Tgfbeta signaling directly induces Arf promoter remodeling by a mechanism involving Smads 2/3 and p38 MAPK

Methyltransferase Inhibition Enables Tgf Driven Induction of CDKN2A and B in Cancer Cells

CDKN2A/B deletion or silencing is common across human cancer, reinforcing the general importance of bypassing its tumor suppression in cancer formation or progression. In rhabdomyosarcoma (RMS) and neuroblastoma, two common childhood cancers, the three CDKN2A/B transcripts are independently expressed to varying degrees, but one, ARF, is uniformly silenced. Although TGFβ induces certain CDKN2A/B transcripts in HeLa cells, it was unable to do so in five tested RMS lines unless the cells were pretreated with a broadly acting methyltransferase inhibitor, DZNep, or one targeting EZH2. CDKN2A/B induction by TGFβ correlated with de novo appearance of three H3K27Ac peaks within a 20 kb cis element ∼150 kb proximal to CDKN2A/B. Deleting that segment prevented their induction by TGFβ but not a basal increase driven by methyltransferase inhibition alone. Expression of two CDKN2A/B transcripts was enhanced by dCas9/CRISPR activation targeting either the relevant promoter or the 20 kb cis elements, and this "precise" manipulation diminished RMS cell propagation in vitro. Our findings show crosstalk between methyltransferase inhibition and TGFβ-dependent activation of a remote enhancer to reverse CDKN2A/B silencing. Though focused on CDKN2A/B here, such crosstalk may apply to other TGFβ-responsive genes and perhaps govern this signaling protein's complex effects promoting or blocking cancer.

Transcriptional regulation of INK4/ARF locus by cis and trans mechanisms

9p21 locus is one of the most reproducible regions in genome-wide association studies (GWAS). The region harbors CDKN2A/B genes that code for p16INK4a, p15INK4b, and p14ARF proteins, and it also harbors a long gene desert adjacent to these genes. The polymorphisms that are associated with several diseases and cancers are present in these genes and the gene desert region. These proteins are critical cell cycle regulators whose transcriptional dysregulation is strongly linked with cellular regeneration, stemness, aging, and cancers. Given the importance of this locus, intense scientific efforts on understanding the regulation of these genes via promoter-driven mechanisms and recently, via the distal regulatory mechanism have provided major insights. In this review, we describe these mechanisms and propose the ways by which this locus can be targeted in pathologies and aging.

Exon skipping in genes encoding lineage-defining myogenic transcription factors in rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is a childhood sarcoma composed of myoblast-like cells, which suggests a defect in terminal skeletal muscle differentiation. To explore potential defects in the differentiation program, we searched for mRNA splicing variants in genes encoding transcription factors driving skeletal muscle lineage commitment and differentiation. We studied two RMS cases and identified altered splicing resulting in "skipping" the second of three exons in MYOD1. RNA-Seq data from 42 tumors and additional RMS cell lines revealed exon 2 skipping in both MYOD1 and MYF5 but not in MYF6 or MYOG. Complementary molecular analysis of MYOD1 mRNA found evidence for exon skipping in 5 additional RMS cases. Functional studies showed that so-called MYODΔEx2 protein failed to robustly induce muscle-specific genes, and its ectopic expression conferred a selective advantage in cultured fibroblasts and an RMS xenograft. In summary, we present previously unrecognized exon skipping within MYOD1 and MYF5 in RMS, and we propose that alternative splicing can represent a mechanism to alter the function of these two transcription factors in RMS.

Identification of Paxillin as a Prognostic Factor for Glioblastoma via Integrated Bioinformatics Analysis

Glioblastoma (GBM) is the most prevalent and aggressive type of brain tumor in the central nervous system. Clinical outcomes for patients with GBM are unsatisfactory. Here, we aimed to identify novel, reliable prognostic factors for GBM. Cox and interactive analyses were used to identify hub genes from The Cancer Genome Atlas and the Chinese Glioma Genome Atlas datasets. After validation using various cohorts, survival analysis, meta-analysis, and prognostic analysis were performed. Coexpression and enrichment analyses were performed to elucidate the biological pathways of hub genes involved in GBM. ESTIMATE and CIBERSORT methods were applied to analyze the association of hub genes with the tumor microenvironment (TME). Paxillin (PXN) was identified as a hub gene with a high expression in GBM. PXN expression was negatively correlated with overall survival, progression-free survival, and disease-free survival in patients with GBM. Meta-analysis and Cox analysis revealed that PXN could act as an independent prognostic factor in GBM. In addition, PXN was significantly coexpressed with signal transducer and activator of transcription 3 and transforming growth factor β1 and participated in focal adhesion, extracellular matrix/receptor interactions, and the phosphatidylinositol 3-kinase/AKT signaling pathway. The results of ESTIMATE and CIBERSORT analyses revealed that PXN was implicated in TME alterations, particularly the infiltration of regulatory T cells, activated memory T cells, and activated natural killer cells. PXN may be a reliable prognostic factor for GBM. Further studies are needed to validate these findings.

