The cannabinoid receptor inverse agonist AM251 regulates the expression of the EGF receptor and its ligands via destabilization of oestrogen-related receptor α protein

Additive anxiolytic-like effect of citicoline and ACPA in the non-acute restraint stress (NARS) and acute restraint stress (ARS) mice

The cannabinoid system plays a key role in stress-related emotional symptoms such as anxiety. Citicoline is a supplemental substance with neuroprotective properties that alleviates anxiety-related behaviors. There is a relation between the actions of cannabinoids and cholinergic systems. So, we decided to evaluate the effects of intracerebroventricular (i.c.v.) infusion of cannabinoid CB1 receptor agents on citicoline-produced response to anxiety-like behaviors in the non-acute restraint stress (NARS) and acute restraint stress (ARS) mice. For i.c.v. microinjection of drugs, a guide cannula was inserted in the left lateral ventricle. ARS was induced by movement restraint for 4 h. Anxiety-related behaviors were assessed using an elevated plus maze (EPM). The results showed that induction of ARS for 4 h decreased the percentage of time spent in the open arms (%OAT) and the percentage of entries to the open arms (%OAE) without affecting locomotor activity, showing anxiogenic-like behaviors. i.c.v. infusion of ACPA (1 µg/mouse) induced an anxiolytic-like effect due to the enhancement of %OAT in the NARS and ARS mice. Nonetheless, i.c.v. microinjection of AM251 (1 µg/mouse) decreased %OAT in the NARS and ARS mice which suggested an anxiogenic-like response. Intraperitoneal (i.p.) administration of citicoline (80 mg/kg) induced an anxiolytic-like effect by the augmentation of %OAT in the ARS mice. Furthermore, when ACPA and citicoline were co-administrated, ACPA potentiated the anxiolytic-like effect induced by citicoline in the NARS and ARS mice. On the other hand, when AM251 and the citicoline were co-injected, AM251 reversed the anxiolytic-like response induced by the citicoline in the NARS and ARS mice. The results of this research exhibited an additive effect between citicoline and ACPA on the induction of anxiolytic-like response in the NARS and ARS mice. Our results indicated an interaction between citicoline and cannabinoid CB1 receptor drugs on the control of anxiety-like behaviors in the NARS and ARS mice.

The cannabinoid receptor 1 antagonist AM6545 stimulates the Akt-mTOR axis and in vivo muscle protein synthesis in a dexamethasone-induced muscle atrophy model

Cannabinoid receptor 1 (CB₁) antagonists were shown to stimulate in vitro muscle protein synthesis, but this has never been confirmed in vivo. Therefore, this study investigated whether treatment with the CB₁ antagonist AM6545 upregulates in vivo muscle anabolism. Chronic AM6545 treatment stimulated the Akt-mTOR axis and protein synthesis (+22%; p = 0.002) in the Tibialis Anterior, which protected mice from dexamethasone-induced muscle loss (-1% vs. -6% compared to healthy controls; p = 0.02). Accordingly, acute AM6545 treatment stimulated protein synthesis (+44%; p = 0.04) in the Tibialis Anterior but not Soleus. The anabolic upregulation was accompanied by ERK1/2 activation, whereas protein kinase A signaling remained unaffected, suggesting a CB₁-independent mechanism. The present study for the first time shows that the CB₁ antagonist AM6545 can upregulate the Akt-mTOR axis and in vivo muscle protein synthesis. However, future work applying genetic approaches should further uncover the signaling pathways via which AM6545 enhances muscle anabolism.

