The insulin response integrates increased TGF-β signaling through Akt-induced enhancement of cell surface delivery of TGF-β receptors

Transforming growth factor-β receptors: versatile mechanisms of ligand activation

Transforming growth factor-β (TGF-β) signaling is initiated by activation of transmembrane TGF-β receptors (TGFBR), which deploys Smad2/3 transcription factors to control cellular responses. Failure or dysregulation in the TGF-β signaling pathways leads to pathological conditions. TGF-β signaling is regulated at different levels along the pathways and begins with the liberation of TGF-β ligand from its latent form. The mechanisms of TGFBR activation display selectivity to cell types, agonists, and TGF-β isoforms, enabling precise control of TGF-β signals. In addition, the cell surface compartments used to release active TGF-β are surprisingly vibrant, using thrombospondins, integrins, matrix metalloproteinases and reactive oxygen species. The scope of TGFBR activation is further unfolded with the discovery of TGFBR activation initiated by other signaling pathways. The unique combination of mechanisms works in series to trigger TGFBR activation, which can be explored as therapeutic targets. This comprehensive review provides valuable insights into the diverse mechanisms underpinning TGFBR activation, shedding light on potential avenues for therapeutic exploration.

A New Era of Integration between Multiomics and Spatio-Temporal Analysis for the Translation of EMT towards Clinical Applications in Cancer

Epithelial-mesenchymal transition (EMT) is crucial to metastasis by increasing cancer cell migration and invasion. At the cellular level, EMT-related morphological and functional changes are well established. At the molecular level, critical signaling pathways able to drive EMT have been described. Yet, the translation of EMT into efficient diagnostic methods and anti-metastatic therapies is still missing. This highlights a gap in our understanding of the precise mechanisms governing EMT. Here, we discuss evidence suggesting that overcoming this limitation requires the integration of multiple omics, a hitherto neglected strategy in the EMT field. More specifically, this work summarizes results that were independently obtained through epigenomics/transcriptomics while comprehensively reviewing the achievements of proteomics in cancer research. Additionally, we prospect gains to be obtained by applying spatio-temporal multiomics in the investigation of EMT-driven metastasis. Along with the development of more sensitive technologies, the integration of currently available omics, and a look at dynamic alterations that regulate EMT at the subcellular level will lead to a deeper understanding of this process. Further, considering the significance of EMT to cancer progression, this integrative strategy may enable the development of new and improved biomarkers and therapeutics capable of increasing the survival and quality of life of cancer patients.

Dysregulation of early gene response to a mixed meal in skeletal muscle in obesity and type 2 diabetes

Obesity- and type 2 diabetes mellitus-induced changes in the expression of protein-coding genes in human skeletal muscle were extensively examined at baseline (after an overnight fast). We aimed to compare the early transcriptomic response to a typical single meal in skeletal muscle of metabolically healthy subjects and obese individuals without and with type 2 diabetes. Transcriptomic response (RNA-seq) to a mixed meal (nutritional drink, ∼25 kJ/kg of body mass) was examined in the vastus lateralis muscle (1 h after a meal) in 7 healthy subjects and 14 obese individuals without or with type 2 diabetes. In all obese individuals, the transcriptome response to a meal was dysregulated (suppressed and altered) and associated with different biological processes compared with healthy control. To search for potential transcription factors regulating transcriptomic response to a meal, the enrichment of transcription factor-binding sites in individual promoters of the human skeletal muscle was examined. In obese individuals, the transcriptomic response is associated with a different set of transcription factors than that in healthy subjects. In conclusion, metabolic disorders are associated with a defect in the regulation of mixed meal/insulin-mediated gene expression-insulin resistance in terms of gene expression. Importantly, this dysregulation occurs in obese individuals without type 2 diabetes, i.e., at the first stage of the development of metabolic disorders.NEW & NOTEWORTHY In skeletal muscle of metabolically healthy subjects, a typical single meal normalized to body mass induces activation of various transcription factors, expression of numerous receptor tyrosine kinases associated with the insulin signaling cascade, and transcription regulators. In skeletal muscle of obese individuals without and with type 2 diabetes, this signaling network is poorly regulated at the transcriptional level, indicating dysregulation of the early gene response to a mixed meal.

Scaffolds containing GAG-mimetic cellulose sulfate promote TGF-β interaction and MSC Chondrogenesis over native GAGs

Cartilage tissue engineering strategies seek to repair damaged tissue using approaches that include scaffolds containing components of the native extracellular matrix (ECM). Articular cartilage consists of glycosaminoglycans (GAGs) which are known to sequester growth factors. In order to more closely mimic the native ECM, this study evaluated the chondrogenic differentiation of mesenchymal stem cells (MSCs), a promising cell source for cartilage regeneration, on fibrous scaffolds that contained the GAG-mimetic cellulose sulfate. The degree of sulfation was evaluated, examining partially sulfated cellulose (pSC) and fully sulfated cellulose (NaCS). Comparisons were made with scaffolds containing native GAGs (chondroitin sulfate A, chondroitin sulfate C and heparin). Transforming growth factor-beta3 (TGF-β3) sequestration, as measured by rate of association, was higher for sulfated cellulose-containing scaffolds as compared to native GAGs. In addition, TGF-β3 sequestration and retention over time was highest for NaCS-containing scaffolds. Sulfated cellulose-containing scaffolds loaded with TGF-β3 showed enhanced chondrogenesis as indicated by a higher Collagen Type II:I ratio over native GAGs. NaCS-containing scaffolds loaded with TGF-β3 had the highest expression of chondrogenic markers and a reduction of hypertrophic markers in dynamic loading conditions, which more closely mimic in vivo conditions. Studies also demonstrated that TGF-β3 mediated its effect through the Smad2/3 signaling pathway where the specificity of TGF-β receptor (TGF- βRI)-phosphorylated SMAD2/3 was verified with a receptor inhibitor. Therefore, studies demonstrate that scaffolds containing cellulose sulfate enhance TGF-β3-induced MSC chondrogenic differentiation and show promise for promoting cartilage tissue regeneration.

Analysis of Why Alzheimer's Dementia Never Spontaneously Reverses, Suggests the Basis for Curative Treatment

A paradox regarding Alzheimer's dementia (AD) and mild cognitive impairment (MCI) is thats spontaneous cure of AD has never been reported, whereas spontaneous cure for MCI occurs fequently. This article analyzes what accounts for this difference. It holds that it is not merely because, for any condition, a stage is reached beyond which it cannot be reversed, since even widely metastatic cancer would be curable were there effective chemotherapy and rheumatoid arthritis became controllable when immune-suppressant treatment was introduced; thus, so could AD be reversible via effective therapy. The analysis presented leads to an explanation of the paradox that is in four categories: (1) levels of transforming growth factor-β are significantly reduced after the transition from MCI to AD; (2) levels of Wnt/β-catenin are significantly reduced after the transition; (3) there is altered epidermal-mesenchymal transition (EMT) in neurons after the transition; (4) there may be risk factors that are either newly operative or pre-existing but worsened at the time of transition, that are particular to individual patients. It is suggested that addressing and ameliorating all of those four categories might cure AD. Medications to address and ameliorate each of the four categories are described.

