Retinoic acid activates monoamine oxidase B promoter in human neuronal cells

Dissection of an impact of VDR and RXRA on the genomic activity of 1,25(OH)2D3 in A431 squamous cell carcinoma

BACKGROUND

Human skin is the natural source, place of metabolism, and target for vitamin D3. The classical active form of vitamin D3, 1,25(OH)2D3, expresses pluripotent properties and is intensively studied in cancer prevention and therapy. To define the specific role of vitamin D3 receptor (VDR) and its co-receptor retinoid X receptor alpha (RXRA) in genomic regulation, VDR or RXRA genes were silenced in the squamous cell carcinoma cell line A431 and treated with 1,25(OH)2D3 at long incubation time points 24 h/72 h. Extending the incubation time of A431 WT (wild-type) cells with 1,25(OH)2D3 resulted in a two-fold increase in DEGs (differentially expressed genes) and a change in the amount of downregulated from 37% to 53%. VDR knockout led to a complete loss of 1,25(OH)2D3-induced genome-wide gene regulation at 24 h time point, but after 72 h, 20 DEGs were found, of which 75% were downregulated, and most of them belonged to the gene ontology group "immune response". This may indicate the existence of an alternative, secondary response to 1,25(OH)2D3. In contrast, treatment of A431 ΔRXRA cells with 1,25(OH)2D3 for 24 h only partially affected DEGs, suggesting RXRA-independent regulation. Interestingly, overexpression of classic 1,25(OH)2D3 targets, like CYP24A1 (family 24 of subfamily A of cytochrome P450 member 1) or CAMP (cathelicidin antimicrobial peptide) was found to be RXRA-independent. Also, immunofluorescence staining of A431 WT cells revealed partial VDR/RXRA colocalization after 24 h and 72 h 1,25(OH)2D3 treatment. Comparison of transcriptome changes induced by 1,25(OH)2D3 in normal keratinocytes vs. cancer cells showed high cell type specific expression pattern with only a few genes commonly regulated by 1,25(OH)2D3. Activation of the genomic pathway at least partially reversed the expression of cancer-related genes, forming a basis for anti-cancer activates of 1,25(OH)2D3. In summary, VDR or RXRA independent genomic activities of 1,25(OH)2D3 suggest the involvement of alternative factors, opening new challenges in this field.

Cholinergic signaling via muscarinic M1 receptor confers resistance to docetaxel in prostate cancer

Docetaxel is the most commonly used chemotherapy for advanced prostate cancer (PC), including castration-resistant disease (CRPC), but the eventual development of docetaxel resistance constitutes a major clinical challenge. Here, we demonstrate activation of the cholinergic muscarinic M1 receptor (CHRM1) in CRPC cells upon acquiring resistance to docetaxel, which is manifested in tumor tissues from PC patients post- vs. pre-docetaxel. Genetic and pharmacological inactivation of CHRM1 restores the efficacy of docetaxel in resistant cells. Mechanistically, CHRM1, via its first and third extracellular loops, interacts with the SEMA domain of cMET and forms a heteroreceptor complex with cMET, stimulating a downstream mitogen-activated protein polykinase program to confer docetaxel resistance. Dicyclomine, a clinically available CHRM1-selective antagonist, reverts resistance and restricts the growth of multiple docetaxel-resistant CRPC cell lines and patient-derived xenografts. Our study reveals a CHRM1-dictated mechanism for docetaxel resistance and identifies a CHRM1-targeted combinatorial strategy for overcoming docetaxel resistance in PC.

Stromal-derived MAOB promotes prostate cancer growth and progression

Prostate cancer (PC) develops in a microenvironment where the stromal cells modulate adjacent tumor growth and progression. Here, we demonstrated elevated levels of monoamine oxidase B (MAOB), a mitochondrial enzyme that degrades biogenic and dietary monoamines, in human PC stroma, which was associated with poor clinical outcomes of PC patients. Knockdown or overexpression of MAOB in human prostate stromal fibroblasts indicated that MAOB promotes cocultured PC cell proliferation, migration, and invasion and co-inoculated prostate tumor growth in mice. Mechanistically, MAOB induces a reactive stroma with activated marker expression, increased extracellular matrix remodeling, and acquisition of a protumorigenic phenotype through enhanced production of reactive oxygen species. Moreover, MAOB transcriptionally activates CXCL12 through Twist1 synergizing with TGFβ1-dependent Smads in prostate stroma, which stimulates tumor-expressed CXCR4-Src/JNK signaling in a paracrine manner. Pharmacological inhibition of stromal MAOB restricted PC xenograft growth in mice. Collectively, these findings characterize the contribution of MAOB to PC and suggest MAOB as a potential stroma-based therapeutic target.

