Control of fibroblast fibronectin expression and alternative splicing via the PI3K/Akt/mTOR pathway

Phosphorylated vimentin-triggered fibronectin matrix disaggregation enhances the dissemination of Treponema pallidum subsp. pallidum across the microvascular endothelial barrier

Fibronectin (FN) is an essential component of the extracellular matrix (ECM) that protects the integrity of the microvascular endothelial barrier (MEB). However, Treponema pallidum subsp. pallidum (Tp) breaches this barrier through elusive mechanisms and rapidly disseminates throughout the host. We aimed to understand the impact of Tp on the surrounding FN matrix of MEB and the underlying mechanisms of this effect. In this study, immunofluorescence assays (IF) were conducted to assess the integrity of the FN matrix surrounding human microvascular endothelial cell-1 (HMEC-1) with/without Tp co-culture, revealing that only live Tp exhibited the capability to mediate FN matrix disaggregation in HMEC-1. Western blotting and IF were employed to determine the protein levels associated with the FN matrix during Tp infection, which showed the unaltered protein levels of total FN and its receptor integrin α5β1, along with reduced insoluble FN and increased soluble FN. Simultaneously, the integrin α5β1-binding protein-intracellular vimentin maintained a stable total protein level while exhibiting an increase in the soluble form, specifically mediated by the phosphorylation of its 39th residue (pSer39-vimentin). Besides, this process of vimentin phosphorylation, which could be hindered by a serine-to-alanine mutation or inhibition of phosphorylated-AKT1 (pAKT1), promoted intracellular vimentin rearrangement and FN matrix disaggregation. Moreover, within the introduction of additional cellular FN rather than other Tp-adhered ECM protein, in vitro endothelial barrier traversal experiment and in vivo syphilitic infectivity test demonstrated that viable Tp was effectively prevented from penetrating the in vitro MEB or disseminating in Tp-challenged rabbits. This investigation revealed the active pAKT1/pSer39-vimentin signal triggered by live Tp to expedite the disaggregation of the FN matrix and highlighted the importance of FN matrix stability in syphilis, thereby providing a novel perspective on ECM disruption mechanisms that facilitate Tp dissemination across the MEB.

Fibronectin and vitronectin alleviate adipose-derived stem cells senescence during long-term culture through the AKT/MDM2/P53 pathway

Cellular senescence plays a role in the development of aging-associated degenerative diseases. Cell therapy is recognized as a candidate treatment for degenerative diseases. To achieve the goal of cell therapy, the quality and good characteristics of cells are concerned. Cell expansion relies on two-dimensional culture, which leads to replicative senescence of expanded cells. This study aimed to investigate the effect of cell culture surface modification using fibronectin (FN) and vitronectin (VN) in adipose-derived stem cells (ADSCs) during long-term expansion. Our results showed that ADSCs cultured in FN and VN coatings significantly enhanced adhesion, proliferation, and slow progression of cellular senescence as indicated by lower SA-β-gal activities and decreased expression levels of genes including p16, p21, and p53. The upregulation of integrin α5 and αv genes influences phosphatidylinositol 4,5-bisphosphate 3-kinase (PI3K), and AKT proteins. FN and VN coatings upregulated AKT and MDM2 leading to p53 degradation. Additionally, MDM2 inhibition by Nutlin-3a markedly elevated p53 and p21 expression, increased cellular senescence, and induced the expression of inflammatory molecules including HMGB1 and IL-6. The understanding of FN and VN coating surface influencing ADSCs, especially senescence characteristics, offers a promising and practical point for the cultivation of ADSCs for future use in cell-based therapies.

Discoidin domain receptor 2 signaling through PIK3C2α in fibroblasts promotes lung fibrosis

Pulmonary fibrosis, especially idiopathic pulmonary fibrosis (IPF), portends significant morbidity and mortality, and current therapeutic options are suboptimal. We have previously shown that type I collagen signaling through discoidin domain receptor 2 (DDR2), a receptor tyrosine kinase expressed by fibroblasts, is critical for the regulation of fibroblast apoptosis and progressive fibrosis. However, the downstream signaling pathways for DDR2 remain poorly defined and could also be attractive potential targets for therapy. A recent phosphoproteomic approach indicated that PIK3C2α, a poorly studied member of the PI3 kinase family, could be a downstream mediator of DDR2 signaling. We hypothesized that collagen I/DDR2 signaling through PIK3C2α regulates fibroblast activity during progressive fibrosis. To test this hypothesis, we found that primary murine fibroblasts and IPF-derived fibroblasts stimulated with endogenous or exogenous type I collagen led to the formation of a DDR2/PIK3C2α complex, resulting in phosphorylation of PIK3C2α. Fibroblasts treated with an inhibitor of PIK3C2α or with deletion of PIK3C2α had fewer markers of activation after stimulation with TGFβ and more apoptosis after stimulation with a Fas-activating antibody. Finally, mice with fibroblast-specific deletion of PIK3C2α had less fibrosis after bleomycin treatment than did littermate control mice with intact expression of PIK3Cα. Collectively, these data support the notion that collagen/DDR2/PIK3C2α signaling is critical for fibroblast function during progressive fibrosis, making this pathway a potential target for antifibrotic therapy. © 2024 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Formation of an invasion-permissive matrix requires TGFβ/SNAIL1-regulated alternative splicing of fibronectin

BACKGROUND

As in most solid cancers, the emergence of cells with oncogenic mutations in the mammary epithelium alters the tissue homeostasis. Some soluble factors, such as TGFβ, potently modify the behavior of healthy stromal cells. A subpopulation of cancer-associated fibroblasts expressing a TGFβ target, the SNAIL1 transcription factor, display myofibroblastic abilities that rearrange the stromal architecture. Breast tumors with the presence of SNAIL1 in the stromal compartment, and with aligned extracellular fiber, are associated with poor survival prognoses.

METHODS

We used deep RNA sequencing and biochemical techniques to study alternative splicing and human tumor databases to test for associations (correlation t-test) between SNAIL1 and fibronectin isoforms. Three-dimensional extracellular matrices generated from fibroblasts were used to study the mechanical properties and actions of the extracellular matrices on tumor cell and fibroblast behaviors. A metastatic mouse model of breast cancer was used to test the action of fibronectin isoforms on lung metastasis.

RESULTS

In silico studies showed that SNAIL1 correlates with the expression of the extra domain A (EDA)-containing (EDA+) fibronectin in advanced human breast cancer and other types of epithelial cancers. In TGFβ-activated fibroblasts, alternative splicing of fibronectin as well as of 500 other genes was modified by eliminating SNAIL1. Biochemical analyses demonstrated that SNAIL1 favors the inclusion of the EDA exon by modulating the activity of the SRSF1 splicing factor. Similar to Snai1 knockout fibroblasts, EDA- fibronectin fibroblasts produce an extracellular matrix  that does not sustain TGFβ-induced fiber organization, rigidity, fibroblast activation, or tumor cell invasion. The presence of EDA+ fibronectin changes the action of metalloproteinases on fibronectin fibers. Critically, in an mouse orthotopic breast cancer model, the absence of the fibronectin EDA domain completely prevents lung metastasis.

CONCLUSIONS

Our results support the requirement of EDA+ fibronectin in the generation of a metastasis permissive stromal architecture in breast cancers and its molecular control by SNAIL1. From a pharmacological point of view, specifically blocking EDA+ fibronectin deposition could be included in studies to reduce the formation of a pro-metastatic environment.

Interactions of Fibroblast Subtypes Influence Osteoclastogenesis and Alveolar Bone Destruction in Periodontitis

Background

To analyze the fibroblasts subtypes in the gingival tissues of healthy controls, gingivitis and periodontitis patients, as well as the effects of interaction between subtypes on alveolar bone destruction.

Methods

Gingival tissues were divided into three groups according to clinical and radiographic examination, and the immunostaining of EDA+FN was assessed. Fibroblasts from gingiva developed colony formation units (CFUs) and induced Trap+MNCs. The expression of osteoclastogenesis-related genes was assessed by real-time PCR. Variances in the gene profiles of CFUs were identified by principal component analysis, and cluster analysis divided CFUs into subtypes. The induction of Trap+MNCs and gene expression were compared among individual or cocultured subtypes. The fibroblast subtypes exerted critical effect on Trap+MNCs formation were selected and edited by CRISPR/Cas to investigate the influence on osteoclastogenesis in the periodontitis in mice.

Results

Most periodontitis samples exhibited intensive EDA+FN staining (P < 0.05), and these fibroblasts also induced most Trap+MNCs among three groups; consistently, fibroblasts from periodontitis highly expressed genes facilitating osteoclastogenesis. According to gene profiles and osteoclastogenic induction, four clusters of CFUs were identified. The proportion of clusters was significantly different (P < 0.05) among three groups, and their interaction influenced osteoclastogenic induction. Although Cluster 4 induced less osteoclasts, it enhanced the effects of Clusters 1 and 3 on Trap+MNCs formation (P < 0.05). EDA knockout in Cluster 4 abrogated this promotion (P < 0.05), and decreased osteoclasts and alveolar bone destruction in experimental periodontitis (P < 0.05).

