Bone morphogenetic protein/SMAD signaling orients cell fate decision by impairing KSRP-dependent microRNA maturation

Down-regulation of hsa-circ-0107593 promotes osteogenic differentiation of hADSCs via miR-20a-5p/SMAD6 signaling

OBJECTIVES

Increasing evidence indicated circRNAs were involved in stem cells osteogenesis differentiation. Herein, we aimed to clarify the role of hsa-circ-0107593 during the osteogenesis process of human adipose-derived stem cells (hADSCs) and the underlying mechanisms.

METHODS

The ring structure of hsa-circ-0107593 was confirmed using RNase R treatment and Sanger sequencing. Nucleoplasmic separation and fluorescence in situ hybridization detected hsa-circ-0107593 distribution. Lentivirus and siRNA were used to modulate the expression of hsa-circ-0107593, and the binding relationship between hsa-circ-0107593 and miR-20a-5p was verified by luciferase assay and RNA immunoprecipitation. We detected the osteogenic activity of hADSCs through alkaline phosphatase staining, alizarin red S staining, real-time polymerase chain reaction (RT-PCR), western blot, and cellular immunofluorescence experiment. In vivo, micro-computed tomography was performed to analyze bone formation around skull defect.

RESULTS

RT-PCR results exhibited that hsa-circ-0107593 was downregulated while miR-20a-5p was upregulated during hADSCs osteogenesis. In vivo and in vitro experiments results indicated that knocking down hsa-circ-0107593 promoted the osteogenic differentiation of hADSCs, while overexpression of hsa-circ-0107593 showed an inhibitory effect on hADSCs osteogenic differentiation. In vitro experiment results showed hsa-circ-0107593 acted as a hADSCs osteogenic differentiation negative factor for it inhibited the suppressing effect of miR-20a-5p on SMAD6.

CONCLUSION

Knocking down hsa-circ-0107593 acts as a positive factor of the osteogenic differentiation of hADSCs via miR-20a-5p/SMAD6 signaling.

Serum-Circulating microRNAs in Sporadic Inclusion Body Myositis

BACKGROUND

Sporadic inclusion body myositis (s-IBM) represents a unique disease within idiopathic inflammatory myopathies with a dual myodegenerative-autoimmune physiopathology and a lack of an efficacious treatment. Circulating miRNA expression could expand our knowledge of s-IBM patho-mechanisms and provide new potential disease biomarkers. To evaluate the expression of selected pre-amplified miRNAs in the serum of s-IBM patients compared to those of a sex- and age-matched healthy control group, we enrolled 14 consecutive s-IBM patients and 8 sex- and age-matched healthy controls. By using two different normalization approaches, we found one downregulated and three upregulated miRNAs. hsa-miR-192-5p was significantly downregulated, while hsa-miR-372-3p was found to be upregulated more in the s-IBM patients compared to the level of the controls. The other two miRNAs had a very low expression levels (raw Ct data > 29). hsa-miR-192-5p and hsa-miR-372-3p were found to be significantly dysregulated in the serum of s-IBM patients. These miRNAs are involved in differentiation and regeneration processes, thus possibly reflecting pathological mechanisms in s-IBM muscles and potentially representing disease biomarkers.

Modulation of osteogenic differentiation by Escherichia coli-derived recombinant bone morphogenetic protein-2

