FUNCTIONAL, STRUCTURAL AND BINDING STUDIES OF THE ATYPICAL ER-RESIDENT PROTEIN FKBP7, A POTENTIAL TARGET IN CHEMORESISTANT PROSTATE CANCER
Résumé
Background: Metastatic Castration Resistant Prostate Cancer is the latest stage of Prostate Cancer (PCa) and remains lethal. We identified FKBP7 as a potential therapeutic target of interest in PCa. FKBP7 is overexpressed in taxane-resistant PCa cells, impacts both cell proliferation and Docetaxel efficacy in chemoresistant models, and interacts with eIF4F, a component of translation initiation. FKBP7 is an ER-resident FKBP still largely unknown. Methods: FKBP7 expression was assessed by Western Blot. Impact of FKBP7 expression on clinical prognosis was examined on public cancer databases. Subcellular localization of FKBP7 was determined by digitonin-based cell fractionation. Structural modeling and sequence alignments were used to obtain FKBP7-predicted structure. Finally, we produced and purified 15N enriched recombinant catalytic domain of FKBP7 and collected high quality 15N HSQC NMR spectra in presence or absence of ligands. Results: FKBP7 expression increased upon treatment with several cytotoxic chemotherapies in PCa-cell lines, and TCGA data underlined FKBP7 impacts survival in other solid cancers than PCa. Subcellular fractionation showed FKBP7 localizes in the Endoplasmic Reticulum (ER) but also in the cytosol, independently of proteasomal degradation. We determined FKBP7 is N45-glycosylated and observed that cytosolic FKBP7 is mainly glycosylated. At last, structural modeling predicted a potential substrate specificity for FKBP7 catalytic pocket with a distinct composition for charge and bulkiness compared to other FKBPs. Accordingly, NMR revealed FKBP7 strongly binds Rapamycin and Everolimus, but surprisingly not FK506. Conclusions: Our results suggest FKBP7 could be a druggable target in adaptive resistance of other solid cancers. They also point atypical properties for an ER-resident protein. We propose a model in which FKBP7 could acquire new functions in the cytosol, such as the reprogramming of the proteome mediated by its interaction with its cytosolic partner eIF4F. Besides, we gathered new structural data showing FKBP7 presents a selective binding profile, encouraging the development of future drug-targeting strategies.