doi: 10.1161/01.RES.0000263446.33849.ed
© 2007 American Heart Association, Inc.
Editorials |
Move On!
Smooth Muscle Cell Motility Paired Down
From the Institute for Medicine and Engineering, Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia.
Correspondence to Peter Lloyd Jones, Associate Professor, Pathology and Laboratory Medicine, Institute for Medicine and Engineering, University of Pennsylvania, 1010 Vagelos Research Laboratories, 3340 Smith Walk, Philadelphia, PA 19104-6383. E-mail jonespl{at}mail.med.upenn.edu
See related article, pages 817–825
Key Words: motility • homeobox genes • Prx1 • matrix • smooth muscle • tenascin-C
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Introduction |
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 Top Introduction Homeobox GenesPaired-Related Homeobox Gene,...Prx1 Responds to, and...References |
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A cardinal feature of the response to injury within the muscularized, adult blood vessel wall is the transformation of an highly organized, isometric, cytoskeletal archetype, housed within vascular smooth muscle cells (SMCs), to one that supports cell migration, the function of which is to elicit repair.1 Such reorganization of the SMC cytoskeleton permits cells to move from the comfort of their controlled environment, which includes the surrounding extracellular matrix (ECM) and their neighboring cells, to the site of injury. Cytoskeletal remodeling also initiates other functions required for the injury-repair response, including SMC proliferation, and the creation of a provisional ECM that supports cell motility, growth and survival.2,3 For the most part, these and many other repair-related processes, including the recruitment and differentiation of inflammatory and stem cells to sites of injury,4,5 are coordinated through changes in cell-cell and cell–matrix adhesion, which collectively act with numerous other intrinsic and extrinsic factors, to stimulate or repress programs of signal transduction and gene expression. Sometimes, however, overexuberant responses to injury lead to hyper-repair of blood vessels, leaving them occluded and functionless.1,6 Thus, identifying molecules and pathways that control cytoskeletal homeostasis and remodeling represents a critical step in comprehending how blood vessels develop, and how SMCs contained therein adapt to injury in the fetal-, neo-, and postnatal periods.
With respect to the general cellular mechanisms leading to increased SMC motility, reorganization of the cytoskeleton relies on the recruitment of multiple signaling and adaptor proteins to focal or fibrillar adhesion sites that reiteratively form, deconstruct and regenerate themselves, allowing cells to detach and reattach to the existing and provisional matrix on which they exert a tractional force.7 In essence, adhesion sites not only contain solid-state, cytoskeleton-enriched scaffolds that transmit force from the outside of the cell to their interior and back again, but they also represent specialized subcellular, multiprotein, signaling nodes that allow cytoskeletal remodeling and movement to occur via their immediate (ie, local phosphorylation of focal adhesion proteins) and long-term (ie, signal transduction and gene expression) effects.
