The Third International Meeting on Genetic Disorders in the RAS/MAPK Pathway: Toward a Therapeutic Approach

The Third International Meeting on Genetic Disorders in the RAS/MAPK Pathway: Towards a Therapeutic Approach was held at the Renaissance Orlando at SeaWorld Hotel (August 2-4, 2013). Seventy-one physicians and scientists attended the meeting, and parallel meetings were held by patient advocacy groups (CFC International, Costello Syndrome Family Network, NF Network and Noonan Syndrome Foundation). Parent and patient advocates opened the meeting with a panel discussion to set the stage regarding their hopes and expectations for therapeutic advances. In keeping with the theme on therapeutic development, the sessions followed a progression from description of the phenotype and definition of therapeutic endpoints, to definition of genomic changes, to identification of therapeutic targets in the RAS/MAPK pathway, to preclinical drug development and testing, to clinical trials. These proceedings will review the major points of discussion

Regulation of Embryonic and Induced Pluripotency by Aurora Kinase-p53 Signaling

SummaryMany signals must be integrated to maintain self-renewal and pluripotency in embryonic stem cells (ESCs) and to enable induced pluripotent stem cell (iPSC) reprogramming. However, the exact molecular regulatory mechanisms remain elusive. To unravel the essential internal and external signals required for sustaining the ESC state, we conducted a short hairpin (sh) RNA screen of 104 ESC-associated phosphoregulators. Depletion of one such molecule, aurora kinase A (Aurka), resulted in compromised self-renewal and consequent differentiation. By integrating global gene expression and computational analyses, we discovered that loss of Aurka leads to upregulated p53 activity that triggers ESC differentiation. Specifically, Aurka regulates pluripotency through phosphorylation-mediated inhibition of p53-directed ectodermal and mesodermal gene expression. Phosphorylation of p53 not only impairs p53-induced ESC differentiation but also p53-mediated suppression of iPSC reprogramming. Our studies demonstrate an essential role for Aurka-p53 signaling in the regulation of self-renewal, differentiation, and somatic cell reprogramming

A novel frizzled-based screening tool identifies genetic modifiers of planar cell polarity in drosophila wings

Most mutant alleles in the Fz-PCP pathway genes were discovered in classic Drosophila screens looking for recessive loss-of-function (LOF) mutations. Nonetheless, although Fz-PCP signaling is sensitive to increased doses of PCP gene products, not many screens have been performed in the wing under genetically engineered Fz overexpression conditions, mostly because the Fz phenotypes were strong and/or not easy to score and quantify. Here, we present a screen based on an unexpected mild Frizzled gain-of-function (GOF) phenotype. The leakiness of a chimeric Frizzled protein designed to be accumulated in the endoplasmic reticulum (ER) generated a reproducible Frizzled GOF phenotype in Drosophila wings. Using this genotype, we first screened a genome-wide collection of large deficiencies and found 16 strongly interacting genomic regions. Next, we narrowed down seven of those regions to finally test 116 candidate genes. We were, thus, able to identify eight new loci with a potential function in the PCP context. We further analyzed and confirmed krasavietz and its interactor short-stop as new genes acting during planar cell polarity establishment with a function related to actin and microtubule dynamics.Trabajo financiado por: Institute and General Medical Sciences and National Eye National Institutes of Health. Beca para Marek Mlodzik Ministerio de Economía y Competitividad. Beca BFU2014-54699-P, para José María Carvajal González Junta de Extremadura. Ayuda para la Atracción y Retención del Talento Invetigador, para José María Carvajal GonzálezpeerReviewe

Esrrb Regulates Specific Feed-Forward Loops to Transit From Pluripotency Into Early Stages of Differentiation