HaCaT‑conditioned medium supplemented with the small molecule inhibitors SB431542 and CHIR99021 and the growth factor PDGF‑AA prevents the dedifferentiation of dermal papilla cells in vitro

Hair loss, including alopecia, is a common and distressing problem for men and women, and as a result, there is considerable interest in developing treatments that can prevent or reverse hair loss. Dermal papillae closely interact with epidermal cells and play a key role during hair follicle induction and hair morphogenesis. As dermal papilla cells (DPCs) lose their hair‑inducing ability in monolayer cultures in vitro, it is difficult to obtain de novo hair follicle structures following DPC transplantation in vivo. The present study aimed to explore culture conditions to maintain DPC characteristics using conditioned media (CM) from the supernatant of cultured HaCaT keratinocyte cells supplemented with other components. Initially, it was observed that during passaging of in vitro monolayer DPC cultures, the Wnt/β‑catenin pathway was repressed, while the TGF‑β/Smad pathway was activated, and that HaCaT cells cultivated in 1% fetal bovine serum had higher levels of expression of Wnt3a and Wnt10b compared with normal keratinocytes. Culturing of high‑passage (P7) DPCs in CM from HaCaT cells (HaCaT‑CM) actively stimulated cell proliferation and maintained Sox2 and Versican expression levels. Supplementation of HaCaT‑CM with SB431542 (SB, a TGF‑β receptor inhibitor), CHIR99021, (CHIR, a GSK3α/β inhibitor and activator of Wnt signaling) and platelet‑derived growth factor (PDGF)‑AA further increased the expression levels of Sox2, Versican and alkaline phosphatase (ALP) in P7 DPCs. Three‑dimensional culture of P7 DPCs using hanging drop cultures in HaCaT‑CM supplemented with SB, CHIR and PDGF‑AA resulted in larger cell aggregates and a further significant upregulation of Sox2, ALP and Versican expression levels. Taken together, these findings demonstrated that HaCaT‑CM supplemented with SB, CHIR and PDGF‑AA may preserve the hair‑inducing ability of high‑passage DPCs and may therefore be useful in reconstructing new hair follicles in vivo.

Post-Translational Regulation of ARF: Perspective in Cancer

Tumorigenesis can be induced by various stresses that cause aberrant DNA mutations and unhindered cell proliferation. Under such conditions, normal cells autonomously induce defense mechanisms, thereby stimulating tumor suppressor activation. ARF, encoded by the CDKN2a locus, is one of the most frequently mutated or deleted tumor suppressors in human cancer. The safeguard roles of ARF in tumorigenesis are mainly mediated via the MDM2-p53 axis, which plays a prominent role in tumor suppression. Under normal conditions, low p53 expression is stringently regulated by its target gene, MDM2 E3 ligase, which induces p53 degradation in a ubiquitin-proteasome-dependent manner. Oncogenic signals induced by MYC, RAS, and E2Fs trap MDM2 in the inhibited state by inducing ARF expression as a safeguard measure, thereby activating the tumor-suppressive function of p53. In addition to the MDM2-p53 axis, ARF can also interact with diverse proteins and regulate various cellular functions, such as cellular senescence, apoptosis, and anoikis, in a p53-independent manner. As the evidence indicating ARF as a key tumor suppressor has been accumulated, there is growing evidence that ARF is sophisticatedly fine-tuned by the diverse factors through transcriptional and post-translational regulatory mechanisms. In this review, we mainly focused on how cancer cells employ transcriptional and post-translational regulatory mechanisms to manipulate ARF activities to circumvent the tumor-suppressive function of ARF. We further discussed the clinical implications of ARF in human cancer.

Bayesian Modeling Identifies PLAG1 as a Key Regulator of Proliferation and Survival in Rhabdomyosarcoma Cells

We recently developed a novel computational algorithm that incorporates Bayesian methodology to identify rhabdomyosarcoma disease genes whose expression level correlates with copy-number variations, and we identified PLAG1 as a candidate oncogenic driver. Although PLAG1 has been shown to contribute to other type of cancers, its role in rhabdomyosarcoma has not been elucidated. We observed that PLAG1 mRNA is highly expressed in rhabdomyosarcoma and is associated with PLAG1 gene copy-number gain. Knockdown of PLAG1 dramatically decreased cell accumulation and induced apoptosis in rhabdomyosarcoma cells, whereas its ectopic expression increased cell accumulation in vitro and as a xenograft and promoted G₁ to S-phase cell-cycle progression. We found that PLAG1 regulates IGF2 expression and influences AKT and MAPK pathways in rhabdomyosarcoma, and IGF2 partially rescues cell death triggered by PLAG1 knockdown. The expression level of PLAG1 correlated with the IC₅₀ of rhabdomyosarcoma cells to BMS754807, an IGF receptor inhibitor. IMPLICATIONS: Our data demonstrate that PLAG1 contributes to proliferation and survival of rhabdomyosarcoma cells at least partially by inducing IGF2, and this new understanding may have the potential for clinical translation.

