Editing Fibronectin

{{Short description|Protein involved in cell adhesion, cell growth, cell migration and differentiation}}
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[[File:The Modular Structure of Fibronectin and its Binding Domains.png|thumb|right|400px|The modular structure of fibronectin and its binding domains]]
'''Fibronectin''' is a high-[[molecular weight]] (~500-~600 [[Dalton (unit)|kDa]])<ref>{{cite journal | vauthors = Mitrović S, Mitrović D, Todorović V | title = [Fibronectin--a multifunctional glycoprotein] | journal = Srpski Arhiv Za Celokupno Lekarstvo | volume = 123 | issue = 7-8 | pages = 198–201 | date = July 1995 | pmid = 17974429 | url = https://pubmed.ncbi.nlm.nih.gov/17974429/#:~:text=Human%20plasma%20fibronectin%20is%20a,to%20their%20C-terminal%20ends. | archive-url = https://web.archive.org/web/20220209115441/https://pubmed.ncbi.nlm.nih.gov/17974429/ | archive-date = 9 February 2022 }}</ref> [[glycoprotein]] of the [[extracellular matrix]] that binds to [[cell membrane|membrane]]-spanning [[receptor proteins]] called [[integrins]].<ref name="pmid12244123">{{cite journal | vauthors = Pankov R, Yamada KM | title = Fibronectin at a glance | journal = Journal of Cell Science | volume = 115 | issue = Pt 20 | pages = 3861–3 | date = Oct 2002 | pmid = 12244123 | doi = 10.1242/jcs.00059 | doi-access = free }}</ref> Fibronectin also binds to other extracellular matrix proteins such as [[collagen]], [[fibrin]], and [[heparan sulfate]] [[proteoglycans]] (e.g. [[syndecans]]).

Fibronectin exists as a [[protein dimer]], consisting of two nearly identical [[monomers]] linked by a pair of [[disulfide bonds]].<ref name="pmid12244123"/> The fibronectin protein is produced from a single gene, but [[alternative splicing]] of its [[pre-mRNA]] leads to the creation of several [[isoforms]].

Two types of fibronectin are present in [[vertebrates]]:<ref name="pmid12244123"/>
* soluble plasma fibronectin (formerly called "cold-insoluble globulin", or CIg) is a major protein component of [[blood plasma]] (300 μg/ml) and is produced in the [[liver]] by [[hepatocytes]].
* insoluble cellular fibronectin is a major component of the extracellular matrix. It is secreted by various [[cell (biology)|cells]], primarily [[fibroblasts]], as a soluble [[protein dimer]] and is then assembled into an insoluble matrix in a complex cell-mediated process.

Fibronectin plays a major role in [[cell adhesion]], [[cell growth|growth]], [[cell migration|migration]], and [[cellular differentiation|differentiation]], and it is important for processes such as [[wound healing]] and [[embryonic development]].<ref name="pmid12244123"/>  Altered fibronectin [[gene expression|expression]], [[protein degradation|degradation]], and organization has been associated with a number of [[pathologies]], including cancer, arthritis, and [[fibrosis]].<ref name="pmid18451144">{{cite journal | vauthors = Williams CM, Engler AJ, Slone RD, Galante LL, Schwarzbauer JE | title = Fibronectin expression modulates mammary epithelial cell proliferation during acinar differentiation | journal = Cancer Research | volume = 68 | issue = 9 | pages = 3185–92 | date = May 2008 | pmid = 18451144 | pmc = 2748963 | doi = 10.1158/0008-5472.CAN-07-2673 }}</ref><ref>{{cite journal | vauthors = Kragstrup TW, Sohn DH, Lepus CM, Onuma K, Wang Q, Robinson WH, Sokolove J | title = Fibroblast-like synovial cell production of extra domain A fibronectin associates with inflammation in osteoarthritis | journal = BMC Rheumatology | volume = 3 | pages = 46 | year = 2019 | pmid = 31819923 | pmc = 6886182 | doi = 10.1186/s41927-019-0093-4 | doi-access = free }}</ref>

