MicroRNA-122-5p alleviates endometrial fibrosis via inhibiting the TGF-β/SMAD pathway in Asherman's syndrome

RESEARCH QUESTION

What is the effect of miR-122 on the progression and recovery of fibrosis in Asherman's syndrome?

DESIGN

Endometrial tissue was collected from 21 patients, 11 with intrauterine adhesion (IUA) and 10 without IUA. Quantitative real-time polymerase chain reaction, immunofluorescence and Western blot were applied to observe the expression of mRNAs/miRNAs and protein, respectively. The endometrial physical injury was carried out in C57BL/6 mice to create an endometrial fibrosis model, with intrauterine injection of adenovirus to compare the antifibrosis and repair function of miR-122 on endometrium. The morphology of the uterus was observed using haematoxylin and eosin staining, and fibrosis markers were detected by immunohistochemistry.

RESULTS

miR-122 expression was reduced in patients with IUAs, accompanied by fibrosis. MiR-122 overexpression reduced the degree of fibrosis in endometrial stromal cells. Further molecular analyses demonstrated that miR-122 inhibited fibrosis through the TGF-β/SMAD pathway by directly targeting the 3' untranslated region of SMAD family member 3, suppressing its expression. Notably, miR-122 promoted endometrial regeneration and recovery of pregnancy capacity in a mouse endometrial injury model.

CONCLUSIONS

miR-122 is a critical regulator for repair of endometrial fibrosis and provided new insight for the clinical treatment of intrauterine adhesions.

Transmembrane anterior posterior transformation 1 regulates BMP signaling and modulates the protein stability of SMAD1/5

The bone morphogenetic protein (BMP) signaling pathway plays pivotal roles in various biological processes during embryogenesis and adult homeostasis. Transmembrane anterior posterior transformation 1 (TAPT1) is an evolutionarily conserved protein involved in murine axial skeletal patterning. Genetic defects in TAPT1 result in complex lethal osteochondrodysplasia. However, the specific cellular activity of TAPT1 is not clear. Herein, we report that TAPT1 inhibits BMP signaling and destabilizes the SMAD1/5 protein by facilitating its interaction with SMURF1 E3 ubiquitin ligase, which leads to SMAD1/5 proteasomal degradation. In addition, we found that the activation of BMP signaling facilitates the redistribution of TAPT1 and promotes its association with SMAD1. TAPT1-deficient murine C2C12 myoblasts or C3H/10T1/2 mesenchymal stem cells exhibit elevated SMAD1/5/9 protein levels, which amplifies BMP activation, in turn leading to a boost in the transdifferentiation or differentiation processing of these distinct TAPT1-deficient cell lines changing into mature osteoblasts. Furthermore, the enhancing effect of TAPT1 deficiency on osteogenic differentiation of C3H/10T1/2 cells was observed in an in vivo ectopic bone formation model. Importantly, a subset of TAPT1 mutations identified in humans with lethal skeletal dysplasia exhibited gain-of-function activity on SMAD1 protein levels. Thus, this finding elucidates the role of TAPT1 in the regulation of SMAD1/5 protein stability for controlling BMP signaling.

β-cell Smad2 null mice have improved β-cell function and are protected from diet-induced hyperglycemia

Understanding signaling pathways that regulate pancreatic β-cell function to produce, store, and release insulin, as well as pathways that control β-cell proliferation, is vital to find new treatments for diabetes mellitus. Transforming growth factor-beta (TGF-β) signaling is involved in a broad range of β-cell functions. The canonical TGF-β signaling pathway functions through intracellular smads, including smad2 and smad3, to regulate cell development, proliferation, differentiation, and function in many organs. Here, we demonstrate the role of TGF-β/smad2 signaling in regulating mature β-cell proliferation and function using β-cell-specific smad2 null mutant mice. β-cell-specific smad2-deficient mice exhibited improved glucose clearance as demonstrated by glucose tolerance testing, enhanced in vivo and ex vivo glucose-stimulated insulin secretion, and increased β-cell mass and proliferation. Furthermore, when these mice were fed a high-fat diet to induce hyperglycemia, they again showed improved glucose tolerance, insulin secretion, and insulin sensitivity. In addition, ex vivo analysis of smad2-deficient islets showed that they displayed increased glucose-stimulated insulin secretion and upregulation of genes involved in insulin synthesis and insulin secretion. Thus, we conclude that smad2 could represent an attractive therapeutic target for type 2 diabetes mellitus.

The evolutionarily conserved deubiquitinase UBH1/UCH-L1 augments DAF7/TGF-β signaling, inhibits dauer larva formation, and enhances lung tumorigenesis

Modification of the transforming growth factor β (TGF-β) signaling components by (de)ubiquitination is emerging as a key regulatory mechanism that controls cell signaling responses in health and disease. Here, we show that the deubiquitinating enzyme UBH-1 in Caenorhabditis elegans and its human homolog, ubiquitin C-terminal hydrolase-L1 (UCH-L1), stimulate DAF-7/TGF-β signaling, suggesting that this mode of regulation of TGF-β signaling is conserved across animal species. The dauer larva-constitutive C. elegans phenotype caused by defective DAF-7/TGF-β signaling was enhanced and suppressed, respectively, by ubh-1 deletion and overexpression in the loss-of-function genetic backgrounds of daf7, daf-1/TGF-βRI, and daf4/R-SMAD, but not of daf-8/R-SMAD. This suggested that UBH-1 may stimulate DAF-7/TGF-β signaling via DAF-8/R-SMAD. Therefore, we investigated the effect of UCH-L1 on TGF-β signaling via its intracellular effectors, i.e. SMAD2 and SMAD3, in mammalian cells. Overexpression of UCH-L1, but not of UCH-L3 (the other human homolog of UBH1) or of the catalytic mutant UCH-L1C90A, enhanced TGF-β/SMAD-induced transcriptional activity, indicating that the deubiquitination activity of UCH-L1 is indispensable for enhancing TGF-β/SMAD signaling. We also found that UCH-L1 interacts, deubiquitinates, and stabilizes SMAD2 and SMAD3. Under hypoxia, UCH-L1 expression increased and TGF-β/SMAD signaling was potentiated in the A549 human lung adenocarcinoma cell line. Notably, UCH-L1-deficient A549 cells were impaired in tumorigenesis, and, unlike WT UCH-L1, a UCH-L1 variant lacking deubiquitinating activity was unable to restore tumorigenesis in these cells. These results indicate that UCH-L1 activity supports DAF-7/TGF-β signaling and suggest that UCH-L1's deubiquitination activity is a potential therapeutic target for managing lung cancer.

Mediator complex subunit 16 is down-regulated in papillary thyroid cancer, leading to increased transforming growth factor-β signaling and radioiodine resistance

Mediator complex subunit 16 (MED16) is a component of the mediator complex and functions as a coactivator in transcriptional events at almost all RNA polymerase II-dependent genes. In this study, we report that the expression of MED16 is markedly decreased in papillary thyroid cancer (PTC) tumors compared with normal thyroid tissues. In vitro, MED16 overexpression in PTC cells significantly inhibited cell migration, enhanced sodium/iodide symporter expression and iodine uptake, and decreased resistance to radioactive ¹³¹I (RAI). Conversely, PTC cells in which MED16 had been further knocked down (MED16^KD) exhibited enhanced cell migration, epithelial-mesenchymal transition, and RAI resistance, accompanied by decreased sodium/iodide symporter levels. Moreover, cell signaling through transforming growth factor β (TGF-β) was highly activated after the MED16 knockdown. Similar results were obtained in MED12^KD PTC cells, and a co-immunoprecipitation experiment verified interactions between MED16 and MED12 and between MED16 and TGF-βR2. Of note, the application of LY2157299, a potent inhibitor of TGF-β signaling, significantly attenuated MED16^KD-induced RAI resistance both in vitro and in vivo In conclusion, our findings indicate that MED16 reduction in PTC contributes to tumor progression and RAI resistance via the activation of the TGF-β pathway.

A variant of human growth differentiation factor-9 that improves oocyte developmental competence

Growth differentiation factor-9 (GDF9) and bone morphogenetic protein-15 (BMP15) are co-expressed exclusively in oocytes throughout most of folliculogenesis and play central roles in controlling ovarian physiology. Although both growth factors exist as homodimers, recent evidence indicates that GDF9 and BMP15 can also heterodimerize to form the potent growth factor cumulin. Within the cumulin complex, BMP15 "activates" latent GDF9, enabling potent signaling in granulosa cells via type I receptors (i.e. activin receptor-like kinase-4/5 (ALK4/5)) and SMAD2/3 transcription factors. In the cumulin heterodimer, two distinct type I receptor interfaces are formed compared with homodimeric GDF9 and BMP15. Previous studies have highlighted the potential of cumulin to improve treatment of female infertility, but, as a noncovalent heterodimer, cumulin is difficult to produce and purify without contaminating GDF9 and BMP15 homodimers. In this study we addressed this challenge by focusing on the cumulin interface formed by the helix of the GDF9 chain and the fingers of the BMP15 chain. We demonstrate that unique BMP15 finger residues at this site (Arg³⁰¹, Gly³⁰⁴, His³⁰⁷, and Met³⁶⁹) enable potent activation of the SMAD2/3 pathway. Incorporating these BMP15 residues into latent GDF9 generated a highly potent growth factor, called hereafter Super-GDF9. Super-GDF9 was >1000-fold more potent than WT human GDF9 and 4-fold more potent than cumulin in SMAD2/3-responsive transcriptional assays in granulosa cells. Our demonstration that Super-GDF9 can effectively promote mouse cumulus cell expansion and improve oocyte quality in vitro represents a potential solution to the current challenges of producing and purifying intact cumulin.