Bidirectional Cross-talk between MAOA and AR Promotes Hormone-Dependent and Castration-Resistant Prostate Cancer

Androgen receptor (AR) is the primary oncogenic driver of prostate cancer, including aggressive castration-resistant prostate cancer (CRPC). The molecular mechanisms controlling AR activation in general and AR reactivation in CRPC remain elusive. Here we report that monoamine oxidase A (MAOA), a mitochondrial enzyme that degrades monoamine neurotransmitters and dietary amines, reciprocally interacts with AR in prostate cancer. MAOA was induced by androgens through direct AR binding to a novel intronic androgen response element of the MAOA gene, which in turn promoted AR transcriptional activity via upregulation of Shh/Gli-YAP1 signaling to enhance nuclear YAP1-AR interactions. Silencing MAOA suppressed AR-mediated prostate cancer development and growth, including CRPC, in mice. MAOA expression was elevated and positively associated with AR and YAP1 in human CRPC. Finally, genetic or pharmacologic targeting of MAOA enhanced the growth-inhibition efficacy of enzalutamide, darolutamide, and apalutamide in both androgen-dependent and CRPC cells. Collectively, these findings identify and characterize an MAOA-AR reciprocal regulatory circuit with coamplified effects in prostate cancer. Moreover, they suggest that cotargeting this complex may be a viable therapeutic strategy to treat prostate cancer and CRPC. SIGNIFICANCE: MAOA and AR comprise a positive feedback loop in androgen-dependent and CRPC, providing a mechanistic rationale for combining MAOA inhibition with AR-targeted therapies for prostate cancer treatment.

MAOA-mediated reprogramming of stromal fibroblasts promotes prostate tumorigenesis and cancer stemness

The tumor microenvironment plays a critical role in prostate cancer (PC) development and progression. Inappropriate activation of the stroma potentiates the growth and transformation of epithelial tumor cells. Here, we show that upregulation of monoamine oxidase A (MAOA), a mitochondrial enzyme that degrades monoamine neurotransmitters and dietary amines, in stromal cells elevates production of reactive oxygen species, triggers an inflammatory response including activation of IL-6, and promotes tumorigenesis in vitro and in vivo. Mechanistically, MAOA enhances IL-6 transcription through direct Twist1 binding to a conserved E-box element at the IL-6 promoter. MAOA in stromal fibroblasts provides tumor cell growth advantages through paracrine IL-6/STAT3 signaling. Tissue microarray analysis revealed co-expression correlations between individual pairs of proteins of the stromal MAOA-induced Twist1/IL-6/STAT3 pathway in clinical specimens. Downstream of stromal MAOA, STAT3 also promotes cell stemness and transcriptionally activates expression of cancer stem cell marker CD44 in PC cells. MAOA inhibitor treatment effectively suppressed prostate tumor growth in mice in a stroma-specific targeted manner. Collectively, these findings characterize the contribution of MAOA to stromal activation in PC pathogenesis and provide a rationale for targeting MAOA in stromal cells to treat PC.

Monoamine oxidase isoenzymes: genes, functions and targets for behavior and cancer therapy

Monoamine oxidase (MAO) catalyzes the oxidative deamination of monoamine neurotransmitters and dietary amines. Two pharmacological types with different substrate and inhibitor specificities were reported. Molecular cloning revealed that the two types of MAO were different genes expressed as different proteins with different functions. MAO A and B have identical intron-exon organization derived by duplication of a common ancestral gene thus they are termed isoenzymes. MAO A knockout mice exhibited aggression, the first clear evidence linking genes to behavior. MAO A KO mice exhibited autistic-like behaviors which could be prevented by reducing serotonin levels at an early developmental age (P1-P7) providing potential therapy. MAO B KO mice were non-aggressive and resistant to Parkinsongenic neurotoxin. More recently it was found that MAO A is overexpressed in prostate cancer and correlates with degree of malignancy. The oncogenic mechanism involves a ROS-activated AKT/FOXO1/TWIST1 signaling pathway. Deletion of MAO A reduced prostate cancer stem cells and suppressed invasive adenocarcinoma. MAO A was also overexpressed in classical Hodgkin lymphoma and glioma brain tumors. MAO B was overexpressed in glioma and non-small cell lung cancer. MAO A inhibitors reduce the growth of prostate cancer, drug sensitive and resistant gliomas and classical Hodgkin lymphoma, and enhance standard chemotherapy. Currently, we are developing NIR dye-conjugated clorgyline (MAO A inhibitor) as a novel dual therapeutic/diagnostic agent for cancer. A phase II clinical trial of MAO inhibitor for biochemical recurrent prostate cancer is ongoing. The role of MAO A and B in several cancer types opens new avenues for cancer therapies.