In this issue of Circulation Research, Jin and colleagues8 report on their discovery of a novel pathway controlling SMC migration, with the paired-related homeobox gene transcription factor, Prx1, at its core. Previously, this group showed that lipoma preferred partner (LPP) is highly expressed at adhesion sites in vascular SMCs and tissues, and that this protein controls SMC motility.9 LPP is a focal adhesion protein containing both proline rich- and LIM -domains, through which LPP is believed to mediate the assembly of multiprotein focal complexes that regulate cell motility and gene expression.10 Furthermore, expression of LPP depends on myocardin and RhoA/ROCK,9 suggesting that LPP responds to changes in actin dynamics. In their latest study, Jin and colleagues extended these findings to show that induction of LPP is accompanied by the appearance of palladin, a cytoskeletal associated protein that interacts with specific LIM domains within LPP. Palladin is a key regulator of actin organization, and it localizes to focal adhesions and periodically along stress fibers. In keeping with their intracellular locale, overexpression of LPP and palladin enhanced cell migration and spreading. Furthermore, expression of LPP and palladin were both regulated by actin dynamics, indicating that cell adhesion in itself controls LPP and palladin. In support of this, focal adhesion kinase (FAK), which is used to remodel focal adhesions to facilitate SMC proliferation and migration,11 was shown to be essential for expression of both LPP and palladin. This led the investigators to determine how FAK regulates LPP- and palladin-dependent cell migration, and for this portion of the study, they focused on Prx1, a paired-related homeobox gene that has been shown to promote cell migration.3 Importantly, expression of Prx1 in FAK-null cells resulted in induction of LPP, palladin, SM gene expression and increased motility. Finally, they showed that LPP and palladin are upregulated in SMCs following vascular injury in vivo. Although the activities of FAK and expression of Prx1 were not explored in vivo, previous work has shown that these molecules operate within injured and remodeling muscularized arteries.11–13 Based on the available evidence, it is likely that activated FAK controls cell motility not only by directly regulating focal adhesion turnover, but also by controlling the expression of key focal adhesion and cytoskeletal-associated molecules, such as LPP and palladin, that also participate in focal adhesion formation and turnover. Significantly, these studies identify LPP and palladin as targets for FAK and its downstream target, Prx1, supporting the general notion that certain homeobox genes not only respond to changes in cell adhesion within developing and diseased blood vessels, but that these transcription factors form part of a dynamic feedback loop which controls cell behavior at the level of cell adhesion.3,14–19
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Homeobox Genes |
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TopIntroductionHomeobox GenesPaired-Related Homeobox Gene,...Prx1 Responds to, and...References |
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Homeobox genes encode highly conserved transcription factors that control positional identity and morphogenesis throughout development.20 All proteins encoded by homeobox genes contain a DNA-binding motif, designated the homeodomain, which folds into 3
-helices. This motif arises from a 180 nucleotide sequence designated the homeobox, so called because mutations in some of these genes result in homeotic transformations, in which one body structure replaces another. Since the discovery of homeobox (Hox) genes in Drosophila, homologous genes have been identified in vertebrates including humans, who possess 39 Hox genes arranged over 4 separate clusters. In addition, at least 160 other divergent homeobox genes have been identified that lie outside the Hox clusters, all of which possess a homeodomain, and this includes Prx1.21 In general, binding of homeobox proteins to target promoter sequences, and subsequent transcriptional activation of downstream genes, represents the predominant manner in which homeobox genes control tissue patterning and cellular events required for development, such as proliferation, migration, differentiation, and survival. Given this, it is of interest that Jin et al report the existence of phylogenetically conserved Prx1 binding sites in the promoter regions of LPP and palladin.8 |
Paired-Related Homeobox Gene, Prx1 |
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TopIntroductionHomeobox GenesPaired-Related Homeobox Gene,...Prx1 Responds to, and...References |
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The paired-related homeobox gene, Prx1 (also known as Mhox, Prrx1, Phox1, Pmx1 and Rhox) encodes a divergent, paired-related homeobox gene that is expressed throughout embryogenesis, predominantly in a mesenchyme-specific pattern.22 In presomite murine embryos, Prx1 appears in the ectoderm, and at later stages in the extraembryonic mesoderm, mandibular arch and hyoid and branchial arches, limb buds, somatopleure, cranial mesenchyme, dermis, prechondrogenic and preosteogenic condensations, and later in the perichondrium and periosteum.23–25 In the developing systemic vasculature, Prx1 is highly evident in prospective connective tissues, including the endocardial cushions and valves, the epicardium, and the wall of the great arteries and veins. In the chick embryo, Prx1 is first evident within the primary vessel wall of coronary and pulmonary arteries, but as the vessels thicken and mature, this pattern becomes more restricted to nonmuscle cells in the adventitial and outer medial layers. Collectively, these data suggest that Prx1 controls the expression of genes involved in early differentiation of ECs, as well as the assembly and segregation of different cell types within the differentiating blood vessel wall, including vascular SMCs and adventitial fibroblasts. In support of this, Prx1-null mice display a spectrum of developmental vascular anomalies, including abnormal positioning and awkward curvature of the aortic arch, and a misdirected and elongated ductus arteriosus.24 Furthermore, Prx1-null mice are cyanotic and die shortly after birth from respiratory distress,25 resulting from an inability to form distal pulmonary blood vessels, because of failed pulmonary vasculogenesis and angiogenesis.26 Of relevance to the present study, we have recently discovered that Prx1-null mice possess SMC differentiation defects within the pulmonary vascular bed (Ihida-Stansbury and Jones, unpublished data, 2006), a finding that is consistent with previous work showing that Prx1 regulates smooth muscle-specific gene expression in vitro by enhancing binding of serum response factor to CarG elements,27 a DNA motif present in many smooth muscle-specific gene promoters.28 Alternatively, it is possible that Prx1-expressing fetal endothelial cells promote the recruitment and subsequent differentiation of adjacent mural cells within the lung, and that this ability is lost when Prx1 is absent.