== Structure ==
Fibronectin exists as a protein dimer, consisting of two nearly identical [[polypeptide]] chains linked by a pair of [[C-terminal]] [[disulfide bonds]].<ref name="pmid16061370">{{cite journal | vauthors = Mao Y, Schwarzbauer JE | title = Fibronectin fibrillogenesis, a cell-mediated matrix assembly process | journal = Matrix Biology | volume = 24 | issue = 6 | pages = 389–99 | date = Sep 2005 | pmid = 16061370 | doi = 10.1016/j.matbio.2005.06.008 | doi-access =  }}</ref>  Each fibronectin [[Protein subunit|subunit]] has a molecular weight of ~230–~275 kDa<ref>{{Cite web| vauthors = Sitterley G |title=Fibronectin|url=https://www.sigmaaldrich.com/IN/en/technical-documents/technical-article/cell-culture-and-cell-culture-analysis/mammalian-cell-culture/fibronectin#:~:text=Fibronectin%20(FN)%20is%20a%20multifunctional,%20extracellular%20matrix%20glycoprotein%20composed%20of%20two%20nearly%20identical%20disulfide%20bound%20polypeptides%20of%20molecular%20weight%20220%20kDa.|website=Sigma Aldrich}}</ref> and contains multiple copies of three types of [[protein module|modules]]: type I, II, and III.  All three modules are composed of two anti-parallel [[β-sheets]] resulting in a [[Beta-sandwich]]; however, [[Fibronectin type I domain|type I]] and [[Fibronectin type II domain|type II]] are stabilized by intra-chain disulfide bonds, while [[Fibronectin type III domain|type III]] modules do not contain any disulfide bonds. The absence of disulfide bonds in type III modules allows them to partially unfold under applied force.<ref name="pmid12785106">{{cite journal | vauthors = Erickson HP | title = Stretching fibronectin | journal = Journal of Muscle Research and Cell Motility | volume = 23 | issue = 5–6 | pages = 575–80 | year = 2002 | pmid = 12785106 | doi = 10.1023/A:1023427026818 | s2cid = 7052723 }}</ref>

Three regions of variable [[RNA splicing|splicing]] occur along the length of the fibronectin [[Protomer (structural biology)|protomer]].  One or both of the "extra" type III modules (EIIIA and EIIIB) may be present in cellular fibronectin, but they are never present in plasma fibronectin.  A "variable" V-region exists between III<sub>14–15</sub> (the 14th and 15th type III module).  The V-region structure is different from the type I, II, and III modules, and its presence and length may vary.  The V-region contains the binding site for [[α4β1]] integrins.  It is present in most cellular fibronectin, but only one of the two subunits in a plasma fibronectin dimer contains a V-region sequence.

The modules are arranged into several functional and [[protein]]-binding [[protein domain|domains]] along the length of a fibronectin [[monomer]]. There are four fibronectin-binding domains, allowing fibronectin to associate with other fibronectin molecules.<ref name="pmid16061370"/>  One of these fibronectin-binding domains, I<sub>1–5</sub>, is referred to as the "assembly domain", and it is required for the initiation of fibronectin matrix assembly. Modules III<sub>9–10</sub> correspond to the "cell-binding domain" of fibronectin. The [[RGD motif|RGD sequence]] (Arg–Gly–Asp) is located in III<sub>10</sub> and is the site of [[cell adhesion|cell attachment]] via [[α5β1]] and [[αVβ3]] integrins on the cell surface. The "synergy site" is in III<sub>9</sub> and has a role in modulating fibronectin's association with [[α5β1]] [[integrins]].<ref name="pmid9398676">{{cite journal | vauthors = Sechler JL, Corbett SA, Schwarzbauer JE | title = Modulatory roles for integrin activation and the synergy site of fibronectin during matrix assembly | journal = Molecular Biology of the Cell | volume = 8 | issue = 12 | pages = 2563–73 | date = Dec 1997 | pmid = 9398676 | pmc = 25728 | doi = 10.1091/mbc.8.12.2563 }}</ref> Fibronectin also contains domains for [[fibrin]]-binding (I<sub>1–5</sub>, I<sub>10–12</sub>), [[collagen]]-binding (I<sub>6–9</sub>), [[fibulin-1]]-binding (III<sub>13–14</sub>),  [[heparin]]-binding and [[syndecan]]-binding (III<sub>12–14</sub>).<ref name="pmid16061370"/>

