Microphthalmia-associated transcription factor/T-box factor-2 axis acts through Cyclin D1 to regulate melanocyte proliferation

Transcriptional and post-translational regulation of MITF mediated by bHLH domain during the melanogenesis and melanocyte proliferation in Crassostrea gigas

Melanocyte differentiation is orchestrated by the master regulator transcription factor MITF. However, its ability to discern distinct binding sites linked to effective gene regulation remains poorly understood. This study aims to assess how co-activator acetyltransferase interacts with MITF to modulate their related lysine action, thereby mediating downstream gene regulation, including DNA affinity, stability, transcriptional activity, particularly in the process of shell pigmentation. Here, we have demonstrated that the CgMITF protein can be acetylated, further enabling selective amplification of the melanocyte maturation program. Collaboration with transcriptional co-regulator p300 advances MITF dynamically interplay with downstream targeted gene promoters. We have established that MITF activation was partially dependent on the bHLH domain, which was well conserved across species. The bHLH domain contained conserved lysine residues, including K6 and K43, which interacted with the E-box motif of downstream targeted-genes. Mutations at K6 and K43 lead to a decrease in the binding affinity of the E-box motif. CgMITF protein bound to the E-box motif within the promoter regions of the tyrosinase-related genes, contributing to melanogenesis, and also interacted with the E-box motif within the TBX2 promoter regions, associated with melanocyte proliferation. We elucidated how the bHLH domain links the transcriptional regulation and acetylation modifications in the melanocyte development in C. gigas.

TBX2 affects proliferation, apoptosis and cholesterol generation by regulating mitochondrial function and autophagy in bovine cumulus cell

BACKGROUND

T-box transcription factor 2 (TBX2) is a member of T-box gene family whose members are highly conserved in evolution and encoding genes and are involved in the regulation of developmental processes. The encoding genes play an important role in growth and development. Although TBX2 has been widely studied in cancer cell growth and development, its biological functions in bovine cumulus cells remain unclear.

OBJECTIVES

This study aimed to investigate the regulatory effects of TBX2 in bovine cumulus cells.

METHODS

TBX2 gene was knockdown with siRNA to clarify the function in cellular physiological processes. Cell proliferation and cycle changes were determined by xCELLigence cell function analyzer and flow cytometry. Mitochondrial membrane potential and autophagy were detected by fluorescent dye staining and immunofluorescence techniques. Western blot and quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) were used to detect the expression changes of proliferation and autophagy-related proteins. Aadenosine triphosphate (ATP) production, glucose metabolism, and cholesterol synthesis of cumulus cells were measured by optical density and chemiluminescence analysis.

RESULTS

After inhibition of TBX2, the cell cycle was disrupted. The levels of apoptosis, ratio of light chain 3 beta II/I, and reactive oxygen species were increased. The proliferation, expansion ability, ATP production, and the amount of cholesterol secreted by cumulus cells were significantly decreased.

CONCLUSIONS

TBX2 plays important roles in regulating the cells' proliferation, expansion, apoptosis, and autophagy; maintaining the mitochondrial function and cholesterol generation of bovine cumulus cells.

Lipopolysaccharide reduces melanin synthesis in vitiligo melanocytes by regulating autophagy

Vitiligo is an autoimmune-related disease with a complex aetiology that involves innate immunity. Toll-like receptors (TLRs) are important parts of innate immunity and are related to a variety of autoimmune diseases, including vitiligo, through an unknown mechanism. In this study, we found that the TLR4 gene expression was increased in blood samples of patients with advanced stage vitiligo, and then we evaluated the effect of TLR4 ligand lipopolysaccharide (LPS) on melanin synthesis in a vitiligo melanocyte cell line PIG3V and along with its mechanism. LPS suppressed melanin synthesis, downregulated the expression of melanin synthesis-related proteins, and activated autophagy in vitiligo melanocytes. Inhibiting autophagy with 3-methyladenine or chloroquine blocked these effects. This suggests that LPS inhibits skin pigmentation by modulating autophagy, thus providing novel insights into the pathogenesis of vitiligo.