Characterization of pluripotent states, in which cells can both self-renew or differentiate, with the irreversible loss of pluripotency, are important research areas in developmental biology. Although microRNAs (miRNAs) have been shown to play a relevant role in cellular differentiation, the role of miRNAs integrated into gene regulatory networks and its dynamic changes during these early stages of embryonic stem cell (ESC) differentiation remain elusive. Here we describe the dynamic transcriptional regulatory circuitry of stem cells that incorporate protein-coding and miRNA genes based on miRNA array expression and quantitative sequencing of short transcripts upon the downregulation of the Estrogen Related Receptor Beta (Esrrb). The data reveals how Esrrb, a key stem cell transcription factor, regulates a specific stem cell miRNA expression program and integrates dynamic changes of feed-forward loops contributing to the early stages of cell differentiation upon its downregulation. Together these findings provide new insights on the architecture of the combined transcriptional post-transcriptional regulatory network in embryonic stem cells

Abstract 19583: Autonomous and Non-Autonomous Defects Underlie Hypertrophic Cardiomyopathy in BRAF-Mutant hiPSC-Derived Cardiomyocytes

Hypertrophic cardiomyopathy (HCM) is a pathological disorder predominantly due to mutations in sarcomeric components. Germline mutations in BRAF cause a developmental syndrome called cardio-facio-cutaneous syndrome (CFCS), in which 40% of patients also develop HCM. Since the role of the RAS/MAPK pathway in HCM is still unclear, we generated a human induced pluripotent stem cell model for CFCS from three patients with activating BRAF T599R or Q257R mutations. In order to examine hiPSC-derived cell-type specific phenotypes and cellular interactions underpinning HCM, we generated a method to purify cardiomyocytes and non-cardiomyocytes simultaneously by cell sorting based on SIRPα and CD90 expression. Purified BRAF-mutant SIRPα+/CD90- cells were >95% cardiomyocytes, displayed cellular hypertrophy with pro-hypertrophic gene expression, and dysregulation of the RAS/MAPK pathway. BRAF-mutant cardiomyocytes also displayed intrinsic calcium handling defects, including increased calcium transient irregularity and increased stored calcium within the sarcoplasmic reticulum. In addition, purified BRAF-mutant SIRPα-/CD90+ cells, which were fibroblast-like, displayed activation of the RAS/MAPK pathway and exhibited a pro-fibrotic phenotype. Cross-culture studies revealed that BRAF-mutant fibroblast-like cells critically modulate cardiomyocyte hypertrophy through TGFβ paracrine signaling, as TGFβ inhibition prevented cardiomyocyte hypertrophy induced by BRAF-mutant fibroblast-like cells. Additionally, inhibition of RAS/MAPK signaling was capable of rescuing BRAF-mutant cardiomyocyte hypertrophy and cardiomyocyte-intrinsic calcium handling abnormalities. Thus, we show for the first time that cell autonomous and non-autonomous defects underlie RASopathy-associated HCM. As fibroblast activation has been documented previously in sarcomeric HCM, our findings suggest that cardiac fibroblasts may contribute to pathologic hypertrophy in addition to causing fibrosis in primary forms of HCM. TGFβ inhibition may be a useful therapeutic option for patients with HCM due to RASopathies or other etiologies

Proteomic analysis of an induced pluripotent stem cell model reveals strategies to treat Juvenile Myelomonocytic Leukaemia

Juvenile myelomonocytic leukemia (JMML) is an aggressive myeloproliferative neoplasm of early childhood with a poor survival rate, thus there is a requirement for improved treatment strategies. Induced pluripotent stem cells offer the ability to model disease and develop new treatment strategies. JMML is frequently associated with mutations in PTPN11. Children with Noonan syndrome, a development disorder, have an increased incidence of JMML associated with specific germline mutations in PTPN11. We undertook a proteomic assessment of myeloid cells derived from induced pluripotent stem cells obtained from Noonan syndrome patients with PTPN11 mutations, either associated or not associated with an increased incidence of JMML. We report that the proteomic perturbations induced by the leukemia-associated PTPN11 mutations are associated with TP53 and NF-Kκb signaling. We have previously shown that MYC is involved in the differential gene expression observed in Noonan syndrome patients associated with an increased incidence of JMML. Thus, we employed drugs to target these pathways and demonstrate differential effects on clonogenic hematopoietic cells derived from Noonan syndrome patients, who develop JMML and those who do not. Further, we demonstrated these small molecular inhibitors, JQ1 and CBL0137, preferentially extinguish primitive hematopoietic cells from sporadic JMML patients as opposed to cells from healthy individuals

