The phosphorylation of the Smad2/3 linker region by nemo-like kinase regulates TGF-β signaling

Glial-Cell-Line-Derived Neurotrophic Factor Promotes Glioblastoma Cell Migration and Invasion via the SMAD2/3-SERPINE1-Signaling Axis

Glial-cell-line-derived neurotrophic factor (GDNF) is highly expressed and is involved in the malignant phenotype in glioblastomas (GBMs). However, uncovering its underlying mechanism for promoting GBM progression is still a challenging work. In this study, we found that serine protease inhibitor family E member 1 (SERPINE1) was a potential downstream gene of GDNF. Further experiments confirmed that SERPINE1 was highly expressed in GBM tissues and cells, and its levels of expression and secretion were enhanced by exogenous GDNF. SERPINE1 knockdown inhibited the migration and invasion of GBM cells promoted by GDNF. Mechanistically, GDNF increased SERPINE1 by promoting the phosphorylation of SMAD2/3. In vivo experiments demonstrated that GDNF facilitated GBM growth and the expressions of proteins related to migration and invasion via SERPINE1. Collectively, our findings revealed that GDNF upregulated SERPINE1 via the SMAD2/3-signaling pathway, thereby accelerating GBM cell migration and invasion. The present work presents a new mechanism of GDNF, supporting GBM development.

Receptor-activated transcription factors and beyond: multiple modes of Smad2/3-dependent transmission of TGF-β signaling

Transforming growth factor β (TGF-β) is a pleiotropic cytokine that is widely distributed throughout the body. Its receptor proteins, TGF-β type I and type II receptors, are also ubiquitously expressed. Therefore, the regulation of various signaling outputs in a context-dependent manner is a critical issue in this field. Smad proteins were originally identified as signal-activated transcription factors similar to signal transducer and activator of transcription proteins. Smads are activated by serine phosphorylation mediated by intrinsic receptor dual specificity kinases of the TGF-β family, indicating that Smads are receptor-restricted effector molecules downstream of ligands of the TGF-β family. Smad proteins have other functions in addition to transcriptional regulation, including post-transcriptional regulation of micro-RNA processing, pre-mRNA splicing, and m6A methylation. Recent technical advances have identified a novel landscape of Smad-dependent signal transduction, including regulation of mitochondrial function without involving regulation of gene expression. Therefore, Smad proteins are receptor-activated transcription factors and also act as intracellular signaling modulators with multiple modes of function. In this review, we discuss the role of Smad proteins as receptor-activated transcription factors and beyond. We also describe the functional differences between Smad2 and Smad3, two receptor-activated Smad proteins downstream of TGF-β, activin, myostatin, growth and differentiation factor (GDF) 11, and Nodal.

Protein phosphatase 6 promotes transforming growth factor-β signaling in mouse embryonic fibroblasts

Transforming growth factor-beta (TGF-β) is a multifunctional cytokine that controls various cellular processes. Protein phosphatase 6 (PP6) is an evolutionarily conserved serine/threonine protein phosphatase with diverse functions in cell signaling. However, it has not been linked to TGF-β signaling. We found that TGF-β treatment increased PP6 protein levels via transcriptional and post-translational regulation. Loss of the Ppp6c gene suppressed TGF-β-induced canonical Smad3 phosphorylation and its transcriptional activity. PP6 knockout also inhibited non-canonical p38 mitogen-activated protein kinase (MAPK) pathway. Moreover, PP6 depletion suppressed cell migration induced by TGF-β. These findings uncovered the role of PP6 as a positive regulator for TGF-β signaling.

A novel pathogenic variant located just upstream of the C-terminal Ser423-X-Ser425 phosphorylation motif in SMAD3 causing Loeys-Dietz syndrome

OBJECTIVE

Loeys-Dietz syndrome (LDS) is a heritable disorder of connective tissue closely related to Marfan syndrome (MFS). LDS is caused by loss-of-function variants of genes that encode components of transforming growth factor-β (TGF-β) signaling; nevertheless, LDS type 1/2 caused by TGFBR1/2 pathogenic variants is frequently found to have paradoxical increases in TGF-β signaling in the aneurysmal aortic wall. Here, we present a Japanese LDS family having a novel SMAD3 variant.

METHODS

The proband was tested via clinical, genetic, and histological analyses. In vitro analysis was performed for pathogenic evaluation.

RESULTS

The novel heterozygous missense variant of SMAD3 [c.1262G>A, p.(Cys421Tyr)], located just upstream of the C-terminal Ser423-X-Ser425 phosphorylation motif, was found in this instance of LDS type 3. This variant led to reduced phospho-SMAD3 (Ser423/Ser425) levels and transcription activity in vitro; however, a paradoxical upregulation of TGF-β signaling was evident in the aortic wall.

CONCLUSIONS

Our results revealed the presence of TGF-β paradox in this case with the novel loss-of-function SMAD3 variant. The precise mechanism underlying the paradox is unknown, but further research is warranted to clarify the influence of the SMAD3 variant type and location on the LDS3 phenotype as well as the molecular mechanism leading to LDS3 aortopathy.