SMAD7 enhances adult β-cell proliferation without significantly affecting β-cell function in mice

The interplay between the transforming growth factor β (TGF-β) signaling proteins, SMAD family member 2 (SMAD2) and 3 (SMAD3), and the TGF-β-inhibiting SMAD, SMAD7, seems to play a vital role in proper pancreatic endocrine development and also in normal β-cell function in adult pancreatic islets. Here, we generated conditional SMAD7 knockout mice by crossing insulin1^Cre mice with SMAD7^fx/fx mice. We also created a β cell-specific SMAD7-overexpressing mouse line by crossing insulin1^Dre mice with HPRT-SMAD7/RosaGFP mice. We analyzed β-cell function in adult islets when SMAD7 was either absent or overexpressed in β cells. Loss of SMAD7 in β cells inhibited proliferation, and SMAD7 overexpression enhanced cell proliferation. However, alterations in basic glucose homeostasis were not detectable following either SMAD7 deletion or overexpression in β cells. Our results show that both the absence and overexpression of SMAD7 affect TGF-β signaling and modulates β-cell proliferation but does not appear to alter β-cell function. Reversible SMAD7 overexpression may represent an attractive therapeutic option to enhance β-cell proliferation without negative effects on β-cell function.

Sirtuin 6 deficiency transcriptionally up-regulates TGF-β signaling and induces fibrosis in mice

Caloric restriction has been associated with increased life span and reduced aging-related disorders and reduces fibrosis in several diseases. Fibrosis is characterized by deposition of excess fibrous material in tissues and organs and is caused by aging, chronic stress, injury, or disease. Myofibroblasts are fibroblast-like cells that secrete high levels of extracellular matrix proteins, resulting in fibrosis. Histological studies have identified many-fold increases of myofibroblasts in aged organs where myofibroblasts are constantly generated from resident tissue fibroblasts and other cell types. However, it remains unclear how aging increases the generation of myofibroblasts. Here, using mouse models and biochemical assays, we show that sirtuin 6 (SIRT6) deficiency plays a major role in aging-associated transformation of fibroblasts to myofibroblasts, resulting in tissue fibrosis. Our findings suggest that SIRT6-deficient fibroblasts transform spontaneously to myofibroblasts through hyperactivation of transforming growth factor β (TGF-β) signaling in a cell-autonomous manner. Importantly, we noted that SIRT6 haploinsufficiency is sufficient for enhancing myofibroblast generation, leading to multiorgan fibrosis and cardiac dysfunction in mice during aging. Mechanistically, SIRT6 bound to and repressed the expression of key TGF-β signaling genes by deacetylating SMAD family member 3 (SMAD3) and Lys-9 and Lys-56 in histone 3. SIRT6 binding to the promoters of genes in the TGF-β signaling pathway decreased significantly with age and was accompanied by increased binding of SMAD3 to these promoters. Our findings reveal that SIRT6 may be a potential candidate for modulating TGF-β signaling to reduce multiorgan fibrosis during aging and fibrosis-associated diseases.

BMP10 preserves cardiac function through its dual activation of SMAD-mediated and STAT3-mediated pathways

Bone morphogenetic protein 10 (BMP10) is a cardiac peptide growth factor belonging to the transforming growth factor β superfamily that critically controls cardiovascular development, growth, and maturation. It has been shown that BMP10 elicits its intracellular signaling through a receptor complex of activin receptor-like kinase 1 with morphogenetic protein receptor type II or activin receptor type 2A. Previously, we generated and characterized a transgenic mouse line expressing BMP10 from the α-myosin heavy chain gene promoter and found that these mice have normal cardiac hypertrophic responses to both physiological and pathological stimuli. In this study, we report that these transgenic mice exhibit significantly reduced levels of cardiomyocyte apoptosis and cardiac fibrosis in response to a prolonged administration of the β-adrenoreceptor agonist isoproterenol. We further confirmed this cardioprotective function with a newly generated conditional Bmp10 transgenic mouse line, in which Bmp10 was activated in adult hearts by tamoxifen. Moreover, the intraperitoneal administration of recombinant human BMP10 was found to effectively protect hearts from injury, suggesting potential therapeutic utility of using BMP10 to prevent heart failure. Gene profiling and biochemical analyses indicated that BMP10 activates the SMAD-mediated canonical pathway and, unexpectedly, also the signal transducer and activator of transcription 3 (STAT3)-mediated signaling pathway both in vivo and in vitro Additional findings further supported the notion that BMP10's cardioprotective function likely is due to its dual activation of SMAD- and STAT3-regulated signaling pathways, promoting cardiomyocyte survival and suppressing cardiac fibrosis.

Activin A receptor type 1-mediated BMP signaling regulates RANKL-induced osteoclastogenesis via canonical SMAD-signaling pathway

Bone morphogenetic proteins (BMPs) are important mediators of osteoclast differentiation. Although accumulating evidence has implicated BMPs in osteoblastogenesis, the mechanisms by which BMPs regulate osteoclastogenesis remain unclear. Activin A receptor type 1 (ACVR1) is a BMP type 1 receptor essential for skeletal development. Here, we observed that BMP-7, which preferentially binds to ACVR1, promotes osteoclast differentiation, suggesting ACVR1 is involved in osteoclastogenesis. To investigate this further, we isolated osteoclasts from either Acvr1-floxed mice or mice with constitutively-activated Acvr1 (caAcvr1) carrying tamoxifen-inducible Cre driven by a ubiquitin promotor and induced Cre activity in culture. Osteoclasts from the Acvr1-floxed mice had reduced osteoclast numbers and demineralization activity, whereas those from the caAcvr1-mutant mice formed large osteoclasts and demineralized pits, suggesting that BMP signaling through ACVR1 regulates osteoclast fusion and activity. It is reported that BMP-2 binds to BMPR1A, another BMP type 1 receptor, whereas BMP-7 binds to ACVR1 to activate SMAD1/5/9 signaling. Here, Bmpr1a-disrupted osteoclasts displayed reduced phospho-SMAD1/5/9 (pSMAD1/5/9) levels when induced by BMP-2, whereas no impacts on pSMAD1/5/9 were observed when induced by BMP-7. In contract, Acvr1-disrupted osteoclasts displayed reduced pSMAD1/5/9 levels when induced either by BMP-2 or BMP-7, suggesting that ACVR1 is the major receptor for transducing BMP-7 signals in osteoclasts. Indeed, LDN-193189 and LDN-212854, which specifically block SMAD1/5/9 phosphorylation, inhibited osteoclastogenesis of caAcvr1-mutant cells. Moreover, increased BMP signaling promoted nuclear translocation of nuclear factor-activated T-cells 1 (NFATc1), which was inhibited by LDN treatments. Taken together, ACVR1-mediated BMP-SMAD signaling activates NFATc1, a regulatory protein crucial for receptor activator of NF-κB ligand (RANKL)-induced osteoclastogenesis.

FOXO1 transcription factor regulates chondrogenic differentiation through transforming growth factor β1 signaling

The forkhead box O (FOXO) proteins are transcription factors involved in the differentiation of many cell types. Type II collagen (Col2) Cre-Foxo1-knockout and Col2-Cre-Foxo1,3,4 triple-knockout mice exhibit growth plate malformation. Moreover, recent studies have reported that in some cells, the expressions and activities of FOXOs are promoted by transforming growth factor β1 (TGFβ1), a growth factor playing a key role in chondrogenic differentiation. Here, using a murine chondrogenic cell line (ATDC5), mouse embryos, and human mesenchymal stem cells, we report the mechanisms by which FOXOs affect chondrogenic differentiation. FOXO1 expression increased along with chondrogenic differentiation, and FOXO1 inhibition suppressed chondrogenic differentiation. TGFβ1/SMAD signaling promoted expression and activity of FOXO1. In ATDC5, FOXO1 knockdown suppressed expression of sex-determining region Y box 9 (Sox9), a master regulator of chondrogenic differentiation, resulting in decreased collagen type II α1 (Col2a1) and aggrecan (Acan) expression after TGFβ1 treatment. On the other hand, chemical FOXO1 inhibition suppressed Col2a1 and Acan expression without suppressing Sox9 To investigate the effects of FOXO1 on chondrogenic differentiation independently of SOX9, we examined FOXO1's effects on the cell cycle. FOXO1 inhibition suppressed expression of p21 and cell-cycle arrest in G₀/G₁ phase. Conversely, FOXO1 overexpression promoted expression of p21 and cell-cycle arrest. FOXO1 inhibition suppressed expression of nascent p21 RNA by TGFβ1, and FOXO1 bound the p21 promoter. p21 inhibition suppressed expression of Col2a1 and Acan during chondrogenic differentiation. These results suggest that FOXO1 is necessary for not only SOX9 expression, but also cell-cycle arrest during chondrogenic differentiation via TGFβ1 signaling.

A comparative analysis of Smad-responsive motifs identifies multiple regulatory inputs for TGF-β transcriptional activation

Smad proteins are transcriptional regulators activated by TGF-β. They are known to bind to two distinct Smad-responsive motifs, namely the Smad-binding element (SBE) (5'-GTCTAGAC-3') and CAGA motifs (5'-AGCCAGACA-3' or 5'-TGTCTGGCT-3'). However, the mechanisms by which these motifs promote Smad activity are not fully elucidated. In this study, we performed DNA CASTing, binding assays, ChIP sequencing, and quantitative RT-PCR to dissect the details of Smad binding and function of the SBE and CAGA motifs. We observed a preference for Smad3 to bind CAGA motifs and Smad4 to bind SBE, and that either one SBE or a triple-CAGA motif forms a cis-acting functional half-unit for Smad-dependent transcription activation; combining two half-units allows efficient activation. Unexpectedly, the extent of Smad binding did not directly correlate with the abilities of Smad-binding sequences to induce gene expression. We found that Smad proteins are more tolerant of single bp mutations in the context of the CAGA motifs, with any mutation in the SBE disrupting function. CAGA and CAGA-like motifs but not SBE are widely distributed among stimulus-dependent Smad2/3-binding sites in normal murine mammary gland epithelial cells, and the number of CAGA and CAGA-like motifs correlates with fold-induction of target gene expression by TGF-β. These data, demonstrating Smad responsiveness can be tuned by both sequence and number of repeats, provide a compelling explanation for why CAGA motifs are predominantly used for Smad-dependent transcription activation in vivo.

