Clear cell renal carcinoma (ccRC), which is the most common form of kidney cancer, is often linked to inactivation of the von Hippel-Lindau tumor suppressor gene (VHL). The VHL gene product, pVHL, has multiple functions including serving as the substrate recognition module of an ubiquitin ligase that targets the alpha subunit of the heterodimeric transcription factor HIF (hypoxia-inducible factor) for proteasomal degradation. The interaction of pVHL with HIF1 requires that HIF? be prolyl hydroxylated by members of the EglN family, which belong to a recently recognized superfamily of 2-oxoglutarate (2OG) and iron-dependent dioxygenases. These enzymes are oxygen-dependent and thus couple HIF? activity to oxygen availability in pVHL-proficient cells. Inhibition of HIF?, and particularly HIF2?, is tightly linked to pVHL's ability to suppress ccRC. pVHL inactivation, however, is not sufficient to cause ccRC. Additional genetic events, frequently involving 5q amplification and 14q loss, appear to be required.
In aim 1 we will ask whether HIF1? is a pathogenically relevant 14q gene in ccRC based on our preliminary data that HIF1?, in stark contrast to HIF2?, can suppress ccRC growth in vitro and in vivo and in aim 2 we will conduct functional screens to identify the relevant 5q gene(s).
In aim 3 we will try to identify the EglN2 substrate responsible for our earlier observation that EglN2 regulates Cyclin D1 and cancer cell proliferation in a HIF-independent manner. IDH1 and IDH2 mutations have recently been found in many brain tumors and leukemias, leading to increased accumulation of 2-hydroxyglutarate (2HG).
In aim 4 we will test the hypothesis that transformation in IDH mutant tumors is linked to the perturbation of one or more 2OG - dependent dioxygenases by 2HG.
Learning that the VHL protein (pVHL), which is often defective in kidney cancer, inhibits the HIF transcription factor has led to 6 new FDA approved drugs for this disease. We wish to identify other genetic alterations that cooperate with VHL loss in hopes of identifying additional kidney cancer targets. HIF is modified by several 2-oxoglutarate (2OG)-dependent enzymes (EglN1-3). Cancers caused by IDH mutations overproduce the related molecule 2-hydroxyglutarate (2HG). We will also explore how EglN2 regulates Cyclin D1 in a HIF-independent manner and will ask whether 2HG promotes cancer by modulating one or more 2-OG-dependent enzymes.
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