Cannabinoid Receptor-1 suppresses M2 macrophage polarization in colorectal cancer by downregulating EGFR

Cannabinoid receptors, CB1 and CB2, have been implicated as emerging targets for cancer therapy. Herein, we investigated the potential regulation mechanism of CB1 and its implications in colorectal cancer. CB1 and EGFR expression were examined in colorectal cancer cell lines. The effects of CB1 agonist ACEA and its antagonist AM251 on the proliferation, migration and invasion of colorectal cancer cells and the expression of M1 and M2 macrophage markers were examined. EGFR overexpression was performed with plasmids containing EGFR gene. Tumor xenografts were constructed to explore the effects of CB1 activation on tumorigenesis. We showed that CB1 was downregulated while EGFR was upregulated in colorectal cancer cells. The activation of CB1 suppressed the proliferation, migration and invasion of colorectal cancer cells and the differentiation of M2 macrophages, while CB1 inhibition had opposite effects. Moreover, the alterations in tumorigenesis and M2 macrophage activation induced by CB1 activation were counteracted by EGFR overexpression. Besides, CB1 silencing promoted tumor cell proliferation and M2 polarization which was counteracted by EGFR knockdown. In vivo, CB1 activation also repressed tumorigenesis and M2 macrophage activation. The present study demonstrated that CB1 activation suppressed M2 macrophage through EGFR downregulation in colorectal cancers. These findings first unveiled the potential avenue of CB1 as a targeted therapy for colorectal cancer.

The Endocannabinoid System: A Potential Target for the Treatment of Various Diseases

The Endocannabinoid System (ECS) is primarily responsible for maintaining homeostasis, a balance in internal environment (temperature, mood, and immune system) and energy input and output in living, biological systems. In addition to regulating physiological processes, the ECS directly influences anxiety, feeding behaviour/appetite, emotional behaviour, depression, nervous functions, neurogenesis, neuroprotection, reward, cognition, learning, memory, pain sensation, fertility, pregnancy, and pre-and post-natal development. The ECS is also involved in several pathophysiological diseases such as cancer, cardiovascular diseases, and neurodegenerative diseases. In recent years, genetic and pharmacological manipulation of the ECS has gained significant interest in medicine, research, and drug discovery and development. The distribution of the components of the ECS system throughout the body, and the physiological/pathophysiological role of the ECS-signalling pathways in many diseases, all offer promising opportunities for the development of novel cannabinergic, cannabimimetic, and cannabinoid-based therapeutic drugs that genetically or pharmacologically modulate the ECS via inhibition of metabolic pathways and/or agonism or antagonism of the receptors of the ECS. This modulation results in the differential expression/activity of the components of the ECS that may be beneficial in the treatment of a number of diseases. This manuscript in-depth review will investigate the potential of the ECS in the treatment of various diseases, and to put forth the suggestion that many of these secondary metabolites of Cannabis sativa L. (hereafter referred to as "C. sativa L." or "medical cannabis"), may also have potential as lead compounds in the development of cannabinoid-based pharmaceuticals for a variety of diseases.

The Complex Interplay between Endocannabinoid System and the Estrogen System in Central Nervous System and Periphery

The endocannabinoid system (ECS) is a lipid cell signaling system involved in the physiology and homeostasis of the brain and peripheral tissues. Synaptic plasticity, neuroendocrine functions, reproduction, and immune response among others all require the activity of functional ECS, with the onset of disease in case of ECS impairment. Estrogens, classically considered as female steroid hormones, regulate growth, differentiation, and many other functions in a broad range of target tissues and both sexes through the activation of nuclear and membrane estrogen receptors (ERs), which leads to genomic and non-genomic cell responses. Since ECS function overlaps or integrates with many other cell signaling systems, this review aims at updating the knowledge about the possible crosstalk between ECS and estrogen system (ES) at both central and peripheral level, with focuses on the central nervous system, reproduction, and cancer.

