Manifestation of Novel Social Challenges of the European Unionin the Teaching Material ofMedical Biotechnology Master’s Programmesat the University of Pécs and at the University of DebrecenIdentification number: TÁMOP-4.1.2-08/1/A-2009-0011

NON-GENOMIC STEROID RECEPTOR SIGNALING PATHWAYS

Tímea Berki and Ferenc BoldizsárSignal transduction

Manifestation of Novel Social Challenges of the European Unionin the Teaching Material ofMedical Biotechnology Master’s Programmesat the University of Pécs and at the University of DebrecenIdentification number: TÁMOP-4.1.2-08/1/A-2009-0011

TÁMOP-4.1.2-08/1/A-2009-0011

Glucocorticoid action

• The name glucocorticoid (glucose + cortex + steroid) derives from their role in the regulation of the metabolism of glucose, their synthesis in the adrenal cortex, and their steroidal structure.

• The glucocorticoid receptor is present in all vertebrate cell type

DexamethasoneCortisol

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Basics

• Some steroid effects can be detected within minutes eg. ion-currents change, membrane changes, phosphorylation changes

• Treatment of acute conditions: asthma, allergies, shock – high dose steroids exert rapid effects

• Apoptosis-inducing capacity

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GR signaling pathways

RE

Plasma membrane

Nucleus

Other cytoplasmic signaling proteins

Hormone

mReceptor

Mitochondrion

Gene expression

?

cReceptor

Cytoplasm

HSP90

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GR signaling pathways

• Genomic (“classical”)• Direct membrane effect• Membrane GR• Interaction with cytoplasmic signaling

proteins• Mitochondrial translocation

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Genomic steroid actions

GRE

Milliseconds (?) Seconds-minutes (?)Hours-days

Multiple co-regulators

TFs

Nucleus

Dimerization

Binding

Molecular assembly

?

?

Levels ofregulation

CBG bindingin blood

MDR in themembrane

Metabolism andnuclear receptor fate

Transcription GRE RE

RNAs

Proteins

TFs

G-ptoteincoupled receptor

Ion channel Ionotropic receptor

Ion pump

Nucleus

MR/GRSteroid G-protein Neurotransmitter

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Slow Medium slow Rapid

Transmembrane currentsPhosphorylation events

Calcium levels

Plasma membrane

Cytoplasm

Glucocorticoid

mGR

cGR

Specific cGRdependent effects

Specific mGRdependent effects Nonspecific GC

effects

GRE

TF

nGRE pGRE

Transrepression Transactivation

Genomic GC effects Nongenomic GC effects

Genomic and non-genomic GC effects

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Evidences

• Binding of corticosteroids to the glucocorticoid receptor (GR) stimulates PIP3K and protein kinase AKT, leading to eNOS activation and vasorelaxation

• Membrane associated GR has been shown to mediate lymphocytolysis

• In addition, some glucocorticoids have been shown to rapidly inhibit the release of the inflammatory prostaglandin PGE2

• A multi-protein complex composed of the unliganded glucocorticoid receptor, Hsp90, and the tyrosine kinases LCK and FYN is recruited to the antigen activated T cell receptor (TCR). This GR complex is necessary for TCR signalling. On binding of glucocorticoids to GR, this multi-protein complex dissociates blocking TCR signalling

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Direct membrane effects

• Human RBC• High-dose steroid treatment influenced the membrane lipid

mobility in mammary cancer cell line • Increased membrane lipid mobility in LPS treated B

lymphocytes • Inhibited membrane transport of Na+ and Ca2+, and increased

the H+ uptake into the mitochondria • In canine kidney epithel cell system there is a direct effect of

DX on tight junction formation • 20 min cortisol treatment caused changes in the excitability of

principal basolateral amygdala neurons

GCs, especially at high doses, could change plasma membrane physico-chemical properties due to their lipid soluble nature.

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Membrane GR

• Rodent and human lymphoid cell lines • Amphibian brain • Correlation between the mGR expression and the cell

cycle-dependent GC-induced apoptosis sensitivity of a human leukaemia cell line

• Presence of the mGR correlates with GC-resistance of a cell type (Sionov)

• Human blood monocytes and B cells • mGR+ monocyte frequency increased in rheumatoid

arthritis, SLE and ankylosing spondylitis patients

What pathways are activated by the mGR???

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Evidences for mitochondrial GR

• Upon ligand binding the glucocorticoid receptor can directly translocate to the mitochondria in both lymphoid and non-lymphoid cells where it can initiate the apoptotic cascade

• Ligand-induced mitochondrial GR translocation showed a close correlation with the GC-induced apoptosis sensitivity of several cell types

• In CD4+CD8+ (DP) thymocytes the GR translocates to the mitochondria rather than to the nucleus upon short-term in vitro GC treatment correlating with the high GC-induced apoptosis sensitivity of this cell type

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Mitochondrial GR actions

In the mitochondria, the GR might act through diverse mechanisms:• Act as mitochondrial transcription factor• Interaction with other mitochondrial transcription

factors• Interaction with pro- and anti-apoptotic proteins (eg.

Bcl-2 family proteins)• Decreasing the mitochondrial membrane potential

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Ligand induced mitochondrial GR translocation in DP thymocytes

DICCD4CD8 GR

CMX-Ros

GR+CMX-Ros DIC

CD4CD8 GR

CMX-Ros

GR+CMX-Ros

Kontroll DX

Number of mitochondria-GR colocalised pixels

*

0

100

200

300

400

500Ctrl

DX

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Mitochondrial GR translocation

Mitochondrion

cReceptor

HSP90

Membranepotential ↓

DNA Bcl-2 family

Otherproteins

APOPTOSIS

Transcriptionfactors

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Summary of genomic and non-genomic glucocorticoid effects

RE

Plasma membrane

Nucleus

Other cytoplasmic signaling proteins

Hormone

mReceptor

Mitochondrion

Gene expression

?

cReceptor

Cytoplasm

HSP90