemia leads to increased expression of angiogenic factors that promote neovascularization. Although therapies targeting the potent angiogenic mediator vascular endothelial growth factor have been remarkably successful for the treatment of diabetic macular edema, this approach has not proven sufficient to prevent the development of retinal neovascularization, implicating additional angiogenic factor(s) in PDR pathogenesis. We demonstrate here that angiopoietin-like 4 is a potent angiogenic mediator with markedly increased expression in the eyes of PDR patients. Our studies identify a novel therapeutic target for the treatment of ocular neovascular disease and may have broad implications for the treatment of other diseases dependent on pathologic angiogenesis.

Hypoxia-inducible factor 1α (HIF-1α) expression is a hallmark of intratumoral hypoxia that is associated with breast cancer metastasis and patient mortality. Previously, we demonstrated that HIF-1 stimulates the expression and activity of TAZ, which is a transcriptional effector of the Hippo signaling pathway, by increasing TAZ synthesis and nuclear localization. Here, we report that direct protein-protein interaction between HIF-1α and TAZ has reciprocal effects: HIF-1α stimulates transactivation mediated by TAZ and TAZ stimulates transactivation mediated by HIF-1α. Inhibition of TAZ expression impairs the hypoxic induction of HIF-1 target genes, such as PDK1, LDHA, BNIP3 and P4HA2 in response to hypoxia, whereas inhibition of HIF-1α expression impairs TAZ-mediated transactivation of the CTGF promoter. Taken together, these results complement our previous findings and establish bidirectional crosstalk between HIF-1α and TAZ that increases their transcriptional activities in hypoxic cells.

The switch to an angiogenic phenotype is a fundamental determinant of neoplastic growth and tumor progression. We demonstrate that homozygous deletion of the p53 tumor suppressor gene via homologous recombination in a human cancer cell line promotes the neovascularization and growth of tumor xenografts in nude mice. We find that p53 promotes Mdm2-mediated ubiquitination and proteasomal degradation of the HIF-1α subunit of hypoxia-inducible factor 1 (HIF-1), a heterodimeric transcription factor that regulates cellular energy metabolism and angiogenesis in response to oxygen deprivation. Loss of p53 in tumor cells enhances HIF-1α levels and augments HIF-1-dependent transcriptional activation of the vascular endothelial growth factor ( VEGF ) gene in response to hypoxia. Forced expression of HIF-1α in p53-expressing tumor cells increases hypoxia-induced VEGF expression and augments neovascularization and growth of tumor xenografts. These results indicate that amplification of normal HIF-1-dependent responses to hypoxia via loss of p53 function contributes to the angiogenic switch during tumorigenesis.

<p>Supplementary Figure S1. Analysis of G6PD mRNA expression. Supplementary Figure S2. Analysis of MCF-7 Subclones. Supplementary Figure S3. Effect of PHGDH knockdown on cell growth. Supplementary Figure S4. Effect of carboplatin on cell viability. Supplementary Figure S5. Effect of doxorubicin treatment. Supplementary Figure S6. Clinical correlates.</p>

<p>PDF file - 135K, Figure S2. Efficiency of PLOD2 knockdown in MDA-MB-435 cells.</p>

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.

Lymphedema is a chronic inflammatory disorder characterized by edema, fat deposition, and fibrotic tissue remodeling. Despite significant advances in lymphatic biology research, our knowledge of lymphedema pathology is incomplete. Currently, there is no approved pharmacological therapy for this debilitating disease. Hypoxia is a recognized feature of inflammation, obesity, and fibrosis. Understanding hypoxia-regulated pathways in lymphedema may provide new insights into the pathobiology of this chronic disorder and help develop new medicinal treatments.

HIF-1 activity in Tie2-lineage cells is required for the mobilization and homing of BMDACs to cutaneous burn wounds and for the vascularization of burn wound tissue.