Recombinant human bone morphogenetic protein-2 (rhBMP-2), a key regulator of osteogenesis, induces the differentiation of mesenchymal cells into cartilage or bone tissues. Early orthopedic and dental studies often used mammalian cell-derived rhBMP-2, especially Chinese hamster ovary (CHO) cells. However, CHO cell-derived rhBMP-2 (C-rhBMP-2) presents disadvantages such as high cost and low production yield. To overcome these problems, Escherichia coli-derived BMP-2 (E-rhBMP-2) was developed; however, the E-rhBMP-2-induced signaling pathways and gene expression profiles during osteogenesis remain unclear. Here, we investigated the E-rhBMP-2-induced osteogenic differentiation pattern in C2C12 cells and elucidated the difference in biological characteristics between E-rhBMP-2 and C-rhBMP-2 via surface plasmon resonance, western blotting, qRT-PCR, RNA-seq, and alkaline phosphatase assays. The binding affinities of E-rhBMP-2 and C-rhBMP-2 towards BMP receptors were similar, both being confirmed at the nanomolecular level. However, the phosphorylation of Smad1/5/9 at 3 h after treatment with E-rhBMP-2 was significantly lower than that on treatment with C-rhBMP-2. The expression profiles of osteogenic marker genes were similar in both the E-rhBMP-2 and C-rhBMP-2 groups, but the gene expression level in the E-rhBMP-2 group was lower than that in the C-rhBMP-2 group at each time point. Taken together, our results suggest that the osteogenic signaling pathways induced by E-rhBMP-2 and C-rhBMP-2 both follow the general Smad-signaling pathway, but the difference in intracellular phosphorylation intensity results in distinguishable transcription profiles on osteogenic marker genes and biological activities of each rhBMP-2. These findings provide an extensive understanding of the biological properties of E-rhBMP-2 and the signaling pathways during osteogenic differentiation.

Investigation of Genetic Polymorphisms in BMP2, BMP4, SMAD6, and RUNX2 and Persistent Apical Periodontitis

INTRODUCTION

This study aimed to evaluate the interplay among single-nucleotide polymorphisms (SNPs) in the encoding genes BMP2, BMP4, SMAD6, and RUNX2 in persistent apical periodontitis (PAP).

METHODS

In this multicentric study, 272 patients diagnosed with pulp necrosis with apical periodontitis before root canal therapy who attended regular follow-up visits for at least 1 year were screened. Periapical radiographs and clinical aspects were evaluated, and the participants were classified as PAP (n = 110) or repaired (n = 162). Genomic DNA was used for the genotyping of the following SNPs: rs1005464 and rs235768 in bone morphogenetic protein 2 (BMP2), rs17563 in bone morphogenetic protein 4 (BMP4), rs2119261 and rs3934908 in SMAD family member 6 (SMAD6), and rs59983488 and rs1200425 in runt-related transcription factor 2 (RUNX2). The chi-square test was used to compare genotype distributions between groups. The multifactor dimensionality reduction method was applied to identify SNP-SNP interactions. The alpha for all the analysis was 5%.

RESULTS

The multifactor dimensionality reduction suggested the rs235768 in BMP2 and rs59983488 in RUNX2 as the best SNP-SNP interaction model (cross-validation = 10/10, testing balanced accuracy = 0.584, P = .026) followed by rs17563 in BMP4 and rs2119261 in SMAD6 (cross validation = 10/10, testing balanced accuracy = 0.580, P = .031). In the rs235768 in BMP2 and rs59983488 in RUNX2 model, the high-risk genotype was TT + TT (odds ratio = 4.36; 95% confidence interval, 0.44-42.1). In model rs17563 in BMP4 and rs2119261 in SMAD6, GG + TT (odds ratio = 2.63; 95% confidence interval, 0.71-11.9) was the high-risk genotype.

CONCLUSIONS

The interactions between rs235768 in BMP2 and rs59983488 in RUNX2 and between rs17563 in BMP4 and rs2119261 in SMAD6 are associated with PAP, suggesting that an interplay of these SNPs is involved in the higher risk of developing PAP.

KSRP suppresses cell invasion and metastasis through miR-23a-mediated EGR3 mRNA degradation in non-small cell lung cancer

