Abstract 2300: Novel conditional knockout of VHL in the kidney leads to precancerous lesions that exhibit an inflammatory response.

Abstract Mutations of the tumor suppressor gene von Hippel-Lindau (VHL) can lead to benign and malignant tumors, including the devastating cancer clear-cell renal cell carcinoma (ccRCC). Using a Cre mouse strain that is driven by the Hoxb7 gene promoter, we have generated a novel Vhl conditional knockout strain that exhibits prominent precancerous lesions in the mutant mouse kidneys. Hoxb7-Cre is expressed in collecting ducts in embryonic and adult kidneys, as well as in the convoluted distal tubules in adult kidneys. Pre-cancerous kidney lesions are observed in as early as 2 month old homozygous viable mice, which are not seen in wild-type littermates. Investigation of H&E sections showed that lesions contained dilated kidney tubules (mini-cysts), cell piling-up, clear cells, and infiltrating immune cells. Collagen accumulation was observed in these lesions indicating fibrosis. Lesions are also dysplastic distinguished by breakdown of the basement membrane and expression of mesenchymal markers. Consistent with the known ccRCC phenotype, increased blood vessel accumulation in Vhl knockouts was also observed when compared to wild-type littermates. Importantly, hyperplasia (presence of Ki67-positive cells) is also prominent. An abundance of macrophages are detected in lesions starting at 2 months and in older mice the immune cell population in lesions expanded to B-cells and T-cells. The pre-cancerous lesion state in our mutants also provides us an opportunity to analyze the potential role of inflammation in ccRCC progression. These lesions co-express well known pro-inflammatory cytokines interleukin-1β (IL-1β) and IL-6 in tubules surrounding precancerous lesions. One of the major functions of VHL is to act as an E3 ubiquitin ligase, in which its major target for proteasomal degradation is hypoxia-inducible factor α (HIFα). HIFα target genes glucose transporter (Glut1) and carbonic anhydrase IX (CAIX), were expressed in lesion tubules, thus suggesting HIFα contribution to the fibrotic defects we have seen. Mechanistically it can be suggested that dual knockdown of HIF-1α or -2α and VHL would restore kidneys to be similar to wild-type littermates. Indeed the frequency of lesions was greatly reduced in double knockouts of VHL HIF1-α and VHL Hif-2α. IL-1β and IL-6 cytokine activity is known to simulate Janus kinase (JAK)-signaling, which has recently emerged as an important promoter of tumor growth. Specifically JAK2 expression is increased in VHL mutant renal cell carcinoma cell lines and has been shown to promote cell invasion. VHL conditional knockouts treated with a JAK2 inhibitor revealed a decrease in the frequency of lesions, suggesting this mechanism is involved in lesion development. Taken together these results suggest a prominent role of the inflammatory response in the early onset of ccRCC. Citation Format: Tracy L. Pritchett, Hannah Bader, Tien Hsu. Novel conditional knockout of VHL in the kidney leads to precancerous lesions that exhibit an inflammatory response. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2300. doi:10.1158/1538-7445.AM2013-2300