Heart and liver defects and reduced transforming growth factor beta2 sensitivity in transforming growth factor beta type III receptor-deficient embryos

TGFBR3 dependent mechanism of TGFB2 in smooth muscle cell differentiation and implications for TGFB2-related aortic aneurysm

INTRODUCTION

Pathogenic variants in canonical transforming growth factor β (TGFβ) signaling genes predispose patients to thoracic aortic aneurysm and dissection (TAAD), predominantly in aortic root. Although TAAD pathogenesis associated with TGFβ receptor defects is well characterized, distinct and redundant mechanisms of TGFβ isoforms in TAAD incidence and severity remain elusive.

OBJECTIVE

Here we examined the biological role of TGFB2 in smooth muscle cell (SMC) differentiation and investigated how TGFB2 defects can lead to regional TAAD manifestations.

METHODS

To characterize the role of TGFB2 in SMC differentiation and function, we employed human-induced pluripotent stem cell (hiPSC)-derived SMC differentiation, CRISPR/Cas9 gene editing, three-dimensional SMC constructs, and human aortic tissue samples.

RESULTS

Despite the similar effects of different TGFβ isoforms on hiPSC-derived SMC differentiation, siRNA experiments revealed that TGFB2 distinctively displays TGFBR3 dependence for signal transduction, an understudied TGFβ receptor in TAAD. Molecular evaluation of different thoracic aorta regions suggested TGFB2 and TGFBR3 enrichment in the aortic root tunica media. TGFB2 haploinsufficiency (TGFB2KO/+) and TGFB2 neutralization impaired the differentiation of second heart field-derived SMCs. TGFBR3KO/KO prevented the molecular rescue of TGFB2KO/+ by TGFB2 supplementation indicating the involvement of TGFBR3 in TGFB2-mediated SMC differentiation. Lastly, a missense TGFB2 variant (TGFB2G276R/+) caused mechanical defects in SMC tissue ring constructs that were rescued by TGFB2 supplementation or genetic correction.

CONCLUSION

Our data suggests the distinct regulation and action of TGFB2 in SMCs populating the aortic root, while redundant activities of TGFβ isoforms provide implications about the milder TAAD aggressiveness of pathogenic TGFB2 variants.

Gonadotropin-releasing hormone regulates transcription of the inhibin B co-receptor, TGFBR3L, via early growth response one

Follicle-stimulating hormone (FSH), a product of pituitary gonadotrope cells, regulates gonadal function and fertility. FSH production is stimulated by gonadotropin-releasing hormone (GnRH) and activin-class ligands of the TGFβ family. Inhibin A and B are TGFβ proteins that suppress FSH synthesis by competitively binding activin type II receptors in concert with the co-receptors betaglycan (TGFBR3) and TGFBR3L. Betaglycan mediates the actions of both inhibins and is broadly expressed. In contrast, TGFBR3L is inhibin B-specific and selectively expressed in gonadotropes. This cell-restricted expression is driven, in part, by steroidogenic factor 1 (SF-1, NR5A1), which stimulates Tgfbr3l/TGFBR3L transcription via two conserved promoter elements. Tgfbr3l expression is lost in mice lacking SF-1 in gonadotropes. However, SF-1 alone is unlikely to fully explain gonadotrope-restricted Tgfbr3l/TGFBR3L expression. Here, we report that GnRH induces binding of the transcription factor, early growth response 1 (EGR1), to the murine Tgfbr3l and human TGFBR3L promoters at a conserved cis-element between the two SF-1 binding sites. In homologous LβT2 cells, GnRH stimulation of Tgfbr3l/TGFBR3L promoter-reporters depends on EGR1 binding to this cis-element. In heterologous cells, over-expressed EGR1 independently and synergistically with SF-1 activates Tgfbr3l/TGFBR3L promoter-reporter activities. In vivo, Tgfbr3l mRNA expression is reduced in the pituitaries of: 1) GnRH-deficient mice, 2) wild-type mice treated with a GnRH receptor antagonist, and 3) gonadotrope-specific Egr1 knockout mice. Gonadectomy, which increases GnRH pulse frequency, enhances Tgfbr3l expression in control but not gonadotrope-specific Egr1 knockouts. Collectively, these data indicate that GnRH stimulates Tgfbr3l/TGFBR3L transcription via EGR1, which acts with SF-1 through conserved promoter elements.

Structures of TGF-β with betaglycan and signaling receptors reveal mechanisms of complex assembly and signaling

Betaglycan (BG) is a transmembrane co-receptor of the transforming growth factor-β (TGF-β) family of signaling ligands. It is essential for embryonic development, tissue homeostasis and fertility in adults. It functions by enabling binding of the three TGF-β isoforms to their signaling receptors and is additionally required for inhibin A (InhA) activity. Despite its requirement for the functions of TGF-βs and InhA in vivo, structural information explaining BG ligand selectivity and its mechanism of action is lacking. Here, we determine the structure of TGF-β bound both to BG and the signaling receptors, TGFBR1 and TGFBR2. We identify key regions responsible for ligand engagement, which has revealed binding interfaces that differ from those described for the closely related co-receptor of the TGF-β family, endoglin, thus demonstrating remarkable evolutionary adaptation to enable ligand selectivity. Finally, we provide a structural explanation for the hand-off mechanism underlying TGF-β signal potentiation.

Adaptation to acidic conditions that mimic the tumor microenvironment, downregulates miR-193b-3p, and induces EMT via TGFβ2 in A549 cells

The acidic tumor microenvironment plays a critical role in the malignant transformation of cancer cells. One mechanism underlying this transformation involves epithelial-mesenchymal transition (EMT). This is induced by prolonged exposure to acidic conditions. EMT is an essential process in cancer progression, with Transforming Growth Factor Beta (TGF-β) playing a central role in its induction. However, little was known about the factors regulating TGF-β under acidic conditions. This study aimed to elucidate the mechanism of EMT under acidic conditions and identify novel therapeutic targets to inhibit cancer cell migration and metastasis. Focusing on lung cancer, we explored microRNAs associated with EMT that were differentially expressed under acidic conditions in A549 cells and identified miR-193b-3p as a novel candidate. Under acidic conditions, miR-193b-3p expression decreased around days 3-14. Downregulation of miR-193b-3p promoted increased TGFβ2 expression, resulting in EMT changes in A549 cells. Our study suggests that the interaction between miR-193b-3p, TGFβ2, and the acidic tumor microenvironment promotes cancer EMT change. Understanding these interactions may not only enhance our biological comprehension of cancer, but also pave the way for the development of targeted therapies to inhibit cancer metastasis.

Modulation of TGF-β signaling new approaches toward kidney disease and fibrosis therapy

The prevalence of chronic kidney disease (CKD) is increasing worldwide, posing a significant healthcare challenge. Despite the immense burden of CKD, optimal therapies remain limited in impact. Kidney fibrosis is a common mediator of all CKD progression, characterized by excessive extracellular matrix deposition and scarring of kidney parenchyma. Transforming growth factor-β (TGF-β) is a potent pro-fibrotic cytokine that signals through canonical and non-canonical pathways to promote kidney cell damage and fibrosis progression, thus garnering much interest as an optimal therapeutic target for CKD. However, the clinical translation of TGF-β inhibition in CKD and other disease settings has faced substantial challenges, particularly due to the highly pleiotropic effects of TGF-β in organ homeostasis and disease. Here, we review the kidney cell-specific biological effects of TGF-β signaling, discuss the current challenges in therapeutic targeting TGF-β in CKD, and provide the rationale for alternative targeting strategies of TGF-β signaling as potential approaches in CKD therapy. Selective inhibition of TGF-β signaling modulators to fine-tune TGF-β inhibition without a broad blockade may lead to new and safer treatments for CKD.

Activins and Inhibins in Cardiovascular Pathophysiology

Activins and inhibins, members of the transforming growth factor β (TGFβ) superfamily, were initially recognized for their opposing effects on the secretion of follicle-stimulating hormone. Subsequent research has demonstrated their broader biological roles across various tissue types. Primarily, activins and inhibins function through the classical TGFβ SMAD signaling pathway, but studies suggest that they also act through other pathways, with their specific signaling being complex and context-dependent. Recent research has identified significant roles for activins and inhibins in the cardiovascular system. Their actions in other systems and their signaling pathways show strong correlations with the development and progression of cardiovascular diseases, indicating potential broader roles in the cardiovascular system. This review summarizes the progress in research on the biological functions and mechanisms of activins and inhibins and their signaling pathways in cardiovascular diseases, offering new insights for the prevention and treatment of cardiovascular diseases.

