Differential regulation of CREB and ERK phosphorylation through corticotropin-releasing factor receptors type 1 and 2 in AtT-20 and A7r5 cells

Basolateral amygdala corticotropin-releasing factor receptor type 1 regulates context-cocaine memory strength during reconsolidation in a sex-dependent manner

The basolateral amygdala (BLA) is a critical brain region for cocaine-memory reconsolidation. Corticotropin-releasing factor receptor type 1 (CRFR1) is densely expressed in the BLA, and CRFR1 stimulation can activate intra-cellular signaling cascades that mediate memory reconsolidation. Hence, we tested the hypothesis that BLA CRFR1 stimulation is necessary and sufficient for cocaine-memory reconsolidation. Using an instrumental model of drug relapse, male and female Sprague-Dawley rats received cocaine self-administration training in a distinct environmental context over 10 days followed by extinction training in a different context over 7 days. Next, rats were re-exposed to the cocaine-paired context for 15 min to initiate cocaine-memory retrieval and destabilization. Immediately or 6 h after this session, the rats received bilateral vehicle, antalarmin (CRFR1 antagonist; 500 ng/hemisphere), or corticotropin-releasing factor (CRF; 0.2, 30 or 500 ng/hemisphere) infusions into the BLA. Resulting changes in drug context-induced cocaine seeking (index of context-cocaine memory strength) were assessed three days later. Female rats self-administered more cocaine infusions and exhibited more extinction responding than males. Intra-BLA antalarmin treatment immediately after memory retrieval (i.e., when cocaine memories were labile), but not 6 h later (i.e., after memory reconsolidation), attenuated drug context-induced cocaine seeking at test independent of sex, relative to vehicle. Conversely, intra-BLA CRF treatment increased this behavior selectively in females, in a U-shaped dose-dependent fashion. In control experiments, a high (behaviorally ineffective) dose of CRF treatment did not reduce BLA CRFR1 cell-surface expression in females. Thus, BLA CRFR1 signaling is necessary and sufficient, in a sex-dependent manner, for regulating cocaine-memory strength.

Filamin A is required for somatostatin receptor type 5 expression and pasireotide-mediated signaling in pituitary corticotroph tumor cells

Somatostatin receptor type 5 (SST5) represents the main pharmacological target in the treatment of adrenocorticotroph hormone (ACTH)-secreting tumors. However, molecular predictors of responsiveness to pasireotide require further investigation. The cytoskeleton protein filamin A (FLNA) modulates the responsiveness to somatostatin analogs (SSA) treatment in other types of pituitary tumors by regulating somatostatin receptor type 2 (SST2)/dopamine receptor type 2 (DRD2) expression and activity. Here, we aimed to test the involvement of FLNA in the modulation of SST5 response to SSA in human and murine tumor corticotrophs. Western blot analysis of human corticotropinomas showed that FLNA and SST5 correlate. Both in human primary cultures and AtT-20 cells, FLNA genetic silencing caused a decrease of receptor expression level. Moreover, pasireotide-mediated SST5 downregulation observed in AtT-20 control cells was no further detected in FLNA silenced cells. In AtT-20 cells, in situ PLA experiments revealed an increased number of SST5-FLNA complexes following pasireotide incubation. Finally, FLNA knock down abolished pasireotide-induced SST5 actions on hormone secretion, cell proliferation and apoptosis. In conclusion, FLNA is implicated in SST5 expression modulation and signaling.

The activation of G protein-coupled receptor 30 increases pro-opiomelanocortin gene expression through cAMP/PKA/NR4A pathway in mouse pituitary corticotroph AtT-20 cells

G protein-coupled receptor 30 (GPR30) signaling plays an important role in many regulatory pathways, such as gene expression, cell proliferation and migration. However, whether GPR30 is involved in transcription of the pro-opiomelanocortin (Pomc) gene in pituitary corticotroph cells is currently unknown. Here, we report that GPR30 signaling, activated by the GPR30 specific agonist G-1, increases Pomc expression in the mouse corticotroph cell line AtT-20. G-1 also increased nuclear receptor subfamily 4 group A member 1- and 2-dependent transcription activity and phosphorylation of cyclic adenosine monophosphate response element binding protein. Furthermore, protein kinase A inhibitors strongly attenuated G-1-mediated transactivation. The findings suggest that G-1 stimulates GPR30-mediated mechanisms via cyclic adenosine monophosphate/protein kinase A/nuclear receptor subfamily 4 group A members activity in the regulation of Pomc in corticotroph cells.

Stress-related endogenous neuropeptides induce neuronal excitation in the Laterodorsal Tegmentum

Stress is a physiological response that promotes maintenance of balance against harmful stimuli. Unfortunately, chronic activation of stress systems facilitates the development of psychiatric disorders. A stress-mediated hypercholinergic state could underlie this facilitation, as cholinergic mechanisms have been suggested to play a role in anxiety, depression, and substance use disorder (SUD). Stimulation by stress hormones, urocortin (Ucn1) or corticotropin-releasing factor (CRF), of the CRF receptor type 1 (CRFR1) of acetylcholine-containing neurons of the laterodorsal tegmental nucleus (LDT) could be involved in modulation of cholinergic transmission during periods of stress hormone activation, which could play a role in psychiatric disorders as cholinergic LDT neurons project to, and control activity in, mood-, arousal- and SUD-controlling regions. The present study investigated for the first time the membrane effects and intracellular outcomes of CRFR1 activation by endogenous stress hormones on LDT neurons. Patch clamp recordings of immunohistochemically-identified cholinergic and non-cholinergic LDT neurons with concurrent calcium imaging were used to monitor cellular responses to CRFR1 stimulation with Ucn1 and CRF. Postsynaptically-mediated excitatory currents were elicited in LDT cholinergic neurons, accompanied by an enhancement in synaptic events. In addition, CRFR1 activation resulted in rises in intracellular calcium levels. CRFR1 stimulation recruited MAPK/ERK and SERCA-ATPase involved pathways. The data presented here provide the first evidence that Ucn1 and CRF exert pre and postsynaptic excitatory membrane actions on LDT cholinergic neurons that could underlie the hypercholinergic state associated with stress which could play a role in the heightened risk of psychiatric disorders associated with a chronic stress state.