Testis-specific Arf promoter expression in a transposase-aided BAC transgenic mouse model

CDKN2A is an evolutionarily conserved gene encoding proteins implicated in tumor suppression, ocular development, aging, and metabolic diseases. Like the human form, mouse Cdkn2a encodes two distinct proteins-p16^Ink4a, which blocks cyclin-dependent kinase activity, and p19^Arf, which is best known as a positive regulator of the p53 tumor suppressor-and their functions have been well-studied in genetically engineered mouse models. Relatively little is known about how expression of the two transcripts is controlled in normal development and in certain disease states. To better understand their coordinate and transcript-specific expression in situ, we used a transposase-aided approach to generate a new BAC transgenic mouse model in which the first exons encoding Arf and Ink4a are replaced by fluorescent reporters. We show that mouse embryo fibroblasts generated from the transgenic lines faithfully display induction of each transgenic reporter in cell culture models, and we demonstrate the expected expression of the Arf reporter in the normal testis, one of the few places where that promoter is normally expressed. Interestingly, the TGFβ-2-dependent induction of the Arf reporter in the eye-a process essential for normal eye development-does not occur. Our findings illustrate the value of BAC transgenesis in mapping key regulatory elements in the mouse by revealing the genomic DNA required for Cdkn2a induction in cultured cells and the developing testis, and the apparent lack of elements driving expression in the developing eye.

Identification of De Novo Enhancers Activated by TGFβ to Drive Expression of CDKN2A and B in HeLa Cells

Disruption of the CDKN2A (INK4A/ARF) and B (INK4B) genes, which encode three function-independent tumor suppressors, is one of the most common events in human cancer. Because their relative importance in tumor prevention appears to be species- and context-specific, studying their regulation can shed light on mechanisms by which they are bypassed in malignant transformation. We previously unveiled a new pathway in which TGFβ selectively induces Arf at mouse Cdkn2a in eye development and cultured fibroblasts. As TGFβ signaling is often derailed in cancer development or progression, we investigated its control of CDKN2A/B in human cancer. Computational analyses of sequencing and array data from nearly 11,000 patients with cancer in TCGA showed discordant expression of ARF and INK4A in most cancer subtypes, with gene copy-number loss and promoter methylation involved in only a subset. Using HeLa cells as a model, we found that exogenous TGFβ induced ARF mRNA and protein, and ARF knockdown limited TGFβ-mediated growth suppression. TGFβ-mediated ARF mRNA induction required SMAD2/3, p38MAPK, and SP1, and ARF mRNA was induced without added RNAPII recruitment. Chromatin immunoprecipitation unveiled a remote enhancer element engaged by TGFβ by a mechanism that partially depended on p38MAPK. CRISPR-based editing of this enhancer limited induction of ARF and INK4B by TGFβ, but not by oncogenic RAS. IMPLICATIONS: Our findings reveal new molecular mechanisms by which CDKN2A/B regulation is coupled to external cues, and those findings represent entry points to further explore pharmacologic strategies to restore their expression in cancer.

ARF promotes the degradation of the Epidermal Growth Factor Receptor by the lysosome

Epidermal Growth Factor Receptor (EGFR) signaling regulates multiple cellular processes including proliferation, survival and apoptosis, and is attenuated by lysosomal receptor degradation. EGFR is a potent oncogene and activating mutations of EGFR are critical determinants of oncogenic transformation as well as therapeutic targets in non-small cell lung cancer. We previously demonstrated that wild type and mutant EGFRs repress the expression of the ARF tumor suppressor to promote the survival of lung tumor cells. In this study, using transient transfection systems in CHO EGFR-null cells as well as in various lung tumor cell lines carrying wild type or activated mutant EGFR, we show that ARF downregulates the expression of EGFR protein by reducing its half life. In wild type EGFR cells, ARF promotes canonical lysosomal degradation of the receptor through enhanced phosphorylation of EGFR-Y1045 and Cbl-Y731. In contrast, in mutant EGFR cells, ARF induces EGFR degradation by activating a non-canonical AKT-dependent lysosomal pathway. Taken together, these results uncover a feedback loop by which ARF may control EGFR turnover to restrain oncogenic signaling. They also highlight distinct degradation promoting pathways between wild type and mutant EGFRs in response to ARF.