Overexpression of cannabinoid receptor 1 promotes renal cell carcinoma progression

Renal cell carcinoma (RCC) is a common urologic tumor with a poor prognosis. Cannabinoid receptor 1 (CB1), which is a G protein-coupled receptor, has recently been reported to participate in the genesis and development of various cancers. However, the exact role of CB1 in RCC is unknown. The aim of this study was to determine the role of CB1 in RCC cell lines and RCC prognosis, thus underlying its potential as a therapeutic target. Immunohistochemistry and western blots were performed to investigate the expression of CB1 in RCC tissues and to determine its clinicopathological significance in RCC patients. Additionally, we explored CB1 expression in RCC cell lines and evaluated the effect of AM251, a CB1 inverse agonist, and in vitro siRNA knockdown of CB1 on the cellular proliferation, migration, and apoptosis of RCC cell lines. CB1 was overexpressed in cancerous tissues compared with adjacent normal tissues. Furthermore, CB1 expression levels were an independent risk factor for overall survival for RCC patients. AM251 significantly decreased tumor cell proliferation and induced cell apoptosis by upregulating the expression of the pro-apoptotic protein Bax and decreasing the expression of the anti-apoptotic proteins survivin and Bcl-2. Migration of the RCC cell lines was also significantly inhibited after treatment with AM251 compared with untreated control groups. In addition, knockdown of CB1 expression significantly decreased cell proliferation and invasion and significantly increased apoptosis of RCC cells. CB1 expression is functionally associated to cellular proliferation, apoptosis, and invasion ability of RCC. Our data suggest that CB1 might be a potential target for RCC clinical therapy.

Selective GPR55 antagonism reduces chemoresistance in cancer cells

G protein-coupled receptor 55 (GPR55) possesses pro-oncogenic activity and its function can be competitively inhibited with (R,R')-4'-methoxy-1-naphthylfenoterol (MNF) through poorly defined signaling pathways. Here, the anti-tumorigenic effect of MNF was investigated in the human pancreatic cancer cell line, PANC-1, by focusing on the expression of known cancer biomarkers and the expression and function of multidrug resistance (MDR) exporters such as P-glycoprotein (Pgp) and breast cancer resistance protein (BCRP). Incubation of PANC1 cells with MNF (1μM) for 24h significantly decreased EGF receptor, pyruvate kinase M2 (PKM2), and β-catenin protein levels and was accompanied by significant reduction in nuclear accumulation of HIF-1α and the phospho-active forms of PKM2 and β-catenin. Inhibition of GPR55 with either MNF or the GPR55 antagonist CID 16020046 lowered the amount of MDR proteins in total cellular extracts while diminishing the nuclear expression of Pgp and BCRP. There was significant nuclear accumulation of doxorubicin in PANC-1 cells treated with MNF and the pre-incubation with MNF increased the cytotoxicity of doxorubicin and gemcitabine in these cells. Potentiation of doxorubicin cytotoxicity by MNF was also observed in MDA-MB-231 breast cancer cells and U87MG glioblastoma cells, which express high levels of GPR55. The data suggest that inhibition of GPR55 activity produces antitumor effects via attenuation of the MEK/ERK and PI3K-AKT pathways leading to a reduction in the expression and function of MDR proteins.

Endocannabinoid system as a regulator of tumor cell malignancy - biological pathways and clinical significance

The endocannabinoid system (ECS) comprises cannabinoid receptors (CBs), endogenous cannabinoids, and enzymes responsible for their synthesis, transport, and degradation of (endo)cannabinoids. To date, two CBs, CB1 and CB2, have been characterized; however, orphan G-protein-coupled receptor GPR55 has been suggested to be the third putative CB. Several different types of cancer present abnormal expression of CBs, as well as other components of ECS, and this has been shown to correlate with the clinical outcome. Although most effects of (endo)cannabinoids are mediated through stimulation of classical CBs, they also interact with several molecules, either prosurvival or proapoptotic molecules. It should be noted that the mode of action of exogenous cannabinoids differs significantly from that of endocannabinoid and results from the studies on their activity both in vivo and in vitro could not be easily compared. This review highlights the main signaling pathways involved in the antitumor activity of cannabinoids and the influence of their activation on cancer cell biology. We also discuss changes in the expression pattern of the ECS in various cancer types that have an impact on disease progression and patient survival. A growing amount of experimental data imply possible exploitation of cannabinoids in cancer therapy.