Structures of TGF-β with betaglycan and the signaling receptors reveal the mechanism whereby betaglycan potentiates receptor complex assembly and signaling

Betaglycan (BG) is a transmembrane co-receptor of the transforming growth factor-β (TGF-β) family of signaling ligands. It is essential for embryonic development and tissue homeostasis and fertility in adults. It functions by enabling binding of the three TGF-β isoforms to their signaling receptors and is additionally required for inhibin A (InhA) activity. Despite its requirement for the functions of TGF-βs and InhA in vivo, structural information explaining BG ligand selectivity and its mechanism of action is lacking. Here, we determine the structure of TGF-β bound both to BG and the signaling receptors, TGFBR1 and TGFBR2. We identify key regions responsible for ligand engagement, which has revealed novel binding interfaces that differ from those described for the closely related co-receptor of the TGF-β family, endoglin, thus demonstrating remarkable evolutionary adaptation to enable ligand selectivity. Finally, we provide a structural explanation for the hand-off mechanism underlying TGF-β signal potentiation.

Glycosaminoglycan modifications of betaglycan regulate ectodomain shedding to fine-tune TGF-β signaling responses in ovarian cancer

In pathologies including cancer, aberrant Transforming Growth Factor-β (TGF-β) signaling exerts profound tumor intrinsic and extrinsic consequences. Intense clinical endeavors are underway to target this pathway. Central to the success of these interventions is pinpointing factors that decisively modulate the TGF-β responses. Betaglycan/type III TGF-β receptor (TβRIII), is an established co-receptor for the TGF-β superfamily known to bind directly to TGF-βs 1-3 and inhibin A/B. Betaglycan can be membrane-bound and also undergo ectodomain cleavage to produce soluble-betaglycan that can sequester its ligands. Its extracellular domain undergoes heparan sulfate and chondroitin sulfate glycosaminoglycan modifications, transforming betaglycan into a proteoglycan. We report the unexpected discovery that the heparan sulfate glycosaminoglycan chains on betaglycan are critical for the ectodomain shedding. In the absence of such glycosaminoglycan chains betaglycan is not shed, a feature indispensable for the ability of betaglycan to suppress TGF-β signaling and the cells' responses to exogenous TGF-β ligands. Using unbiased transcriptomics, we identified TIMP3 as a key inhibitor of betaglycan shedding thereby influencing TGF-β signaling. Our results bear significant clinical relevance as modified betaglycan is present in the ascites of patients with ovarian cancer and can serve as a marker for predicting patient outcomes and TGF-β signaling responses. These studies are the first to demonstrate a unique reliance on the glycosaminoglycan chains of betaglycan for shedding and influence on TGF-β signaling responses. Dysregulated shedding of TGF-β receptors plays a vital role in determining the response and availability of TGF-βs', which is crucial for prognostic predictions and understanding of TGF-β signaling dynamics.

The Role of TGFBR3 in the Development of Lung Cancer

The Transforming Growth Factor-β (TGF-β) mediates embryonic development, maintains cellular homeostasis, regulates immune function, and is involved in a wide range of other biological processes. TGF-β superfamily signaling pathways play an important role in cancer development and can promote or inhibit tumorigenesis. Type III TGF-β receptor (TGFBR3) is a co-receptor in the TGF-β signaling pathway, which often occurs with reduced or complete loss of expression in many cancer patients and can act as a tumor suppressor gene. The reduction or deletion of TGFBR3 is more pronounced compared to other elements in the TGF-β signaling pathway. In recent years, lung cancer is one of the major malignant tumors that endanger human health, and its prognosis is poor. Recent studies have reported that TGFBR3 expression decreases to varying degrees in different types of lung cancer, both at the tissue level and at the cellular level. The invasion, metastasis, angiogenesis, and apoptosis of lung cancer cells are closely related to the expression of TGFBR3, which strengthens the inhibitory function of TGFBR3 in the evolution of lung cancer. This article reviews the mechanism of TGFBR3 in lung cancer and the influencing factors associated with TGFBR3. Clarifying the physiological function of TGFBR3 and its molecular mechanism in lung cancer is conducive to the diagnosis and treatment of lung cancer.

TGM6, a helminth secretory product, mimics TGF-β binding to TβRII to antagonize TGF-β signaling in fibroblasts

The murine helminth parasite Heligmosomoides polygyrus expresses a family of proteins structurally related to TGF-β Mimic 1 (TGM1), a secreted five domain protein that activates the TGF-β pathway and converts naïve T lymphocytes to immunosuppressive Tregs. TGM1 signals through the TGF-β type I and type II receptors, TβRI and TβRII, with domains 1-2 and 3 binding TβRI and TβRII, respectively, and domains 4-5 binding CD44, a co-receptor abundant on T cells. TGM6 is a homologue of TGM1 that is co-expressed with TGM1, but lacks domains 1 and 2. Herein, we show that TGM6 binds TβRII through domain 3, but does not bind TβRI, or other type I or type II receptors of the TGF-β family. In TGF-β reporter assays in fibroblasts, TGM6, but not truncated TGM6 lacking domains 4 and 5, potently inhibits TGF-β- and TGM1-induced signaling, consistent with its ability to bind TβRII but not TβRI or other receptors of the TGF-β family. However, TGM6 does not bind CD44 and is unable to inhibit TGF-β and TGM1 signaling in T cells. To understand how TGM6 binds TβRII, the X-ray crystal structure of the TGM6 domain 3 bound to TβRII was determined at 1.4 Å. This showed that TGM6 domain 3 binds TβRII through an interface remarkably similar to the TGF-β:TβRII interface. These results suggest that TGM6 has adapted its domain structure and sequence to mimic TGF-β binding to TβRII and function as a potent TGF-β and TGM1 antagonist in fibroblasts. The coexpression of TGM6, along with the immunosuppressive TGMs that activate the TGF-β pathway, may prevent tissue damage caused by the parasite as it progresses through its life cycle from the intestinal lumen to submucosal tissues and back again.

The Research Progress in Transforming Growth Factor-β2

Transforming growth factor-beta 2 (TGF-β2), an important member of the TGF-β family, is a secreted protein that is involved in many biological processes, such as cell growth, proliferation, migration, and differentiation. TGF-β2 had been thought to be functionally identical to TGF-β1; however, an increasing number of recent studies uncovered the distinctive features of TGF-β2 in terms of its expression, activation, and biological functions. Mice deficient in TGF-β2 showed remarkable developmental abnormalities in multiple organs, especially the cardiovascular system. Dysregulation of TGF-β2 signalling was associated with tumorigenesis, eye diseases, cardiovascular diseases, immune disorders, as well as motor system diseases. Here, we provide a comprehensive review of the research progress in TGF-β2 to support further research on TGF-β2.

From shape-shifting embryonic cells to oncology: The fascinating history of epithelial mesenchymal transition

Epithelial-to-mesenchymal transition or transformation (EMT) is a cell shape-changing process that is utilized repeatedly throughout embryogenesis and is critical to the attainment of a precise body plan. In the adult, EMT is observed under both normal and pathological conditions, such as during normal wounding healing, during development of certain fibrotic states and vascular anomalies, as well as in some cancers when malignant cells progress to become more aggressive, invasive, and metastatic. Epithelia derived from any of the three embryonic germ layers can undergo EMT, including those derived from mesoderm, such as endothelial cells (sometimes termed Endo-MT) and those derived from endoderm such as fetal liver stroma. At the cellular level, EMT is defined as the transformation of epithelial cells towards a mesenchymal phenotype and is marked by attenuation of expression of epithelial markers and de novo expression of mesenchymal markers. This process is induced by extracellular factors and can be reversible, resulting in mesenchymal-to-epithelial transformation (MET). It is now clear that a cell can simultaneously express properties of both epithelia and mesenchyme, and that such transitional cell-types drive tumor cell heterogeneity, an important aspect of cancer progression, development of a stem-like cell state, and drug resistance. Here we review some of the earliest studies demonstrating the existence of EMT during embryogenesis and discuss the discovery of the extracellular factors and intracellular signaling pathways that contribute to this process, with components of the TGFβ signaling superfamily playing a prominent role. We mention early controversies surrounding in vivo EMT during embryonic development and in adult diseased states, and the maturation of the field to a stage wherein targeting EMT to control disease states is an aspirational goal.

Betaglycan promoter activity is differentially regulated during myogenesis in zebrafish embryo somites

BACKGROUND

Betaglycan, also known as the TGFβ type III receptor (Tgfbr3), is a co-receptor that modulates TGFβ family signaling. Tgfbr3 is upregulated during C2C12 myoblast differentiation and expressed in mouse embryos myocytes.

RESULTS

To investigate tgfbr3 transcriptional regulation during zebrafish embryonic myogenesis, we cloned a 3.2 kb promoter fragment that drives reporter transcription during C2C12 myoblasts differentiation and in the Tg(tgfbr3:mCherry) transgenic zebrafish. We detect tgfbr3 protein and mCherry expression in the adaxial cells concomitantly with the onset of their radial migration to become slow-twitch muscle fibers in the Tg(tgfbr3:mCherry). Remarkably, this expression displays a measurable antero-posterior somitic gradient expression.

