Dominant negative FTase (DNFTalpha) inhibits ERK5, MEF2C and CREB activation in adipogenesis

HMG20A Inhibit Adipogenesis by Transcriptional and Epigenetic Regulation of MEF2C Expression

Obesity and its associated metabolic disease do serious harm to human health. The transcriptional cascade network with transcription factors as the core is the focus of current research on adipogenesis and its mechanism. Previous studies have found that HMG domain protein 20A (HMG20A) is highly expressed in the early stage of adipogenic differentiation of porcine intramuscular fat (IMF), which may be involved in regulating adipogenesis. In this study, HMG20A was found to play a key negative regulatory role in adipogenesis. Gain- and loss-of-function studies revealed that HMG20A inhibited the differentiation of SVF cells and C3H10T1/2 cells into mature adipocytes. RNA-seq was used to screen differentially expressed genes after HMG20A knockdown. qRT-PCR and ChIP-PCR confirmed that MEF2C was the real target of HMG20A, and HMG20A played a negative regulatory role through MEF2C. HMG20A binding protein LSD1 was found to alleviate the inhibitory effect of HMG20A on adipogenesis. Further studies showed that HMG20A could cooperate with LSD1 to increase the H3K4me2 of the MEF2C promoter and then increase the expression of MEF2C. Collectively, these findings highlight a role for HMG20A-dependent transcriptional and epigenetic regulation in adipogenesis.

Function analysis of Mef2c promoter in muscle differentiation

Regeneration of adult skeletal muscle following injury occurs through the activation of satellite cells that proliferates, differentiates, and fuses with injured myofibers. Myocyte enhancer factor 2 (MEF2) proteins are reported to have the potential contributions to adult muscle regeneration. To further understand Mef2c gene, the promoter of pig Mef2c gene was analyzed in this paper. Quantitative real-time PCR (qRT-PCR) revealed the expression pattern of Mef2c gene in muscle of eight tissues. The Mef2c promoter had the higher transcriptional activity in differentiated C2C12 cells than that in proliferating C2C12 cells, which was accompanied by the upregulation of mRNA expression of Mef2c gene. Function deletion and mutation analyses showed that MyoD and MEF2 binding sites within the Mef2c promoter were responsible for the regulation of Mef2c transcription. MEF2C could upregulate the transcriptional activities of Mef2c promoter constructs, which contained a 3'-end nucleotide sequence with p300 binding site. The electrophoretic mobility shift assays and chromatin immunoprecipitation assays determined the MyoD binding site in Mef2c promoter. These results advanced our knowledge of the promoter of the pig Mef2c gene, and the study of Mef2c promoter regulator elements helped to elucidate the regulation mechanisms of Mef2c in muscle differentiation or muscle repair and regeneration.

Platelet-derived growth factor (PDGF)-induced activation of Erk5 MAP-kinase is dependent on Mekk2, Mek1/2, PKC and PI3-kinase, and affects BMP signaling

Platelet-derived growth factor-BB (PDGF-BB) binds to its tyrosine kinase receptors (PDGFRs) and stimulates mitogenicity and survival of cells of mesenchymal origin. Activation of PDGFRs initiates a number of downstream signaling pathways, including phosphatidyl 3'-inositol kinase (PI3-kinase), phospholipase Cγ and MAP kinase pathways. In this report, we show that Erk5 MAP kinase is activated in response to PDGF-BB in the smooth muscle cell line MOVAS in a manner dependent on Mekk2, Mek1/2, Mek5, PI3-kinase and protein kinase C (PKC). The co-operation of Mek1/2 and Mekk2 in the activation of Erk5, suggests a close co-regulation between the Erk1/2 and Erk5 MAP kinase pathways. Furthermore, we found that classical PKCs are important for Erk5 activation. In addition, we found that PKCζ interacts with Erk5 and may exert a negative feed-back effect. We observed no nuclear accumulation of Erk5 in response to PDGF-BB stimulation, however, we identified a mechanism by which cytoplasmic Erk5 influences gene expression; Erk5 was essential for PDGF-BB-mediated Smad1/5/8 signaling by stimulating release and/or activation of bone morphogenetic protein(s) (BMPs). Thus, PDGF-BB-induced Erk5 activation involves parallel stimulatory and inhibitory pathways and promotes Smad1/5/8 signaling.