Research progress on the reproductive and non-reproductive endocrine tumors by estrogen-related receptors

Oncologists have traditionally considered that tumorigenesis are closely related to classical nuclear estrogen receptors (ERs), such as estrogen receptor alpha (ERα) and estrogen receptor beta (ERβ), through the ligands binding and target gene transcription induction. Estrogen-related receptors (ERRs) have similar structures with ERs, which are also gradually thought to be relevant to reproductive endocrine tumor diseases, even non-reproductive endocrine tumors. In this review, different subtypes of ERRs and their structures firstly will be introduced, then the expression patterns in gynecological oncology (i.e., breast cancer, endometrial cancer, and ovarian cancer), male genitourinary system malignancy especially prostatic cancer along with other non-reproductive endocrine tumors (i.e., lung cancer, colorectal cancer, and liver cancer) will be described, and simultaneously the role of tumorigenesis related to ERRs will be discussed. Therefore, the review is benefit to explore the way of tumor prevention and treatment.

Encapsulation of cannabinoid drugs in nanostructured lipid carriers

This study describes the development and optimization of a method to encapsulate the potent and expensive cannabinoids drugs in nanostructured lipid carriers; namely, URB597, AM251 and rimonabant have been considered. NLC production by melt and ultrasonication protocol has been specifically designed to optimize nanoparticle recovery and drug encapsulation efficiency. Special care has been devoted to the modality of oil and water phase emulsification and the entire production has been studied and discussed. NLC recovery, morphology, dimensional distribution and encapsulation efficiency are presented.

AM251 induces apoptosis and G2/M cell cycle arrest in A375 human melanoma cells

Human cutaneous melanoma is an aggressive and chemotherapy-resistant type of cancer. AM251 is a cannabinoid type 1 (CB1) receptor antagonist/inverse agonist with off-target antitumor activity against pancreatic and colon cancer cells. The current study aimed to characterize the in-vitro antimelanoma activity of AM251. The BRAF V600E mutant melanoma cell line, A375, was used as an in-vitro model system. Characterization tools included a cell viability assay, nuclear morphology assessment, gene expression, western blot, flow cytometry with Annexin V-FITC/7-AAD double staining, cell cycle analyses, and measurements of changes in intracellular cAMP and calcium concentrations. AM251 exerted a marked cytotoxic effect against A375 human melanoma cells with potency comparable with that observed for cisplatin without significant changes in the human dermal fibroblasts viability. AM251, at a concentration that approximates the IC50, downregulated genes encoding antiapoptotic proteins (BCL2 and survivin) and increased transcription levels of proapoptotic BAX, induced alteration of Annexin V reactivity, DNA fragmentation, chromatin condensation in the cell nuclei, and G2/M phase arrest.AM251 also induced a 40% increase in the basal cAMP levels, but it did not affect intracellular calcium concentrations. The involvement of GPR55, TRPA1, and COX-2 in the AM251 mechanism of action was excluded. The combination of AM251 with celecoxib produced a synergistic antitumor activity, although the mechanism underlying this effect remains to be elucidated. This study provides the first evidence of a proapoptotic effect and G2/M cell cycle arrest of AM251 on A375 cells. This compound may be a potential prototype for the development of promising diarylpyrazole derivatives to be evaluated in human cutaneous melanoma.

Estrogen-related receptor α is required for efficient human cytomegalovirus replication

An shRNA-mediated screen of the 48 human nuclear receptor genes identified multiple candidates likely to influence the production of human cytomegalovirus in cultured human fibroblasts, including the estrogen-related receptor α (ERRα), an orphan nuclear receptor. The 50-kDa receptor and a 76-kDa variant were induced posttranscriptionally following infection. Genetic and pharmacological suppression of the receptor reduced viral RNA, protein, and DNA accumulation, as well as the yield of infectious progeny. In addition, RNAs encoding multiple metabolic enzymes, including enzymes sponsoring glycolysis (enolase 1, triosephosphate isomerase 1, and hexokinase 2), were reduced when the function of ERRα was inhibited in infected cells. Consistent with the effect on RNAs, a substantial number of metabolites, which are normally induced by infection, were either not increased or were increased to a reduced extent in the absence of normal ERRα activity. We conclude that ERRα is needed for the efficient production of cytomegalovirus progeny, and we propose that the nuclear receptor contributes importantly to the induction of a metabolic environment that supports optimal cytomegalovirus replication.