Impact of USP8 Gene Mutations on Protein Deregulation in Cushing Disease

CONTEXT

Cushing disease (CD) is a rare disorder with severe sequels and incompletely understood pathogenesis. The underlying corticotroph adenomas harbor frequently somatic mutations in the ubiquitin-specific peptidase 8 (USP8) gene. These mutations render USP8 hyperactive and prevent client proteins from degradation.

OBJECTIVE

To investigate the impact of USP8 mutations on proteins deregulated in CD.

DESIGN

One hundred eight pituitary adenomas (75 corticotroph [58 USP8 wild type (WT) and 17 USP8 mutated], 14 somatotroph, and 19 nonfunctioning) were investigated by immunohistochemistry. All evaluated proteins [USP8, arginine vasopressin receptor 1b and 2, corticotropin-releasing hormone receptor, cAMP response element-binding protein (CREB), p27/kip1, cyclin E, heat shock protein 90 (HSP90), orphan nuclear receptor 4, epidermal growth factor receptor, histone deacetylase 2, glucocorticoid receptor, cyclin-dependent kinase 5 and Abelson murine leukemia viral oncogene homolog 1 enzyme substrate 1] were known to be deregulated in CD. Furthermore, AtT20 cells were transfected with USP8 to investigate the expression of possible downstream proteins by immunoblot.

RESULTS

Whereas most of the investigated proteins were not differentially expressed, the cell-cycle inhibitor p27 was significantly reduced in USP8 mutated corticotroph adenoma (H-score 2.0 ± 1.0 vs 1.1 ± 1.1 in WT adenomas; P = 0.004). In contrast, the chaperone HSP90 was expressed higher (0.5 ± 0.4 vs 0.2 ± 0.4; P = 0.29), and the phosphorylation of the transcription factor CREB was increased in USP8 mutated adenomas (1.30.5 ± 0.40.9 vs 0.70.5 ± 0.40.7; P = 0.014). Accordingly, AtT20 cells transfected with the USP8 P720R mutant had higher phosphorylated CREB (pCREB) levels than WT transfected cells (1.3 ± 0.14 vs 1 ± 0.23; P = 0.13).

CONCLUSIONS

We could demonstrate that USP8 mutations are associated with deregulation of p27/kip1, HSP90, and pCREB. These findings suggest that these proteins are direct or indirect clients of USP8 and could therefore be potential targets for therapeutic approaches in patients with CD.

CRF1 Receptor Signaling via the ERK1/2-MAP and Akt Kinase Cascades: Roles of Src, EGF Receptor, and PI3-Kinase Mechanisms

In the present study, we determined the cellular regulators of ERK1/2 and Akt signaling pathways in response to human CRF₁ receptor (CRF₁R) activation in transfected COS-7 cells. We found that Pertussis Toxin (PTX) treatment or sequestering Gβγ reduced CRF₁R-mediated activation of ERK1/2, suggesting the involvement of a G_i-linked cascade. Neither G_s/PKA nor G_q/PKC were associated with ERK1/2 activation. Besides, CRF induced EGF receptor (EGFR) phosphorylation at Tyr¹⁰⁶⁸, and selective inhibition of EGFR kinase activity by AG1478 strongly inhibited the CRF₁R-mediated phosphorylation of ERK1/2, indicating the participation of EGFR transactivation. Furthermore, CRF-induced ERK1/2 phosphorylation was not altered by pretreatment with batimastat, GM6001, or an HB-EGF antibody indicating that metalloproteinase processing of HB-EGF ligands is not required for the CRF-mediated EGFR transactivation. We also observed that CRF induced Src and PYK2 phosphorylation in a Gβγ-dependent manner. Additionally, using the specific Src kinase inhibitor PP2 and the dominant-negative-SrcYF-KM, it was revealed that CRF-stimulated ERK1/2 phosphorylation depends on Src activation. PP2 also blocked the effect of CRF on Src and EGFR (Tyr⁸⁴⁵) phosphorylation, further demonstrating the centrality of Src. We identified the formation of a protein complex consisting of CRF₁R, Src, and EGFR facilitates EGFR transactivation and CRF₁R-mediated signaling. CRF stimulated Akt phosphorylation, which was dependent on G_i/βγ subunits, and Src activation, however, was only slightly dependent on EGFR transactivation. Moreover, PI3K inhibitors were able to inhibit not only the CRF-induced phosphorylation of Akt, as expected, but also ERK1/2 activation by CRF suggesting a PI3K dependency in the CRF₁R ERK signaling. Finally, CRF-stimulated ERK1/2 activation was similar in the wild-type CRF₁R and the phosphorylation-deficient CRF₁R-Δ386 mutant, which has impaired agonist-dependent β-arrestin-2 recruitment; however, this situation may have resulted from the low β-arrestin expression in the COS-7 cells. When β-arrestin-2 was overexpressed in COS-7 cells, CRF-stimulated ERK1/2 phosphorylation was markedly upregulated. These findings indicate that on the base of a constitutive CRF₁R/EGFR interaction, the G_i/βγ subunits upstream activation of Src, PYK2, PI3K, and transactivation of the EGFR are required for CRF₁R signaling via the ERK1/2-MAP kinase pathway. In contrast, Akt activation via CRF₁R is mediated by the Src/PI3K pathway with little contribution of EGFR transactivation.

Comprehensive review of mechanisms of pathogenesis involved in Alzheimer's disease and potential therapeutic strategies

AD is a progressive neurodegenerative disorder and a leading cause of dementia in an aging population worldwide. The enormous challenge which AD possesses to global healthcare makes it as urgent as ever for the researchers to develop innovative treatment strategies to fight this disease. An in-depth analysis of the extensive available data associated with the AD is needed for a more comprehensive understanding of underlying molecular mechanisms and pathophysiological pathways associated with the onset and progression of the AD. The currently understood pathological and biochemical manifestations include cholinergic, Aβ, tau, excitotoxicity, oxidative stress, ApoE, CREB signaling pathways, insulin resistance, etc. However, these hypotheses have been criticized with several conflicting reports for their involvement in the disease progression. Several issues need to be addressed such as benefits to cost ratio with cholinesterase therapy, the dilemma of AChE selectivity over BChE, BBB permeability of peptidic BACE-1 inhibitors, hurdles related to the implementation of vaccination and immunization therapy, and clinical failure of candidates related to newly available targets. The present review provides an insight to the different molecular mechanisms involved in the development and progression of the AD and potential therapeutic strategies, enlightening perceptions into structural information of conventional and novel targets along with the successful applications of computational approaches for the design of target-specific inhibitors.

