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Mori K, Nakagawa Y, Watanabe B, Miyata H, Morita T, Hayashi K. Novel ability of diflubenzuron as an inhibitor of mitochondrial function. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2024; 167:104088. [PMID: 38342197 DOI: 10.1016/j.ibmb.2024.104088] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/12/2023] [Revised: 01/18/2024] [Accepted: 01/29/2024] [Indexed: 02/13/2024]
Abstract
Compounds classified as benzoylphenylurea (BPU), such as diflubenzuron (DFB), are used as insecticides. Although BPU disrupts molting by inhibiting chitin biosynthesis and exhibits insecticidal activity, their exact mode of action remains unknown. Since epidermal cells proliferate and morphologically change from squamous to columnar cells during the early stages of insect molting, we speculate that a transition similar to that from epithelium to mesenchyme occurs and that BPU may inhibit this transition. Here, we addressed this possibility. We found that DFB decreases actin expression in insect cells (the tissue cultures of insect integument). Detailed analysis in Schneider S2 cells reveals that DFB inhibits the expression of actin isoforms (Act5C and Act42A) and the Drosophila ortholog of myocardin-related transcription factor (Mrtf), leading to cell growth suppression. Proteomics identified the Drosophila ortholog of prohibitin (Phb1D and Phb2E) as one of the DFB-binding proteins. DFB inhibits the interaction between Phb1D and Phb2E and induces mitochondrial dysfunction. The knock-down of Phb2E suppresses the expression of Act5C, Act42A, and Mrtf, leading to cell growth inhibition. Thus, the disruption of Phb function is a possible novel target of DFB.
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Affiliation(s)
- Kotaro Mori
- Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kitashirakawa-Oiwakecho, Sakyo-ku, Kyoto, 606-8502, Japan
| | - Yoshiaki Nakagawa
- Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kitashirakawa-Oiwakecho, Sakyo-ku, Kyoto, 606-8502, Japan
| | - Bunta Watanabe
- Chemistry Laboratory, The Jikei University School of Medicine, 8-3-1 Kokuryo, Chofu, Tokyo, 182-8570, Japan
| | - Hiroshi Miyata
- Department of Surgery, Osaka International Cancer Institute, 3-1-69 Otemae, Chuo-ku, Osaka, 541-8567, Japan
| | - Tsuyoshi Morita
- Department of Biology, Wakayama Medical University School of Medicine, 580 Mikazura, Wakayama, 641-0011, Japan
| | - Ken'ichiro Hayashi
- Department of Ophthalmology, Yamaguchi University Graduate School of Medicine, Minami-Kogushi 1-1-1, Ube, Yamaguchi, 755-8505, Japan; Department of RNA Biology and Neuroscience, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita, Osaka, 565-0871, Japan.
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Tarnick J, Elhendawi M, Holland I, Chang Z, Davies JA. Innervation of the developing kidney in vivo and in vitro. Biol Open 2023; 12:bio060001. [PMID: 37439314 PMCID: PMC10411870 DOI: 10.1242/bio.060001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2023] [Accepted: 07/03/2023] [Indexed: 07/14/2023] Open
Abstract
Within the adult kidney, renal neurites can be observed alongside the arteries where they play a role in regulating blood flow. However, their role and localization during development has so far not been described in detail. In other tissues, such as the skin of developing limb buds, neurons play an important role during arterial differentiation. Here, we aim to investigate whether renal nerves could potentially carry out a similar role during arterial development in the mouse kidney. In order to do so, we used whole-mount immunofluorescence staining to identify whether the timing of neuronal innervation correlates with the recruitment of arterial smooth muscle cells. Our results show that neurites innervate the kidney between day 13.5 and 14.5 of development, arriving after the recruitment of smooth muscle actin-positive cells to the renal arteries.