Conclusion

Heterogeneous fibroblast subtypes affect the switch or development of periodontitis. A subtype (Cluster 4) played important role during alveolar bone destruction, by regulating other subtypes via EDA+FN paracrine.

The Fibrotic Effects of LINC00663 in Human Hepatic Stellate LX-2 Cells and in Bile Duct-Ligated Cholestasis Mice Are Mediated through the Splicing Factor 2-Fibronectin

Hepatic fibrosis can develop into cirrhosis or even cancer without active therapy at an early stage. Long non-coding RNAs (lncRNAs) have been shown to be involved in the regulation of a wide variety of important biological processes. However, lncRNA mechanism(s) involved in cholestatic liver fibrosis remain unclear. RNA sequence data of hepatic stellate cells from bile duct ligation (BDL) mice or controls were analyzed by weighted gene co-expression network analysis (WGCNA). Based on WGCNA analysis, a competing endogenous RNA network was constructed. We identified LINC00663 and evaluated its function using a panel of assays, including a wound healing assay, a dual-luciferase reporter assay, RNA binding protein immunoprecipitation and chromatin immunoprecipitation. Functional research showed that LINC00663 promoted the activation, migration and epithelial-mesenchymal transition (EMT) of LX-2 cells and liver fibrosis in BDL mice. Mechanistically, LINC00663 regulated splicing factor 2 (SF2)-fibronectin (FN) alternative splicing through the sponging of hsa-miR-3916. Moreover, forkhead box A1 (FOXA1) specifically interacted with the promoter of LINC00663. In summary, we elaborated the fibrotic effects of LINC00663 in human hepatic stellate LX-2 cells and in bile duct-ligated cholestasis mice. We established a FOXA1/LINC00663/hsa-miR-3916/SF2-FN axis that provided a potential target for the diagnosis and targeted therapy of cholestatic liver fibrosis.

To Explore Ideas From the Altered Metabolites: The Metabolomics of Pathological Scar

BACKGROUND

Pathological scars are dermal fibroproliferative disorders due to rapid inflammatory response after dermal injury. The altered metabolites could reflect pathophysiological changes directly. However, it has not cleared how the metabolites change scars.

OBJECTIVE

To explore new ideas of pathological scars from the altered metabolites by using ultra-performance liquid chromatography coupled to tandem mass spectrometry and identifying the key genes.

METHODS

Keloid (KS, n = 10), hypertrophic scar (HS, n = 10), and normal skin (NS, n = 10) were collected. Ultra-performance liquid chromatography coupled to tandem mass spectrometry was used to identify and characterize metabolites. Differential metabolites were analyzed by orthogonal partial least square discriminant analysis and Student t test. The key pathways were analyzed via Kyoto Encyclopedia of Genes and Genomes, and the related enzymes were verified by real-time Polymerase Chain Reaction, both in tissues and their dermal fibroblasts.

RESULTS

Two hundred fourteen metabolites were detected in total, mostly were fatty acids and amino acids. In the KS and NS groups, 65 different metabolites were screened (P < 0.05), and the polyunsaturated fatty acids (PUFAs) metabolism and butyric acid in keloid should be concerned. The messenger Ribonucleic Acid expression of fatty acid desaturase 1 and fatty acid desaturase 2, which are the key enzyme of PUFA metabolism, were lower in KS and keloid-derived fibroblasts, P < 0.05. In HS group, 17 metabolites were significantly different and branched chain amino acids degradation was the key pathway. Moreover, branched chain keto acid dehydrogenase E1 subunit alpha was lower expressed in HS and their fibroblasts compared with NS, P < 0.05.

CONCLUSIONS

Polyunsaturated fatty acids and butyric acid may be associated with the generation of keloids. The pathogenesis of hypertrophic scars may be involved in branched chain amino acids degradation, which is worth paying attention to.

Aberrant Methylation and Immune Microenvironment Are Associated With Overexpressed Fibronectin 1: A Diagnostic and Prognostic Target in Head and Neck Squamous Cell Carcinoma

Background: Fibronectin 1 (FN1) is involved in cell adhesion and migration processes such as metastasis, wound healing, embryogenesis, blood coagulation, and host defense. However, the role of FN1 in the diagnosis and prognosis of head and neck squamous cell carcinoma (HNSCC) is far from understood. Methods: FN1 expression profiles and clinical parameters from multiple HNSCC datasets were applied to evaluate the association between FN1 expression and HNSCC survival. We also identified FN1 expression in the mRNA and protein levels in 20 pairs of clinical samples by quantitative polymerase chain reaction (qPCR) and immunohistochemistry. Receiver operator characteristic (ROC) analysis was used to demonstrate the potential diagnostic value of FN1 in HNSCC. Aberrant methylation PPI networks were established using multiple bioinformatic tools based on TCGA database. The immune microenvironment and levels of immune checkpoints were investigated between groups with high and low FN1 expression. Results: FN1 was significantly upregulated in HNSCC compared with para-carcinoma tissues on the basis of TCGA database and our clinical samples. Univariate and multivariate Cox regression analysis revealed that FN1 could be an independent indicator for prognosis of HNSCC. GO enrichment and KEGG pathway analysis demonstrated that cell adhesion, focal adhesion, and the PI3K-Akt signaling pathway might be involved in the potential mechanisms of FN1's prognostic performance in HNSCC. Methylation of FN1 was also higher and closely associated with poorer survival in HNSCC. In addition, FN1 expression was positively correlated with three DNA methyltransferases (DNMT1, DNMT3A, and DNMT3B). Furthermore, FN1 was positively associated with CD4⁺ T cells, endothelial cells, macrophages, and NK cells and negatively correlated with CD8⁺ T cells Conclusion: FN1 might be an independent prognostic biomarker for HNSCC patients. Hypermethylation, the aberrant proportions of immune cells, and the PI3K/Akt signaling pathway might be involved in the mechanism of FN1's oncogene role in HNSCC.

Coordination of RNA Processing Regulation by Signal Transduction Pathways

Signal transduction pathways transmit the information received from external and internal cues and generate a response that allows the cell to adapt to changes in the surrounding environment. Signaling pathways trigger rapid responses by changing the activity or localization of existing molecules, as well as long-term responses that require the activation of gene expression programs. All steps involved in the regulation of gene expression, from transcription to processing and utilization of new transcripts, are modulated by multiple signal transduction pathways. This review provides a broad overview of the post-translational regulation of factors involved in RNA processing events by signal transduction pathways, with particular focus on the regulation of pre-mRNA splicing, cleavage and polyadenylation. The effects of several post-translational modifications (i.e., sumoylation, ubiquitination, methylation, acetylation and phosphorylation) on the expression, subcellular localization, stability and affinity for RNA and protein partners of many RNA-binding proteins are highlighted. Moreover, examples of how some of the most common signal transduction pathways can modulate biological processes through changes in RNA processing regulation are illustrated. Lastly, we discuss challenges and opportunities of therapeutic approaches that correct RNA processing defects and target signaling molecules.

Hyaluronan, Transforming Growth Factor β, and Extra Domain A-Fibronectin: A Fibrotic Triad

Significance: Inflammation is a critical aspect of injury repair. Nonresolving inflammation, however, is perpetuated by the local generation of extracellular matrix-derived damage-associated molecular pattern molecules (DAMPs), such as the extra domain A (EDA) isoform of fibronectin and hyaluronic acid (HA) that promote the eventual acquisition of a fibrotic response. DAMPs contribute to the inflammatory environment by engaging Toll-like, integrin, and CD44 receptors while stimulating transforming growth factor (TGF)-β signaling to activate a fibroinflammatory genomic program leading to the development of chronic disease. Recent Advances: Signaling through TLR4, CD44, and the TGF-β pathways impact the amplitude and duration of the innate immune response to endogenous DAMPs synthesized in the context of tissue injury. New evidence indicates that crosstalk among these three networks regulates phase transitions as well as the repertoire of expressed genes in the wound healing program determining, thereby, repair outcomes. Clarifying the molecular mechanisms underlying pathway integration is necessary for the development of novel therapeutics to address the spectrum of fibroproliferative diseases that result from maladaptive tissue repair. Critical Issues: There is an increasing appreciation for the role of DAMPs as causative factors in human fibroinflammatory disease regardless of organ site. Defining the involved intermediates essential for the development of targeted therapies is a daunting effort, however, since various classes of DAMPs activate different direct and indirect signaling pathways. Cooperation between two matrix-derived DAMPs, HA, and the EDA isoform of fibronectin, is discussed in this review as is their synergy with the TGF-β network. This information may identify nodes of signal intersection amenable to therapeutic intervention. Future Directions: Clarifying mechanisms underlying the DAMP/growth factor signaling nexus may provide opportunities to engineer the fibroinflammatory response to injury and, thereby, wound healing outcomes. The identification of shared and unique DAMP/growth factor-activated pathways is critical to the design of optimized tissue repair therapies while preserving the host response to bacterial pathogens.