Regulatory Network of ARF in Cancer Development

ARF is a tumor suppressor protein that has a pivotal role in the prevention of cancer development through regulating cell proliferation, senescence, and apoptosis. As a factor that induces senescence, the role of ARF as a tumor suppressor is closely linked to the p53-MDM2 axis, which is a key process that restrains tumor formation. Thus, many cancer cells either lack a functional ARF or p53, which enables them to evade cell oncogenic stress-mediated cycle arrest, senescence, or apoptosis. In particular, the ARF gene is a frequent target of genetic and epigenetic alterations including promoter hyper-methylation or gene deletion. However, as many cancer cells still express ARF, pathways that negatively modulate transcriptional or post-translational regulation of ARF could be potentially important means for cancer cells to induce cellular proliferation. These recent findings of regulators affecting ARF protein stability along with its low levels in numerous human cancers indicate the significance of an ARF post-translational mechanism in cancers. Novel findings of regulators stimulating or suppressing ARF function would provide new therapeutic targets to manage cancer- and senescence-related diseases. In this review, we present the current knowledge on the regulation and alterations of ARF expression in human cancers, and indicate the importance of regulators of ARF as a prognostic marker and in potential therapeutic strategies.

Aberrant Expression of p14ARF in Human Cancers: A New Biomarker?

The ARF and INK4a genes are located on the CDKN2a locus, both showing tumor suppressive activity. ARF has been shown to monitor potentially harmful oncogenic signalings, making early stage cancer cells undergo senescence or programmed cell death to prevent cancer. Conversely, INK4a detects both aging and incipient cancer cell signals, and thus these two gene functions are different. The efficiency of detection of oncogenic signals is more efficient for the for the former than the latter in the mouse system. Both ARF and INK4a genes are inactivated by gene deletion, promoter methylation, frame shift, aberrant splicing although point mutations for the coding region affect only the latter. Recent studies show the splicing alterations that affect only ARF or both ARF and INK4a genes suggesting that ARF is inactivated in human tumors more frequently than what was previously thought. The ARF gene is activated by E2Fs and Dmp1 transcription factors while it is repressed by Bmi1, Tbx2/3, Twist1, and Pokemon nuclear proteins. It is also regulated at protein levels by Arf ubiquitin ligase named ULF, MKRN1, and Siva1. The prognostic value of ARF overexpression is controversial since it is induced in early stage cancer cells to eliminate pre-malignant cells (better prognosis); however, it may also indicate that the tumor cells have mutant p53 associated with worse prognosis. The ARF tumor suppressive protein can be used as a biomarker to detect early stage cancer cells as well as advanced stage tumors with p53 inactivation.

Dynamics of ARF regulation that control senescence and cancer

ARF is an alternative reading frame product of the INK4a/ARF locus, inactivated in numerous human cancers. ARF is a key regulator of cellular senescence, an irreversible cell growth arrest that suppresses tumor cell growth. It functions by sequestering MDM2 (a p53 E3 ligase) in the nucleolus, thus activating p53. Besides MDM2, ARF has numerous other interacting partners that induce either cellular senescence or apoptosis in a p53-independent manner. This further complicates the dynamics of the ARF network. Expression of ARF is frequently disrupted in human cancers, mainly due to epigenetic and transcriptional regulation. Vigorous studies on various transcription factors that either positively or negatively regulate ARF transcription have been carried out. However, recent focus on posttranslational modifications, particularly ubiquitination, indicates wider dynamic controls of ARF than previously known. In this review, we discuss the role and dynamic regulation of ARF in senescence and cancer.

The epigenetic modifier JMJD6 is amplified in mammary tumors and cooperates with c-Myc to enhance cellular transformation, tumor progression, and metastasis

Background

Oncogene overexpression in primary cells often triggers the induction of a cellular safeguard response promoting senescence or apoptosis. Secondary cooperating genetic events are generally required for oncogene-induced tumorigenesis to overcome these biologic obstacles. We employed comparative genomic hybridization for eight genetically engineered mouse models of mammary cancer to identify loci that might harbor genes that enhance oncogene-induced tumorigenesis.

Results

Unlike many other mammary tumor models, the MMTV-Myc tumors displayed few copy number variants except for amplification of distal mouse chromosome 11 in 80 % of the tumors (syntenic to human 17q23-qter often amplified in human breast cancer). Analyses of candidate genes located in this region identified JMJD6 as an epigenetic regulatory gene that cooperates with Myc to enhance tumorigenesis. It suppresses Myc-induced apoptosis under varying stress conditions through inhibition of p19ARF messenger RNA (mRNA) and protein, leading to reduced levels of p53. JMJD6 binds to the p19ARF promoter and exerts its inhibitory function through demethylation of H4R3me2a. JMJD6 overexpression in MMTV-Myc cell lines increases tumor burden, induces EMT, and greatly enhances tumor metastasis. Importantly, we demonstrate that co-expression of high levels of JMJD6 and Myc is associated with poor prognosis for human ER+ breast cancer patients.