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Affiliation(s)
- Julia Tarnick
- Deanery of Biomedical Science, University of Edinburgh, Edinburgh EH8 9XD, UK
| | - Mona Elhendawi
- Deanery of Biomedical Science, University of Edinburgh, Edinburgh EH8 9XD, UK
| | - Ian Holland
- Deanery of Biomedical Science, University of Edinburgh, Edinburgh EH8 9XD, UK
| | - Ziyuan Chang
- Deanery of Biomedical Science, University of Edinburgh, Edinburgh EH8 9XD, UK
| | - Jamie A. Davies
- Deanery of Biomedical Science, University of Edinburgh, Edinburgh EH8 9XD, UK
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3
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Massett MP, Bywaters BC, Gibbs HC, Trzeciakowski JP, Padgham S, Chen J, Rivera G, Yeh AT, Milewicz DM, Trache A. Loss of smooth muscle α-actin effects on mechanosensing and cell-matrix adhesions. Exp Biol Med (Maywood) 2020; 245:374-384. [PMID: 32064918 DOI: 10.1177/1535370220903012] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Mutations in ACTA2, encoding smooth muscle α-actin, are a frequent cause of heritable thoracic aortic aneurysm and dissections. These mutations are associated with impaired vascular smooth muscle cell function, which leads to decreased ability of the cell to sense matrix-mediated mechanical stimuli. This study investigates how loss of smooth muscle α-actin affects cytoskeletal tension development and cell adhesion using smooth muscle cells explanted from aorta of mice lacking smooth muscle α-actin. We tested the hypothesis that reduced vascular smooth muscle contractility due to a loss of smooth muscle α-actin decreases cellular mechanosensing by dysregulating cell adhesion to the matrix. Assessment of functional mechanical properties of the aorta by stress relaxation measurements in thoracic aortic rings suggested two functional regimes for Acta2−/− mice. Lower stress relaxation was recorded in aortic rings from Acta2−/− mice at tensions below 10 mN compared with wild type, likely driven by cytoskeletal-dependent contractility. However, no differences were recorded between the two groups above the 10 mN threshold, since at higher tension the matrix-dependent contractility may be predominant. In addition, our results showed that at any given level of stretch, transmural pressure is lower in aortic rings from Acta2−/− mice than wild type mice. In addition, a three-dimensional collagen matrix contractility assay showed that collagen pellets containing Acta2−/− smooth muscle cells contracted less than the pellets containing the wild type cells. Moreover, second harmonic generation non-linear microscopy revealed that Acta2−/− cells locally remodeled the collagen matrix fibers to a lesser extent than wild type cells. Quantification of protein fluorescence measurements in cells also showed that in absence of smooth muscle α-actin, there is a compensatory increase in smooth muscle γ-actin. Moreover, specific integrin recruitment at cell–matrix adhesions was reduced in Acta2−/− cells. Thus, our findings suggest that Acta2−/− cells are unable to generate external forces to remodel the matrix due to reduced contractility and interaction with the matrix. Impact statement Thoracic aneurysm formation is characterized by progressive enlargement of the ascending aorta, which predisposes the aorta to acute aortic dissection that can lead to sudden death. SMCs in the aorta play an integral role in regulating vessel wall contractility and matrix deposition in the medial layer. Recent studies show that mutations in genes associated with actomyosin apparatus reduce SMC contractility, increasing susceptibility to TAAD. Single-cell experiments enable discrete measurements of transient microscopic events that may be masked by a macroscopic average tissue behavior. Biophysical methods combined with microscopy techniques aid in understanding the specific roles of adhesion and cytoskeletal proteins in regulating SMC mechanosensing when SMα-actin is disrupted. Our findings suggest that Acta2− /− cells have increased SMγ-actin and decreased integrin recruitment at cell–matrix adhesion, hence a synthetic phenotype with reduced cellular mechanosensing.