== Function ==
Fibronectin has numerous functions that ensure the normal functioning of [[vertebrate]] organisms.<ref name="pmid12244123"/>  It is involved in [[cell adhesion]], [[cell growth|growth]], [[cell migration|migration]], and [[cellular differentiation|differentiation]].  Cellular fibronectin is assembled into the [[extracellular matrix]], an insoluble network that separates and supports the [[organ (anatomy)|organs]] and [[tissue (biology)|tissues]] of an organism.

Fibronectin plays a crucial role in [[wound healing]].<ref>{{cite journal | vauthors = Grinnell F | title = Fibronectin and wound healing | journal = Journal of Cellular Biochemistry | volume = 26 | issue = 2 | pages = 107–116 | year = 1984 | pmid = 6084665 | doi = 10.1002/jcb.240260206 | s2cid = 28645109 }}</ref><ref name="pmid15992798">{{cite journal | vauthors = Valenick LV, Hsia HC, Schwarzbauer JE | title = Fibronectin fragmentation promotes alpha4beta1 integrin-mediated contraction of a fibrin-fibronectin provisional matrix | journal = Experimental Cell Research | volume = 309 | issue = 1 | pages = 48–55 | date = Sep 2005 | pmid = 15992798 | doi = 10.1016/j.yexcr.2005.05.024 }}</ref>  Along with [[fibrin]], [[blood plasma|plasma]] fibronectin is deposited at the site of injury, forming a [[blood clot]] that stops bleeding and protects the underlying [[tissue (biology)|tissue]].  As repair of the injured tissue continues, [[fibroblasts]] and [[macrophages]] begin to remodel the area, degrading the proteins that form the provisional [[blood clot]] matrix and replacing them with a [[extracellular matrix|matrix]] that more resembles the normal, surrounding tissue. Fibroblasts secrete [[proteases]], including [[matrix metalloproteinases]], that digest the plasma fibronectin, and then the fibroblasts secrete [[cell (biology)|cellular]] fibronectin and assemble it into an insoluble [[extracellular matrix|matrix]].  Fragmentation of fibronectin by proteases has been suggested to promote wound contraction, a critical step in [[wound healing]]. Fragmenting fibronectin further exposes its V-region, which contains the site for [[α4β1]] [[integrin]] binding. These fragments of fibronectin are believed to enhance the binding of α4β1 integrin-expressing cells, allowing them to adhere to and forcefully contract the surrounding matrix.

Fibronectin is necessary for [[embryogenesis]], and [[gene knockout|inactivating]] the [[gene]] for fibronectin results in early embryonic lethality.<ref name="pmid8306876">{{cite journal | vauthors = George EL, Georges-Labouesse EN, Patel-King RS, Rayburn H, Hynes RO | title = Defects in mesoderm, neural tube and vascular development in mouse embryos lacking fibronectin | journal = Development | volume = 119 | issue = 4 | pages = 1079–91 | date = Dec 1993 | doi = 10.1242/dev.119.4.1079 | pmid = 8306876 | url = https://dev.biologists.org/cgi/content/abstract/119/4/1079 }}</ref> Fibronectin is important for guiding [[cell adhesion|cell attachment]] and [[cell migration|migration]] during [[embryonic development]].  In [[mammalian]] development, the absence of fibronectin leads to defects in [[mesodermal]], [[neural tube]], and [[Blood vessel|vascular]] development.  Similarly, the absence of a normal fibronectin matrix in developing [[amphibians]] causes defects in [[mesodermal]] patterning and inhibits [[gastrulation]].<ref name="pmid10727862">{{cite journal | vauthors = Darribère T, Schwarzbauer JE | title = Fibronectin matrix composition and organization can regulate cell migration during amphibian development | journal = Mechanisms of Development | volume = 92 | issue = 2 | pages = 239–50 | date = Apr 2000 | pmid = 10727862 | doi = 10.1016/S0925-4773(00)00245-8 | s2cid = 2640979 | doi-access =  }}</ref>

