The activity of the glucocorticoid receptor is regulated by SUMO conjugation to FKBP51.

FK506-binding protein 51 (FKBP51) regulates the activity of the glucocorticoid receptor (GR), and is therefore a key mediator of the biological actions of glucocorticoids. However, the understanding of the molecular mechanisms that govern its activity remains limited. Here, we uncover a novel regulatory switch for GR activity by the post-translational modification of FKBP51 with small ubiquitin-like modifier (SUMO). The major SUMO-attachment site, lysine 422, is required for FKBP51-mediated inhibition of GR activity in hippocampal neuronal cells. Importantly, impairment of SUMO conjugation to FKBP51 impacts on GR-dependent neuronal signaling and differentiation. We demonstrate that SUMO conjugation to FKBP51 is enhanced by the E3 ligase PIAS4 and by environmental stresses such as heat shock, which impact on GR-dependent transcription. SUMO conjugation to FKBP51 regulates GR hormone-binding affinity and nuclear translocation by promoting FKBP51 interaction within the GR complex. SUMOylation-deficient FKBP51 fails to interact with Hsp90 and GR thus facilitating the recruitment of the closely related protein, FKBP52, which enhances GR transcriptional activity. Moreover, we show that the modification of FKBP51 with SUMO modulates its binding to Hsp90. Our data establish SUMO conjugation as a novel regulatory mechanism in the Hsp90 cochaperone activity of FKBP51 with a functional impact on GR signaling in a neuronal context.

Beware of your Cre-Ation: lacZ expression impairs neuronal integrity and hippocampus-dependent memory.

Expression of the lacZ-sequence is a widely used reporter-tool to assess the transgenic and/or transfection efficacy of a target gene in mice. Once activated, lacZ is permanently expressed. However, protein accumulation is one of the hallmarks of neurodegenerative diseases. Furthermore, the protein product of the bacterial lacZ gene is ß-galactosidase, an analog to the mammalian senescence-associated ß-galactosidase, a molecular marker for aging. Therefore we studied the behavioral, structural and molecular consequences of lacZ expression in distinct neuronal sub-populations. lacZ expression in cortical glutamatergic neurons resulted in severe impairments in hippocampus-dependent memory accompanied by marked structural alterations throughout the CNS. In contrast, GFP expression or the expression of the ChR2/YFP fusion product in the same cell populations did not result in either cognitive or structural deficits. GABAergic lacZ expression caused significantly decreased hyper-arousal and mild cognitive deficits. Attenuated structural and behavioral consequences of lacZ expression could also be induced in adulthood, and lacZ transfection in neuronal cell cultures significantly decreased their viability. Our findings provide a strong caveat against the use of lacZ reporter mice for phenotyping studies and point to a particular sensitivity of the hippocampus formation to detrimental consequences of lacZ expression. © 2016 Wiley Periodicals, Inc.

FKBP51 inhibits GSK3ß and augments the effects of distinct psychotropic medications.

Psychotropic medications target glycogen synthase kinase 3ß (GSK3ß), but the functional integration with other factors relevant for drug efficacy is poorly understood. We discovered that the suggested psychiatric risk factor FK506 binding protein 51 (FKBP51) increases phosphorylation of GSK3ß at serine 9 (pGSK3ß(S9)). FKBP51 associates with GSK3ß mainly through its FK1 domain; furthermore, it also changes GSK3ß's heterocomplex assembly by associating with the phosphatase PP2A and the kinase cyclin-dependent kinase 5. FKBP51 acts through GSK3ß on the downstream targets Tau, ß-catenin and T-cell factor/lymphoid enhancing factor (TCF/LEF). Lithium and the antidepressant (AD) paroxetine (PAR) functionally synergize with FKBP51, as revealed by reporter gene and protein association analyses. Deletion of FKBP51 blunted the PAR- or lithium-induced increase in pGSK3ß(S9) in cells and mice and attenuated the behavioral effects of lithium treatment. Clinical improvement in depressive patients was predicted by baseline GSK3ß pathway activity and by pGSK3ß(S9) reactivity to ex vivo treatment of peripheral blood mononuclear lymphocytes with lithium or PAR. In sum, FKBP51-directed GSK3ß activity contributes to the action of psychotropic medications. Components of the FKBP51-GSK3ß pathway may be useful as biomarkers predicting AD response and as targets for the development of novel ADs.