State- and stimulus-specific dynamics of SMAD signaling determine fate decisions in individual cells

SMAD-mediated signaling regulates apoptosis, cell cycle arrest, and epithelial-to-mesenchymal transition to safeguard tissue homeostasis. However, it remains elusive how the relatively simple pathway can determine such a broad range of cell fate decisions and how it differentiates between varying ligands. Here, we systematically investigate how SMAD-mediated responses are modulated by various ligands of the transforming growth factor β (TGFβ) family and compare these ligand responses in quiescent and proliferating MCF10A cells. We find that the nature of the phenotypic response is mainly determined by the proliferation status, with migration and cell cycle arrest being dominant in proliferating cells for all tested TGFβ family ligands, whereas cell death is the major outcome in quiescent cells. In both quiescent and proliferating cells, the identity of the ligand modulates the strength of the phenotypic response proportional to the dynamics of induced SMAD nuclear-to-cytoplasmic translocation and, as a consequence, the corresponding gene expression changes. Interestingly, the proliferation state of a cell has little impact on the set of genes induced by SMAD signaling; instead, it modulates the relative cellular sensitivity to TGFβ superfamily members. Taken together, diversity of SMAD-mediated responses is mediated by differing cellular states, which determine ligand sensitivity and phenotypic effects, while the pathway itself merely serves as a quantitative relay from the cell membrane to the nucleus.

The liver kinase B1 supports mammary epithelial morphogenesis by inhibiting critical factors that mediate epithelial-mesenchymal transition

The liver kinase B1 (LKB1) controls cellular metabolism and cell polarity across species. We previously established a mechanism for negative regulation of transforming growth factor β (TGFβ) signaling by LKB1. The impact of this mechanism in the context of epithelial polarity and morphogenesis remains unknown. After demonstrating that human mammary tissue expresses robust LKB1 protein levels, whereas invasive breast cancer exhibits significantly reduced LKB1 levels, we focused on mammary morphogenesis studies in three dimensional (3D) acinar organoids. CRISPR/Cas9-introduced loss-of-function mutations of STK11 (LKB1) led to profound defects in the formation of 3D organoids, resulting in amorphous outgrowth and loss of rotation of young organoids embedded in matrigel. This defect was associated with an enhanced signaling by TGFβ, including TGFβ auto-induction and induction of transcription factors that mediate epithelial-mesenchymal transition (EMT). Protein marker analysis confirmed a more efficient EMT response to TGFβ signaling in LKB1 knockout cells. Accordingly, chemical inhibition of the TGFβ type I receptor kinase largely restored the morphogenetic defect of LKB1 knockout cells. Similarly, chemical inhibition of the bone morphogenetic protein pathway or the TANK-binding kinase 1, or genetic silencing of the EMT factor SNAI1, partially restored the LKB1 knockout defect. Thus, LKB1 sustains mammary epithelial morphogenesis by limiting pathways that promote EMT. The observed downregulation of LKB1 expression in breast cancer is therefore predicted to associate with enhanced EMT induced by SNAI1 and TGFβ family members.

Genomic organization, intragenic tandem duplication, and expression analysis of chicken TGFBR2 gene

Transforming growth factor beta receptor Ⅱ (TGFBR2), a core member of the transforming growth factor-β (TGF-β) signaling pathway. To date, chicken TGFBR2 (cTGFBR2) genomic structure has not been fully explored. Here, the complete sequences of cTGFBR2 transcript isoforms were determined by 5′ and 3′ rapid amplification of cDNA ends (5′ & 3′ RACE) and reverse transcription polymerase chain reaction (RT-PCR); the tissue expression profiling of cTGFBR2 transcript isoforms was performed using quantitative real-time polymerase chain reaction (qRT-PCR). The results showed that cTGFBR2 gene produced 3 transcript isoforms though alternative transcription initiation, splicing, and polyadenylation, which were designated as cTGFBR2-1, cTGFBR2-2, and cTGFBR2-3, respectively. These 3 cTGFBR2 transcript isoforms encoded 3 protein isoforms: cTGFBR2-1, cTGFBR2-2, and cTGFBR2-3. Duplication analysis revealed that, unlike other animal species, cTGFBR2 gene harbored a 5.5-kb intragenic tandem duplication. Tissue expression profiling in the 4-wk-old Arbor Acres (AA) broiler chickens showed that cTGFBR2-1 was ubiquitously expressed, with high expression in abdominal fat, subcutaneous fat, lung, gizzard, and muscle; cTGFBR2-2 was highly expressed in heart, kidney, gizzard, and muscle; cTGFBR2-3 was weakly expressed in all the tested chicken tissues. Tissue expression profiling in the 7-wk-old broiler chickens of the fat and lean lines of Northeast Agricultural University broiler lines divergently selected for abdominal fat content (NEAUHLF) showed that cTGFBR2-1 was significantly differentially expressed in all the tested tissues except heart, cTGFBR2-2 was significantly differentially expressed in all the tested tissues except subcutaneous fat and liver, and cTGFBR2-3 was significantly differentially expressed in all the tested tissues between the lean and fat lines. Intriguingly, in the fat line, the 3 cTGFBR2 transcript isoforms were expressed to varying degrees in all the 3 tested fat tissues, while in the lean line, only cTGFBR2-1 was expressed in all the 3 tested fat tissues. This is the first report of intragenic tandem duplication within TGFBR2 gene. Our findings pave the way for further studies on the functions and regulation of cTGFBR2 gene.

Modeling human extraembryonic mesoderm cells using naive pluripotent stem cells

A hallmark of primate postimplantation embryogenesis is the specification of extraembryonic mesoderm (EXM) before gastrulation, in contrast to rodents where this tissue is formed only after gastrulation. Here, we discover that naive human pluripotent stem cells (hPSCs) are competent to differentiate into EXM cells (EXMCs). EXMCs are specified by inhibition of Nodal signaling and GSK3B, are maintained by mTOR and BMP4 signaling activity, and their transcriptome and epigenome closely resemble that of human and monkey embryo EXM. EXMCs are mesenchymal, can arise from an epiblast intermediate, and are capable of self-renewal. Thus, EXMCs arising via primate-specific specification between implantation and gastrulation can be modeled in vitro. We also find that most of the rare off-target cells within human blastoids formed by triple inhibition (Kagawa et al., 2021) correspond to EXMCs. Our study impacts our ability to model and study the molecular mechanisms of early human embryogenesis and related defects.

Roflumilast-Mediated Phosphodiesterase 4D Inhibition Reverses Diabetes-Associated Cardiac Dysfunction and Remodeling: Effects Beyond Glucose Lowering

Patients with type 2 diabetes have a substantial risk of developing cardiovascular disease. Phosphodiesterase 4 (PDE4) dysregulation is of pathophysiological importance in metabolic disorders. For determination of the role of PDE4 in diabetic cardiac dysfunction, mice fed with a high-fat diet (HFD) were treated by pharmacological inhibition of PDE4 or cardiac specific knocking down of PDE4D. Mice on HFD developed diabetes and cardiac dysfunction with increased cardiac PDE4D5 expression. PDE4 inhibitor roflumilast can reverse hyperglycemia and cardiac dysfunction, accompanied by the decrease of PDE4D expression and increase of muscle specific miRNA miR-1 level in hearts. Either cardiac specific PDE4D knockdown or miR-1 overexpression significantly reversed cardiac dysfunction in HFD mice, despite persistence of hyperglycemia. Findings of gain- and loss-of-function studies of PDE4D in cardiomyocytes indicated that inhibition of insulin-induced PDE4D protected cardiac hypertrophy by preserving miR-1 expression in cardiomyocytes through promoting cAMP-CREB-Sirt1 signaling-induced SERCA2a expression. We further revealed that insulin also induced PDE4D expression in cardiac fibroblasts, which causes cardiac fibrosis through TGF-β1 signaling-mediated miR-1 reduction. Importantly, the expression of PDE4D5 was increased in human failing hearts of individuals with diabetes. These studies elucidate a novel mechanism by which hyperinsulinemia-induced cardiac PDE4D expression contributes to diabetic cardiac remodeling through reducing the expression of miR-1 and upregulation of miR-1 target hypertrophy and fibrosis-associated genes. Our study suggests a therapeutic potential of PDE4 inhibitor roflumilast in preventing or treating cardiac dysfunction in diabetes in addition to lowering glucose.

