The von Hippel-Lindau (VHL) Tumor Suppressor Gene Inactivation and Its Involvement in Tumorgenesis

1. The von Hippel-Lindau (VHL) Tumor Suppressor Gene Inactivation and Its Involvement in Tumorgenesis Pavel Yarmolenko Biology 169, Spring 2005

2. Overview • 1) von Hippel-Lindau disease – biallelic mutation/inactivation of VHL gene • 2) Cell response to hypoxia – What VHL does. • 3) pVHL role – the protein VHL gene codes for. • Its function • How it was studied • Knockouts • Possible treatment options • 4) New Research, Future Directions

3. Bottom Line von Hippel-Lindau Disease • Hereditary cancer syndrome affects 1 in 35,000 individuals. • Transmitted in an autosomal dominant manner. • >150 different mutations in the VHL gene cause VHL disease. • Many of them are categorized by phenotype in humans. • Sporadic tumors – both copies of VHL mutated after conception. • Lesions associated with VHL disease include, among others: • CNS and retinal hemangioblastomas • clear-cell renal carcinomas • Pheochromocytomas VHL Disease • Highly vascular lesions that overproduce angiogenic, hypoxia-inducible markers • (such as vascular endothelial growth factor (VEGF) and erythropoeitin (Epo))

4. What is HIF? Angiogenesis ECM dissolution Migration Angiogenesis Dedifferentiation Proliferation Migration Normal Cellular Response to Hypoxia Modified from WY Kim and WG Kaelin. J Clin Oncol 22:4991-5004

5. What controls HIF? HIF Examined • It is a hypoxia-inducible transcription factor • Heterodimer formed by HIFα and HIFβ • HIFβ is a stable protein • HIFα is degraded in presence of O2 HIFα activity controlled by OXYGEN-DEPENDENT hydroxylation at either the ODDD or CTAD domain. Bind HIF-1β Bind to DNA and Activate Transcription

6. Control of HIF Modified from WY Kim and WG Kaelin. J Clin Oncol 22:4991-5004

7. Ubiquitin Mediated Proteolysis Courtesy of Dr. Robert Duronio

8. 2002 FIH-1 and its action identified 1993-99 CBP/p300 coactivator recruitment studied 2000 1999 CBP/p300 and its action identified 1990 What controls HIFα? 1988 Mapped by linkage analysis 1993 Isolated by positional cloning 2000 1993-99 VHL interaction studied 1999 VHL complex Identified (E3 Ubiquitin Ligase) 2000 How does the ODDD make HIFα unstable in high [O2]? 2001 EGLN hydroxylate (Pro)n in ODDD HIF prolyl hydroxylase gene identified in How it was figured out What else does VHL do? 1. VHL = inactive in disease. 2. Hypoxia-inducible mRNAs overproduced.

9. Altered Cell Cycle • pVHL -/- cells are unable to exit the cell cycle under certain experimental conditions, such as growth in low serum. • Ability to exit the cell cycle is restored by reintroduction of wild-type pVHL. • pVHL is a negative regulator of cyclin D1, which is a mitogen. • pVHL also negatively regulates TGFα (HIF target gene). Renal tubular epithelial cells are very sensitive to the mitogenic effects of TGFα.

10. Poor ECM More Tumor-like behavior of normal epithelial cells ECM Connection • pVHL -/- cells do not deposit a proper extracellular fibronectin matrix • pVHL +/+ cells restore the function. • Epithelial cells exhibit increased proliferation and decreased differention when grown on specific matrices. • Cells lacking pVHL are more invasive and secrete higher levels of matrix metalloproteases. • VEGF upregulates matrix metalloprotease synthesis, so this process is HIF-dependent.

11. Cytoskeleton Connection • 2003 Turcotte et al., Am J Physiol Renal Physiol. 2004 Feb;286(2):F338-48 Rho proteins (GTPases) that regulate the organization of the actin cytoskeleton Disruption of actin and microtubule networks by chemicals or hypoxia 2.5 x pVHL expression -2003 A Hergovich et al., Nat Cell Biol. 2003 Jan;5(1):64-70. pVHL stabilizes microtubules through direct interaction. Does not require E3 Ubiquitin Ligase function -2004 MP Lolkema et al., Experimental Cell Research 301 (2004) 139– 146 pVHL influences microtubule dynamics at the cell periphery independently of its effects on HIFα - done in cells that don’t accumulate HIFα - the cell line is tumorigenic in mouse xenografts – pVHL inactivation causes tumors without HIFα accumulation.

12. Mouse Knockouts • VHL-/- mice die during early embryogenesis. • VHL+/- mice - normal life span, but may develop vascular tumors in the liver that overexpress HIF target genes. • Conflicting reports on the above (tumors may or may not develop). • Same lesions can be induced by inactivation of VHL in the liver.

13. Treatment Options Inhibition of HIF2α is sufficient to suppress VHL-/- tumor growth in vivo. -Kondo K et al., PLoS Biol 1:E83, 2003 -Zimmer M et al., Mol Cancer Res 2:89-95, 2004 WY Kim and WG Kaelin. J Clin Oncol 22:4991-5004

14. Unanswered Questions • Why is VHL upregulated in tumors? • How does VHL affect secreted fibronectin? • Why does VHL stabilize microtubules at the cell periphery while it’s present throughout the cytoplasm? • Transduction pathway? • What other non-HIF related functions does VHL have?

15. That’s IT!!!