Fibronectin is also found in normal human saliva, which helps prevent [[colonisation (biology)|colonization]] of the [[oral cavity]] and [[pharynx]] by [[pathogenic bacteria]].<ref name="pmid3305363">{{cite journal | vauthors = Hasty DL, Simpson WA | title = Effects of fibronectin and other salivary macromolecules on the adherence of Escherichia coli to buccal epithelial cells | journal = Infection and Immunity | volume = 55 | issue = 9 | pages = 2103–9 | date = Sep 1987 | pmid = 3305363 | pmc = 260663 | doi =  10.1128/IAI.55.9.2103-2109.1987| url = }}</ref>

== Matrix assembly ==
[[Cell (biology)|Cellular]] fibronectin is assembled into an [[insoluble]] [[fibrillar]] [[extracellular matrix|matrix]] in a complex cell-mediated process.<ref name="pmid12857786">{{cite journal | vauthors = Wierzbicka-Patynowski I, Schwarzbauer JE | title = The ins and outs of fibronectin matrix assembly | journal = Journal of Cell Science | volume = 116 | issue = Pt 16 | pages = 3269–76 | date = Aug 2003 | pmid = 12857786 | doi = 10.1242/jcs.00670 | s2cid = 16975447 | doi-access =  }}</ref>  Fibronectin matrix assembly begins when soluble, compact fibronectin [[protein dimer|dimers]] are [[secreted]] from cells, often [[fibroblasts]].  These soluble dimers bind to [[α5β1]] [[integrin]] receptors on the cell surface and aid in clustering the integrins.  The local [[concentration]] of integrin-bound fibronectin increases, allowing bound fibronectin [[macromolecule|molecules]] to more readily interact with one another.  Short fibronectin [[fibrils]] then begin to form between adjacent cells.  As matrix assembly proceeds, the soluble fibrils are converted into larger insoluble fibrils that comprise the [[extracellular matrix]].

Fibronectin's shift from [[soluble]] to insoluble fibrils proceeds when cryptic fibronectin-binding sites are exposed along the length of a bound fibronectin molecule. Cells are believed to stretch fibronectin by pulling on their fibronectin-bound integrin receptors. This [[force]] partially unfolds the fibronectin [[ligand (biochemistry)|ligand]], unmasking cryptic fibronectin-binding sites and allowing nearby fibronectin molecules to associate. This fibronectin-fibronectin interaction enables the soluble, cell-associated fibrils to branch and stabilize into an insoluble fibronectin [[extracellular matrix|matrix]].

A transmembrane protein, [[CD93]], has been shown to be essential for fibronectin matrix assembly (fibrillogenesis) in human dermal blood endothelial cells.<ref name="Lugano_2018">{{cite journal | vauthors = Lugano R, Vemuri K, Yu D, Bergqvist M, Smits A, Essand M, Johansson S, Dejana E, Dimberg A | title = CD93 promotes β1 integrin activation and fibronectin fibrillogenesis during tumor angiogenesis | journal = The Journal of Clinical Investigation | volume = 128 | issue = 8 | pages = 3280–3297 | date = August 2018 | pmid = 29763414 | pmc = 6063507 | doi = 10.1172/JCI97459 }}</ref> As a consequence, knockdown of CD93 in these cells resulted in the disruption of the fibronectin fibrillogenesis. Moreover, the CD93 knockout mice retinas displayed disrupted fibronectin matrix at the retinal sprouting front.<ref name="Lugano_2018" />