R1 Regulates Prostate Tumor Growth and Progression By Transcriptional Suppression of the E3 Ligase HUWE1 to Stabilize c-Myc

Prostate cancer is a prevalent public health problem, especially because noncutaneous advanced malignant forms significantly affect the lifespan and quality of life of men worldwide. New therapeutic targets and approaches are urgently needed. The current study reports elevated expression of R1 (CDCA7L/RAM2/JPO2), a c-Myc-interacting protein and transcription factor, in human prostate cancer tissue specimens. In a clinical cohort, high R1 expression is associated with disease recurrence and decreased patient survival. Overexpression and knockdown of R1 in human prostate cancer cells indicate that R1 induces cell proliferation and colony formation. Moreover, silencing R1 dramatically reduces the growth of prostate tumor xenografts in mice. Mechanistically, R1 increases c-Myc protein stability by inhibiting ubiquitination and proteolysis through transcriptional suppression of HUWE1, a c-Myc-targeting E3 ligase, via direct interaction with a binding element in the promoter. Moreover, transcriptional repression is supported by a negative coexpression correlation between R1 and HUWE1 in a prostate cancer clinical dataset. Collectively, these findings, for the first time, characterize the contribution of R1 to prostate cancer pathogenesis. IMPLICATIONS: These findings provide evidence that R1 is a novel regulator of prostate tumor growth by stabilizing c-Myc protein, meriting further investigation of its therapeutic and prognostic potential.

Monoamine Oxidase Deficiency Causes Prostate Atrophy and Reduces Prostate Progenitor Cell Activity

Monoamine oxidases (MAOs) degrade a number of biogenic and dietary amines, including monoamine neurotransmitters, and play an essential role in many biological processes. Neurotransmitters and related neural events have been shown to participate in the development, differentiation, and maintenance of diverse tissues and organs by regulating the specialized cellular function and morphological structures of innervated organs such as the prostate. Here we show that mice lacking both MAO isoforms, MAOA and MAOB, exhibit smaller prostate mass and develop epithelial atrophy in the ventral and dorsolateral prostates. The cellular composition of prostate epithelium showed reduced CK5⁺ or p63⁺ basal cells, accompanied by lower Sca-1 expression in p63⁺ basal cells, but intact differentiated CK8⁺ luminal cells in MAOA/B-deficient mouse prostates. MAOA/B ablation also decreased epithelial cell proliferation without affecting cell apoptosis in mouse prostates. Using a human prostate epithelial cell line, we found that stable knockdown of MAOA and MAOB impaired the capacity of prostate stem cells to form spheres, coinciding with a reduced CD133⁺ /CD44⁺ /CD24^- stem cell population and less expression of CK5 and select stem cell markers, including ALDH1A1, TROP2, and CD166. Alternative pharmacological inhibition of MAOs also repressed prostate cell stemness. In addition, we found elevated expression of MAOA and MAOB in epithelial and/or stromal components of human prostate hyperplasia samples compared with normal prostate tissues. Taken together, our findings reveal critical roles for MAOs in the regulation of prostate basal progenitor cells and prostate maintenance. Stem Cells 2018;36:1249-1258.

Heptamethine carbocyanine dye-mediated near-infrared imaging of canine and human cancers through the HIF-1α/OATPs signaling axis

Near-infrared (NIR) fluorescence imaging agents are promising tools for noninvasive cancer imaging. This study explored the specific uptake and retention of a NIR heptamethine carbocyanine MHI-148 dye by canine cancer cells and tissues and human prostate cancer (PCa) specimens and also the dye uptake mechanisms. The accumulation of MHI-148 was detected specifically in canine cancer cells and tissues and freshly harvested human PCa tissues xenografted in mice by NIR fluorescence microscopy and whole-body NIR optical imaging. Specific dye uptake in canine spontaneous tumors was further confirmed by PET imaging. Higher hypoxia-inducible factor-1α (HIF-1α) and organic anion-transporting polypeptide (OATP) protein and mRNA expression was demonstrated by multiplex quantum dots labeling and qPCR in tumors over that of normal tissues. Treating cancer cells with HIF-1α stabilizers activated HIF-1α downstream target genes, induced OATP superfamily gene expression and enhanced cellular uptake and retention of NIR dyes. Moreover, silencing HIF-1α by siRNA significantly decreased OATP mRNA expression and blocked NIR dye uptake in cancer cells. Together, these results demonstrated the preferential uptake of NIR dyes by canine and human cancer cells and tissues via the HIF-1α/OATPs signaling axis, which provides insights into future application of these dyes for cancer detection and treatment.

