Nucleocytoplasmic Shuttling of the Glucocorticoid Receptor is Modulated by TPR-Domain Proteins

MAZAIRA GI; ECHEVERRIA PC; GALIGNIANA MD

Congreso; The 35th Virtual Anniversary Symposium of the Protein Society; 2021

Protein Society

HSP90 dimers shape an acceptor site for co-chaperones carrying tetratricopeptide-repeats (TPR), where they bind in vivo in a competitive and mutually exclusive manner. We aimed to study the impact of TPR protein overexpression on the biological properties of the GR-HSP90 complex. GR nucleocytoplasmic shuttling was analysed by confocal microscopy, steroid-dependent transcriptional regulation by gene-reporter studies, GR attachment to nucleoskeleton by biochemical copurification, and the heterocomplex composition by co-immunoprecipitation assays. It is demonstrated that the overexpression of the TPR domain of the Ser/Thr-phosphatase PP5 impairs GR nuclear translocation rate by preventing: a)-the assembly of FKBP52?dynein/dynactin complexes, b)-binding to the adaptor/transporter importin-1, and c)-binding to the nuclear pore-associated glycoprotein Nup62. These disruptions slow-down the GR passage through the nuclear pore complex (NPC) and its nuclear anchorage to the nuclear matrix. Both FKBP52 and PP5 co-purify with the nucleoskeleton in a TPR-competed fashion and show colocalization with GR and NuMa in intact cells. TPR-peptide overexpression prompts the GR release from nuclear anchoring sites and its export rate. While leptomycin-B shows no effect on GR nuclear export, it abolishes the effect of TPR peptide overexpression, suggesting the existence of a TPR domain-dependent export mechanism. While FKBP52 favours GR transcriptional activity and its nuclear retrotransport, FKBP51 and 14-3-3sigma (whose 3D-structure mimics that of the TPR domain of PP5) impairs this effect. In turn, the TPR-protein SGT1α shows no effect on GR trafficking but inhibits its transcriptional activity like FKBP51. PP5 promotes an equal nuclear-cytoplasmic redistribution of GR that is independent of its phosphorylation status, while it shows biphasic transcriptional action. It is proposed that the pleiotropic actions of GR in different cell types may depend on the relative abundance of TPR-domain interacting co-chaperones, which affect the GR trafficking mechanism, its passage through NPC, the anchorage to the nuclear matrix, and steroid-dependent transcriptional regulation.