The Corticotropin-Releasing Factor Family: Physiology of the Stress Response

The physiological stress response is responsible for the maintenance of homeostasis in the presence of real or perceived challenges. In this function, the brain activates adaptive responses that involve numerous neural circuits and effector molecules to adapt to the current and future demands. A maladaptive stress response has been linked to the etiology of a variety of disorders, such as anxiety and mood disorders, eating disorders, and the metabolic syndrome. The neuropeptide corticotropin-releasing factor (CRF) and its relatives, the urocortins 1–3, in concert with their receptors (CRFR1, CRFR2), have emerged as central components of the physiological stress response. This central peptidergic system impinges on a broad spectrum of physiological processes that are the basis for successful adaptation and concomitantly integrate autonomic, neuroendocrine, and behavioral stress responses. This review focuses on the physiology of CRF-related peptides and their cognate receptors with the aim of providing a comprehensive up-to-date overview of the field. We describe the major molecular features covering aspects of gene expression and regulation, structural properties, and molecular interactions, as well as mechanisms of signal transduction and their surveillance. In addition, we discuss the large body of published experimental studies focusing on state-of-the-art genetic approaches with high temporal and spatial precision, which collectively aimed to dissect the contribution of CRF-related ligands and receptors to different levels of the stress response. We discuss the controversies in the field and unravel knowledge gaps that might pave the way for future research directions and open up novel opportunities for therapeutic intervention.

MAGI Proteins Regulate the Trafficking and Signaling of Corticotropin-Releasing Factor Receptor 1 via a Compensatory Mechanism

Corticotropin-releasing factor (CRF) receptor1 (CRFR1) is associated with psychiatric illness and is a proposed target for the treatment of anxiety and depression. Similar to many G protein-coupled receptors (GPCRs), CRFR1 harbors a PDZ (PSD-95/Disc Large/Zona Occludens)-binding motif at the end of its carboxyl-terminal tail. The interactions of PDZ proteins with GPCRs are crucial for the regulation of receptor function. In the present study, we characterize the interaction of all members of the membrane-associated guanylate kinase with inverted orientation PDZ (MAGI) proteins with CRFR1. We show using co-immunoprecipitation that CRFR1 interacts with MAGI-1 and MAGI-3 in human embryonic kidney (HEK293) cells in a PDZ motif-dependent manner. We find that overexpression as well as knockdown of MAGI proteins result in a significant reduction in CRFR1 endocytosis. This effect is dependent on an intact PDZ binding motif for MAGI-2 and MAGI-3 but not MAGI-1. We show that the alteration in expression levels of MAGI-1, MAGI-2 or MAGI-3 can interfere with β-arrestin recruitment to CRFR1. This could explain the effects observed with receptor internalization. We also find that knockdown of endogenous MAGI-1, MAGI-2 or MAGI-3 in HEK293 cells can lead to an enhancement in ERK1/2 signaling but has no effect on cAMP formation. Interestingly, we observe a compensation effect between MAGI-1 and MAGI-3. Taken together, our data suggest that the MAGI proteins, MAGI-1, MAGI-2 and MAGI-3 can regulate β-arrestin-mediated internalization of CRFR1 as well as its signaling and that there is a compensatory mechanism involved in regulating the function of the MAGI subfamily.

Inhibition of heat shock protein 90 decreases ACTH production and cell proliferation in AtT-20 cells

PURPOSE

Cushing's disease is primarily caused by adrenocorticotropic hormone (ACTH)-producing pituitary adenomas. If excision of the tumor from the pituitary, which is the primary treatment for Cushing's disease, is unsuccessful, further medical therapy is needed to treat the resultant hypercortisolism. Some of the drugs used to treat this condition have shown potential therapeutic benefits, but a more effective treatment should be explored for the treatment of Cushing's disease. In the present study, we determined the effect of heat shock protein 90 inhibitors on ACTH production and cell proliferation of AtT-20 corticotroph tumor cells.

METHODS

AtT-20 pituitary corticotroph tumor cells were cultured. The expression levels of mouse proopiomelanocortin (POMC) and pituitary tumor transforming gene 1 (PTTG1) mRNA were evaluated using quantitative real-time PCR. Cellular DNA content was analyzed with fluorescence-activated cell sorting (FACS) analysis. The protein levels were determined by Western blot analysis.

RESULTS

Both 17-allylamino-17-demethoxygeldanamycin and CCT018159 decreased POMC mRNA levels in AtT-20 cells and ACTH levels in the culture medium of these cells, suggesting that both drugs suppress ACTH synthesis and secretion in corticotroph tumor cells. Both drugs also decreased cell proliferation and induced apoptosis. FACS analyses revealed that both agents increased the percentage of AtT-20 cells in the G2/M phase. These drugs decreased cell proliferation, presumably due to the induction of cell death and arrest of the cell cycle in AtT-20 cells. Tumor weight in mice xenografted with AtT-20 cells and treated with CCT018159 was lower than in AtT-20-xenografted control mice. CCT018159 also decreased plasma ACTH levels, and POMC and PTTG1 mRNA levels in the tumor cells.

CONCLUSIONS

CCT018159 inhibits ACTH production and corticotroph tumor cell proliferation in vitro and in vivo.

