Abstract 1418: CLIC4 regulates carcinogenesis in a TGF-β context-dependent manner.
Authors: Shukla Anjali , Edwards Rebecca , Yang Yihan , Hahn Alexandra , Padmakumar VC , Ryscavage Andrew , Suh Kwang S. , Yuspa Stuart H. 
Published: August 2014

CLIC4 is a 28kD, ubiquitously expressed, redox-regulated, multifunctional protein. It is dimorphic and can transition between membrane bound or soluble forms in the cytoplasm. Cytoplasmic CLIC4 translocates to the nucleus in multiple cell types under conditions of metabolic stress and nuclear CLIC4 causes growth arrest, terminal differentiation and apoptosis. In vivo, CLIC4 is nuclear in quiescent epithelial cells with little stromal expression. In contrast, nuclear CLIC4 is lost from tumor epithelium and is highly upregulated in tumor stroma. We show that CLIC4 expression is reduced in chemically induced mouse skin papillomas, mouse and human squamous carcinomas and squamous cancer cell lines. The extent of reduction in CLIC4 coincides with progression of squamous tumors from benign to malignant. Adenoviral targeting of CLIC4 to the nucleus of tumor cells in orthografts of oncogenic ras transformed keratinocytes inhibits tumor growth, while elevation of CLIC4 in transgenic epidermis reduces de novo chemically induced skin tumor formation. In parallel, overexpression of exogenous CLIC4 in squamous tumor orthografts suppresses tumor growth. These results identify CLIC4 as a tumor suppressor. We show that CLIC4 is an integral intermediate in TGF-β signaling, that overexpressing CLIC4 in tumor cell lines restores TGF-β mediated growth inhibition, and tumor cells in vivo overexpressing CLIC4 have enhanced TGF-β signaling. We have also analyzed the substantial upregulation of CLIC4 in tumor stroma. Reconstituting orthografts of mammary or squamous tumors with stromal cells overexpressing CLIC4 enhances tumor growth.Correspondingly, tumor growth is significantly inhibited in orthografts of tumor cells to hosts that lack stromal CLIC4. CLIC4 expression is increased in stromal cells by conditioned medium from tumor cells in a TGF-β dependent manner. In stromal cells genetically deleted of CLIC4, the conversion of fibroblasts to cancer associated myofibroblasts by TGF-β through p38 activation is prevented. CLIC4 is essential for preventing the de-activation of p38 by its phosphatase PPM1a. Stromal cells that overexpress CLIC4 enhance tumor cell invasion and EMT in vitro. Thus CLIC4, like TGF-β, has context dependent dual influence on tumor cell growth and progression. CLIC4 is an attractive therapeutic target both in cancer stages where TGF-β signal augmentation or inhibition is required due to responses in separate tissue compartments. Targeting CLIC4 would also be a more specific approach in therapy that would mitigate some of the severe side effects of global targeting of the multifunctional TGF-β pathway.

Citation Format: Anjali Shukla, Rebecca Edwards, Yihan Yang, Alexandra Hahn, VC Padmakumar, Andrew Ryscavage, Kwang S. Suh, Stuart H. Yuspa. CLIC4 regulates carcinogenesis in a TGF-β context-dependent manner. [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 1418. doi:10.1158/1538-7445.AM2013-1418