The estrogen-related receptor α inverse agonist XCT 790 is a nanomolar mitochondrial uncoupler

XCT 790 is widely used to inhibit estrogen-related receptor α (ERRα) activity as an inverse agonist. Here, we report that XCT 790 potently activates AMP kinase (AMPK) in a dose-dependent and ERRα-independent manner, with active concentrations more than 25-fold below those typically used to perturb ERRα. AMPK activation is secondary to inhibition of energy production as XCT 790 rapidly depletes the pool of cellular ATP. A concomitant increase in oxygen consumption rates suggests uncoupling of the mitochondrial electron transport chain. Consistent with this, XCT 790 decreased mitochondrial membrane potential without affecting mitochondrial mass. Therefore, XCT 790 is a potent, fast-acting, mitochondrial uncoupler independent of its inhibition of ERRα. The biological activity together with structural features in common with the chemical uncouplers FCCP and CCCP indicates likely mode of action as a proton ionophore.

The influence of monoacylglycerol lipase inhibition upon the expression of epidermal growth factor receptor in human PC-3 prostate cancer cells

Background

It has been reported that direct activation of the cannabinoid CB₁ receptor in epidermal growth factor (EGR)-stimulated PC-3 prostate cancer cells results in an anti-proliferative effect accompanied by a down-regulation of EGF receptors (EGFR). In the present study, we investigated whether similar effects are seen following inhibition of the endocannabinoid hydrolytic enzyme monoacylglycerol lipase (MGL).

Results

CB₁ receptor expression levels were found to differ greatly between two experimental series conducted using PC-3 cells. The monoacylglycerol lipase inhibitor JZL184 increased levels of 2-arachidonoylglycerol in the PC-3 cells without producing changes in the levels of anandamide and related N-acylethanolamines. In the first series of experiments, JZL184 produced a small mitogenic effect for cells that had not been treated with EGF, whereas an anti-proliferative effect was seen for EGF-treated cells. An anti-proliferative effect for the EGF-treated cells was also seen with the CB receptor agonist CP55,940. In the second batch of cells, there was an interaction between JZL184 and CB₁ receptor expression densities in linear regression analyses with EGFR expression as the dependent variable.

Conclusions

Inhibition of MGL by JZL184 can affect EGFR expression. However, the use in our hands of PC-3 cells as a model to investigate the therapeutic potential of MGL inhibitors and related compounds is compromised by their variability of CB₁ receptor expression.

Novel drugs that target the estrogen-related receptor alpha: their therapeutic potential in breast cancer

THE INCIDENCE OF BREAST CANCER CONTINUES TO RISE

1.7 million women were diagnosed with and 521,000 women died from breast cancer in 2012. This review considers first current treatment options: surgery; radiotherapy; and systemic endocrine, anti-biological, and cytotoxic therapies. Clinical management includes prevention, early detection by screening, treatment with curative intent, management of chronic disease, and palliative control of advanced breast cancer. Next, the potential of novel drugs that target DNA repair, growth factor dependence, intracellular and intercellular signal transduction, and cell cycle are considered. Estrogen-related receptor alpha has attracted attention as a therapeutic target in triple-negative breast cancers with de novo resistance to, and in breast cancers with acquired resistance to, endocrine therapies such as antiestrogens and aromatase inhibitors. Estrogen-related receptor alpha is an orphan receptor and transcription factor. Its activity is regulated by coregulator proteins and posttranslational modification. It is an energy sensor that controls adaptation to energy demand and may facilitate glycolytic metabolism and mitochondrial oxidative respiration in breast cancer cells. Estrogen-related receptor alpha increases breast cancer cell migration, proliferation, and tumor development. It is expressed at high levels in estrogen receptor-negative tumors, and is proposed to activate estrogen-responsive genes in endocrine-resistant tumors. The structures and functions of the ligand-binding domains of estrogen receptor alpha and estrogen-related receptor alpha, their ability to bind estrogens, phytoestrogens, and synthetic ligands, and the effects of ligand agonists, antagonists, and inverse agonists on biological activity, are evaluated. Synthetic ligands of estrogen-related receptor alpha have activity in preclinical models of metabolic disorders, diabetes, osteoporosis, and oncology. The clinical settings in which these novel drugs might have utility in the management of advanced breast cancer, and biomarkers for stratification of patients likely to benefit, are discussed. Finally, the potential side effects of the novel drugs on metabolism, osteoporosis, osteo-metastasis, and cachexia are considered.