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Affiliation(s)
- M P Massett
- Department of Health and Kinesiology, Texas A&M University, College Station, TX 77843, USA
| | - B C Bywaters
- Department of Veterinary Pathobiology, Texas A&M University, College Station, TX 77843, USA
| | - H C Gibbs
- Department of Biomedical Engineering, Texas A&M University, College Station, TX 77843, USA
| | - J P Trzeciakowski
- Department of Medical Physiology, Texas A&M University Health Science Center, Bryan, TX 77807, USA
| | - S Padgham
- Department of Medical Physiology, Texas A&M University Health Science Center, Bryan, TX 77807, USA
| | - J Chen
- Department of Internal Medicine, McGovern Medical School, University of Texas Health Science Center, Houston, TX 77030, USA
| | - G Rivera
- Department of Veterinary Pathobiology, Texas A&M University, College Station, TX 77843, USA
| | - A T Yeh
- Department of Biomedical Engineering, Texas A&M University, College Station, TX 77843, USA
| | - D M Milewicz
- Department of Internal Medicine, McGovern Medical School, University of Texas Health Science Center, Houston, TX 77030, USA
| | - A Trache
- Department of Biomedical Engineering, Texas A&M University, College Station, TX 77843, USA.,Department of Medical Physiology, Texas A&M University Health Science Center, Bryan, TX 77807, USA
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Bildyug N. Matrix metalloproteinases: an emerging role in regulation of actin microfilament system. Biomol Concepts 2017; 7:321-329. [PMID: 27763882 DOI: 10.1515/bmc-2016-0022] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2016] [Accepted: 09/20/2016] [Indexed: 12/13/2022] Open
Abstract
Matrix metalloproteinases (MMPs) are implicated in many physiological and pathological processes, including contraction, migration, differentiation, and proliferation. These processes all involve cell phenotype changes, known to be accompanied by reorganization of actin cytoskeleton. Growing evidence indicates a correlation between MMP activity and the dynamics of actin system, suggesting their mutual regulation. Here, data on the influence of MMPs on the actin microfilament system, on the one hand, and the dependence of MMP expression and activation on the organization of actin structures, on the other hand, are reviewed. The different mechanisms of putative actin-MMP regulation are discussed.
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Effects of reduced cyclic stretch on vascular smooth muscle cell function of pig carotids perfused ex vivo. Am J Hypertens 2008; 21:425-31. [PMID: 18219296 DOI: 10.1038/ajh.2007.72] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
BACKGROUND With advancing age arteries stiffen, reducing arterial compliance and leading to the development of systolic hypertension and to a substantial increase in pulse pressure. An augmented pulse pressure can be a predictor of the development of hypertension, which has been linked to several cardiovascular diseases including atherosclerosis, and to pathologies such as diabetes and renal dysfunction. In this study, we tested the hypothesis that reduced wall compliance induces pulse-pressure-mediated changes in arterial wall metabolism and remodeling. METHODS Porcine carotid arteries were perfused for 24 h using an ex vivo arterial support system. Control arteries were exposed to a pulse shear stress (6 +/- 3 dynes/cm(2)) combined with a pulse pressure of 80 +/- 10 mm Hg, yielding a physiological cyclic stretch of 4-5%. A reduced compliance group was also studied, in which arteries were wrapped with an external band, thereby decreasing cyclic stretch to levels <1%. RESULTS The experimentally reduced compliance caused a decreased contraction capacity induced by norepinephrine(NE), and this was associated with lower levels of alpha-smooth muscle cell-actin (alpha-SMC-actin) and desmin protein expressions. Arteries that were exposed to a reduced cyclic stretch exhibited a higher level of matrix metalloproteinase-2 (MMP-2) expression activity as well as an increase in Ki67 expression, thereby suggesting that matrix degradation and cellular proliferation had been initiated. Furthermore, the expression of plasminogen activator inhibitor-1 (PAI-1) in stiffened arteries was lower than in the control arteries. CONCLUSIONS These findings underline the importance of cyclic stretch in the maintenance of a differentiated and fully functional phenotype of vascular SMCs, as well as in the regulation of migratory properties, proliferation, and matrix turnover.
