Transformation Of Fibroblasts Research Articles

MicroRNA-mediated transformation by the Kaposi's sarcoma-associated herpesvirus Kaposin locus.

The human oncogenic Kaposi's sarcoma-associated herpesvirus (KSHV) expresses a set of ∼20 viral microRNAs (miRNAs). miR-K10a stands out among these miRNAs because its entire stem-loop precursor overlaps the coding sequence for the Kaposin (Kap) A/C proteins. The ectopic expression of KapA has been reported to lead to transformation of rodent fibroblasts. However, these experiments inadvertently also introduced miR-K10a, which raises the question whether the transforming activity of the locus could in fact be due to miR-K10a expression. To answer this question, we have uncoupled miR-K10a and KapA expression. Our experiments revealed that miR-K10a alone transformed cells with an efficiency similar to that when it was coexpressed with KapA. Maintenance of the transformed phenotype was conditional upon continued miR-K10a but not KapA protein expression, consistent with its dependence on miRNA-mediated changes in gene expression. Importantly, miR-K10a taps into an evolutionarily conserved network of miR-142-3p targets, several of which are expressed in 3T3 cells and are also known inhibitors of cellular transformation. In summary, our studies of miR-K10a serve as an example of an unsuspected function of an mRNA whose precursor is embedded within a coding transcript. In addition, our identification of conserved miR-K10a targets that limit transformation will point the way to a better understanding of the role of this miRNA in KSHV-associated tumors. Kaposi's sarcoma-associated herpesvirus (KSHV) is a human tumor virus. The viral Kaposin locus has known oncogenic potential, which has previously been attributed to the encoded KapA protein. Here we show that the virally encoded miR-K10a miRNA, whose precursor overlaps the KapA-coding region, may account for the oncogenic properties of this locus. Our data suggest that miR-K10a mimics the cellular miRNA miR-142-3p and thereby represses several known inhibitors of oncogenic transformation. Our work demonstrates that functional properties attributed to a coding region may in fact be carried out by an embedded noncoding element and sheds light on the functions of viral miR-K10a.

BCL6 Enables RAS-Mediated Pre-B Cell Transformation in Childhood Acute Lymphoblastic Leukemia

Background & Hypothesis: The transcriptional repressor and proto-oncogene BCL6 has recently been identified as a therapeutic target in subtypes of diffuse large B cell lymphoma (DLBCL) and as mediator of a novel for of drug-resistance in Ph+ acute lymphoblastic leukemia (ALL; Duy et al., Nature 2011). A previous senescence rescue screen identified BCL6 as a key factor that bypassed senescence and thereby enabled RAS-mediated transformation of mouse embryonic fibroblasts (Shvarts et al., Genes Dev 2002). Since ~50% of pediatric cases of ALL carry genetic lesions that result in hyperactivation of the Ras-Erk pathway (Zhang et al., Blood 2012), we tested the role of Bcl6 in this large subgroup of childhood leukemia.Results: Mutations leading to hyperactivation of the Ras-Erk pathway are found in about 50% of childhood ALL cases (Zhang et al., 2012). Among 26 ALL xenografts, we found 9 cases with constitutive Erk-T202/Y204 phosphorylation, which was paralleled by elevated expression levels of BCL6 in these cases. Studying mouse pre-B cells that were engineered with a doxycycline-inducible NRASG12D mutant, we were able to directly measure the consequences of acute activation of the Ras-Erk pathway on BCL6 expression levels. First we incubated the cells with doxycycline to induce the expression of NRASG12D and then harvested the cells at different times point to test for BCL6 protein and mRNA expression levels. Interestingly, after 24h NRASG12D-TetO pre-B cells cells showed strong upregulation of BCL6 at the mRNA (352-fold) and protein level (15-fold). Upregulation of BCL6 in response to NRASG12D-activation was sensitive to treatment with the MEK kinase inhibitor PD325901, upstream of Erk, suggesting that BCL6 expression is a consequence of Erk activation in pre-B cells. Likewise, treatment of patient-derived pre-B ALL cells with the MEK inhibitor PD325901 reversed BCL6 expression, as demonstrated by quantitative RT-PCR and Western blot. From one patient, a diagnostic (KRAS wildtype) and a relapse sample with an acquired KRASG12V mutation were available. Consistent with specific expression of BCL6 in the KRASG12V relapse ALL sample, only KRASG12V ALL cells from the relapse but not wildtype cells from the diagnostic sample were sensitive to a retro inversoBCL6 peptide inhibitor (RI-BPI; Cerchietti et al., 2009).Development of a genetic mouse model for inducible ablation of Bcl6. These findings suggest an important role of BCL6 as a cofactor of RAS-driven pre-B cell transformation, comparable to previous findings in mouse embryonic fibroblasts. To directly test a mechanistic role of Bcl6 in RAS-mediated pre-B cell transformation, we generated a novel mouse model for inducible Cre-mediated deletion of Bcl6 exons 5-10, flanked by loxP sites. For lineage-specific deletion in vivo, we crossed these mice with an Mb1-Cre deleter strain, in which Bcl6 was deleted in pro-B cells, resulting in a differentiation block at the pre-B cell stage. Interestingly, Mb1-Cre x Bcl6fl/fl B cell lineage cells could be transduced with NRASG12D retroviral vectors, however these cells did not give rise to leukemia when injected into congenic recipients, whereas NRASG12D-transduced Bcl6fl/fl pro-B cells that retained Bcl6 function developed B cell lineage leukemia in all transplant recipients. In a second experiment, we transformed Bcl6fl/fl pro-B cells with NRASG12D and induced Cre with a second, tamoxifen-inducible vector in full-blown leukemia cells. Acute ablation of Bcl6 in NRASG12D ALL cells completely abrogated the ability of NRASG12DALL cells to form colonies in methylcellulose and resulted in rapid apoptosis and depletion from the cell culture. We conclude that BCL6 is not only required for the initiation of RAS-driven ALL in vivo but also for the maintenance of fully established RAS-driven leukemia.Conclusion: These findings provide genetic evidence for BCL6 function as a critical cofactor of RAS-mediated transformation in childhood ALL. Inhibition of BCL6 in RAS-driven ALL may be useful to prevent leukemia relapse after initial remission (Bcl6-dependent leukemia-initiation) and also to achieve profound remission by combining conventional cytotoxic therapies with BCL6 inhibition (e.g. RI-BPI). DisclosuresNo relevant conflicts of interest to declare.