Size matters: Large copy number losses in Hirschsprung disease patients reveal genes involved in enteric nervous system development

Hirschsprung disease (HSCR) is a complex genetic disease characterized by absence of ganglia in the intestine. HSCR etiology can be explained by a unique combination of genetic alterations: rare coding variants, predisposing haplotypes and Copy Number Variation (CNV). Approximately 18% of patients have additional anatomical malformations or neurological symptoms (HSCR-AAM). Pinpointing the responsible culprits within a CNV is challenging as often many genes are affected. Therefore, we selected candidate genes based on gene enrichment strategies using mouse enteric nervous system transcriptomes and constraint metrics. Next, we used a zebrafish model to investigate whether loss of these genes affects enteric neuron development in vivo.

This study included three groups of patients, two groups without coding variants in disease associated genes: HSCR-AAM and HSCR patients without associated anomalies (HSCR-isolated). The third group consisted of all HSCR patients in which a confirmed pathogenic rare coding variant was identified. We compared these patient groups to unaffected controls. Predisposing haplotypes were determined, confirming that every HSCR subgroup had increased contributions of predisposing haplotypes, but their contribution was highest in isolated HSCR patients without RET coding variants. CNV profiling proved that specifically HSCR-AAM patients had larger Copy Number (CN) losses. Gene enrichment strategies using mouse enteric nervous system transcriptomes and constraint metrics were used to determine plausible candidate genes located within CN losses. Validation in zebrafish using CRISPR/Cas9 targeting confirmed the contribution of UFD1L, TBX2, SLC8A1, and MAPK8 to ENS development. In addition, we revealed epistasis between reduced Ret and Gnl1 expression and between reduced Ret and Tubb5 expression in vivo. Rare large CN losses—often de novo—contribute to HSCR in HSCR-AAM patients. We proved the involvement of six genes in enteric nervous system development and Hirschsprung disease.

Hirschsprung disease is a congenital disorder characterized by the absence of intestinal neurons in the distal part of the intestine. It is a complex genetic disorder in which multiple variations in our genome combined, result in disease. One of these variations are Copy Number Variations (CNVs): large segments of our genome that are duplicated or deleted. Patients often have Hirschsprung disease without other symptoms. However, a proportion of patients has additional associated anatomical malformations and neurological symptoms. We found that CNVs, present in patients with associated anomalies, are more often larger compared to unaffected controls or Hirschsprung patients without other symptoms. Furthermore, Copy Number (CN) losses are enriched for constrained coding regions (CCR; genes usually not impacted by genomic alterations in unaffected controls) of which the expression is higher in the developing intestinal neurons compared to the intestine. We modelled loss of these candidate genes in zebrafish by disrupting the zebrafish orthologues by genome editing. For several genes this resulted in changes in intestinal neuron development, reminiscent of HSCR observed in patients. The results presented here highlight the importance of Copy Number profiling, zebrafish validation and evaluating all CCR expressed in developing intestinal neurons during diagnostic evaluation.

Syntenin regulates melanogenesis via the p38 MAPK pathway

Melanogenesis is the synthesis of the skin pigment melanin, which serves a critical role in the study of pigmentary skin diseases. Syntenin has been identified as a melanosome protein, but its role in melanogenesis is not completely understood. The present study aimed to investigate the effects and mechanisms underlying syntenin on melanogenesis in immortalized human melanocytes. Depletion of syntenin expression increased both tyrosinase (Tyr) activity and melanin content. Syntenin silencing also increased the protein expression levels of Tyr, pre‑melanosomal protein and microphthalmia‑associated transcription factor. In addition, the results indicated that syntenin regulated melanogenesis by upregulating the phosphorylation of p38 mitogen‑activated protein kinase (p38 MAPK). Taken together, these findings suggested that the regulation of melanogenesis by syntenin may be mediated by the activation of p38 MAPK and that syntenin might provide new insights into the pathogenesis of pigmented diseases.