RBM4-MEF2C network constitutes a feed-forward circuit that facilitates the differentiation of brown adipocytes

Myocyte enhancer factor 2c (MEF2C) is the MADS-box type transcription factor involved in the differentiation of cardiac and skeletal muscle and synaptic formation. Alternatively spliced transcripts of the MEF2C gene were proven to encode isoforms which exert distinct functions in transcriptional regulation. During the differentiation of brown adipocytes, upregulated RBM4 enhanced skipping of the MEF2Cγ region which functions as a transcriptional repressor. The presence of an overexpressed MEF2Cγ- isoform in turn induced transcriptional activity of the RBM4 promoter, constituting a positive feedback circuit in differentiating brown adipocytes. The RBM4-MEF2Cγ- network induced the expression of "myogenic" miR-1 to a greater extent than did PRDM17, BMP7 C/EBPβ, or UCP1 transcripts in C3H10T1/2 cells. Overexpression of miR-1 independently exerted the same activity as RBM4 and the MEF2Cγ- isoform of upregulating brown adipocyte-specific factors in C3H10T1/2 cells, which suggests a potential effect of miR-1 on brown adipocytes. These results indicated that the RBM4-MEF2C-miR-1 network constitutes a novel mechanism which programs the gene expression profile toward the development of brown adipocytes.

Phosphorylation of ERK5 on Thr732 is associated with ERK5 nuclear localization and ERK5-dependent transcription

Extracellular signal-regulated kinases (ERKs) play critical roles in numerous cellular processes, including proliferation and differentiation. ERK5 contains a kinase domain at the N-terminal, and the unique extended C-terminal includes multiple autophosphorylation sites that enhance ERK5-dependent transcription. However, the impact of phosphorylation at the various sites remain unclear. In this study, we examined the role of phosphorylation at the ERK5 C-terminal. We found that a constitutively active MEK5 mutant phosphorylated ERK5 at the TEY motif, resulting in the sequential autophosphorylation of multiple C-terminal residues, including Thr732 and Ser769/773/775. However, when ERK1/2 was selectively activated by an oncogenic RAS mutant, ERK5 phosphorylation at Thr732 was induced without affecting the phosphorylation status at TEY or Ser769/773/775. The Thr732 phosphorylation was U0126-sensitive and was observed in a kinase-dead mutant of ERK5 as well, suggesting that ERK1/2 can phosphorylate ERK5 at Thr732. This phosphorylation was also promoted by epidermal growth factor and nerve growth factor in HEK293 and PC12 cells, respectively. The ERK5–T732A mutant was localized in the cytosol under basal conditions. In contrast, ERK5 phosphorylated at Thr732 via the RAS-ERK1/2 pathway and ERK5–T732E, which mimics the phosphorylated form, were localized in both the nucleus and cytosol. Finally, ER–32A and U0126 blocked ERK5-dependent MEF2C transcriptional activity. Based on these findings, we propose a novel cross-talk mechanism in which ERK1/2, following activation by growth factor stimulation, phosphorylates ERK5 at Thr732. This phosphorylation event is responsible for ERK5 nuclear localization and ERK5-dependent transcription.

MicroRNA regulation of adipose derived stem cells in aging rats

Background

Perturbations in abdominal fat secreted adipokines play a key role in metabolic syndrome. This process is further altered during the aging process, probably due to alterations in the preadipocytes (aka. stromal vascular fraction cells-SVF cells or adipose derived stem cells-ASCs) composition and/or function. Since microRNAs regulate genes involved both in development and aging processes, we hypothesized that the impaired adipose function with aging is due to altered microRNA regulation of adipogenic pathways in SVF cells.

Methodology and Principal Findings

Alterations in mRNA and proteins associated with adipogenic differentiation (ERK5 and PPARg) but not osteogenic (RUNX2) pathways were observed in SVF cells isolated from visceral adipose tissue with aging (6 to 30 mo) in female Fischer 344 x Brown Norway Hybrid (FBN) rats. The impaired differentiation capacity with aging correlated with altered levels of miRNAs involved in adipocyte differentiation (miRNA-143) and osteogenic pathways (miRNA-204). Gain and loss of function studies using premir or antagomir-143 validated the age associated adipocyte dysfunction.

