The role of chaperones in maturation and regulation of the androgen receptor – ARCHAP

Androgens, such as testosterone and dihydrotestosterone, drive development and homeostasis of the male phenotype and play important roles in non-sexual tissues through, for example, regulation of bone homeostasis and muscle mass for both genders. Their actions are mediated by the androgen receptor (AR), a transcription factor from the nuclear receptor superfamily. Dysregulations of AR lead a range of disorders. Notably, AR signalling drives tumour development and progression in prostate cancer and in some breast cancer and the presence of AR variants can induce resistance to existing therapies.

AR is composed of a disordered N-terminal domain, a DNA binding domain and a C-terminal ligand binding domain (LBD). Hormone binding to the LBD induces AR dissociation from the chaperone complex, dimerization and translocation to the nucleus where it interacts with DNA and other cofactors to regulate gene expression.

Before it can bind to its hormone ligand, it goes through a poorly understood chaperone assisted maturation process involving the Hsp70 and Hsp90 systems. Chaperones are key players in AR regulation. Not only do they allow proper folding of the receptor, but they also prevent proteasomal degradation and maintain the pool of inactive AR ready for hormone activation. Chaperone were shown to interact with the LBD for its folding and activation but also to regulate action of the intrinsically disordered NTD.

The ARCHAP project propose to explore the structural basis of AR maturation and regulation by chaperones and its perturbation in pathological AR variants. On the one hand, we will focus on interactions of the Hsp70 system with a transactivation unit of the disordered NTD. On the other hand, we will dissect the maturation process of the LBD by the Hsp90 system. We will use an integrative structural approach combining spectroscopy and imaging:
- fluorescence cellular imaging to probe interactions directly in the cell (including FLIM-FRET and FCS).
- nuclear magnetic resonance spectroscopy, SAXS and other biophysical methods to characterise disordered regions and transient interactions
- cryo-electron microscopy for dynamic multi-protein AR:chaperone complexes.

Better understanding of the heterogeneous and dynamic complexes involved and their regulatory mechanisms will allow to propose new strategies for specific targeting of AR in a pathological context. More generally, we hope to get better understanding of how chaperones regulate complex signalling processes involving flexible and disordered proteins.