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Prx1 Responds to, and Regulates Extracellular Matrix Composition |
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TopIntroductionHomeobox GenesPaired-Related Homeobox Gene,...Prx1 Responds to, and...References |
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Although the in vivo functions of Prx1 in the developing vasculature are still not fully understood, a number of studies indicate that this gene modifies the behavior of adult arteries, postinjury, by regulating the expression of tenascin-C (TN-C), an ECM glycoprotein which supports SMC proliferation, survival and motility,2,29,30 as well as fibroblast motility.3 TN-C has also been shown to be crucial for neointimal hyperplasia at anastomotic sites,31 as well as for myofibroblast recruitment, albeit in the myocardium.32 Since analysis of null mice revealed that Prx1 is required for TN-C expression during vascular development,26 these and other studies strongly indicate that Prx1 controls SMC behavior at the level of focal adhesions,8 the cytoskeleton,3,8 and the extracellular matrix.2,3,26,30 To understand these interrelated functions, most investigations have focused on the regulation of TN-C as a suitable Prx1 end point.
Multiple factors induce TN-C, including ECM-degrading matrix metalloproteinases (MMPs). For example, inhibition of MMP activity suppresses TN-C expression and pulmonary artery SMC proliferation, and reduces the severity of vascular lesions.2,30 These studies indicate that MMPs lie upstream in an adhesion-dependent signaling pathway that controls TN-C. Consistent with this, the TN-C gene promoter contains an ECM-responsive element that is silenced on native type I collagen, but is activated on type I collagen that has been remodeled by MMPs.33 The ECM-responsive element in the TN-C gene promoter was subsequently shown to harbor an homeodomain binding site which was essential for TN-C gene promoter activity on denatured collagen, suggesting that induction of TN-C in response to changes in cell adhesion potentially depends on homeobox proteins.12,33 In this regard, Prx1 represented an ideal candidate. For example, like TN-C, Prx1 is expressed during embryogenesis, predominantly in a mesenchyme-specific pattern.34 In the developing cardiovascular system, Prx1 expression overlaps with TN-C in the endocardial cushions and valves, the epicardium and the wall of the great arteries and veins.23 Furthermore, as stated above, vascular analomalies that arise in Prx1-null mice are accompanied by a failure to produce TN-C26. In further support of a link between Prx1 and TN-C expression, examination of hypertensive adult rats lungs29 and humans with familial forms of pulmonary hypertension13 showed that Prx1 is induced within remodeling pulmonary arteries, colocalizing with TN-C and proliferating SMCs. Moreover, identical to TN-C, Prx1 expression is suppressed and induced by native and denatured type I collagen respectively, whereas overexpression of Prx1 drives TN-C gene transcription and SMC proliferation.12 Because expression of Prx1 and TN-C both depend on changes in cell adhesion to the ECM and integrins, and because Prx1 promotes TN-C gene transcription,12 it was hypothesized that activation (ie, tyrosine phosphorylation) of FAK would promote Prx1-dependent induction of TN-C. In keeping with this, embryonic fibroblasts and embryos that are devoid of FAK, express significantly reduced levels of Prx1 and TN-C, when compared with their wild-type counterparts.26 On the other hand, reintroduction of activated FAK into FAK-null cells restored expression of Prx1 and TN-C. Furthermore, reexpression of Prx1 in FAK-null cells reactivated TN-C expression, and at a functional level, FAK-dependent induction of Prx1 and TN-C was shown to be essential for haptotactic cell migration.3