==Role in cancer==
Several morphological changes has been observed in [[tumors]] and tumor-derived [[cell lines]] that have been attributed to decreased fibronectin [[gene expression|expression]], increased fibronectin [[protein degradation|degradation]], and/or decreased [[gene expression|expression]] of fibronectin-binding [[receptor (biochemistry)|receptors]], such as [[α5β1]] [[integrins]].<ref name="isbn0-387-97050-9">{{cite book | author = Hynes, Richard O. | title = Fibronectins | publisher = Springer-Verlag | location = Berlin | year = 1990 | isbn = 978-0-387-97050-9 }}</ref>

Fibronectin has been implicated in [[carcinoma]] development.<ref name="pmid16397245">{{cite journal | vauthors = Han S, Khuri FR, Roman J | title = Fibronectin stimulates non-small cell lung carcinoma cell growth through activation of Akt/mammalian target of rapamycin/S6 kinase and inactivation of LKB1/AMP-activated protein kinase signal pathways | journal = Cancer Research | volume = 66 | issue = 1 | pages = 315–23 | date = Jan 2006 | pmid = 16397245 | doi = 10.1158/0008-5472.CAN-05-2367 | doi-access = free }}</ref> In [[lung carcinoma]], fibronectin [[gene expression|expression]] is increased especially in [[non-small cell lung carcinoma]]. The [[cell adhesion|adhesion]] of lung carcinoma cells to fibronectin enhances [[carcinogen|tumorigenicity]] and confers [[drug resistance|resistance]] to [[apoptosis]]-inducing [[chemotherapeutic agents]]. Fibronectin has been shown to stimulate the [[gonadal steroids]] that interact with [[vertebrate]] [[androgen receptors]], which are capable of controlling the [[gene expression|expression]] of [[cyclin D]] and related [[genes]] involved in [[cell cycle]] control. These observations suggest that fibronectin may promote lung [[neoplasm|tumor growth]]/survival and resistance to therapy, and it could represent a novel [[biological target|target]] for the development of new [[anticancer drugs]].

Fibronectin 1 acts as a potential [[biomarker]] for [[radioresistance]]<ref name="pmid20930522">{{cite journal | vauthors = Jerhammar F, Ceder R, Garvin S, Grénman R, Grafström RC, Roberg K | title = Fibronectin 1 is a potential biomarker for radioresistance in head and neck squamous cell carcinoma | journal = Cancer Biology & Therapy | volume = 10 | issue = 12 | pages = 1244–1251 | date = December 2010 | pmid = 20930522 | doi = 10.4161/cbt.10.12.13432 | doi-access = free }}</ref> and for pan-cancer prognosis.<ref name="ChiccoAlameerRahmati2022">{{cite journal | vauthors = Chicco D, Alameer A, Rahmati S, Jurman G | title = Towards a potential pan-cancer prognostic signature for gene expression based on probesets and ensemble machine learning | journal = BioData Mining | volume = 15 | issue = 1 | pages = 28 | date = November 2022 | pmid = 36329531 | pmc = 9632055 | doi = 10.1186/s13040-022-00312-y | eissn = 1756-0381 | doi-access = free }}</ref>

FN1-FGFR1 fusion is frequent in phosphaturic mesenchymal tumours.<ref>{{cite journal | vauthors = Wasserman JK, Purgina B, Lai CK, Gravel D, Mahaffey A, Bell D, Chiosea SI | title = Phosphaturic Mesenchymal Tumor Involving the Head and Neck: A Report of Five Cases with FGFR1 Fluorescence In Situ Hybridization Analysis | journal = Head and Neck Pathology | date = Jan 2016 | pmid = 26759148 | doi = 10.1007/s12105-015-0678-1 | volume=10 | issue = 3 | pmc=4972751 | pages=279–85}}</ref><ref>{{cite journal | vauthors = Lee JC, Jeng YM, Su SY, Wu CT, Tsai KS, Lee CH, Lin CY, Carter JM, Huang JW, Chen SH, Shih SR, Mariño-Enríquez A, Chen CC, Folpe AL, Chang YL, Liang CW | title = Identification of a novel FN1-FGFR1 genetic fusion as a frequent event in phosphaturic mesenchymal tumour | journal = The Journal of Pathology | volume = 235 | issue = 4 | pages = 539–45 | date = Mar 2015 | pmid = 25319834 | doi = 10.1002/path.4465 | s2cid = 9887919 }}</ref>