All-trans retinoic acid up-regulates the human CD2AP gene expression through Sp1/Sp3 binding sites

All-trans retinoic acid (ATRA), an active metabolite of vitamin A, plays an important role in regulating cell differentiation, proliferation, and apoptosis. It was reported that ATRA could cause an up-regulation of protein expression of CD2AP in nephrotic animals. However, the mechanism of ATRA-mediated up-regulation is not well understood. In the present study, deletion analysis and luciferase assays demonstrated that ATRA caused a marked increase in the activity of the CD2AP promoter, and the region between nt -599 and -328 from the transcription start site, where there are two clusters of Sp1/3 binding sites, was indispensable for ATRA-mediated up-regulation. Chromatin immunoprecipitation assays revealed that ATRA activated the CD2AP transcription through enhancing the DNA-binding activity of Sp1 and Sp3 with the CD2AP promoter. Taken together, this study provided evidence for the first time showing the stimulating effect of ATRA on CD2AP and new therapeutic strategies for the treatment of nephritic syndrome and other associated diseases of CD2AP deficiency.

Inhibition of Excessive Monoamine Oxidase A/B Activity Protects Against Stress-induced Neuronal Death in Huntington Disease

Monoamine oxidases (MAO) are important components of the homeostatic machinery that maintains the levels of monoamine neurotransmitters, including dopamine, in balance. Given the imbalance in dopamine levels observed in Huntington disease (HD), the aim of this study was to examine MAO activity in a mouse striatal cell model of HD and in human neural cells differentiated from control and HD patient-derived induced pluripotent stem cell (hiPSC) lines. We show that mouse striatal neural cells expressing mutant huntingtin (HTT) exhibit increased MAO expression and activity. We demonstrate using luciferase promoter assays that the increased MAO expression reflects enhanced epigenetic activation in striatal neural cells expressing mutant HTT. Using cellular stress paradigms, we further demonstrate that the increase in MAO activity in mutant striatal neural cells is accompanied by enhanced susceptibility to oxidative stress and impaired viability. Treatment of mutant striatal neural cells with MAO inhibitors ameliorated oxidative stress and improved cellular viability. Finally, we demonstrate that human HD neural cells exhibit increased MAO-A and MAO-B expression and activity. Altogether, this study demonstrates abnormal MAO expression and activity and suggests a potential use for MAO inhibitors in HD.

Near-infrared fluorescence imaging of cancer mediated by tumor hypoxia and HIF1α/OATPs signaling axis

Near-infrared fluorescence (NIRF) imaging agents are promising tools for noninvasive cancer imaging. Here, we explored the mechanistic properties of a specific group of NIR heptamethine carbocyanines including MHI-148 dye we identified and synthesized, and demonstrated these dyes to achieve cancer-specific imaging and targeting via a hypoxia-mediated mechanism. We found that cancer cells and tumor xenografts exhibited hypoxia-dependent MHI-148 dye uptake in vitro and in vivo, which was directly mediated by hypoxia-inducible factor 1α (HIF1α). Microarray analysis and dye uptake assay further revealed a group of hypoxia-inducible organic anion-transporting polypeptides (OATPs) responsible for dye uptake, and the correlation between OATPs and HIF1α was manifested in progressive clinical cancer specimens. Finally, we demonstrated increased uptake of MHI-148 dye in situ in perfused clinical tumor samples with activated HIF1α/OATPs signaling. Our results establish these NIRF dyes as potential tumor hypoxia-dependent cancer-targeting agents and provide a mechanistic rationale for continued development of NIRF imaging agents for improved cancer detection, prognosis and therapy.

Monoamine oxidase A mediates prostate tumorigenesis and cancer metastasis

Tumors from patients with high-grade aggressive prostate cancer (PCa) exhibit increased expression of monoamine oxidase A (MAOA), a mitochondrial enzyme that degrades monoamine neurotransmitters and dietary amines. Despite the association between MAOA and aggressive PCa, it is unclear how MAOA promotes PCa progression. Here, we found that MAOA functions to induce epithelial-to-mesenchymal transition (EMT) and stabilize the transcription factor HIF1α, which mediates hypoxia through an elevation of ROS, thus enhancing growth, invasiveness, and metastasis of PCa cells. Knockdown and overexpression of MAOA in human PCa cell lines indicated that MAOA induces EMT through activation of VEGF and its coreceptor neuropilin-1. MAOA-dependent activation of neuropilin-1 promoted AKT/FOXO1/TWIST1 signaling, allowing FOXO1 binding at the TWIST1 promoter. Importantly, the MAOA-dependent HIF1α/VEGF-A/FOXO1/TWIST1 pathway was activated in high-grade PCa specimens, and knockdown of MAOA reduced or even eliminated prostate tumor growth and metastasis in PCa xenograft mouse models. Pharmacological inhibition of MAOA activity also reduced PCa xenograft growth in mice. Moreover, high MAOA expression in PCa tissues correlated with worse clinical outcomes in PCa patients. These findings collectively characterize the contribution of MAOA in PCa pathogenesis and suggest that MAOA has potential as a therapeutic target in PCa.

