Browsing by Subject "SRF"

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  • Guenther, Carla; Faisal, Imrul; Uotila, Liisa; Llort Asens, Marc; Harjunpää, Heidi; Savinko, Terhi; Öhman, Tiina; Yao, Sean; Moser, Markus; Morris, Stephan W.; Tojkander, Sari; Fagerholm, Susanna (2019)
    beta2-integrins are essential for immune system function because they mediate immune cell adhesion and signaling. Consequently, a loss of beta2-integrin expression or function causes the immunodeficiency disorders, Leukocyte Adhesion Deficiency (LAD) type I and III. LAD-III is caused by mutations in an important integrin regulator, kindlin-3, but exactly how kindlin-3 regulates leukocyte adhesion has remained incompletely understood. Here we demonstrate that mutation of the kindlin-3 binding site in the b2-integrin (TTT/AAA-b2-integrin knock-in mouse/KI) abolishes activation of the actin-regulated myocardin related transcription factor A/serum response factor (MRTF-A/SRF) signaling pathway in dendritic cells and MRTF-A/SRF-dependent gene expression. We show that Ras homolog gene family, member A (RhoA) activation and filamentous-actin (F-actin) polymerization is abolished in murine TTT/AAA-b2-integrin KI dendritic cells, which leads to a failure ofMRTF-A to localize to the cell nucleus to coactivate genes together with SRF. In addition, we show that dendritic cell gene expression, adhesion and integrin-mediated traction forces on ligand coated surfaces is dependent on the MRTF-A/SRF signaling pathway. The participation of b2-integrin and kindlin-3-mediated cell adhesion in the regulation of the ubiquitous MRTF-A/SRF signaling pathway in immune cells may help explain the role of b2-integrin and kindlin-3 in integrin-mediated gene regulation and immune system function.
  • Pawlowski, Rafal; Rajakylä, Eeva; Vartiainen, Maria K.; Treisman, Richard (2010)
  • Heliste, Juho; Chheda, Himanshu; Paatero, Ilkka; Salminen, Tiina A.; Akimov, Yevhen; Paavola, Jere; Elenius, Klaus; Aittokallio, Tero (2020)
    Background: To tackle the missing heritability of sporadic heart failure, we screened for novel heart failure associated genetic variants in the Finnish population and functionally characterized a novel variant in vitro and in vivo. Methods and results: Heart failure-associated variants were screened in genotyping array data of the FINRISK study, consisting of 994 cases and 20,118 controls. Based on logistic regression analysis, a potentially damaging variant in TRIM55 (rs138811034), encoding an E140K variant, was selected for validations. In HL-1 cardiomyocytes, we used CRISPR/Cas9 technology to introduce the variant in the endogenous locus, and additionally TRIM55 wildtype or E140K was overexpressed from plasmid. Functional responses were profiled using whole-genome RNA sequencing, RT-PCR and Western analyses, cell viability and cell cycle assays and cell surface area measurements. In zebrafish embryos, cardiac contractility was measured using videomicroscopy after CRISPR-mediated knockout of trim55a or plasmid overexpression of TRIM55 WT or E140K. Genes related to muscle contraction and cardiac stress were highly regulated in Trim55 E140K/- cardiomyocytes. When compared to the WT/WT cells, the variant cells demonstrated reduced viability, significant hypertrophic response to isoproterenol, p21 protein overexpression and impaired cell cycle progression. In zebrafish embryos, the deletion of trim55a or overexpression of TRIM55 E140K reduced cardiac contractility as compared to embryos with wild type genotype or overexpression of WT TRIM55, respectively. Conclusions: A previously uncharacterized TRIM55 E140K variant demonstrated a number of functional implications for cardiomyocyte functions in vitro and in vivo. These findings suggest a novel role for TRIM55 polymorphism in predisposing to heart failure.
  • Sprenkeler, Evelien G. G.; Guenther, Carla; Faisal, Imrul; Kuijpers, Taco W.; Fagerholm, Susanna C. (2021)
    Megakaryoblastic leukemia 1 (MKL1) deficiency is one of the most recently discovered primary immunodeficiencies (PIDs) caused by cytoskeletal abnormalities. These immunological "actinopathies" primarily affect hematopoietic cells, resulting in defects in both the innate immune system (phagocyte defects) and adaptive immune system (T-cell and B-cell defects). MKL1 is a transcriptional coactivator that operates together with serum response factor (SRF) to regulate gene transcription. The MKL/SRF pathway has been originally described to have important functions in actin regulation in cells. Recent results indicate that MKL1 also has very important roles in immune cells, and that MKL1 deficiency results in an immunodeficiency affecting the migration and function of primarily myeloid cells such as neutrophils. Interestingly, several actinopathies are caused by mutations in genes which are recognized MKL(1/2)-dependent SRF-target genes, namely ACTB, WIPF1, WDR1, and MSN. Here we summarize these and related (ARPC1B) actinopathies and their effects on immune cell function, especially focusing on their effects on leukocyte adhesion and migration. Furthermore, we summarize recent therapeutic efforts targeting the MKL/SRF pathway in disease.
  • Sharili, Amir S.; Kenny, Fiona N.; Vartiainen, Maria K.; Connelly, John T. (2016)
    The actin cytoskeleton is a classic biomechanical mediator of cell migration. While it is known that actin also shuttles in and out of the nucleus, its functions within this compartment remain poorly understood. In this study, we investigated how nuclear actin regulates keratinocyte gene expression and cell behavior. Gene expression profiling of normal HaCaT keratinocytes compared to HaCaTs over-expressing wild-type beta-actin or beta-actin tagged with a nuclear localization sequence (NLS-actin), identified multiple adhesive and cytoskeletal genes, such as MYL9, ITGB1, and VCL, which were significantly down-regulated in keratinocytes with high levels of nuclear actin. In addition, genes associated with transcriptional regulation and apoptosis were up-regulated in cells over expressing NLS-actin. Functionally, accumulation of actin in the nucleus altered cytoskeletal and focal adhesion organization and inhibited cell motility. Exclusion of endogenous actin from the nucleus by knocking down Importin 9 reversed this phenotype and enhanced cell migration. Based on these findings, we conclude that the level of actin in the nucleus is a transcriptional regulator for tuning keratinocyte migration.
  • Hyrskyluoto, Alise; Vartiainen, Maria K. (2020)
    Actin has essential functions both in the cytoplasm and in the nucleus, where it has been linked to key nuclear processes, from transcription to DNA damage response. The multifunctional nature of actin suggests that the cell must contain mechanisms to accurately control the cellular actin balance. Indeed, recent results have demonstrated that nuclear actin levels fluctuate to regulate the transcriptional activity of the cell and that controlled nuclear actin polymerization is required for transcription activation, cell cycle progression, and DNA repair. Intriguingly, aberrant nuclear actin regulation has been observed, for example, in cancer, signifying the importance of this process for cellular homeostasis. This review discussed the latest research on how nuclear actin is regulated, and how this influences actin-dependent nuclear processes.