Conclusions and Significance

Our studies for the first time indicate a role for miRNA mediated regulation of SVF cells with aging. This discovery is important in the light of the findings that dysfunctional adipose derived stem cells contribute to age related chronic diseases.

ERK5: a novel IKKα-kinase in rat hippocampal neurons

BACKGROUND

Alzheimer's Disease (AD) is characterized in part by the increased presence of neurofibrillary tangles and amyloid beta (Aβ) plaques. Alzheimer's Disease is considered an inflammatory disease and, as such, nuclear factor-kappaB (NFκB) plays an important role in the pathophysiology of AD. Insulin acts as a neurotrophic factor. Yet, in the context of insulin resistance, concomitant hyperinsulinemia may contribute to the pathogenesis of AD.

METHODS

Rat Primmary Hippocampal Neurons (RPHN) were treated with insulin in the absence and presence of Wortmannin and ERK5 small inhibitory RNA and assayed for downstream effectors of activated ERK5.

RESULTS

Here we demonstrate that genetic inhibition of ERK5 blocks insulin stimulated (1) activation and translocation of ERK5 and NFκB, (2) phosphorylation of IKKα via association with ERK5, (3) increases in Aβ1-40 and Aβ1-42 soluble proteins 3-fold and 2.2-fold, respectively, and (4) increases in tau phosphorylation in RPHN.

CONCLUSIONS

ERK5 plays an active role in insulin signaling in neurons and may be a potential therapeutic target for neurodegenerative diseases.

Apoptotic cell-derived factors induce arginase II expression in murine macrophages by activating ERK5/CREB

Apoptotic cell (AC)-derived factors alter the physiology of macrophages (MΦs) towards a regulatory phenotype, characterized by reduced nitric oxide (NO) production. Impaired NO formation in response to AC-conditioned medium (CM) was facilitated by arginase II (ARG II) expression, which competes with inducible NO synthase for L-arginine. Here we explored signaling pathways allowing CM to upregulate ARG II in RAW264.7 MΦs. Sphingosine-1-phosphate (S1P) was required and acted synergistically with a so far unidentified factor to elicit high ARG II expression. S1P activated S1P(2), since S1P(2) knockdown prevented ARG II upregulation. Furthermore, ERK5 knockdown attenuated CM-mediated ARG II protein induction. CREB was implicated as shown by EMSA analysis and decoy-oligonucleotides scavenging CREB in RAW264.7 MΦs, which blocked ARG II expression. We conclude that AC-derived S1P binds to S1P(2) and acts synergistically with other factors to activate ERK5 and concomitantly CREB. This signaling cascade shapes an anti-inflammatory MΦ phenotype by ARG II induction.

Vertebrate paralogous MEF2 genes: origin, conservation, and evolution

Background

The myocyte enhancer factor 2 (MEF2) gene family is broadly expressed during the development and maintenance of muscle cells. Although a great deal has been elucidated concerning MEF2 transcription factors' regulation of specific gene expression in diverse programs and adaptive responses, little is known about the origin and evolution of the four members of the MEF2 gene family in vertebrates.

Methodology/Principal Findings

By phylogenetic analyses, we investigated the origin, conservation, and evolution of the four MEF2 genes. First, among the four MEF2 paralogous branches, MEF2B is clearly distant from the other three branches in vertebrates, mainly because it lacks the HJURP_C (Holliday junction recognition protein C-terminal) region. Second, three duplication events might have occurred to produce the four MEF2 paralogous genes and the latest duplication event occurred near the origin of vertebrates producing MEF2A and MEF2C. Third, the ratio (K_a/K_s) of non-synonymous to synonymous nucleotide substitution rates showed that MEF2B evolves faster than the other three MEF2 proteins despite purifying selection on all of the four MEF2 branches. Moreover, a pair model of M0 versus M3 showed that variable selection exists among MEF2 proteins, and branch-site analysis presented that sites 53 and 64 along the MEF2B branch are under positive selection. Finally, and interestingly, substitution rates showed that type II MADS genes (i.e., MEF2-like genes) evolve as slowly as type I MADS genes (i.e., SRF-like genes) in animals, which is inconsistent with the fact that type II MADS genes evolve much slower than type I MADS genes in plants.