In summary, it is apparent that Prx1 plays multiple roles in controlling SMC behavior, including motility, not only by creating an appropriate signaling scenario at focal adhesions and the cytoskeleton that supports this function, but also by generating an ECM on which SMCs are able to migrate and proliferate. Future studies will no doubt reveal additional mechanistic insights into how cell adhesion and Prx1 are coupled within vascular SMCs, and whether Prx1 and its downstream genes represent suitable therapeutic targets for vascular pathologies characterized by increased SMC proliferation, migration, as well as differentiation defects and ectopic ECM deposition. In keeping with this, anti–TN-C based strategies have already being evaluated in phase II clinical trials for targeting solid tumors that also possess SM differentiation defects.35,36 Whether these types of adhesion-based approaches can be extrapolated to treat the injured blood vessel wall awaits investigation.
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Acknowledgments |
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Sources of Funding
This work was supported by NIH/NHLBI grants R01 HL68798-01 and R01HL079196-02.
Disclosures
None.
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Footnotes |
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The opinions expressed in this editorial are not necessarily those of the editors or of the American Heart Association.
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References |
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TopIntroductionHomeobox GenesPaired-Related Homeobox Gene,...Prx1 Responds to, and...References |
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1. Owens GK, Kumar MS, Wamhoff BR. Molecular regulation of vascular smooth muscle cell differentiation in development and disease. Physiol Rev. 2004; 84: 767–801.
2. Jones PL, Crack J, Rabinovitch M. Regulation of tenascin-C, a vascular smooth muscle cell survival factor that interacts with the alpha v beta 3 integrin to promote epidermal growth factor receptor phosphorylation and growth. J Cell Biol. 1997; 139: 279–293.
3. McKean DM, Sisbarro L, Ilic D, Kaplan-Alburquerque N, Nemenoff R, Weiser-Evans M, Kern MJ, Jones PL. FAK induces expression of Prx1 to promote tenascin-C-dependent fibroblast migration. J Cell Biol. 2003; 161: 393–402.
4. Schober A, Weber C. Mechanisms of monocyte recruitment in vascular repair after injury. Antioxid Redox Signal. 2005; 7: 1249–1257.[CrossRef][Medline] [Order article via Infotrieve]
5. Nikolova G, Strilic B, Lammert E. The vascular niche and its basement membrane. Trends Cell Biol. 2007; 17: 19–25.[CrossRef][Medline] [Order article via Infotrieve]
6. Loirand G, Guerin P, Pacaud P. Rho kinases in cardiovascular physiology and pathophysiology. Circ Res. 2006; 98: 322–334.
7. Boudreau NJ, Jones PL. Extracellular matrix and integrin signalling: the shape of things to come. Biochem J. 1999; 339 (Pt 3): 481–488.[CrossRef][Medline] [Order article via Infotrieve]
8. Jin L, Kern MJ, Otey CA, Wamhoff BR, Somlyo AV. Angiotensin II, focal adhesion kinase, and PRX1 enhance smooth muscle expression of lipoma preferred partner and its newly identified binding partner palladin to promote cell migration. Circ Res. 2007; 100: 817–825.