Does isotretinoin therapy of acne cure or cause depression?

Cosmetic defects in acne may provoke a wide range of mental disorders (depressive, social-phobic, etc.). Isotretinoin is a very effective acne treatment; hence, it usually resolves the associated mental disorders. However, more available data show the possible association of taking isotretinoin and the onset of a depressive syndrome that includes frank depression and even suicidal ideation. The frequency of depressive disorders during isotretinoin treatment varies from 1% to 11% in different studies, and it is unclear whether this is a consequence of isotretinoin therapy. Since it crosses the blood-brain barrier, isotretinoin affects the expression of a broad spectrum of genes in the limbic structures, thus affecting the function of the dopaminergic, serotonergic, and noradrenergic neurons involved in the regulation of mood and emotion. It was suggested that isotretinoin in high concentrations inhibits hippocampal neurogenesis and induces apoptosis of hippocampal cells. However, some studies do not confirm this pathogenic role, and isotretinoin was even reported to have a therapeutic effect in acne-associated depression. In this review, we highlight epidemiological data, the underlying molecular pathogenesis, and the aspects of prevention concerning retinoid-induced depression in acne from the practical point of view of a dermatologist.

Sp sites contribute to basal and inducible expression of the human TNIP1 (TNFα-inducible protein 3-interacting protein 1) promoter

TNIP1 [TNFα (tumour necrosis factor α)-induced protein 3-interacting protein 1] is a co-repressor of RAR (retinoic acid receptor) and PPAR (peroxisome-proliferator-activated receptor). Additionally, it can reduce signalling stemming from cell membrane receptors such as those for TNFα and EGF (epidermal growth factor). Consequently, it influences a variety of receptor-mediated events as diverse as transcription, programmed cell death and cell cycling. Thus changes in TNIP1 expression levels are likely to affect multiple important biological end points. TNIP1 expression level changes have been linked to psoriasis and systemic sclerosis. As such, it is crucial to determine what controls its expression levels, starting with constitutive control of its promoter. Our analysis of the TNIP1 promoter revealed multiple transcription start sites in its GC-rich proximal regions along with two transcriptionally active Sp (specificity protein) sites, responsive to both Sp1 and Sp3. EMSA (electrophoretic mobility-shift assay) and ChIP (chromatin immunoprecipitation) demonstrated physical binding between Sp1 and Sp3 at these sites. A decrease in Sp1 protein levels via siRNA (short interfering RNA) or diminished Sp1 DNA binding by mithramycin decreased TNIP1 mRNA levels. This Sp-binding GC-rich region of the TNIP1 promoter also participates in transcriptional activation by ligand-bound RAR. Together, these results demonstrate newly identified regulators of TNIP1 expression and suggest possible transcription factor targets which in turn control TNIP1-related biological end points ranging from apoptosis to inflammatory diseases.

The expression of KLF11 (TIEG2), a monoamine oxidase B transcriptional activator in the prefrontal cortex of human alcohol dependence

BACKGROUND

The biochemical pathways underlying alcohol abuse and dependence are not well understood, although brain cell loss and neurotoxicity have been reported in subjects with alcohol dependence. Monoamine oxidase B (MAO B; an enzyme that catabolizes neurotransmitters such as dopamine) is consistently increased in this psychiatric illness. MAO B has been implicated in the pathogenesis of alcohol dependence and alcohol-induced brain neurotoxicity. Recently, the cell growth inhibitor protein, Kruppel-like factor 11 (KLF11), has been reported to be an MAO transcriptional activator. KLF11 is also known as TIEG2 (transforming growth factor-beta-inducible early gene 2) and mediates apoptotic cell death. This study investigates the protein expression of KLF11 and its relationship with MAO B using human postmortem prefrontal cortex from subjects with alcohol dependence.

METHODS

Twelve subjects with alcohol dependence and the respective psychiatrically normal control subjects were investigated. Expression of KLF11 and MAO B proteins in the prefrontal cortex was measured by Western blot analysis. Correlation studies involving KLF11 and MAO B protein expression were performed. Localization of KLF11 in the human prefrontal cortex was also determined by immunohistochemistry.

RESULTS

Levels of KLF11 protein were significantly increased by 44% (p < 0.03) in the postmortem prefrontal cortex of subjects with alcohol dependence as compared to age- and gender-matched, psychiatrically normal control subjects. Furthermore, KLF11 levels were significantly and positively correlated with both the increased MAO B protein levels and blood alcohol content in alcohol-dependent subjects. In addition, KLF11 protein expression was visualized in both neuronal and glial cells.