CONCLUSIONS

tgfbr3 is transcriptionally regulated during somitic muscle development in zebrafish with an antero-posterior gradient expression that preferentially marks the adaxial cells and their descendants.

Heparan sulfate modifications of betaglycan promote TIMP3-dependent ectodomain shedding to fine-tune TGF-β signaling

In pathologies such as cancer, aberrant Transforming Growth Factor-β (TGF-β) signaling exerts profound tumor intrinsic and extrinsic consequences. Intense clinical endeavors are underway to target this pivotal pathway. Central to the success of these interventions is pinpointing factors that decisively modulate the TGF-β responses. Betaglycan/type III TGF-β receptor (TβRIII), is an established co-receptor for the TGF-β superfamily known to bind directly to TGF-βs 1-3 and inhibin A/B. While betaglycan can be membrane-bound, it can also undergo ectodomain cleavage to produce soluble-betaglycan that can sequester its ligands. The extracellular domain of betaglycan undergoes heparan sulfate and chondroitin sulfate glycosaminoglycan modifications, transforming betaglycan into a proteoglycan. Here we report the unexpected discovery that the heparan sulfate modifications are critical for the ectodomain shedding of betaglycan. In the absence of such modifications, betaglycan is not shed. Such shedding is indispensable for the ability of betaglycan to suppress TGF-β signaling and the cells' responses to exogenous TGF-β ligands. Using unbiased transcriptomics, we identified TIMP3 as a key regulator of betaglycan shedding and thereby TGF-β signaling. Our results bear significant clinical relevance as modified betaglycan is present in the ascites of patients with ovarian cancer and can serve as a marker for predicting patient outcomes and TGF-β signaling responses. These studies are the first to demonstrate a unique reliance on the glycosaminoglycan modifications of betaglycan for shedding and influence on TGF-β signaling responses. Dysregulated shedding of TGF-β receptors plays a vital role in determining the response and availability of TGF-βs', which is crucial for prognostic predictions and understanding of TGF-β signaling dynamics.

Structural insights into regulation of CCN protein activities and functions

CCN proteins play important functions during development, in repair mechanisms following tissue injury, as well as in pathophysiologic mechanisms of metastasis of cancer. CCNs are secreted proteins that have a multimodular structure and are categorized as matricellular proteins. Although the prevailing view is that CCN proteins regulate biologic processes by interacting with a wide array of other proteins in the microenvironment of the extracellular matrix, the molecular mechanisms of action of CCN proteins are still poorly understood. Not dissuading the current view, however, the recent appreciation that these proteins are signaling proteins in their own right and may even be considered preproproteins controlled by endopeptidases to release a C-terminal bioactive peptide has opened new avenues of research. Also, the recent resolution of the crystal structure of two of the domains of CCN3 have provided new knowledge with implications for the entire CCN family. These resolved structures in combination with structural predictions based upon the AlphaFold artificial intelligence tool provide means to shed new light on CCN functions in context of the notable literature in the field. CCN proteins have emerged as important therapeutic targets in several disease conditions, and clinical trials are currently ongoing. Thus, a review that critically discusses structure - function relationship of CCN proteins, in particular as it relates to interactions with other proteins in the extracellular milieu and on the cell surface, as well as to cell signaling activities of these proteins, is very timely. Suggested mechanism for activation and inhibition of signaling by the CCN protein family (graphics generated with BioRender.com ).

Dynamics of Chromatin Accessibility During Hematopoietic Stem Cell Differentiation Into Progressively Lineage-Committed Progeny

Epigenetic mechanisms regulate the multilineage differentiation capacity of hematopoietic stem cells (HSCs) into a variety of blood and immune cells. Mapping the chromatin dynamics of functionally defined cell populations will shed mechanistic insight into 2 major, unanswered questions in stem cell biology: how does epigenetic identity contribute to a cell type's lineage potential, and how do cascades of chromatin remodeling dictate ensuing fate decisions? Our recent work revealed evidence of multilineage gene priming in HSCs, where open cis-regulatory elements (CREs) exclusively shared between HSCs and unipotent lineage cells were enriched for DNA binding motifs of known lineage-specific transcription factors. Oligopotent progenitor populations operating between the HSCs and unipotent cells play essential roles in effecting hematopoietic homeostasis. To test the hypothesis that selective HSC-primed lineage-specific CREs remain accessible throughout differentiation, we used ATAC-seq to map the temporal dynamics of chromatin remodeling during progenitor differentiation. We observed epigenetic-driven clustering of oligopotent and unipotent progenitors into distinct erythromyeloid and lymphoid branches, with multipotent HSCs and MPPs associating with the erythromyeloid lineage. We mapped the dynamics of lineage-primed CREs throughout hematopoiesis and identified both unique and shared CREs as potential lineage reinforcement mechanisms at fate branch points. Additionally, quantification of genome-wide peak count and size revealed overall greater chromatin accessibility in HSCs, allowing us to identify HSC-unique peaks as putative regulators of self-renewal and multilineage potential. Finally, CRISPRi-mediated targeting of ATACseq-identified putative CREs in HSCs allowed us to demonstrate the functional role of selective CREs in lineage-specific gene expression. These findings provide insight into the regulation of stem cell multipotency and lineage commitment throughout hematopoiesis and serve as a resource to test functional drivers of hematopoietic lineage fate.

Computational modeling of TGF-β2:TβRI:TβRII receptor complex assembly as mediated by the TGF-β coreceptor betaglycan

Transforming growth factor-β1, -β2, and -β3 (TGF-β1, -β2, and -β3) are secreted signaling ligands that play essential roles in tissue development, tissue maintenance, immune response, and wound healing. TGF-β ligands form homodimers and signal by assembling a heterotetrameric receptor complex comprised of two type I receptor (TβRI):type II receptor (TβRII) pairs. TGF-β1 and TGF-β3 ligands signal with high potency due to their high affinity for TβRII, which engenders high-affinity binding of TβRI through a composite TGF-β:TβRII binding interface. However, TGF-β2 binds TβRII 200-500 more weakly than TGF-β1 and TGF-β3 and signals with lower potency compared with these ligands. Remarkably, the presence of an additional membrane-bound coreceptor, known as betaglycan, increases TGF-β2 signaling potency to levels similar to TGF-β1 and -β3. The mediating effect of betaglycan occurs even though it is displaced from and not present in the heterotetrameric receptor complex through which TGF-β2 signals. Published biophysics studies have experimentally established the kinetic rates of the individual ligand-receptor and receptor-receptor interactions that initiate heterotetrameric receptor complex assembly and signaling in the TGF-β system; however, current experimental approaches are not able to directly measure kinetic rates for the intermediate and latter steps of assembly. To characterize these steps in the TGF-β system and determine the mechanism of betaglycan in the potentiation of TGF-β2 signaling, we developed deterministic computational models with different modes of betaglycan binding and varying cooperativity between receptor subtypes. The models identified conditions for selective enhancement of TGF-β2 signaling. The models provide support for additional receptor binding cooperativity that has been hypothesized but not evaluated in the literature. The models further showed that betaglycan binding to the TGF-β2 ligand through two domains provides an effective mechanism for transfer to the signaling receptors that has been tuned to efficiently promote assembly of the TGF-β2(TβRII)2(TβRI)2 signaling complex.

Transforming growth factor receptor III (Betaglycan) regulates the generation of pathogenic Th17 cells in EAE

The transforming growth factor receptor III (TβRIII) is commonly recognized as a co-receptor that promotes the binding of TGFβ family ligands to type I and type II receptors. Within the immune system, TβRIII regulates T cell development in the thymus and is differentially expressed through activation; however, its function in mature T cells is unclear. To begin addressing this question, we developed a conditional knock-out mouse with restricted TβRIII deletion in mature T cells, necessary because genomic deletion of TβRIII results in perinatal mortality. We determined that TβRIII null mice developed more severe autoimmune central nervous neuroinflammatory disease after immunization with myelin oligodendrocyte peptide (MOG35-55) than wild-type littermates. The increase in disease severity in TβRIII null mice was associated with expanded numbers of CNS infiltrating IFNγ+ CD4+ T cells and cells that co-express both IFNγ and IL-17 (IFNγ+/IL-17+), but not IL-17 alone expressing CD4 T cells compared to Tgfbr3fl/fl wild-type controls. This led us to speculate that TβRIII may be involved in regulating conversion of encephalitogenic Th17 to Th1. To directly address this, we generated encephalitogenic Th17 and Th1 cells from wild type and TβRIII null mice for passive transfer of EAE into naïve mice. Remarkably, Th17 encephalitogenic T cells from TβRIII null induced EAE of much greater severity and earlier in onset than those from wild-type mice. The severity of EAE induced by encephalitogenic wild-type and Tgfbr3fl/fl.dLcKCre Th1 cells were similar. Moreover, in vitro restimulation of in vivo primed Tgfbr3fl/fl.dLcKCre T cells, under Th17 but not Th1 polarizing conditions, resulted in a significant increase of IFNγ+ T cells. Altogether, our data indicate that TβRIII is a coreceptor that functions as a key checkpoint in controlling the pathogenicity of autoreactive T cells in neuroinflammation probably through regulating plasticity of Th17 T cells into pathogenic Th1 cells. Importantly, this is the first demonstration that TβRIII has an intrinsic role in T cells.