The SH2 Domain of BCR-ABL1 Regulates Kinase Autophosphorylation By Controlling Activation Loop Accessibility

Chronic myelogenous leukemia (CML) is caused by BCR-ABL1, which is a constitutively active form of the Abelson tyrosine kinase (ABL1). While treatment with the tyrosine kinase inhibitors imatinib, nilotinib, dasatinib, bosutinib or ponatinib that target the ATP binding pocket of BCR-ABL1 leads to durable cytogenetic and molecular remissions in the majority CML patients, primary and secondary drug resistance remains a clinical problem. Targeting additional sites in the BCR-ABL1 kinase outside the highly conserved ATP binding pocket may be an alternative strategy to restrict drug resistance and limit side effects of ATP-competitive drugs with low selectivity. Our recent work has shown that an allosteric intramolecular interaction of the BCR-ABL1 SH2 domain with its kinase domain is critical for leukemogenesis and can be targeted with an engineered high-affinity binding protein.We have now elucidated the molecular mechanisms responsible for the regulation of BCR-ABL1 kinase activity by its SH2 domain: To this end, we set-up an efficient expression system for the BCR-ABL1 SH2-kinase domain unit in E.coli with excellent yield, purity and activity. Detailed biophysical and biochemical analysis of the purified recombinant proteins in vitro recapitulated SH2-dependent regulation of BCR-ABL1 in CML cells and enabled a quantitative enzymatic analysis of BCR-ABL1 activation. Unexpectedly, we found that the interaction of the SH2 domain with the kinase domain is the critical switch that shifts the BCR-ABL1 activation loop from an otherwise closed to a fully open conformation and enables its autophosphorylation. The activation loop is a central and almost universally used control element that regulates the activity of protein kinases, as the conformation and phosphorylation status of the activation loop determines substrate binding to the active site. In BCR-ABL1, activation loop phosphorylation is required for transformation of fibroblasts and haematopoietic progenitors. We show that the SH2-kinase interaction enables autophosphorylation of the activation loop in trans by rendering a key phosphorylation site (Tyr-412) highly accessible. This requires prior phosphorylation of Tyr-245 in the SH2-kinase linker of BCR-ABL1. Mutational disruption of the SH2-kinase interaction abolished activation loop phosphorylation. Importantly, this effect was independent of the phosphotyrosine binding ability of the SH2 domain, which indicated that the SH2 domain is a true allosteric activator of BCR-ABL1 kinase activity. We also show that the spectrum of tyrosine phosphorylation sites that we mapped by mass spectrometry in vitro were vastly overlapping with the observed BCR-ABL1 phosphorylation sites in CML cells indicating that BCR-ABL1 autophosphorylation might be the major mechanism that determines its cellular phosphorylation status.In summary, our study demonstrates a novel mechanism by which a protein-protein interaction domain may allosterically mediate the transition of an inactive to an active kinase conformation in a key oncoprotein. This work may serve as an archetype to identify further allosteric regulatory mechanisms in other tyrosine kinases that are activated in haematological malignancies and facilitate the development of new allosteric inhibitors targeting oncogenic tyrosine kinases. DisclosuresNo relevant conflicts of interest to declare.