Transforming growth factor-β (TGF-β)-induced up-regulation of TGF-β receptors at the cell surface amplifies the TGF-β response

Functional activation of the transforming growth factor-β (TGF-β) receptors (TGFBRs) is carefully regulated through integration of post-translational modifications, spatial regulation at the cellular level, and TGFBR availability at the cell surface. Although the bulk of TGFBRs resides inside the cells, AKT Ser/Thr kinase (AKT) activation in response to insulin or other growth factors rapidly induces transport of TGFBRs to the cell surface, thereby increasing the cell's responsiveness to TGF-β. We now demonstrate that TGF-β itself induces a rapid translocation of its own receptors to the cell surface and thus amplifies its own response. This mechanism of response amplification, which hitherto has not been reported for other cell-surface receptors, depended on AKT activation and TGF-β type I receptor kinase. In addition to an increase in cell-surface TGFBR levels, TGF-β treatment promoted TGFBR internalization, suggesting an overall amplification of TGFBR cycling. The TGF-β-induced increase in receptor presentation at the cell surface amplified TGF-β-induced SMAD family member (SMAD) activation and gene expression. Furthermore, bone morphogenetic protein 4 (BMP-4), which also induces AKT activation, increased TGFBR levels at the cell surface, leading to enhanced autocrine activation of TGF-β-responsive SMADs and gene expression, providing context for the activation of TGF-β signaling in response to BMP during development. In summary, our results indicate that TGF-β- and BMP-induced activation of low levels of cell surface-associated TGFBRs rapidly mobilizes additional TGFBRs from intracellular stores to the cell surface, increasing the abundance of cell-surface TGFBRs and cells' responsiveness to TGF-β signaling.

PDZK1-interacting protein 1 (PDZK1IP1) traps Smad4 protein and suppresses transforming growth factor-β (TGF-β) signaling

Transforming growth factor (TGF)-β signaling in humans is stringently regulated to prevent excessive TGF-β signaling. In tumors, TGF-β signaling can both negatively and positively regulate tumorigenesis dependent on tumor type, but the reason for these opposite effects is unclear. TGF-β signaling is mainly mediated via the Smad-dependent pathway, and herein we found that PDZK1-interacting protein 1 (PDZK1IP1) interacts with Smad4. PDZK1IP1 inhibited both the TGF-β and the bone morphogenetic protein (BMP) pathways without affecting receptor-regulated Smad (R-Smad) phosphorylation. Rather than targeting R-Smad phosphorylation, PDZK1IP1 could interfere with TGF-β- and BMP-induced R-Smad/Smad4 complex formation. Of note, PDZK1IP1 retained Smad4 in the cytoplasm of TGF-β-stimulated cells. To pinpoint PDZK1IP1's functional domain, we created several PDZK1IP1 variants and found that its middle region, from Phe⁴⁰ to Ala⁴⁹, plays a key role in its Smad4-regulating activity. PDZK1IP1 knockdown enhanced the expression of the TGF-β target genes Smad7 and prostate transmembrane protein androgen-induced (TMEPAI) upon TGF-β stimulation. In contrast, PDZK1IP1 overexpression suppressed TGF-β-induced reporter activities, cell migration, and cell growth inhibition. In a xenograft tumor model in which TGF-β was previously shown to elicit tumor-promoting effects, PDZK1IP1 gain of function decreased tumor size and increased survival rates. Taken together, these findings indicate that PDZK1IP1 interacts with Smad4 and thereby suppresses the TGF-β signaling pathway.

SMAD family member 3 (SMAD3) and SMAD4 repress HIF2α-dependent iron-regulatory genes

Hypoxia-inducible factor 2α (HIF2α) directly regulates a battery of genes essential for intestinal iron absorption. Interestingly, iron deficiency and overload disorders do not result in increased intestinal expression of glycolytic or angiogenic HIF2α target genes. Similarly, inflammatory and tumor foci can induce a distinct subset of HIF2α target genes in vivo These observations indicate that different stimuli activate distinct subsets of HIF2α target genes via mechanisms that remain unclear. Here, we conducted a high-throughput siRNA-based screen to identify genes that regulate HIF2α's transcriptional activity on the promoter of the iron transporter gene divalent metal transporter-1 (DMT1). SMAD family member 3 (SMAD3) and SMAD4 were identified as potential transcriptional repressors. Further analysis revealed that SMAD4 signaling selectively represses iron-absorptive gene promoters but not the inflammatory or glycolytic HIF2α or HIF1α target genes. Moreover, the highly homologous SMAD2 did not alter HIF2α transcriptional activity. During iron deficiency, SMAD3 and SMAD4 expression was significantly decreased via proteasomal degradation, allowing for derepression of iron target genes. Several iron-regulatory genes contain a SMAD-binding element (SBE) in their proximal promoters; however, mutation of the putative SBE on the DMT1 promoter did not alter the repressive function of SMAD3 or SMAD4. Importantly, the transcription factor forkhead box protein A1 (FOXA1) was critical in SMAD4-induced DMT1 repression, and DNA binding of SMAD4 was essential for the repression of HIF2α activity, suggesting an indirect repressive mechanism through DNA binding. These results provide mechanistic clues to how HIF signaling can be regulated by different cellular cues.

Transforming growth factor β (TGFβ) induces NUAK kinase expression to fine-tune its signaling output

TGFβ signaling via SMAD proteins and protein kinase pathways up- or down-regulates the expression of many genes and thus affects physiological processes, such as differentiation, migration, cell cycle arrest, and apoptosis, during developmental or adult tissue homeostasis. We here report that NUAK family kinase 1 (NUAK1) and NUAK2 are two TGFβ target genes. NUAK1/2 belong to the AMP-activated protein kinase (AMPK) family, whose members control central and protein metabolism, polarity, and overall cellular homeostasis. We found that TGFβ-mediated transcriptional induction of NUAK1 and NUAK2 requires SMAD family members 2, 3, and 4 (SMAD2/3/4) and mitogen-activated protein kinase (MAPK) activities, which provided immediate and early signals for the transient expression of these two kinases. Genomic mapping identified an enhancer element within the first intron of the NUAK2 gene that can recruit SMAD proteins, which, when cloned, could confer induction by TGFβ. Furthermore, NUAK2 formed protein complexes with SMAD3 and the TGFβ type I receptor. Functionally, NUAK1 suppressed and NUAK2 induced TGFβ signaling. This was evident during TGFβ-induced epithelial cytostasis, mesenchymal differentiation, and myofibroblast contractility, in which NUAK1 or NUAK2 silencing enhanced or inhibited these responses, respectively. In conclusion, we have identified a bifurcating loop during TGFβ signaling, whereby transcriptional induction of NUAK1 serves as a negative checkpoint and NUAK2 induction positively contributes to signaling and terminal differentiation responses to TGFβ activity.

High-throughput screens for agonists of bone morphogenetic protein (BMP) signaling identify potent benzoxazole compounds

Bone morphogenetic protein (BMP) signaling is critical in renal development and disease. In animal models of chronic kidney disease (CKD), re-activation of BMP signaling is reported to be protective by promoting renal repair and regeneration. Clinical use of recombinant BMPs, however, requires harmful doses to achieve efficacy and is costly because of BMPs' complex synthesis. Therefore, alternative strategies are needed to harness the beneficial effects of BMP signaling in CKD. Key aspects of the BMP signaling pathway can be regulated by both extracellular and intracellular molecules. In particular, secreted proteins like noggin and chordin inhibit BMP activity, whereas kielin/chordin-like proteins (KCP) enhance it and attenuate kidney fibrosis or CKD. Clinical development of KCP, however, is precluded by its size and complexity. Therefore, we propose an alternative strategy to enhance BMP signaling by using small molecules, which are simpler to synthesize and more cost-effective. To address our objective, here we developed a small-molecule high-throughput screen (HTS) with human renal cells having an integrated luciferase construct highly responsive to BMPs. We demonstrate the activity of a potent benzoxazole compound, sb4, that rapidly stimulated BMP signaling in these cells. Activation of BMP signaling by sb4 increased the phosphorylation of key second messengers (SMAD-1/5/9) and also increased expression of direct target genes (inhibitors of DNA binding, Id1 and Id3) in canonical BMP signaling. Our results underscore the feasibility of utilizing HTS to identify compounds that mimic key downstream events of BMP signaling in renal cells and have yielded a lead BMP agonist.

Activin/Smad2 and Wnt/β-catenin up-regulate HAS2 and ALDH3A2 to facilitate mesendoderm differentiation of human embryonic stem cells

Activin and Wnt signaling are necessary and sufficient for mesendoderm (ME) differentiation of human embryonic stem cells (ESCs). In this study, we report that during ME differentiation induced by Activin and Wnt, Activin/Smad2 induces a decrease of the repressive histone modification of H3K27me3 by promoting the proteasome-dependent degradation of enhancer of zeste 2 polycomb (EZH2)-repressive complex 2 subunit. As a result, recruitment of the forkhead protein FOXH1 on open chromatin regions integrates the signals of Activin/Smad2 and Wnt/β-catenin to activate the expression of the ME genes including HAS2 and ALDH3A2 Consistently, H3K27me3 decrease is enriched on open chromatin around regulatory regions. Furthermore, knockdown of HAS2 or ALDH3A2 greatly attenuates ME differentiation. These findings unveil a pathway from extracellular signals to epigenetic modification-mediated gene activation during ME commitment.