Resistin induces cardiac fibroblast-myofibroblast differentiation through JAK/STAT3 and JNK/c-Jun signaling

Cardiac fibrosis is characterized by excessive deposition of extracellular matrix proteins and myofibroblast differentiation. Our previous findings have implicated resistin in cardiac fibrosis; however, the molecular mechanisms underlying this process are still unclear. Here we investigated the role of resistin in fibroblast-to-myofibroblast differentiation and elucidated the pathways involved in this process. Fibroblast-to-myofibroblast transdifferentiation was induced with resistin or TGFβ1 in NIH-3T3 and adult cardiac fibroblasts. mRNA and protein expression of fibrotic markers were analyzed by qPCR and immunoblotting. Resistin-knockout mice, challenged with a high-fat diet (HFD) for 20 weeks to stimulate cardiac impairment, were analyzed for cardiac function and fibrosis using histologic and molecular methods. Cardiac fibroblasts stimulated with resistin displayed increased fibroblast-to-myofibroblast conversion, with increased levels of αSma, col1a1, Fn, Ccn2 and Mmp9, with remarkable differences in the actin network appearance. Mechanistically, resistin promotes fibroblast-to-myofibroblast transdifferentiation and fibrogenesis via JAK2/STAT3 and JNK/c-Jun signaling pathways, independent of TGFβ1. Resistin-null mice challenged with HFD showed an improvement in cardiac function and a decrease in tissue fibrosis and reduced mRNA levels of fibrogenic markers. These findings are the first to delineate the role of resistin in the process of cardiac fibroblast-to-myofibroblast differentiation via JAK/STAT3 and JNK/c-Jun pathways, potentially leading to stimulation of cardiac fibrosis.

Deletion of delta-like 1 homologue accelerates fibroblast-myofibroblast differentiation and induces myocardial fibrosis

AIMS

Myocardial fibrosis is associated with profound changes in ventricular architecture and geometry, resulting in diminished cardiac function. There is currently no information on the role of the delta-like homologue 1 (Dlk1) in the regulation of the fibrotic response. Here, we investigated whether Dlk1 is involved in cardiac fibroblast-to-myofibroblast differentiation and regulates myocardial fibrosis and explored the molecular mechanism underpinning its effects in this process.

METHODS AND RESULTS

Using Dlk1-knockout mice and adenoviral gene delivery, we demonstrate that overexpression of Dlk1 in cardio-fibroblasts resulted in inhibition of fibroblast proliferation and differentiation into myofibroblasts. This process is mediated by TGF-β1 signalling, since isolated fibroblasts lacking Dlk1 exhibited a higher activation of the TGF-β1/Smad-3 pathway at baseline, leading to an earlier acquisition of a myofibroblast phenotype. Likewise, Dlk1-null mice displayed increased TGF-β1/Smad3 cardiac activity, resulting in infiltration/accumulation of myofibroblasts, induction and deposition of extra-domain A-fibronectin isoform and collagen, and activation of pro-fibrotic markers. Furthermore, these profibrotic events were associated with disrupted myofibril integrity, myocyte hypertrophy, and cardiac dysfunction. Interestingly, Dlk1 expression was down-regulated in ischaemic human and porcine heart tissues. Mechanistically, miR-370 mediated Dlk1's regulation of cardiac fibroblast-myofibroblast differentiation by directly targeting TGFβ-R2/Smad-3 signalling, while the Dlk1 canonical target, Notch pathway, does not seem to play a role in this process.

CONCLUSION

These findings are the first to demonstrate an inhibitory role of Dlk1 of cardiac fibroblast-to-myofibroblast differentiation by interfering with TGFβ/Smad-3 signalling in the myocardium. Given the deleterious effects of continuous activation of this pathway, we propose Dlk1 as a new potential candidate for therapy in cases where aberrant TGFβ signalling leads to chronic fibrosis.

Transforming growth factor beta 1 induces methylation changes in lung fibroblasts

Idiopathic pulmonary fibrosis is a complex disease of unknown etiology. Environmental factors can affect disease susceptibility via epigenetic effects. Few studies explore global DNA methylation in lung fibroblasts, but none have focused on transforming growth factor beta-1 (TGF-β1) as a potential modifier of the DNA methylome. Here we analyzed changes in methylation and gene transcription in normal and IPF fibroblasts following TGF-β1 treatment. We analyzed the effects of TGF-β1 on primary fibroblasts derived from normal or IPF lungs treated for 24 hours and 5 days using the Illumina 450k Human Methylation array and the Prime View Human Gene Expression Array. TGF-β1 induced an increased number of gene expression changes after short term treatment in normal fibroblasts, whereas greater methylation changes were observed following long term stimulation mainly in IPF fibroblasts. DNA methyltransferase 3 alpha (DMNT3a) and tet methylcytosine dioxygenase 3 (TET3) were upregulated after 5-days TGF-β1 treatment in both cell types, whereas DNMT3a was upregulated after 24h only in IPF fibroblasts. Our findings demonstrate that TGF-β1 induced the upregulation of DNMT3a and TET3 expression and profound changes in the DNA methylation pattern of fibroblasts, mainly in those derived from IPF lungs.

Signaling Mechanisms of Myofibroblastic Activation: Outside-in and Inside-Out

Myofibroblasts are central mediators of fibrosis. Typically derived from resident fibroblasts, myofibroblasts represent a heterogeneous population of cells that are principally defined by acquired contractile function and high synthetic ability to produce extracellular matrix (ECM). Current literature sheds new light on the critical role of ECM signaling coupled with mechanotransduction in driving myofibroblastic activation. In particular, transforming growth factor β1 (TGF-β1) and extra domain A containing fibronectin (EDA-FN) are thought to be the primary ECM signaling mediators that form and also induce positive feedback loops. The outside-in and inside-out signaling circuits are transmitted and integrated by TGF-β receptors and integrins at the cell membrane, ultimately perpetuating the abundance and activities of TGF-β1 and EDA-FN in the ECM. In this review, we highlight these conceptual advances in understanding myofibroblastic activation, in hope of revealing its therapeutic anti-fibrotic implications.

Glycogen synthase kinase-3 and alternative splicing

Glycogen synthase kinase-3 (GSK-3) is a highly conserved negative regulator of receptor tyrosine kinase, cytokine, and Wnt signaling pathways. Stimulation of these pathways inhibits GSK-3 to modulate diverse downstream effectors that include transcription factors, nutrient sensors, glycogen synthesis, mitochondrial function, circadian rhythm, and cell fate. GSK-3 also regulates alternative splicing in response to T-cell receptor activation, and recent phosphoproteomic studies have revealed that multiple splicing factors and regulators of RNA biosynthesis are phosphorylated in a GSK-3-dependent manner. Furthermore, inhibition of GSK-3 alters the splicing of hundreds of mRNAs, indicating a broad role for GSK-3 in the regulation of RNA processing. GSK-3-regulated phosphoproteins include SF3B1, SRSF2, PSF, RBM8A, nucleophosmin 1 (NPM1), and PHF6, many of which are mutated in leukemia and myelodysplasia. As GSK-3 is inhibited by pathways that are pathologically activated in leukemia and loss of Gsk3 in hematopoietic cells causes a severe myelodysplastic neoplasm in mice, these findings strongly implicate GSK-3 as a critical regulator of mRNA processing in normal and malignant hematopoiesis. This article is categorized under: RNA Processing > Splicing Mechanisms RNA Processing > Splicing Regulation/Alternative Splicing RNA in Disease and Development > RNA in Disease RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications.

