Hana Jeong

TAZ as a novel enhancer of MyoD-mediated myogenic differentiation

Myoblast differentiation is indispensable for skeletal muscle formation and is governed by the precisely coordinated regulation of a series of transcription factors, including MyoD and myogenin, and transcriptional coregulators. TAZ (transcriptional coactivator with PDZ‐binding motif) has been characterized as a modulator of mesenchymal stem cell differentiation into osteoblasts and adipocytes through its regulation of lineage‐specific master transcription factors. In this study, we investigated whether TAZ affects myoblast differentiation, which is one of the differentiated lineages of mesenchymal stem cells. Ectopic overexpression of TAZ in myoblasts increases myogenic gene expression in a MyoD‐dependent manner and hastens myofiber formation, whereas TAZ knockdown delays myogenic differentiation. In addition, enforced coexpression of TAZ and MyoD in fibroblasts accelerates MyoD‐induced myogenic differentiation. TAZ physically interacts with MyoD through the WW domain and activates MyoD‐dependent gene transcription. TAZ additionally enhances the interaction of MyoD with the myogenin gene promoter. These results strongly suggest that TAZ functions as a novel transcriptional modulator of myogenic differentiation by promoting MyoD‐mediated myogenic gene expression.—Jeong, H., Bae, S., An, S. Y., Byun, M. R., Hwang, J.‐H., Yaffe, M. B., Hong, J.‐H., Hwang, E. S. TAZ as a novel enhancer of MyoD‐mediated myogenic differentiation. FASEB J. 24, 3310–3320 (2010). www.fasebj.org

TAZ is required for the osteogenic and anti-adipogenic activities of kaempferol

Kaempferol (KMP) exerts protective effects against both osteoporosis and obesity by regulating cellular activities, but the underlying molecular mechanisms have not been fully elucidated. TAZ (transcriptional coactivator with PDZ-binding motif) modulates both osteoblast and adipocyte differentiation from mesenchymal stem cells by stimulating the activities of RUNX2 (runt-related transcription factor 2) and suppressing the activities of PPARγ (peroxisome proliferator-activated receptor γ). In this study, we investigated the effects of KMP on TAZ regulated osteoblast and adipocyte differentiation. KMP increased the osteoblast differentiation of mesenchymal cells by facilitating the physical interaction between TAZ and RUNX2, thus the increasing transcriptional activities of RUNX2. KMP also enhanced the association of TAZ with PPARγ, thereby suppressing the gene transcription of PPARγ targets and resulting in diminished adipocyte differentiation. Interestingly, the regulatory effects of kaempferol on RUNX2 and PPARγ-mediated transcriptional activity were impaired in TAZ-null mouse embryonic fibroblasts but recovered by restoration of TAZ expression. Our results demonstrate that KMP fortifies TAZ activity, which enhances RUNX2-mediated osteoblast differentiation and suppresses PPARγ-stimulated adipocyte differentiation, indicating the potential of KMP as an effective therapeutic reagent for controlling bone loss and adiposity through TAZ activation.

TM-25659 enhances osteogenic differentiation and suppresses adipogenic differentiation by modulating the transcriptional co-activator TAZ.

BACKGROUND AND PURPOSE The transcriptional co‐activator with PDZ‐binding motif (TAZ) is characterized as a transcriptional modulator of mesenchymal stem cell differentiation into osteoblasts and adipocytes. Moreover, increased TAZ activity in the nucleus enhances osteoblast differentiation and suppresses adipocyte development by interacting with runt‐related transcription factor 2 (RUNX2) and PPARγ, respectively. Therefore, it would be of interest to identify low MW compounds that modulate nuclear TAZ activity.

