Von Hippel-Lindau (VHL) tumour suppressor gene inactivation is linked to the development of haemangioblastomas in the central nervous system and retina, often in association with other tumours, such as clear-cell carcinomas of the kidney and phaeochromocytomas. Here we show that the VHL protein (pVHL) is a microtubule-associated protein that can protect microtubules from depolymerization in vivo. Both the microtubule binding and stabilization functions of pVHL depend on amino acids 95-123 of pVHL, a mutational 'hot-spot' in VHL disease. From analysis of naturally occurring pVHL mutants, it seems that only point mutations such as pVHL(Y98H) and pVHL(Y112H) (that predispose to haemangioblastoma and phaeochromocytoma, but not to renal cell carcinoma) disrupt pVHL's microtubule-stabilizing function. Our data identify a role for pVHL in the regulation of microtubule dynamics and potentially provide a link between this function of pVHL and the pathogenesis of haemangioblastoma and phaeochromocytoma in the context of VHL disease.

Insulin secretion from pancreatic ␤ cells is stimulated by glucose metabolism. However, the relative importance of metabolizing glucose via mitochondrial oxidative phosphorylation versus glycolysis for insulin secretion remains unclear. von Hippel-Lindau (VHL) tumor suppressor protein, pVHL, negatively regulates hypoxia-inducible factor HIF1␣, a transcription factor implicated in promoting a glycolytic form of metabolism. Here we report a central role for the pVHL-HIF1␣ pathway in the control of ␤-cell glucose utilization, insulin secretion, and glucose homeostasis. Conditional inactivation of Vhlh in ␤ cells promoted a diversion of glucose away from mitochondria into lactate production, causing cells to produce high levels of glycolytically derived ATP and to secrete elevated levels of insulin at low glucose concentrations. Vhlh-deficient mice exhibited diminished glucose-stimulated changes in cytoplasmic Ca 2+ concentration, electrical activity, and insulin secretion, which culminate in impaired systemic glucose tolerance. Importantly, combined deletion of Vhlh and Hif1␣ rescued these phenotypes, implying that they are the result of HIF1␣ activation. Together, these results identify pVHL and HIF1␣ as key regulators of insulin secretion from pancreatic ␤ cells. They further suggest that changes in the metabolic strategy of glucose metabolism in ␤ cells have profound effects on whole-body glucose homeostasis.[Keywords: HIF; VHL; glucose intolerance; islet; pancreas] Supplemental material is available at http://www.genesdev.org. Received July 14, 2008; revised version accepted September 5, 2008. During adulthood, cell type-specific growth that exceeds the normal physiological constraints is a common feature of adaptive processes of tissues to changes in metabolic homeostasis and underlies the development of many human diseases, including cancer, heart disease, and diabetes (De Boer et al. 2003;Bouwens and Rooman 2005). Adaptive cell mass expansion, whether neoplastic or nonneoplastic, creates a requirement for compensatory neovascularization to supply oxygen, metabolic substances, and growth/survival factors to the growing tissue (Marti 2005). Therefore, adaptive cell growth responses are generally accompanied, at least initially, by relative states of hypoxia as a result of a mismatch between oxygen demand caused by tissue expansion and oxygen supply provided by the vasculature. An immediate consequence of decreased tissue oxygen availability is that cells shift cellular fuel metabolism from mitochondrial respiration to glycolysis and activate an angiogenic program to increase oxygen delivery in order to overcome the imbalance between tissue mass and vascularization (Semenza 2001;Brahimi-Horn et al. 2007). In this way, tissue function is supported and further mass expansion can occur.At the molecular level, the central regulators of the cellular response to low-oxygen availability are the hypoxia-inducible transcription factors (HIF). HIF are heterodimeric transcription factors composed of HIF1␣, HIF2␣, or HI...

The majority of breast cancers metastasizing to bone secrete parathyroid hormone-related protein (PTHrP). PTHrP induces local osteolysis that leads to activation of bone matrix-borne transforming growth factor ␤ (TGF␤). In turn, TGF␤ stimulates PTHrP expression and, thereby, accelerates bone destruction. We studied the mechanism by which TGF␤ activates PTHrP in invasive MDA-MB-231 breast cancer cells. We demonstrate that TGF␤1 up-regulates specifically the level of PTHrP P3 promoter-derived RNA in an actinomycin D-sensitive fashion. Transient transfection studies revealed that TGF␤1 and its effector Smad3 are able to activate the P3 promoter. This effect depended upon an AGAC box and a previously described Ets binding site. Addition of Ets1 greatly enhanced the Smad3/TGF␤-mediated activation. Ets2 had also some effect, whereas other Ets proteins, Elf-1, Ese-1, and Erf-1, failed to cooperate with Smad3. In comparison, Ets1 did not increase Smad3/TGF␤-induced stimulation of the TGF␤-responsive plasminogen activator inhibitor 1 (PAI-1) promoter. Smad3 and Smad4 were able to specifically interact with the PTHrP P3-AGAC box and to bind to the P3 promoter together with Ets1. Inhibition of endogenous Ets1 expression by calphostin C abrogated TGF␤-induced up-regulation of the P3 transcript, whereas it did not affect the TGF␤ effect on PAI expression. In TGF␤ receptor II-and Ets1-deficient, noninvasive MCF-7 breast cancer cells, TGF␤1 neither influenced endogenous PTHrP expression nor stimulated the PTHrP P3 promoter. These data suggest that TGF␤ activates PTHrP expression by specifically up-regulating transcription from the PTHrP P3 promoter through a novel Smad3/Ets1 synergism.Parathyroid hormone-related protein (PTHrP)

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