== Role in wound healing ==
Fibronectin has profound effects on [[wound healing]], including the formation of proper substratum for migration and growth of cells during the development and organization of [[granulation tissue]], as well as remodeling and resynthesis of the connective tissue matrix.<ref name="pmid 7240787 ">{{cite journal | vauthors = Grinnell F, Billingham RE, Burgess L | title = Distribution of fibronectin during wound healing in vivo | journal = The Journal of Investigative Dermatology | volume = 76 | issue = 3 | pages = 181–189  | date = Mar 1981 | pmid = 7240787 | doi = 10.1111/1523-1747.ep12525694 | doi-access = free }}</ref> The biological significance of fibronectin ''in vivo'' was studied during the mechanism of wound healing.<ref name="pmid 7240787 " />  Plasma fibronectin levels are decreased in acute inflammation or following surgical trauma and in patients with [[disseminated intravascular coagulation]].<ref name="pmid1002003">{{cite journal | vauthors = Bruhn HD, Heimburger N | title = Factor-VIII-related antigen and cold-insoluble globulin in leukemias and carcinomas | journal = Haemostasis | volume = 5 | issue = 3 | pages = 189–192 | year = 1976 | pmid = 1002003 | doi = 10.1159/000214134 }}</ref>

Fibronectin is located in the extracellular matrix of embryonic and adult tissues (not in the [[basement membrane]]s of the adult tissues), but may be more widely distributed in inflammatory lesions.  During blood clotting, the fibronectin remains associated with the clot, covalently cross-linked to [[fibrin]] with the help of [[Factor XIII]] (fibrin-stabilizing factor).<ref name="pmid1158872">{{cite journal | vauthors = Mosher DF | title = Cross-linking of cold-insoluble globulin by fibrin-stabilizing factor | journal = The Journal of Biological Chemistry | volume = 250 | issue = 16 | pages = 6614–6621 | date = Aug 1975 | doi = 10.1016/S0021-9258(19)41110-1 | pmid = 1158872 | doi-access = free }}</ref><ref name="pmid56335">{{cite journal | vauthors = Mosher DF | title = Action of fibrin-stabilizing factor on cold-insoluble globulin and alpha2-macroglobulin in clotting plasma | journal = The Journal of Biological Chemistry | volume = 251 | issue = 6 | pages = 1639–1645 | date = Mar 1976 | doi = 10.1016/S0021-9258(17)33696-7 | pmid = 56335 | doi-access = free }}</ref> [[Fibroblast]]s play a major role in wound healing by adhering to fibrin. Fibroblast adhesion to fibrin requires fibronectin, and was strongest when the fibronectin was cross-linked to the fibrin. Patients with Factor XIII deficiencies display impairment in wound healing as fibroblasts don't grow well in fibrin lacking Factor XIII. Fibronectin promotes particle [[phagocytosis]] by both [[macrophage]]s and fibroblasts. Collagen deposition at the wound site by fibroblasts takes place with the help of fibronectin. Fibronectin was also observed to be closely associated with the newly deposited [[collagen]] fibrils. Based on the size and [[Histology|histological]] staining characteristics of the fibrils, it is likely that at least in part they are composed of type III collagen ([[reticulin]]). An ''in vitro'' study with native collagen demonstrated that fibronectin binds to type III collagen rather than other types.<ref name="pmid 567240 ">{{cite journal | vauthors = Engvall E, Ruoslahti E, Miller EJ | title = Affinity of fibronectin to collagens of different genetic types and to fibrinogen | journal = The Journal of Experimental Medicine | volume = 147 | issue = 6 | pages = 1584–1595 | date = Jun 1978 | pmid = 567240 | pmc = 2184308 | doi = 10.1084/jem.147.6.1584 }}</ref>