LEM domain-containing protein 3 antagonizes TGFβ-SMAD2/3 signaling in a stiffness-dependent manner in both the nucleus and cytosol

Transforming growth factor-β (TGFβ) signaling through SMAD2/3 is an important driver of pathological fibrosis in multiple organ systems. TGFβ signaling and extracellular matrix (ECM) stiffness form an unvirtuous pathological circuit in which matrix stiffness drives activation of latent TGFβ, and TGFβ signaling then drives cellular stress and ECM synthesis. Moreover, ECM stiffness also appears to sensitize cells to exogenously activated TGFβ through unknown mechanisms. Here, using human fibroblasts, we explored the effect of ECM stiffness on a putative inner nuclear membrane protein, LEM domain-containing protein 3 (LEMD3), which is physically connected to the cell's actin cytoskeleton and inhibits TGFβ signaling. We showed that LEMD3-SMAD2/3 interactions are inversely correlated with ECM stiffness and TGFβ-driven luciferase activity and that LEMD3 expression is correlated with the mechanical response of the TGFβ-driven luciferase reporter. We found that actin polymerization but not cellular stress or LEMD3-nuclear-cytoplasmic couplings were necessary for LEMD3-SMAD2/3 interactions. Intriguingly, LEMD3 and SMAD2/3 frequently interacted in the cytosol, and we discovered LEMD3 was proteolytically cleaved into protein fragments. We confirmed that a consensus C-terminal LEMD3 fragment binds SMAD2/3 in a stiffness-dependent manner throughout the cell and is sufficient for antagonizing SMAD2/3 signaling. Using human lung biopsies, we observed that these nuclear and cytosolic interactions are also present in tissue and found that fibrotic tissues exhibit locally diminished and cytoplasmically shifted LEMD3-SMAD2/3 interactions, as noted in vitro Our work reveals novel LEMD3 biology and stiffness-dependent regulation of TGFβ by LEMD3, providing a novel target to antagonize pathological TGFβ signaling.

The regulatory protein SnoN antagonizes activin/Smad2 protein signaling and thereby promotes adipocyte differentiation and obesity in mice

Ski-related oncogene SnoN (SnoN or SKIL) regulates multiple signaling pathways in a tissue- and developmental stage-dependent manner and has broad functions in embryonic angiogenesis, mammary gland alveologenesis, cancer, and aging. Here, we report that SnoN also plays a critical role in white adipose tissue (WAT) development by regulating mesenchymal stem cell (MSC) self-renewal and differentiation. We found that SnoN promotes MSC differentiation in the adipocyte lineage by antagonizing activin A/Smad2, but not TGFβ/Smad3 signaling. Mice lacking SnoN or expressing a mutant SnoN defective in binding to the Smads were protected from high-fat diet-induced obesity and insulin resistance, and MSCs lacking a functional SnoN exhibited defective differentiation. We further demonstrated that activin, via Smad2, appears to be the major regulator of WAT development in vivo We also noted that activin A is abundantly expressed in WAT and adipocytes through an autocrine mechanism and promotes MSC self-renewal and inhibits adipogenic differentiation by inducing expression of the gene encoding the homeobox transcription factor Nanog. Of note, SnoN repressed activin/Smad2 signaling and activin A expression, enabling expression of adipocyte-specific transcription factors and promoting adipogenic differentiation. In conclusion, our study has revealed that SnoN plays an important in vivo role in adipocyte differentiation and WAT development in vivo by decreasing activity in the activin/Smad2 signaling pathway.

Transforming growth factor β2 (TGFβ2) signaling plays a key role in glucocorticoid-induced ocular hypertension

Elevation of intraocular pressure (IOP) is a serious adverse effect of glucocorticoid (GC) therapy. Increased extracellular matrix (ECM) accumulation and endoplasmic reticulum (ER) stress in the trabecular meshwork (TM) is associated with GC-induced IOP elevation. However, the molecular mechanisms by which GCs induce ECM accumulation and ER stress in the TM have not been determined. Here, we show that a potent GC, dexamethasone (Dex), activates transforming growth factor β (TGFβ) signaling, leading to GC-induced ECM accumulation, ER stress, and IOP elevation. Dex increased both the precursor and bioactive forms of TGFβ2 in conditioned medium and activated TGFβ-induced SMAD signaling in primary human TM cells. Dex also activated TGFβ2 in the aqueous humor and TM of a mouse model of Dex-induced ocular hypertension. We further show that Smad3^-/- mice are protected from Dex-induced ocular hypertension, ER stress, and ECM accumulation. Moreover, treating WT mice with a selective TGFβ receptor kinase I inhibitor, LY364947, significantly decreased Dex-induced ocular hypertension. Of note, knockdown of the ER stress-induced activating transcription factor 4 (ATF4), or C/EBP homologous protein (CHOP), completely prevented Dex-induced TGFβ2 activation and ECM accumulation in TM cells. These observations suggested that chronic ER stress promotes Dex-induced ocular hypertension via TGFβ signaling. Our results indicate that TGFβ2 signaling plays a central role in GC-induced ocular hypertension and provides therapeutic targets for GC-induced ocular hypertension.

Arginine methylation of SMAD7 by PRMT1 in TGF-β-induced epithelial-mesenchymal transition and epithelial stem-cell generation

The epithelial-to-mesenchymal transdifferentiation (EMT) is crucial for tissue differentiation in development and drives essential steps in cancer and fibrosis. EMT is accompanied by reprogramming of gene expression and has been associated with the epithelial stem-cell state in normal and carcinoma cells. The cytokine transforming growth factor β (TGF-β) drives this program in cooperation with other signaling pathways and through TGF-β-activated SMAD3 as the major effector. TGF-β-induced SMAD3 activation is inhibited by SMAD7 and to a lesser extent by SMAD6, and SMAD6 and SMAD7 both inhibit SMAD1 and SMAD5 activation in response to the TGF-β-related bone morphogenetic proteins (BMPs). We previously reported that, in response to BMP, protein arginine methyltransferase 1 (PRMT1) methylates SMAD6 at the BMP receptor complex, thereby promoting its dissociation from the receptors and enabling BMP-induced SMAD1 and SMAD5 activation. We now provide evidence that PRMT1 also facilitates TGF-β signaling by methylating SMAD7, which complements SMAD6 methylation. We found that PRMT1 is required for TGF-β-induced SMAD3 activation, through a mechanism similar to that of BMP-induced SMAD6 methylation, and thus promotes the TGF-β-induced EMT and epithelial stem-cell generation. This critical mechanism positions PRMT1 as an essential mediator of TGF-β signaling that controls the EMT and epithelial cell stemness through SMAD7 methylation.

Smad4 deficiency impairs chondrocyte hypertrophy via the Runx2 transcription factor in mouse skeletal development

Chondrocyte hypertrophy is the terminal step in chondrocyte differentiation and is crucial for endochondral bone formation. How signaling pathways regulate chondrocyte hypertrophic differentiation remains incompletely understood. In this study, using a Tbx18:Cre (Tbx18^Cre/+) gene-deletion approach, we selectively deleted the gene for the signaling protein SMAD family member 4 (Smad4^f/f ) in the limbs of mice. We found that the Smad4-deficient mice develop a prominent shortened limb, with decreased expression of chondrocyte differentiation markers, including Col2a1 and Acan, in the humerus at mid-to-late gestation. The most striking defects in these mice were the absence of stylopod elements and failure of chondrocyte hypertrophy in the humerus. Moreover, expression levels of the chondrocyte hypertrophy-related markers Col10a1 and Panx3 were significantly decreased. Of note, we also observed that the expression of runt-related transcription factor 2 (Runx2), a critical mediator of chondrocyte hypertrophy, was also down-regulated in Smad4-deficient limbs. To determine how the skeletal defects arose in the mouse mutants, we performed RNA-Seq with ChIP-Seq analyses and found that Smad4 directly binds to regulatory elements in the Runx2 promoter. Our results suggest a new mechanism whereby Smad4 controls chondrocyte hypertrophy by up-regulating Runx2 expression during skeletal development. The regulatory mechanism involving Smad4-mediated Runx2 activation uncovered here provides critical insights into bone development and pathogenesis of chondrodysplasia.

RhoA, Rac1, and Cdc42 differentially regulate αSMA and collagen I expression in mesenchymal stem cells

Mesenchymal stem cells (MSC) are suggested to be important progenitors of myofibroblasts in fibrosis. To understand the role of Rho GTPase signaling in TGFβ-induced myofibroblast differentiation of MSC, we generated a novel MSC line and its descendants lacking functional Rho GTPases and Rho GTPase signaling components. Unexpectedly, our data revealed that Rho GTPase signaling is required for TGFβ-induced expression of α-smooth muscle actin (αSMA) but not of collagen I α1 (col1a1). Whereas loss of RhoA and Cdc42 reduced αSMA expression, ablation of the Rac1 gene had the opposite effect. Although actin polymerization and MRTFa were crucial for TGFβ-induced αSMA expression, neither Arp2/3-dependent actin polymerization nor cofilin-dependent severing and depolymerization of F-actin were required. Instead, F-actin levels were dependent on cell contraction, and TGFβ-induced actin polymerization correlated with increased cell contraction mediated by RhoA and Cdc42. Finally, we observed impaired collagen I secretion in MSC lacking RhoA or Cdc42. These data give novel molecular insights into the role of Rho GTPases in TGFβ signaling and have implications for our understanding of MSC function in fibrosis.