EPDR1 is a noncanonical effector of insulin-mediated angiogenesis regulated by an endothelial-specific TGF-β receptor complex

Insulin signaling in blood vessels primarily functions to stimulate angiogenesis and maintain vascular homeostasis through the canonical PI3K and MAPK signaling pathways. However, angiogenesis is a complex process coordinated by multiple other signaling events. Here, we report a distinct crosstalk between the insulin receptor and endoglin/activin receptor-like kinase 1 (ALK1), an endothelial cell-specific TGF-β receptor complex essential for angiogenesis. While the endoglin-ALK1 complex normally binds to TGF-β or bone morphogenetic protein 9 (BMP9) to promote gene regulation via transcription factors Smad1/5, we show that insulin drives insulin receptor oligomerization with endoglin-ALK1 at the cell surface to trigger rapid Smad1/5 activation. Through quantitative proteomic analysis, we identify ependymin-related protein 1 (EPDR1) as a major Smad1/5 gene target induced by insulin but not by TGF-β or BMP9. We found endothelial EPDR1 expression is minimal at the basal state but is markedly enhanced upon prolonged insulin treatment to promote cell migration and formation of capillary tubules. Conversely, we demonstrate EPDR1 depletion strongly abrogates these angiogenic effects, indicating that EPDR1 is a crucial mediator of insulin-induced angiogenesis. Taken together, these results suggest important therapeutic implications for EPDR1 and the TGF-β pathways in pathologic angiogenesis during hyperinsulinemia and insulin resistance.

MiR-92a/KLF4/p110δ regulates titanium particles-induced macrophages inflammation and osteolysis

As total joint replacement is widely applied for severe arthropathy, peri-prosthetic aseptic loosening as one of the main causes of implant failure has drawn wide attention. Wear particles such as titanium particles (TiPs) derived from prosthesis can initiate macrophages inflammation and sequentially activate osteoclasts, which results in bone resorption and osteolysis for long-term. Therefore, inhibiting wear particles induced macrophages inflammation is considered as a promising therapy for AL. In this research, we found that the inhibition of p110δ, a member of class IA PI3Ks family, could significantly dampen the TiPs-induced secretion of TNFα and IL-6. By the transfection of siRNA targeting p110δ, we confirmed that p110δ was responsible for TNFα and IL-6 trafficking out of Golgi complex without affecting their expression in TiPs-treated macrophages. As the upstream transcription-repressor of p110δ, Krüppel-like factor 4 (KLF4), targeted by miR-92a, could also attenuate TiPs-induced inflammation by mediating NF-κB pathway and M1/M2 polarization. To further ascertain the roles of KLF4/p110δ, TiPs-induced mice cranial osteolysis model was established and vivo experiments validated that KLF4-knockdown could exacerbate TiPs-induced osteolysis, which was strikingly ameliorated by knockdown of p110δ. In summary, our study suggests the key role of miR-92a/KLF4/p110δ signal in TiPs-induced macrophages inflammation and osteolysis.

TGFβ: Signaling Blockade for Cancer Immunotherapy

Discovered over four decades ago, transforming growth factor β (TGFβ) is a potent pleiotropic cytokine that has context-dependent effects on most cell types. It acts as a tumor suppressor in some cancers and/or supports tumor progression and metastasis through its effects on the tumor stroma and immune microenvironment. In TGFβ-responsive tumors it can promote invasion and metastasis through epithelial-mesenchymal transformation, the appearance of cancer stem cell features, and resistance to many drug classes, including checkpoint blockade immunotherapies. Here we consider the biological activities of TGFβ action on different cells of relevance toward improving immunotherapy outcomes for patients, with a focus on the adaptive immune system. We discuss recent advances in the development of drugs that target the TGFβ signaling pathway in a tumor-specific or cell type–specific manner to improve the therapeutic window between response rates and adverse effects.

Upregulated flotillins and sphingosine kinase 2 derail AXL vesicular traffic to promote epithelial-mesenchymal transition

Altered endocytosis and vesicular trafficking are major players during tumorigenesis. Flotillin overexpression, a feature observed in many invasive tumors and identified as a marker of poor prognosis, induces a deregulated endocytic and trafficking pathway called upregulated flotillin-induced trafficking (UFIT). Here, we found that in non-tumoral mammary epithelial cells, induction of the UFIT pathway promotes epithelial-to-mesenchymal transition (EMT) and accelerates the endocytosis of several transmembrane receptors, including AXL, in flotillin-positive late endosomes. AXL overexpression, frequently observed in cancer cells, is linked to EMT and metastasis formation. In flotillin-overexpressing non-tumoral mammary epithelial cells and in invasive breast carcinoma cells, we found that the UFIT pathway-mediated AXL endocytosis allows its stabilization and depends on sphingosine kinase 2, a lipid kinase recruited in flotillin-rich plasma membrane domains and endosomes. Thus, the deregulation of vesicular trafficking following flotillin upregulation, and through sphingosine kinase 2, emerges as a new mechanism of AXL overexpression and EMT-inducing signaling pathway activation.

Akt acts as a switch for GPCR transactivation of the TGF-β receptor type 1

Transforming growth factor (TGF)-β signalling commences with the engagement of TGF-β ligand to cell surface TGF-β receptors (TGFBR) stimulating Smad2 carboxyl-terminal phosphorylation (phospho-Smad2C) and downstream biological responses. In several cell models, G protein-coupled receptors (GPCRs) transactivate the TGF-β receptors type-1 (TGFBR1) leading to phospho-Smad2C, however, we have recently published that in keratinocytes thrombin did not transactivate the TGFBR1. The bulk of TGFBRs reside in the cytosol and in response to protein kinase B (Akt phosphorylation) can translocate to the cell surface increasing the cell's responsiveness to TGF-β. In this study, we investigate the role of Akt in GPCR transactivation of the TGFBR1. We demonstrate that angiotensin II and thrombin do not phosphorylate Smad2C in human vascular smooth muscle cells and in keratinocytes respectively. We used Akt agonist, SC79 to sensitise the cells to Akt and observed that Ang II and thrombin phosphorylate Smad2C via Akt/AS160-dependent pathways. We show that SC79 rapidly translocates TGFBRs to the cell surface thus increasing the cell's response to the GPCR agonist. These findings highlight novel mechanistic insight for the role of Akt in GPCR transactivation of the TGFBR1.

Endometrial PTEN Deficiency Leads to SMAD2/3 Nuclear Translocation

Simple Summary

PTEN is a protein highly altered in endometrial cancer. PTEN mutation or deficiency leads to the activation of other downstream proteins that are important to the development of cancers. In this study, we have identified the SMAD2/3 proteins as targets of PTEN deficiency. We have found that loss of PTEN in endometrial cells leads to SMAD2/3 activation. To investigate the role of SMAD2/3 activation downstream of PTEN deficiency, we have used endometrial cells lacking both PTEN and SMAD2/3 proteins. These cells display even more tumorigenic potential than cells lacking only PTEN. These results suggest that SMAD2/3 acts as an obstacle for cancer development triggered by PTEN loss.