Abstract A20: ARHGEF2 inhibition impairs cell growth and viability in KRAS-dependent cancer cells

Abstract Sporadic tumours carrying activating mutations of the RAS family of GTPases are characterized by a progressive and multiple step tumorigenesis. Among the three isoforms, K-RAS is the most commonly mutated (Prior et al., 2012). ARHGEF2 is a microtubule-associated guanine nucleotide exchange factor (GEF) for the Rho family of small GTPases whose expression is up-regulated (more than 30 times) upon Ras neoplastic transformation in Rat fibroblasts (Zuber et al., 2000). A truncated version of the protein can transform NIH 3T3 cells (Whitehead et al., 1995) and induce tumour formation in nude mice (Brecht et al., 2005). We recently identified ARHGEF2 as a transcriptional target of the RAS/MAPK pathway and its expression contributes to cell survival and growth in RAS-transformed cells (Cullis et al., in revision). We aimed to determine if ARHGEF2 is required for tumour cell viability in different KRAS mutant cancer cell lines. We used an RNAi approach using two different ARHGEF2 and KRAS shRNAs to monitor cell growth and viability in six different cancer cell lines harbouring a KRAS mutation: four pancreatic adenocarcinomas (PL45, Panc 02.03, Panc 04.03 and KP4), one endometrial adenocarcinoma (HEC-1-A) and one colorectal adenocarcinoma (LS 174T). We found that ARHGEF2 is required for cell growth and survival in half of the cell lines analyzed. We established an ARHGEF2 and KRAS dependency index for those cell lines and further analysis allowed us to determine a positive correlation (correlation coefficient of 0.64, p value <0.03) between ARHGEF2 and KRAS dependency. In conclusion, our findings suggest that: i/ ARHGEF2 plays a role in the tumorigenesis and survival of KRAS dependent cell lines, but further in vitro and in vivo studies are required; ii/ ARHGEF2 inhibition could be a potential therapeutic target in tumours harbouring KRAS mutations.

Mesenchymal stem cell-mediated suppression of hypertrophic scarring is p53 dependent in a rabbit ear model.

IntroductionMesenchymal stem cells (MSCs) are considered to play important roles in wound repair and tissue remodeling. Hypertrophic scar (HTS) is a cutaneous condition characterized by deposits of excessive amount of collagen after an acute skin injury. However, currently there is little knowledge about the direct relationship between MSCs and HTS.MethodsThe hypertrophic scar model was established on rabbit ears. MSCs were isolated from rabbit femur bone marrow and transplanted through ear artery injection. Hypertrophic scar formation was examined using frozen-section analysis, hematoxylin and eosin (HE) staining, Masson’s trichrome staining, and scar elevation index. The role of p53 in the MSCs-mediated anti-scarring effect was examined by gene knockdown using p53 shRNA.ResultsIn this study, MSCs engraftment through ear artery injection significantly inhibited the hypertrophic scarring in a rabbit ear hypertrophic scar model, while this anti-scarring function could be abrogated by p53 gene knockdown in MSCs. Additionally, we found that MSCs down-regulated the expression of TGF-β receptor I (TβRI) and alpha-smooth muscle actin (α-SMA) at both mRNA and protein levels in a paracrine manner, and this down-regulation was rescued by p53 gene knockdown. Moreover, our results showed that MSCs with p53 gene knockdown promoted the proliferation of fibroblasts through increasing nitric oxide (NO) production.ConclusionsThese results suggest that MSCs inhibit the formation of HTS in a p53 dependent manner through at least two mechanisms: inhibition of the transformation of HTS fibroblast to myofibroblast; and inhibition of the proliferation of fibroblasts through inhibition of NO production.