TGFBR3 supports anoikis through suppressing ATF4 signaling

Epithelial morphogenesis and oncogenic transformation can cause loss of cell adhesion, and detached cells are eliminated by anoikis. Here, we reveal that transforming growth factor beta receptor 3 (TGFBR3) acts as an anoikis mediator through the coordination of activating transcription factor 4 (ATF4). In breast cancer, TGFBR3 is progressively lost, but elevated TGFBR3 is associated with a histologic subtype characterized by cellular adhesion defects. Dissecting the impact of extracellular matrix (ECM) deprivation, we demonstrate that ECM loss promotes TGFBR3 expression, which in turn differentiates cell aggregates to a prosurvival phenotype and drives the intrinsic apoptotic pathway. We demonstrate that inhibition of TGFBR3 impairs epithelial anoikis by activating ATF4 signaling. These preclinical findings provide a rationale for therapeutic inhibition of ATF4 in the subgroup of breast cancer patients with low TGFBR3 expression.

Role of Betaglycan in TGF-β Signaling and Wound Healing in Human Endometriotic Epithelial Cells and in Endometriosis

Endometriosis is characterized by the presence of ectopic endometrium most often in the pelvis. The transforming growth factor-beta (TGF-β) superfamily is also involved in the pathogenesis; however, betaglycan (BG, syn. TGF-β type III receptor) as an important co-receptor was not studied. We analyzed mainly BG ectodomain shedding because released soluble BG (sBG) often antagonizes TGF-β signaling. Furthermore, we studied the role of TGF-βs and BG in wound healing and evaluated the suitability of BG measurements in serum and endocervical mucus for non-invasive diagnosis of endometriosis. Evaluation of the BG shedding and signaling pathways involved as well as wound healing was performed with enzyme-linked immune assays (ELISAs), reverse transcription-quantitative polymerase chain reaction (RT-qPCR), small interfering RNA (siRNA) knockdown, and scratch assays with human endometriotic epithelial cells. TGF-β1/2 stimulation resulted in a significant dose-dependent reduction in BG shedding in endometriotic cells, which was TGF-β/activin receptor-like kinase-5 (ALK-5)/mother against decapentaplegic homolog3 (SMAD3)- but not SMAD2-dependent. Inhibition of matrix metalloproteinases (MMPs) using the pan-MMP inhibitor GM6001 and tissue inhibitor of MMPs (TIMP3) equally attenuated BG shedding, signifying the involvement of MMPs in shedding. Likewise, recombinant BG moderately reduced the secretion of TGF-β1/2 and wound healing of endometriotic cells. TGF-β1 significantly enhanced the secretion of MMP2 and MMP3 and moderately promoted wound healing. In order to evaluate the role of BG in endometriosis, serum (n = 238) and mucus samples (n = 182) were analyzed. Intriguingly, a significant reduction in the levels of sBG in endocervical mucus but not in the serum of endometriosis patients compared to controls was observed. Collectively, these observations support a novel role for BG in the pathophysiology of endometriosis.

Coreceptor Functions of Cell Surface Heparan Sulfate Proteoglycans

Receptor-ligand interactions play an important role in many biological processes by triggering specific cellular responses. These interactions are frequently regulated by coreceptors that facilitate, alter, or inhibit signaling. Coreceptors work in parallel with other specific and accessory molecules to coordinate receptor-ligand interactions. Cell surface heparan sulfate proteoglycans (HSPGs) function as unique coreceptors because they can bind to many ligands and receptors through their HS and core protein motifs. Cell surface HSPGs are typically expressed in abundance of the signaling receptors and, thus, are capable of mediating the initial binding of ligands to the cell surface. HSPG coreceptors do not possess kinase domains or intrinsic enzyme activities and, for the most part, binding to cell surface HSPGs does not directly stimulate intracellular signaling. Because of these features, cell surface HSPGs primarily function as coreceptors for many receptor-ligand interactions. Given that cell surface HSPGs are widely conserved, they likely serve fundamental functions to preserve basic physiological processes. Indeed, cell surface HSPGs can support specific cellular interactions with growth factors, morphogens, chemokines, extracellular matrix (ECM) components, and microbial pathogens and their secreted virulence factors. Through these interactions, HSPG coreceptors regulate cell adhesion, proliferation, migration and differentiation, and impact the onset, progression, and outcome of pathophysiological processes, such as development, tissue repair, inflammation, infection, and tumorigenesis. This review seeks to provide an overview of the various mechanisms of how cell surface HSPGs function as coreceptors.

TGF-β superfamily co-receptors in cancer

Transforming growth factor-β (TGF-β) superfamily signaling via their cognate receptors is frequently modified by TGF-β superfamily co-receptors. Signaling through SMAD-mediated pathways may be enhanced or depressed depending on the specific co-receptor and cell context. This dynamic effect on signaling is further modified by the release of many of the co-receptors from the membrane to generate soluble forms that are often antagonistic to the membrane-bound receptors. The co-receptors discussed here include TβRIII (betaglycan), endoglin, BAMBI, CD109, SCUBE proteins, neuropilins, Cripto-1, MuSK, and RGMs. Dysregulation of these co-receptors can lead to altered TGF-β superfamily signaling that contributes to the pathophysiology of many cancers through regulation of growth, metastatic potential, and the tumor microenvironment. Here we describe the role of several TGF-β superfamily co-receptors on TGF-β superfamily signaling and the impact on cellular and physiological functions with a particular focus on cancer, including a discussion on recent pharmacological advances and potential clinical applications targeting these co-receptors.

Fast Quantitation of TGF-β Signaling Using Adenoviral Reporter

The transforming growth factor-β (TGF-β) is a multifunctional cytokine critical for embryogenesis and tissue homeostasis. Alterations in TGF-β signaling pathway are observed in several types of malignant tumors and often related with cancer progression and metastasis. TGF-β signaling is transduced across the plasma membrane after ligand-receptor binding and consequent phosphorylation of the intracellular effectors SMAD2/3 by TGF-β receptors. Phosphorylated SMAD2/3 accumulates in the nucleus after complex formation with SMAD4 to act as transcription factors and regulate the expression of genes critically associated with cell proliferation and differentiation. Traditional methodologies used to assess TGF-β signaling pathway lack accuracy and/or show poor scalability, limiting in vitro experiments and almost excluding their use in vivo. Here, we describe a fast method to quantitate TGF-β signaling pathway activity in vitro and in vivo by using adenoviral reporters. Its implementation in vitro allows quantitating cell response to TGF-β at concentrations as low as pictograms/mL. Additionally, the use of an in vivo imaging system (IVIS) enables quantitating and monitoring TGF-β signaling pathway activity over time during cancer progression, eliminating the requirement of animal euthanasia at multiple time points for this purpose. Importantly, this protocol has been consistently used in different models and effectively led to the visualization and measurement of TGF-β activity levels. Improving the sensitivity, specificity, and scalability of methods focused on characterizing this and other molecular pathways will result in a better understanding of their biology in physiological and pathological processes.

TGFBR3L is an inhibin B co-receptor that regulates female fertility

Follicle-stimulating hormone (FSH), a key regulator of ovarian function, is often used in infertility treatment. Gonadal inhibins suppress FSH synthesis by pituitary gonadotrope cells. The TGFβ type III receptor, betaglycan, is required for inhibin A suppression of FSH. The inhibin B co-receptor was previously unknown. Here, we report that the gonadotrope-restricted transmembrane protein, TGFBR3L, is the elusive inhibin B co-receptor. TGFBR3L binds inhibin B but not other TGFβ family ligands. TGFBR3L knockdown or overexpression abrogates or confers inhibin B activity in cells. Female Tgfbr3l knockout mice exhibit increased FSH levels, ovarian follicle development, and litter sizes. In contrast, female mice lacking both TGFBR3L and betaglycan are infertile. TGFBR3L’s function and cell-specific expression make it an attractive new target for the regulation of FSH and fertility.