Conclusions

A novel epigenetic mechanism has been identified for how JMJD6 cooperates with Myc during oncogenic transformation. Combined high expression of Myc and JMJD6 confers a more aggressive phenotype in mouse and human tumors. Given the pleiotropic pro-tumorigenic activities of JMJD6, it may be useful as a prognostic factor and a therapeutic target for Myc-driven mammary tumorigenesis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13148-016-0205-6) contains supplementary material, which is available to authorized users.

Acute Effects of Transforming Growth Factor-β1 on Neuronal Excitability and Involvement in the Pain of Rats with Chronic Pancreatitis

Background/Aims

This study was to investigate whether transforming growth factor-β1 (TGF-β1) plays a role in hyperalgesia in chronic pancreatitis (CP) and the underlying mechanisms.

Methods

CP was induced in male adult rats by intraductal injection of trinitrobenzene sulfonic acid (TNBS). Abdominal hyperalgesia was assessed by referred somatic behaviors to mechanical stimulation of rat abdomen. Dil dye injected into the pancreas was used to label pancreas-specific dorsal root ganglion (DRG) neurons. Whole cell patch clamp recordings and calcium imaging were performed to examine the effect of TGF-β1 on acutely isolated pancreas-specific DRG neurons. Western blot analysis was carried out to measure the expression of TGF-β1 and its receptors.

Results

TNBS injection significantly upregulated expression of TGF-β1 in the pancreas and DRGs, and TGF-β1 receptors in DRGs (T9-T13) in CP rats. Intrathecal injection of TGF-β receptor I antagonist SB431542 attenuated abdominal hyperalgesia in CP rats. TGF-β1 application depolarized the membrane potential and caused firing activity of DRG neurons. TGF-β1 application also reduced rheobase, hyperpolarized action potential threshold, and increased numbers of action potentials evoked by current injection of pancreas-specific DRG neurons. TGF-β1 application also increased the concentration of intracellular calcium of DRG neurons, which was inhibited by SB431542. Furthermore, intrathecal injection of TGF-β1 produced abdominal hyperalgesia in healthy rats.

Conclusions

These results suggest that TGF-β1 enhances neuronal excitability and increases the concentration of intracellular calcium. TGF-β1 and its receptors are involved in abdominal hyperalgesia in CP. This and future study might identify a potentially novel target for the treatment of abdominal pain in CP.

p19(Arf) limits primary vitreous cell proliferation driven by PDGF-B

Arf encodes an important tumor suppressor, p19(Arf), which also plays a critical role to control hyperplasia in the primary vitreous during mouse eye development. In the absence of Arf, mice are born blind and display a phenotype closely mimicking severe forms of the human eye disease, persistent hyperplastic primary vitreous (PHPV). In this report, we characterize p19(Arf) expression in perivascular cells that normally populate the primary vitreous and express the Arf promoter. Using a new ex vivo model, we show that these cells respond to exogenous Tgfβ, despite being isolated at a time when Tgfβ has already turned on the Arf promoter. Treatment of the cells with PDGF-B ligand doubles the population of cells in S-phase and ectopic expression of Arf blunts that effect. We show this effect is mediated through Pdgfrβ as expression of Arf represses expression of Pdgfrβ mRNA and protein to approximately 60%. p53 is not required for Arf-dependent blockade of PDGF-B driven proliferation and repression of Pdgfrβ protein as ectopic expression of Arf is still able to inhibit the 2-fold increase in the S-phase fraction of cells upon treatment with PDGF-B. Finally, induction of mature miR-34a, a microRNA previously identified to be regulated by p19(Arf) does not depend on p53 while the expression of the primary transcript does require p53. These data corroborate that, as in vivo, p19(Arf) functions to inhibit PDGF-B driven proliferation ex vivo.