Cellular stress and AMPK activation as a common mechanism of action linking the effects of metformin and diverse compounds that alleviate accelerated aging defects in Hutchinson-Gilford progeria syndrome

Hutchinson-Gilford progeria syndrome (HGPS) is a rare genetic disorder characterized by an accelerated aging phenotype that typically leads to death via stroke or myocardial infarction at approximately 14.6 years of age. Most cases of HGPS have been linked to the extensive use of a cryptic splice donor site located in the LMNA gene due to a de novo mutation, generating a truncated and toxic protein known as progerin. Progerin accumulation in the nuclear membrane and within the nucleus distorts the nuclear architecture and negatively effects nuclear processes including DNA replication and repair, leading to accelerated cellular aging and premature senescence. The serine-arginine rich splicing factor SRSF1 (also known as ASF/SF2) has recently been shown to modulate alternative splicing of the LMNA gene, with SRSF1 inhibition significantly reducing progerin at both the mRNA and protein levels. In 2014, we hypothesized for the first time that compounds including metformin that induce activation of AMP-activated protein kinase (AMPK), a master metabolic regulator activated by cellular stress (e.g. increases in intracellular calcium, reactive oxygen species, and/or an AMP(ADP)/ATP ratio increase, etc.), will beneficially alter gene splicing in progeria cells by inhibiting SRSF1, thus lowering progerin levels and altering the LMNA pre-mRNA splicing ratio. Recent evidence has substantiated this hypothesis, with metformin significantly reducing the mRNA and protein levels of both SRSF1 and progerin, activating AMPK, and alleviating pathological defects in HGPS cells. Metformin has also recently been shown to beneficially alter gene splicing in normal humans. Interestingly, several chemically distinct compounds, including rapamycin, methylene blue, all-trans retinoic acid, MG132, 1α,25-dihydroxyvitamin D3, sulforaphane, and oltipraz have each been shown to alleviate accelerated aging defects in patient-derived HGPS cells. Each of these compounds has also been independently shown to induce AMPK activation. Because these compounds improve accelerated aging defects in HGPS cells either by enhancing mitochondrial functionality, increasing Nrf2 activity, inducing autophagy, or by altering gene splicing and because AMPK activation beneficially modulates each of the aforementioned processes, it is our hypothesis that cellular stress-induced AMPK activation represents an indirect yet common mechanism of action linking such chemically diverse compounds with the beneficial effects of those compounds observed in HGPS cells. As normal humans also produce progerin at much lower levels through a similar mechanism, compounds that safely induce AMPK activation may have wide-ranging implications for both normal and pathological aging.

hnRNP L controls HPV16 RNA polyadenylation and splicing in an Akt kinase-dependent manner

Inhibition of the Akt kinase activates HPV16 late gene expression by reducing HPV16 early polyadenylation and by activating HPV16 late L1 mRNA splicing. We identified ‘hot spots’ for RNA binding proteins at the early polyA signal and at splice sites on HPV16 late mRNAs. We observed that hnRNP L was associated with sequences at all HPV16 late splice sites and at the early polyA signal. Akt kinase inhibition resulted in hnRNP L dephosphorylation and reduced association of hnRNP L with HPV16 mRNAs. This was accompanied by an increased binding of U2AF65 and Sam68 to HPV16 mRNAs. Furthermore, siRNA knock-down of hnRNP L or Akt induced HPV16 gene expression. Treatment of HPV16 immortalized keratinocytes with Akt kinase inhibitor reduced hnRNP L binding to HPV16 mRNAs and induced HPV16 L1 mRNA production. Finally, deletion of the hnRNP L binding sites in HPV16 subgenomic expression plasmids resulted in activation of HPV16 late gene expression. In conclusion, the Akt kinase inhibits HPV16 late gene expression at the level of RNA processing by controlling the RNA-binding protein hnRNP L. We speculate that Akt kinase activity upholds an intracellular milieu that favours HPV16 early gene expression and suppresses HPV16 late gene expression.

Integrin α4β1 and TLR4 Cooperate to Induce Fibrotic Gene Expression in Response to Fibronectin's EDA Domain

Alternative splicing of fibronectin increases expression of the EDA⁺ isoform of fibronectin (EDA⁺Fn), a damage-associated molecular pattern molecule, which promotes fibro-inflammatory disease through the activation of toll-like receptors. Our studies indicate that the fibronectin EDA domain drives two waves of gene expression in human dermal fibroblasts. The first wave, seen at 2 hours, consisted of inflammatory genes, VCAM1, and tumor necrosis factor. The second wave, evaluated at 24 hours, was composed of the fibrosis-associated cytokines IL-10 and IL-13 and extracellular matrix genes fibronectin and osteopontin. Gene expression was coordinately regulated by the α4β1 integrin and the innate immune receptor toll-like receptor 4. Additionally, we found a significant toll-like receptor 4/α4β1-dependent enrichment in the ratio of EDA⁺Fn to total fibronectin in response to EDA, consistent with EDA⁺Fn initiating further production of EDA⁺Fn. Our data also suggest that the EDA/α4β1 integrin interaction primes the cell for an enhanced response to toll-like receptor 4 ligands. Our studies provide evidence that remodeling of the fibronectin matrix in injured or diseased tissue elicits an EDA-dependent fibro-inflammatory response in dermal fibroblasts. The data suggest a paradigm of damage-associated molecular pattern-based signaling whereby damage-associated molecular pattern binding integrins cooperate with innate immune receptors to stimulate inflammation and fibrosis.

Modulation of nonsense mediated decay by rapamycin

Rapamycin is a naturally occurring macrolide whose target is at the core of nutrient and stress regulation in a wide range of species. Despite well-established roles as an inhibitor of cap-dependent mRNA translation, relatively little is known about its effects on other modes of RNA processing. Here, we characterize the landscape of rapamycin-induced post-transcriptional gene regulation. Transcriptome analysis of rapamycin-treated cells reveals genome-wide changes in alternative mRNA splicing and pronounced changes in NMD-sensitive isoforms. We demonstrate that despite well-documented attenuation of cap-dependent mRNA translation, rapamycin can augment NMD of certain transcripts. Rapamycin-treatment significantly reduces the levels of both endogenous and exogenous Premature Termination Codon (PTC)-containing mRNA isoforms and its effects are dose-, UPF1- and 4EBP-dependent. The PTC-containing SRSF6 transcript exhibits a shorter half-life upon rapamycin-treatment as compared to the non-PTC isoform. Rapamycin-treatment also causes depletion of PTC-containing mRNA isoforms from polyribosomes, underscoring the functional relationship between translation and NMD. Enhanced NMD activity also correlates with an enrichment of the nuclear Cap Binding Complex (CBC) in rapamycin-treated cells. Our data demonstrate that rapamycin modulates global RNA homeostasis by NMD.

Self-assembled nanofiber coatings for controlling cell responses

Nanofibers are thought to enhance cell adhesion, growth, and function. We demonstrate that the choice of building blocks in self-assembling nanofiber systems can be used to control cell behavior. The use of 2 D-coated, self-assembled nanofibers in controlling lens epithelial cells, fibroblasts, and mesenchymal stem cells was investigated, focusing on gene and protein expression related to the fibrotic response. To this end, three nanofibers with different characteristics (morphology, topography, and wettability) were compared with two standard materials frequently used in culturing cells, TCPS, and a collagen type I coating. Cell metabolic activity, cell morphology, and gene and protein expression were analyzed. The most hydrophilic nanofiber with more compact network consisting of small fibers proved to provide a beneficial 2 D environment for cell proliferation and matrix formation while decreasing the fibrotic/stress behavior in all cell lines when compared with TCPS and the collagen type I coating. This nanofiber demonstrates the potential to be used as a biomimetic coating to study the development of fibrosis through epithelial-to-mesenchymal transition. This study also shows that nanofiber structures do not enhance cell function by definition, because the physico-chemical characteristics of the nanofibers influence cell behavior as well and actually can be used to regulate cell behavior toward suboptimal performance. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2252-2265, 2017.

The Complexity of Targeting PI3K-Akt-mTOR Signalling in Human Acute Myeloid Leukaemia: The Importance of Leukemic Cell Heterogeneity, Neighbouring Mesenchymal Stem Cells and Immunocompetent Cells

Therapeutic targeting of PI3K-Akt-mTOR is considered a possible strategy in human acute myeloid leukaemia (AML); the most important rationale being the proapoptotic and antiproliferative effects of direct PI3K/mTOR inhibition observed in experimental studies of human AML cells. However, AML is a heterogeneous disease and these effects caused by direct pathway inhibition in the leukemic cells are observed only for a subset of patients. Furthermore, the final effect of PI3K-Akt-mTOR inhibition is modulated by indirect effects, i.e., treatment effects on AML-supporting non-leukemic bone marrow cells. In this article we focus on the effects of this treatment on mesenchymal stem cells (MSCs) and monocytes/macrophages; both these cell types are parts of the haematopoietic stem cell niches in the bone marrow. MSCs have unique membrane molecule and constitutive cytokine release profiles, and mediate their support through bidirectional crosstalk involving both cell-cell contact and the local cytokine network. It is not known how various forms of PI3K-Akt-mTOR targeting alter the molecular mechanisms of this crosstalk. The effect on monocytes/macrophages is also difficult to predict and depends on the targeted molecule. Thus, further development of PI3K-Akt-mTOR targeting into a clinical strategy requires detailed molecular studies in well-characterized experimental models combined with careful clinical studies, to identify patient subsets that are likely to respond to this treatment.