CONCLUSIONS

This novel study shows the important role of KLF11, an MAO transcriptional activator, in human alcohol dependence. It further supports that the KLF11-MAO B cell death cascade may contribute to chronic alcohol-induced brain damage. This argues a case for KLF11-MAO B inhibition as a novel therapeutic strategy that may impact this highly prevalent illness.

Csn3 gene is regulated by all-trans retinoic acid during neural differentiation in mouse P19 cells

κ-Casein (CSN3) is known to play an essential role in controlling the stability of the milk micelles. We found that the expression of Csn3 was induced by all-trans retinoic acid (ATRA) during neural differentiation in P19 embryonal carcinoma cells from our study using DNA microarray. In this paper, we describe the detailed time course of Csn3 expression and the induction mechanism of Csn3 transcription activation in this process. The Csn3 expression was induced rapidly and transiently within 24 h of ATRA treatment. Retinoic acid receptor (RAR)-specific agonists were used in expression analysis to identify the RAR subtype involved upregulation of Csn3; a RARα-specific agonist mimicked the effects of ATRA on induction of Csn3 expression. Therefore, RARα may be the RAR subtype mediating the effects of ATRA on the induction of Csn3 gene transcription in this differentiation-promoting process of P19 cells. We found that the promoter region of Csn3 contained a typical consensus retinoic acid response element (RARE), and this RARE was necessary for ATRA-dependent transcriptional regulation. We confirmed that RARα bound to this RARE sequence in P19 cells. These findings indicated that the Csn3 expression is upregulated via ATRA-bound RARα and binding of this receptor to the RARE in the Csn3 promoter region. This will certainly serve as a first step forward unraveling the mysteries of induction of Csn3 in the process of neural differentiation.

Monoamine oxidases in development

Monoamine oxidases (MAOs) are flavoproteins of the outer mitochondrial membrane that catalyze the oxidative deamination of biogenic and xenobiotic amines. In mammals there are two isoforms (MAO-A and MAO-B) that can be distinguished on the basis of their substrate specificity and their sensitivity towards specific inhibitors. Both isoforms are expressed in most tissues, but their expression in the central nervous system and their ability to metabolize monoaminergic neurotransmitters have focused MAO research on the functionality of the mature brain. MAO activities have been related to neurodegenerative diseases as well as to neurological and psychiatric disorders. More recently evidence has been accumulating indicating that MAO isoforms are expressed not only in adult mammals, but also before birth, and that defective MAO expression induces developmental abnormalities in particular of the brain. This review is aimed at summarizing and critically evaluating the new findings on the developmental functions of MAO isoforms during embryogenesis.

Human TNFα-induced protein 3-interacting protein 1 (TNIP1) promoter activation is regulated by retinoic acid receptors

Coregulator proteins play key roles in transcriptional control by members of the nuclear receptor superfamily. Previously, we demonstrated that tumor necrosis factor α (TNFα)-induced protein 3-interacting protein 1 (TNIP1) is a corepressor of agonist-bound retinoic acid receptors (RARs). Additionally, TNIP1 has been shown to repress peroxisome proliferator-activated receptors (PPAR) and NF-κB activity and interact with HIV proteins nef and matrix. TNIP1 transcriptional regulation, however, is under studied. Here we show that under permissive epigenetic conditions, TNIP1 expression is induced by all trans retinoic acid (ATRA). Within a 6000 bp region of the human TNIP1 promoter we cloned, both proximal and distal promoter regions are RAR responsive with the latter having RA response elements (RAREs) recognizable by their sequence and functionality in native promoter and synthetic RARE luciferase constructs, EMSA, and ChIP assays. These findings suggest a feedback loop whereby RARs activate expression of TNIP1, which then attenuates their activity. Together with anticipated constitutive transcription factors and the previously described NF-κB-responsiveness of the proximal TNIP1 promoter, the expected combinatorial control of TNIP1 expression could likely modulate TNIP1's impact in any of its target pathways. The degree of control by RARs or other transcription factors would in turn depend on their cell-specific level of expression and/or activation from signals in the environment such as ATRA and TNFα.

Retinoic acid receptor α mediates all-trans-retinoic acid-induced Klf4 gene expression by regulating Klf4 promoter activity in vascular smooth muscle cells