Abstract A16: Overexpression and ubiquitination of kinase suppressor of Ras 1 (KSR1) in human colon tumor cells

Abstract Kinase Suppressor of Ras 1 (KSR1) is required for oncogenic Ras-induced transformation in mouse embryonic fibroblasts (MEFs) and human colon tumor cells, but is dispensable for normal cellular development. It is also overexpressed in a variety of human tumors, including human colon tumor cells. Seven human colon tumor cell lines with mutated and activated Ras (GEO, CBS, FET, SW480, HCT15, DLD1, and HCT116), one with wild type Ras (CaCo2), and non-transformed human colonic epithelial cells (HCECs) were assessed for KSR1 by western blot. Compared to HCECs, all eight tumor cell lines showed a marked decrease in electrophoretic motility. Seven of eight cell lines had a clear increase in KSR1 expression regardless of Ras mutation status. The purpose of the study is to examine the mechanism by which KSR1 is up-regulated in cancer cells. Previous studies indicate that KSR proteins interact with multiple E3 ubiquitin ligase complexes including members homologous to the E6AP carboxyl terminus (HECT) domain family and the really interesting new gene (RING) family, including Cullin (Cul) 1, Cul4A, Cul4B, Cul7, damage-specific DNA binding protein 1 (DDB1), and DDB1-Cullin associating factor 1 (DCAF1), and ubiquitin protein ligase E3 component N-recognin 5 (UBR5/EDD1). Using tagged expression vectors and immunoprecipitation techniques, we investigated whether KSR1 is a substrate or a component of E3 ligase complexes. Both FLAG-tagged and endogenous KSR1 are ubiquitinated in the human colon tumor cell line, HCT-116. In HEK 293T cells, truncated KSR1 constructs were used to determine that KSR1 ubiquitination is dependent on the presence of the putative kinase domain in the C-terminal region. Furthermore, the kinase domain is sufficient for KSR1 ubiquitination by Cul4A/4B RING ligases (CRLs); however, silencing of Cul4A/4B by RNAi does not inhibit KSR1 ubiquitination. These data indicate that multiple Cullin family members may function to ubiquitinate KSR1. Additionally, KSR1 does not exclusively bind to Cullins, but also interacts with other components of the multi-subunit CRLs, including DDB1 and DCAF1. Therefore, KSR1 may not only be a direct substrate but also a member of the large complex helping to modulate activity of the CRL. Overall, these data suggest that Cul4A/4B-dependent ubiquitination of the KSR1 putative kinase may function to modulate KSR1-dependent signaling. Citation Format: Jamie L. McCall, Ken Kono, Kurt W. Fisher, Manabu Furukawa, Robert E. Lewis. Overexpression and ubiquitination of kinase suppressor of Ras 1 (KSR1) in human colon tumor cells. [abstract]. In: Proceedings of the AACR Special Conference on RAS Oncogenes: From Biology to Therapy; Feb 24-27, 2014; Lake Buena Vista, FL. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(12 Suppl):Abstract nr A16. doi: 10.1158/1557-3125.RASONC14-A16

Abstract 12192: MBNL1 Directly Regulates the Alternative Splicing of mRNAs That Promote Myofibroblast Differentiation

Rationale: During the cardiac injury response fibroblasts differentiate into myofibroblasts, a cell type that enhances extracellular matrix production and facilitates ventricular remodeling. To better understand the molecular mechanisms whereby myofibroblasts are generated in the heart we performed a genome-wide screen with 18,000 cDNAs, which identified the RNA-binding protein muscleblind-like splicing regulator 1 (MBNL1), suggesting a novel association between mRNA alternative splicing and the regulation of myofibroblast differentiation. Objective: To determine the mechanism whereby MBNL1 regulates myofibroblast differentiation and the cardiac fibrotic response. Methods and Results: Confirming the results from our genome wide screen, adenoviral-mediated overexpression of MBNL1 promoted transformation of rat cardiac fibroblasts and mouse embryonic fibroblasts (MEFs) into myofibroblasts, similar to the level of conversion obtained by the profibrotic agonist transforming growth factor β (TGFβ). Antithetically, Mbnl1 -/- MEFs were refractory to TGFβ-induced myofibroblast differentiation. MBNL1 expression is induced in transforming fibroblasts in response to TGFβ and angiotensin II. These results were extended in vivo by analysis of dermal wound healing, a process dependent on myofibroblast differentiation and their proper activity. By day 6 control mice had achieved 82% skin wound closure compared with only 40% in Mbnl1 -/- mice. Moreover, Mbnl1 -/- mice had reduced survival following myocardial infarction injury due to defective fibrotic scar formation and healing. High throughput RNA sequencing (RNAseq) and RNA immunoprecipitation revealed that MBNL1 directly regulates the alternative splicing of transcripts for myofibroblast signaling factors and cytoskeletal-assembly elements. Functional analysis of these factors as mediators of MBNL1 activity is also described here. Conclusions: Collectively, our data suggest that MBNL1 coordinates myofibroblast transformation by directly mediating the alternative splicing of an array of mRNAs encoding differentiation-specific signaling transcripts, which then alter the fibroblast proteome for myofibroblast structure and function.