Upregulation of cell proliferation via Shc and ERK1/2 MAPK signaling in SaOS-2 osteoblasts grown on magnesium alloy surface coating with tricalcium phosphate

Magnesium (Mg) alloys have been demonstrated to be viable orthopedic implants because of mechanical and biocompatible properties similar to natural bone. In order to improve its osteogenic properties, a porous β-tricalcium phosphate (β-TCP) was coated on the Mg-3AI-1Zn alloy by alkali-heat treatment technique. The human bone-derived cells (SaOS-2) were cultured on (β-TCP)-Mg-3AI-1Zn in vitro, and the osteoblast response, the morphology and the elements on this alloy surface were investigated. Also, the regulation of key intracellular signalling proteins was investigated in the SaOS-2 cells cultured on alloy surface. The results from scanning electron microscope and immunofluorescence staining demonstrated that (β-TCP)-Mg-3AI-1Zn induced significant osteogenesis. SaOS-2 cell proliferation was improved by β-TCP coating. Moreover, the (β-TCP)-Mg-3AI-1Zn surface induced activation of key intracellular signalling proteins in SaOS-2 cells. We observed an enhanced activation of Src homology and collagen (Shc), a common point of integration between bone morphogenetic protein 2, and the Ras/mitogen-activated protein kinase (MAPK) pathway. ERK1/2 MAP kinase activation was also upregulated, suggesting a role in mediating osteoblastic cell interactions with biomaterials. The signalling pathway involving c-fos (member of the activated protein-1) was also shown to be upregulated in osteoblasts cultured on the (β-TCP)-Mg-3AI-1Zn. These results suggest that β-TCP coating may contribute to successful osteoblast function on Mg alloy surface. (β-TCP)-Mg-3AI-1Zn may upregulate cell proliferation via Shc and ERK1/2 MAPK signaling in SaOS-2 osteoblasts grown on Mg alloy surface.

miR-27 negatively regulates pluripotency-associated genes in human embryonal carcinoma cells

Human embryonic stem cells and human embryonal carcinoma cells have been studied extensively with respect to the transcription factors (OCT4, SOX2 and NANOG), epigenetic modulators and associated signalling pathways that either promote self-renewal or induce differentiation in these cells. The ACTIVIN/NODAL axis (SMAD2/3) of the TGFß signalling pathway coupled with FGF signalling maintains self-renewal in these cells, whilst the BMP (SMAD1,5,8) axis promotes differentiation. Here we show that miR-27, a somatic-enriched miRNA, is activated upon RNAi-mediated suppression of OCT4 function in human embryonic stem cells. We further demonstrate that miR-27 negatively regulates the expression of the pluripotency-associated ACTIVIN/NODAL axis (SMAD2/3) of the TGFß signalling pathway by targeting ACVR2A, TGFßR1 and SMAD2. Additionally, we have identified a number of pluripotency-associated genes such as NANOG, LIN28, POLR3G and NR5A2 as novel miR-27 targets. Transcriptome analysis revealed that miR-27 over-expression in human embryonal carcinoma cells leads indeed to a significant up-regulation of genes involved in developmental pathways such as TGFß- and WNT-signalling.

Isolation and characterization of mammalian cells expressing the Arf promoter during eye development

Although many researchers have successfully uncovered novel functions of the tumor suppressor p19(Arf) utilizing various types of cultured cancer cells and immortalized fibroblasts, these systems do not accurately reflect the endogenous environment in which Arf is developmentally expressed. We addressed this by isolating perivascular cells (PVCs) from the primary vitreous of the mouse eye. This rare cell type normally expresses the p19(Arf) tumor suppressor in a non-pathological, developmental context. We utilized fluorescence activated cell sorting (FACS) to purify the cells by virtue of a GFP reporter driven by the native Arf promoter and then characterized their morphology and gene expression pattern. We further examined the effects of reintroduction of Arf expression in the Arf(GFP/GFP) PVCs to verify expected downstream effectors of p19(Arf) as well as uncover novel functions of Arf as a regulator of vasculogenesis. This methodology and cell culture model should serve as a useful tool to examine p19(Arf) biology.

Varied manifestations of persistent hyperplastic primary vitreous with graded somatic mosaic deletion of a single gene

PURPOSE

Persistent hyperplastic primary vitreous (PHPV) represents a developmental eye disease known to have diverse manifestations ranging from a trivial remnant of hyaloid vessels to a dense fibrovascular mass causing lens opacity and retinal detachment. PHPV can be modeled in mice lacking individual genes, but certain features of such models differ from the clinical realm. For example, mice lacking the Arf gene have uniformly severe disease with consistent autosomal recessive disease penetrance. We tested whether the graded somatic loss of Arf in a subset of cells in chimeric mice mimics the range of disease in a non-heritable manner.

METHODS

Wild type ↔ Arf(-/-) mouse chimeras were generated by morulae fusion, and when the mice were 10 weeks old, fundoscopic, slit-lamp, and histological evaluations were performed. The relative fraction of cells of the Arf(-/-) lineage was assessed with visual, molecular genetic, and histological analysis. Objective quantification of various aspects of the phenotype was correlated with the genotype.

