Nuclear and cytoplasmic c-Ski differently modulate cellular functions.

Department of Molecular Pathology, Graduate School of Medicine, University of Tokyo, Tokyo 113-0033, Japan.
Genes to Cells (Impact Factor: 2.86). 12/2006; 11(11):1267-80. DOI: 10.1111/j.1365-2443.2006.01018.x
Source: PubMed

ABSTRACT c-Ski is a proto-oncogene product that induces morphologic transformation, anchorage independence, and myogenic differentiation when it is over-expressed in mesenchymal cells. c-Ski also inhibits signaling of transforming growth factor-beta (TGF-beta) superfamily members through interaction with Smad proteins. Although c-Ski is predominantly localized in the nucleus, aberrant cytoplasmic localization of it has also been reported in some tumor tissues and cell lines. In the present study, we identified the nuclear localization signal (NLS) in c-Ski. By introducing a mutation to abolish NLS activity, we examined the function of cytoplasmic c-Ski. Although cytoplasmic c-Ski suppressed TGF-beta superfamily-induced Smad signaling through sequestration of activated Smad complex to the cytoplasm, it failed to exhibit some of the activities that require nuclear localization of c-Ski, including suppression of basal transcription of the Smad7 gene. These findings indicate that subcellular localization of c-Ski affects its biologic activities. We also found that c-Ski accumulated in the cytoplasm when proteasome activity was inhibited. Mapping of the regions required for cytoplasmic accumulation by proteasome inhibitors suggests that subcellular localization of c-Ski may be regulated by proteasome-sensitive processes through amino acid residues 94-210 and 491-548.

Download full-text


Available from: Keiji Miyazawa, Mar 27, 2015
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Background: Cardiac fibrosis is linked to fibroblast to myofibroblast phenoconversion and proliferation; mechanisms underlying this phenoconversion are poorly understood. c-Ski (Ski) is a negative regulator of TGF-β/Smad signaling in myofibroblasts, and may redirect the myofibroblast phenotype back to fibroblasts. Meox2 may alter TGF-β-mediated cellular processes and is repressed by Zeb2. Hypothesis: Ski diminishes the myofibroblast phenotype by de-repressing Meox2 expression and function via repression of Zeb2 expression. Results: Meox1 and Meox2 mRNA expression, Meox2 protein expression are reduced during phenoconversion of fibroblasts to myofibroblasts. Meox2 over-expression shifts the myofibroblasts to fibroblasts, whereas the Meox2 DNA-binding mutant has no effect on myofibroblast phenotype. Ski over-expression partially restores Meox2 mRNA expression levels to those in cardiac fibroblasts. Expression of Zeb2 increased during phenoconversion and Ski over-expression reduces Zeb2 expression in first-passage myofibroblasts. Meox2 expression is decreased in scar following myocardial infarction, whereas Zeb2 protein expression increases in the infarct scar. Thus Ski modulates the cardiac myofibroblast phenotype and function via suppression of Zeb2 by up-regulating Meox2. This cascade may regulate cardiac myofibroblast phenotype and presents therapeutic options for treatment of cardiac fibrosis.
    Journal of Cell Science 10/2013; 127(1). DOI:10.1242/jcs.126722 · 5.33 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Ski and SnoN are two highly related transcription factors that are transcribed from two separate genes named SKI and SKIL, respectively. They are both co-repressors of the Smad-mediated transforming growth factor beta (TGFβ) signaling pathway. Originally they were classified as oncogenes as they have the ability to transform quail fibroblasts. However, they have also been found to have anti-proliferative properties so they are also considered tumor suppressors. They are involved in normal growth and development and thought to be essential as there is evidence that a homozygous mouse knockout of either SKI or SKIL is embryonic lethal. Both Ski and SnoN have been found to be overexpressed in some cancers. This overexpression has been found to be prognostic in some cases. Another prognostic factor in certain cancers is the cytoplasmic localization of these normally nuclear proteins. Other than with the TGFβ signaling pathway, Ski and SnoN are known to have interactions with retinoic acid receptor signaling and the retinoblastoma protein. In order to obtain a better understanding of Ski and SnoN we have studied several aspects of the proteins. First, we identified the nuclear localization signal (NLS) of Ski and proved that this sequence was both necessary and sufficient for nuclear localization. Next, we looked into the correlation of Ski subcellular location and serine phosphorylation status. Here we found that serine phosphorylated Ski is found predominately in the cytoplasm. Finally, we looked at possible involvement of Ski and SnoN in the pediatric cancer rhabdomyosarcoma (RMS). We found there was expression of both of these proteins in cell lines derived from the cancer and in tumor tissue samples. We also found that Ski protein levels in RMS tumor tissue are negatively correlated with RMS tumor group. The data from the Ski phosphorylation studies suggest that this modification may work with the NLS to regulate the subcellular location of Ski. Misregulation of this process may be responsible for the cytoplasmic localization of Ski that we found in RMS. Biomedical Sciences Doctoral University of New Mexico. Biomedical Sciences Graduate Program Bear, David Larson, Richard Winter, Stuart Hartley, Rebecca
  • [Show abstract] [Hide abstract]
    ABSTRACT: The aim of the present work was to investigate the mechanism of transforming growth factor (TGF)-β1 and Sloan-Kettering Institute (Ski) in the pathogenesis of hypertrophic scars (HS). Wound healing is an inherent process, but the aberrant wound healing of skin injury may lead to HS. There has been growing evidence suggesting a role for TGF-β1 and Ski in the pathogenesis of fibrosis. The MTT assay was used to detect the cell proliferation induced by TGF-β1. The Ski gene was transduced into cells with an adenovirus, and then the function of Ski in cell proliferation and differentiation was observed. Ski mRNA levels were measured by RT-PCR. Western blotting was used to detect the protein expression of α-SMA, E-cadherin, Meox1, Meox2, Zeb1 and Zeb2. TGF-β1 can promote human skin fibroblast (HSF) cell proliferation in a time-dependent manner, but the promoting effect could be suppressed by Ski. TGF-β1 also induces the formation of the myofibroblast phenotype and the effect of TGF-β1 could be diminished by Ski. Also, Ski modulates the cardiac myofibroblast phenotype and function through suppression of Zeb2 by up-regulating the expression of Meox2. Ski diminishes the myofibroblast phenotype induced by TGF-β1 through the suppression of Zeb2 by up-regulating the expression of Meox2. Copyright © 2014 Elsevier Inc. All rights reserved.
    Experimental and Molecular Pathology 11/2014; 97(3):542-549. DOI:10.1016/j.yexmp.2014.11.002 · 2.88 Impact Factor