A mechanism controlling Cullin-dependent ubiquitin E3 ligases (Cul-UbE3) with particular focus on the COP9 Signalosome (CSN). We have found that the CSN plays a critical role in differentially regulating Cul-UbE3s. This is particularly important in tumor development as Cul-UbE3s regulate the degradation of multiple oncogenes and tumor suppressors including p27, p21, Cyclin B1, Cyclin D1, Cyclin E, Cdc25A, Wee1, c-myc, p53, HIF-1/2α, c-myb, E2F1, IkBa, NF-kB/p105, NF-kB/p100, SMAD4, b-catenin, IRS-1, IRS-2, Nrf2, CI, SMAD3, SMAD4, Notch1, Notch4,Vav, RhoBTB2, DDB2, CSA, Cdt1,...etc). Not surprisingly, the catalytic component of the CSN, CSN5, is one of the most highly amplified regions in several cancers, particularly breast cancer and is necessary and sufficient for the angiogenic phenotype in breast cancer. We are currently in the process of characterizing CSN regulation within various contexts and in a collaboration with the Trent lab have recently developed small molecule CSN antagonists that elicit specific tumor suppressive effects. These exciting studies have produced several lead compounds and are currently in phase 0 studies.
A mechanism controlling hypoxia- and reperfusion- induced G2/M arrest. We have recently identified a hypoxia/reperfusion responsive RING-H2 protein that forms a functional ubiquitin E3-ligase (UbE3) with the IAP, Survivin. We are currently testing the hypothesis that this UbE3 controls an oxygen-sensitive assembly of the Chromosomal Passenger Complex (CPC) and acts as a Spindle checkpoint control. We are also developing small molecule antagonists of the RING-H2 protein as radiation and chemo-sensitizers as antagonism of the RING-H2 protein leads to Spindle (G2/M) arrest which is the most damage-sensitive phase of the cell cycle.
A novel functionality associated with pVHL. We have isolated an oxygen-labile ribonuclease inhibitor (RI) and are in the process of characterizing it function. Interestingly, early studies of pVHL ascribed mRNA stabilization function to this tumor suppressor. We have found that the pVHL interaction controls the expression of greater than 400 genes, many of which are dependent on it's interaction with pRI with 82% of gene expression that is regulated by RI also being regulated by pVHL. Interestingly, a similar pattern is found under hypoxia, where RI dissociates from pVHL. Further, RI is a target for mono-ubiquitylation, leading to RI subcellular localization and sequestration from the ribonuclease, angiogenin. This is a significant finding as it mechanistically links a completely novel function to an important tumor suppressor.
The role of secreted factors regulating renal cancer development. We have found that amongst the milieu of secreted factors controlled by pVHL, two factors are required & sufficient for tumor growth and angiogenesis, IL8 and angiogenin. IL8 is regulated by VHL in a RI independent fashion whereas, angiogenin is a direct target of RI. When examined in conjunction, high levels of IL8 and angiogenin predicted renal cancer in a stage-dependent manner in mouse models of renal cancer and simultaneous inhibition of both factors (but not each singly) results in significant inhibition of renal cancer xenograft growth. Current research will evaluate these factors further as biomarkers of renal cancer stage/grade and metastasis. As FDA-approved inhibitory antibodies to IL-8 and small molecule inhibitors of angiogenin are available, I will begin a clinical trial in metastatic renal cancer as soon as possible.
The development of high throughput screening methodologies for radiation sensitization and hypoxia-specific cytotoxins. A major focus of my lab will be the development of high throughput screening methodologies for radiation sensitization and hypoxia-specific cytotoxins. We will validate lead compounds using in vitro, cellular and xenograft studies in combination with radiation and/or other genotoxic chemotherapies.
Mapping the Oxygen Sensing and Response Network. Since the inception of my lab over the past 8 years, this huge project has generated the leads to all of my currently funded projects. Due to the largely exploratory nature of the project, it is unlikely to be a candidate for grant funding. Despite this, this project will undoubtedly continue to be the main generator of more focused projects (see projects 1-4) and will be very useful for collaborations. This project is also the most exciting project in my lab and something that everyone in the lab contributes to, providing a common theme for all lab members.