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Risinger GM, Hunt TS, Updike DL, Bullen EC, Howard EW. Matrix metalloproteinase-2 expression by vascular smooth muscle cells is mediated by both stimulatory and inhibitory signals in response to growth factors. J Biol Chem 2006; 281:25915-25. [PMID: 16854986 DOI: 10.1074/jbc.m513513200] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In response to growth factors, vascular smooth muscle cells (VSMCs) undergo a phenotypic modulation from a contractile, non-proliferative state to an activated, migratory state. This transition is characterized by changes in their gene expression profile, particularly by a significant down-regulation of contractile proteins. Platelet-derived growth factor (PDGF)-BB has long been known to initiate VSMC de-differentiation and mitogenesis. Insulin-like growth factor (IGF)-I, on the other hand, has differing effects depending on the model studied. Here, we report that both IGF-I and PDGF-BB stimulated VSMC de-differentiation of rat heart-derived SMCs in culture, although only PDGF-BB was capable of inducing proliferation. Although both PDGF-BB and IGF-I stimulation resulted in decreased smooth muscle alpha-actin expression and increased matrix metalloproteinase (MMP)-2 expression, the response to IGF-I was significantly more rapid. The increased MMP-2 expression in response to both growth factors was due to increased transcription rates and was dependent on the action of phosphatidylinositol 3-kinase (PI3K) and its downstream effector, Akt. Both PDGF-BB and IGF-I activated PI3K/Akt to similar degrees; however, only PDGF-BB concomitantly stimulated an inhibitory signaling pathway that antagonized the effects of Akt but did not alter the extent or duration of Akt activation. Together, these findings suggest that changes in MMP-2 expression are part of the program of VSMC phenotypic modulation and that both PDGF-BB and IGF-I, despite their different abilities to induce proliferation in this model, are capable of inducing VSMC activation.
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Affiliation(s)
- George M Risinger
- Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104, USA
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Shynlova O, Tsui P, Dorogin A, Chow M, Lye SJ. Expression and Localization of Alpha-Smooth Muscle and Gamma-Actins in the Pregnant Rat Myometrium1. Biol Reprod 2005; 73:773-80. [PMID: 15972885 DOI: 10.1095/biolreprod.105.040006] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
The myometrium undergoes dramatic changes as pregnancy progresses through phases of proliferation, hypertrophy, contractile state and labor. In this study, we showed that the composition of the muscle actin isoforms, a major component of the myometrial contractile apparatus and cytoskeleton, was modified during pregnancy. The expression of smooth muscle alpha-actin (Acta2, which we abbreviate as alpha-SM-actin) and gamma-actin mRNAs and proteins was examined by real-time polymerase chain reaction and Western immunoblot, and was localized with immunohistochemistry, in the nonpregnant, pregnant, and postpartum rat uterus. Both alpha-SM-actin (vascular specific actin isoform) and gamma-actin (predominant in visceral smooth muscle) were detected in the rat myometrium. Myometrial expression of alpha-SM-actin mRNA and protein was high throughout pregnancy. The transcript and protein levels of gamma-actin were increased significantly in the second part of gestation (31.8-fold increase for mRNA and 16.7-fold increase for protein relative to nonpregnant). The localization of gamma-actin was markedly altered during pregnancy. In early gestation, myometria from empty and gravid uterine horns of the unilaterally pregnant rats showed abundant gamma-actin immunostaining in the longitudinal layer but weak staining in the circular layer. Gamma-actin immunostaining increased in only the circular layer of the gravid horn after midgestation and remained low in the empty one. Gamma-actin protein translocated to the membranous region of uterine myocytes at late gestation. The temporal alteration in gamma-actin expression and localization at late gestation suggested that this change in myometrial composition of contractile proteins is important to adequately prepare the myometrium for the development of optimal contractions during labor.
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Affiliation(s)
- Oksana Shynlova
- Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada
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Yoshida K, Nishida W, Hayashi K, Ohkawa Y, Ogawa A, Aoki J, Arai H, Sobue K. Vascular Remodeling Induced by Naturally Occurring Unsaturated Lysophosphatidic Acid In Vivo. Circulation 2003; 108:1746-52. [PMID: 14504178 DOI: 10.1161/01.cir.0000089374.35455.f3] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND We previously identified unsaturated (16:1, 18:1, and 18:2) but not saturated (12:0, 14:0, 16:0, and 18:0) lysophosphatidic acids (LPAs) as potent factors for vascular smooth muscle cell (VSMC) dedifferentiation. Unsaturated LPAs strongly induce VSMC dedifferentiation via the coordinated activation of the extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase (p38MAPK), resulting in the proliferation and migration of dedifferentiated VSMCs. Here, we investigated the effects of 18:1 and 18:0 LPAs (as representative unsaturated and saturated LPAs, respectively) on the vasculature in vivo. METHODS AND RESULTS Rat common carotid arteries (CCAs) were treated transiently with 18:1 or 18:0 LPA and then examined by histological and biochemical analyses. The 18:1 but not 18:0 LPA potently induced vascular remodeling that was composed primarily of neointima. The incorporation of [3H]18:1 LPA into the CCAs revealed that a sufficient amount of unmetabolized [3H]18:1 LPA to induce VSMC dedifferentiation was present in the vascular wall. The 18:1 LPA-induced neointimal formation in vivo was also dependent on the coordinated activation of ERK and p38MAPK. Unlike balloon-injured CCAs, the 18:1 LPA-treated CCAs showed a histological similarity to human atherosclerotic arteries. CONCLUSIONS This is the first report demonstrating a role for a naturally occurring unsaturated LPA in inducing vascular remodeling in vivo and provides a novel animal model for neointimal formation.