Conclusion

Our findings shed light on the relationship of MEF2A, B, C, and D with functional conservation and evolution in vertebrates. This study provides a rationale for future experimental design to investigate distinct but overlapping regulatory roles of the four MEF2 genes in various tissues.

ERK5 signalling in prostate cancer promotes an invasive phenotype

Background:

Aberrant mitogen/extracellular signal-regulated kinase 5 (MEK5)–extracellular signal-regulated protein kinase 5 (ERK5)-mediated signalling has been implicated in a number of tumour types including prostate cancer (PCa). The molecular basis of ERK5-driven carcinogenesis and its clinical relevance remain to be fully characterised.

Methods:

Modulation of ERK5 expression or function in human PCa PC3 and PC3–ERK5 (stably transfected with ERK5) cells was performed using siRNA-mediated knockdown or the MEK inhibitor PD18435 respectively. In vitro significance of ERK5 signalling was assessed by assays for proliferation, motility, invasion and invadopodia. Expression of matrix metalloproteinases/tissue inhibitors of metalloproteases was determined by Q-RT–PCR. Extracellular signal-regulated protein kinase 5 expression in primary and metastatic PCa was examined using immunohistochemistry.

Results:

Reduction of ERK5 expression or signalling significantly inhibited the motility and invasive capability of PC3 cells. Extracellular signal-regulated protein kinase 5-mediated signalling significantly promoted formation of in vivo metastasis in an orthotopic PCa model (P<0.05). Invadopodia formation was also enhanced by forced ERK5 expression in PC3 cells. Furthermore, in metastatic PCa, nuclear ERK5 immunoreactivity was significantly upregulated when compared with benign prostatic hyperplasia and primary PCa (P=0.013 and P<0.0001, respectively).

Conclusion:

Our in vitro, in vivo and clinical data support an important role for the MEK5–ERK5 signalling pathway in invasive PCa, which represents a potential target for therapy in primary and metastatic PCa.

Activation of ERK5 in angiotensin II-induced hypertrophy of human aortic smooth muscle cells

Extracellular signal-regulated kinase 5 (ERK5), a recently discovered mitogen-activated protein kinase (MAPK), plays a key role in the development and pathogenesis of cardiovascular disease. In order to clarify the pathophysiological significance of ERK5 in vascular remodeling, we investigated ERK5 phosphorylation in hypertrophy of human aortic smooth muscle cells (HASMCs) induced by angiotensin II (Ang II). The AT1 receptor was involved in Ang II-induced ERK5 activity. Hypertrophy was detected by the measurement of protein synthesis with [(3)H]-Leu incorporation in cultured HASMCs. Ang II rapidly induced phosphorylation of ERK5 at Thr218/Tyr220 residues in a time- and dose-dependent manner. Activation of myocyte enhancer factor-2C (MEF2C) by ERK5 was inhibited by PD98059. Transfecting HASMCs with small interfering RNA (siRNA) to silence ERK5 inhibited Ang II-induced cell hypertrophy. Thus, ERK5 phosphorylation contributes to MEF2C activation and subsequent HASMC hypertrophy induced by Ang II, for a novel molecular mechanism in cardiovascular diseases induced by Ang II.

Regulation of ERK5 by insulin and angiotensin-II in vascular smooth muscle cells

ERK5 is involved in proliferation of vascular smooth muscle cells (VSMC). The proliferative actions of insulin and angiotensin-II (A-II) in VSMC are mediated in part by ERK1/2. We hypothesized that insulin and A-II also regulate ERK5 activity in VSMC. Acute treatment (<60min) with insulin or A-II increased phosphorylation of ERK1/2 at 15min and ERK5 at 5min. Chronic treatment (< or = 8h) with insulin increased ERK1/2 phosphorylation by 4h and ERK5 by 8h. A-II-stimulated phosphorylation of ERK1/2 by 8h and ERK5 by 4h. The EC(50) for insulin treatment effecting ERK1/2 and ERK5 phosphorylation was 1.5 and 0.1nM, whereas the EC(50) for A-II was 2nM, each. Insulin plus A-II induced an additive effect only on ERK5 phosphorylation. Inhibition of insulin- and A-II-stimulated phosphorylation of ERK5 and ERK1/2 by PD98059 and Wortmannin exhibited differential and time-dependent effects. Taken together, these data indicate that insulin and A-II regulate the activity of ERK5, but different from that seen for ERK1/2.