PPAR{gamma} Ligand-induced Annexin A1 Expression Determines Chemotherapy Response via Deubiquitination of Death Domain Kinase RIP in Triple Negative Breast Cancers

Metastatic breast cancer is still remain incurable so far, new specifically targeted and more effective therapies for triple negative breast cancer (TNBC) are required in the clinic. In this study, our clinical data has established that basal and claudin-low subtypes of breast cancer (TNBC types) express significantly higher levels of Annexin A1 (ANXA1) with poor survival outcomes. Using human cancer cell lines which model the TNBC subtype, we observed a strong positive correlation between expression of ANXA1 and Peroxisome Proliferator-Activated Receptor gamma (PPAR). A similar correlation between these two markers was also established in our clinical breast cancer patients' specimens. To establish a link between these two markers in TNBC, we show de novo expression of ANXA1 is induced by activation of PPAR both in vitro and invivo and it has a predictive value in determining chemo-sensitivity to PPAR ligands. Mechanistically, we show for the first time PPAR-induced ANXA1 protein directly interacts with Receptor Interacting Protein-1 (RIP1), promoting its deubiquitination and thereby activating the caspase 8-dependent death pathway. We further identified this underlying mechanism also involved a PPAR-induced ANXA1-dependent autoubiquitination of cIAP1, the direct E3 ligase of RIP1, shifting cIAP1 towards proteosomal degradation. Collectively, our study provides first insight for the suitability of using drug-induced expression of ANXA1 as a new player in RIP1-induced death machinery in TNBCs. Hitherto, presenting itself both as an inclusion criterion for patient selection and surrogate marker for drug response in future PPAR chemotherapy trials.

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