Mesenchyme homeobox 1 mediates transforming growth factor-β (TGF-β)-induced smooth muscle cell differentiation from mouse mesenchymal progenitors

Differentiation of smooth muscle cells (SMCs) is critical for proper vasculogenesis and angiogenesis. However, the molecular mechanisms controlling SMC differentiation are not completely understood. During embryogenesis, the transcription factor mesenchyme homeobox 1 (Meox1) is expressed in the early developing somite, which is one of the origins of SMCs. In the present study, we identified Meox1 as a positive regulator of SMC differentiation. We found that transforming growth factor-β (TGF-β) induces Meox1 expression in the initial phase of SMC differentiation of pluripotent murine C3H10T1/2 cells. shRNA-mediated Meox1 knockdown suppressed TGF-β-induced expression of SMC early markers, whereas Meox1 overexpression increased expression of these markers. Mechanistically, Meox1 promoted SMAD family member 3 (Smad3) nuclear retention during the early stage of TGF-β stimulation because Meox1 inhibited protein phosphatase Mg²⁺/Mn²⁺-dependent 1A (PPM1A) and thereby prevented PPM1A-mediated Smad3 dephosphorylation. Meox1 appears to promote PPM1A degradation, leading to sustained Smad3 phosphorylation, thus allowing Smad3 to stimulate SMC gene transcription. In vivo, Meox1 knockdown in mouse embryos impaired SMC marker expression in the descending aorta of neonatal mice, indicating that Meox1 is essential for SMC differentiation during embryonic development. In summary, the transcriptional regulator Meox1 controls TGF-β-induced SMC differentiation from mesenchymal progenitor cells by preventing PPM1A-mediated Smad3 dephosphorylation, thereby supporting SMC gene expression.

Brain cytoplasmic RNA 1 suppresses smooth muscle differentiation and vascular development in mice

The cardiovascular system develops during the early stages of embryogenesis, and differentiation of smooth muscle cells (SMCs) is essential for that process. SMC differentiation is critically regulated by transforming growth factor (TGF)-β/SMAD family member 3 (SMAD3) signaling, but other regulators may also play a role. For example, long noncoding RNAs (lncRNAs) regulate various cellular activities and events, such as proliferation, differentiation, and apoptosis. However, whether long noncoding RNAs also regulate SMC differentiation remains largely unknown. Here, using the murine cell line C3H10T1/2, we found that brain cytoplasmic RNA 1 (BC1) is an important regulator of SMC differentiation. BC1 overexpression suppressed, whereas BC1 knockdown promoted, TGF-β-induced SMC differentiation, as indicated by altered cell morphology and expression of multiple SMC markers, including smooth muscle α-actin (αSMA), calponin, and smooth muscle 22α (SM22α). BC1 appeared to block SMAD3 activity and inhibit SMC marker gene transcription. Mechanistically, BC1 bound to SMAD3 via RNA SMAD-binding elements (rSBEs) and thus impeded TGF-β-induced SMAD3 translocation to the nucleus. This prevented SMAD3 from binding to SBEs in SMC marker gene promoters, an essential event in SMC marker transcription. In vivo, BC1 overexpression in mouse embryos impaired vascular SMC differentiation, leading to structural defects in the artery wall, such as random breaks in the elastic lamina, abnormal collagen deposition on SM fibers, and disorganized extracellular matrix proteins in the media of the neonatal aorta. Our results suggest that BC1 is a suppressor of SMC differentiation during vascular development.

The mixed lineage leukemia 4 (MLL4) methyltransferase complex is involved in transforming growth factor beta (TGF-β)-activated gene transcription

Sma and Mad related (SMAD)-mediated Transforming Growth Factor β (TGF-β) and Bone Morphogenetic Protein (BMP) signaling is required for various cellular processes. The activated heterotrimeric SMAD protein complexes associate with nuclear proteins such as the histone acetyltransferases p300, PCAF and the Mixed Lineage Leukemia 4 (MLL4) subunit Pax Transactivation domain-Interacting Protein (PTIP) to regulate gene transcription.

We investigated the functional role of PTIP and PTIP Interacting protein 1 (PA1) in relation to TGF-β-activated SMAD signaling. We immunoprecipitated PTIP and PA1 with all SMAD family members to identify the TGF-β and not BMP-specific SMADs as interacting proteins. Gene silencing experiments of MLL4 and the subunits PA1 and PTIP confirm TGF-β-specific genes to be regulated by the MLL4 complex, which links TGF-β signaling to transcription regulation by the MLL4 methyltransferase complex.

TGF-β1 regulates the expression and transcriptional activity of TAZ protein via a Smad3-independent, myocardin-related transcription factor-mediated mechanism

Hippo pathway transcriptional coactivators TAZ and YAP and the TGF-β1 (TGFβ) effector Smad3 regulate a common set of genes, can physically interact, and exhibit multilevel cross-talk regulating cell fate-determining and fibrogenic pathways. However, a key aspect of this cross-talk, TGFβ-mediated regulation of TAZ or YAP expression, remains uncharacterized. Here, we show that TGFβ induces robust TAZ but not YAP protein expression in both mesenchymal and epithelial cells. TAZ levels, and to a lesser extent YAP levels, also increased during experimental kidney fibrosis. Pharmacological or genetic inhibition of Smad3 did not prevent the TGFβ-induced TAZ up-regulation, indicating that this canonical pathway is dispensable. In contrast, inhibition of p38 MAPK, its downstream effector MK2 (e.g. by the clinically approved antifibrotic pirferidone), or Akt suppressed the TGFβ-induced TAZ expression. Moreover, TGFβ elevated TAZ mRNA in a p38-dependent manner. Myocardin-related transcription factor (MRTF) was a central mediator of this effect, as MRTF silencing/inhibition abolished the TGFβ-induced TAZ expression. MRTF overexpression drove the TAZ promoter in a CC(A/T-rich)₆GG (CArG) box-dependent manner and induced TAZ protein expression. TGFβ did not act by promoting nuclear MRTF translocation; instead, it triggered p38- and MK2-mediated, Nox4-promoted MRTF phosphorylation and activation. Functionally, higher TAZ levels increased TAZ/TEAD-dependent transcription and primed cells for enhanced TAZ activity upon a second stimulus (i.e. sphingosine 1-phosphate) that induced nuclear TAZ translocation. In conclusion, our results uncover an important aspect of the cross-talk between TGFβ and Hippo signaling, showing that TGFβ induces TAZ via a Smad3-independent, p38- and MRTF-mediated and yet MRTF translocation-independent mechanism.

Clock1a affects mesoderm development and primitive hematopoiesis by regulating Nodal-Smad3 signaling in the zebrafish embryo

Circadian clock and Smad2/3/4-mediated Nodal signaling regulate multiple physiological and pathological processes. However, it remains unknown whether Clock directly cross-talks with Nodal signaling and how this would regulate embryonic development. Here we show that Clock1a coordinated mesoderm development and primitive hematopoiesis in zebrafish embryos by directly up-regulating Nodal-Smad3 signaling. We found that Clock1a is expressed both maternally and zygotically throughout early zebrafish development. We also noted that Clock1a alterations produce embryonic defects with shortened body length, lack of the ventral tail fin, or partial defect of the eyes. Clock1a regulates the expression of the mesodermal markers ntl, gsc, and eve1 and of the hematopoietic markers scl, lmo2, and fli1a Biochemical analyses revealed that Clock1a stimulates Nodal signaling by increasing expression of Smad2/3/4. Mechanistically, Clock1a activates the smad3a promoter via its E-box1 element (CAGATG). Taken together, these findings provide mechanistic insight into the role of Clock1a in the regulation of mesoderm development and primitive hematopoiesis via modulation of Nodal-Smad3 signaling and indicate that Smad3a is directly controlled by the circadian clock in zebrafish.

Bone morphogenetic protein 9 (BMP9) and BMP10 enhance tumor necrosis factor-α-induced monocyte recruitment to the vascular endothelium mainly via activin receptor-like kinase 2

Bone morphogenetic proteins 9 and 10 (BMP9/BMP10) are circulating cytokines with important roles in endothelial homeostasis. The aim of this study was to investigate the roles of BMP9 and BMP10 in mediating monocyte-endothelial interactions using an in vitro flow adhesion assay. Herein, we report that whereas BMP9/BMP10 alone had no effect on monocyte recruitment, at higher concentrations both cytokines synergized with tumor necrosis factor-α (TNFα) to increase recruitment to the vascular endothelium. The BMP9/BMP10-mediated increase in monocyte recruitment in the presence of TNFα was associated with up-regulated expression levels of E-selectin, vascular cell adhesion molecule (VCAM-1), and intercellular adhesion molecule 1 (ICAM-1) on endothelial cells. Using siRNAs to type I and II BMP receptors and the signaling intermediaries (Smads), we demonstrated a key role for ALK2 in the BMP9/BMP10-induced surface expression of E-selectin, and both ALK1 and ALK2 in the up-regulation of VCAM-1 and ICAM-1. The type II receptors, BMPR-II and ACTR-IIA were both required for this response, as was Smad1/5. The up-regulation of cell surface adhesion molecules by BMP9/10 in the presence of TNFα was inhibited by LDN193189, which inhibits ALK2 but not ALK1. Furthermore, LDN193189 inhibited monocyte recruitment induced by TNFα and BMP9/10. BMP9/10 increased basal IκBα protein expression, but did not alter p65/RelA levels. Our findings suggest that higher concentrations of BMP9/BMP10 synergize with TNFα to induce the up-regulation of endothelial selectins and adhesion molecules, ultimately resulting in increased monocyte recruitment to the vascular endothelium. This process is mediated mainly via the ALK2 type I receptor, BMPR-II/ACTR-IIA type II receptors, and downstream Smad1/5 signaling.