Role of cystic fibrosis transmembrane conductance regulator-associated ligand (CAL) in regulating the trafficking and signaling of corticotropin-releasing factor receptor 1

Corticotropin releasing factor (CRF) receptor1 (CRFR1) is associated with psychiatric illness and is a proposed target for the treatment of anxiety and depression. Like many G protein-coupled receptors (GPCRs), CRFR1 harbors a PDZ (PSD95/Disc Large/Zona Occludens 1)-binding motif at the end of its carboxyl terminal tail. The interactions of PDZ proteins with GPCRs are crucial for the regulation of their receptor function. In the present study, we characterize the interaction of the cystic fibrosis transmembrane conductance regulator-associated ligand (CAL) with CRFR1. We show using co-immunoprecipitation that the two proteins interact in human embryonic kidney (HEK293) cells in a PDZ motif-dependent manner. We find that the interaction occurs at the Golgi apparatus and that overexpression of CAL retains a proportion of CRFR1 in the intracellular compartment and prevents trafficking to the cell surface. We also demonstrate a significant reduction in the levels of receptor at the plasma membrane upon CAL overexpression, as well as a reduction in internalization. We find that the overexpression of CAL in HEK293 cells resulted in a significant decrease in CRF-stimulated extracellular-regulated protein kinase 1/2 (ERK1/2) phosphorylation, but has no effect on cAMP signaling mediated by the receptor. This effect was dependent on an intact PDZ motif and knockdown of CAL expression using CAL siRNA results in a significant enhancement in ERK1/2 signaling. We show that CAL contributes to the regulation of CRFR1 glycosylation and utilize glycosylation-deficient CRFR1 mutants to further examine the role of glycosylation in the cell surface trafficking of CRFR1. We find that the mutation of Asn residues 90 and 98 results in a reduction in cell surface CRFR1 that is comparable to the effect of CAL overexpression and that these mutants are retained in the Golgi apparatus. Mutation of Asn residues 90 and 98 also results in a decrease in the efficacy for CRF-stimulated cAMP formation mediated by CRFR1. Taken together, our data suggest that CAL can regulate the anterograde trafficking, the internalization as well as the signaling of CRFR1 via modulating the post-translational modifications that the receptor undergoes at the Golgi apparatus.

Aphidicolin inhibits cell proliferation via the p53-GADD45β pathway in AtT-20 cells

Cushing's disease is primarily caused by pituitary corticotroph adenomas, which autonomically secrete adrenocorticotropic hormone (ACTH). ACTH production may be associated with tumor cell proliferation; however, the effects of cell cycle progression on ACTH production and cell proliferation are little known in corticotroph tumor cells. A DNA polymerase inhibitor, aphidicolin, arrests cells at the entrance to the S phase and blocks the cell cycle; aphidicolin also induces apoptosis in tumor cells. In the present study, we determined ACTH production and cell proliferation of AtT-20 corticotroph tumor cells following treatment with aphidicolin. Aphidicolin decreased proopiomelanocortin mRNA levels in AtT-20 cells and the levels of ACTH in the culture medium of these cells. Aphidicolin also decreased cell proliferation and induced apoptosis in AtT-20 cells. Fluorescence-activated cell sorting analyses revealed that this agent increased the percentage of G0/G1 phase cells, and decreased S phase cells. Aphidicolin decreased the phosphorylation of cyclic adenosine monophosphate response element-binding protein and Akt. Aphidicolin increased the levels of tumor protein 27 (p27) and 53 (p53), while it decreased cyclin E levels. Aphidicolin also increased the mRNA levels of the stress response gene growth arrest and DNA damage-inducible 45β (GADD45β), a putative downstream target of p53. The p53 knockdown increased GADD45β mRNA levels. The GADD45β knockdown inhibited the decreases in cell proliferation. Thus, aphidicolin inhibits cell proliferation via the p53-GADD45β pathway in AtT-20 cells.

Inhibitory effects of SOM230 on adrenocorticotropic hormone production and corticotroph tumor cell proliferation in vitro and in vivo

Adrenocorticotropic hormone (ACTH) production by pituitary corticotroph adenomas is the main cause of Cushing's disease. A drug that targets pituitary ACTH-secreting adenomas would aid treatment of Cushing's disease. Octreotide, a somatostatin receptor type 2 (SSTR2)-preferring somatostatin analogue, has no effect on ACTH secretion in patients with Cushing's disease. The multiligand SOM230 (pasireotide) displays a much higher affinity for SSTR1 and SSTR5 than octreotide and suppresses ACTH secretion in cultures of human corticotroph tumors to a greater extent than octreotide. In the present in vitro and in vivo study, we determined the effect of SOM230 on ACTH production and cell proliferation of AtT-20 corticotroph tumor cells. SOM230 decreased proopiomelanocortin (POMC) mRNA levels in AtT-20 cells and ACTH levels in the culture medium of these cells, suggesting that SOM230 suppresses ACTH synthesis and secretion in corticotroph tumor cells. SOM230 also decreased cell proliferation and both cyclic adenosine monophosphate response element-binding protein and Akt phosphorylation in AtT-20 cells. SSTR5 knockdown inhibited the SOM230-induced decreases in cell proliferation. Fluorescence-activated cell sorting analyses revealed that SOM230 did not attenuate cell cycle progression. Tumor weight in mice xenografted with AtT-20 cells and treated with SOM230 was significantly lower than in AtT-20-xenografted control mice. SOM230 also significantly decreased plasma ACTH levels, and POMC and pituitary tumor transforming gene mRNA levels in the tumor cells. Thus, SOM230 inhibits ACTH production and corticotroph tumor cell proliferation in vitro and in vivo.

Tonic modulation of anxiety-like behavior by corticotropin-releasing factor (CRF) type 1 receptor (CRF1) within the medial prefrontal cortex (mPFC) in male mice: role of protein kinase A (PKA)

The medial prefrontal cortex (mPFC) and the neuropeptide corticotropin-releasing factor (CRF) have recently been receiving more attention from those interested in the neurobiology of anxiety. Here, we investigated the CRF pathway in the modulation of anxiety-like behaviors in male mice exposed to the elevated plus-maze (EPM), through intra-mPFC injections of CRF, CP376395 [N-(1-ethylpropyl)-3,6-dimethyl-2-(2,4,6-trimethylphenoxy)-4-pyridinamine hydrochloride, a CRF type 1 receptor antagonist (CR F1)] or H-89 [N-[2-[[3-(4-bromophenyl)-2-propenyl]amino]ethyl]-5-isoquinolinesulfonamide dihydrochloride, a protein kinase (PKA) inhibitor]. We also investigated the effects of intra-mPFC injections of H-89 on the behavioral effects induced by CRF. Mice received bilateral intra-mPFC injections of CRF (0, 37.5, 75 or 150pmol), CP376395 (0, 0.75, 1.5 or 3nmol) or H-89 (0, 1.25, 2.5 or 5nmol) and were exposed to the EPM, to record conventional and complementary measures of anxiety for 5min. Results showed that while CRF (75 and 150pmol) produced an anxiogenic-like effect, CP376395 (all doses) and H-89 (5nmol) attenuated anxiety-like behavior. When injected before CRF (150pmol), intra-mPFC H-89 (2.5nmol, a dose devoid of intrinsic effects on anxiety) completely blocked the anxiogenic-like effects of CRF. These results suggest that (i) CRF plays a tonic anxiogenic-like role at CRF1 receptors within the mPFC, since their blockade per se attenuated anxiety indices and (ii) the anxiogenic-like effects following CRF1 receptor activation depend on cAMP/PKA cascade activation in this limbic forebrain area.