Targeting the Mammalian Target of Rapamycin in Lung Cancer

Lung cancer is the leading cause of cancer death worldwide. Despite advances in its prevention and management, the prognosis of patients with lung cancer remains poor. Therefore, much attention is being given to factors that contribute to the development of this disease, the mechanisms that drive oncogenesis and tumor progression and the search for novel targets that could lead to the development of more effective treatments. One cellular pathway implicated in lung cancer development and progression is that of the mammalian target of rapamycin. Studies involving human tissues have linked lung cancer with abnormalities in this pathway. Furthermore, studies in vitro and in vivo using animal models of lung cancer reveal that targeting this pathway might represent an effective means of treating this disease. As a result, there is significant effort invested in the development of drugs targeting mammalian target of rapamycin and related pathways in the clinical setting.

The Phosphorylation and Distribution of Cortactin Downstream of Integrin α9β1 Affects Cancer Cell Behaviour

Integrins, a family of heterodimeric adhesion receptors are implicated in cell migration, development and cancer progression. They can adopt conformations that reflect their activation states and thereby impact adhesion strength and migration. Integrins in an intermediate activation state may be optimal for migration and we have shown previously that fully activated integrin α9β1 corresponds with less migratory behaviour in melanoma cells. Here, we aimed to identify components associated with the activation status of α9β1. Using cancer cell lines with naturally occuring high levels of this integrin, activation by α9β1-specific ligands led to upregulation of fibronectin matrix assembly and tyrosine phosphorylation of cortactin on tyrosine 470 (Y470). Specifically, cortactin phosphorylated on Y470, but not Y421, redistributed together with α9β1 to focal adhesions where active β1 integrin also localises, upon integrin activation. This was commensurate with reduced migration. The localisation and phosphorylation of cortactin Y470 was regulated by Yes kinase and PTEN phosphatase. Cortactin levels influenced fibronectin matrix assembly and active β1 integrin on the cell surface, being inversely correlated with migratory behaviour. This study underlines the complex interplay between cortactin and α9β1 integrin that regulates cell-extracellular matrix interactions.

Oocyte activation and latent HIV-1 reactivation: AMPK as a common mechanism of action linking the beginnings of life and the potential eradication of HIV-1

In all mammalian species studied to date, the initiation of oocyte activation is orchestrated through alterations in intracellular calcium (Ca(2+)) signaling. Upon sperm binding to the oocyte plasma membrane, a sperm-associated phospholipase C (PLC) isoform, PLC zeta (PLCζ), is released into the oocyte cytoplasm. PLCζ hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP2) to produce diacylglycerol (DAG), which activates protein kinase C (PKC), and inositol 1,4,5-trisphosphate (IP3), which induces the release of Ca(2+) from endoplasmic reticulum (ER) Ca(2+) stores. Subsequent Ca(2+) oscillations are generated that drive oocyte activation to completion. Ca(2+) ionophores such as ionomycin have been successfully used to induce artificial human oocyte activation, facilitating fertilization during intra-cytoplasmic sperm injection (ICSI) procedures. Early studies have also demonstrated that the PKC activator phorbol 12-myristate 13-acetate (PMA) acts synergistically with Ca(2+) ionophores to induce parthenogenetic activation of mouse oocytes. Interestingly, the Ca(2+)-induced signaling cascade characterizing sperm or chemically-induced oocyte activation, i.e. the "shock and live" approach, bears a striking resemblance to the reactivation of latently infected HIV-1 viral reservoirs via the so called "shock and kill" approach, a method currently being pursued to eradicate HIV-1 from infected individuals. PMA and ionomycin combined, used as positive controls in HIV-1 latency reversal studies, have been shown to be extremely efficient in reactivating latent HIV-1 in CD4(+) memory T cells by inducing T cell activation. Similar to oocyte activation, T cell activation by PMA and ionomycin induces an increase in intracellular Ca(2+) concentrations and activation of DAG, PKC, and downstream Ca(2+)-dependent signaling pathways necessary for proviral transcription. Interestingly, AMPK, a master regulator of cell metabolism that is activated thorough the induction of cellular stress (e.g. increase in Ca(2+) concentration, reactive oxygen species generation, increase in AMP/ATP ratio) is essential for oocyte maturation, T cell activation, and mitochondrial function. In addition to the AMPK kinase LKB1, CaMKK2, a Ca(2+)/calmodulin-dependent kinase that also activates AMPK, is present in and activated on T cell activation and is also present in mouse oocytes and persists until the zygote and two-cell stages. It is our hypothesis that AMPK activation represents a central node linking T cell activation-induced latent HIV-1 reactivation and both physiological and artificial oocyte activation. We further propose the novel observation that various compounds that have been shown to reactivate latent HIV-1 (e.g. PMA, ionomycin, metformin, bryostatin, resveratrol, etc.) or activate oocytes (PMA, ionomycin, ethanol, puromycin, etc.) either alone or in combination likely do so via stress-induced activation of AMPK.

Palladin mediates stiffness-induced fibroblast activation in the tumor microenvironment

Mechanical properties of the tumor microenvironment have emerged as key factors in tumor progression. It has been proposed that increased tissue stiffness can transform stromal fibroblasts into carcinoma-associated fibroblasts. However, it is unclear whether the three to five times increase in stiffness seen in tumor-adjacent stroma is sufficient for fibroblast activation. In this study we developed a three-dimensional (3D) hydrogel model with precisely tunable stiffness and show that a physiologically relevant increase in stiffness is sufficient to lead to fibroblast activation. We found that soluble factors including CC-motif chemokine ligand (CCL) chemokines and fibronectin are necessary for this activation, and the combination of C-C chemokine receptor type 4 (CCR4) chemokine receptors and β1 and β3 integrins are necessary to transduce these chemomechanical signals. We then show that these chemomechanical signals lead to the gene expression changes associated with fibroblast activation via a network of intracellular signaling pathways that include focal adhesion kinase (FAK) and phosphoinositide 3-kinase (PI3K). Finally, we identify the actin-associated protein palladin as a key node in these signaling pathways that result in fibroblast activation.

Mechanistic Target of Rapamycin Complex 1 (mTORC1) and mTORC2 as Key Signaling Intermediates in Mesenchymal Cell Activation

Fibrotic diseases display mesenchymal cell (MC) activation with pathologic deposition of matrix proteins such as collagen. Here we investigate the role of mTOR complex 1 (mTORC1) and mTORC2 in regulating MC collagen expression, a hallmark of fibrotic disease. Relative to normal MCs (non-Fib MCs), MCs derived from fibrotic human lung allografts (Fib-MCs) demonstrated increased phosphoinositide-3kinase (PI3K) dependent activation of both mTORC1 and mTORC2, as measured by increased phosphorylation of S6K1 and 4E-BP1 (mTORC1 substrates) and AKT (an mTORC2 substrate). Dual ATP-competitive TORC1/2 inhibitor AZD8055, in contrast to allosteric mTORC1-specific inhibitor rapamycin, strongly inhibited 4E-BP1 phosphorylation and collagen I expression in Fib-MCs. In non-Fib MCs, increased mTORC1 signaling was shown to augment collagen I expression. mTORC1/4E-BP1 pathway was identified as an important driver of collagen I expression in Fib-MCs in experiments utilizing raptor gene silencing and overexpression of dominant-inhibitory 4E-BP1. Furthermore, siRNA-mediated knockdown of rictor, an mTORC2 partner protein, reduced mTORC1 substrate phosphorylation and collagen expression in Fib-, but not non-Fib MCs, revealing a dependence of mTORC1 signaling on mTORC2 function in activated MCs. Together these studies suggest a novel paradigm where fibrotic activation in MCs increases PI3K dependent mTORC1 and mTORC2 signaling and leads to increased collagen I expression via the mTORC1-dependent 4E-BP1/eIF4E pathway. These data provide rationale for targeting specific components of mTORC pathways in fibrotic states and underscore the need to further delineate mTORC2 signaling in activated cell states.

Identification of important long non-coding RNAs and highly recurrent aberrant alternative splicing events in hepatocellular carcinoma through integrative analysis of multiple RNA-Seq datasets

Hepatocellular carcinoma (HCC) is an aggressive and deadly cancer. The molecular pathogenesis of the disease remains poorly understood. To better understand HCC biology and explore potential biomarkers and therapeutic targets, we investigated the whole transcriptome of HCC. Considering the genetic heterogeneity of HCC, four datasets from four studies consisting of 15 pairs of HCC and adjacent normal samples were analyzed. We observed that the number of lncRNAs expressed in each HCC sample was consistently greater than the adjacent normal sample. Moreover, 15 lncRNAs were identified expressed in five to seven HCC tissues but were not detected in any adjacent normal tissue. Differential expression analysis detected 35 up- and 80 down-regulated lncRNAs in HCC samples compared with adjacent normal samples. In addition, five differentially expressed lncRNAs were predicted to play a role in oxidation and reduction process. With regard to splicing alterations, we identified nine highly recurrent differential splicing events belonging to eight genes USO1, RPS24, CCDC50, THNSL2, NUMB, FN1 (two events), SLC39A14 and NR1I3. Of them, splicing alterations of SLC39A14 and NR1I3 were reported for the association with HCC for the first time. The splicing dysregulation in HCC may be influenced by three splicing factors ESRP2, CELF2 and SRSF5 which were significantly down-regulated in HCC samples. This study revealed uncharacterized aspects of HCC transcriptome and identified important lncRNAs and splicing isoforms with the potential to serve as biomarkers and therapeutic targets for the disease.