Chronic inhibition of cyclic guanosine monophosphate-specific phosphodiesterase 5 prevented cardiac fibrosis through inhibition of transforming growth factor β-induced Smad signaling.

Recent evidences suggested that cyclic guanosine monophosphate-specific phosphodiesterase 5 (PDE5) inhibitor represents an important therapeutic target for cardiovascular diseases. Whether and how it ameliorates cardiac fibrosis, a major cause of diastolic dysfunction and heart failure, is unknown. The purpose of this study was to investigate the effects of PDE5 inhibitor on cardiac fibrosis. We assessed cardiac fibrosis and pathology in mice subjected to transverse aortic constriction (TAC). Oral sildenafil, a PDE5 inhibitor, was administered in the therapy group. In control mice, 4 weeks of TAC induced significant cardiac dysfunction, cardiac fibrosis, and cardiac fibroblast activation (proliferation and transformation to myofibroblasts). Sildenafil treatment markedly prevented TAC-induced cardiac dysfunction, cardiac fibrosis and cardiac fibroblast activation but did not block TAC-induced transforming growth factor-β1 (TGF-β1) production and phosphorylation of Smad2/3. In isolated cardiac fibroblasts, sildenafil blocked TGF-β1-induced cardiac fibroblast transformation, proliferation and collagen synthesis. Furthermore, we found that sildenafil induced phosphorylated cAMP response element binding protein (CREB) and reduced CREB-binding protein 1 (CBP1) recruitment to Smad transcriptional complexes. PDE5 inhibition prevents cardiac fibrosis by reducing CBP1 recruitment to Smad transcriptional complexes through CREB activation in cardiac fibroblasts.

Cell-based approach for treatment of corneal endothelial dysfunction.

Decompensation of the corneal endothelium causes severe visual impairments that lead to blindness. Although corneal transplantation is a well-known effective therapy for corneal endothelial dysfunction, many patients are not afforded that therapeutic opportunity owing to the worldwide shortage of donor corneas. Thus, a tissue engineering-based therapy for treating corneal endothelial dysfunction is highly anticipated. Obstacles associated with the development of tissue engineering therapy include in vitro culture of corneal endothelial cells (CECs) and the techniques used to transplant those cells. Limited proliferation ability, cellular senescence, and fibroblastic transformation during culture are all problems associated with the cultivation of CECs. In addition, transplantation of cultured CECs is technically difficult because the corneal endothelium is composed of a fragile monolayer sheet of cells located at the posterior cornea. In this review article, we present our recent findings using a novel cell culture protocol and show that modulation of CEC adhesion properties through a Rho-kinase inhibitor enables transplantation of CECs in the form of a cell suspension without the use of a carrier. Finally, we provide an update on the clinical application status of a cell-based therapy for treating corneal endothelial dysfunction.

Abstract 3512: MYCN and survivin cooperatively contribute to malignant transformation of fibroblasts

Abstract The oncogenes MYCN and survivin (BIRC5) maintain aggressiveness of diverse cancers including sarcomas. To investigate whether these oncogenes cooperate in initial malignant transformation, we transduced them into Rat-1 fibroblasts. Indeed, survivin enhanced MYCN-driven contact-uninhibited and anchorage-independent growth in vitro. Importantly, upon subcutaneous transplantation into mice, cells overexpressing both instead of either one of the oncogenes generated tumors with shortened latency, marked anaplasia and an increased proliferation-to-apoptosis ratio resulting in accelerated growth. Mechanistically, the increased tumorigenicity was associated with an enhanced Warburg effect and HIF1α-linked vascular remodeling. This cooperation between MYCN and survivin may be important in the genesis of several cancers. Citation Format: Nora Hipp, Lisa Christner, Thomas Wirth, Wolfgang Mueller-Klieser, Stefan Walenta, Evelin Schröck, Klaus-Michael Debatin, Christian Beltinger. MYCN and survivin cooperatively contribute to malignant transformation of fibroblasts. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3512. doi:10.1158/1538-7445.AM2014-3512

Functions of galectin-3 and its role in fibrotic diseases.

