Glucocorticoid receptor condensates link DNA-dependent receptor dimerization and transcriptional transactivation

The glucocorticoid receptor (GR) is a ligand-regulated transcription factor (TF) that controls the tissue- and gene-specific transactivation and transrepression of thousands of target genes. Distinct GR DNA-binding sequences with activating or repressive activities have been identified, but how they modulate transcription in opposite ways is not known. We show that GR forms phase-separated condensates that specifically concentrate known coregulators via their intrinsically disordered regions (IDRs) in vitro. A combination of dynamic, multivalent (between IDRs) and specific, stable interactions (between LxxLL motifs and the GR ligand-binding domain) control the degree of recruitment. Importantly, GR DNA binding directs the selective partitioning of coregulators within GR condensates such that activating DNAs cause enhanced recruitment of coactivators. Our work shows that condensation controls GR function by modulating coregulator recruitment and provides a mechanism for the up- and down-regulation of GR target genes controlled by distinct DNA recognition elements.

Glucocorticoid Receptor Condensates Link DNA-Dependent Receptor Dimerization and Transcriptional Transactivation

The glucocorticoid receptor (GR) is a ligand-regulated transcription factor (TF) that controls the tissue- and gene-specific transactivation and transrepression of thousands of target genes. Distinct GR DNA binding sequences with activating or repressive activities have been identified, but how they modulate transcription in opposite ways is not known. We show that GR forms phase-separated condensates that specifically concentrate known co-regulators via their intrinsically disordered regions (IDRs) in vitro. A combination of dynamic, multivalent (between IDRs) and specific, stable interactions (between LxxLL motifs and the GR ligand binding domain) control the degree of recruitment. Importantly, GR DNA-binding directs the selective partitioning of co-regulators within GR condensates such that activating DNAs cause enhanced recruitment of co-activators. Our work shows that condensation controls GR function by modulating co-regulator recruitment and provides a mechanism for the up- and down-regulation of GR target genes controlled by distinct DNA recognition elements.

In silico investigation of the potential interaction between two entomological peptides and human androgen receptor

Objective: We aim to evaluate the potential interaction of two insect hemolymph peptides, MDF3 and MDF4, with the human androgen receptor, on the premise that the proliferative effects of the two peptides are (at least in part) a consequence of AR binding. Methods: We employed a bioinformatic approach for the prediction of protein-peptide interaction and peptide aggregation, using various in silico on-line tools such as docking servers, aggregation prediction servers and visualization and analysis software in order to evaluate our results. Results: Our evaluation indicates that MDF3 and MDF4 interact with the androgen human androgen receptor by binding to a helix shown to be involved the receptor dimerization. Out of the two peptides, MDF3 appears to form a more extensive bond network with the receptor. Conclusion: Our analysis indicates that MDF 3 and 4 may be able to activate the human androgen receptor and warrant further investigation of the potential effect on receptor function. MDF3 appears to be the most promising out of the two peptides and its interaction should be further evaluated by both computational and experimental methods.

Characterization of clostridium botulinum neurotoxin serotype A (BoNT/A) and fibroblast growth factor receptor interactions using novel receptor dimerization assay

Clostridium botulinum neurotoxin serotype A (BoNT/A) is a potent neurotoxin that serves as an effective therapeutic for several neuromuscular disorders via induction of temporary muscular paralysis. Specific binding and internalization of BoNT/A into neuronal cells is mediated by its binding domain (HC/A), which binds to gangliosides, including GT1b, and protein cell surface receptors, including SV2. Previously, recombinant HC/A was also shown to bind to FGFR3. As FGFR dimerization is an indirect measure of ligand-receptor binding, an FCS & TIRF receptor dimerization assay was developed to measure rHC/A-induced dimerization of fluorescently tagged FGFR subtypes (FGFR1-3) in cells. rHC/A dimerized FGFR subtypes in the rank order FGFR3c (EC50 ≈ 27 nM) > FGFR2b (EC50 ≈ 70 nM) > FGFR1c (EC50 ≈ 163 nM); rHC/A dimerized FGFR3c with similar potency as the native FGFR3c ligand, FGF9 (EC50 ≈ 18 nM). Mutating the ganglioside binding site in HC/A, or removal of GT1b from the media, resulted in decreased dimerization. Interestingly, reduced dimerization was also observed with an SV2 mutant variant of HC/A. Overall, the results suggest that the FCS & TIRF receptor dimerization assay can assess FGFR dimerization with known and novel ligands and support a model wherein HC/A, either directly or indirectly, interacts with FGFRs and induces receptor dimerization.

Establishment of fluorescence-based affinity assay systems for the investigation of nuclear receptor dimerization and ligand modulated coregulator recruitment