The Regulation of TGFβ1 Induced Fibronectin EDA Exon Alternative Splicing in Human Renal Proximal Tubule Epithelial Cells

The EDA+ splice variant of fibronectin (Fn) is an early and important component of the extracellular matrix in renal fibrosis. In this work, we investigate cellular mechanisms of EDA+Fn production in human primary proximal tubule epithelial cells (PTECs). TGFβ1-induced EDA+Fn production was assessed by immunocytochemistry, PCR, and Western blotting. SRp40 knockdown was achieved by siRNA. The role of the PI3 kinase-AKT signalling and splicing regulatory protein SRp40 in the production of EDA+Fn was studied by using the chemical inhibitor LY294002 and siRNA targeted to SRp40 respectively. Interaction between PI3 kinase-AKT signalling and SRp40 were assessed by immunofluorescence and immunoprecipitation. To assess the specificity of SRp40 in regulating the splicing of EDA+ exon, we studied the effect of SRp40 knockdown on TGFβ1 induced splicing of FGF receptor 2. Primary human PTECs expressed EDA+ and EDA- Fn. TGFβ1 treatment resulted in increases in the production and deposition of EDA+ Fn as well as an increase in the ratio of EDA+/EDA- Fn mRNA. The TGFβ1 induced EDA+ production was dependent on PI3 kinase-AKT signalling and SRp40 expression. Immunoprecipitation experiments demonstrated direct binding between AKT and SRp40 with an increase in the amount of SRp40 bound to AKT upon TGFβ1 treatment. TGFβ1 treatment resulted in reduction in the FGF receptor2 IIIb splice variant which was unaffected by SRp40 knockdown. In this work, we have presented the first evidence for the regulation of Fn pre-mRNA splicing by PI3 kinase-AKT signalling and SRp40 in human PTECs. Targeting the splicing of Fn pre-mRNA to skip the EDA exon is an attractive option to combat fibrosis.

Novel mechanism of transcriptional regulation of cell matrix protein through CREB

The transcription mechanism(s) of renal cell matrix accumulation in diabetes does not explored. Phosphorylation of the transcription factor cAMP-responsive element binding protein (CREB) significantly increased in cells treated with high glucose (HG) compared to cell grown in normal glucose (NG). Cells pretreated with rapamycin before exposure to HG showed significant decrease phosphorylation of CREB, increase in AMPK activity and decrease protein/mRNA and promoter activity of fibronectin. In addition, cells transfected with siRNA against CREB showed significant increase in AMPK activity, decrease in protein/mRNA and promoter activity of fibronectin. Cells treated with HG showed nuclear localization of p-CREB while pretreated cells with rapamycin reversed HG effect. Moreover, gel shift analysis shows increase binding of CREB to fibronectin promoter in cells treated with HG while cells pretreated with rapamycin reversed the effect of HG. Furthermore, db/db mice treated with rapamycin showed significant increase in AMPK activity, decrease in expression of p-CREB and protein/mRNA of fibronectin. Strong staining of fibronectin and p-CREB was detected in kidney cortex of db/db mice while treated mice with rapamycin reversed hyperglycemia effect. In summary, our data provide a novel mechanism of transcriptional regulation of fibronectin through CREB that may be used as therapeutic approach to prevent diabetes complications.

Favorable effect of myofibroblasts on collagen synthesis and osteocalcin production in the periodontal ligament

INTRODUCTION

In this study, we aimed to explore the expressions of α-smooth muscle actin, collagen type I, collagen type III, and osteocalcin in the periodontal ligament (PDL) under orthodontic loading, and to investigate the effect of myofibroblasts on collagen synthesis and osteocalcin production.

METHODS

The teeth in the right maxillae of the rats were orthodontically loaded while the contralateral teeth remained unloaded as controls. The total 30 rats were divided into 5 groups, with each group corresponding to a treatment duration (0, 3, 5, 7, or 14 days, respectively). The expressions of α-smooth muscle actin, collagen type I, collagen type III, and osteocalcin in the tension area of the PDL over time were analyzed by immunochemistry staining. For the in-vitro study, the expressions of α-smooth muscle actin, collagen type I, collagen type III, and osteocalcin in the myofibroblasts and human osteoblast-like cells (MG63) coculture and PDL cells-MG63 coculture systems were examined by Western blot and real-time polymerase chain reaction.

RESULTS

Enhanced expression of α-smooth muscle actin, collagen type I, collagen type III, and osteocalcin in the tension area of the PDL under orthodontic loading were observed in vivo, and increased expressions of α-smooth muscle actin, collagen type I, collagen type III, and osteocalcin in the myofibroblasts-MG63 coculture system were observed compared with the controls.

CONCLUSIONS

Expressions of α-smooth muscle actin, collagen type I, collagen type III, and osteocalcin are up-regulated in the PDL under orthodontic tensile loading. Myofibroblasts have a more positive effect on collagen synthesis and osteocalcin expression than do PDL cells.

FibronectinEDA promotes chronic cutaneous fibrosis through Toll-like receptor signaling

Scleroderma is a progressive autoimmune disease affecting multiple organs. Fibrosis, the hallmark of scleroderma, represents transformation of self-limited wound healing into a deregulated self-sustaining process. The factors responsible for maintaining persistent fibroblast activation in scleroderma and other conditions with chronic fibrosis are not well understood. Toll-like receptor 4 (TLR4) and its damage-associated endogenous ligands are implicated in immune and fibrotic responses. We now show that fibronectin extra domain A (Fn(EDA)) is an endogenous TLR4 ligand markedly elevated in the circulation and lesional skin biopsies from patients with scleroderma, as well as in mice with experimentally induced cutaneous fibrosis. Synthesis of Fn(EDA) was preferentially stimulated by transforming growth factor-β in normal fibroblasts and was constitutively up-regulated in scleroderma fibroblasts. Exogenous Fn(EDA) was a potent stimulus for collagen production, myofibroblast differentiation, and wound healing in vitro and increased the mechanical stiffness of human organotypic skin equivalents. Each of these profibrotic Fn(EDA) responses was abrogated by genetic, RNA interference, or pharmacological disruption of TLR4 signaling. Moreover, either genetic loss of Fn(EDA) or TLR4 blockade using a small molecule mitigated experimentally induced cutaneous fibrosis in mice. These observations implicate the Fn(EDA)-TLR4 axis in cutaneous fibrosis and suggest a paradigm in which aberrant Fn(EDA) accumulation in the fibrotic milieu drives sustained fibroblast activation via TLR4. This model explains how a damage-associated endogenous TLR4 ligand might contribute to converting self-limited tissue repair responses into intractable fibrogenesis in chronic conditions such as scleroderma. Disrupting sustained TLR4 signaling therefore represents a potential strategy for the treatment of fibrosis in scleroderma.

The alternative splicing side of cancer

Alternative splicing emerges as a potent and pervasive mechanism of gene expression regulation that expands the coding capacity of the genome and forms an intermediate layer of regulation between transcriptional and post-translational networks. Indeed, alternative splicing occupies a pivotal position in developmental programs and in the cell response to external and internal stimuli. Not surprisingly, therefore, its deregulation frequently leads to human disease. In this review we provide an updated overview of the impact of alternative splicing on tumorigenesis. Moreover, we discuss the intricacy of the reciprocal interactions between alternative splicing programs and signal transduction pathways, which appear to be crucially linked to cancer progression in response to the tumor microenvironment. Finally, we focus on the recently described interplay between splicing and chromatin organization which is expected to shed new lights into gene expression regulation in normal and cancer cells.

Persea americana Mill. Seed: Fractionation, Characterization, and Effects on Human Keratinocytes and Fibroblasts

Methanolic avocado (Persea americana Mill., Lauraceae) seed extracts were separated by preparative HSCCC. Partition and HSCCC fractions were principally characterized by LC-ESI-MS/MS analysis. Their in vitro influence was investigated on proliferation, differentiation, cell viability, and gene expression on HaCaT and normal human epidermal keratinocytes (NHEK) and normal human dermal fibroblasts (NHDF). The methanol-water partition (M) from avocado seeds and HSCCC fraction 3 (M.3) were mostly composed of chlorogenic acid and its isomers. Both reduced NHDF but enhanced HaCaT keratinocytes proliferation. HSCCC fraction M.2 composed of quinic acid among chlorogenic acid and its isomers inhibited proliferation and directly induced differentiation of keratinocytes as observed on gene and protein level. Furthermore, M.2 increased NHDF proliferation via upregulation of growth factor receptors. Salidrosides and ABA derivatives present in HSCCC fraction M.6 increased NHDF and keratinocyte proliferation that resulted in differentiation. The residual solvent fraction M.7 contained among low concentrations of ABA derivatives high amounts of proanthocyanidins B1 and B2 as well as an A-type trimer and stimulated proliferation of normal cells and inhibited the proliferation of immortalized HaCaT keratinocytes.