IGFBP-3 and TGF-β inhibit growth in epithelial cells by stimulating type V TGF-β receptor (TβR-V)-mediated tumor suppressor signaling

The TGF-β type V receptor (TβR-V) mediates growth inhibition by IGFBP-3 and TGF-β in epithelial cells and loss of TβR-V expression in these cells leads to development of carcinoma. The mechanisms by which TβR-V mediates growth inhibition (tumor suppressor) signaling remain elusive. Previous studies revealed that IGFBP-3 and TGF-β inhibit growth in epithelial cells by stimulating TβR-V-mediated IRS-1/2-dependent activation and cytoplasm-to-nucleus translocation of IGFBP-3- or TGF-β-stimulated protein phosphatase (PPase), resulting in dephosphorylation of pRb-related proteins (p107, p130) or pRb, and growth arrest. To define the signaling, we characterized/identified the IGFBP-3- and TGF-β-stimulated PPases in cell lysates and nucleus fractions in Mv1Lu cells treated with IGFBP-3 and TGF-β, using a cell-free assay with 32P-labeled casein as a substrate. Both IGFBP-3- and TGF-β-stimulated PPase activities in cell lysates are abolished when cells are co-treated with TGF-β/IGFBP-3 antagonist or RAP (LRP-1/TβR-V antagonist). However, the IGFBP-3-stimulated PPase activity, but not TGF-β-stimulated PPase activity, is sensitive to inhibition by okadaic acid (OA). In addition, OA or PP2Ac siRNA reverses IGFBP-3 growth inhibition, but not TGF-β growth inhibition, in Mv1Lu and 32D cells. These suggest that IGFBP-3- and TGF-β-stimulated PPases are identical to PP2A and PP1, respectively. By Western blot/phosphorimager/immunofluorescence-microscopy analyses, IGFBP-3 and TGF-β stimulate TβR-V-mediated IRS-2-dependent activation and cytoplasm-to-nucleus translocation of PP2Ac and PP1c, resulting in dephosphorylation of p130/p107 and pRb, respectively, and growth arrest. Small molecule TGF-β enhancers, which potentiate TGF-β growth inhibition by enhancing TβR-I-TβR-II-mediated canonical signaling and thus activating TβR-V-mediated tumor suppressor signaling cascade (TβR-V/IRS-2/PP1/pRb), could be used to prevent and treat carcinoma.

Chordacentrum mineralization is delayed in zebrafish betaglycan-null mutants

BACKGROUND

The Transforming Growth Factor β (TGFβ) family is a group of related proteins that signal through a type I and type II receptors. Betaglycan, also known as the type III receptor (Tgfbr3), is a coreceptor for various ligands of the TGFβ family that participates in heart, liver and kidney development as revealed by the tgfbr3-null mouse, as well as in angiogenesis as revealed by Tgfbr3 downregulation in morphant zebrafish.

RESULTS

Here, we present CRISPR/Cas9-derived zebrafish Tgfbr3-null mutants, which exhibited unaltered embryonic angiogenesis and developed into fertile adults. One reproducible phenotype displayed by these Tgfbr3-null mutants is delayed chordacentra mineralization, which nonetheless does not result in vertebral abnormalities in the adult fishes. We also report that the canonical TGFβ signaling pathway is needed for proper chordacentra mineralization and that Tgfbr3 absence decreases this signal in the notochordal cells responsible for this process.

CONCLUSION

Betaglycan's "ligand presentation" function contributes to the optimal TGFβ signaling required for zebrafish chordacentra mineralization.

A bioinformatic analysis of the inhibin-betaglycan-endoglin/CD105 network reveals prognostic value in multiple solid tumors

Inhibins and activins are dimeric ligands belonging to the TGFβ superfamily with emergent roles in cancer. Inhibins contain an α-subunit (INHA) and a β-subunit (either INHBA or INHBB), while activins are mainly homodimers of either βA (INHBA) or βB (INHBB) subunits. Inhibins are biomarkers in a subset of cancers and utilize the coreceptors betaglycan (TGFBR3) and endoglin (ENG) for physiological or pathological outcomes. Given the array of prior reports on inhibin, activin and the coreceptors in cancer, this study aims to provide a comprehensive analysis, assessing their functional prognostic potential in cancer using a bioinformatics approach. We identify cancer cell lines and cancer types most dependent and impacted, which included p53 mutated breast and ovarian cancers and lung adenocarcinomas. Moreover, INHA itself was dependent on TGFBR3 and ENG/CD105 in multiple cancer types. INHA, INHBA, TGFBR3, and ENG also predicted patients' response to anthracycline and taxane therapy in luminal A breast cancers. We also obtained a gene signature model that could accurately classify 96.7% of the cases based on outcomes. Lastly, we cross-compared gene correlations revealing INHA dependency to TGFBR3 or ENG influencing different pathways themselves. These results suggest that inhibins are particularly important in a subset of cancers depending on the coreceptor TGFBR3 and ENG and are of substantial prognostic value, thereby warranting further investigation.

Whole-genome resequencing reveals loci with allelic transmission ratio distortion in F1 chicken population

Allelic transmission ratio distortion (TRD) is the significant deviation from the expected ratio under Mendelian inheritance theory, which may be resulted from multiple disrupted biological processes, including germline selection, meiotic drive, gametic competition, imprint error, and embryo lethality. However, it is less known that whether or what extent the allelic TRD is present in farm animals. In this study, whole-genome resequencing technology was applied to reveal TRD loci in chicken by constructing a full-sib F₁ hybrid population. Through the whole-genome resequencing data of two parents (30 ×) and 38 offspring (5 ×), we detected a total of 2850 TRD SNPs (p-adj < 0.05) located within 400 genes showing TRD, and all of them were unevenly distributed on macrochromosomes and microchromosomes. Our findings suggested that TRD in the chicken chromosome 16 might play an important role in chicken immunity and disease resistance and the MYH1F with significant TRD and allele-specific expression could play a key role in the fast muscle development. In addition, functional enrichment analyses revealed that many genes (e.g., TGFBR2, TGFBR3, NOTCH1, and NCOA1) with TRD were found in the significantly enriched biological process and InterPro terms in relation to embryonic lethality and germline selection. Our results suggested that TRD is considerably prevalent in the chicken genome and has functional implications.

TGFβ Signaling in the Tumor Microenvironment

Transforming growth factor beta (TGFβ) is a pleiotropic growth factor. Under normal physiological conditions, TGFβ maintains homeostasis in mammalian tissues by restraining the growth of cells and stimulating apoptosis. However, the role of TGFβ signaling in the carcinogenesis is complex. TGFβ acts as a tumor suppressor in the early stages of disease and as a tumor promoter in its later stages where cancer cells have been relieved from TGFβ growth controls. Overproduction of TGFβ by cancer cells lead to a local fibrotic and immune-suppressive microenvironment that fosters tumor growth and correlates with invasive and metastatic behavior of the cancer cells. Here, we present an overview of the complex biology of the TGFβ family, and we discuss the roles of TGFβ signaling in carcinogenesis and how this knowledge is being leveraged to develop TGFβ inhibition therapies against the tumor.

Identification and functional analysis of transforming growth factor-β type III receptor (TβR3) from Scylla paramamosain: The first evidence of TβR3 involved in development and innate immunity in invertebrates

Transforming growth factor-β type III receptor (TβR3), as a co-receptor of TGF-β superfamily, plays critical roles in development and growth as well as some disease pathogeneses by presenting ligands to other receptors in vertebrates. However, the identification and functional characterization of TβR3 had not been reported yet in invertebrates. In the present study, TβR3 was first identified and characterized in mud crab Scylla paramamosain. The obtained cDNA length of SpTβR3 was 2, 424 bp with a 1, 854 bp open reading frame, which encoded a putative peptide of 617 amino acids containing a typical transmembrane region and a Zona pellucida (ZP) domain. Real-time PCR results showed that SpTβR3 was predominantly expressed at early embryonic development stage and early postmolt stage, suggesting its participation in development and growth. We report, for the first time in invertebrates, the challenge of both Vibro alginolyticus and Poly (I:C) could alter the expression patterns of SpTβR3. Notably, the expression levels of SpIKK, two NF-κB members (SpRelish and SpDorsal), and five antimicrobial peptide genes (SpCrustin and SpALF1-4) were significantly suppressed when SpTβR3 was interfered in vivo. Secondly, the overexpression of SpTβR3 in vitro could activate NF-κB signaling through the dual-luciferase reporter assays. Furthermore, the bacterial clearance assay after SpTβR3 was silenced in vivo highlighted the potential of SpTβR3 in activating the innate immune responses. These results implied the involvement of SpTβR3 in the innate immune responses by regulating the NF-κB pathway. This study first indicated that TβR3 was present in invertebrate, and it participated in not only the development and growth but also the innate immunity of S. paramamosain. It also provided new insights into the origin or evolution of TGF-β receptors in crustacean species and even in invertebrates.

On-Target Anti-TGF-β Therapies Are Not Succeeding in Clinical Cancer Treatments: What Are Remaining Challenges?