Die Funktion nukleärer Rezeptoren (NR) beruht auf einem empfindlichen Zusammenspiel zwischen ihren Domänen, Coregulatoren und Liganden. Die meisten Rezeptoren binden die DNA als Homo- oder Heterodimere und transregulieren die Gentranskription in Folge von Ligandenbindung. Klassische Assay-Systeme, die sich auf die Untersuchung der NR-Funktion oder auf die Charakterisierung von Substanzen richten, bilden nur die Coregulator-Rekrutierung zu isolierten NR-Ligandenbindungsdomänen (LBDs) ab und vernachlässigen dabei die NR:NR-Interaktion. Damit klammern sie die NR:NR-Wechselwirkung aus, obwohl die Rekrutierung von Cofaktoren durch allosterischen Crosstalk mit der Oligomerisierung verbunden ist. Dies war die Motivation dafür, Assay-Systeme zu entwickeln, welche die Untersuchung von NR-Interaktionen, insbesondere der NR-Dimerisierung, und deren Modulation durch verschiedene Arten von Liganden ermöglichen. Im Rahmen dieser Doktorarbeit wird ein vielfältiges modulares Set von Assays für die Untersuchung der NR-Dimerisierung und NR-Coregulator-Rekrutierung vorgestellt und deren Anwendbarkeit auf eine Vielzahl von NRs demonstriert. Die Verwendung einer rekrutierungsunfähigen RXRα-Variante mit einer mutierten AF-2-Domäne ermöglichte den spezifischen Nachweis der Coaktivatorrekrutierung durch PPARγ im Kontext des Heterodimers mit seinem obligatorischen Dimerpartner RXRα. Außerdem konnte gezeigt werden, dass die Aktivierung der RXRα LBD mit ihrem Agonisten SR11237 zu einer Destabilisierung des RXRα-Homodimers, aber zu einer Förderung der Bildung des Heterodimers mit der PPARγ LBD führte. Ein zentrales Ergebnis war das Phänomen, dass der Einbau von PPARγ in das Heterodimer zu einem erheblichen Anstieg an Affinität gegenüber Coaktivatoren führt, auch in Abwesenheit von Liganden. Somit fördert die RXRα-Aktivierung die Coaktivator-Rekrutierung von PPARγ indirekt durch eine Verschiebung der Oligomerisierungspräferenz von RXRα in Richtung des Heterodimers. Zusätzlich wurde die Wirkung von Tetrac, einem nicht-klassischen Schilddrüsenhormon, auf PPARγ und RXRα untersucht und dessen Aktivierungsvermögen gegenüber beiden Rezeptoren mit einer deutlich vervielfachten Wirkung auf das Heterodimer demonstriert. Mit Hilfe des neu etablierten Cofaktor-Rekrutierungsscreens konnte die Dynamik zwischen dem Nurr1 NR und 29 kanonischen Coregulatoren, von denen einige ligandenabhängig hohe Affinitäten zum Rezeptor aufwiesen, beleuchtet werden. Diese Interaktionen wurden bidirektional durch eine Reihe von strukturell unterschiedlichen nicht-steroidalen Antirheumatika moduliert, die auch die Affinitäten sowohl des Nurr1-Homodimers als auch des Heterodimers mit der RXRα LBD beeinflussen konnten. Die Nurr1-Dimere zeigten zudem auch eine hohe Empfindlichkeit gegenüber dem Endocannabinoid Anandamid. Zusätzlich zu PPARγ, RXRα und Nurr1 wurden erste Schritte zur Untersuchung der TLX NR-Funktion unternommen. Unter Anwendung der entwickelten Assays konnte die Heterodimerbildung der TLX und der RXRα LBD beschrieben und die ligandenabhängige Rekrutierung des Corepressors SMRT beobachtet werden. Zusammenfassend beschreibt diese Arbeit einen Satz von Werkzeugen für die Untersuchung von ligandenabhängiger NR-Coregulator-Interaktion und Oligomerisierung. Auf diese Weise trug sie zu einer umfassenderen Identifizierung und Charakterisierung von NR-Liganden bei und stellt eine valide Basis für die weitere Assayentwicklung und Ligandendesign dar.

Glucocorticoid receptor condensates link DNA-dependent receptor dimerization and transcriptional transactivation

The glucocorticoid receptor (GR) is a ligand-regulated transcription factor (TF) that controls the tissue- and gene-specific transactivation and transrepression of thousands of target genes. Distinct GR DNA binding sequences with activating or repressive activities have been identified, but how they modulate transcription in opposite ways is not known. We show that GR forms phase-separated condensates that specifically concentrate known co-regulators via their intrinsically disordered regions (IDRs) in vitro. A combination of dynamic, multivalent (between IDRs) and specific, stable interactions (between LxxLL motifs and the GR ligand binding domain) control the degree of recruitment. Importantly, GR DNA-binding directs the selective partitioning of co-regulators within GR condensates such that activating DNAs cause enhanced recruitment of co-activators. Our work shows that condensation controls GR function by modulating co-regulator recruitment and provides a mechanism for the up- and down-regulation of GR target genes controlled by distinct DNA recognition elements.

Engineering Stem Cell Factor Ligands with Different c-Kit Agonistic Potencies

Receptor tyrosine kinases (RTKs) are major players in signal transduction, regulating cellular activities in both normal regeneration and malignancy. Thus, many RTKs, c-Kit among them, play key roles in the function of both normal and neoplastic cells, and as such constitute attractive targets for therapeutic intervention. We thus sought to manipulate the self-association of stem cell factor (SCF), the cognate ligand of c-Kit, and hence its suboptimal affinity and activation potency for c-Kit. To this end, we used directed evolution to engineer SCF variants having different c-Kit activation potencies. Our yeast-displayed SCF mutant (SCFM) library screens identified altered dimerization potential and increased affinity for c-Kit by specific SCF-variants. We demonstrated the delicate balance between SCF homo-dimerization, c-Kit binding, and agonistic potencies by structural studies, in vitro binding assays and a functional angiogenesis assay. Importantly, our findings showed that a monomeric SCF variant exhibited superior agonistic potency vs. the wild-type SCF protein and vs. other high-affinity dimeric SCF variants. Our data showed that action of the monomeric ligands in binding to the RTK monomers and inducing receptor dimerization and hence activation was superior to that of the wild-type dimeric ligand, which has a higher affinity to RTK dimers but a lower activation potential. The findings of this study on the binding and c-Kit activation of engineered SCF variants thus provides insights into the structure–function dynamics of ligands and RTKs.