The transcription factor Krüppel-like factor 4 (KLF4) plays a critical role in vascular smooth muscle cell (VSMC) differentiation induced by all-trans-retinoic acid (ATRA). Although it has been demonstrated that ATRA stimulation augments both KLF4 protein and mRNA levels in VSMCs, the molecular mechanisms by which ATRA regulates Klf4 transcription are unknown. In this study, we examined the roles of ATRA-selective nuclear retinoic acid receptors (RARs) in the transcriptional regulation of Klf4. The introduction of small interfering RNA and an RAR antagonist demonstrated that RARα, but not RARβ or RARγ, mediated ATRA-induced Klf4 expression. A luciferase assay for the Klf4 promoter showed that three GC boxes in the proximal Klf4 promoter were indispensible for ATRA-induced Klf4 transcription and that RARα enhanced Klf4 promoter activity in a GC box-dependent manner. Furthermore, chromatin immunoprecipitation and oligonucleotide pulldown assays demonstrated that the transcription factors KLF4, Sp1, and YB1 directly bound to the GC boxes of the proximal Klf4 promoter. Upon RARα agonist stimulation, RARα was recruited to the Klf4 promoter through its interaction with KLF4, Sp1, and YB1 to form a transcriptional activation complex on the three GC boxes of the Klf4 promoter. These results suggest that RARα serves as an essential co-activator for ATRA signaling and that the recruitment of RARα to the KLF4-Sp1-YB1 complex, which leads to Klf4 expression in VSMCs, is independent of a retinoic acid response element.

Adaptive basal phosphorylation of eIF2α is responsible for resistance to cellular stress-induced cell death in Pten-null hepatocytes

The α-subunit of eukaryotic initiation factor 2 (eIF2α) is a key translation regulator that plays an important role in cellular stress responses. In the present study, we investigated how eIF2α phosphorylation can be regulated by a tumor suppressor PTEN (phosphatase and tensin homolog deleted on chromosome 10) and how such regulation is used by PTEN-deficient hepatocytes to adapt and cope with oxidative stress. We found that eIF2α was hyperphosphorylated when Pten was deleted, and this process was AKT dependent. Consistent with this finding, we found that the Pten-null cells developed resistance to oxidative glutamate and H(2)O(2)-induced cellular toxicity. We showed that the messenger level of CReP (constitutive repressor of eIF2α phosphorylation), a constitutive phosphatase of eIF2α, was downregulated in Pten-null hepatocytes, providing a possible mechanism through which PTEN/AKT pathway regulates eIF2α phosphorylation. Ectopic expression of CReP restored the sensitivity of the Pten mutant hepatocytes to oxidative stress, confirming the functional significance of the downregulated CReP and upregulated phospho-eIF2α in the resistance of Pten mutant hepatocytes to cellular stress. In summary, our study suggested a novel role of PTEN in regulating stress response through modulating the CReP/eIF2α pathway.

Valproic acid induces monoamine oxidase A via Akt/forkhead box O1 activation

Valproic acid (VPA) has been widely used in clinics for the treatment of multiple neuropsychiatric disorders, such as epilepsy and bipolar disorder. One of the mechanisms by which VPA exerts its effect is through regulating the brain levels of serotonin. However, the molecular basis of this VPA action is not fully understood. Here, we report for the first time that VPA activates monoamine oxidase (MAO) A catalytic activity, mRNA level, and promoter activity. MAO A is a key enzyme that degrades a number of monoamine neurotransmitters, including serotonin. Our results show that VPA increased the phosphorylation of both Akt and Forkhead box O1 (FoxO1), whereas pretreatment of cells with 2-(4-morpholinyl)-8-phenyl-1(4H)-benzopyran-4-one hydrochloride (LY294002) (a phosphoinositide 3-kinase inhibitor) reduced the VPA activation of MAO A. Overexpression of FoxO1 dramatically repressed both the basal and VPA-induced MAO A catalytic and promoter activities to 30 to 60%. Small interfering RNA knockdown of FoxO1 attenuated the stimulating effect of VPA on MAO A. Moreover, introduction of a constitutively active form of FoxO1 abolished the activation of MAO A by VPA and Akt. These results suggest that FoxO1 is a repressor for MAO A transcription, and its phosphorylation is involved in VPA activation of MAO A. Sequence analysis, electrophoretic mobility shift and chromatin immunoprecipitation assays further showed the presence of a functional FoxO1-binding site in MAO A core promoter. Taken together, these results demonstrate that MAO A is a novel target for VPA via Akt/FoxO1 signaling pathway. This information provides new insights into the pharmacological mechanisms and therapeutic implications of VPA action.

Transcriptional regulation and multiple functions of MAO genes

Monoamine oxidase (MAO) A and MAO B are a crucial pair of isoenzymes, which oxidatively deaminate monoamine neurotransmitters and dietary amines with a production of hydrogen peroxide. These two isoenzymes have different but overlapping substrate and inhibitor specificities. MAO A and MAO B share 70% amino acid sequence identity and show different temporal and spatial expressions in both humans and mice. Abnormal MAO A or MAO B activity has been implicated in numerous neurological and psychiatric disorders. A better understanding of the transcriptional regulation of MAO A and MAO B genes may help explain the differential tissue-specific expression of these two isoenzymes and provide insights into the molecular basis of the disorders associated with MAO dysfunction. This review discusses the recent progress in the transcriptional regulation and multiple functions of MAO A and MAO B genes.