Abstract

TGF-β has a dichotomous function, acting as tumor suppressor in premalignant cells but as a tumor promoter for cancerous cells. These contradictory functions of TGF-β are caused by different cellular contexts, including both intracellular and environmental determinants. The TGF-β/SMAD and the PI3K/PTEN/AKT signal transduction pathways have an important role in the regulation of epithelial cell homeostasis and perturbations in either of these two pathways’ contributions to endometrial carcinogenesis. We have previously demonstrated that both PTEN and SMAD2/3 display tumor-suppressive functions in the endometrium, and genetic ablation of either gene results in sustained activation of PI3K/AKT signaling that suppresses TGF-β-induced apoptosis and enhances cell proliferation of mouse endometrial cells. However, the molecular and cellular effects of PTEN deficiency on TGF-β/SMAD2/3 signaling remain controversial. Here, using an in vitro and in vivo model of endometrial carcinogenesis, we have demonstrated that loss of PTEN leads to a constitutive SMAD2/3 nuclear translocation. To ascertain the function of nuclear SMAD2/3 downstream of PTEN deficiency, we analyzed the effects of double deletion PTEN and SMAD2/3 in mouse endometrial organoids. Double PTEN/SMAD2/3 ablation results in a further increase of cell proliferation and enlarged endometrial organoids compared to those harboring single PTEN, suggesting that nuclear translocation of SMAD2/3 constrains tumorigenesis induced by PTEN deficiency.

Insulin/IGF-1 signaling promotes immunosuppression via the STAT3 pathway: impact on the aging process and age-related diseases

BACKGROUND

The insulin/IGF-1 signaling pathway has a major role in the regulation of longevity both in Caenorhabditis elegans and mammalian species, i.e., reduced activity of this pathway extends lifespan, whereas increased activity accelerates the aging process. The insulin/IGF-1 pathway controls protein and energy metabolism as well as the proliferation and differentiation of insulin/IGF-1-responsive cells. Insulin/IGF-1 signaling also regulates the functions of the innate and adaptive immune systems. The purpose of this review was to elucidate whether insulin/IGF-1 signaling is linked to immunosuppressive STAT3 signaling which is known to promote the aging process.

METHODS

Original and review articles encompassing the connections between insulin/IGF-1 and STAT3 signaling were examined from major databases including Pubmed, Scopus, and Google Scholar.

RESULTS

The activation of insulin/IGF-1 receptors stimulates STAT3 signaling through the JAK and AKT-driven signaling pathways. STAT3 signaling is a major activator of immunosuppressive cells which are able to counteract the chronic low-grade inflammation associated with the aging process. However, the activation of STAT3 signaling stimulates a negative feedback response through the induction of SOCS factors which not only inhibit the activity of insulin/IGF-1 receptors but also that of many cytokine receptors. The inhibition of insulin/IGF-1 signaling evokes insulin resistance, a condition known to be increased with aging. STAT3 signaling also triggers the senescence of both non-immune and immune cells, especially through the activation of p53 signaling.

CONCLUSIONS

Given that cellular senescence, inflammaging, and counteracting immune suppression increase with aging, this might explain why excessive insulin/IGF-1 signaling promotes the aging process.

Epithelial plasticity, epithelial-mesenchymal transition, and the TGF-β family

Epithelial cells repress epithelial characteristics and elaborate mesenchymal characteristics to migrate to other locations and acquire new properties. Epithelial plasticity responses are directed through cooperation of signaling pathways, with TGF-β and TGF-β-related proteins playing prominent instructive roles. Epithelial-mesenchymal transitions (EMTs) directed by activin-like molecules, bone morphogenetic proteins, or TGF-β regulate metazoan development and wound healing and drive fibrosis and cancer progression. In carcinomas, diverse EMTs enable stem cell generation, anti-cancer drug resistance, genomic instability, and localized immunosuppression. This review discusses roles of TGF-β and TGF-β-related proteins, and underlying molecular mechanisms, in epithelial plasticity in development and wound healing, fibrosis, and cancer.

Canonical TGFβ Signaling and Its Contribution to Endometrial Cancer Development and Progression-Underestimated Target of Anticancer Strategies

Endometrial cancer is one of the leading gynecological cancers diagnosed among women in their menopausal and postmenopausal age. Despite the progress in molecular biology and medicine, no efficient and powerful diagnostic and prognostic marker is dedicated to endometrial carcinogenesis. The canonical TGFβ pathway is a pleiotropic signaling cascade orchestrating a variety of cellular and molecular processes, whose alterations are responsible for carcinogenesis that originates from different tissue types. This review covers the current knowledge concerning the canonical TGFβ pathway (Smad-dependent) induced by prototypical TGFβ isoforms and the involvement of pathway alterations in the development and progression of endometrial neoplastic lesions. Since Smad-dependent signalization governs opposed cellular processes, such as growth arrest, apoptosis, tumor cells growth and differentiation, as well as angiogenesis and metastasis, TGFβ cascade may act both as a tumor suppressor or tumor promoter. However, the final effect of TGFβ signaling on endometrial cancer cells depends on the cancer disease stage. The multifunctional role of the TGFβ pathway indicates the possible utilization of alterations in the TGFβ cascade as a potential target of novel anticancer strategies.

Roles of microRNAs in Regulating Cancer Stemness in Head and Neck Cancers

Head and neck squamous cell carcinomas (HNSCCs) are epithelial malignancies with 5-year overall survival rates of approximately 40-50%. Emerging evidence indicates that a small population of cells in HNSCC patients, named cancer stem cells (CSCs), play vital roles in the processes of tumor initiation, progression, metastasis, immune evasion, chemo-/radioresistance, and recurrence. The acquisition of stem-like properties of cancer cells further provides cellular plasticity for stress adaptation and contributes to therapeutic resistance, resulting in a worse clinical outcome. Thus, targeting cancer stemness is fundamental for cancer treatment. MicroRNAs (miRNAs) are known to regulate stem cell features in the development and tissue regeneration through a miRNA-target interactive network. In HNSCCs, miRNAs act as tumor suppressors and/or oncogenes to modulate cancer stemness and therapeutic efficacy by regulating the CSC-specific tumor microenvironment (TME) and signaling pathways, such as epithelial-to-mesenchymal transition (EMT), Wnt/β-catenin signaling, and epidermal growth factor receptor (EGFR) or insulin-like growth factor 1 receptor (IGF1R) signaling pathways. Owing to a deeper understanding of disease-relevant miRNAs and advances in in vivo delivery systems, the administration of miRNA-based therapeutics is feasible and safe in humans, with encouraging efficacy results in early-phase clinical trials. In this review, we summarize the present findings to better understand the mechanical actions of miRNAs in maintaining CSCs and acquiring the stem-like features of cancer cells during HNSCC pathogenesis.

Intranasal insulin improves mitochondrial function and attenuates motor deficits in a rat 6-OHDA model of Parkinson's disease

Aims

Experimental and clinical evidences demonstrate that common dysregulated pathways are involved in Parkinson’s disease (PD) and type 2 diabetes. Recently, insulin treatment through intranasal (IN) approach has gained attention in PD, although the underlying mechanism of its potential therapeutic effects is still unclear. In this study, we investigated the effects of insulin treatment in a rat model of PD with emphasis on mitochondrial function indices in striatum.

