Abstract 1767: Rho-GTPase inhibits claudin-2 expression to promote proximal tubular epithelial cell plasticity and renal cell carcinoma
Authors: Kumar Balawant , Ahmad Rizwan , Kapitsino Pinelopi , Giannico Giovanna A. , Zent Roy , Harris Raymond Clement , Clark Peter , Dhawan Punita , Singh Amar B. 
Published: August 2019

Abstract
The clear-cell renal cell carcinoma (ccRCC) is the most prevalent and malignant type of kidney cancer, for which there are no effective treatment. Moreover, the incidence of ccRCC has been increasing steadily. Disruption of epithelial cell polarity, assisted by tight junction (TJ) deregulation, facilitates rewiring of oncogene and tumor suppressor signaling pathways. In this regard, proximal tubular epithelium (PTE), where ccRCC originates is the sole nephron segment that expresses claudin-2 (hereon Cldn2), a TJ- protein. However, role of Cldn2 in ccRCC remains unknown despite well-recognized role of Cldn2 in regulating other cancers. We here report a novel role for Cldn2 in maintaining epithelial differentiation among PTE cells as its loss induces mesenchymal traits and associates with ccRCC progression. In specific, we found a specific (among claudin proteins) loss of Cldn2 expression in PTE cells subjected to stimuli, like EGF, TGF-ß and hypoxia, known to induce EMT in PTE cells as well as in a murine model of spontaneous renal tumorigenesis. Further analysis of a large renal cancer patient cohort revealed a significant decrease in Cldn2 levels in the ccRCC, and its positive association with cancer metastasis. In vitro, genetic ablation of claudin-2 expression in HK-2 or MDCK-II cells potentiated mesenchymal traits (upregulated Vimentin and Fibronectin; p&lt;0.002) and cell motility (p&lt;0.0002 versus control). In contrast, forced claudin-2 expression in RCC-derived (and claudin-2 low) Caki-2 cells (P&lt;0.002) promoted epithelial differentiation (downregulation of Vimentin and Fibronectin; P&lt;0.0012& P&lt;0.00025), inhibited cell invasion (P&lt;0.0001) and proliferation (P&lt;0.001). Overall, our findings support a novel and tissue-specific role of claudin-2 in maintaining epithelial differentiation among renal proximal tubular epithelium and tumor suppressor. Further analysis identified a key role of Rho-GTPase in regulating renal claudin-2 expression as ROCK inhibitor (Y-27632) not only reverted EMT-associated loss of Cldn2 but also in Caci-2 cells. An ELISA assay further confirmed an early induction of Rho-GTPase activity in PTE cells subjected to the EMT. Of note, inhibiting Rho-GTPase not only improves renal fibrosis but also inhibits ccRCC. Taken together, we here report a novel role of claudin-2 in maintaining epithelial phenotype in PTE cells with potential clinical significance in acute and chronic renal diseases, and ccRCC progression.

Citation Format: Balawant Kumar, Rizwan Ahmad, Pinelopi Kapitsino, Giovanna A. Giannico, Roy Zent, Raymond Clement Harris, Peter Clark, Punita Dhawan, Amar B. Singh. Rho-GTPase inhibits claudin-2 expression to promote proximal tubular epithelial cell plasticity and renal cell carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1767.