Transcription factor E2F-associated phosphoprotein (EAPP), RAM2/CDCA7L/JPO2 (R1), and simian virus 40 promoter factor 1 (Sp1) cooperatively regulate glucocorticoid activation of monoamine oxidase B

Glucocorticoid steroid hormones play important roles in many neurophysiological processes such as responses to stress, behavioral adaption, and mood. One mechanism by which glucocorticoids exert functions in the brain is via the modulation of neurotransmission systems. Glucocorticoids are capable of inducing the activities of monoamine oxidases (MAOs), which degrade monoamine neurotransmitters including serotonin, norepinephrine, phenylethylamine, and dopamine. However, the molecular mechanisms for such induction are not yet fully understood. Here, we report that dexamethasone, a synthetic glucocorticoid hormone, stimulates MAO B (an isoform of MAOs) promoter and catalytic activities via both the fourth glucocorticoid response element (GRE) and simian virus 40 promoter factor 1 (Sp1) binding sites in MAO B promoter. Electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation analysis demonstrated that glucocorticoid receptor binds to the fourth GRE in vitro and in vivo. Using Sp1-binding motifs as bait in a yeast one-hybrid system, we identified two novel transcriptional repressors of MAO B, E2F-associated phosphoprotein (EAPP) and R1 (RAM2/CDCA7L/JPO2), that down-regulate MAO B via MAO B core promoter, which contains Sp1 sites. EMSA suggested that EAPP and R1 competed with Sp1 for binding to the Sp1 site in vitro. Moreover, EAPP and R1 reduced Sp1-activated glucocorticoid activation of MAO B promoter. In response to dexamethasone, lower occupancy by EAPP and R1 and higher occupancy by Sp1 were shown at the natural MAO B core promoter. Together, this study uncovers for the first time the molecular mechanisms for glucocorticoid activation of MAO B gene and provides new insights into the hormonal regulation of MAO.

Interactive roles of Ets-1, Sp1, and acetylated histones in the retinoic acid-dependent activation of guanylyl cyclase/atrial natriuretic peptide receptor-A gene transcription

Cardiac hormones atrial and brain natriuretic peptides activate guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA), which plays a critical role in reduction of blood pressure and blood volume. Currently, the mechanisms responsible for regulating the Npr1 gene (coding for GC-A/NPRA) transcription are not well understood. The present study was conducted to examine the interactive roles of all-trans retinoic acid (ATRA), Ets-1, Sp1, and histone acetylation on the transcriptional regulation and function of the Npr1 gene. Deletion analysis of the Npr1 promoter and luciferase assays showed that ATRA enhanced a 16-fold Npr1 promoter activity and greatly stimulated guanylyl cyclase (GC) activity of the receptor protein in both atrial natriuretic peptide (ANP)-dependent and -independent manner. As confirmed by gel shift and chromatin immunoprecipitation assays, ATRA enhanced the binding of both Ets-1 and Sp1 to the Npr1 promoter. The retinoic acid receptor α (RARα) was recruited by Ets-1 and Sp1 to form a transcriptional activator complex with their binding sites in the Npr1 promoter. Interestingly, ATRA also increased the acetylation of histones H3 and H4 and enhanced their recruitment to Ets-1 and Sp1 binding sites within the Npr1 promoter. Collectively, the present results demonstrate that ATRA regulates Npr1 gene transcription and GC activity of the receptor by involving the interactive actions of Ets-1, Sp1, and histone acetylation.

Regulation of monoamine oxidase A by the SRY gene on the Y chromosome

Monoamine oxidase A (MAO A), encoded by the X chromosome, catalyzes the oxidative deamination of monoamine neurotransmitters, such as serotonin, and plays a critically important role in brain development and functions. Abnormal MAO A activity has been implicated in several neuropsychiatric disorders, such as depression, autism, and attention deficit hyperactivity disorder, which show sexual dimorphism. However, the molecular basis for these disease processes is unclear. Recently, we found that MAO A was a putative target gene directly regulated by a transcription factor encoded by the sex-determining region Y (SRY) gene located on the Y chromosome. We demonstrated that SRY activates both MAO A-promoter and catalytic activities in a human male neuroblastoma BE(2)C cell line. A functional SRY-binding site in the MAO A core promoter was identified and validated by electrophoretic mobility shift and chromatin immunoprecipitation (ChIP) analyses. Coimmunoprecipitation and ChIP assays showed that SRY and Sp1 form a transcriptional complex and synergistically activate MAO A transcription. This is the first study demonstrating that the Y-encoded transcription factor SRY is capable of regulating an X-located gene, suggesting a novel molecular mechanism for sexual dimorphism in neural development, brain functions, and initiation/progression of neural disorders associated with MAO A dysfunction.