Subcellular Rearrangement of Hsp90-binding Immunophilins Accompanies Neuronal Differentiation and Neurite Outgrowth

QUINTá HR, MASCHI D, PIWIEN PILIPUK G, GALIGNIANA MD

les Diablerets

Congreso; 5th International Conference on the Hsp90 Chaperone Machinery; 2010

Hsp90 Organization

FKBP51 and FKBP52 are TPR-domain immunophilins belonging to the TPR-protein•hsp90•hsp70•p23 heterocomplex bound to steroid receptors. These immunophilins have been related to receptor folding, subcellular localization, and hormone-dependent transcription. Also, they bind the immunosuppressant macrolide FK506, which shows neuroregenerative and neuroprotective actions by a still unknown mechanism. In this study, we demonstrate that in both undifferentiated neuroblastoma cells and primary cultures of embryonic hippocampal neurons, the FKBP52•hsp90•p23 heterocomplex concentrates in a perinuclear structure. Upon cell differentiation with FK506 (in the absence of any other trophic stimulus), these annular structures disassemble in a MAPK-(ERK1/2)-dependent manner, the chaperones redistribute in the cytoplasm, and the perinuclear area becomes transcriptionally hyperactive. The rapid acquisition of a neuronal phenotype is accompanied by increased expression of typical markers such as âIII-tubulin, Map2, Tau-1, but also by a higher expression of hsp90, hsp70, p23, and FKBP52. During the early differentiation steps, the heterocomplex redistributes along the cytoplasm and nascent neurites, p23 binds to intermediate filaments, and microtubules acquired higher filamentary organization. Importantly, hsp90 concentrates in a cytoplasmic speckle that marks the polarization of the cell facing the growing axon. While FKBP52 moves towards neurites and concentrates in arborization bodies and terminal axons, FKBP51, whose expression remains constant, replaces FKBP52 in the perinuclear structure. Importantly, neurite outgrowth is favored by FKBP52 overexpression or FKBP51 knock-down, and is impaired by FKBP52 knock-down or FKBP51 overexpression, indicating that the balance between these two FK506-binding proteins plays a key role during the early steps of neuronal differentiation.