Methods

Rats were treated with a daily low dose (4IU/day) of IN insulin, starting 72 h after 6‐OHDA‐induced lesion and continued for 14 days. Motor performance, dopaminergic cell survival, mitochondrial dehydrogenases activity, mitochondrial swelling, mitochondria permeability transition pore (mPTP), mitochondrial membrane potential (Δψ_m), reactive oxygen species (ROS) formation, and glutathione (GSH) content in mitochondria, mitochondrial adenosine triphosphate (ATP), and the gene expression of PGC‐1α, TFAM, Drp‐1, GFAP, and Iba‐1 were assessed.

Results

Intranasal insulin significantly reduces 6‐OHDA‐induced motor dysfunction and dopaminergic cell death. In parallel, it improves mitochondrial function indices and modulates mitochondria biogenesis and fission as well as activation of astrocytes and microglia.

Conclusion

Considering the prominent role of mitochondrial dysfunction in PD pathology, IN insulin as a disease‐modifying therapy for PD should be considered for extensive research.

Photobiomodulation with a 645 nm Diode Laser of Saos-2 Cells and Platelet-Rich Plasma: The Potential for a New Mechanism of Action

Objective: The main focus of this in vitro study was to highlight possible differences between outcomes of photobiomodulation performed in the presence or absence of growth factors derived from platelet-rich plasma. Background: Photobiomodulation has garnered increasing attention, thanks to a large number of controlled clinical trials that have proven its efficacy in various oral pathologies. Nevertheless, the mechanism of action is still a matter of debate. Materials and methods: The cell model used was Saos-2ATTC HTB-85, a human osteosarcoma cell line that retains an osteogenic potential matching that of osteoblastic cells. Photobiomodulation was performed with a 645 nm diode laser; we investigated three different fluence values (2, 5, and 10 J/cm²) delivered with 3 different irradiation times (1, 2, and 4 min). The design of the study included a case-control structure. Cell viability was assessed by resazurin reduction assay before laser irradiation. We assessed cell differentiation by Alizarin-red Sigma Aldrich assay 48 h after the last laser irradiation. Results: Results show that the combination of photobiomodulation and platelet-rich plasma can lead to a statistically significant increase in both proliferation and differentiation rates. Conclusions: Only a defined amount of energy, that is, a fluence of 5 J/cm² delivered in 2 min and of 10 J/cm² in 4 min, was proven to be the most effective in the presence of platelet-rich plasma to induce cell proliferation and calcium deposition.

Transforming Growth Factor Beta 1 Alters Glucose Uptake but Not Insulin Signalling in Human Primary Myotubes From Women With and Without Polycystic Ovary Syndrome

Women with polycystic ovary syndrome (PCOS), commonly have profound skeletal muscle insulin resistance which can worsen other clinical features. The heterogeneity of the condition has made it challenging to identify the precise mechanisms that cause this insulin resistance. A possible explanation for the underlying insulin resistance may be the dysregulation of Transforming Growth Factor-beta (TGFβ) signalling. TGFβ signalling contributes to the remodelling of reproductive and hepatic tissues in women with PCOS. Given the systemic nature of TGFβ signalling and its role in skeletal muscle homeostasis, it may be possible that these adverse effects extend to other peripheral tissues. We aimed to determine if TGFβ1 could negatively regulate glucose uptake and insulin signalling in skeletal muscle of women with PCOS. We show that both myotubes from women with PCOS and healthy women displayed an increase in glucose uptake, independent of changes in insulin signalling, following short term (16 hr) TGFβ1 treatment. This increase occurred despite pro-fibrotic signalling increasing via SMAD3 and connective tissue growth factor in both groups following treatment with TGFβ1. Collectively, our findings show that short-term treatment with TGFβ1 does not appear to influence insulin signalling or promote insulin resistance in myotubes. These findings suggest that aberrant TGFβ signalling is unlikely to directly contribute to skeletal muscle insulin resistance in women with PCOS in the short term but does not rule out indirect or longer-term effects.

Lysophosphatidic acid receptor 5 transactivation of TGFBR1 stimulates the mRNA expression of proteoglycan synthesizing genes XYLT1 and CHST3

Lysophosphatidic acid (LPA) via transactivation dependent signalling pathways contributes to a plethora of physiological and pathophysiological responses. In the vasculature, hyperelongation of glycosaminoglycan (GAG) chains on proteoglycans leads to lipid retention in the intima resulting in the early pathogenesis of atherosclerosis. Therefore, we investigated and defined the contribution of transactivation dependent signalling in LPA mediated GAG chain hyperelongation in human vascular smooth muscle cells (VSMCs). LPA acting via the LPA receptor 5 (LPAR5) transactivates the TGFBR1 to stimulate the mRNA expression of GAG initiation and elongation genes xylosyltransferase-1 (XYLT1) and chondroitin 6-sulfotransferase-1 (CHST3), respectively. We found that LPA stimulates ROS and Akt signalling in VSMCs, however they are not associated in LPAR5 transactivation of the TGFBR1. We observed that LPA via ROCK dependent pathways transactivates the TGFBR1 to stimulate genes associated with GAG chain elongation. We demonstrate that GPCR transactivation of the TGFBR1 occurs via a universal biochemical mechanism and the identified effectors represent potential therapeutic targets to inhibit pathophysiological effects of GPCR transactivation of the TGFBR1.

Chemical induced pathognomonic features observed in human vitiligo are mediated through miR-2909 RNomics pathway

BACKGROUND

Chemicals like Monobenzyl Ether of Hydroquinone (MBEH) and 4-Tertiary Butyl Phenol (4-TBP) have been widely recognized to induce clinical lesions that resemble vitiligo, but exact molecular pathway through which these chemicals initiate vitiligo is still far from clear.

OBJECTIVES

Since vitiligo is widely considered as an autoimmune disease, this study was an attempt to understand miR-2909 RNomics in vitiligo pathogenesis using MBEH treated primary melanocytes as an archetype cellular model because MBEH causes pathological features indistinguishable from clinical vitiligo.

METHODS

Primary melanocytes were treated with MBEH and 4-TBP and the role of miR-2909 RNomics at transcriptional and translational level was explored through qRT-PCR, western blot analysis, flow cytometry, immunocytochemistry, immunohistochemistry and in silico binding affinities. 4 mm punch biopsies were also obtained from lesional sites of vitiligo patients to validate the results observed in cell culture experiments.

RESULTS

MBEH induced miR-2909 RNomics led to downregulation of MITF, TYR, TYRP1, and TYRP2 leading to decreased melanin synthesis which in turn is a characteristic trait of vitiligo. On the other hand, 4-TBP increased TGF-β which also has the intrinsic capacity to downregulate MITF leading to decreased melanin synthesis and thereby initiation of vitiligo.

CONCLUSION

Based upon our results we propose a molecular pathway which has the inherent capacity to resolve the mechanism through which these chemicals may induce vitiligo. This mechanism was also found to be involved in the lesional biopsies of vitiligo patients. These results could be exploited in better understanding the pathogenesis as well as in treatment of vitiligo.