Metastasis is the leading cause of death for cancer patients. During cancer progression, the initial detachment of cells from the primary tumor and the later colonization of a secondary organ are characterized as limiting steps for metastasis. Epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET) are opposite dynamic multistep processes that enable these critical events in metastasis by altering the phenotype of cancer cells and improving their ability to migrate, invade and seed at distant organs. Among the molecular pathways that promote tumorigenesis in late-stage cancers, transforming growth factor-β (TGF-β) is described as an EMT master inducer by controlling different genes and proteins related to cytoskeleton assembly, cell-cell attachment and extracellular matrix remodeling. Still, despite the successful outcomes of different TGF-β pharmacological inhibitors in cell culture (in vitro) and animal models (in vivo), results in cancer clinical trials are poor or inconsistent at least, highlighting the existence of crucial components in human cancers that have not been properly explored. Here we review most recent findings to provide perspectives bridging the gap between on-target anti-TGF-β therapies in vitro and in pre-clinical models and the poor clinical outcomes in treating cancer patients. Specifically, we focus on (i) the dual roles of TGF-β signaling in cancer metastasis; (ii) dynamic signaling; (iii) functional differences of TGF-β free in solution vs. in exosomes; (iv) the regulatory effects of tumor microenvironment (TME) – particularly by cancer-associated fibroblasts – on TGF-β signaling pathway. Clearly identifying and establishing those missing links may provide strategies to revitalize and clinically improve the efficacy of TGF-β targeted therapies.

TGF-β Signaling

Transforming growth factor-β (TGF-β) represents an evolutionarily conserved family of secreted polypeptide factors that regulate many aspects of physiological embryogenesis and adult tissue homeostasis. The TGF-β family members are also involved in pathophysiological mechanisms that underlie many diseases. Although the family comprises many factors, which exhibit cell type-specific and developmental stage-dependent biological actions, they all signal via conserved signaling pathways. The signaling mechanisms of the TGF-β family are controlled at the extracellular level, where ligand secretion, deposition to the extracellular matrix and activation prior to signaling play important roles. At the plasma membrane level, TGF-βs associate with receptor kinases that mediate phosphorylation-dependent signaling to downstream mediators, mainly the SMAD proteins, and mediate oligomerization-dependent signaling to ubiquitin ligases and intracellular protein kinases. The interplay between SMADs and other signaling proteins mediate regulatory signals that control expression of target genes, RNA processing at multiple levels, mRNA translation and nuclear or cytoplasmic protein regulation. This article emphasizes signaling mechanisms and the importance of biochemical control in executing biological functions by the prototype member of the family, TGF-β.

On-Target Anti-TGF-β Therapies Are Not Succeeding in Clinical Cancer Treatments: What Are Remaining Challenges?

Metastasis is the leading cause of death for cancer patients. During cancer progression, the initial detachment of cells from the primary tumor and the later colonization of a secondary organ are characterized as limiting steps for metastasis. Epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET) are opposite dynamic multistep processes that enable these critical events in metastasis by altering the phenotype of cancer cells and improving their ability to migrate, invade and seed at distant organs. Among the molecular pathways that promote tumorigenesis in late-stage cancers, transforming growth factor-β (TGF-β) is described as an EMT master inducer by controlling different genes and proteins related to cytoskeleton assembly, cell-cell attachment and extracellular matrix remodeling. Still, despite the successful outcomes of different TGF-β pharmacological inhibitors in cell culture (in vitro) and animal models (in vivo), results in cancer clinical trials are poor or inconsistent at least, highlighting the existence of crucial components in human cancers that have not been properly explored. Here we review most recent findings to provide perspectives bridging the gap between on-target anti-TGF-β therapies in vitro and in pre-clinical models and the poor clinical outcomes in treating cancer patients. Specifically, we focus on (i) the dual roles of TGF-β signaling in cancer metastasis; (ii) dynamic signaling; (iii) functional differences of TGF-β free in solution vs. in exosomes; (iv) the regulatory effects of tumor microenvironment (TME) - particularly by cancer-associated fibroblasts - on TGF-β signaling pathway. Clearly identifying and establishing those missing links may provide strategies to revitalize and clinically improve the efficacy of TGF-β targeted therapies.

A Tale of Two Proteins: Betaglycan, IGSF1, and the Continuing Search for the Inhibin B Receptor

Inhibins are gonadal hormones that suppress follicle-stimulating hormone (FSH) synthesis by pituitary gonadotrope cells. The structurally related activins stimulate FSH by signaling through complexes of type I and type II receptors. Two models of inhibin action were proposed in 2000. First, inhibins function as competitive receptor antagonists, binding activin type II receptors with high affinity in the presence of the TGF-β type III coreceptor, betaglycan. Second, immunoglobulin superfamily, member 1 (IGSF1, then called p120) was proposed to mediate inhibin B antagonism of activin signaling via its type I receptor. These ideas have been challenged over the past few years. Rather than playing a role in inhibin action, IGSF1 is involved in the central control of the thyroid gland. Betaglycan binds inhibin A and inhibin B with high affinity, but only functions as an obligate inhibin A coreceptor in murine gonadotropes. There is likely to be a distinct, but currently unidentified coreceptor for inhibin B.

Structural biology of betaglycan and endoglin, membrane-bound co-receptors of the TGF-beta family

Betaglycan and endoglin, membrane-bound co-receptors of the TGF-β family, are required to mediate the signaling of a select subset of TGF-β family ligands, TGF-β2 and InhA, and BMP-9 and BMP-10, respectively. Previous biochemical and biophysical methods suggested alternative modes of ligand binding might be responsible for these co-receptors to selectively recognize and potentiate the functions of their ligands, yet the molecular details were lacking. Recent progress determining structures of betaglycan and endoglin, both alone and as bound to their cognate ligands, is presented herein. The structures reveal relatively minor, but very significant structural differences that lead to entirely different modes of ligand binding. The different modes of binding nonetheless share certain commonalities, such as multivalency, which imparts the co-receptors with very high affinity for their cognate ligands, but at the same time provides a mechanism for release by stepwise binding of the signaling receptors, both of which are essential for their functions.

Betaglycan drives the mesenchymal stromal cell osteogenic program and prostate cancer-induced osteogenesis

Bone metastatic prostate cancer provokes extensive osteogenesis by driving the recruitment and osteoblastic differentiation of mesenchymal stromal cells (MSCs). The resulting lesions greatly contribute to patient morbidity and mortality, underscoring the need for defining how prostate metastases subvert the MSC-osteoblast differentiation program. To gain insights into this process we profiled the effects of co-culture of primary MSCs with validated bone metastatic prostate cancer cell line models. These analyses revealed a cast of shared differentially induced genes in MSC, including betaglycan, a co-receptor for TGFβ. Betaglycan has not been studied in the context of bone metastatic disease previously. Here we report that loss of betaglycan in MSC is sufficient to augment TGFβ signaling, proliferation and migration, and completely blocks the MSC-osteoblast differentiation program. Further, betaglycan was revealed as necessary for prostate cancer-induced osteogenesis in vivo. Mechanistically, gene expression analysis revealed betaglycan controls the expression of a large repertoire of genes in MSCs, and that betaglycan loss provokes >60-fold increase in the expression of Wnt5a that plays important roles in stemness. In accord with the increased Wnt5a levels, there was a marked induction of canonical Wnt signaling in betaglycan ablated MSCs, and the addition of recombinant Wnt5a to MSCs was sufficient to impair osteogenic differentiation. Finally, the addition of Wnt5a neutralizing antibody was sufficient to induce the expression of osteogenic genes in betaglycan-ablated MSCs. Collectively, these findings suggest a betaglycan-Wnt5a circuit represents an attractive vulnerability to ameliorate prostate cancer-induced osteogenesis.

MicroRNA let-7-TGFBR3 signalling regulates cardiomyocyte apoptosis after infarction

Background

Myocardial infarction (MI) is a life-threatening disease, often leading to heart failure. Defining therapeutic targets at an early time point is important to prevent heart failure.

Methods

MicroRNA screening was performed at early time points after MI using paired samples isolated from the infarcted and remote myocardium of pigs. We also examined the microRNA expression in plasma of MI patients and pigs. For mechanistic studies, AAV9-mediated microRNA knockdown and overexpression were administrated in mice undergoing MI.

Findings

MicroRNAs let-7a and let-7f were significantly downregulated in the infarct area within 24 h post-MI in pigs. We also observed a reduction of let-7a and let-7f in plasma of MI patients and pigs. Inhibition of let-7 exacerbated cardiomyocyte apoptosis, induced a cardiac hypertrophic phenotype, and resulted in worsened left ventricular ejection fraction. In contrast, ectopic let-7 overexpression significantly reduced those phenotypes and improved heart function. We then identified TGFBR3 as a target of let-7, and found that induction of Tgfbr3 in cardiomyocytes caused apoptosis, likely through p38 MAPK activation. Finally, we showed that the plasma TGFBR3 level was elevated after MI in plasma of MI patients and pigs.