TAZ Suppresses NFAT5 Activity through Tyrosine Phosphorylation

ABSTRACT Transcriptional coactivator with PDZ-binding motif (TAZ) physically interacts with a variety of transcription factors and modulates their activities involved in cell proliferation and mesenchymal stem cell differentiation. TAZ is highly expressed in the kidney, and a deficiency of this protein results in multiple renal cysts and urinary concentration defects; however, the molecular functions of TAZ in renal cells remain largely unknown. In this study, we examined the effects of osmotic stress on TAZ expression and activity in renal cells. We found that hyperosmotic stress selectively increased protein phosphorylation at tyrosine 316 of TAZ and that this was enhanced by c-Abl activation in response to hyperosmotic stress. Interestingly, phosphorylated TAZ physically interacted with nuclear factor of activated T cells 5 (NFAT5), a major osmoregulatory transcription factor, and subsequently suppressed DNA binding and transcriptional activity of NFAT5. Furthermore, TAZ deficiency elicited an increase in NFAT5 activity in vitro and in vivo, which then reverted to basal levels following restoration of wild-type TAZ but not mutant TAZ (Y316F). Collectively, the data suggest that TAZ modulates cellular responses to hyperosmotic stress through fine-tuning of NFAT5 activity via tyrosine phosphorylation.

Novel TAZ modulators enhance myogenic differentiation and muscle regeneration.

The transcriptional co‐activator with PDZ‐binding motif (TAZ) is a key controller of mesenchymal stem cell differentiation through its nuclear localization and subsequent interaction with master transcription factors. In particular, TAZ directly associates with myoblast determining protein D (MyoD) and activates MyoD‐induced myogenic gene expression, thereby enhancing myogenic differentiation. Here, we have synthesized and characterized low MW compounds modulating myogenic differentiation via induction of TAZ nuclear localization.

Anti‐Adipogenic Activity of the Naturally Occurring Phenanthroindolizidine Alkaloid Antofine via Direct Suppression of PPARγ Expression

Antofine (ANTF) is a phenanthroindolizidine alkaloid isolated from the root of Cynanchum paniculatum Kitagawa (Asclepiadaceae), which is used as an herbal remedy for pain and inflammation. ANTF also possesses antiviral and antitumorigenic activities. In this study, we investigated the role of ANTF in adipogenesis. Chronic ABTF administration suppressed adipocyte differentiation and marker expression in a dose‐dependent manner. Furthermore, acute administration of ANTF at early stages of differentiation process inhibited lipid droplet formation and adipogenic gene expression. ANTF Treatment decreased expression of PPARγ protein, a master transcription factor in the regulation of adipocyte differentiation, leading to a suppression of aP2 promoter activity. These results suggest that ANTF exerts potent anti‐adipogenic effects via direct suppression of PPARγ protein expression, with consequent downregulation of adipogenic gene expression.

Hesperedin promotes MyoD‐induced myogenic differentiation in vitro and in vivo

BACKGROUND AND PURPOSE The bioflavonoid, hesperedin, promotes osteoblast differentiation in human mesenchymal stem cells, indicating an anabolic effect of hesperedin on bone metabolism. Murine bone marrow mesenchymal stem cells undergo myogenic differentiation as well as osteogenic differentiation. We therefore explored whether hesperedin modulates muscle cell differentiation.

TM-25659-Induced Activation of FGF21 Level Decreases Insulin Resistance and Inflammation in Skeletal Muscle via GCN2 Pathways

The TAZ activator 2-butyl-5-methyl-6-(pyridine-3-yl)-3-[2′-(1H-tetrazole-5-yl)-biphenyl-4-ylmethyl]-3H-imidazo[4,5-b]pyridine] (TM-25659) inhibits adipocyte differentiation by interacting with peroxisome proliferator-activated receptor gamma. TM-25659 was previously shown to decrease weight gain in a high fat (HF) diet-induced obesity (DIO) mouse model. However, the fundamental mechanisms underlying the effects of TM-25659 remain unknown. Therefore, we investigated the effects of TM-25659 on skeletal muscle functions in C2 myotubes and C57BL/6J mice. We studied the molecular mechanisms underlying the contribution of TM-25659 to palmitate (PA)-induced insulin resistance in C2 myotubes. TM-25659 improved PA-induced insulin resistance and inflammation in C2 myotubes. In addition, TM-25659 increased FGF21 mRNA expression, protein levels, and FGF21 secretion in C2 myotubes via activation of GCN2 pathways (GCN2-phosphoeIF2α-ATF4 and FGF21). This beneficial effect of TM-25659 was diminished by FGF21 siRNA. C57BL/6J mice were fed a HF diet for 30 weeks. The HF-diet group was randomly divided into two groups for the next 14 days: the HF-diet and HF-diet + TM-25659 groups. The HF diet + TM-25659-treated mice showed improvements in their fasting blood glucose levels, insulin sensitivity, insulin-stimulated Akt phosphorylation, and inflammation, but neither body weight nor food intake was affected. The HF diet + TM-25659-treated mice also exhibited increased expression of both FGF21 mRNA and protein. These data indicate that TM-25659 may be beneficial for treating insulin resistance by inducing FGF21 in models of PA-induced insulin resistance and HF diet-induced insulin resistance.