Fibrotic diseases occur in a variety of organs and lead to continuous organ injury, function decline, and even failure. Currently effective treatment options are limited. Galectin-3 (Gal-3) is a pleiotropic lectin that plays an important role in cell proliferation, adhesion, differentiation, angiogenesis, and apoptosis. Accumulating evidence indicates that Gal-3 activates a variety of profibrotic factors, promotes fibroblast proliferation and transformation, and mediates collagen production. Recent studies have defined key roles for Gal-3 in fibrogenesis in diverse organ systems, including liver, kidney, lung, and myocardial. To help set the stage for future research, we review recent advances about the role played by Gal-3 in fibrotic diseases. Herein we discuss the potential profibrotic role of Gal-3, inhibition of which may represent a promising therapeutic strategy against tissue fibrosis.

Cyclic decidualization of the human endometrium in reproductive health and failure.

Decidualization denotes the transformation of endometrial stromal fibroblasts into specialized secretory decidual cells that provide a nutritive and immunoprivileged matrix essential for embryo implantation and placental development. In contrast to most mammals, decidualization of the human endometrium does not require embryo implantation. Instead, this process is driven by the postovulatory rise in progesterone levels and increasing local cAMP production. In response to falling progesterone levels, spontaneous decidualization causes menstrual shedding and cyclic regeneration of the endometrium. A growing body of evidence indicates that the shift from embryonic to maternal control of the decidual process represents a pivotal evolutionary adaptation to the challenge posed by invasive and chromosomally diverse human embryos. This concept is predicated on the ability of decidualizing stromal cells to respond to individual embryos in a manner that either promotes implantation and further development or facilitates early rejection. Furthermore, menstruation and cyclic regeneration involves stem cell recruitment and renders the endometrium intrinsically capable of adapting its decidual response to maximize reproductive success. Here we review the endocrine, paracrine, and autocrine cues that tightly govern this differentiation process. In response to activation of various signaling pathways and genome-wide chromatin remodeling, evolutionarily conserved transcriptional factors gain access to the decidua-specific regulatory circuitry. Once initiated, the decidual process is poised to transit through distinct phenotypic phases that underpin endometrial receptivity, embryo selection, and, ultimately, resolution of pregnancy. We discuss how disorders that subvert the programming, initiation, or progression of decidualization compromise reproductive health and predispose for pregnancy failure.

β-Arrestins regulate human cardiac fibroblast transformation and collagen synthesis in adverse ventricular remodeling

Cardiac fibroblasts (CFs) produce and degrade the myocardial extracellular matrix and are critical in maladaptive ventricular remodeling that can result in heart failure (HF). β-Arrestins are important signaling molecules involved in β-adrenergic receptor (β-AR) desensitization and can also mediate signaling in a G protein-independent fashion. We hypothesize that β-arrestins play an important role in the regulation of adult human CF biology with regard to myofibroblast transformation, increased collagen synthesis, and myocardial fibrosis which are important in the development of HF. β-Arrestin1 & 2 expression is significantly upregulated in adult human CF isolated from failing left ventricles and β-AR signaling is uncoupled with loss of β-agonist-mediated inhibition of collagen synthesis versus normal control CF. Knockdown of either β-arrestin1 or 2 restored β-AR signaling and β-agonist mediated inhibition of collagen synthesis. Overexpression of β-arrestins in normal CF led to a failing phenotype with increased baseline collagen synthesis, impaired β-AR signaling, and loss of β-agonist-mediated inhibition of collagen synthesis. β-Arrestin knockdown in failing CF diminished TGF-β stimulated collagen synthesis and also inhibited ERK phosphorylation. Overexpression of β-arrestins in normal CF increased basal ERK1/2 and Smad2/3 phosphorylation and enhanced TGF-β-stimulated collagen synthesis. This was prevented by pre-treatment with a MEK1/2 inhibitor. Enhanced β-arrestin signaling appears to be deleterious in CF by promoting a pro-fibrotic phenotype via uncoupling of β-AR signaling as well as potentiating ERK and Smad signaling. Targeted inhibition of β-arrestins in CF may represent a therapeutic strategy to prevent maladaptive myocardial fibrosis.

Concomitant inhibition of primary equine bronchial fibroblast proliferation and differentiation by selective β2-adrenoceptor agonists and dexamethasone