Inhibitory signaling by CB1 receptors in smooth muscle mediated by GRK5/β-arrestin activation of ERK1/2 and Src kinase

We examined whether CB1 receptors in smooth muscle conform to the signaling pattern observed with other Gi-coupled receptors that stimulate contraction via two Gβγ-dependent pathways (PLC-β3 and phosphatidylinositol 3-kinase/integrin-linked kinase). Here we show that the anticipated Gβγ-dependent signaling was abrogated. Except for inhibition of adenylyl cyclase via Gαi, signaling resulted from Gβγ-independent phosphorylation of CB1 receptors by GRK5, recruitment of β-arrestin1/2, and activation of ERK1/2 and Src kinase. Neither uncoupling of CB1 receptors from Gi by pertussis toxin (PTx) or Gi minigene nor expression of a Gβγ-scavenging peptide had any effect on ERK1/2 activity. The latter was abolished in muscle cells expressing β-arrestin1/2 siRNA. CB1 receptor internalization and both ERK1/2 and Src kinase activities were abolished in cells expressing kinase-deficient GRK5(K215R). Activation of ERK1/2 and Src kinase endowed CB1 receptors with the ability to inhibit concurrent contractile activity. We identified a consensus sequence (102KSPSKLSP109) for phosphorylation of RGS4 by ERK1/2 and showed that expression of a RGS4 mutant lacking Ser103/Ser108 blocked the ability of anandamide to inhibit acetylcholine-mediated phosphoinositide hydrolysis or enhance Gαq:RGS4 association and inactivation of Gαq. Activation of Src kinase by anandamide enhanced both myosin phosphatase RhoA-interacting protein (M-RIP):RhoA and M-RIP:MYPT1 association and inhibited Rho kinase activity, leading to increase of myosin light chain (MLC) phosphatase activity and inhibition of sustained muscle contraction. Thus, unlike other Gi-coupled receptors in smooth muscle, CB1 receptors did not engage Gβγ but signaled via GRK5/β-arrestin activation of ERK1/2 and Src kinase: ERK1/2 accelerated inactivation of Gαq by RGS4, and Src kinase enhanced MLC phosphatase activity, leading to inhibition of ACh-stimulated contraction.

(R,R')-4'-methoxy-1-naphthylfenoterol targets GPR55-mediated ligand internalization and impairs cancer cell motility

(R,R')-4'-Methoxy-1-naphthylfenoterol (MNF) promotes growth inhibition and apoptosis of human HepG2 hepatocarcinoma cells via cannabinoid receptor (CBR) activation. The synthetic CB1R inverse agonist, AM251, has been shown to block the anti-mitogenic effect of MNF in these cells; however, AM251 is also an agonist of the recently deorphanized, lipid-sensing receptor, GPR55, whose upregulation contributes to carcinogenesis. Here, we investigated the role of MNF in GPR55 signaling in human HepG2 and PANC-1 cancer cell lines in culture by focusing first on internalization of the fluorescent ligand Tocrifluor 1117 (T1117). Initial results indicated that cell pretreatment with GPR55 agonists, including the atypical cannabinoid O-1602 and l-α-lysophosphatidylinositol, dose-dependently reduced the rate of cellular T1117 uptake, a process that was sensitive to MNF inhibition. GPR55 internalization and signaling mediated by O-1602 was blocked by MNF in GPR55-expressing HEK293 cells. Pretreatment of HepG2 and PANC-1 cells with MNF significantly abrogated the induction of ERK1/2 phosphorylation in response to AM251 and O-1602. Moreover, MNF exerted a coordinated negative regulation of AM251 and O-1602 inducible processes, including changes in cellular morphology and cell migration using scratch wound healing assay. This study shows for the first time that MNF impairs GPR55-mediated signaling and, therefore, may have therapeutic potential in the management of cancer.