KH-type splicing regulatory protein (KSRP) is a single-strand RNA binding protein which regulates mRNA stability either by binding to AU-rich elements (AREs) of mRNA 3'UTR or by facilitating miRNA biogenesis to target mRNA. Unlike its well-characterized function at the molecular level in maintaining RNA homeostasis, the role of KSRP in cancer progression remains largely unknown. Here we investigate the role of KSRP in non-small cell lung cancer (NSCLC). We first examined KSRP expression by immunohistochemistry in a cohort containing 196 NSCLC patients and observed a strong positive correlation between KSRP expression and survival of NSCLC patients. Multivariate analysis further identified KSRP as an independent prognostic factor. Manipulating KSRP expression significantly affected in vitro cell mobility and in vivo metastatic ability of NSCLC cells. Microarray analysis identified an ARE-containing gene, EGR3, as a downstream effector of KSRP in NSCLC. Interestingly, we found that KSRP decreased EGR3 mRNA stability in an ARE-independent manner. By screening KSRP-regulated miRNAs in NSCLC cells, we further found that miR-23a directly binds to EGR3 3'UTR, reducing EGR3 expression and thereby inhibiting NSCLC cell mobility. Our findings implicate a targetable KSRP/miR-23a/EGR3 signaling axis in advanced tumor phenotypes.

LncRNA MALAT1 sponges miR-204 to promote osteoblast differentiation of human aortic valve interstitial cells through up-regulating Smad4

BACKGROUND

Emerging evidences have indicated that long non-coding RNAs (lncRNAs) play vital roles in cardiovascular physiology and pathology. The lncRNA MALAT1, a highly abundant and conserved imprinted gene, has been implicated in many cardiovascular diseases. However, the function of MALAT1 in calcific aortic valve disease (CAVD) remains unknown. This study sought to document the function and underlying mechanism of MALAT1 in regulating CAVD.

METHODS

Protein level was determined by immunoblotting and immunofluorescence staining. MALAT1, miR-204 and mRNA expressions were detected by qRT-PCR. Mineralized bone matrix formation was assessed by Alizarin Red staining. The interaction between MALAT1 and miR-204 was studied using luciferase reporter assay, RNA pull-down assay and RNA-binding protein immunoprecipitation assay.

RESULTS

Ectopic expression of MALAT1 was observed in calcific valves and after osteogenic induction in human aortic valve interstitial cells (VICs). In vitro experiments revealed that MALAT1 acted as a positive regulator of osteogenic differentiation by repressing miR-204 expression and activity and thereby promoting expression of osteoblast-specific markers, including alkaline phosphatase, mineralized bone matrix formation and osteocalcin. Mechanistically, we identified Smad4 as a direct target of miR-204. Importantly, MALAT1 could directly interact with miR-204 and overexpression of miR-204 efficiently reversed the upregulation of Smad4 induced by MALAT1. Thus, MALAT1 positively regulated the expression of Smad4 through sponging miR-204, and promoted osteogenic differentiation of VICs.

CONCLUSIONS

Our study provides novel mechanistic insights into a critical role for lncRNA MALAT1 as a miRNA sponge in CAVD and sheds new light on lncRNA-directed diagnostics and therapeutics in CAVD.

K-homology splicing regulatory protein (KSRP) promotes post-transcriptional destabilization of Spry4 transcripts in non-small cell lung cancer

AU-rich element-binding proteins (ARE-BPs) offer post-transcriptional regulation of gene expression via physical interaction and recruitment of RNA decay machinery to the AU-rich elements within the 3′-UTR of the target transcripts. However, the role of ARE-BPs in lung cancer remains poorly understood. In this study, we have identified that K-homology splicing regulatory protein (KSRP), an ARE-BP, is robustly up-regulated in human lung cancer. Importantly, Kaplan-Meier survival analysis indicated that elevated KSRP expression was correlated with poor overall survival of lung cancer patients. Furthermore, cigarette smoke, a leading risk factor for lung cancer, was also identified to be an important contributor to increased KSRP expression. Remarkably, silencing of KSRP decreased cell proliferation, reversed anchorage-independent growth, and reduced migration/invasion, suggesting an oncogenic role for KSRP in lung cancer. Finally, we provide mechanistic evidence that KSRP promotes the down-regulation of Spry4 by a previously unidentified mechanism, i.e. post-transcriptional mRNA regulation.