The lysine methyltransferase SMYD2 methylates the kinase domain of type II receptor BMPR2 and stimulates bone morphogenetic protein signaling

Lysine methylation of chromosomal and nuclear proteins is a well-known mechanism of epigenetic regulation, but relatively little is known about the role of this protein modification in signal transduction. Using an RNAi-based functional screening of the SMYD family of lysine methyltransferases (KMTs), we identified SMYD2 as a KMT essential for robust bone morphogenic protein (BMP)- but not TGFβ-induced target gene expression in HaCaT keratinocyte cells. A role for SMYD2 in BMP-induced gene expression was confirmed by shRNA knockdown and CRISPR/Cas9-mediated knock-out of SMYD2 We further demonstrate that SMYD2 knockdown or knock-out impairs BMP-induced phosphorylation of the signal-transducing protein SMAD1/5 and SMAD1/5 nuclear localization and interaction with SMAD4. The SMYD2 KMT activity was required to facilitate BMP-mediated signal transduction, as treatment with the SMYD2 inhibitor AZ505 suppressed BMP2-induced SMAD1/5 phosphorylation. Furthermore, we present evidence that SMYD2 likely modulates the BMP response through its function in the cytosol. We show that, although SMYD2 interacted with multiple components in the BMP pathway, it specifically methylated the kinase domain of BMP type II receptor BMPR2. Taken together, our findings suggest that SMYD2 may promote BMP signaling by directly methylating BMPR2, which, in turn, stimulates BMPR2 kinase activity and activation of the BMP pathway.

The BMP4-Smad signaling pathway regulates hyperandrogenism development in a female mouse model

Polycystic ovary syndrome is a common endocrine disorder and a major cause of anovulatory sterility in women at reproductive age. Most patients with polycystic ovary syndrome have hyperandrogenism, caused by excess androgen synthesis. Bone morphogenetic protein 4 (BMP4) is an essential regulator of embryonic development and organ formation, and recent studies have also shown that BMP4 may be involved in female steroidogenesis process. However, the effect of BMP4 on hyperandrogenism remains unknown. Here, using a female mouse model of hyperandrogenism, we found that ovarian BMP4 levels were significantly decreased in hyperandrogenism. Elevated androgens inhibited BMP4 expression via activation of androgen receptors. Moreover, BMP4 treatment suppressed androgen synthesis in theca cells and promoted estrogen production in granulosa cells by regulating the expression of steroidogenic enzymes, including CYP11A, HSD3B2, CYP17A1, and CYP19A1 Consistently, knockdown of BMP4 augmented androgen levels and inhibited estrogen levels. Mechanistically, Smad signaling rather than the p38 MAPK pathway regulated androgen and estrogen formation, thereby mediating the effect of BMP4. Of note, BMP4-transgenic mice were protected against hyperandrogenism. Our observations clarify a vital role of BMP4 in controlling sex hormone levels and offer new insights into intervention for managing hyperandrogenism by targeting the BMP4-Smad signaling pathway.

Transforming Growth Factor-β (TGF-β) Directly Activates the JAK1-STAT3 Axis to Induce Hepatic Fibrosis in Coordination with the SMAD Pathway

Transforming growth factor-β (TGF-β) signals through both SMAD and non-SMAD pathways to elicit a wide array of biological effects. Existing data have shown the association and coordination between STATs and SMADs in mediating TGF-β functions in hepatic cells, but it is not clear how STATs are activated under these circumstances. Here, we report that JAK1 is a constitutive TGFβRI binding protein and is absolutely required for phosphorylation of STATs in a SMAD-independent manner within minutes of TGF-β stimulation. Following the activation of SMADs, TGF-β also induces a second phase of STAT phosphorylation that requires SMADs, de novo protein synthesis, and contribution from JAK1. Our global gene expression profiling indicates that the non-SMAD JAK1/STAT pathway is essential for the expression of a subset of TGF-β target genes in hepatic stellate cells, and the cooperation between the JAK1-STAT3 and SMAD pathways is critical to the roles of TGF-β in liver fibrosis.

TMED10 Protein Interferes with Transforming Growth Factor (TGF)-β Signaling by Disrupting TGF-β Receptor Complex Formation

The intensity and duration of TGF-β signaling determine the cellular biological response. How this is negatively regulated is not well understood. Here, we identified a novel negative regulator of TGF-β signaling, transmembrane p24-trafficking protein 10 (TMED10). TMED10 disrupts the complex formation between TGF-β type I (also termed ALK5) and type II receptors (TβRII). Misexpression studies revealed that TMED10 attenuated TGF-β-mediated signaling. A 20-amino acid-long region from Thr⁹¹ to Glu¹¹⁰ within the extracellular region of TMED10 was found to be crucial for TMED10 interaction with both ALK5 and TβRII. Synthetic peptides corresponding to this region inhibit both TGF-β-induced Smad2 phosphorylation and Smad-dependent transcriptional reporter activity. In a xenograft cancer model, where previously TGF-β was shown to elicit tumor-promoting effects, gain-of-function and loss-of-function studies for TMED10 revealed a decrease and increase in the tumor size, respectively. Thus, we determined herein that TMED10 expression levels are the key determinant for efficiency of TGF-β receptor complex formation and signaling.

TGF-β1/Smad3 Pathway Targets PP2A-AMPK-FoxO1 Signaling to Regulate Hepatic Gluconeogenesis

Maintenance of glucose homeostasis is essential for normal physiology. Deviation from normal glucose levels, in either direction, increases susceptibility to serious medical complications such as hypoglycemia and diabetes. Maintenance of glucose homeostasis is achieved via functional interactions among various organs: liver, skeletal muscle, adipose tissue, brain, and the endocrine pancreas. The liver is the primary site of endogenous glucose production, especially during states of prolonged fasting. However, enhanced gluconeogenesis is also a signature feature of type 2 diabetes (T2D). Thus, elucidating the signaling pathways that regulate hepatic gluconeogenesis would allow better insight into the process of normal endogenous glucose production as well as how this process is impaired in T2D. Here we demonstrate that the TGF-β1/Smad3 signaling pathway promotes hepatic gluconeogenesis, both upon prolonged fasting and during T2D. In contrast, genetic and pharmacological inhibition of TGF-β1/Smad3 signals suppressed endogenous glucose production. TGF-β1 and Smad3 signals achieved this effect via the targeting of key regulators of hepatic gluconeogenesis, protein phosphatase 2A (PP2A), AMP-activated protein kinase (AMPK), and FoxO1 proteins. Specifically, TGF-β1 signaling suppressed the LKB1-AMPK axis, thereby facilitating the nuclear translocation of FoxO1 and activation of key gluconeogenic genes, glucose-6-phosphatase and phosphoenolpyruvate carboxykinase. These findings underscore an important role of TGF-β1/Smad3 signaling in hepatic gluconeogenesis, both in normal physiology and in the pathophysiology of metabolic diseases such as diabetes, and are thus of significant medical relevance.

SMAD3 Regulates Follicle-stimulating Hormone Synthesis by Pituitary Gonadotrope Cells in Vivo

Pituitary follicle-stimulating hormone (FSH) is an essential regulator of fertility in females and of quantitatively normal spermatogenesis in males. Pituitary-derived activins are thought to act as major stimulators of FSH synthesis by gonadotrope cells. In vitro, activins signal via SMAD3, SMAD4, and forkhead box L2 (FOXL2) to regulate transcription of the FSHβ subunit gene (Fshb). Consistent with this model, gonadotrope-specific Smad4 or Foxl2 knock-out mice have greatly reduced FSH and are subfertile. The role of SMAD3 in vivo is unresolved; however, residual FSH production in Smad4 conditional knock-out mice may derive from partial compensation by SMAD3 and its ability to bind DNA in the absence of SMAD4. To test this hypothesis and determine the role of SMAD3 in FSH biosynthesis, we generated mice lacking both the SMAD3 DNA binding domain and SMAD4 specifically in gonadotropes. Conditional knock-out females were hypogonadal, acyclic, and sterile and had thread-like uteri; their ovaries lacked antral follicles and corpora lutea. Knock-out males were fertile but had reduced testis weights and epididymal sperm counts. These phenotypes were consistent with those of Fshb knock-out mice. Indeed, pituitary Fshb mRNA levels were nearly undetectable in both male and female knock-outs. In contrast, gonadotropin-releasing hormone receptor mRNA levels were significantly elevated in knock-outs in both sexes. Interestingly, luteinizing hormone production was altered in a sex-specific fashion. Overall, our analyses demonstrate that SMAD3 is required for FSH synthesis in vivo.

Activin/Smad2-induced Histone H3 Lys-27 Trimethylation (H3K27me3) Reduction Is Crucial to Initiate Mesendoderm Differentiation of Human Embryonic Stem Cells

Differentiation of human embryonic stem cells into mesendoderm (ME) is directed by extrinsic signals and intrinsic epigenetic modifications. However, the dynamics of these epigenetic modifications and the mechanisms by which extrinsic signals regulate the epigenetic modifications during the initiation of ME differentiation remain elusive. In this study, we report that levels of histone H3 Lys-27 trimethylation (H3K27me3) decrease during ME initiation, which is essential for subsequent differentiation induced by the combined effects of activin and Wnt signaling. Furthermore, we demonstrate that activin mediates the H3K27me3 decrease via the Smad2-mediated reduction of EZH2 protein level. Our results suggest a two-step process of ME initiation: first, epigenetic priming via removal of H3K27me3 marks and, second, transcription activation. Our findings demonstrate a critical role of H3K27me3 priming and a direct interaction between extrinsic signals and epigenetic modifications during ME initiation.