Neuronal extracellular signal-regulated kinase (ERK) activity as marker and mediator of alcohol and opioid dependence

Early pioneering work in the field of biochemistry identified phosphorylation as a crucial post-translational modification of proteins with the ability to both indicate and arbitrate complex physiological processes. More recent investigations have functionally linked phosphorylation of extracellular signal-regulated kinase (ERK) to a variety of neurophysiological mechanisms ranging from acute neurotransmitter action to long-term gene expression. ERK phosphorylation serves as an intracellular bridging mechanism that facilitates neuronal communication and plasticity. Drugs of abuse, including alcohol and opioids, act as artificial yet powerful rewards that impinge upon natural reinforcement processes critical for survival. The graded progression from initial exposure to addiction (or substance dependence) is believed to result from drug- and drug context-induced adaptations in neuronal signaling processes across brain reward and stress circuits following excessive drug use. In this regard, commonly abused drugs as well as drug-associated experiences are capable of modifying the phosphorylation of ERK within central reinforcement systems. In addition, chronic drug and alcohol exposure may drive ERK-regulated epigenetic and structural alterations that underlie a long-term propensity for escalating drug use. Under the influence of such a neurobiological vulnerability, encountering drug-associated cues and contexts can produce subsequent alterations in ERK signaling that drive relapse to drug and alcohol seeking. Current studies are determining precisely which molecular and regional ERK phosphorylation-associated events contribute to the addiction process, as well as which neuroadaptations need to be targeted in order to return dependent individuals to a healthy state.

Melatonin receptor activation suppresses adrenocorticotropin production via BMP-4 action by pituitary AtT20 cells

The role of melatonin, a regulator of circadian rhythm, in adrenocorticotropin (ACTH) production by corticotrope cells has not been elucidated. In this study, we investigated the effect of melatonin on ACTH production in relation to the biological activity of bone morphogenetic protein (BMP)-4 using mouse corticotrope AtT20 cells that express melatonin type-1 (MT1R) but not type-2 (MT2R) receptors. We previously reported that BMP-4 inhibits corticotropin-releasing hormone (CRH)-induced ACTH production and proopiomelanocortin (POMC) transcription by inhibiting MAPK signaling. Both melatonin and an MT1R/MT2R agonist, ramelteon, suppressed CRH-induced ACTH production, POMC transcription and cAMP synthesis. The inhibitory effects of ramelteon on basal and CRH-induced POMC mRNA and ACTH levels were more potent than those of melatonin. Treatment with melatonin or ramelteon in combination with BMP-4 additively suppressed CRH-induced ACTH production. Of note, the level of MT1R expression was upregulated by BMP-4 stimulation. The suppressive effects of melatonin and ramelteon on POMC transcription and cAMP synthesis induced by CRH were not affected by an MT2R antagonist, luzindole. On the other hand, BMP-4-induced Smad1/5/8 phosphorylation and the expression of a BMP target gene, Id-1, were augmented in the presence of melatonin and ramelteon. Considering that the expression levels of BMP receptors, ALK-3/BMPRII, were increased by ramelteon, MT1R action may play an enhancing role in BMP-receptor signaling. Among the MT1R signaling pathways including AKT, ERK and JNK pathways, inhibition of AKT signaling functionally reversed the MT1R effects on both CRH-induced POMC transcription and BMP-4-induced Id-1 transcription. Collectively, MT1R signaling and BMP-4 actions were mutually augmented, leading to fine-tuning of ACTH production by corticotrope cells.

Role of SAP97 protein in the regulation of corticotropin-releasing factor receptor 1 endocytosis and extracellular signal-regulated kinase 1/2 signaling

The corticotropin-releasing factor (CRF) receptor 1 (CRFR1) is a target for the treatment of psychiatric diseases such as depression, schizophrenia, anxiety disorder, and bipolar disorder. The carboxyl-terminal tail of the CRFR1 terminates in a PDZ-binding motif that provides a potential site for the interaction of PSD-95/Discs Large/Zona Occludens 1 (PDZ) domain-containing proteins. In this study, we found that CRFR1 interacts with synapse-associated protein 97 (SAP97; also known as DLG1) by co-immunoprecipitation in human embryonic 293 (HEK 293) cells and cortical brain lysates and that this interaction is dependent upon an intact PDZ-binding motif at the end of the CRFR1 carboxyl-terminal tail. Similarly, we demonstrated that SAP97 is recruited to the plasma membrane in HEK 293 cells expressing CRFR1 and that mutation of the CRFR1 PDZ-binding motif results in the redistribution of SAP97 into the cytoplasm. Overexpression of SAP97 antagonized agonist-stimulated CRFR1 internalization, whereas single hairpin (shRNA) knockdown of endogenous SAP97 in HEK 293 cells resulted in increased agonist-stimulated CRFR1 endocytosis. CRFR1 was internalized as a complex with SAP97 resulting in the redistribution of SAP97 to endocytic vesicles. Overexpression or shRNA knockdown of SAP97 did not significantly affect CRFR1-mediated cAMP formation, but SAP97 knockdown did significantly attenuate CRFR1-stimulated ERK1/2 phosphorylation in a PDZ interaction-independent manner. Taken together, our studies show that SAP97 interactions with CRFR1 attenuate CRFR1 endocytosis and that SAP97 is involved in coupling G protein-coupled receptors to the activation of the ERK1/2 signaling pathway.