Opsin3 Downregulation Induces Apoptosis of Human Epidermal Melanocytes via Mitochondrial Pathway

G protein‐coupled receptors (GPCRs) are core switches connecting excellular survival or death signals with cellular signaling pathways in a context‐dependent manner. Opsin 3 (OPN3) belongs to the GPCR superfamily. However, whether OPN3 can control the survival or death of human melanocytes is not known. Here, we try to investigate the inherent function of OPN3 on the survival of melanocytes. Our results demonstrate that OPN3 knockdown by RNAi‐OPN3 in human epidermal melanocytes leads to cell apoptosis. The downregulation of OPN3 markedly reduces intracellular calcium levels and decreases phosphorylation of BAD. Attenuated BAD phosphorylation and elevated BAD protein level alter mitochondria membrane permeability, which trigger activation of BAX and inhibition of BCL‐2 and raf‐1. Activated BAX results in the release of cytochrome c and the loss of mitochondrial membrane potential. Cytochrome c complexes associate with caspase 9, forming a postmitochondrial apoptosome that activate effector caspases including caspase 3 and caspase 7. The release of apoptotic molecules eventually promotes the occurrence of apoptosis. In conclusion, we hereby are the first to prove that OPN3 is a key signal responsible for cell survival through a calcium‐dependent G protein‐coupled signaling and mitochondrial pathway.

TBX2 is a neuroblastoma core regulatory circuitry component enhancing MYCN/FOXM1 reactivation of DREAM targets

Chromosome 17q gains are almost invariably present in high-risk neuroblastoma cases. Here, we perform an integrative epigenomics search for dosage-sensitive transcription factors on 17q marked by H3K27ac defined super-enhancers and identify TBX2 as top candidate gene. We show that TBX2 is a constituent of the recently established core regulatory circuitry in neuroblastoma with features of a cell identity transcription factor, driving proliferation through activation of p21-DREAM repressed FOXM1 target genes. Combined MYCN/TBX2 knockdown enforces cell growth arrest suggesting that TBX2 enhances MYCN sustained activation of FOXM1 targets. Targeting transcriptional addiction by combined CDK7 and BET bromodomain inhibition shows synergistic effects on cell viability with strong repressive effects on CRC gene expression and p53 pathway response as well as several genes implicated in transcriptional regulation. In conclusion, we provide insight into the role of the TBX2 CRC gene in transcriptional dependency of neuroblastoma cells warranting clinical trials using BET and CDK7 inhibitors.

In high-risk neuroblastoma cases, gains in chromosome 17q are common. Here, the authors investigate the epigenomics and transcriptomics of neuroblastoma, identifying TBX2 as a core regulatory circuitry component enhancing the reactivation of DREAM targets by MYCN/FOXM1.

The T-Box Transcription Factor TBX2 Regulates Cell Proliferation in the Retinal Pigment Epithelium

PURPOSE

Vertebrate eye development and function critically depend on the regulation of proliferation of retinal pigment epithelium (RPE) cells. Hence, a thorough analysis of the molecular parameters controlling RPE cell proliferation is crucial for our understanding of the physiology of this cell type both in health and in disease. The T-box transcription factor TBX2 is an important cell cycle regulator in development and oncogenesis, but its specific role in RPE cell proliferation is far from clear. The purpose of the present study is to investigate whether TBX2 plays any role in regulating RPE cell proliferation.

MATERIALS AND METHODS

The expression of TBX2 in RPE cells was analyzed in wildtype mice and ARPE-19 cells by co-staining for RPE-specific markers and cell proliferation. In vitro, the role of TBX2 was studied by manipulating its levels using RNAi and analyzing the effects on DNA synthesis and cell growth and on gene expression at the RNA and protein levels.