Resveratrol limits epithelial to mesenchymal transition through modulation of KHSRP/hnRNPA1-dependent alternative splicing in mammary gland cells

Resveratrol (RESV) is a natural polyphenolic compound endowed with anti-inflammatory, anti-proliferative, as well as pro-apoptotic activities that make it a potential anti-tumor compound. Here we show that RESV counteracts the TGF-β-induced Epithelial to Mesenchymal Transition (EMT) phenotype in mammary gland cells and affects the alternative exon usage of pre-mRNAs that encode crucial factors in adhesion and migration -including CD44, ENAH, and FGFR2- in a panel of immortalized and transformed mammary gland cells. RESV causes a shift from the mesenchymal-specific forms of these factors to the respective epithelial forms and increases the expression of the RNA-binding proteins KHSRP and hnRNPA1. From a mechanistic point of view, we show that the combined silencing of KHSRP and hnRNPA1 prevents the RESV-dependent inclusion of the epithelial-type exons in the Cd44 pre-mRNA. Our findings support an unexpected regulatory mechanism where RESV limits EMT by controlling gene expression at post-transcriptional level.

Overexpression of KH-type splicing regulatory protein regulates proliferation, migration, and implantation ability of osteosarcoma

Osteosarcoma is a common malignant bone tumor in children and adolescents. The current 5-year survival rate is ~60% and that seems to be reaching a plateau. In order to improve treatment outcomes of osteosarcoma, a better understanding of tumorigenesis and underlying molecular mechanisms is required for searching out possible new treatment targets. This study aimed to identify the potential proteins involving the pathogenesis of osteosarcoma using a proteomics approach. Proteins extracted from primary cell culture of osteosarcoma (n=7) and osteoblasts of cancellous bone (n=7) were studied. Using 2-DE based proteomics and LC-MS/MS analysis, we successfully determined seven differentially expressed protein spots. Four upregulated proteins and three downregulated proteins were observed in this study in which KH-type splicing regulatory protein (KSRP) was selected for further exploration. KSRP was significantly upregulated in osteosarcoma cells compared to osteoblasts using western blot assay. In addition, immunohistochemistry demonstrated that KSRP was also highly expressed in osteosarcoma tissue of independent cases from the experimental group. More importantly, KSRP silencing of osteosarcoma cell lines significantly decreased cell proliferation, migration ability, as well as implantation and growth ability in chick chorioallantoic membrane assay. Taken together, these findings demonstrate, that KSRP plays important roles in regulatory controls of osteosarcoma pathogenesis and serves as a potentially therapeutic target of osteosarcoma.

Diverse roles of the nucleic acid-binding protein KHSRP in cell differentiation and disease

The single-stranded nucleic acid-binding protein KHSRP (KH-type splicing regulatory protein) modulates RNA life and gene expression at various levels. KHSRP controls important cellular functions as different as proliferation, differentiation, metabolism, and response to infectious agents. We summarize and discuss experimental evidence providing a potential link between changes in KHSRP expression/function and human diseases including neuromuscular disorders, obesity, type II diabetes, and cancer.

Akbu-LAAO exhibits potent anti-tumor activity to HepG2 cells partially through produced H2O2 via TGF-β signal pathway

Previously, we characterized the biological properties of Akbu-LAAO, a novel L-amino acid oxidase from Agkistrodon blomhoffii ussurensis snake venom (SV). Current work investigated its in vitro anti-tumor activity and underlying mechanism on HepG2 cells. Akbu-LAAO inhibited HepG2 growth time and dose-dependently with an IC50 of ~38.82 μg/mL. It could induce the apoptosis of HepG2 cells. Akbu-LAAO exhibited cytotoxicity by inhibiting growth and inducing apoptosis of HepG2 as it showed no effect on its cell cycle. The inhibition of Akbu-LAAO to HepG2 growth partially relied on enzymatic-released H2O2 as catalase only partially antagonized this effect. cDNA microarray results indicated TGF-β signaling pathway was linked to the cytotoxicity of Akbu-LAAO on HepG2. TGF-β pathway related molecules CYR61, p53, GDF15, TOB1, BTG2, BMP2, BMP6, SMAD9, JUN, JUNB, LOX, CCND1, CDK6, GADD45A, CDKN1A were deregulated in HepG2 following Akbu-LAAO stimulation. The presence of catalase only slightly restored the mRNA changes induced by Akbu-LAAO for differentially expressed genes. Meanwhile, LDN-193189, a TGF-β pathway inhibitor reduced Akbu-LAAO cytotoxicity on HepG2. Collectively, we reported, for the first time, SV-LAAO showed anti-tumor cell activity via TGF-β pathway. It provides new insight of SV-LAAO exhibiting anti-tumor effect via a novel signaling pathway.

