Glucocorticoid Receptors. Owen Roth Kristin Mar-Elia

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1 Glcocorticoid Receptors Owen Roth Kristin Mar-Elia

2 What are Glcocorticoids? Glcocorticoids is a term se to encompass any steroid hormone, prodced in the adrenal gland or synthesized in the lab that binds to the glcocorticoid receptor. Synthesized from cholesterol, secreted in the blood stream when blood glcose levels are low or dring psychological stress. Metabolism of carbohydrates, fats, and proteins. Responsible for anti-inflammatory response. Lipophilic natre allows them to readily diffse across celllar membrane. Major physiological glcocorticoid, Cortisol.

3 The Glcocorticoid Receptor (GR), is a sbclass of Nclear Receptors. Nclear receptors are not membrane bond. Bind DNA in presence or absence of ligand. Increase or decrease transcription of target genes in response to ligand binding. Physiological responses are controlled via 3 parameters: Cell-specific expression. Bioavailability of ligands. Differential accessibility to DNA.

4 Nclear Receptors Ligand binding recrits coreglatory proteins (Ex. TIF2) throgh proteinprotein interactions. Receptors exist as two major classes that differ based off of: Conserved amino acid seqence binding. Ligand grop binding activation.

5 Glcocorticoid Receptor 90-kDa homodimeric protein expressed in variety of cell types. In absence of a ligand, reside in cytoplasm forming a chaperon complex with heat shock protein. Ligand binding indces conformational change, travels to ncles to exert biological effects. GR DNA binding domain consists of short αhelical region stabilized by two zinc ions coordinated to cysteine resides. Active sites of GR shown with cortisol (in red) bond.

6 Glcocorticoid Receptor GR DNA-binding domain interacts with a DNA region containing the seqence 5 -AGAACAtgaTGTTCT-3 where the palindromic portion is shown in ppercase letters. Pair of zinc atoms on top of the dimer stabilize protein dimer interface. Pair of zinc atoms in the middle stabilize the α-helical region by optimizing amino acid contact with the DNA.

7 Glcocorticoid receptor bond to DNA α-helical amino acids interacting with major groove ncleotides. Zinc atoms in red Zing Finger biding motifs.

8 Competitive inhibitors & Drg design Glcocorticoids (GCs) bind in the hydrophilic pocket of the GR, where they interact with an α-helix to recrit a coreglatory protein. Flticasone is a potent anti-inflammatory drg that has higher binding affinity for GR that cortisol. Many pharmacetical GCs have been Developed to treat inflammation and asthma. Glcocorticoid receptor with bond asthma drg, flticasone (red, space filling). Shown with TIF2 coreglatory protein (yellow).

9 Pharmacology Cortisol Minor chemical modifications distingish pharmacological GCs from cortisol, allowing for increased binding affinity and biological effect. GR binding affinity = 5x

10 How do Glcocorticoids illicit a physiological response? Direct or indirect reglation of gene expression. In the case of the anti-inflammatory response, GRs indce the expression of the annexin I protein (lipcortin-1). Inhibits prostaglandins. GRs inhibit transcriptional reglatory fnctions of NFκB throgh protein-protein interactions. Decrease in cyclooxygnease-2 (COX), the target of asprin and ibprofen. NFκB heterodimer (P50 & P65) bond to COX gene.

11 Downstream GR signaling reglates the anti-inflammatory pathway in target cells The ligand activated GR translocates to the ncles where it binds to glcocorticoid response elements (GREs). Decreases cyclooxygenase-2-gene protein expression. Leading to decrease in COX2 protein, a mediator of prostaglandin synthesis from arachidonic acid.

12 Conclsions Glcocorticoid Receptors are a type of nclear receptor known as steroid receptors, which are head to head homodimers. Ligands for GRs are physiological hormones derived from cholesterol or steroid like componds synthesized in the lab. Bind to target DNA seqences sing a zing finger DNA binding motif. Binding affinity is determined by amino acids in α-helical region making contact with DNA. Binding DNA seqence mst be palindromic. Pharmacetical GCs bind GRs with greater affinity de to minor chemical modifications in strctre to exert greater biological effect. Ligand bond GRs recrit coreglatory proteins to modlate rates of transcription. Ligand bond GRs bind Glcocorticoid Response Elements to reglate transcription.

13 Thank yo. Glcocorticoid Receptor Overview & Signaling Mechanism. Biochemistry 4420, Spring Professor Koni Stone.