In vivo role of alternative splicing and serine phosphorylation of the microphthalmia-associated transcription factor

Gene expression profiles of skin from cyclin dependent kinases 5-knockdown mice

OBJECTIVE

This study aimed to identify genes regulated by cyclin dependent kinases 5 (CDK5) that participate in hair pigmentation in mice.

METHODS

The mRNA expression profiles of skin samples from CDK5-knockdown mice were constructed using high-throughput RNA sequencing and compared with those of wild-type mice.

RESULTS

In total, 8,002 known genes were differentially expressed between CDK5-knockdown and wild-type mice. Of these, 3,658 were upregulated and 4,344 were downregulated in the skin of CDK5-knockdown mice. An additional 318 previously unknown genes were also differentially expressed, with 171 downregulated and 147 upregulated genes in the skin of CDK5-knockdown mice. Of the known genes expressed in mouse skin, 80 were associated with hair color, with 61 showing lower expression and 19 exhibiting higher expression in skin of CDK5-knockdown mice. Importantly, the expression of the tyrosinase-related protein 1 (TYRP1) and the calcium signaling pathway were also found to be regulated by CDK5, suggesting that pigmentation is regulated by CDK5 via the calcium signaling pathway and TYRP1.

CONCLUSION

The transcriptome profiles obtained from the skin of CDK5-knockdown mice compared to wild-type mice provide a valuable resource to help understand the mechanism by which CDK5 regulates melanogenesis in mice and other animals.

Phenolic from apple blossom "Hongro" inhibits the expression of proteins related to melanogenesis in B16F10 melanoma cells

This study aimed to assess apple blossom extracts as potential natural whitening agents due to their ability to inhibit melanogenesis. Ethanol extracts of apple blossom (ABE) were assessed for biological activity in the B16F10 mouse melanoma cell line. ABE toxicity was assessed by thiazolyl blue tetrazolium bromide (MTT) assay. Levels of melanogenic enzyme expression in response to ABE supplementation were assessed by western blotting. Also assessed purified kaempferol, one of the phenolic compounds extracted from apple blossom, was evaluated using western blot analysis. The expression levels of cellular tyrosinase, microphthalmia-associated transcription factor (MITF), tyrosinase-related protein (TRP)-1, and TRP-2 proteins related to melanogenesis decreased in a dose-dependent manner with ABE treatment of cells. Using nuclear magnetic resonance, we identified kaempferol in the ABE. Treatment of cells with purified kaempferol decreased the expression levels of tyrosinase and the MITF protein to a similar degree as that observed with ABE treatment. This suggests that the efficacy of melanogenesis-related inhibition demonstrated by ABE was due to kaempferol. ABE has an inhibitive effect on melanogenic enzymes and potentially can be applied to functional foods and cosmetics having a whitening effect as a natural material.

User guide to MiT-TFE isoforms and post-translational modifications

The microphthalmia-associated transcription factor (MITF) is at the core of melanocyte and melanoma fate specification. The related factors TFEB and TFE3 have been shown to be instrumental for transcriptional regulation of genes involved in lysosome biogenesis and autophagy, cellular processes important for mediating nutrition signals and recycling of cellular materials, in many cell types. The MITF, TFEB, TFE3, and TFEC proteins are highly related. They share many structural and functional features and are targeted by the same signaling pathways. However, the existence of several isoforms of each factor and the increasing number of residues shown to be post-translationally modified by various signaling pathways poses a difficulty in indexing amino acid residues in different isoforms across the different proteins. Here, we provide a resource manual to cross-reference amino acids and post-translational modifications in all isoforms of the MiT-TFE family in humans, mice, and zebrafish and summarize the protein accession numbers for each isoform of these factors in the different genomic databases. This will facilitate future studies on the signaling pathways that regulate different isoforms of the MiT-TFE transcription factor family.

MITF-the first 25 years

In this review, Goding and Arnheiter present the current understanding of MITF's role and regulation in development and disease and highlight key areas where our knowledge of MITF regulation and function is limited.

All transcription factors are equal, but some are more equal than others. In the 25 yr since the gene encoding the microphthalmia-associated transcription factor (MITF) was first isolated, MITF has emerged as a key coordinator of many aspects of melanocyte and melanoma biology. Like all transcription factors, MITF binds to specific DNA sequences and up-regulates or down-regulates its target genes. What marks MITF as being remarkable among its peers is the sheer range of biological processes that it appears to coordinate. These include cell survival, differentiation, proliferation, invasion, senescence, metabolism, and DNA damage repair. In this article we present our current understanding of MITF's role and regulation in development and disease, as well as those of the MITF-related factors TFEB and TFE3, and highlight key areas where our knowledge of MITF regulation and function is limited.