Transcriptional coactivator with PDZ-binding motif is required to sustain testicular function on aging

Transcriptional coactivator with PDZ‐binding motif (TAZ) directly interacts with transcription factors and regulates their transcriptional activity. Extensive functional studies have shown that TAZ plays critical regulatory roles in stem cell proliferation, differentiation, and survival and also modulates the development of organs such as the lung, kidney, heart, and bone. Despite the importance of TAZ in stem cell maintenance, TAZ function has not yet been evaluated in spermatogenic stem cells of the male reproductive system. Here, we investigated the expression and functions of TAZ in mouse testis. TAZ was expressed in spermatogenic stem cells; however, its deficiency caused significant structural abnormalities, including atrophied tubules, widened interstitial space, and abnormal Leydig cell expansion, thereby resulting in lowered sperm counts and impaired fertility. Furthermore, TAZ deficiency increased the level of apoptosis and senescence in spermatogenic cells and Leydig cells upon aging. The expression of senescence‐associated β‐galactosidase (SA‐βgal), secretory phenotypes, and cyclin‐dependent kinase inhibitors (p16, p19, and p21) significantly increased in the absence of TAZ. TAZ downregulation in testicular cells further increased SA‐βgal and p21 expression induced by oxidative stress, whereas TAZ overexpression decreased p21 induction and prevented senescence. Mechanistic studies showed that TAZ suppressed DNA‐binding activity of p53 through a direct interaction and thus attenuated p53‐induced p21 gene transcription. Our results suggested that TAZ may suppress apoptosis and premature senescence in spermatogenic cells by inhibiting the p53‐p21 signaling pathway, thus playing important roles in the maintenance and control of reproductive function.

Novel benzoxazole derivatives DCPAB and HPAB attenuate Th1 cell-mediated inflammation through T-bet suppression

Interferon-γ (IFN-γ), a critical inflammatory cytokine, is primarily produced by T helper 1 (Th1) cells and accelerates the pathogenesis of inflammatory colitis. Pharmacological suppression of IFN-γ production attenuates dysregulated inflammatory responses and may be beneficial for treating inflammatory disease. In this study, we aimed to discover potent anti-inflammatory compounds that suppress IFN-γ production and found that the novel benzoxazole derivatives, 2-((3,4-dichlorophenyl) amino) benzo[d]xazol-5-ol (DCPAB) and 2-((3,4-hydroxyphenyl) amino) benzo[d]xazol-5-ol (HPAB), suppressed IFN-γ production by T cells. Treatment of CD4+ T cells with DCPAB and HPAB selectively inhibited Th1 cell development, and DCPAB more potently suppressed IFN-γ than HPAB did. Interestingly, DCPAB and HPAB significantly suppressed the expression of T-box containing protein expressed in T cells (T-bet) that activates IFN-γ gene transcription. DCPAB additionally suppressed transcriptional activity of T-bet on IFN-γ gene promoter, whereas HPAB had no effect on T-bet activity. IFN-γ suppressive activity of DCPAB and HPAB was impaired in the absence of T-bet but was retrieved by the restoration of T-bet in T-bet-deficient T cells. Furthermore, DCPAB and HPAB attenuated inflammatory colitis development that was induced by CD4+ T cells in vivo. We suggest that the novel benzoxazole derivatives, DCPAB and HPAB, may have therapeutic effects on inflammatory colitis.