Autonomous and Non-autonomous Defects Underlie Hypertrophic Cardiomyopathy in BRAF-Mutant hiPSC-Derived Cardiomyocytes

Germline mutations in BRAF cause cardio-facio-cutaneous syndrome (CFCS), whereby 40% of patients develop hypertrophic cardiomyopathy (HCM). As the role of the RAS/MAPK pathway in HCM pathogenesis is unclear, we generated a human induced pluripotent stem cell (hiPSC) model for CFCS from three patients with activating BRAF mutations. By cell sorting for SIRPα and CD90, we generated a method to examine hiPSC-derived cell type-specific phenotypes and cellular interactions underpinning HCM. BRAF-mutant SIRPα+/CD90− cardiomyocytes displayed cellular hypertrophy, pro-hypertrophic gene expression, and intrinsic calcium-handling defects. BRAF-mutant SIRPα−/CD90+ cells, which were fibroblast-like, exhibited a pro-fibrotic phenotype and partially modulated cardiomyocyte hypertrophy through transforming growth factor β (TGFβ) paracrine signaling. Inhibition of TGFβ or RAS/MAPK signaling rescued the hypertrophic phenotype. Thus, cell autonomous and non-autonomous defects underlie HCM due to BRAF mutations. TGFβ inhibition may be a useful therapeutic option for patients with HCM due to RASopathies or other etiologies

Immortalized mouse mammary fibroblasts lacking dioxin receptor have impaired tumorigenicity in a subcutaneous mouse xenograft model

11 páginas, 9 figuras.-- PMID: 15946950 [PubMed].-- et al.Although the dioxin receptor, the aryl hydrocarbon receptor (AhR), is considered a major regulator of xenobiotic-induced carcinogenesis, its role in tumor formation in the absence of xenobiotics is still largely unknown. Trying to address this question, we have produced immortalized cell lines from wild-type (T-FGM-AhR+/+) and mutant (T-FGM-AhR-/-) mouse mammary fibroblasts by stable co-transfection with the simian virus 40 (SV-40) large T antigen and proto-oncogenic c-H-Ras. Both cell lines had a myofibroblast phenotype and similar proliferation, doubling time, SV-40 and c-H-Ras expression and activity, and cell cycle distribution. AhR+/+ and AhR-/- cells were also equally able to support growth factor- and anchorage-independent proliferation. However, the ability of T-FGM-AhR-/- to induce subcutaneous tumors (leimyosarcomas) in NOD/SCID-immunodeficient mice was close to 4-fold lower than T-FGM-AhR+/+. In culture, T-FGM-AhR-/- had diminished migration in collagen-I and decreased lamellipodia formation. VEGFR-1/Flt-1, a VEGF receptor that regulates cell migration and blood vessel formation, was also down-regulated in AhR-/- cells. Signaling through the ERK-FAK-PKB/AKT-Rac-1 pathway, which contributes to cell motility and invasion, was also significantly inhibited in T-FGM-AhR-/-. Thus, the lower tumorigenic potential of T-FGM-AhR-/- could result from a compromised adaptability of these cells to the in vivo microenvironment, possibly because of an impaired ability to migrate and to respond to angiogenesis.This work has been funded by Grant SAF2002-00034 from the Spanish Ministry of Science and Technology and from the Junta de Extremadura (2PR01A092) (to P. M. F.-S.). Work in the I. S. G. laboratory was supported by grants from the MCyT (BIO2000-0453-01, SAF2003-01103, and FIT-010000-2004-157), Junta de Castilla y León (CSI06/13), ADE Castilla y León (04/04/SA/0001), FIS (PI020138, G03/179, and G03/136) and the USAL-CIBASA project.Peer reviewe

Distinct epigenetic programs regulate cardiac myocyte development and disease in the human heart in vivo

How the cardiac myocyte epigenome is rearranged during development, postnatal maturation and disease is not well understood. Here, the authors investigate the human cardiac myocyte epigenome during development and chronic heart failure and identify distinct epigenetic programs regulating these processes