Altered airway cell proliferation plays an important role in the pathogenesis of human bronchial asthma and chronic obstructive pulmonary disease (COPD) as well as the equine recurrent airway obstruction (RAO) with consistent changes, i.e. narrowing the airway wall, explained by proliferation and differentiation of fibroblasts. In permanent cell lines, it has been suggested that β2-adrenoceptor agonists and glucocorticoids regulate cell proliferation via the β2-adrenoceptor pathway; indeed, no study was carried out in fresh isolated primary equine bronchial fibroblasts (EBF). We characterized the β-adrenoceptors in EBF, and compared effects of long-acting (clenbuterol) and short-acting (salbutamol and isoproterenol) β2-agonists and dexamethasone on proliferation, differentiation and collagen synthesis. High density (Bmax; 5037±494 sites/cell) of β2-adrenoceptor subtype was expressed in EBF. β2-agonists inhibited concentration-dependently EBF proliferation with potency of clenbuterol>salbutamol »isoproterenol which was inhibited by ICI 118.551 and propranolol but not by CGP 20712A. In contrast, dexamethasone alone inhibited less EBF proliferation, but the effect was high when dexamethasone was combined with β2-agonists. Transforming growth factor-β1 (TGF-β1) increased transformation of fibroblasts into myofibroblasts, which was inhibited by clenbuterol and dexamethasone alone and drug combination resulted in high inhibition rate. Collagen synthesis in EBF was rather hampered by dexamethasone than by β-agonists. Collectively, the expression of β2-adrenoceptor subtype in EBF and the anti-proliferative effect of clenbuterol suggest that β2-adrenoceptors are growth inhibitory and anti-fibrotic in EBF. These β2-agonist effects in EBF were synergistically enhanced by dexamethasone, providing the additive effects of glucocorticoids to counteract airway remodelling and morbidity of asthma and RAO.

Thrombospondin-1 repression is mediated via distinct mechanisms in fibroblasts and epithelial cells.

Tumor-associated angiogenesis is postulated to be regulated by the balance between pro- and anti-angiogenic factors. We demonstrate here that the critical step in establishing the angiogenic capability of human tumor cells is the repression of a key secreted anti-angiogenic factor, thrombospondin-1 (Tsp-1). This repression is essential for tumor formation by mammary epithelial cells and kidney cells engineered to express SV40 early region proteins, hTERT, and H-RasV12. In transformed epithelial cells, a signaling pathway leading from Ras to Tsp-1 repression induces the sequential activation of PI3 kinase, Rho and ROCK, leading to activation of Myc through phosphorylation, thereby enabling Myc to repress Tsp-1 transcription. In transformed fibroblasts, however, the repression of Tsp-1 can be achieved by an alternative mechanism involving inactivation of both p53 and pRb. We thus describe novel mechanisms by which the activation of oncogenes in epithelial cells and the inactivation of tumor suppressors in fibroblasts permits angiogenesis and, in turn, tumor formation.

The use of transformed IMR90 cell model to identify the potential extra-telomeric effects of hTERT in cell migration and DNA damage response.

BackgroundHuman telomerase reverse transcriptase (hTERT), the catalytic subunit of telomesase, is responsible for telomere maintenance and its reactivation is implicated in almost 90% human cancers. Recent evidences show that hTERT is essential for neoplastic transformation independent of its canonical function. However, the roles of hTERT in the process remain elusive. In the current work, we explore the extra-telomeric role of hTERT in the neoplastic transformation of fibroblast IMR90.ResultsHere we established transformed IMR90 cells by co-expression of three oncogenic factors, namely, H-Ras, SV40 Large-T antigen and hTERT (RSH). The RSH-transformed cells acquired hallmarks of cancer, such as they can grow under anchorage independent conditions; self-sufficient in growth signals; attenuated response to apoptosis; and possessed recurrent chromosomal abnormalities. Furthermore, the RSH-transformed cells showed enhanced migration capability which was also observed in IMR90 cells expressing hTERT alone, indicating that hTERT plays a role in cell migration, and thus possibly contribute to their metastatic potential during tumor transformation. This notion was further supported by our microarray analysis. In addition, we found that Ku70 were exclusively upregulated in both RSH-transformed IMR90 cells and hTERT-overexpressing IMR90 cells, suggesting the potential role of hTERT in DNA damage response (DDR).ConclusionsCollectively, our study revealed the extra-telomeric effects of hTERT in cell migration and DDR during neoplastic transformation.

Rho/Rock cross-talks with transforming growth factor-β/Smad pathway participates in lung fibroblast-myofibroblast differentiation.