TGF-β/SMAD3 Pathway Stimulates Sphingosine-1 Phosphate Receptor 3 Expression: IMPLICATION OF SPHINGOSINE-1 PHOSPHATE RECEPTOR 3 IN LUNG ADENOCARCINOMA PROGRESSION

Previously, we showed that levels of sphingosine-1 phosphate receptor 3 (S1PR3) are increased in a panel of cultured human lung adenocarcinoma cell lines, and that S1PR3-mediated signaling pathways regulate proliferation, soft agar growth, and invasion of human lung adenocarcinoma cells in vitro In the present study, we examine S1PR3 levels in human lung adenocarcinoma specimens. cDNA array and tumor microarray analysis shows that mRNA and protein levels of S1PR3 are significantly increased in human lung adenocarcinomas when compared with normal lung epithelial cells. Promoter analysis shows 16 candidate SMAD3 binding sites in the promoter region of S1PR3. ChIP indicates that TGF-β treatment stimulates the binding of SMAD3 to the promoter region of S1PR3. Luciferase reporter assay demonstrates that SMAD3 transactivates S1PR3 promoter. TGF-β stimulation or ectopic expression of TGF-β up-regulates S1PR3 levels in vitro and ex vivo Pharmacologic inhibition of TGF-β receptor or SMAD3 abrogates the TGF-β-stimulated S1PR3 up-regulation. Moreover, S1PR3 knockdown dramatically inhibits tumor growth and lung metastasis, whereas ectopic expression of S1PR3 promotes the growth of human lung adenocarcinoma cells in animals. Pharmacological inhibition of S1PR3 profoundly inhibits the growth of lung carcinoma in mice. Our studies suggest that levels of S1PR3 are up-regulated in human lung adenocarcinomas, at least in part due to the TGF-β/SMAD3 signaling axis. Furthermore, S1PR3 activity promotes the progression of human lung adenocarcinomas. Therefore, S1PR3 may represent a novel therapeutic target for the treatment of deadly lung adenocarcinomas.

Quantitative Proteomics of the SMAD (Suppressor of Mothers against Decapentaplegic) Transcription Factor Family Identifies Importin 5 as a Bone Morphogenic Protein Receptor SMAD-specific Importin

Gene-specific transcription factors (GSTFs) control gene transcription by DNA binding and specific protein complex recruitment, which regulates promoter accessibility for transcription initiation by RNA polymerase II. Mutations in the GSTFs Suppressor of Mothers Against Decapentaplegic 2 (SMAD2) and SMAD4 are frequently associated with colon and rectal carcinomas. These proteins play an important role in bone morphogenic protein (BMP) and transforming growth factor β (TGF-β) signaling pathways controlling cell fate and proliferation. To study the protein interactome of the SMAD protein family we generated a quantitative proteomics pipeline that allows for inducible expression of GFP-tagged SMAD proteins followed by affinity purification and quantitative mass spectrometry analysis. Data are available via ProteomeXchange with identifier PXD004529. The nuclear importin IPO5 was identified as a novel interacting protein of SMAD1. Overexpression of IPO5 in various cell lines specifically increases nuclear localization of BMP receptor-activated SMADs (R-SMADs) confirming a functional relationship between IPO5 and BMP but not TGF-β R-SMADs. Finally, we provide evidence that variation in length of the lysine stretch of the nuclear localization sequence is a determinant for importin specificity.

SUMO Modification Reverses Inhibitory Effects of Smad Nuclear Interacting Protein-1 in TGF-β Responses

SNIP1 (Smad nuclear interacting protein 1) is a transcription repressor for the TGF-β and NF-κB signaling pathways through disrupting the recruitment of co-activator p300. However, it is unclear how the functions of SNIP1 in the TGF-β signaling pathway are controlled. Our present studies show that SNIP1 is covalently modified by small ubiquitin-like modifier (SUMO) in vitro and in vivo at three lysine sites: Lys⁵, Lys³⁰, and Lys¹⁰⁸, with Lys³⁰ being the major SUMO modification site. SUMOylation of SNIP1 is enhanced by SUMO E3 ligase PIAS proteins and inhibited by SUMO proteases SENP1/2. Furthermore, we find that SUMOylation of SNIP1 attenuates its inhibitory effect in TGF-β signaling because the SUMO-conjugated form of SNIP1 exhibits impaired ability to disrupt the formation of Smad complex and the interaction between p300 and Smads. Subsequently, SUMOylation of SNIP1 leads to the loss of SNIP1-mediated inhibition on expression of the TGF-β target genes PAI-1 and MMP2 and eventually enhances TGF-β-regulated cell migration and invasion.

Transforming Growth Factor β1 (TGF-β1) Activates Hepcidin mRNA Expression in Hepatocytes

The hepatic hormone hepcidin is the master regulator of systemic iron homeostasis. Its expression level is adjusted to alterations in iron levels, inflammatory cues, and iron requirements for erythropoiesis. Bone morphogenetic protein 6 (BMP6) contributes to the iron-dependent control of hepcidin. In addition, TGF-β1 may stimulate hepcidin mRNA expression in murine hepatocytes and human leukocytes. However, receptors and downstream signaling proteins involved in TGF-β1-induced hepcidin expression are still unclear. Here we show that TGF-β1 treatment of mouse and human hepatocytes, as well as ectopic expression of TGF-β1 in mice, increases hepcidin mRNA levels. The hepcidin response to TGF-β1 depends on functional TGF-β1 type I receptor (ALK5) and TGF-β1 type II receptor (TβRII) and is mediated by a noncanonical mechanism that involves Smad1/5/8 phosphorylation. Interestingly, increasing availability of canonical Smad2/3 decreases TGF-β1-induced hepcidin regulation, whereas the BMP6-hepcidin signal was enhanced, indicating a signaling component stoichiometry-dependent cross-talk between the two pathways. Although ALK2/3-dependent hepcidin activation by BMP6 can be modulated by each of the three hemochromatosis-associated proteins: HJV (hemojuvelin), HFE (hemochromatosis protein), and TfR2 (transferrin receptor 2), these proteins do not control the ALK5-mediated hepcidin response to TGF-β1. TGF-β1 mRNA levels are increased in mouse models of iron overload, indicating that TGF-β1 may contribute to hepcidin synthesis under these conditions. In conclusion, these data demonstrate that a complex regulatory network involving TGF-β1 and BMP6 may control the sensing of systemic and/or hepatic iron levels.

Regulation of Bone Morphogenetic Protein Signaling by ADP-ribosylation

We previously established a mechanism of negative regulation of transforming growth factor β signaling mediated by the nuclear ADP-ribosylating enzyme poly-(ADP-ribose) polymerase 1 (PARP1) and the deribosylating enzyme poly-(ADP-ribose) glycohydrolase (PARG), which dynamically regulate ADP-ribosylation of Smad3 and Smad4, two central signaling proteins of the pathway. Here we demonstrate that the bone morphogenetic protein (BMP) pathway can also be regulated by the opposing actions of PARP1 and PARG. PARG positively contributes to BMP signaling and forms physical complexes with Smad5 and Smad4. The positive role PARG plays during BMP signaling can be neutralized by PARP1, as demonstrated by experiments where PARG and PARP1 are simultaneously silenced. In contrast to PARG, ectopic expression of PARP1 suppresses BMP signaling, whereas silencing of endogenous PARP1 enhances signaling and BMP-induced differentiation. The two major Smad proteins of the BMP pathway, Smad1 and Smad5, interact with PARP1 and can be ADP-ribosylated in vitro, whereas PARG causes deribosylation. The overall outcome of this mode of regulation of BMP signal transduction provides a fine-tuning mechanism based on the two major enzymes that control cellular ADP-ribosylation.

Smad2/3 Proteins Are Required for Immobilization-induced Skeletal Muscle Atrophy

Skeletal muscle atrophy promotes muscle weakness, limiting activities of daily living. However, mechanisms underlying atrophy remain unclear. Here, we show that skeletal muscle immobilization elevates Smad2/3 protein but not mRNA levels in muscle, promoting atrophy. Furthermore, we demonstrate that myostatin, which negatively regulates muscle hypertrophy, is dispensable for denervation-induced muscle atrophy and Smad2/3 protein accumulation. Moreover, muscle-specific Smad2/3-deficient mice exhibited significant resistance to denervation-induced muscle atrophy. In addition, expression of the atrogenes Atrogin-1 and MuRF1, which underlie muscle atrophy, did not increase in muscles of Smad2/3-deficient mice following denervation. We also demonstrate that serum starvation promotes Smad2/3 protein accumulation in C2C12 myogenic cells, an in vitro muscle atrophy model, an effect inhibited by IGF1 treatment. In vivo, we observed IGF1 receptor deactivation in immobilized muscle, even in the presence of normal levels of circulating IGF1. Denervation-induced muscle atrophy was accompanied by reduced glucose intake and elevated levels of branched-chain amino acids, effects that were Smad2/3-dependent. Thus, muscle immobilization attenuates IGF1 signals at the receptor rather than the ligand level, leading to Smad2/3 protein accumulation, muscle atrophy, and accompanying metabolic changes.

MicroRNA-127 Promotes Mesendoderm Differentiation of Mouse Embryonic Stem Cells by Targeting Left-Right Determination Factor 2

Specification of the three germ layers is a fundamental process and is essential for the establishment of organ rudiments. Multiple genetic and epigenetic factors regulate this dynamic process; however, the function of specific microRNAs in germ layer differentiation remains unknown. In this study, we established that microRNA-127 (miR-127) is related to germ layer specification via microRNA array analysis of isolated three germ layers of E7.5 mouse embryos and was verified through differentiation of mouse embryonic stem cells. miR-127 is highly expressed in endoderm and primitive streak. Overexpression of miR-127 increases and inhibition of miR-127 decreases the expression of mesendoderm markers. We further show that miR-127 promotes mesendoderm differentiation through the nodal pathway, a determinative signaling pathway in early embryogenesis. Using luciferase reporter assay, left-right determination factor 2 (Lefty2), an antagonist of nodal, is identified to be a novel target of miR-127. Furthermore, the role of miR-127 in mesendoderm differentiation is attenuated by Lefty2 overexpression. Altogether, our results indicate that miR-127 accelerates mesendoderm differentiation of mouse embryonic stem cells through nodal signaling by targeting Lefty2.