New insights into melatonin/CRH signaling in hamster Leydig cells

We have previously described that melatonin inhibits androgen production in hamster testes via melatonin subtype 1a (mel1a) receptors and the local corticotrophin-releasing hormone (CRH) system. This study attempted to determine the initial events of the melatonin/CRH signaling pathway. In Leydig cells from reproductively active Syrian hamsters, Western blotting, reverse transcription quantitative polymerase chain reaction (RT-qPCR) and a colorimetric assay demonstrated that melatonin and CRH activate tyrosine phosphatases and subsequently reduce the phosphorylation levels of extracellular signal-regulated kinase (erk) and c-jun N-terminal kinase (jnk), down-regulate the expression of c-jun, c-fos and steroidogenic acute regulatory (StAR), and inhibit the production of testosterone. These effects were prevented by a highly selective CRH antagonist, thus indicating that melatonin does not exert a direct role. Specific mitogen-activated protein kinase kinase (MEK) and jnk blockers inhibited expression of c-jun, c-fos, StAR and the production of testosterone, confirming that these are events triggered downstream of erk and jnk. In Leydig cells from photoperiodically regressed adult hamsters, CRH inhibited the production of androstane-3α,17β-diol (3α-diol), the main androgen produced, through the same signaling pathway. Testicular melatonin concentration was 3-4-fold higher in reproductively inactive hamsters than that detected in active animals. Since melatonin, CRH, and their receptors are present not only in hamster testes but also in testicular biopsies of infertile men, we can conjecture about the relevance of this previously uncharacterized pathway in human fertility disorders. In summary, our study identifies crucial intracellular events triggered by melatonin/CRH in the testis that lead to a down-regulation of the steroidogenic process.

Differential regulation of gonadotropin-releasing hormone by corticotropin-releasing factor family peptides in hypothalamic N39 cells

Corticotropin-releasing factor (CRF) is involved in a variety of physiological functions including regulation of hypothalamo-pituitary-adrenal axis activity during stressful periods. Urocortins (Ucns) are known to be members of the CRF family peptides. CRF has a high affinity for CRF receptor type 1 (CRF(1) receptor). Both Ucn2 and Ucn3 have very high affinity for CRF receptor type 2 (CRF(2) receptor) with little or no binding affinity for the CRF(1) receptor. Gonadotropin-releasing hormone (GnRH) is known to be involved in the regulation of the stress response. Gonadotropin-inhibitory hormone (GnIH) neurons interact directly with GnRH neurons, and the action of GnIH is mediated by a novel G-protein coupled receptor, Gpr147. This study aimed to explore the possible function of CRF family peptides and the regulation of GnRH mRNA in hypothalamic GnRH cells. Both mRNA and protein expression of the CRF(1) receptor and CRF(2) receptor were found in hypothalamic GnRH N39 cells. CRF suppressed GnRH mRNA levels via the CRF(1) receptor, while Ucn2 increased the levels via the CRF(2) receptor. Both CRF and Ucn2 increased Gpr147 mRNA levels. The results indicate that CRF and Ucn2 can modulate GnRH mRNA levels via each specific CRF receptor subtype. Finally, CRF suppressed GnRH protein levels, while Ucn2 increased the levels. Differential regulation of GnRH by CRF family peptides may contribute to the stress response and homeostasis in GnRH cells.

CRH and SRIF have opposite effects on the Wnt/β-catenin signalling pathway through PKA/GSK-3β in corticotroph pituitary cells

The Wnt/ß-catenin signalling pathway is involved in tumorigenesis including endocrine tumors. We investigated the Wnt/ß-catenin pathway's modulation by corticotropin-releasing hormone (CRH) and somatostatin or somatotropin release-inhibiting factor (SRIF) in mouse pituitary AtT-20 corticotroph cells. The Wnt/β-catenin signalling pathway was activated by CRH and inhibited by SRIF. We provide evidence that cAMP/PKA signalling is involved affecting the GSK-3β phosphorylation status at phospho-GSK-3β (Ser9), thereby altering β-catenin degradation downstream. Furthermore, CRH and SRIF showed concordant effects on cell proliferation. Our data demonstrate an important role of the Wnt/β-catenin pathway in the proliferative control of pituitary corticotroph cells and describe a mechanism for its regulation by CRH and SRIF.

Roles of two subtypes of corticotrophin-releasing factor receptor in the corticostriatal long-term potentiation under cocaine withdrawal condition

The roles of two subtypes of corticotrophin-releasing factor (CRF) receptor in corticostriatal synaptic plasticity under cocaine withdrawal condition were examined in this study. Neither the resting membrane potential and input resistance of striatal neurons nor the long-term potentiation (LTP) of corticostriatal slices were affected by cocaine withdrawal. CRF dose-dependently enhanced in vitro corticostriatal LTP in rats from both cocaine-withdrawal and saline-control groups. Yet, the enhancement of corticostriatal LTP by CRF (20, 40, 80 nM) was significantly greater in the cocaine-withdrawal group than in the control group. CRF(1)-selective antagonist (NBI 27914, 100 nM) attenuated the CRF-induced enhancement of corticostriatal LTP in both groups, whereas the CRF(2)-selective antagonist (astression2B, 100 nM) attenuated the enhanced corticostriatal LTP only in the cocaine-withdrawal group. Importantly, urocortin2 (a CRF(2)-selective agonist, 40 nM) selectively increased corticostriatal LTP in the cocaine-withdrawal group, but not in the saline controls. The urocortin2-induced enhancement of LTP was totally blocked by astression2B (100 nM). These results suggest that the CRF system modulate neuroadaptive changes in the corticostriatal circuit during cocaine withdrawal, and the CRF(2) in this area mediate an important mechanism that contributes to the relapse of cocaine addiction.