RESULTS

Here, we find that TBX2 is expressed in RPE cells both in vivo and in vitro. Specific knockdown of TBX2 in the human RPE cell line ARPE-19 leads to an accumulation of cells at G1. This cell cycle arrest is accompanied by changes in the levels of known cell cycle regulators and, in particular, by an increase in the levels of the tumor-suppressor gene CCAAT/enhancer-binding protein delta (CEBPD). In fact, simultaneous knockdown of both TBX2 and CEBPD interferes with the reduction in cell proliferation brought about by TBX2 reduction alone.

CONCLUSIONS

Our results provide novel insights into the regulatory mechanisms of cell proliferation in the RPE and may contribute to our understanding of normal RPE maintenance and its pathology in degenerative and proliferative disorders of the eye.

Inhibition of NAT10 Suppresses Melanogenesis and Melanoma Growth by Attenuating Microphthalmia-Associated Transcription Factor (MITF) Expression

N-acetyltransferase 10 (NAT10) has been considered a target for the treatment of human diseases such as cancer and laminopathies; however, its functional role in the biology of melanocytes is questionable. Using a small molecule or small interfering RNA targeting NAT10, we examined the effect of NAT10 inhibition on melanogenesis and melanoma growth in human and mouse melanoma cells. Genetic silencing or chemical inhibition of NAT10 resulted in diminished melanin synthesis through the suppression of melanogenesis-stimulating genes such as those encoding dopachrome tautomerase (DCT) and tyrosinase in B16F10 melanoma cells. In addition, NAT10 inhibition significantly increased cell cycle arrest in S-phase, thereby suppressing the growth and proliferation of malignant melanoma cells in vitro and in vivo. These results demonstrate the potential role of NAT10 in melanogenesis and melanoma growth through the regulation of microphthalmia-associated transcription factor (MITF) expression and provide a promising strategy for the treatment of various skin diseases (melanoma) and pigmentation disorders (chloasma and freckles).

Bifunctional effects of O-methylated flavones from Scutellaria baicalensis Georgi on melanocytes: Inhibition of melanin production and intracellular melanosome transport

The growing interest in skin lightening has recently renewed attention on the esthetic applications of Chinese herbal medicine. Although Scutellaria baicalensis Georgi is used for antipyretic and antiinflammatory purposes, its whitening effect remains unclear. This study reports three major findings: (1) S. baicalensis has a potent inhibitory effect on melanogenesis; (2) wogonin and its glycoside are the active components of S. baicalensis; and (3) O-methylated flavones from S. baicalensis, such as wogonin, inhibit intracellular melanosome transport. Using a melanin quantification assay, we showed that S. baicalensis potently inhibits melanogenesis in B16F10 cells. Componential analyses revealed that the main components of S. baicalensis are baicalin, wogonoside, baicalein, wogonin, and oroxylin A. Among these five flavones, wogonin and wogonoside consistently inhibited melanogenesis in both B16F10 melanoma cells and primary melanocytes. Wogonin exhibited the strongest inhibition of melanin production and markedly lightened the color of skin equivalents. We identified microphthalmia-associated transcription factor and tyrosinase-related proteins as potential targets of wogonin- and wogonoside-induced melanogenesis suppression. In culture, we found that the melanosomes in wogonin-treated B16F10 cells were localized to the perinuclear region. Immunoblotting analyses revealed that wogonin significantly reduced in melanophilin protein, which is required for actin-based melanosome transport. Other actin-based melanosome transport-related molecules, i.e., Rab27A and myosin Va, were not affected by wogonin. Cotreatment with MG132 blocked the wogonin-induced decrease in melanophilin, suggesting that wogonin promotes the proteolytic degradation of melanophilin via the calpain/proteasomal pathway. We determined that the structural specificities of the mono-O-methyl group in the flavone A-ring and the aglycone form were responsible for reducing melanosome transport. Furthermore, wogonin and two wogonin analogs, mono-O-methyl flavones, strongly suppressed melanosome transport. Our findings suggest the applicability of S. baicalensis in the esthetic field. Thus, we propose a novel pharmacologic approach for the treatment of hyperpigmentation.