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MESH Headings
- Animals
- Arterial Occlusive Diseases/chemically induced
- Arterial Occlusive Diseases/enzymology
- Arterial Occlusive Diseases/pathology
- Arteriosclerosis/pathology
- Carotid Artery, Common/drug effects
- Carotid Artery, Common/enzymology
- Carotid Artery, Common/pathology
- Carotid Stenosis/chemically induced
- Carotid Stenosis/enzymology
- Carotid Stenosis/pathology
- Cells, Cultured
- Endothelium, Vascular/drug effects
- Endothelium, Vascular/metabolism
- Fats, Unsaturated/toxicity
- Humans
- Lysophospholipids/chemistry
- Lysophospholipids/toxicity
- Male
- Mitogen-Activated Protein Kinases/physiology
- Muscle, Smooth, Vascular/drug effects
- Muscle, Smooth, Vascular/metabolism
- NF-kappa B/metabolism
- Rats
- Rats, Sprague-Dawley
- p38 Mitogen-Activated Protein Kinases
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Affiliation(s)
- Kenji Yoshida
- Department of Neuroscience, Osaka University Graduate School of Medicine (D13), 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan
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Ohkawa Y, Hayashi K, Sobue K. Calcineurin-mediated pathway involved in the differentiated phenotype of smooth muscle cells. Biochem Biophys Res Commun 2003; 301:78-83. [PMID: 12535643 DOI: 10.1016/s0006-291x(02)02965-0] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The calcineurin-mediated pathway is involved in skeletal and cardiac hypertrophy and vascular development in vivo, but the relationship between this pathway and the phenotype of smooth muscle cells (SMCs) remains unknown. Using visceral SMCs in culture as a model system of differentiated SMCs, we investigated the role of the calcineurin-mediated pathway in maintaining the differentiated phenotype of SMCs, which depends on the insulin-like growth factor (IGF-I)-triggered activation of the phosphatidylinositol 3-kinase (PI3-K)/protein kinase B (PKB(Akt)) pathway. Treatment with calcineurin inhibitors, cyclosporin A or FK506, or the forced expression of the natural calcineurin inhibitor, CAIN, induced SMC dedifferentiation. Notably, suppression of the promoter activities of the SMC molecular markers caldesmon and alpha1 integrin by blocking the PI3-K/PKB(Akt) pathway was rescued by the forced expression of constitutively active calcineurin Aalpha, suggesting that the calcineurin-mediated pathway is critical for maintaining the differentiated phenotype of SMCs and works downstream of the PI3-K/PKB(Akt) pathway.
