FKBP51 modulates steroid sensitivity and NFκB signalling: A novel anti-inflammatory drug target.

Steroid refractory inflammation is an unmet medical need in the management of inflammatory diseases. Thus, mechanisms, improving steroid sensitivity and simultaneously decreasing inflammation have potential therapeutic utility. The FK506-binding protein 51 (FKBP51) is reported to influence steroid sensitivity in mental disorders. Moreover, biochemical data highlight a connection between FKBP51 and the IKK complex. The aim of this study was to elucidate whether FKBP51 inhibition had utility in modulating steroid resistant inflammation by increasing the sensitivity of the glucocorticoid receptor (GR) signalling and simultaneously inhibiting NFκB-driven inflammation. We have demonstrated that FKBP51 silencing in a bronchial epithelial cell line resulted in a 10-fold increased potency for dexamethasone towards IL1beta-induced IL6 and IL8, whilst FKBP51 over-expression of FKBP51 reduced significantly the prednisolone sensitivity in a murine HDM-driven pulmonary inflammation model. Immunoprecipitation experiments with anti-FKBP51 antibodies, confirmed the presence of FKBP51 in a complex comprising Hsp90, GR and members of the IKK family. FKBP51 silencing reduced NFκB (p50/p65) nucleus translocation, resulting in reduced ICAM expression, cytokine and chemokine secretion. In conclusion, we demonstrate that FKBP51 has the potential to control inflammation in steroid insensitive patients in a steroid-dependent and independent manner and thus may be worthy of further study as a drug target.

Molecular structure of human GM-CSF in complex with a disease-associated anti-human GM-CSF autoantibody and its potential biological implications.

Polyclonal autoantibodies against human GM-CSF (granulocyte/macrophage colony-stimulating factor) are a hallmark of PAP (pulmonary alveolar proteinosis) and several other reported autoimmune diseases. MB007 is a high-affinity anti-(human GM-CSF) autoantibody isolated from a patient suffering from PAP which shows only modest neutralization of GM-CSF bioactivity. We describe the first crystal structure of a cytokine-directed human IgG1λ autoantibody-binding fragment (Fab) at 1.9 Å (1 Å=0.1 nm) resolution. Its CDR3-H substantially differs from all VH7 germline IgG1 structures reported previously. We derive a reliable model of the antigen-autoantibody complex by using NMR chemical shift perturbation data in combination with computational methods. Superposition of the modelled complex structure with the human GM-CSF-GM-CSF ternary receptor complex reveals only little overlap between receptor and Fab when bound to GM-CSF. Our model provides a structural basis for understanding the mode of action of the MB007 autoantibody.

High content screening of CXCR2-dependent signalling pathways.

Stimulation of CXC-type chemokine receptor 2 (CXCR2)-transfected cells by Gro-alpha or IL-8 induced (i) CXCR2 internalization, (ii) phosphorylation of ERK1/2 (pERK) and (iii) translocation of nuclear factor of activated T cells (NFAT) into the nucleus. Employing high content screening (HCS; i.e. fluorimetric imaging combined with image analysis) these three ligand-induced events were quantified by using a CXCR2-specific antibody, an antibody recognizing phosphorylated ERK1/2 (pERK) and a red fluorescent protein (RFP) in fusion to transiently overexpressed NFAT, respectively. As an RFP, we applied a recently developed mutant of an Entacmaea quadricolor fluorescent protein with favorable properties for HCS, such as high fluorescence brightness, photostability, large Stokes shift, and stability with regard to formaldehyde. Receptor internalization was closely coupled with ERK signalling both when analyzed in regard of stimulation by physiological CXCR2 ligands and when observed in the presence of antagonistic test compounds. A means of increasing the throughput or of broadening the pharmacological characterization of test compounds is the use of multiplexed imaging. Indeed, CXCR2 internalization could be multiplexed with the NFAT nuclear translocation by fixation at approximately 45 min after Gro-alpha stimulation. This multiplexing demonstrated that Gro-alpha-induced CXCR2 internalization was tightly correlated with Gro-alpha-induced NFAT translocation, also on the single cell level. The analysis of ERK phosphorylation, NFAT translocation and receptor internalization enabled the profiling of antagonistic test compounds with respect to G-protein signalling and possible receptor desensitization liabilities.

CXCR2 inverse agonism detected by arrestin redistribution.

To study CXCR2 modulated arrestin redistribution, the authors employed arrestin as a fusion protein containing either the Aequorea victoria-derived enhanced green fluorescent protein (EGFP) or a recently developed mutant of eqFP611, a red fluorescent protein derived from Entacmaea quadricolor. This mutant, referred to as RFP611, had earlier been found to assume a dimeric quarternary structure. It was therefore employed in this work as a "tandem" (td) construct for pseudo-monomeric fusion protein labeling. Both arrestin fusion proteins, containing either td-RFP611 (Arr-td-RFP611) or enhanced green fluorescent protein (EGFP; Arr-EGFP), were found to colocalize with internalized fluorescently labeled Gro-alpha a few minutes after Gro-alpha addition. Intriguingly, however, Arr-td-RFP611 and Arr-EGFP displayed distinct cellular distribution patterns in the absence of any CXCR2-activating ligand. Under these conditions, Arr-td-RFP611 showed a largely homogeneous cytosolic distribution, whereas Arr-EGFP segregated, to a large degree, into granular spots. These observations indicate a higher sensitivity of Arr EGFP to the constitutive activity of CXCR2 and, accordingly, an increased arrestin redistribution to coated pits and endocytic vesicles. In support of this interpretation, the authors found the known CXCR2 antagonist Sch527123 to act as an inverse agonist with respect to Arr-EGFP redistribution. The inverse agonistic properties of Sch527123 were confirmed in vitro in a guanine nucleotide binding assay, revealing an IC(50) value similar to that observed for Arr-EGFP redistribution. Thus, the redistribution assay, when based on Arr-EGFP, enables the profiling of antagonistic test compounds with respect to inverse agonism. When based on Arr-td-RFP611, the assay may be employed to study CXCR2 agonism or neutral antagonism.