KSRP is critical in governing hepatic lipid metabolism through controlling Per2 expression

Hepatic lipid metabolism is controlled by integrated metabolic pathways. Excess accumulation of hepatic TG is a hallmark of nonalcoholic fatty liver disease, which is associated with obesity and insulin resistance. Here, we show that KH-type splicing regulatory protein (KSRP) ablation reduces hepatic TG levels and diet-induced hepatosteatosis. Expression of period 2 (Per2) is increased during the dark period, and circadian oscillations of several core clock genes are altered with a delayed phase in Ksrp(-/-) livers. Diurnal expression of some lipid metabolism genes is also disturbed with reduced expression of genes involved in de novo lipogenesis. Using primary hepatocytes, we demonstrate that KSRP promotes decay of Per2 mRNA through an RNA-protein interaction and show that increased Per2 expression is responsible for the phase delay in cycling of several clock genes in the absence of KSRP. Similar to Ksrp(-/-) livers, both expression of lipogenic genes and intracellular TG levels are also reduced in Ksrp(-/-) hepatocytes due to increased Per2 expression. Using heterologous mRNA reporters, we show that the AU-rich element-containing 3' untranslated region of Per2 is responsible for KSRP-dependent mRNA decay. These findings implicate that KSRP is an important regulator of circadian expression of lipid metabolism genes in the liver likely through controlling Per2 mRNA stability.

H19 long noncoding RNA controls the mRNA decay promoting function of KSRP

Long noncoding RNAs (lncRNAs) interact with protein factors to regulate different layers of gene expression transcriptionally or posttranscriptionally. Here we report on the functional consequences of the unanticipated interaction of the RNA binding protein K homology-type splicing regulatory protein (KSRP) with the H19 lncRNA (H19). KSRP directly binds to H19 in the cytoplasm of undifferentiated multipotent mesenchymal C2C12 cells, and this interaction favors KSRP-mediated destabilization of labile transcripts such as myogenin. AKT activation induces KSRP dismissal from H19 and, as a consequence, myogenin mRNA is stabilized while KSRP is repurposed to promote maturation of myogenic microRNAs, thus favoring myogenic differentiation. Our data indicate that H19 operates as a molecular scaffold that facilitates effective association of KSRP with myogenin and other labile transcripts, and we propose that H19 works with KSRP to optimize an AKT-regulated posttranscriptional switch that controls myogenic differentiation.

KSRP ablation enhances brown fat gene program in white adipose tissue through reduced miR-150 expression

Brown adipose tissue oxidizes chemical energy for heat generation and energy expenditure. Promoting brown-like transformation in white adipose tissue (WAT) is a promising strategy for combating obesity. Here, we find that targeted deletion of KH-type splicing regulatory protein (KSRP), an RNA-binding protein that regulates gene expression at multiple levels, causes a reduction in body adiposity. The expression of brown fat-selective genes is increased in subcutaneous/inguinal WAT (iWAT) of Ksrp(-/-) mice because of the elevated expression of PR domain containing 16 and peroxisome proliferator-activated receptor gamma coactivator 1α, which are key regulators promoting the brown fat gene program. The expression of microRNA (miR)-150 in iWAT is decreased due to impaired primary miR-150 processing in the absence of KSRP. We show that miR-150 directly targets and represses Prdm16 and Ppargc1a, and that forced expression of miR-150 attenuates the elevated expression of brown fat genes caused by KSRP deletion. This study reveals the in vivo function of KSRP in controlling brown-like transformation of iWAT through post-transcriptional regulation of miR-150 expression.