The Role of Aberrant Metabolism in Cancer: Insights Into the Interplay Between Cell Metabolic Reprogramming, Metabolic Syndrome, and Cancer

Metabolic syndrome (MetS) is characterized by hyperglycemia, hypertension, dyslipidemia and abdominal obesity. Patients with MetS or other metabolic disorders are more susceptible to cancer development and recurrence and have a worse long-term prognosis. Moreover, the metabolic reprogramming observed in cancer cells has also been described as one of the new hallmarks of cancer. Thus, aberrant metabolism has been proposed as an important risk factor for cancer. Chronic inflammation, reactive oxygen species (ROS), and oncogenic signaling pathways are considered as main potential triggers. Considering the strong association between metabolism and cancer, metabolism-modulating drugs, including metformin and statins, as well as adopting a healthy lifestyle, have been extensively investigated as strategies to combat cancer. Furthermore, strategies that interfere with the metabolic rewiring of cells may also have potent anti-cancer effects. In this article, we provide a comprehensive review of current knowledge on the relationship between aberrant metabolism and cancer and discuss the potential use of metabolism-targeting strategy for the treatment of cancer.

PI3K in stemness regulation: from development to cancer

The PI3K/AKT pathway is a key target in oncology where most efforts are focussed on phenotypes such as cell proliferation and survival. Comparatively, little attention has been paid to PI3K in stemness regulation, despite the emerging link between acquisition of stem cell-like features and therapeutic failure in cancer. The aim of this review is to summarise current known and unknowns of PI3K-dependent stemness regulation, by integrating knowledge from the fields of developmental, signalling and cancer biology. Particular attention is given to the role of the PI3K pathway in pluripotent stem cells (PSCs) and the emerging parallels to dedifferentiated cancer cells with stem cell-like features. Compelling evidence suggests that PI3K/AKT signalling forms part of a 'core molecular stemness programme' in both mouse and human PSCs. In cancer, the oncogenic PIK3CAH1047R variant causes constitutive activation of the PI3K pathway and has recently been linked to increased stemness in a dose-dependent manner, similar to observations in mouse PSCs with heterozygous versus homozygous Pten loss. There is also evidence that the stemness phenotype may become 'locked' and thus independent of the original PI3K activation, posing limitations for the success of PI3K monotherapy in cancer. Ongoing therapeutic developments for PI3K-associated cancers may therefore benefit from a better understanding of the pathway's two-layered and highly context-dependent regulation of cell growth versus stemness.

Insulin impedes osteogenesis of BMSCs by inhibiting autophagy and promoting premature senescence via the TGF-β1 pathway

The dysfunction of bone marrow stromal cells (BMSCs) may be a core factor in Type 2 diabetes mellitus (T2DM) associated osteoporosis. However, the underlying mechanism is not well understood. Here, we delineated the critical role of insulin impeding osteogenesis of BMSCs in T2DM. Compared with BMSCs from healthy people (H-BMSCs), BMSCs from T2DM patient (DM-BMSCs) showed decreased osteogenic differentiation and autophagy level, and increased senescent phenotype. H-BMSCs incubated in hyperglycemic and hyperinsulinemic conditions similarly showed these phenotypes of DM-BMSCs. Notably, enhanced TGF-β1 expression was detected not only in DM-BMSCs and high-glucose and insulin-treated H-BMSCs, but also in bone callus of streptozocin-induced diabetic rats. Moreover, inhibiting TGF-β1 signaling not only enhanced osteogenic differentiation and autophagy level of DM-BMSCs, but also delayed senescence of DM-BMSCs, as well as promoted mandible defect healing of diabetic rats. Finally, we further verified that it was TGF-β receptor II (TβRII), not TβRI, markedly increased in both DM-BMSCs and insulin-treated H-BMSCs. Our data revealed that insulin impeded osteogenesis of BMSCs by inhibiting autophagy and promoting premature senescence, which it should be responsible for T2DM-induced bone loss, at least in part. These findings suggest that inhibiting TGF-β1 pathway may be a potential therapeutic target for T2DM associated bone disorders.

TGF-β/Smad3 Signalling Modulates GABA Neurotransmission: Implications in Parkinson's Disease

γ-Aminobutiryc acid (GABA) is found extensively in different brain nuclei, including parts involved in Parkinson’s disease (PD), such as the basal ganglia and hippocampus. In PD and in different models of the disorder, an increase in GABA neurotransmission is observed and may promote bradykinesia or L-Dopa-induced side-effects. In addition, proteins involved in GABA_A receptor (GABA_AR) trafficking, such as GABARAP, Trak1 or PAELR, may participate in the aetiology of the disease. TGF-β/Smad3 signalling has been associated with several pathological features of PD, such as dopaminergic neurodegeneration; reduction of dopaminergic axons and dendrites; and α-synuclein aggregation. Moreover, TGF-β/Smad3 intracellular signalling was recently shown to modulate GABA neurotransmission in the context of parkinsonism and cognitive alterations. This review provides a summary of GABA neurotransmission and TGF-β signalling; their implications in PD; and the regulation of GABA neurotransmission by TGF-β/Smad3. There appear to be new possibilities to develop therapeutic approaches for the treatment of PD using GABA modulators.

Subendothelial stiffness alters endothelial cell traction force generation while exerting a minimal effect on the transcriptome

Endothelial cells respond to changes in subendothelial stiffness by altering their migration and mechanics, but whether those responses are due to transcriptional reprogramming remains largely unknown. We measured traction force generation and also performed gene expression profiling for two endothelial cell types grown in monolayers on soft or stiff matrices: primary human umbilical vein endothelial cells (HUVEC) and immortalized human microvascular endothelial cells (HMEC-1). Both cell types respond to changes in subendothelial stiffness by increasing the traction stresses they exert on stiffer as compared to softer matrices, and exhibit a range of altered protein phosphorylation or protein conformational changes previously implicated in mechanotransduction. However, the transcriptome has only a minimal role in this conserved biomechanical response. Only few genes were differentially expressed in each cell type in a stiffness-dependent manner, and none were shared between them. In contrast, thousands of genes were differentially regulated in HUVEC as compared to HMEC-1. HUVEC (but not HMEC-1) upregulate expression of TGF-β2 on stiffer matrices, and also respond to application of exogenous TGF-β2 by enhancing their endogenous TGF-β2 expression and their cell-matrix traction stresses. Altogether, these findings provide insights into the relationship between subendothelial stiffness, endothelial mechanics and variation of the endothelial cell transcriptome, and reveal that subendothelial stiffness, while critically altering endothelial cells’ mechanical behavior, minimally affects their transcriptome.

Integration of TGF-β-induced Smad signaling in the insulin-induced transcriptional response in endothelial cells

Insulin signaling governs many processes including glucose homeostasis and metabolism, and is therapeutically used to treat hyperglycemia in diabetes. We demonstrated that insulin-induced Akt activation enhances the sensitivity to TGF-β by directing an increase in cell surface TGF-β receptors from a pool of intracellular TGF-β receptors. Consequently, increased autocrine TGF-β signaling in response to insulin participates in insulin-induced angiogenic responses of endothelial cells. With TGF-β signaling controlling many cell responses, including differentiation and extracellular matrix deposition, and pathologically promoting fibrosis and cancer cell dissemination, we addressed to which extent autocrine TGF-β signaling participates in insulin-induced gene responses of human endothelial cells. Transcriptome analyses of the insulin response, in the absence or presence of a TGF-β receptor kinase inhibitor, revealed substantial positive and negative contributions of autocrine TGF-β signaling in insulin-responsive gene responses. Furthermore, insulin-induced responses of many genes depended on or resulted from autocrine TGF-β signaling. Our analyses also highlight extensive contributions of autocrine TGF-β signaling to basal gene expression in the absence of insulin, and identified many novel TGF-β-responsive genes. This data resource may aid in the appreciation of the roles of autocrine TGF-β signaling in normal physiological responses to insulin, and implications of therapeutic insulin usage.