Interpretation

Together, we conclude that the let-7-Tgfbr3-p38 MAPK signalling plays an important role in cardiomyocyte apoptosis after MI. Furthermore, microRNA let-7 and Tgfbr3 may serve as therapeutic targets and biomarkers for myocardial damage.

Fund

Ministry of Science and Technology, National Health Research Institutes, Academia Sinica Program for Translational Innovation of Biopharmaceutical Development-Technology Supporting Platform Axis, Thematic Research Program and the Summit Research Program, Taiwan.

Structural Adaptation in Its Orphan Domain Engenders Betaglycan with an Alternate Mode of Growth Factor Binding Relative to Endoglin

Betaglycan (BG) and endoglin (ENG), homologous co-receptors of the TGF-β family, potentiate the signaling activity of TGF-β2 and inhibin A, and BMP-9 and BMP-10, respectively. BG exists as monomer and forms 1:1 growth factor (GF) complexes, while ENG exists as a dimer and forms 2:1 GF complexes. Herein, the structure of the BG orphan domain (BG_O) reveals an insertion that blocks the region that the endoglin orphan domain (ENG_O) uses to bind BMP-9, preventing it from binding in the same manner. Using binding studies with domain-deleted forms of TGF-β and BG_O, as well as small-angle X-ray scattering data, BG_O is shown to bind its cognate GF in an entirely different manner compared with ENG_O. The alternative interfaces likely engender BG and ENG with the ability to selectively bind and target their cognate GFs in a unique temporal-spatial manner, without interfering with one another or other TGF-β family GFs.

TGF-β2 uses the concave surface of its extended finger region to bind betaglycan's ZP domain via three residues specific to TGF-β and inhibin-α

Betaglycan (BG) is a membrane-bound co-receptor of the TGF-β family that selectively binds transforming growth factor-β (TGF-β) isoforms and inhibin A (InhA) to enable temporal-spatial patterns of signaling essential for their functions in vivo Here, using NMR titrations of methyl-labeled TGF-β2 with BG's C-terminal binding domain, BGZP-C, and surface plasmon resonance binding measurements with TGF-β2 variants, we found that the BGZP-C-binding site on TGF-β2 is located on the inner surface of its extended finger region. Included in this binding site are Ile-92, Lys-97, and Glu-99, which are entirely or mostly specific to the TGF-β isoforms and the InhA α-subunit, but they are unconserved in other TGF-β family growth factors (GFs). In accord with the proposed specificity-determining role of these residues, BG bound bone morphogenetic protein 2 (BMP-2) weakly or not at all, and TGF-β2 variants with the corresponding residues from BMP-2 bound BGZP-C more weakly than corresponding alanine variants. The BGZP-C-binding site on InhA previously was reported to be located on the outside of the extended finger region, yet at the same time to include Ser-112 and Lys-119, homologous to TGF-β2 Ile-92 and Lys-97, on the inside of the fingers. Therefore, it is likely that both TGF-β2 and InhA bind BGZP-C through a site on the inside of their extended finger regions. Overall, these results identify the BGZP-C-binding site on TGF-β2 and shed light on the specificity of BG for select TGF-β-type GFs and the mechanisms by which BG influences their signaling.

Betaglycan (TGFBR3) Functions as an Inhibin A, but Not Inhibin B, Coreceptor in Pituitary Gonadotrope Cells in Mice

Inhibins are gonadal hormones that act on pituitary gonadotrope cells to suppress FSH synthesis and secretion. Inhibin A and B are heterodimers of the inhibin ⍺-subunit disulfide-linked to one of two inhibin β-subunits. Homodimers or heterodimers of the inhibin β-subunits form the activins, which stimulate FSH production. Activins signal through complexes of type I and II receptor serine/threonine kinases to increase transcription of the FSHβ subunit gene. According to in vitro observations, inhibins impair FSH synthesis by competitively binding to activin type II receptors, particularly in the presence of the TGFβ type III receptor (TGFBR3, or betaglycan). The role of TGFBR3 in inhibin action in vivo has not been determined. Here, we ablated Tgfbr3 specifically in murine gonadotropes. Conditional knockout females were supra-fertile, exhibiting enhanced folliculogenesis, numbers of ovulated eggs per cycle, and litter sizes relative to control mice. Despite these phenotypes, FSH levels appeared to be unaltered in knockout mice, and the mechanisms underlying their enhanced fertility remain unexplained. Inhibin B is the predominant form of the hormone in males and in females during most stages of the estrous cycle. Remarkably, inhibin A, but not inhibin B, suppression of FSH synthesis was impaired in cultured pituitaries of knockout mice, which may explain the absence of discernible changes in FSH levels in vivo. Collectively, these data challenge current dogma by demonstrating that TGFBR3 (betaglycan) functions as an inhibin A, but not an inhibin B, coreceptor in gonadotrope cells in vivo. Mechanisms of inhibin B action merit further investigation.

TGF-β Signaling and the Epithelial-Mesenchymal Transition during Palatal Fusion

Signaling by transforming growth factor (TGF)-β plays an important role in development, including in palatogenesis. The dynamic morphological process of palatal fusion occurs to achieve separation of the nasal and oral cavities. Critically and specifically important in palatal fusion are the medial edge epithelial (MEE) cells, which are initially present at the palatal midline seam and over the course of the palate fusion process are lost from the seam, due to cell migration, epithelial-mesenchymal transition (EMT), and/or programed cell death. In order to define the role of TGF-β signaling during this process, several approaches have been utilized, including a small interfering RNA (siRNA) strategy targeting TGF-β receptors in an organ culture context, the use of genetically engineered mice, such as Wnt1-cre/R26R double transgenic mice, and a cell fate tracing through utilization of cell lineage markers. These approaches have permitted investigators to distinguish some specific traits of well-defined cell populations throughout the palatogenic events. In this paper, we summarize the current understanding on the role of TGF-β signaling, and specifically its association with MEE cell fate during palatal fusion. TGF-β is highly regulated both temporally and spatially, with TGF-β3 and Smad2 being the preferentially expressed signaling molecules in the critical cells of the fusion processes. Interestingly, the accessory receptor, TGF-β type 3 receptor, is also critical for palatal fusion, with evidence for its significance provided by Cre-lox systems and siRNA approaches. This suggests the high demand of ligand for this fine-tuned signaling process. We discuss the new insights in the fate of MEE cells in the midline epithelial seam (MES) during the palate fusion process, with a particular focus on the role of TGF-β signaling.

TGF-β Signaling-Related Genes and Thoracic Aortic Aneurysms and Dissections

Transforming growth factor-β (TGF)-β signaling plays a crucial role in the development and maintenance of various organs, including the vasculature. Accordingly, the mutations in TGF-β signaling pathway-related genes cause heritable disorders of the connective tissue, such as Marfan syndrome (MFS), Loeys-Dietz syndrome (LDS), and Shprintzen-Goldberg syndrome (SGS), and these syndromes may affect skeletal, ocular, pulmonary, and cardiovascular systems. Aortic root aneurysms are common problems that can result in aortic dissection or rupture, which is the leading cause of sudden death in the natural history of MFS and LDS, and recent improvements in surgical treatment have improved life expectancy. However, there is currently no genotype-specific medical treatment. Accumulating evidence suggest that not only structural weakness of connective tissue but also increased TGF-β signaling contributes to the complicated pathogenesis of aortic aneurysm formation, but a comprehensive understanding of governing molecular mechanisms remains lacking. Inhibition of angiotensin II receptor signaling and endothelial dysfunction have gained attention as a possible MFS treatment strategy, but interactions with TGF-β signaling remain elusive. Heterozygous loss-of-function mutations in TGF-β receptors 1 and 2 (TGFBR1 and TGFBR2) cause LDS, but TGF-β signaling is activated in the aorta (referred to as the TGF-β paradox) by mechanisms yet to be elucidated. In this review, we present and discuss the current understanding of molecular mechanisms responsible for aortopathies of MFS and related disorders.

Ras enhances TGF-β signaling by decreasing cellular protein levels of its type II receptor negative regulator SPSB1

Background

Transformation by oncogene Ras overcomes TGF-β mediated growth inhibition in epithelial cells. However, it cooperates with each other to mediate epithelial to mesenchymal transition (EMT). The mechanism of how these two pathways interact with each other is controversial.

Methods

Molecular techniques were used to engineer expression plasmids for Ras, SPRY, TGF-β receptors, type I and II and ubiquitin. Immunoprecipitation and western blots were employed to determine protein-protein interactions, preotein levels, protein phosphorylation while immunofluorecesent staining for molecular co-localization. TGF-β signalling activities is also determined by its luciferase reporter assay. Trans-well assays were used to measure cell migration and invasion.