RESULTS

Sixteen chimeras were generated and shown to have low, medium, and high contributions of Arf(-/-) cells to tail DNA, the cornea, and the retinal pigment epithelium (RPE), with excellent correlation between chimerism in the tail DNA and the RPE. Phenotypic differences (coat color and severity of eye disease) were evident, objectively quantified, and found to correlate with the contribution of Arf(-/-) cells to the RPE and tail-derived DNA, but not the cornea.

CONCLUSIONS

Generating animals composed of different numbers of Arf(-/-) cells mimicked the range of disease severity observed in patients with PHPV. This establishes the potential for full manifestations of PHPV to be caused by somatic mutations of a single gene during development.

Arf induction by Tgfβ is influenced by Sp1 and C/ebpβ in opposing directions

Recent studies show that Arf, a bona fide tumor suppressor, also plays an essential role during mouse eye development. Tgfβ is required for Arf promoter activation in developing mouse eyes, and its capacity to induce Arf depends on Smads 2/3 as well as p38 Mapk. Substantial delay between activation of these pathways and increased Arf transcription imply that changes in the binding of additional transcription factors help orchestrate changes in Arf expression. Focusing on proteins with putative DNA binding elements near the mouse Arf transcription start, we now show that Tgfβ induction of this gene correlated with decreased expression and DNA binding of C/ebpβ to the proximal Arf promoter. Ectopic expression of C/ebpβ in mouse embryo fibroblasts (MEFs) blocked Arf induction by Tgfβ. Although basal levels of Arf mRNA were increased by C/ebpβ loss in MEFs and in the developing eye, Tgfβ was still able to increase Arf, indicating that derepression was not the sole factor. Chromatin immunoprecipitation (ChIP) assay showed increased Sp1 binding to the Arf promotor at 24 and 48 hours after Tgfβ treatment, at which time points Arf expression was significantly induced by Tgfβ. Chemical inhibition of Sp1 and its knockdown by RNA interference blocked Arf induction by Tgfβ in MEFs. In summary, our results indicate that C/ebpβ and Sp1 are negative and positive Arf regulators that are influenced by Tgfβ.

A distant, cis-acting enhancer drives induction of Arf by Tgfβ in the developing eye

The Arf tumor suppressor represents one of several genes encoded at the Cdkn2a and Cdkn2b loci in the mouse. Beyond its role blunting the growth of incipient cancer cells, the Arf gene also plays an essential role in development: its gene product, p19(Arf), is induced by Tgfβ2 in the developing eye to dampen proliferative signals from Pdgfrβ, which effect ultimately fosters the vascular remodeling required for normal vision in the mouse. Mechanisms underlying Arf induction by Tgfβ2 are not fully understood. Using the chr4(Δ70 kb/Δ70 kb) mouse, we now show that deletion of the coronary artery disease (CAD) risk interval lying upstream of the Cdkn2a/b locus represses developmentally-timed induction of Arf resulting in eye disease mimicking the persistent hyperplastic primary vitreous (PHPV) found in Arf-null mice and in children. Using mouse embryo fibroblasts, we demonstrate that Arf induction by Tgfβ is blocked in cis to the 70 kb deletion, but Arf induction by activated RAS and cell culture "shock" is not. Finally, we show that Arf induction by Tgfβ is derailed by preventing RNA polymerase II recruitment following Smad 2/3 binding to the promoter. These findings provide the first evidence that the CAD risk interval, located at a distance from Arf, acts as a cis enhancer of Tgfβ2-driven induction of Arf during development.

TGF-β-operated growth inhibition and translineage commitment into smooth muscle cells of periodontal ligament-derived endothelial progenitor cells through Smad- and p38 MAPK-dependent signals

The periodontal ligament (PDL) is a fibrous connective tissue that attaches the tooth to the alveolar bone. We previously demonstrated the ability of PDL fibroblast-like cells to construct an endothelial cell (EC) marker-positive blood vessel-like structure, indicating the potential of fibroblastic lineage cells in PDL tissue as precursors of endothelial progenitor cells (EPCs) to facilitate the construction of a vascular system around damaged PDL tissue. A vascular regeneration around PDL tissue needs proliferation of vascular progenitor cells and the subsequent differentiation of the cells. Transforming growth factor-β (TGF-β) is known as an inducer of endothelial-mesenchymal transition (EndMT), however, it remains to be clarified what kinds of TGF-β signals affect growth and mesenchymal differentiation of PDL-derived EPC-like fibroblastic cells. Here, we demonstrated that TGF-β1 not only suppressed the proliferation of the PDL-derived EPC-like fibroblastic cells, but also induced smooth muscle cell (SMC) markers expression in the cells. On the other hand, TGF-β1 stimulation suppressed EC marker expression. Intriguingly, overexpression of Smad7, an inhibitor for TGF-β-induced Smad-dependent signaling, suppressed the TGF-β1-induced growth inhibition and SMC markers expression, but did not the TGF-β1-induced downregulation of EC marker expression. In contrast, p38 mitogen-activated protein kinase (MAPK) inhibitor SB 203580 suppressed the TGF-β1-induced downregulation of EC marker expression. In addition, the TGF-β1-induced SMC markers expression of the PDL-derived cells was reversed upon stimulation with fibroblast growth factor (FGF), suggesting that the TGF-β1 might not induce terminal SMC differentiation of the EPC-like fibroblastic cells. Thus, TGF-β1 not only negatively controls the growth of PDL-derived EPC-like fibroblastic cells via a Smad-dependent manner but also positively controls the SMC-differentiation of the cells possibly at the early stage of the translineage commitment via Smad- and p38 MAPK-dependent manners.