The differentiation of fibroblasts, which are promoted by transforming growth factor-β (TGF-β)/Smad, is involved in the process of pulmonary fibrosis. The Rho/Rho-associated coiled-coil-forming protein kinase (Rock) pathway may regulate the fibroblast differentiation and myofibroblast expression of α-smooth muscle actin (α-SMA), however, the mechanism is not clear. The aim of the present study was to evaluate the role of Rho/Rock and TGF-β/Smad in TGF-β1-induced lung fibroblasts differentiation. Human embryonic lung fibroblasts were stimulated by TGF-β1, Y-27632 (inhibitor of Rho/Rock signaling) and staurosporine (inhibitor of TGF-β/Smad signaling). The α-SMA expression, cell cycle progression, content of the extracellular matrix (ECM) in cell culture supernatants and the expression of RhoA, RhoC, Rock1 and Smad2 were detected. The results demonstrated that α-SMA-positive cells significantly increased following TGF-β1 stimulation. Rho/Rock and TGF-β/Smad inhibitors suppressed TGF-β1-induced lung fibroblast differentiation. The inhibitors increased G0/G1 and decreased S and G2/M percentages. The concentrations of the ECM proteins in the supernatant were significantly increased by TGF-β1 stimulation, whereas they were decreased by inhibitor stimulation. RhoA, RhoC, Rock1, Smad2 and tissue inhibitor of metalloproteinase-1 were upregulated by TGF-β1 stimulation. The Rho/Rock inhibitor downregulated Smad2 expression and the TGF-β/Smad inhibitor downregulated RhoA, RhoC and Rock1 expression. Therefore, the Rho/Rock pathway and Smad signaling were involved in the process of lung fibroblasts transformation, induced by TGF-β1, to myofibroblasts. The two pathways may undergo cross-talk in the lung fibroblasts differentiation in vitro.

Phosphorylation of Dok1 by Abl family kinases inhibits CrkI transforming activity.

The Crk SH2/SH3 adaptor and the Abl nonreceptor tyrosine kinase were first identified as oncoproteins, and both can induce tumorigenesis when overexpressed or mutationally activated. We previously reported the surprising finding that inhibition or knockdown of Abl family kinases enhanced transformation of mouse fibroblasts by CrkI. Abl family inhibitors are currently used or are being tested for treatment of human malignancies, and our finding raised concerns that such inhibitors might actually promote the growth of tumors overexpressing CrkI. Here, we identify the Dok1 adaptor as the key effector for the enhancement of CrkI transformation by Abl inhibition. We show that phosphorylation of tyrosines 295 and 361 of Dok1 by Abl family kinases suppresses CrkI transforming activity, and that upon phosphorylation these tyrosines bind the SH2 domains of the Ras inhibitor p120 RasGAP. Knockdown of RasGAP resulted in a similar enhancement of CrkI transformation, consistent with a critical role for Ras activity. Imaging studies using a FRET sensor of Ras activation revealed alterations in the localization of activated Ras in CrkI-transformed cells. Our results support a model in which Dok1 phosphorylation normally suppresses localized Ras pathway activity in Crk-transformed cells via recruitment and/or activation of RasGAP, and that preventing this negative feedback mechanism by inhibiting Abl family kinases leads to enhanced transformation by Crk.

Targeted injection of a biocomposite material alters macrophage and fibroblast phenotype and function following myocardial infarction: relation to left ventricular remodeling.

A treatment target for progressive left ventricular (LV) remodeling prevention following myocardial infarction (MI) is to affect structural changes directly within the MI region. One approach is through targeted injection of biocomposite materials, such as calcium hydroxyapatite microspheres (CHAM), into the MI region. In this study, the effects of CHAM injections upon key cell types responsible for the MI remodeling process, the macrophage and fibroblast, were examined. MI was induced in adult pigs before randomization to CHAM injections (20 targeted 0.1-ml injections within MI region) or saline. At 7 or 21 days post-MI (n = 6/time point per group), cardiac magnetic resonance imaging was performed, followed by macrophage and fibroblast isolation. Isolated macrophage profiles for monocyte chemotactic macrophage inflammatory protein-1 as measured by real-time polymerase chain reaction increased at 7 days post-MI in the CHAM group compared with MI only (16.3 ± 6.6 versus 1.7 ± 0.6 cycle times values, P < 0.05), and were similar by 21 days post-MI. Temporal changes in fibroblast function and smooth muscle actin (SMA) expression relative to referent control (n = 5) occurred with MI. CHAM induced increases in fibroblast proliferation, migration, and SMA expression-indicative of fibroblast transformation. By 21 days, CHAM reduced LV dilation (diastolic volume: 75 ± 2 versus 97 ± 4 ml) and increased function (ejection fraction: 48 ± 2% versus 38 ± 2%) compared with MI only (both P < 0.05). This study identified that effects on macrophage and fibroblast differentiation occurred with injection of biocomposite material within the MI, which translated into reduced adverse LV remodeling. These unique findings demonstrate that biomaterial injections impart biologic effects upon the MI remodeling process over any biophysical effects.

101: SWAP-70 is required for spontaneous transformation of mouse embryo fibroblasts

101: SWAP-70 is required for spontaneous transformation of mouse embryo fibroblasts