MicroRNAs and post-transcriptional regulation of skeletal development

MicroRNAs (miRNAs) have become integral nodes of post-transcriptional control of genes that confer cellular identity and regulate differentiation. Cell-specific signaling and transcriptional regulation in skeletal biology are extremely dynamic processes that are highly reliant on dose-dependent responses. As such, skeletal cell-determining genes are ideal targets for quantitative regulation by miRNAs. So far, large amounts of evidence have revealed a characteristic temporal miRNA signature in skeletal cell differentiation and confirmed the essential roles that numerous miRNAs play in bone development and homeostasis. In addition, microarray expression data have provided evidence for their role in several skeletal pathologies. Mouse models in which their expression is altered have provided evidence of causal links between miRNAs and bone abnormalities. Thus, a detailed understanding of the function of miRNAs and their tight relationship with bone diseases would constitute a powerful tool for early diagnosis and future therapeutic approaches.

KSRP and MicroRNA 145 are negative regulators of lipolysis in white adipose tissue

White adipose tissue (WAT) releases fatty acids from stored triacylglycerol for an energy source. Here, we report that targeted deletion of KH-type splicing regulatory protein (KSRP), an RNA-binding protein that regulates gene expression at multiple levels, enhances lipolysis in epididymal WAT (eWAT) because of the upregulation of genes promoting lipolytic activity. Expression of microRNA 145 (miR-145) is decreased because of impaired primary miR-145 processing in Ksrp(-/-) eWAT. We show that miR-145 directly targets and represses Foxo1 and Cgi58, activators of lipolytic activity, and forced expression of miR-145 attenuates lipolysis. This study reveals a novel in vivo function of KSRP in controlling adipose lipolysis through posttranscriptional regulation of miR-145 expression.

KSRP controls pleiotropic cellular functions

The single-strand-RNA binding protein KSRP is able to negatively regulate gene expression operating with at least two distinct and integrated postranscriptional mechanisms: (i) by promoting decay of unstable mRNAs and (ii) by favoring maturation from precursors of select microRNAs (miRNAs) including the prototypical tumor suppressor let-7. Studies performed in primary and cultured cells as well as in mice proved that the ability of KSRP to integrate different levels of gene expression is required for proper immune response, lipid metabolism, cell-fate decisions, tissue regeneration, and DNA damage response.

mRNA fate: Life and death of the mRNA in the cytoplasm

The life of an mRNA molecule begins with transcription and ultimately ends in degradation. In the course of its life, however, mRNA is examined, modified in various ways and transported before eventually being translated into proteins. All these processes are performed by proteins and non-coding RNAs whose complex interplay in the cell contributes to determining the proteome changes and the phenotype of cells. On May 23‒26, 2012, over 150 scientists from around the world convened in the sunny shores of Riva del Garda, Italy, for the workshop entitled: "mRNA fate: Life and Death of mRNA in the Cytoplasm." Sessions included mRNA trafficking, mRNA translational control, RNA metabolism and disease, RNA-protein structures and systems biology of RNA. This report highlights some of the prominent and recurring themes at the meeting and emerging arenas of future research.

KSRP silencing favors neural differentiation of P19 teratocarcinoma cells

Understanding the molecular mechanisms that control the balance between multipotency and differentiation is of great importance to elucidate the genesis of both developmental disorders and cell transformation events. To investigate the role of the RNA binding protein KSRP in controlling neural differentiation, we used the P19 embryonal carcinoma cell line that is able to differentiate into neuron-like cells under appropriate culture conditions. We have recently reported that KSRP controls the differentiative fate of multipotent mesenchymal cells owing to its ability to promote decay of unstable transcripts and to favor maturation of selected micro-RNAs (miRNAs) from precursors. Here we report that KSRP silencing in P19 cells favors neural differentiation increasing the expression of neuronal markers. Further, the expression of two master transcriptional regulators of neurogenesis, ASCL1 and JMJD3, was enhanced while the maturation of miR-200 family members from precursors was impaired in KSRP knockdown cells. These molecular changes can contribute to the reshaping of P19 cells transcriptome that follows KSRP silencing. Our data suggests that KSRP function is required to maintain P19 cells in a multipotent undifferentiated state and that its inactivation can orient cells towards neural differentiation.