== ''In vivo'' vs ''in vitro'' ==
Plasma fibronectin, which is synthesized by [[hepatocyte]]s,<ref name="pmid6339502">{{cite journal | vauthors = Tamkun JW, Hynes RO | title = Plasma fibronectin is synthesized and secreted by hepatocytes | journal = The Journal of Biological Chemistry | volume = 258 | issue = 7 | pages = 4641–7 | date = Apr 1983 | doi = 10.1016/S0021-9258(18)32672-3 | pmid = 6339502 | doi-access = free }}</ref> and fibronectin synthesized by [[cell culture|cultured]] [[fibroblast]]s are similar but not identical; immunological, structural, and functional differences have been reported.<ref name="pmid6480605"/> It is likely that these differences result from differential processing of a single nascent mRNA. Nevertheless, plasma fibronectin can be insolubilized into the tissue [[extracellular matrix]] ''in vitro'' and ''in vivo''. Both plasma and cellular fibronectins in the matrix form high molecular weight, [[disulfide bond|disulfide-bonded]] [[oligomer|multimers]]. The mechanism of formation of these multimers is not presently known. Plasma fibronectin has been shown to contain two free [[thiol|sulfhydryls]] per subunit (X), and cellular fibronectin has been shown to contain at least one. These sulfhydryls probably are buried within the [[Biomolecular structure#Tertiary structure|tertiary structure]], because sulfhydryls are exposed when the fibronectin is denatured. Such denaturation results in the oxidation of free sulfhydryls and formation of disulfide-bonded fibronectin multimers. This has led to speculation that the free sulfhydryls may be involved in formation of disulfide-bonded fibronectin multimers in the extracellular matrix. Consistent with this, sulfhydryl modification of fibronectin with [[N-ethylmaleimide]] prevents binding to cell layers. [[Trypsin|Tryptic]] cleavage patterns of multimeric fibronectin do not reveal the disulfide-bonded fragments that would be expected if multimerization involved one or both of the free sulfhydryls. The free sulfhydryls of fibronectin are not required for the binding of fibronectin to the cell layer or for its subsequent incorporation into the extracellular matrix. Disulfide-bonded multimerization of fibronectin in the cell layer occurs by disulfide bond exchange in the disulfide-rich [[N-terminus|amino-terminal]] one-third of the molecule.<ref name="pmid6480605">{{cite journal | vauthors = McKeown-Longo PJ, Mosher DF | title = Mechanism of formation of disulfide-bonded multimers of plasma fibronectin in cell layers of cultured human fibroblasts | journal = The Journal of Biological Chemistry | volume = 259 | issue = 19 | pages = 12210–12215 | date = Oct 1984 | doi = 10.1016/S0021-9258(20)71340-2 | pmid = 6480605 | doi-access = free }}</ref>

== Fibronectin genetic variation as a protective factor against Alzheimer's disease ==
A specific genetic variation in Fibronectin gene was shown to reduce the risk of developing Alzheimer's disease in a multicenter, multiethnic genetic epidemiology and functional genomics study. This effect is believed to be through enhancing the brain's ability to clear the toxic waste and protein accumulation through the blood–brain barrier.<ref name="pmid38598053">{{cite journal | vauthors = Bhattarai P, Gunasekaran TI, Belloy ME, Reyes-Dumeyer D, Jülich D, Tayran H, Yilmaz E, Flaherty D, Turgutalp B, Sukumar G, Alba C, McGrath EM, Hupalo DN, Bacikova D, Le Guen Y, Lantigua R, Medrano M, Rivera D, Recio P, Nuriel T, Ertekin-Taner N, Teich AF, Dickson DW, Holley S, Greicius M, Dalgard CL, Zody M, Mayeux R, Kizil C, Vardarajan BN | title = Rare genetic variation in fibronectin 1 (FN1) protects against APOEε4 in Alzheimer's disease | journal = Acta Neuropathologica | volume = 147 | issue = 1 | pages = 70 | date = Apr 2024 | doi = 10.1007/s00401-024-02721-1 | pmid = 38598053| doi-access = free | pmc = 11006751 }}</ref>