SMAD signaling and redox imbalance cooperate to induce prostate cancer cell dormancy

Metastasis involves the dissemination of single or small clumps of cancer cells through blood or lymphatic vessels and their extravasation into distant organs. Despite the strong regulation of metastases development by a cell dormancy phenomenon, the dormant state of cancer cells remains poorly characterized due to the difficulty of in vivo studies. We have recently shown in vitro that clonogenicity of prostate cancer cells is regulated by a dormancy phenomenon that is strongly induced when cells are cultured both at low cell density and in a slightly hypertonic medium. Here, we characterized by RT-qPCR a genetic expression signature of this dormant state which combines the presence of both stemness and differentiation markers. We showed that both TFGβ/BMP signaling and redox imbalance are required for the full induction of this dormancy signature and cell quiescence. Moreover, reconstruction experiments showed that TFGβ/BMP signaling and redox imbalance are sufficient to generate a pattern of genetic expression displaying all characteristic features of the dormancy signature. Finally, we observed that low cell density was sufficient to activate TGFβ/BMP signaling and to generate a slight redox imbalance thus priming cells for dormancy that can be attained with a co-stimulus like hypertonicity, most likely through an increased redox imbalance. The identification of a dual regulation of dormancy provides a framework for the interpretation of previous reports showing a restricted ability of BMP signaling to regulate cancer cell dormancy in vivo and draws attention on the role of oxidative stress in the metastatic process.

FAT1 cadherin acts upstream of Hippo signalling through TAZ to regulate neuronal differentiation

The Hippo pathway is emerging as a critical nexus that balances self-renewal of progenitors against differentiation; however, upstream elements in vertebrate Hippo signalling are poorly understood. High expression of Fat1 cadherin within the developing neuroepithelium and the manifestation of severe neurological phenotypes in Fat1-knockout mice suggest roles in neurogenesis. Using the SH-SY5Y model of neuronal differentiation and employing gene silencing techniques, we show that FAT1 acts to control neurite outgrowth, also driving cells towards terminal differentiation via inhibitory effects on proliferation. FAT1 actions were shown to be mediated through Hippo signalling where it activated core Hippo kinase components and antagonised functions of the Hippo effector TAZ. Suppression of FAT1 promoted the nucleocytoplasmic shuttling of TAZ leading to enhanced transcription of the Hippo target gene CTGF together with accompanying increases in nuclear levels of Smad3. Silencing of TAZ reversed the effects of FAT1 depletion thus connecting inactivation of TAZ-TGFbeta signalling with Hippo signalling mediated through FAT1. These findings establish FAT1 as a new upstream Hippo element regulating early stages of differentiation in neuronal cells.

Transforming Growth Factor β1-induced Apoptosis in Podocytes via the Extracellular Signal-regulated Kinase-Mammalian Target of Rapamycin Complex 1-NADPH Oxidase 4 Axis

TGF-β is a pleiotropic cytokine that accumulates during kidney injuries, resulting in various renal diseases. We have reported previously that TGF-β1 induces the selective up-regulation of mitochondrial Nox4, playing critical roles in podocyte apoptosis. Here we investigated the regulatory mechanism of Nox4 up-regulation by mTORC1 activation on TGF-β1-induced apoptosis in immortalized podocytes. TGF-β1 treatment markedly increased the phosphorylation of mammalian target of rapamycin (mTOR) and its downstream targets p70S6K and 4EBP1. Blocking TGF-β receptor I with SB431542 completely blunted the phosphorylation of mTOR, p70S6K, and 4EBP1. Transient adenoviral overexpression of mTOR-WT and constitutively active mTORΔ augmented TGF-β1-treated Nox4 expression, reactive oxygen species (ROS) generation, and apoptosis, whereas mTOR kinase-dead suppressed the above changes. In addition, knockdown of mTOR mimicked the effect of mTOR-KD. Inhibition of mTORC1 by low-dose rapamycin or knockdown of p70S6K protected podocytes through attenuation of Nox4 expression and subsequent oxidative stress-induced apoptosis by TGF-β1. Pharmacological inhibition of the MEK-ERK cascade, but not the PI3K-Akt-TSC2 pathway, abolished TGF-β1-induced mTOR activation. Inhibition of either ERK1/2 or mTORC1 did not reduce the TGF-β1-stimulated increase in Nox4 mRNA level but significantly inhibited total Nox4 expression, ROS generation, and apoptosis induced by TGF-β1. Moreover, double knockdown of Smad2 and 3 or only Smad4 completely suppressed TGF-β1-induced ERK1/2-mTORactivation. Our data suggest that TGF-β1 increases translation of Nox4 through the Smad-ERK1/2-mTORC1 axis, which is independent of transcriptional regulation. Activation of this pathway plays a crucial role in ROS generation and mitochondrial dysfunction, leading to podocyte apoptosis. Therefore, inhibition of the ERK1/2-mTORC1 pathway could be a potential therapeutic and preventive target in proteinuric and chronic kidney diseases.

Smad7 Protein Interacts with Receptor-regulated Smads (R-Smads) to Inhibit Transforming Growth Factor-β (TGF-β)/Smad Signaling

TGF-β is a pleiotropic cytokine that regulates a wide range of cellular actions and pathophysiological processes. TGF-β signaling is spatiotemporally fine-tuned. As a key negative regulator of TGF-β signaling, Smad7 exerts its inhibitory effects by blocking receptor activity, inducing receptor degradation or interfering with Smad-DNA binding. However, the functions and the molecular mechanisms underlying the actions of Smad7 in TGF-β signaling are still not fully understood. In this study we report a novel mechanism whereby Smad7 antagonizes TGF-β signaling at the Smad level. Smad7 oligomerized with R-Smad proteins upon TGF-β signaling and directly inhibited R-Smad activity, as assessed by Gal4-luciferase reporter assays. Mechanistically, Smad7 competes with Smad4 to associate with R-Smads and recruits the E3 ubiquitin ligase NEDD4L to activated R-Smads, leading to their polyubiquitination and proteasomal degradation. Similar to the R-Smad-Smad4 oligomerization, the interaction between R-Smads and Smad7 is mediated by their mad homology 2 (MH2) domains. A positive-charged basic region including the L3/β8 loop-strand module and adjacent amino acids in the MH2 domain of Smad7 is essential for the interaction. These results shed new light on the regulation of TGF-β signaling by Smad7.

Bone Morphogenetic Protein-2 (BMP-2) Activates NFATc1 Transcription Factor via an Autoregulatory Loop Involving Smad/Akt/Ca2+ Signaling

Bone remodeling is controlled by dual actions of osteoclasts (OCs) and osteoblasts (OBs). The calcium-sensitive nuclear factor of activated T cells (NFAT) c1 transcription factor, as an OC signature gene, regulates differentiation of OCs downstream of bone morphogenetic protein-2 (BMP-2)-stimulated osteoblast-coded factors. To analyze a functional link between BMP-2 and NFATc1, we analyzed bones from OB-specific BMP-2 knock-out mice for NFATc1 expression by immunohistochemical staining and found significant reduction in NFATc1 expression. This indicated a requirement of BMP-2 for NFATc1 expression in OBs. We showed that BMP-2, via the receptor-specific Smad pathway, regulates expression of NFATc1 in OBs. Phosphatidylinositol 3-kinase/Akt signaling acting downstream of BMP-2 also drives NFATc1 expression and transcriptional activation. Under the basal condition, NFATc1 is phosphorylated. Activation of NFAT requires dephosphorylation by the calcium-dependent serine/threonine phosphatase calcineurin. We examined the role of calcium in BMP-2-stimulated regulation of NFATc1 in osteoblasts. 1,2Bis(2aminophenoxy)ethaneN,N,N',N'-tetraacetic acid acetoxymethyl ester, an inhibitor of intracellular calcium abundance, blocked BMP-2-induced transcription of NFATc1. Interestingly, BMP-2 induced calcium release from intracellular stores and increased calcineurin phosphatase activity, resulting in NFATc1 nuclear translocation. Cyclosporin A, which inhibits calcineurin upstream of NFATc1, blocked BMP-2-induced NFATc1 mRNA and protein expression. Expression of NFATc1 directly increased its transcription and VIVIT peptide, an inhibitor of NFATc1, suppressed BMP-2-stimulated NFATc1 transcription, confirming its autoregulation. Together, these data show a role of NFATc1 downstream of BMP-2 in mouse bone development and provide novel evidence for the presence of a cross-talk among Smad, phosphatidylinositol 3-kinase/Akt, and Ca(2+) signaling for BMP-2-induced NFATc1 expression through an autoregulatory loop.

Procollagen Lysyl Hydroxylase 2 Expression Is Regulated by an Alternative Downstream Transforming Growth Factor β-1 Activation Mechanism

PLOD2 (procollagen-lysine, 2-oxoglutarate 5-dioxygenase 2) hydroxylates lysine residues in collagen telopeptides and is essential for collagen pyridinoline cross-link formation. PLOD2 expression and subsequent pyridinoline cross-links are increased in fibrotic pathologies by transforming growth factor β-1 (TGFβ1). In this report we examined the molecular processes underlying TGFβ1-induced PLOD2 expression. We found that binding of the TGFβ1 pathway related transcription factors SMAD3 and SP1-mediated TGFβ1 enhanced PLOD2 expression and could be correlated to an increase of acetylated histone H3 and H4 at the PLOD2 promoter. Interestingly, the classical co-activators of SMAD3 complexes, p300 and CBP, were not responsible for the enhanced H3 and H4 acetylation. Depletion of SMAD3 reduced PLOD2 acetylated H3 and H4, indicating that another as of yet unidentified histone acetyltransferase binds to SMAD3 at PLOD2. Assessing histone methylation marks at the PLOD2 promoter depicted an increase of the active histone mark H3K79me2, a decrease of the repressive H4K20me3 mark, but no role for the generally strong transcription-related modifications: H3K4me3, H3K9me3 and H3K27me3. Collectively, our findings reveal that TGFβ1 induces a SP1- and SMAD3-dependent recruitment of histone modifying enzymes to the PLOD2 promoter other than the currently known TGFβ1 downstream co-activators and epigenetic modifications. This also suggests that additional activation strategies are used downstream of the TGFβ1 pathway, and hence their unraveling could be of great importance to fully understand TGFβ1 activation of genes.