A novel control of human keratin expression: cannabinoid receptor 1-mediated signaling down-regulates the expression of keratins K6 and K16 in human keratinocytes in vitro and in situ

Cannabinoid receptors (CB) are expressed throughout human skin epithelium. CB1 activation inhibits human hair growth and decreases proliferation of epidermal keratinocytes. Since psoriasis is a chronic hyperproliferative, inflammatory skin disease, it is conceivable that the therapeutic modulation of CB signaling, which can inhibit both proliferation and inflammation, could win a place in future psoriasis management. Given that psoriasis is characterized by up-regulation of keratins K6 and K16, we have investigated whether CB1 stimulation modulates their expression in human epidermis. Treatment of organ-cultured human skin with the CB1-specific agonist, arachidonoyl-chloro-ethanolamide (ACEA), decreased K6 and K16 staining intensity in situ. At the gene and protein levels, ACEA also decreased K6 expression of cultured HaCaT keratinocytes, which show some similarities to psoriatic keratinocytes. These effects were partly antagonized by the CB1-specific antagonist, AM251. While CB1-mediated signaling also significantly inhibited human epidermal keratinocyte proliferation in situ, as shown by K6/Ki-67-double immunofluorescence, the inhibitory effect of ACEA on K6 expression in situ was independent of its anti-proliferative effect. Given recent appreciation of the role of K6 as a functionally important protein that regulates epithelial wound healing in mice, it is conceivable that the novel CB1-mediated regulation of keratin 6/16 revealed here also is relevant to wound healing. Taken together, our results suggest that cannabinoids and their receptors constitute a novel, clinically relevant control element of human K6 and K16 expression.

The biarylpyrazole compound AM251 alters mitochondrial physiology via proteolytic degradation of ERRα

The orphan nuclear receptor estrogen-related receptor alpha (ERRα) directs the transcription of nuclear genes involved in energy homeostasis control and the regulation of mitochondrial mass and function. A crucial role for controlling ERRα-mediated target gene expression has been ascribed to the biarylpyrazole compound 1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-1-piperidinyl-1H-pyrazole-3-carboxamide (AM251) through direct binding to and destabilization of ERRα protein. Here, we provide evidence that structurally related AM251 analogs also have negative impacts on ERRα protein levels in a cell-type-dependent manner while having no deleterious actions on ERRγ. We show that these off-target cellular effects of AM251 are mediated by proteasomal degradation of nuclear ERRα. Cell treatment with the nuclear export inhibitor leptomycin B did not prevent AM251-induced destabilization of ERRα protein, whereas proteasome inhibition with MG132 stabilized and maintained its DNA-binding function, indicative of ERRα being a target of nuclear proteasomal complexes. NativePAGE analysis revealed that ERRα formed a ∼220-kDa multiprotein nuclear complex that was devoid of ERRγ and the coregulator peroxisome proliferator-activated receptor γ coactivator-1. AM251 induced SUMO-2,3 incorporation in ERRα in conjunction with increased protein kinase C activity, whose activation by phorbol ester also promoted ERRα protein loss. Down-regulation of ERRα by AM251 or small interfering RNA led to increased mitochondria biogenesis while negatively impacting mitochondrial membrane potential. These results reveal a novel molecular mechanism by which AM251 and related compounds alter mitochondrial physiology through destabilization of ERRα.