Akt1 mediates α-smooth muscle actin expression and myofibroblast differentiation via myocardin and serum response factor

Myofibroblast (MF) differentiation, marked by the de novo expression of smooth muscle α-actin (αSMA) stress fibers, plays a central role in wound healing and its persistence is a hallmark of fibrotic diseases. We have previously shown that Akt1 is necessary for wound healing through matrix regulation. However, the role of Akt1 in regulating MF differentiation with implications in fibrosis remains poorly defined. Here, we show that sustained activation of Akt1 was associated with a 6-fold increase in αSMA expression and assembly; an effect that is blunted in cells expressing inactive Akt1 despite TGFβ stimulation. Mechanistically, Akt1 mediated TGFβ-induced αSMA synthesis through the contractile gene transcription factors myocardin and serum response factor (SRF), independent of mammalian target of rapamycin in mouse embryonic fibroblasts and fibroblasts overexpressing active Akt1. Akt1 deficiency was associated with decreased myocardin, SRF, and αSMA expressions in vivo. Furthermore, sustained Akt1-induced αSMA synthesis markedly decreased upon RNA silencing of SRF and myocardin. In addition to its integral role in αSMA synthesis, we also show that Akt1 mediates fibronectin splice variant expression, which is required for MF differentiation, as well as total fibronectin, which generates the contractile force that promotes MF differentiation. In summary, our results constitute evidence that sustained Akt1 activation is crucial for TGFβ-induced MF formation and persistent differentiation. These findings highlight Akt1 as a novel potential therapeutic target for fibrotic diseases.

Regulation of the Ras-MAPK and PI3K-mTOR Signalling Pathways by Alternative Splicing in Cancer

Alternative splicing is a fundamental step in regulation of gene expression of many tumor suppressors and oncogenes in cancer. Signalling through the Ras-MAPK and PI3K-mTOR pathways is misregulated and hyperactivated in most types of cancer. However, the regulation of the Ras-MAPK and PI3K-mTOR signalling pathways by alternative splicing is less well established. Recent studies have shown the contribution of alternative splicing regulation of these signalling pathways which can lead to cellular transformation, cancer development, and tumor maintenance. This review will discuss findings in the literature which describe new modes of regulation of components of the Ras-MAPK and PI3K-mTOR signalling pathways by alternative splicing. We will also describe the mechanisms by which signals from extracellular stimuli can be communicated to the splicing machinery and to specific RNA-binding proteins that ultimately control exon definition events.

Modification of Akt by SUMO conjugation regulates alternative splicing and cell cycle

Akt/PKB is a key signaling molecule in higher eukaryotes and a crucial protein kinase in human health and disease. Phosphorylation, acetylation, and ubiquitylation have been reported as important regulatory post-translational modifications of this kinase. We describe here that Akt is modified by SUMO conjugation, and show that lysine residues 276 and 301 are the major SUMO attachment sites within this protein. We found that phosphorylation and SUMOylation of Akt appear as independent events. However, decreasing Akt SUMOylation levels severely affects the role of this kinase as a regulator of fibronectin and Bcl-x alternative splicing. Moreover, we observed that the Akt mutant (Akt E17K) found in several human tumors displays increased levels of SUMOylation and also an enhanced capacity to regulate fibronectin splicing patterns. This splicing regulatory activity is completely abolished by decreasing Akt E17K SUMO conjugation levels. Additionally, we found that SUMOylation controls Akt regulatory function at G₁/S transition during cell cycle progression. These findings reveal SUMO conjugation as a novel level of regulation for Akt activity, opening new areas of exploration related to the molecular mechanisms involved in the diverse cellular functions of this kinase.

Tissue-specific and SRSF1-dependent splicing of fibronectin, a matrix protein that controls host cell invasion

Matching sets of human primary fibroblasts cocultured with placenta explants are used to compare tissue capacities to support trophoblast invasion. Substituting endometrium with dermis dramatically reduces EVCT interstitial invasion, a phenomenon related to the ECM fibronectin content, FN alternative splicing, and expression of the SR protein SRSF1.

Cell invasion targets specific tissues in physiological placental implantation and pathological metastasis, which raises questions about how this process is controlled. We compare dermis and endometrium capacities to support trophoblast invasion, using matching sets of human primary fibroblasts in a coculture assay with human placental explants. Substituting endometrium, the natural trophoblast target, with dermis dramatically reduces trophoblast interstitial invasion. Our data reveal that endometrium expresses a higher rate of the fibronectin (FN) extra type III domain A+ (EDA+) splicing isoform, which displays stronger matrix incorporation capacity. We demonstrate that the high FN content of the endometrium matrix, and not specifically the EDA domain, supports trophoblast invasion by showing that forced incorporation of plasma FN (EDA–) promotes efficient trophoblast invasion. We further show that the serine/arginine-rich protein serine/arginine-rich splicing factor 1 (SRSF1) is more highly expressed in endometrium and, using RNA interference, that it is involved in the higher EDA exon inclusion rate in endometrium. Our data therefore show a mechanism by which tissues can be distinguished, for their capacity to support invasion, by their different rates of EDA inclusion, linked to their SRSF1 protein levels. In the broader context of cancer pathology, the results suggest that SRSF1 might play a central role not only in the tumor cells, but also in the surrounding stroma.

Detecting splicing variants in idiopathic pulmonary fibrosis from non-differentially expressed genes

Idiopathic pulmonary fibrosis (IPF) is an interstitial lung disease of unknown cause that lacks a proven therapy for altering its high mortality rate. Microarrays have been employed to investigate the pathogenesis of IPF, but are presented mostly at the gene-expression level due to technologic limitations. In as much as, alternative RNA splicing isoforms are increasingly identified as potential regulators of human diseases, including IPF, we propose a new approach with the capacity to detect splicing variants using RNA-seq data. We conducted a joint analysis of differential expression and differential splicing on annotated human genes and isoforms, and identified 122 non-differentially expressed genes with a high degree of "switch" between major and minor isoforms. Three cases with variant mechanisms for alternative splicing were validated using qRT-PCR, among the group of genes in which expression was not significantly changed at the gene level. We also identified 35 novel transcripts that were unique to the fibrotic lungs using exon-exon junction evidence, and selected a representative for qRT-PCR validation. The results of our study are likely to provide new insight into the pathogenesis of pulmonary fibrosis and may eventuate in new treatment targets.

Phosphoinositides: tiny lipids with giant impact on cell regulation

Phosphoinositides (PIs) make up only a small fraction of cellular phospholipids, yet they control almost all aspects of a cell's life and death. These lipids gained tremendous research interest as plasma membrane signaling molecules when discovered in the 1970s and 1980s. Research in the last 15 years has added a wide range of biological processes regulated by PIs, turning these lipids into one of the most universal signaling entities in eukaryotic cells. PIs control organelle biology by regulating vesicular trafficking, but they also modulate lipid distribution and metabolism via their close relationship with lipid transfer proteins. PIs regulate ion channels, pumps, and transporters and control both endocytic and exocytic processes. The nuclear phosphoinositides have grown from being an epiphenomenon to a research area of its own. As expected from such pleiotropic regulators, derangements of phosphoinositide metabolism are responsible for a number of human diseases ranging from rare genetic disorders to the most common ones such as cancer, obesity, and diabetes. Moreover, it is increasingly evident that a number of infectious agents hijack the PI regulatory systems of host cells for their intracellular movements, replication, and assembly. As a result, PI converting enzymes began to be noticed by pharmaceutical companies as potential therapeutic targets. This review is an attempt to give an overview of this enormous research field focusing on major developments in diverse areas of basic science linked to cellular physiology and disease.

mTOR: a link from the extracellular milieu to transcriptional regulation of oligodendrocyte development

Oligodendrocyte development is controlled by numerous extracellular signals that regulate a series of transcription factors that promote the differentiation of oligodendrocyte progenitor cells to myelinating cells in the central nervous system. A major element of this regulatory system that has only recently been studied is the intracellular signalling from surface receptors to transcription factors to down-regulate inhibitors and up-regulate inducers of oligodendrocyte differentiation and myelination. The current review focuses on one such pathway: the mTOR (mammalian target of rapamycin) pathway, which integrates signals in many cell systems and induces cell responses including cell proliferation and cell differentiation. This review describes the known functions of mTOR as they relate to oligodendrocyte development, and its recently discovered impact on oligodendrocyte differentiation and myelination. A potential model for its role in oligodendrocyte development is proposed.

