TY - JOUR

T1 - Hyperosmotic stress regulates the distribution and stability of myocardin-related transcription factor, a key modulator of the cytoskeleton

AU - Ly, Donald L.

AU - Waheed, Faiza

AU - Lodyga, Monika

AU - Speight, Pam

AU - Masszi, András

AU - Nakano, Hiroyasu

AU - Hersom, Maria Nathalie Selch

AU - Pedersen, Stine Helene Falsig

AU - Szászi, Katalin

AU - Kapus, András

PY - 2013

Y1 - 2013

N2 - Hyperosmotic stress initiates several adaptive responses, including the remodeling of the cytoskeleton. Besides maintaining structural integrity, the cytoskeleton has emerged as an important regulator of gene transcription. Myocardin-related transcription factor (MRTF), an actin-regulated coactivator of serum response factor, is a major link between the actin skeleton and transcriptional control. We therefore investigated whether MRTF is regulated by hyperosmotic stress. Here we show that hypertonicity induces robust, rapid, and transient translocation of MRTF from the cytosol to the nucleus in kidney tubular cells. We found that the hyperosmolarity-triggered MRTF translocation is mediated by the RhoA/Rho kinase (ROK) pathway. Moreover, the Rho guanine nucleotide exchange factor GEF-H1 is activated by hyperosmotic stress, and it is a key contributor to the ensuing RhoA activation and MRTF translocation, since siRNA-mediated GEF-H1 downregulation suppresses these responses. While the osmotically induced RhoA activation promotes nuclear MRTF accumulation, the concomitant activation of p38 MAP kinase mitigates this effect. Moderate hyperosmotic stress (600 mosM) drives MRTF-dependent transcription through the cis-element CArG box. Silencing or pharmacological inhibition of MRTF prevents the osmotic stimulation of CArG-dependent transcription and renders the cells susceptible to osmotic shock-induced structural damage. Interestingly, strong hyperosmolarity promotes proteasomal degradation of MRTF, concomitant with apoptosis. Thus, MRTF is an osmosensitive and osmoprotective transcription factor, whose intracellular distribution is regulated by the GEF-H1/RhoA/ROK and p38 pathways. However, strong osmotic stress destabilizes MRTF, concomitant with apoptosis, implying that hyperosmotically induced cell death takes precedence over epithelial-myofibroblast transition, a potential consequence of MRTF-mediated phenotypic reprogramming.

AB - Hyperosmotic stress initiates several adaptive responses, including the remodeling of the cytoskeleton. Besides maintaining structural integrity, the cytoskeleton has emerged as an important regulator of gene transcription. Myocardin-related transcription factor (MRTF), an actin-regulated coactivator of serum response factor, is a major link between the actin skeleton and transcriptional control. We therefore investigated whether MRTF is regulated by hyperosmotic stress. Here we show that hypertonicity induces robust, rapid, and transient translocation of MRTF from the cytosol to the nucleus in kidney tubular cells. We found that the hyperosmolarity-triggered MRTF translocation is mediated by the RhoA/Rho kinase (ROK) pathway. Moreover, the Rho guanine nucleotide exchange factor GEF-H1 is activated by hyperosmotic stress, and it is a key contributor to the ensuing RhoA activation and MRTF translocation, since siRNA-mediated GEF-H1 downregulation suppresses these responses. While the osmotically induced RhoA activation promotes nuclear MRTF accumulation, the concomitant activation of p38 MAP kinase mitigates this effect. Moderate hyperosmotic stress (600 mosM) drives MRTF-dependent transcription through the cis-element CArG box. Silencing or pharmacological inhibition of MRTF prevents the osmotic stimulation of CArG-dependent transcription and renders the cells susceptible to osmotic shock-induced structural damage. Interestingly, strong hyperosmolarity promotes proteasomal degradation of MRTF, concomitant with apoptosis. Thus, MRTF is an osmosensitive and osmoprotective transcription factor, whose intracellular distribution is regulated by the GEF-H1/RhoA/ROK and p38 pathways. However, strong osmotic stress destabilizes MRTF, concomitant with apoptosis, implying that hyperosmotically induced cell death takes precedence over epithelial-myofibroblast transition, a potential consequence of MRTF-mediated phenotypic reprogramming.

KW - Active Transport, Cell Nucleus

KW - Animals

KW - Apoptosis

KW - Cell Line

KW - Cytoskeleton

KW - Gene Expression Regulation

KW - Gene Silencing

KW - Guanine Nucleotide Exchange Factors

KW - Hypertonic Solutions

KW - Kidney Tubules

KW - MAP Kinase Signaling System

KW - Nuclear Proteins

KW - Osmotic Pressure

KW - Promoter Regions, Genetic

KW - Proteasome Endopeptidase Complex

KW - Protein Stability

KW - Stress, Physiological

KW - Swine

KW - Trans-Activators

KW - Transcription Factors

KW - rho-Associated Kinases

U2 - 10.1152/ajpcell.00290.2012

DO - 10.1152/ajpcell.00290.2012

M3 - Journal article

C2 - 23054059

VL - 304

SP - C115-C127

JO - American Journal of Physiology: Cell Physiology

JF - American Journal of Physiology: Cell Physiology

SN - 0363-6143

IS - 2

ER -