Targeting the Nuclear Cathepsin L- CCAAT-displacement protein/cut homeobox Transcription Factor-Epithelial Mesenchymal Transition Pathway in Prostate and Breast Cancer Cells with Z-FY-CHO Inhibitor.

The Epithelial Mesenchymal Transition (EMT) promotes tumor migration and invasion by downregulating epithelial markers such as E-cadherin and upregulating mesenchymal markers such as vimentin. Cathepsin L (Cat L) is a cysteine protease that can proteolytically activate CCAAT-displacement protein/cut homeobox transcription factor (CUX1). We hypothesized that nuclear Cat L may promote EMT via CUX1, and that this could be antagonized with Cat L specific inhibitor, Z-FY-CHO. Mesenchymal prostate (ARCaP-M, ARCaP-E overexpressing Snail) and breast (MDA-MB-468, MDA-MB-231, and MCF-7 overexpressing Snail) cancer cells expressed lower E-cadherin, higher Snail, vimentin, Cat L activity, and p110/p90 active CUX1 form, as compared to epithelial prostate (ARCaP-E, ARCaP-Neo) and breast (MCF-7, MCF-7 Neo) cancer cells. There was increased binding of CUX1 to Snail and E-cadherin promoter in mesenchymal cells, as compared to epithelial prostate and breast cells. Treatment of mesenchymal cells with Cat L inhibitor, Z-FY-CHO, led to nuclear to cytoplasmic relocalization of Cat L, decreased binding of CUX1 to Snail and E-cadherin promoter, reversed EMT, and decreased cell migration/invasion. Overall, our novel data suggests that a positive feedback loop between Snail-nuclear Cat L-CUX1 drives EMT which can be antagonized by Z-FY-CHO. Therefore, Z-FY-CHO may be an important therapeutic tool to antagonize EMT and cancer progression.