9. Gorenne I, Jin L, Yoshida T, Sanders JM, Sarembock IJ, Owens GK, Somlyo AP, Somlyo AV. LPP expression during in vitro smooth muscle differentiation and stent-induced vascular injury. Circ Res. 2006; 98: 378–385.
10. Majesky MW. Organizing motility: LIM domains, LPP, and smooth muscle migration. Circ Res. 2006; 98: 306–308.
11. Taylor JM, Mack CP, Nolan K, Regan CP, Owens GK, Parsons JT. Selective expression of an endogenous inhibitor of FAK regulates proliferation and migration of vascular smooth muscle cells. Mol Cell Biol. 2001; 21: 1565–1572.
12. Jones FS, Meech R, Edelman DB, Oakey RJ, Jones PL. Prx1 controls vascular smooth muscle cell proliferation and tenascin-C expression and is upregulated with Prx2 in pulmonary vascular disease. Circ Res. 2001; 89: 131–138.
13. Ihida-Stansbury K, McKean D, Lane K, Loyd J, Wheeler L, Morrell NW, Jones PL. Tenascin-C is induced by mutated BMP type II receptors in familial forms of pulmonary arterial hypertension. Am J Physiol Lung Cell Mol Physiol. 2006; 291: 694–702.
14. Carrio M, Arderiu G, Myers C, Boudreau NJ. Homeobox D10 induces phenotypic reversion of breast tumor cells in a three-dimensional culture model. Cancer Res. 2005; 65: 7177–7185.
15. Hansen SL, Myers CA, Charboneau A, Young DM, Boudreau N. HoxD3 accelerates wound healing in diabetic mice. Am J Pathol. 2003; 163: 2421–2431.
16. Mace KA, Hansen SL, Myers C, Young DM, Boudreau N. HOXA3 induces cell migration in endothelial and epithelial cells promoting angiogenesis and wound repair. J Cell Sci. 2005; 118 (Pt 12): 2567–2577.
17. Myers C, Charboneau A, Boudreau N. Homeobox B3 promotes capillary morphogenesis and angiogenesis. J Cell Biol. 2000; 148: 343–351.
18. Myers C, Charboneau A, Cheung I, Hanks D, Boudreau N. Sustained expression of homeobox D10 inhibits angiogenesis. Am J Pathol. 2002; 161: 2099–2109.
19. Witzenbichler B, Kureishi Y, Luo Z, Le Roux A, Branellec D, Walsh K. Regulation of smooth muscle cell migration and integrin expression by the Gax transcription factor. J Clin Invest. 1999; 104: 1469–1480.[Medline] [Order article via Infotrieve]
20. McGinnis W, Krumlauf R. Homeobox genes and axial patterning. Cell. 1992; 68: 283–302.[CrossRef][Medline] [Order article via Infotrieve]
21. Jones PL. Homeobox genes in pulmonary vascular development and disease. Trends Cardiovasc Med. 2003; 13: 336–345.[CrossRef][Medline] [Order article via Infotrieve]
22. Cserjesi P, Lilly B, Bryson L, Wang Y, Sassoon DA, Olson EN. MHox: a mesodermally restricted homeodomain protein that binds an essential site in the muscle creatine kinase enhancer. Development. 1992; 115: 1087–1101.[Abstract]
23. Bergwerff M, Gittenberger-de Groot AC, DeRuiter MC, van Iperen L, Meijlink F, Poelmann RE. Patterns of paired-related homeobox genes PRX1 and PRX2 suggest involvement in matrix modulation in the developing chick vascular system. Dev Dyn. 1998; 213: 59–70.[CrossRef][Medline] [Order article via Infotrieve]
24. Bergwerff M, Gittenberger-de Groot AC, Wisse LJ, DeRuiter MC, Wessels A, Martin JF, Olson EN, Kern MJ. Loss of function of the Prx1 and Prx2 homeobox genes alters architecture of the great elastic arteries and ductus arteriosus. Virchows Arch. 2000; 436: 12–19.[CrossRef][Medline] [Order article via Infotrieve]
25. Martin JF, Bradley A, Olson EN. The paired-like homeo box gene MHox is required for early events of skeletogenesis in multiple lineages. Genes Dev. 1995; 9: 1237–1249.