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Affiliation(s)
- Yasuyuki Ohkawa
- Department of Neuroscience, Osaka University Graduate School of Medicine (D13), 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan
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Zheng Y, Weber WT, Wang S, Wein AJ, Zderic SA, Chacko S, DiSanto ME. Generation of a cell line with smooth muscle phenotype from hypertrophied urinary bladder. Am J Physiol Cell Physiol 2002; 283:C373-82. [PMID: 12055106 DOI: 10.1152/ajpcell.00002.2002] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We have established a cell line from hypertrophied rabbit urinary bladder smooth muscle (SM) that stably expresses SM myosin (SMM). These cells, termed BSM, are spindle shaped and form swirls, similar to the "hills and valleys" described for cultured aortic SM cells. Western blotting revealed that BSM expresses the amino-terminal SMM heavy chain isoform SM-B, the carboxy-terminal SM1 and SM2 isoforms, and SM alpha-actin. In addition, they express cGMP-dependent protein kinase G, made by contractile SM cells in vitro but not by noncontractile cells synthesizing extracellular matrix. Immunofluorescence studies indicate a homogeneous population of cells expressing alpha-actin and SMM, including the SM-B isoform, and karyotyping demonstrates a stable 4N chromosomal pattern. These cells also express calcium-dependent myosin light chain kinase and phosphatase activity and contract in response to the muscarinic agonist bethanechol. To our knowledge, BSM is the first visceral SM cell line that expresses the SM-B isoform and might serve as a useful model to study the transcriptional regulation of tissue-specific SMM isoforms in differentiation and pathological SM.
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Affiliation(s)
- Yongmu Zheng
- Division of Urology, University of Pennsylvania, Philadelphia 19104, USA
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Nishida W, Nakamura M, Mori S, Takahashi M, Ohkawa Y, Tadokoro S, Yoshida K, Hiwada K, Hayashi K, Sobue K. A triad of serum response factor and the GATA and NK families governs the transcription of smooth and cardiac muscle genes. J Biol Chem 2002; 277:7308-17. [PMID: 11744740 DOI: 10.1074/jbc.m111824200] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Serum response factor and the (CC(A/T)(6)GG) (CArG) box interact to promote the transcription of c-fos and muscle genes; this tissue-specific activity may require co-regulators for serum response factor. The alpha(1) integrin promoter contains two cis-elements besides the CArG box: a TAAT sequence, a consensus binding site for homeoproteins, and a GATA-binding box. As a candidate TAAT-binding factor, we cloned an NK family homeobox gene, Nkx-3.2, which is expressed mainly in smooth muscle tissues and skeletal structures. Nkx-3.2, serum response factor, and GATA-6 were co-expressed only in the medial smooth muscle layer of arteries. These three transcription factors formed a complex with their corresponding cis-elements and cooperatively transactivated smooth muscle genes, including alpha(1) integrin, SM22alpha, and caldesmon. Cardiac muscle-specific members of the NK and GATA families exist, and the triad of Nkx-2.5, serum response factor, and GATA-4 also transactivated the cardiac atrial natriuretic factor gene, which contains a CArG-like box, a GATA-binding box, and an NK-binding element. Our findings demonstrate that smooth and cardiac muscle have a shared transcriptional machinery and that the GATA and NK families confer muscle specificity on the serum response factor/CArG interaction.
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Affiliation(s)
- Wataru Nishida
- Department of Neuroscience (D13), Osaka University Graduate School of Medicine, Yamadaoka 2-2, Suita City, Osaka 565-0871, Japan
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Abstract
Evidence is accumulating to suggest that actin filament remodeling is critical for smooth muscle contraction, which implicates actin filament ends as important sites for regulation of contraction. Tropomodulin (Tmod) and smooth muscle leiomodin (SM-Lmod) have been found in many tissues containing smooth muscle by protein immunoblot and immunofluorescence microscopy. Both proteins cofractionate with tropomyosin in the Triton-insoluble cytoskeleton of rabbit stomach smooth muscle and are solubilized by high salt. SM-Lmod binds muscle tropomyosin, a biochemical activity characteristic of Tmod proteins. SM-Lmod staining is present along the length of actin filaments in rat intestinal smooth muscle, while Tmod stains in a punctate pattern distinct from that of actin filaments or the dense body marker α-actinin. After smooth muscle is hypercontracted by treatment with 10 mM Ca2+, both SM-Lmod and Tmod are found near α-actinin at the periphery of actin-rich contraction bands. These data suggest that SM-Lmod is a novel component of the smooth muscle actin cytoskeleton and, furthermore, that the pointed ends of actin filaments in smooth muscle may be capped by Tmod in localized clusters.
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Affiliation(s)
- C A Conley
- Space Life Sciences, MS 239-11, National Aeronautics and Space Administration Ames Research Center, Moffett Field, CA 94035-1000, USA.
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