Core-shell insulin-loaded nanofibrous scaffolds for repairing diabetic wounds

Patients with diabetes mellitus have up to a 15% lifetime risk of non-healing and poorly healing wounds. This work develops core-shell nanofibrous bioactive insulin-loaded poly-D-L-lactide-glycolide (PLGA) scaffolds that release insulin in a sustained manner for repairing wounds in diabetic rats. To prepare the biodegradable core-shell nanofibers, PLGA and insulin solutions were fed into two capillary tubes of different sizes that were coaxially electrospun using two independent pumps. The scaffolds sustainably released insulin for four weeks. The hydrophilicity and water-containing capacity of core-shell nanofibrous insulin/PLGA scaffolds significantly exceeded those of blended nanofibrous scaffolds. The nanofibrous core-shell insulin-loaded scaffold reduced the amount of type I collagen in vitro, increased the transforming growth factor-beta content in vivo, and promoted diabetic would repair. The core-shell insulin-loaded nanofibrous scaffolds prolong the release of insulin and promote diabetic wound healing.

The role of FSH and TGF-β superfamily in follicle atresia

Most of the mammalian follicles undergo a degenerative process called “follicle atresia”. Apoptosis of granulosa cells is the main characteristic of follicle atresia. Follicle stimulating hormone (FSH) and the transforming growth factor β (TGF-β) superfamily have important regulatory functions in this process. FSH activates protein kinase A and cooperating with insulin receptor substrates, it promotes the PI3K/Akt pathway which weakens apoptosis. Both Smad or non-Smad signaling of the transforming growth factor β superfamily seem to be related to follicle atresia, and the effect of several important family members on follicle atresia is concluded in this article. FSH and TGF-β are likely to mutually influence each other and what we have already known about the possible underlying molecular mechanism is also discussed below.

Insulin resistance mediates high-fat diet-induced pulmonary fibrosis and airway hyperresponsiveness through the TGF-β1 pathway

Prior studies have reported the presence of lung fibrosis and enhanced airway hyperresponsiveness (AHR) in mice with high-fat-diet (HFD)-induced obesity. This study evaluated the role of TGF-β1 in HFD-induced AHR and lung fibrosis in a murine model. We generated HFD-induced obesity mice and performed glucose and insulin tolerance tests. HFD mice with or without ovalbumin sensitization and challenge were also treated with an anti-TGF-β1 neutralizing antibody. AHR to methacholine, inflammatory cells in the bronchoalveolar lavage fluid (BALF), and histological features were evaluated. Insulin was intranasally administered to normal diet (ND) mice, and in vitro insulin stimulation of BEAS-2b cells was performed. HFD-induced obesity mice had increased insulin resistance, enhanced AHR, peribronchial and perivascular fibrosis, and increased numbers of macrophages in the BALF. However, they did not have meaningful eosinophilic or neutrophilic inflammation in the lungs compared with ND mice. The HFD enhanced TGF-β1 expression in the bronchial epithelium, but we found no differences in the expression of interleukin (IL)−4 or IL-5 in lung homogenates. Administration of the anti-TGF-β1 antibody attenuated HFD-induced AHR and lung fibrosis. It also attenuated goblet cell hyperplasia, but did not affect the AHR and inflammatory cell infiltration induced by OVA challenge. The intranasal administration of insulin enhanced TGF-β1 expression in the bronchial epithelium and lung fibrosis. Stimulating BEAS-2b cells with insulin also increased TGF-β1 production by 24 h. We concluded that HFD-induced obesity-associated insulin resistance enhances TGF-β1 expression in the bronchial epithelium, which may play an important role in the development of lung fibrosis and AHR in obesity.

Insulin resistance may be an important causative factor underlying the increased risk of asthma and other respiratory issues in obese individuals. Obesity doubles the likelihood of developing asthma, with symptoms that are more difficult to control than in non-obese patients. The connection between these conditions is poorly understood, but researchers led by Jung-Won Park, Yonsei University College of Medicine, Seoul, South Korea, have identified a potential mechanism. They demonstrated that a signaling molecule called TGF-β1 contributes to airway sensitivity and tissue scarring in a mouse model of diet-induced obesity. Subsequent experiments showed that treatment with insulin also gives rise to increased TGF-β1 production in the mouse lung. Since insulin resistance is a common feature of obesity, resulting in abnormally high levels of circulating insulin, this could also account for the increased risk of respiratory problems.

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.

Specificity, versatility, and control of TGF-β family signaling

Encoded in mammalian cells by 33 genes, the transforming growth factor-β (TGF-β) family of secreted, homodimeric and heterodimeric proteins controls the differentiation of most, if not all, cell lineages and many aspects of cell and tissue physiology in multicellular eukaryotes. Deregulation of TGF-β family signaling leads to developmental anomalies and disease, whereas enhanced TGF-β signaling contributes to cancer and fibrosis. Here, we review the fundamentals of the signaling mechanisms that are initiated upon TGF-β ligand binding to its cell surface receptors and the dependence of the signaling responses on input from and cooperation with other signaling pathways. We discuss how cells exquisitely control the functional presentation and activation of heteromeric receptor complexes of transmembrane, dual-specificity kinases and, thus, define their context-dependent responsiveness to ligands. We also introduce the mechanisms through which proteins called Smads act as intracellular effectors of ligand-induced gene expression responses and show that the specificity and impressive versatility of Smad signaling depend on cross-talk from other pathways. Last, we discuss how non-Smad signaling mechanisms, initiated by distinct ligand-activated receptor complexes, complement Smad signaling and thus contribute to cellular responses.

Enhanced TGF-β Signaling Contributes to the Insulin-Induced Angiogenic Responses of Endothelial Cells

Angiogenesis, the development of new blood vessels, is a key process in disease. We reported that insulin promotes translocation of transforming growth factor β (TGF-β) receptors to the plasma membrane of epithelial and fibroblast cells, thus enhancing TGF-β responsiveness. Since insulin promotes angiogenesis, we addressed whether increased autocrine TGF-β signaling participates in endothelial cell responses to insulin. We show that insulin enhances TGF-β responsiveness and autocrine TGF-β signaling in primary human endothelial cells, by inducing a rapid increase in cell surface TGF-β receptor levels. Autocrine TGF-β/Smad signaling contributed substantially to insulin-induced gene expression associated with angiogenesis, including TGF-β target genes encoding angiogenic mediators; was essential for endothelial cell migration; and participated in endothelial cell invasion and network formation. Blocking TGF-β signaling impaired insulin-induced microvessel outgrowth from neonatal aortic rings and modified insulin-stimulated blood vessel formation in zebrafish. We conclude that enhanced autocrine TGF-β signaling is integral to endothelial cell and angiogenic responses to insulin.