26. Ihida-Stansbury K, McKean DM, Gebb SA, Martin JF, Stevens T, Nemenoff R, Akeson A, Vaughn J, Jones PL. Paired-related homeobox gene Prx1 is required for pulmonary vascular development. Circ Res. 2004; 94: 1507–1514.
27. Hautmann MB, Thompson MM, Swartz EA, Olson EN, Owens GK. Angiotensin II-induced stimulation of smooth muscle alpha-actin expression by serum response factor and the homeodomain transcription factor MHox. Circ Res. 1997; 81: 600–610.
28. Sun Q, Chen G, Streb JW, Long X, Yang Y, Stoeckert CJ Jr, Miano JM. Defining the mammalian CArGome. Genome Res. 2006; 16: 197–207.
29. Jones PL, Rabinovitch M. Tenascin-C is induced with progressive pulmonary vascular disease in rats and is functionally related to increased smooth muscle cell proliferation. Circ Res. 1996; 79: 1131–1142.
30. Cowan KN, Jones PL, Rabinovitch M. Elastase and matrix metalloproteinase inhibitors induce regression, and tenascin-C antisense prevents progression, of vascular disease. J Clin Invest. 2000; 105: 21–34.[Medline] [Order article via Infotrieve]
31. Yamamoto K, Onoda K, Sawada Y, Fujinaga K, Imanaka-Yoshida K, Shimpo H, Yoshida T, Yada I. Tenascin-C is an essential factor for neointimal hyperplasia after aortotomy in mice. Cardiovasc Res. 2005; 65: 737–742.
32. Tamaoki M, Imanaka-Yoshida K, Yokoyama K, Nishioka T, Inada H, Hiroe M, Sakakura T, Yoshida T. Tenascin-C regulates recruitment of myofibroblasts during tissue repair after myocardial injury. Am J Pathol. 2005; 167: 71–80.
33. Jones PL, Jones FS, Zhou B, Rabinovitch M. Induction of vascular smooth muscle cell tenascin-C gene expression by denatured type I collagen is dependent upon a beta3 integrin-mediated mitogen-activated protein kinase pathway and a 122-base pair promoter element. J Cell Sci. 1999; 112 (Pt 4): 435–445.[Abstract]
34. Leussink B, Brouwer A, el Khattabi M, Poelmann RE, Gittenberger-de Groot AC, Meijlink F. Expression patterns of the paired-related homeobox genes MHox/Prx1 and S8/Prx2 suggest roles in development of the heart and the forebrain. Mech Dev. 1995; 52: 51–64.[CrossRef][Medline] [Order article via Infotrieve]
35. Reardon DA, Akabani G, Coleman RE, Friedman AH, Friedman HS, Herndon JE, 2nd, McLendon RE, Pegram CN, Provenzale JM, Quinn JA, Rich JN, Vredenburgh JJ, Desjardins A, Gururangan S, Badruddoja M, Dowell JM, Wong TZ, Zhao XG, Zalutsky MR, Bigner DD. Salvage radioimmunotherapy with murine iodine-131-labeled antitenascin monoclonal antibody 81C6 for patients with recurrent primary and metastatic malignant brain tumors: phase II study results. J Clin Oncol. 2006; 24: 115–122.
36. Wesseling P, Schlingemann RO, Rietveld FJ, Link M, Burger PC, Ruiter DJ. Early and extensive contribution of pericytes/vascular smooth muscle cells to microvascular proliferation in glioblastoma multiforme: an immuno-light and immuno-electron microscopic study. J Neuropathol Exp Neurol. 1995; 54: 304–310.[Medline] [Order article via Infotrieve]
Related Article:
Circ. Res. 2007 100: 817-825.
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