New targets of urocortin-mediated cardioprotection

The urocortin (UCN) hormones UCN1 and UCN2 have been shown previously to confer significant protection against myocardial ischaemia/reperfusion (I/R) injury; however, the molecular mechanisms underlying their action are poorly understood. To further define the transcriptional effect of UCNs that underpins their cardioprotective activity, a microarray analysis was carried out using an in vivo rat coronary occlusion model of I/R injury. Infusion of UCN1 or UCN2 before the onset of reperfusion resulted in the differential regulation of 66 and 141 genes respectively, the majority of which have not been described previously. Functional analysis demonstrated that UCN-regulated genes are involved in a wide range of biological responses, including cell death (e.g. X-linked inhibitor of apoptosis protein), oxidative stress (e.g. nuclear factor erythroid derived 2-related factor 1/nuclear factor erythroid derived 2-like 1) and metabolism (e.g. Prkaa2/AMPK). In addition, both UCN1 and UCN2 were found to modulate the expression of a host of genes involved in G-protein-coupled receptor (GPCR) signalling including Rac2, Gnb1, Dab2ip (AIP1), Ralgds, Rnd3, Rap1a and PKA, thereby revealing previously unrecognised signalling intermediates downstream of CRH receptors. Moreover, several of these GPCR-related genes have been shown previously to be involved in mitogen-activated protein kinase (MAPK) activation, suggesting a link between CRH receptors and induction of MAPKs. In addition, we have shown that both UCN1 and UCN2 significantly reduce free radical damage following myocardial infarction, and comparison of the UCN gene signatures with that of the anti-oxidant tempol revealed a significant overlap. These data uncover novel gene expression changes induced by UCNs, which will serve as a platform to further understand their mechanism of action in normal physiology and cardioprotection.

Effects of bone morphogenetic protein (BMP) on adrenocorticotropin production by pituitary corticotrope cells: involvement of up-regulation of BMP receptor signaling by somatostatin analogs

The mechanism by which somatostatin analogs suppress ACTH production by corticotropinomas has yet to be fully elucidated. We here studied the effects of somatostatin analogs on ACTH secretion using mouse corticotrope AtT20 cells focusing on the biological activity of bone morphogenetic proteins (BMPs). BMP ligands, receptors and Smads, and somatostatin receptors (SSTRs)-2, -3, and -5 were expressed in AtT20 cells. BMP-2, -4, -6, and -7 decreased basal ACTH production with BMP-4 effects being the most prominent. BMP-4 also inhibited CRH-induced ACTH production and proopiomelanocortin (POMC) transcription. However, the decrease in CRH-induced cAMP accumulation caused by BMP-4 was not sufficient to completely account for BMP-4 actions, indicating that ACTH suppression by BMPs was not directly linked to cAMP inhibition. CRH-activated ERK1/ERK2, p38-MAPK, stress-activated protein kinase/c-Jun NH(2)-terminal kinase, protein kinase C, and Akt pathways and CRH-induced ACTH synthesis was significantly decreased in the presence of U0126 or SB203580. Because BMPs attenuated CRH-induced ERK and p38 phosphorylation, it was suggested that BMP-4 suppresses ACTH production by inhibiting CRH-induced ERK and p38 phosphorylation. Somatostatin analogs octreotide and pasireotide (SOM230) significantly suppressed CRH-induced ACTH and cAMP production in AtT20 cells and reduced ERK and p38 phosphorylation. Notably, CRH-induced ACTH production was enhanced in the presence of noggin, a BMP-binding protein. The inhibitory effects of octreotide and SOM230 on CRH-induced ACTH production were also attenuated by noggin, implying that the endogenous BMP system plays a key role in inhibiting CRH-induced ACTH production by AtT20 cells. The findings that OCT and SOM230 up-regulated BMP-Smad1/Smad5/Smad8 signaling and ALK-3 and BMPRII and down-regulated inhibitory Smad6/7 establish that the activation of endogenous BMP system is functionally involved in the mechanism by which somatostatin analogs suppress CRH-induced ACTH production.

Neurobiological mechanisms contributing to alcohol-stress-anxiety interactions

This article summarizes the proceedings of a symposium that was presented at a conference entitled "Alcoholism and Stress: A Framework for Future Treatment Strategies." The conference was held in Volterra, Italy on May 6-9, 2008 and this symposium was chaired by Jeff L. Weiner. The overall goal of this session was to review recent findings that may shed new light on the neurobiological mechanisms that underlie the complex relationships between stress, anxiety, and alcoholism. Dr. Danny Winder described a novel interaction between D1 receptor activation and the corticotrophin-releasing factor (CRF) system that leads to an increase in glutamatergic synaptic transmission in the bed nucleus of the stria terminalis. Dr. Marisa Roberto presented recent data describing how protein kinase C epsilon, ethanol, and CRF interact to alter GABAergic inhibition in the central nucleus of the amygdala. Dr. Jeff Weiner presented recent advances in our understanding of inhibitory circuitry within the basolateral amygdala (BLA) and how acute ethanol exposure enhances GABAergic inhibition in these pathways. Finally, Dr. Brian McCool discussed recent findings on complementary glutamatergic and GABAergic adaptations to chronic ethanol exposure and withdrawal in the BLA. Collectively, these investigators have identified novel mechanisms through which neurotransmitter and neuropeptide systems interact to modulate synaptic activity in stress and anxiety circuits. Their studies have also begun to describe how acute and chronic ethanol exposure influence excitatory and inhibitory synaptic communication in these pathways. These findings point toward a number of novel neurobiological targets that may prove useful for the development of more effective treatment strategies for alcohol use disorders.

Corticotropin releasing factor-induced ERK phosphorylation in AtT20 cells occurs via a cAMP-dependent mechanism requiring EPAC2

CRF-induced ERK phosphorylation has been shown to be an important mechanism underlying expression of pro-opiomelanocortin, a key precursor molecule in the hypothalamic pituitary adrenal axis. In AtT20 cells, CRF signalling has been investigated but the mechanism behind CRF-induced ERK activity is not fully understood. This paper elucidates the signalling cascade involved in this phenomenon. Involvement of CRF(1) receptor on ERK phosphorylation was shown by using CRF and urocortin 1. The lack of inhibitory effect of pertussis toxin and BAPTA-AM excluded involvement of G(i)-coupling and calcium mobilization respectively. In contrast, the process is suggested to be driven by cAMP since treatment of AtT20 cells with forskolin triggered strong ERK phosphorylation. Treatment with PKA inhibitors had a minor effect on CRF-induced ERK signalling while phosphorylation of CREB was completely abolished. This ruled out involvement of PKA and suggested a role for exchange protein directly activated by cAMP (EPAC). Moreover, an activator of EPACs 8-(4-methoxyphenylthio)-2'-O-methyladenosine-3',5'-cyclic monophosphate mimicked CRF-induced ERK phosphorylation. Gene expression analysis showed high levels of EPAC2 mRNA and protein but low levels of EPAC1. Knockdown of EPAC2 expression by the use of specific siRNAs abolished CRF- and forskolin-induced ERK phosphorylation. The current study demonstrates a clear cAMP-dependent but PKA-independent mechanism underlying CRF-induced ERK activity that proceeds via EPAC2 signalling. Further research will provide more insight in the role of EPAC2 in CRF signalling.