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Insulin promotes enhanced autocrine TGF-β responsiveness in endothelial cells

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Autocrine TGF-β signaling contributes to insulin-induced angiogenesis gene expression

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Insulin-induced endothelial migration and sprouting require autocrine TGF-β signaling

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Enhanced autocrine TGF-β signaling is integral to angiogenic responses to insulin

Cholesterol depletion enhances TGF-β Smad signaling by increasing c-Jun expression through a PKR-dependent mechanism

Transforming growth factor-β (TGF-β) plays critical roles in numerous physiological and pathological responses. Cholesterol, a major plasma membrane component, can have pronounced effects on signaling responses. Cells continually monitor cholesterol content and activate multilayered transcriptional and translational signaling programs, following perturbations to cholesterol homeostasis (e.g., statins, the commonly used cholesterol-reducing drugs). However, the cross-talk of such programs with ligand-induced signaling responses (e.g., TGF-β signaling) remained unknown. Here, we studied the effects of a mild reduction in free (membrane-associated) cholesterol on distinct components of TGF-β-signaling pathways. Our findings reveal a new regulatory mechanism that enhances TGF-β-signaling responses by acting downstream from receptor activation. Reduced cholesterol results in PKR-dependent eIF2α phosphorylation, which enhances c-Jun translation, leading in turn to higher levels of JNK-mediated c-Jun phosphorylation. Activated c-Jun enhances transcription and expression of Smad2/3. This leads to enhanced sensitivity to TGF-β stimulation, due to increased Smad2/3 expression and phosphorylation. The phospho/total Smad2/3 ratio remains unchanged, indicating that the effect is not due to altered receptor activity. We propose that cholesterol depletion induces overactivation of PKR, JNK, and TGF-β signaling, which together may contribute to the side effects of statins in diverse disease settings.

FOXO1 inhibits the invasion and metastasis of hepatocellular carcinoma by reversing ZEB2-induced epithelial-mesenchymal transition

The epithelial-to-mesenchymal transition (EMT) program is critical for epithelial cell cancer progression and fibrotic diseases. FOXO1 influences a broad range of physiological and pathological processes. However, the mechanism by which FOXO1 inhibits EMT is not fully understood. In this study, we demonstrated that FOXO1 overexpression inhibited cell motility and invasiveness in vitro and inhibited lung metastasis in vivo. In addition, we found that FOXO1 couldreverse the EMT program. FOXO1 silencing by siRNA in hepatocellular carcinoma (HCC) cell lines enhanced the expression of mesenchymal markers and decreased the expression of the epithelial markers. Consistent with these findings, FOXO1 overexpression exerted opposite effects. Furthermore, we found that FOXO1 levels were inversely correlated with the levels of EMT inducers, including Snail, Slug, ZEB1, ZEB2 and Twist1 in HCC cells. Co-immunoprecipitation and immunohistochemistry assays revealed that an interaction between FOXO1 and ZEB2. A dual-luciferase reporter assay and a ChIP assay further demonstrated that FOXO1 binds to the ZEB2 promoter. Together, these findings suggest that FOXO1 overexpression or ZEB2 inhibition might be potential therapeutic strategies for treating HCC.

The TGFβ superfamily in Lisbon: navigating through development and disease

The 10th FASEB meeting 'The TGFβ Superfamily: Signaling in Development and Disease' took place in Lisbon, Portugal, in July 2017. As we review here, the findings presented at the meeting highlighted the important contributions of TGFβ family signaling to normal development, adult homeostasis and disease, and also revealed novel mechanisms by which TGFβ signals are transduced.

Intracellular trafficking of transforming growth factor β receptors

Transforming growth factor β (TGFβ) family members signal via heterotetrameric complexes of type I (TβRI) and type II (TβRII) dual specificity kinase receptors. The availability of the receptors on the cell surface is controlled by several mechanisms. Newly synthesized TβRI and TβRII are delivered from the Golgi apparatus to the cell surface via separate routes. On the cell surface, TGFβ receptors are distributed between different microdomains of the plasma membrane and can be internalized via clathrin- and caveolae-mediated endocytic mechanisms. Although receptor endocytosis is not essential for TGFβ signaling, localization of the activated receptor complexes on the early endosomes promotes TGFβ-induced Smad activation. Caveolae-mediated endocytosis, which is widely regarded as a mechanism that facilitates the degradation of TGFβ receptors, has been shown to be required for TGFβ signaling via non-Smad pathways. The importance of proper control of TGFβ receptor intracellular trafficking is emphasized by clinical data, as mislocalization of receptors has been described in connection with several human diseases. Thus, control of intracellular trafficking of the TGFβ receptors together with the regulation of their expression, posttranslational modifications and down-regulation, ensure proper regulation of TGFβ signaling.

Mechanistic insight into contextual TGF-β signaling

Transforming growth factor-β (TGF-β) controls a wide range of cellular functions by activating both SMADs and non-SMAD pathways. In different tissue or physiological environment, cellular responses to TGF-β can be diverse, even opposite. Complex regulations at the level of ligand mobilization, receptor presentation, and the network of intracellular signal transducers afford the TGF-β pathway with versatile means to induce precise cellular responses in accordance to specific contextual demands. This article summarizes recent development in how cells manage their responses to TGF-β through ligand activation, receptor abundance, as well as SMAD-dependent and SMAD-independent mechanisms.

Insulin Receptor Isoforms in Physiology and Disease: An Updated View

The insulin receptor (IR) gene undergoes differential splicing that generates two IR isoforms, IR-A and IR-B. The physiological roles of IR isoforms are incompletely understood and appear to be determined by their different binding affinities for insulin-like growth factors (IGFs), particularly for IGF-2. Predominant roles of IR-A in prenatal growth and development and of IR-B in metabolic regulation are well established. However, emerging evidence indicates that the differential expression of IR isoforms may also help explain the diversification of insulin and IGF signaling and actions in various organs and tissues by involving not only different ligand-binding affinities but also different membrane partitioning and trafficking and possibly different abilities to interact with a variety of molecular partners. Of note, dysregulation of the IR-A/IR-B ratio is associated with insulin resistance, aging, and increased proliferative activity of normal and neoplastic tissues and appears to sustain detrimental effects. This review discusses novel information that has generated remarkable progress in our understanding of the physiology of IR isoforms and their role in disease. We also focus on novel IR ligands and modulators that should now be considered as an important strategy for better and safer treatment of diabetes and cancer and possibly other IR-related diseases.

Transforming Growth Factor-β Receptors and Smads: Regulatory Complexity and Functional Versatility

Transforming growth factor (TGF)-β family proteins control cell physiology, proliferation, and growth, and direct cell differentiation, thus playing key roles in normal development and disease. The mechanisms of how TGF-β family ligands interact with heteromeric complexes of cell surface receptors to then activate Smad signaling that directs changes in gene expression are often seen as established. Even though TGF-β-induced Smad signaling may be seen as a linear signaling pathway with predictable outcomes, this pathway provides cells with a versatile means to induce different cellular responses. Fundamental questions remain as to how, at the molecular level, TGF-β and TGF-β family proteins activate the receptor complexes and induce a context-dependent diversity of cell responses. Among the areas of progress, we summarize new insights into how cells control TGF-β responsiveness by controlling the TGF-β receptors, and into the key roles and versatility of Smads in directing cell differentiation and cell fate selection.

WITHDRAWN: Modulation of adipocyte function by the TGF-β family

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Signaling Receptors for TGF-β Family Members

Transforming growth factor β (TGF-β) family members signal via heterotetrameric complexes of type I and type II dual specificity kinase receptors. The activation and stability of the receptors are controlled by posttranslational modifications, such as phosphorylation, ubiquitylation, sumoylation, and neddylation, as well as by interaction with other proteins at the cell surface and in the cytoplasm. Activation of TGF-β receptors induces signaling via formation of Smad complexes that are translocated to the nucleus where they act as transcription factors, as well as via non-Smad pathways, including the Erk1/2, JNK and p38 MAP kinase pathways, and the Src tyrosine kinase, phosphatidylinositol 3'-kinase, and Rho GTPases.