p19Arf represses platelet-derived growth factor receptor β by transcriptional and posttranscriptional mechanisms

In addition to cancer surveillance, p19(Arf) plays an essential role in blocking signals stemming from platelet-derived growth factor receptor β (Pdgfrβ) during eye development, but the underlying mechanisms have not been clear. We now show that without Arf, pericyte hyperplasia in the eye results from enhanced Pdgfrβ-dependent proliferation from embryonic day 13.5 (E13.5) of mouse development. Loss of Arf in the eye increases Pdgfrβ expression. In cultured fibroblasts and pericyte-like cells, ectopic p19(Arf) represses and Arf knockdown enhances the expression of Pdgfrβ mRNA and protein. Ectopic Arf also represses primary Pdgfrβ transcripts and a plasmid driven by a minimal promoter, including one missing the CCAAT element required for high-level expression. p19(Arf) uses both p53-dependent and -independent mechanisms to control Pdgfrβ. In vivo, without p53, Pdgfrβ mRNA is elevated and eye development abnormalities resemble the Arf (-/-) phenotype. However, effects of p53 on Pdgfrβ mRNA do not appear to be due to direct p53 or RNA polymerase II recruitment to the promoter. Although p19(Arf) controls Pdgfrβ mRNA in a p53-dependent manner, it also blunts Pdgfrβ protein expression by blocking new protein synthesis in the absence of p53. Thus, our findings demonstrate a novel capacity for p19(Arf) to control Pdgfrβ expression by p53-dependent and -independent mechanisms involving RNA transcription and protein synthesis, respectively, to promote the vascular remodeling needed for normal vision.

TGF-β signals the formation of a unique NF1/Smad4-dependent transcription repressor-complex in human diploid fibroblasts

We earlier reported the formation of a unique nuclear NF1/Smad complex in serum-restricted fibroblasts that acts as an NF1-dependent repressor of the human adenine nucleotide translocase-2 gene (ANT2) [K. Luciakova, G. Kollarovic, P. Barath, B.D. Nelson, Growth-dependent repression of human adenine nucleotide translocator-2 (ANT2) transcription: evidence for the participation of Smad and Sp family proteins in the NF1-dependent repressor complex, Biochem. J. 412 (2008) 123-130]. In the present study, we show that TGF-β, like serum-restriction: (a) induces the formation of NF1/Smad repressor complexes, (b) increases binding of the complexes to the repressor elements (Go elements) in the ANT2 promoter, and (c) inhibits ANT2 expression. Repression of ANT2 by TGF-β is eliminated by mutating the NF1 binding sites in the Go repressor elements. All of the above responses to TGF-β are prevented by inhibitors of TGF-β RI and MAPK p38. These inhibitors also prevent NF1/Smad4 repressor complex formation and repression of ANT2 expression in serum-restricted cells, suggesting that similar signaling pathways are initiated by TGF-β and serum-restriction. The present finding that NF1/Smad4 repressor complexes are formed through TGF-β signaling pathways suggests a new, but much broader, role for these complexes in the initiation or maintenance of the growth-inhibited state.

Role of Smads in TGFβ signaling

Transforming growth factor-β (TGFβ) is the prototype for a large family of pleiotropic factors that signal via heterotetrameric complexes of type I and type II serine/threonine kinase receptors. Important intracellular mediators of TGFβ signaling are members of the Smad family. Smad2 and 3 are activated by C-terminal receptor-mediated phosphorylation, whereafter they form complexes with Smad4 and are translocated to the nucleus where they, in cooperation with other transcription factors, co-activators and co-repressors, regulate the transcription of specific genes. Smads have key roles in exerting TGFβ-induced programs leading to cell growth arrest and epithelial-mesenchymal transition. The activity and stability of Smad molecules are carefully regulated by a plethora of post-translational modifications, including phosphorylation, ubiquitination, sumoylation, acetylation and poly(ADP)-ribosylation. The Smad function has been shown to be perturbed in certain diseases such as cancer.