Constitutive somatostatin receptor activity determines tonic pituitary cell response

Somatostatin (SRIF) binds G protein-coupled SRIF receptor subtypes (SST1, -2, -3, -4, and -5) to regulate cell secretion and proliferation. Hypothalamic SRIF inhibits pituitary growth hormone, thyroid stimulating hormone, and ACTH secretion. We tested SRIF-independent constitutive SST activity in AtT20 mouse pituitary corticotroph cells in which ACTH secretion is highly sensitive to SRIF action. Stable transfectants expressing SST2 or SST5 were sensitized to selective agonist action, and constitutive SST receptor activity was demonstrated by forskolin and pertussis toxin cAMP cell responses. Persistent constitutive SST activity decreased cell ACTH responses to CRH through decreased expression of CRH receptor subtype 1. Decreased dopamine receptor type 1 expression was associated with attenuated dopamine agonist action, whereas responses to isoproterenol were enhanced through increased beta2-adrenoreceptor expression. Thus, integrated pituitary cell ACTH regulation is determined both by phasic SRIF action, as well as by tonic constitutive SST activity, independently of SRIF.

CRHR1-dependent effects on protein expression and posttranslational modification in AtT-20 cells

Corticotropin-releasing hormone (CRH) plays a major role in coordinating the organism's stress response, including the activity of the hypothalamic-pituitary-adrenocortical axis. The molecular underpinnings of CRH-dependent signal transduction mechanisms in the anterior pituitary have not yet been revealed in detail. In order to dissect the signal transduction cascades activated by CRH receptor type 1, a comparative proteome approach was performed in vitro utilizing murine corticotroph AtT-20 cells. Alterations in protein expression and posttranslational modification in response to CRH stimulation were studied by 2D gel electrophoresis. Selected candidates were analyzed by immunoblotting and quantitative real-time PCR. The differential analyses revealed proteins regulated or modified related to diverse cellular processes. Amongst others we identified alterations in PRKAR1A, the regulatory subunit of protein kinase A; in PGK1 and PGAM1, key regulators of glycolysis; and in proteins involved in proteasome-mediated proteolysis, PSMC2 and PSMA3. These results offer novel entry points to molecular mechanisms underlying stress responses elicited via the hypothalamic-pituitary-adrenocortical axis.

Protein kinase C epsilon mediation of CRF- and ethanol-induced GABA release in central amygdala

In the central amygdala (CeA), ethanol acts via corticotrophin-releasing factor (CRF) type 1 receptors to enhance GABA release. Amygdala CRF mediates anxiety associated with stress and drug dependence, and it regulates ethanol intake. Because mutant mice that lack PKCepsilon exhibit reduced anxiety-like behavior and alcohol consumption, we investigated whether PKCepsilon lies downstream of CRF(1) receptors in the CeA. Compared with PKCepsilon(+/+) CeA neurons, PKCepsilon(-/-) neurons showed increased GABAergic tone due to enhanced GABA release. CRF and ethanol stimulated GABA release in the PKCepsilon(+/+) CeA, but not in the PKCepsilon(-/-) CeA. A PKCepsilon-specific inhibitor blocked both CRF- and ethanol-induced GABA release in the PKCepsilon(+/+) CeA, confirming findings in the PKCepsilon(-/-) CeA. These results identify a PKCepsilon signaling pathway in the CeA that is activated by CRF(1) receptor stimulation, mediates GABA release at nerve terminals, and regulates anxiety and alcohol consumption.

Pro-inflammatory cytokine-induced SAPK/MAPK and JAK/STAT in rheumatoid arthritis and the new anti-depression drugs

BACKGROUND

Adult rheumatoid arthritis (RA) patients are frequently clinically depressed. Peripheral inflammation in RA may influence neurotransmitter metabolism, neuroendocrine function, synaptic plasticity, as well as growth factor production, which can modify neural circuitry and contribute to depression.

OBJECTIVE

A convergence between pro-inflammatory cytokine-induced synovial joint inflammation in RA and the effects of pro-inflammatory cytokines on the brain may occur through activation of the stress-activated/mitogen-activated protein kinases (SAPK/MAPK) and/or Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathways.

METHODS

The PubMed and Medlines databases were critically evaluated for evidence of SAPK/MAPK and/or JAK/STAT pathway activation in RA and depression.

RESULTS/CONCLUSION

Some novel anti-depression drugs that were employed in animal models of 'sickness behavior' and in human depression clinical trials suppressed clinical markers of inflammation, as well as SAPK/MAPK and/or JAK/STAT signaling in vitro. Modifying pro-inflammatory cytokine signaling pathways in the brain with antidepressants may also be useful in ameliorating peripheral inflammation in RA.

Inhibitory effects of glucocorticoids on urocortin-mediated increases in interleukin-6 gene expression in rat aortic smooth muscle cells

Urocortin (Ucn) 1, Ucn2, and Ucn3 have potent effects on appetite and the cardiovascular system. Endogenous Ucns in combination with CRF receptor type 2beta may have a physiological role in the cardiovascular system. We previously demonstrated that both Ucn1 and Ucn2 increased IL-6 output levels in A7r5 aortic smooth muscle cells. In the present study, we extended observations on stress or hormone-induced changes in IL-6 gene expression in the cardiovascular system, and determined the effects of glucocorticoids on Ucn-mediated increases in IL-6 mRNA levels, protein levels, and gene transcription activity in A7r5 cells. Ucn1, Ucn2, and Ucn3 all increased IL-6 mRNA levels via CRF receptor type 2. Dexamethasone blocked the ability of Ucn1 to increase IL-6 mRNA and protein levels, while it failed to attenuate the Ucns-mediated changes in cyclic AMP (cAMP)-response element binding protein or extracellular signal-related kinases phosphorylation. Dexamethasone also suppressed Ucn1- or cAMP-stimulated IL-6 gene transcription via a glucocorticoid receptor. Together, these findings demonstrate that glucocorticoids suppress IL-6 gene transcription via Ucn-induced cAMP-dependent pathways in A7r5 cells.