Results

Ras interacts with the SPSB1’s SPRY domain to enhance TGF-β signaling. Ras interacts and colocalizes with the TGF-β type II receptor’s (TβRII) negative regulator SPSB1 on the cell membrane, consequently promoting SPSB1 protein degradation via enhanced mono- and di-ubiquitination. Reduced SPSB1 levels result in the stablization of TβRII, in turn the increase of receptor levels significantly enhance Smad2/3 phosphorylation and signaling. Importantly, forced expression of SPSB1 in Ras transformed cells suppresses TGF-β signaling and its mediated migration and invasion.

Conclusion

Ras positively cooperates with TGF-β signaling by reducing the cellular protein levels of TβRII negative regualtor SPSB1.

Electronic supplementary material

The online version of this article (10.1186/s12964-018-0223-4) contains supplementary material, which is available to authorized users.

microRNA-193a stimulates pancreatic cancer cell repopulation and metastasis through modulating TGF-β2/TGF-βRIII signalings

BACKGROUND

Pancreatic cancer characterizes high recurrence and poor prognosis. In clinical practice, radiotherapy is widely used for pancreatic cancer treatment. However, the outcome remains undesirable due to tumor repopulation and following recurrence and metastasis after radiation. So, it is highly needed to explore the underlying molecular mechanisms and accordingly develop therapeutic strategies. Our previous studies revealed that dying cells from chemoradiation could stimulate repopulation of surviving pancreatic cancer cells. However, we still knew little how dying cells provoke pancreatic cancer cell repopulation. We herein would explore the significance of TGF-β2 changes and investigate the modulation of microRNA-193a (miR-193a), and identify their contributions to pancreatic cancer repopulation and metastasis.

METHODS

In vitro and in vivo repopulation models were established to mimic the biological processes of pancreatic cancer after radiation. Western blot, real-time PCR and dual-luciferase reporter assays were accordingly used to detect miR-193a and TGF-β2/TGF-βRIII signalings at the level of molecular, cellular and experimental animal model, respectively. Flow cytometry analysis, wound healing and transwell assay, vascular endothelial cell penetration experiment, and bioluminescence imaging were employed to assessthe biological behaviors of pancreatic cancer after different treatments. Patient-derived tumor xenograft (PDX) mice models were established to evaluate the therapeutic potential of miR-193a antagonist on pancreatic cancer repopulation and metastasis after radiation.

RESULTS

miR-193a was highly expressed in the irradiated pancreatic cancer dying cells, accordingly elevated the level of miR-193a in surviving cells, and further promoted pancreatic cancer repopulation and metastasis in vitro and in vivo. miR-193a accelerated pancreatic cancer cell cycle and stimulated cell proliferation and repopulation through inhibiting TGF-β2/TGF-βRIII/SMADs/E2F6/c-Myc signaling, and even destroyed normal intercellular junctions and promoted metastasis via repressing TGF-β2/TGF-βRIII/ARHGEF15/ABL2 pathway. Knockdown of miR-193a or restoration of TGF-β2/TGF-βRIII signaling in pancreatic cancer cells was found to block pancreatic cancer repopulation and metastasis after radiation. In PDX models, the treatment in combination with miR-193a antagonist and radiation was found to dramatically inhibit pancreatic cancer cell repopulation and metastasis, and further improved the survival after radiation.

CONCLUSIONS

Our findings demonstrated that miR-193a stimulated pancreatic cancer cell repopulation and metastasis through modulating TGF-β2/TGF-βRIII signalings, and miR-193a might be a potential therapeutic target for pancreatic cancer repopulation and metastasis.

From Consternation to Revelation: Discovery of a Role for IGSF1 in Pituitary Control of Thyroid Function

Immunoglobulin superfamily, member 1 (IGSF1) is a transmembrane glycoprotein highly expressed in the mammalian pituitary gland. Shortly after its discovery in 1998, the protein was proposed to function as a coreceptor for inhibins (and was even temporarily renamed inhibin binding protein). However, subsequent investigations, both in vitro and in vivo, failed to support a role for IGSF1 in inhibin action. Research on IGSF1 nearly ground to a halt until 2011, when next-generation sequencing identified mutations in the X-linked IGSF1 gene in boys and men with congenital central hypothyroidism. IGSF1 was localized to thyrotrope cells, implicating the protein in pituitary control of the thyroid. Investigations in two Igsf1 knockout mouse models converged to show that IGSF1 deficiency leads to reduced expression of the receptor for thyrotropin-releasing hormone (TRH) and impaired TRH stimulation of thyrotropin secretion, providing a candidate mechanism for the central hypothyroidism observed in patients. Nevertheless, the normal functions of IGSF1 in thyrotropes and other cells remain unresolved. Moreover, IGSF1 mutations are also commonly associated with other clinical phenotypes, including prolactin and growth hormone dysregulation, and macroorchidism. How the loss of IGSF1 produces these characteristics is unknown. Although early studies of IGSF1 ran into roadblocks and blind alleys, armed with the results of detailed clinical investigations, powerful mouse models, and new reagents, the field is now poised to discover IGSF1’s function in endocrine tissues, including the pituitary and testes.

TGF-β Signaling in Control of Cardiovascular Function

Genetic studies in animals and humans indicate that gene mutations that functionally perturb transforming growth factor β (TGF-β) signaling are linked to specific hereditary vascular syndromes, including Osler-Rendu-Weber disease or hereditary hemorrhagic telangiectasia and Marfan syndrome. Disturbed TGF-β signaling can also cause nonhereditary disorders like atherosclerosis and cardiac fibrosis. Accordingly, cell culture studies using endothelial cells or smooth muscle cells (SMCs), cultured alone or together in two- or three-dimensional cell culture assays, on plastic or embedded in matrix, have shown that TGF-β has a pivotal effect on endothelial and SMC proliferation, differentiation, migration, tube formation, and sprouting. Moreover, TGF-β can stimulate endothelial-to-mesenchymal transition, a process shown to be of key importance in heart valve cushion formation and in various pathological vascular processes. Here, we discuss the roles of TGF-β in vasculogenesis, angiogenesis, and lymphangiogenesis and the deregulation of TGF-β signaling in cardiovascular diseases.

Dually modified transmembrane proteoglycans in development and disease

Aberrant cell signaling in response to secreted growth factors has been linked to the development of multiple diseases, including cancer. As such, understanding mechanisms that control growth factor availability and receptor-growth factor interaction is vital. Dually modified transmembrane proteoglycans (DMTPs), which are classified as cell surface macromolecules composed of a core protein decorated with covalently linked heparan sulfated (HS) and/or chondroitin sulfated (CS) glycosaminoglycan (GAG) chains, provide one type of regulatory mechanism. Specifically, DMTPs betaglycan and syndecan-1 (SDC1) play crucial roles in modulating key cell signaling pathways, such as Wnt, transforming growth factor-β and fibroblast growth factor signaling, to affect epithelial cell biology and cancer progression. This review outlines current and potential functions for betaglycan and SDC1, with an emphasis on comparing individual roles for HS and CS modified DMTPs. We highlight the mutual dependence of DMTPs' GAG chains and core proteins and provide comprehensive knowledge on how these DMTPs, through regulation of ligand availability and receptor internalization, control cell signaling pathways involved in development and disease.

Binding Properties of the Transforming Growth Factor-β Coreceptor Betaglycan: Proposed Mechanism for Potentiation of Receptor Complex Assembly and Signaling

Transforming growth factor (TGF) β1, β2, and β3 (TGF-β1–TGF-β3, respectively) are small secreted signaling proteins that each signal through the TGF-β type I and type II receptors (TβRI and TβRII, respectively). However, TGF-β2, which is well-known to bind TβRII several hundred-fold more weakly than TGF-β1 and TGF-β3, has an additional requirement for betaglycan, a membrane-anchored nonsignaling receptor. Betaglycan has two domains that bind TGF-β2 at independent sites, but how it binds TGF-β2 to potentiate TβRII binding and how the complex with TGF-β, TβRII, and betaglycan undergoes the transition to the signaling complex with TGF-β, TβRII, and TβRI are not understood. To investigate the mechanism, the binding of the TGF-βs to the betaglycan extracellular domain, as well as its two independent binding domains, either directly or in combination with the TβRI and TβRII ectodomains, was studied using surface plasmon resonance, isothermal titration calorimetry, and size-exclusion chromatography. These studies show that betaglycan binds TGF-β homodimers with a 1:1 stoichiometry in a manner that allows one molecule of TβRII to bind. These studies further show that betaglycan modestly potentiates the binding of TβRII and must be displaced to allow TβRI to bind. These findings suggest that betaglycan functions to bind and concentrate TGF-β2 on the cell surface and thus promote the binding of TβRII by both membrane-localization effects and allostery. These studies further suggest that the transition to the signaling complex is mediated by the recruitment of TβRI, which simultaneously displaces betaglycan and stabilizes the bound TβRII by direct receptor–receptor contact.