Influence of age on wound healing and fibrosis

The incidence and severity of fibrotic lung diseases increase with age, but very little is known about how age-related changes affect the mechanisms that underlie disease emergence and progression. Normal ageing includes accumulation of DNA mutations, oxidative and cell stresses, mitochondria dysfunction, increased susceptibility to apoptosis, telomere length dysfunction and differential gene expression as a consequence of epigenetic changes and miR regulation. These inevitable ageing-related phenomena may cause dysfunction and impaired repair capacity of lung epithelial cells, fibroblasts and MSCs. As a consequence, the composition of the extracellular matrix changes and the dynamic interaction between cells and their environment is damaged, resulting ultimately in predisposition for several diseases. This review summarizes what is known about age-related molecular changes that are implicated in the pathobiology of lung fibrosis in lung tissue.

Beyond control of protein translation: what we have learned about the non-canonical regulation and function of mammalian target of rapamycin (mTOR)

Mammalian target of rapamycin (mTOR) is a serine-threonine kinase involved in almost every aspect of mammalian cell function. This kinase was initially believed to control protein translation in response to amino acids and trophic factors, and this function has become a canonical role for mTOR. However, mTOR can form two separate protein complexes (mTORCs). Recent advances clearly demonstrate that both mTORCs can respond to various stimuli and change myriad cellular processes. Therefore, our current view of the cellular roles of TORCs has rapidly expanded and cannot be fully explained without appreciating recent findings about the new modes of mTOR regulation and identification of non-canonical effectors of mTOR that contribute to transcription, cytoskeleton dynamics, and membrane trafficking. This review discusses the molecular details of these newly discovered non-canonical functions that allow mTORCs to control the cellular environment at multiple levels. This article is part of a Special Issue entitled: Inhibitors of Protein Kinases (2012).

RNA metabolism and ubiquitin/ubiquitin-like modifications collide

Alternative splicing and post-translational modifications are key events for the generation of proteome diversity in eukaryotes. The study of the molecular mechanisms governing these processes, and every other step of gene expression, has underscored the existing interconnectedness among them. Therefore, molecules that could concertedly regulate different stages from transcription to pre-mRNA processing, translation and even protein activity have called our attention. Serine/arginine-rich proteins, initially identified as splicing regulators, are involved in diverse aspects of gene expression. Although most of the roles exerted by members of this family are related to mRNA biogenesis and metabolism, few recently uncovered ones link these proteins to other regulatory steps along gene expression, particularly the regulation of post-translational modification by conjugation of the small ubiquitin-related modifier. This along with the established link between ubiquitin, transcription and pre-mRNA processing points to a general mechanism of interaction between different cellular machineries, such as ubiquitin/ubiquitin-like conjugation pathways, transcription apparatus and the spliceosome.

Post-transcriptional regulation in cancer progression : Microenvironmental control of alternative splicing and translation

The microenvironment acts as a conduit for cellular communication, delivering signals that direct development and sustain tissue homeostasis. In pathologies such as cancer, this integral function of the microenvironment is hijacked to support tumor growth and progression. Cells sense the microenvironment via signal transduction pathways culminating in altered gene expression. In addition to induced transcriptional changes, the microenvironment exerts its effect on the cell through regulation of post-transcriptional processes including alternative splicing and translational control. Here we describe how alternative splicing and protein translation are controlled by microenvironmental parameters such as oxygen availability. We also emphasize how these pathways can be utilized to support processes that are hallmarks of cancer such as angiogenesis, proliferation, and cell migration. We stress that cancer cells respond to their microenvironment through an integrated regulation of gene expression at multiple levels that collectively contribute to disease progression.

Keloid disease can be inhibited by antagonizing excessive mTOR signaling with a novel dual TORC1/2 inhibitor

Keloid disease (KD) is a fibroproliferative lesion of unknown etiopathogenesis that possibly targets the PI3K/Akt/mTOR pathway. We investigated whether PI3K/Akt/mTOR inhibitor, Palomid 529 (P529), which targets both mammalian target of rapamycin complex 1 (mTORC-1) and mTORC-2 signaling, could exert anti-KD effects in a novel KD organ culture assay and in keloid fibroblasts (KF). Treatment of KF with P529 significantly (P < 0.05) inhibited cell spreading, attachment, proliferation, migration, and invasive properties at a low concentration (5 ng/mL) and induced substantial KF apoptosis when compared with normal dermal fibroblasts. P529 also inhibited hypoxia-inducible factor-1α expression and completely suppressed Akt, GSK3β, mTOR, eukaryotic initiation factor 4E-binding protein 1, and S6 phosphorylation. P529 significantly (P < 0.05) inhibited proliferating cell nuclear antigen and cyclin D and caused considerable apoptosis. Compared with rapamycin and wortmannin, P529 also significantly (P < 0.05) reduced keloid-associated phenotypic markers in KF. P529 caused tissue shrinkage, growth arrest, and apoptosis in keloid organ cultures and substantially inhibited angiogenesis. pS6, pAkt-Ser473, and mTOR phosphorylation were also suppressed in situ. P529 reduced cellularity and expression of collagen, fibronectin, and α-smooth muscle actin (substantially more than rapamycin). These pre-clinical in vitro and ex vivo observations are evidence that the mTOR pathway is a promising target for future KD therapy and that the dual PI3K/Akt/mTOR inhibitor P529 deserves systematic exploration as a candidate agent for the future treatment of KD.

Predisposition for disrepair in the aged lung

INTRODUCTION

Idiopathic pulmonary fibrosis (IPF) is a devastating progressive lung disease with an average survival of only 3 to 5 years. The mechanisms underlying the initiation and progression of IPF are poorly understood, and treatments available have only modest effect on disease progression. Interestingly, the incidence of IPF is approximately 60 times more common in individuals aged 75 years and older, but the mechanism by which aging promotes fibrosis is unclear. The authors hypothesized that aged lungs have a profibrotic phenotype that render it susceptible to disrepair after injury.

METHODS

Young and old mice were treated with bleomycin to examine disrepair in the aged lung. In addition, uninjured young and old mouse lungs were analyzed for transforming growth factor-beta 1 (TGF-β1) production, extracellular matrix composition and lung fibroblast phenotype. Lung fibroblasts were treated with a DNA methyltransferase inhibitor to examine the potential epigenetic mechanisms involved in age-associated phenotypic alterations.

RESULTS

The lungs of old mice showed worse fibrosis after bleomycin-induced injury compared with the lungs from young mice. At baseline, aged lungs expressed a profibrotic phenotype characterized by increased mRNA expression for fibronectin extracellular domain A (Fn-EDA) and the matrix metalloproteinases (MMPs) MMP-2 and MMP-9. Old lungs also expressed higher levels of TGF-β receptor 1 and TGF-β1 mRNA, protein and activity as determined by increased Smad3 expression, protein phosphorylation and DNA binding. Lung fibroblasts harvested from aged lungs showed reduced expression of the surface molecule Thy-1, a finding also implicated in lung fibrosis; the latter did not seem related to Thy-1 gene methylation.

CONCLUSION

Altogether, aged lungs manifest a profibrotic phenotype characterized by enhanced fibronectin extracellular domain A and MMP expression and increased TGF-β1 expression and signaling and are populated by Thy-1-negative fibroblasts, all implicated in the pathogenesis of lung fibrosis.

Tuberin inhibits production of the matrix protein fibronectin in diabetes

Exposure of proximal tubular epithelial cells to high glucose contributes to the accumulation of tubulointerstitial and matrix proteins in diabetic nephropathy, but how this occurs is not well understood. We investigated the effect of the signaling molecule tuberin, which modulates the mammalian target of rapamycin pathway, on renal hypertrophy and fibronectin expression. We found that the kidney mass was significantly greater in partially tuberin-deficient (TSC2(+/-) ) diabetic rats than wild-type diabetic rats. Furthermore, TSC2(+/-) rats exhibited significant increases in the basal levels of phospho-tuberin and fibronectin expression in the kidney cortex. Increased levels of phosphorylated tuberin associated with an increase in fibronectin expression in both wild-type and TSC2(+/-) diabetic rats. Treatment with insulin abrogated the diabetes-induced increase in fibronectin expression. In vitro, high glucose enhanced fibronectin expression in TSC2(+/-) primary proximal tubular epithelial cells; both inhibition of Akt and inhibition of the mammalian target of rapamycin could prevent this effect of glucose. In addition, forced expression of tuberin in tuberin-null cells abolished the expression of fibronectin protein. Taken together, these data suggest that tuberin plays a central role in the development of renal hypertrophy and in modulating the production of the matrix protein fibronectin in diabetes.