MircroRNA-92b as a negative regulator of the TGF-β signaling by targeting the type I receptor

Transforming growth factor β1 (TGFβ1) has been identified as a major pathogenic factor underlying the development of chronic kidney disease (CKD). This study investigated the role of miR-92b-3p in the progression of renal fibrosis in unilateral ureteral occlusion (UUO) and unilateral ischemia-reperfusion injury (uIRI) mouse models, as well as explored its underlying mechanisms in human proximal tubular epithelial (HK2) cells. We found that renal fibrosis increased in UUO mice after miR-92b knockout, while it reduced in miR-92b overexpressing mice. MiR-92b knockout aggravated renal fibrosis in uIRI mice. RNA-sequencing analysis, the luciferase reporter assay, qPCR analysis, and western blotting confirmed that miR-92b-3p directly targeted TGF-β receptor 1, thereby ameliorating renal fibrosis by suppressing the TGF-β signaling pathway. Furthermore, we found that TGF-β suppressed miR-92b transcription through Snail family transcriptional repressors 1 and 2. Our results suggest that miR-92b-3p may serve as a novel therapeutic for mitigating fibrosis in CKD.

Exosomal miR-21-5p derived from multiple myeloma cells promote renal epithelial-mesenchymal transition through targeting TGF-β/SMAD7 signalling pathway

The prognosis of multiple myeloma (MM) patients combined with renal insufficiency is poor. Renal fibrosis is an important pathological cause for MM patients combined with renal insufficiency. It is reported that epithelial-mesenchymal transition (EMT) of renal proximal tubular epithelial cells is an important mechanism in renal fibrosis. We speculated that EMT might play an important role in the renal insufficiency of MM with unclear mechanism. MM cells derived exosomes could affect the function of targeted cells by delivering microRNAs (miRNAs). Literature has shown that the expression of miR-21 is closely related to EMT. In this research, we found that co-culture of HK-2 cells (human renal proximal tubular epithelial cells) and exosomes derived from MM cells promoted the EMT of HK-2 cells, resulting in the down-regulation of epithelial-related marker (E-cadherin), and up-regulation of stroma-related marker (Vimentin). Meanwhile, the expression of SMAD7, one of the downstream targets in the TGF-β signalling pathway, was suppressed and the expression of TGF-β was increased. After transfecting the inhibitor of miR-21 in MM cells, the expression of miR-21 in exosomes secreted by MM cells was significantly decreased, and the co-culture of these treated exosomes and HK-2 cells inhibited the EMT of HK-2 cells. In conclusion, these findings showed that exosomal miR-21 derived from MM cells could promote renal EMT through targeting TGF-β/SMAD7 signalling pathway.

Decreased DANCR contributes to high glucose-induced extracellular matrix accumulation in human renal mesangial cell via regulating the TGF-β/Smad signaling

Glomerulosclerosis is one of the major histopathologic changes in diabetic kidney diseases (DKD), which is characterized by excessive deposition of extracellular matrix (ECM) in the glomerulus mainly produced by mesangial cells in response to transforming growth factor-β (TGF-β) stimuli under diabetic conditions. Despite TGF-β has been implicated as a major pathogenic factor in the development of diabetic glomerulosclerosis, clinical trials of monoclonal antibodies against TGF-β failed to demonstrate therapeutic benefits. Thus, developing alternative therapeutic strategies to effectively block the TGF-β/Smad signaling could be of paramount importance for DKD treatment. Emerging evidence indicates that dysregulation of certain lncRNAs can lead to aberrant activation of TGF-β/Smad signaling. Herein, we identified a novel lncRNA, named DANCR, which could efficiently function as a negative regulator of TGF-β/Smad signaling in mesangial cells. Ectopic expression of DANCR could specifically block the activation of TGF-β/Smad signaling induced by high-glucose or TGF-β in human renal mesangial cells (HRMCs). Mechanistically, DANCR functions to stabilize nemo-like kinase (NLK) mRNA through interaction with insulin-like growth factor 2 mRNA-binding protein 2 (IGF2BP2), resulting in enhanced phosphorylating on the linker region of activated Smad2/3 in the nucleus. Taken together, our data have uncovered an lncRNA-based regulatory modality of the TGF-β/Smad signaling and identified DANCR as an endogenous blocker of TGF-β/Smad signaling in HRMCs, which may represent a potential therapeutic target against the diabetic glomerulosclerosis.

Prospective use of amniotic mesenchymal stem cell metabolite products for tissue regeneration

Chronic disease can cause tissue and organ damage constituting the largest obstacle to therapy which, in turn, reduces patients' quality-adjusted life-year. Degenerative diseases such as osteoporosis, Alzheimer's disease, Parkinson's disease, and infectious conditions such as hepatitis, cause physical injury to organs. Moreover, damage resulting from chronic conditions such as diabetes can also culminate in the loss of organ function. In these cases, organ transplantation constitutes the therapy of choice, despite the associated problems of immunological rejection, potential disease transmission, and high morbidity rates. Tissue regeneration has the potential to heal or replace tissues and organs damaged by age, disease, or trauma, as well as to treat disabilities. Stem cell use represents an unprecedented strategy for these therapies. However, product availability and mass production remain challenges. A novel therapeutic alternative involving amniotic mesenchymal stem cell metabolite products (AMSC-MP) has been developed using metabolites from stem cells which contain cytokines and growth factors. Its potential role in regenerative therapy has recently been explored, enabling broad pharmacological applications including various gastrointestinal, lung, bladder and renal conditions, as well as the treatment of bone wounds, regeneration and skin aging due to its low immunogenicity and anti-inflammatory effects. The various kinds of growth factors present in AMSC-MP, namely bFGF, VEGF, TGF-β, EGF and KGF, have their respective functions and activities. Each growth factor is formed by different proteins resulting in molecules with various physicochemical properties and levels of stability. This knowledge will assist in the manufacture and application of AMSC-MP as a therapeutic agent.