A wide variety of Mitf transcript variants are expressed in the Xenopus laevis periodic albino mutant

The periodic albino mutant of Xenopus laevis has been used to study the development of pigment cells because both the retinal pigment epithelium (RPE) and melanophores are affected. In this mutant, "white pigment cells" containing both melanophore-specific and iridophore-specific pigment organelles appear. The present experiments were designed to investigate the structural organization and expression of microphthalmia-associated transcription factor (Mitf) in the mutant since Mitf is known to regulate the development of melanocytes and RPE. The exon structures of X. laevis mitf genes (mitf.L and mitf.S) were defined using newly obtained Mitf transcripts and X. laevis genomic data. Compared to mouse mitf, exons 3 and 6a were absent in X. laevis mitf. The four exons between exons 4 and 6b in X. laevis mitf were named 5α, 5β, 5γ, and 5δ. Exons 5α and 5δ were specific to X. laevis mitf, whereas the continuous exons 5β/γ were identical to exon 5 of mouse mitf. A wide variety of A-Mitf and M-Mitf transcript variants lacking one or more exons were found in X. laevis; however, different types of Mitf transcripts were expressed in the mutant. In addition, white pigment cells and melanophores expressed both the mitf and dopachrome tautomerase (dct) genes.

Tfe3 and Tfeb Transcriptionally Regulate Peroxisome Proliferator-Activated Receptor γ2 Expression in Adipocytes and Mediate Adiponectin and Glucose Levels in Mice

Members of the MiT transcription factor family are pivotal regulators of several lineage-selective differentiation programs. We show that two of these, Tfeb and Tfe3, control the regulator of adipogenesis, peroxisome proliferator-activated receptor γ2 (Pparγ2). Knockdown of Tfeb or Tfe3 expression during in vitro adipogenesis causes dramatic downregulation of Pparγ2 expression as well as adipogenesis. Additionally, we found that these factors regulate Pparγ2 in mature adipocytes. Next, we demonstrated that Tfeb and Tfe3 act directly by binding to consensus E-boxes within the Pparγ transcriptional regulatory region. This transcriptional control also exists in vivo, as we discovered that wild-type mice in the fed state increased their expression of Tfe3, Tf3b, and Pparγ in white adipose tissue. Furthermore, Tfe3 knockout (Tfe3KO) mice in the fed state failed to upregulate Pparγ and the adiponectin gene, a Pparγ-dependent gene, confirming the in vivo role for Tfe3. Lastly, we found that blood glucose is elevated and serum adiponectin levels are suppressed in the Tfe3KO mice, indicating that the Tfe3/Tfeb/Pparγ2 axis may contribute to whole-body energy balance. Thus, we offer new insights into the upstream regulation of Pparγ by Tfe3/Tf3b and propose that targeting these transcription factors may offer opportunities to complement existing approaches for the treatment of diseases that have dysregulated energy metabolism.

Mitf regulates osteoclastogenesis by modulating NFATc1 activity

Transcription factors Mitf and NFATc1 share many downstream targets that are critical for osteoclastogenesis. Since RANKL signals induce/activate both NFATc1 and Mitf isoform-E (Mitf-E), a tissue-restricted Mitf isoform in osteoclasts, it is plausible that the two factors work together to promote osteoclastogenesis. Although Mitf was shown to function upstream of NFATc1 previously, this study showed that expression of Mitf had little effects on NFATc1 and NFATc1 was critical for the induction of Mitf-E. In Mitf(mi/mi) mice, the semi-dominant mutation in Mitf gene leads to arrest of osteoclastogenesis in the early stages. However, when stimulated by RANKL, the Mitf(mi/mi) preosteoclasts responded with a significant induction of NFATc1, despite that the cells cannot differentiate into functional osteoclasts. In the absence of RANKL stimulation, very high levels of NFATc1 are required to drive osteoclast development. Our data indicate that Mitf functions downstream of NFATc1 in the RANKL pathway, and it plays an important role in amplifying NFATc1-dependent osteoclastogenic signals, which contributes to the significant synergy between the two factors during osteoclastogenesis. We propose that Mitf-E functions as a tissue-specific modulator for events downstream of NFATc1 activation during osteoclastogenesis.

A polymorphism in IRF4 affects human pigmentation through a tyrosinase-dependent MITF/TFAP2A pathway

Sequence polymorphisms linked to human diseases and phenotypes in genome-wide association studies often affect noncoding regions. A SNP within an intron of the gene encoding Interferon Regulatory Factor 4 (IRF4), a transcription factor with no known role in melanocyte biology, is strongly associated with sensitivity of skin to sun exposure, freckles, blue eyes, and brown hair color. Here, we demonstrate that this SNP lies within an enhancer of IRF4 transcription in melanocytes. The allele associated with this pigmentation phenotype impairs binding of the TFAP2A transcription factor that, together with the melanocyte master regulator MITF, regulates activity of the enhancer. Assays in zebrafish and mice reveal that IRF4 cooperates with MITF to activate expression of Tyrosinase (TYR), an essential enzyme in melanin synthesis. Our findings provide a clear example of a noncoding polymorphism that affects a phenotype by modulating a developmental gene regulatory network.