Adiponectin (15-36) stimulates steroidogenic acute regulatory (StAR) protein expression and cortisol production in human adrenocortical cells:role of AMPK and MAPK kinase pathways

Adiponectin is an abundantly circulating adipokine, orchestrating its effects through two 7-transmembrane receptors (AdipoR1 and AdipoR2). Steroidogenesis is regulated by a variety of neuropeptides and adipokines. Earlier studies have reported adipokine mediated steroid production. A key rate-limiting step in steroidogenesis is cholesterol transportation across the mitochondrial membrane by steroidogenic acute regulatory protein (StAR). Several signalling pathways regulate StAR expression. The actions of adiponectin and its role in human adrenocortical steroid biosynthesis are not fully understood. The aim of this study was to investigate the effects of adiponectin on StAR protein expression, steroidogenic genes, and cortisol production and to dissect the signalling cascades involved in the activation of StAR expression. Using qRT-PCR, Western blot analysis and ELISA, we have demonstrated that stimulation of human adrenocortical H295R cells with adiponectin results in increased cortisol secretion. This effect is accompanied by increased expression of key steroidogenic pathway genes including StAR protein expression via ERK1/2 and AMPK-dependent pathways. This has implications for our understanding of adiponectin receptor activation and peripheral steroidogenesis. Finally, our study aims to emphasise the key role of adipokines in the integration of metabolic activity and energy balance partly via the regulation of adrenal steroid production.

The mammalian MAPK/ERK pathway exhibits properties of a negative feedback amplifier

Three-tiered kinase modules, such as the Raf-MEK (mitogen-activated or extracellular signal-regulated protein kinase kinase)-ERK (extracellular signal-regulated kinase) mitogen-activated protein kinase pathway, are widespread in biology, suggesting that this structure conveys evolutionarily advantageous properties. We show that the three-tiered kinase amplifier module combined with negative feedback recapitulates the design principles of a negative feedback amplifier (NFA), which is used in electronic circuits to confer robustness, output stabilization, and linearization of nonlinear signal amplification. We used mathematical modeling and experimental validation to demonstrate that the ERK pathway has properties of an NFA that (i) converts intrinsic switch-like activation kinetics into graded linear responses, (ii) conveys robustness to changes in rates of reactions within the NFA module, and (iii) stabilizes outputs in response to drug-induced perturbations of the amplifier. These properties determine biological behavior, including activation kinetics and the response to drugs.

Compartmentalization of the MAPK scaffold protein KSR1 modulates synaptic plasticity in hippocampal neurons

ERK1/2 is required for certain forms of synaptic plasticity, including the long-term potentiation of synaptic strength. However, the molecular mechanisms regulating synaptically localized ERK1/2 signaling are poorly understood. Here, we show that the MAPK scaffold protein kinase suppressor of Ras 1 (KSR1) is directly phosphorylated by the downstream kinase ERK1/2. Quantitative Western blot analysis further demonstrates that expression of mutated, feedback-deficient KSR1 promotes sustained ERK1/2 activation in HEK293 cells in response to EGF stimulation, compared to a more transient activation in control cells expressing wild-type KSR1. Immunocytochemistry and confocal imaging of primary hippocampal neurons from newborn C57BL6 mice further show that feedback phosphorylation of KSR1 significantly reduces its localization to dendritic spines. This effect can be reversed by tetrodotoxin (1 μM) or PD184352 (2 μM) treatment, further suggesting that neuronal activity and phosphorylation by ERK1/2 lead to KSR1 removal from the postsynaptic compartment. Consequently, electrophysiological recordings in hippocampal neurons expressing wild-type or feedback-deficient KSR1 demonstrate that KSR1 feedback phosphorylation restricts the potentiation of excitatory postsynaptic currents. Our findings, therefore, suggest that feedback phosphorylation of the scaffold protein KSR1 prevents excessive ERK1/2 signaling in the postsynaptic compartment and thus contributes to maintaining physiological levels of synaptic excitability. © FASEB.

Negative feedback regulation of the ERK1/2 MAPK pathway

The extracellular signal-regulated kinase 1/2 (ERK1/2) mitogen-activated protein kinase (MAPK) signalling pathway regulates many cellular functions, including proliferation, differentiation, and transformation. To reliably convert external stimuli into specific cellular responses and to adapt to environmental circumstances, the pathway must be integrated into the overall signalling activity of the cell. Multiple mechanisms have evolved to perform this role. In this review, we will focus on negative feedback mechanisms and examine how they shape ERK1/2 MAPK signalling. We will first discuss the extensive number of negative feedback loops targeting the different components of the ERK1/2 MAPK cascade, specifically the direct posttranslational modification of pathway components by downstream protein kinases and the induction of de novo gene synthesis of specific pathway inhibitors. We will then evaluate how negative feedback modulates the spatiotemporal signalling dynamics of the ERK1/2 pathway regarding signalling amplitude and duration as well as subcellular localisation. Aberrant ERK1/2 activation results in deregulated proliferation and malignant transformation in model systems and is commonly observed in human tumours. Inhibition of the ERK1/2 pathway thus represents an attractive target for the treatment of malignant tumours with increased ERK1/2 activity. We will, therefore, discuss the effect of ERK1/2 MAPK feedback regulation on cancer treatment and how it contributes to reduced clinical efficacy of therapeutic agents and the development of drug resistance.

Identification des voies de MAPK activées par la surexpression du récepteur [alpha]₁�-adrénergique dans le coeur de souris

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Cartographe dynamique des voies de signalisation MAPK chez la levure Saccharomyces cerevisiae

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Upstream mechanisms responsible for H₂O₂-induced activation of MAPK and PKB in vascular smooth muscle cells

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Mécanisme d'intégration des signaux RTK-dépendants par la protéine d'échafaudage CNK au sein de la voie de signalsiation RAS/MAPK chez la drosophile

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

Caractérisation de la fonction de CNK dans la régulation du mécanisme de signalisation du module MAPK/ERK chez la drosophile

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

Régulation de la MAPK atypique ERK3 par le système ubiquitine-protéasome

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

Identification des voies de MAPK activées par la surexpression du récepteur [alpha]₁�-adrénergique dans le coeur de souris

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Cartographe dynamique des voies de signalisation MAPK chez la levure Saccharomyces cerevisiae

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Upstream mechanisms responsible for H₂O₂-induced activation of MAPK and PKB in vascular smooth muscle cells

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Mécanisme d'intégration des signaux RTK-dépendants par la protéine d'échafaudage CNK au sein de la voie de signalsiation RAS/MAPK chez la drosophile.

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

Caractérisation de la fonction de CNK dans la régulation du mécanisme de signalisation du module MAPK/ERK chez la drosophile

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.