== Interactions ==
Besides integrin, fibronectin binds to many other host and non-host molecules. For example, it has been shown to interact with proteins such [[fibrin]], [[tenascin]], TNF-α, BMP-1, rotavirus NSP-4, and many fibronectin-binding proteins from bacteria (like FBP-A; FBP-B on the N-terminal domain), as well as the [[glycosaminoglycan]], [[heparan sulfate]].

Fibronectin has been shown to [[Protein-protein interaction|interact]] with:
* [[CD44]]<ref name="pmid1730778">{{cite journal | vauthors = Jalkanen S, Jalkanen M | title = Lymphocyte CD44 binds the COOH-terminal heparin-binding domain of fibronectin | journal = The Journal of Cell Biology | volume = 116 | issue = 3 | pages = 817–25 | date = Feb 1992 | pmid = 1730778 | pmc = 2289325 | doi = 10.1083/jcb.116.3.817 }}</ref>
* [[Collagen, type VII, alpha 1|COL7A1]],<ref name="pmid7963647">{{cite journal | vauthors = Lapiere JC, Chen JD, Iwasaki T, Hu L, Uitto J, Woodley DT | title = Type VII collagen specifically binds fibronectin via a unique subdomain within the collagenous triple helix | journal = The Journal of Investigative Dermatology | volume = 103 | issue = 5 | pages = 637–41 | date = Nov 1994 | pmid = 7963647 | doi = 10.1111/1523-1747.ep12398270 | doi-access =  }}</ref><ref name="pmid9169408">{{cite journal | vauthors = Chen M, Marinkovich MP, Veis A, Cai X, Rao CN, O'Toole EA, Woodley DT | title = Interactions of the amino-terminal noncollagenous (NC1) domain of type VII collagen with extracellular matrix components. A potential role in epidermal-dermal adherence in human skin | journal = The Journal of Biological Chemistry | volume = 272 | issue = 23 | pages = 14516–22 | date = Jun 1997 | pmid = 9169408 | doi = 10.1074/jbc.272.23.14516 | doi-access = free }}</ref>
* [[Lipoprotein(a)|LPA]],<ref name="pmid2531657">{{cite journal | vauthors = Salonen EM, Jauhiainen M, Zardi L, Vaheri A, Ehnholm C | title = Lipoprotein(a) binds to fibronectin and has serine proteinase activity capable of cleaving it | journal = The EMBO Journal | volume = 8 | issue = 13 | pages = 4035–40 | date = Dec 1989 | pmid = 2531657 | pmc = 401578 | doi =  10.1002/j.1460-2075.1989.tb08586.x}}</ref>
* [[IGFBP3]],<ref name="pmid12127836">{{cite journal | vauthors = Martin JA, Miller BA, Scherb MB, Lembke LA, Buckwalter JA | title = Co-localization of insulin-like growth factor binding protein 3 and fibronectin in human articular cartilage | journal = Osteoarthritis and Cartilage | volume = 10 | issue = 7 | pages = 556–63 | date = Jul 2002 | pmid = 12127836 | doi = 10.1053/joca.2002.0791 | doi-access = free }}</ref><ref name="pmid11344214">{{cite journal | vauthors = Gui Y, Murphy LJ | title = Insulin-like growth factor (IGF)-binding protein-3 (IGFBP-3) binds to fibronectin (FN): demonstration of IGF-I/IGFBP-3/fn ternary complexes in human plasma | journal = The Journal of Clinical Endocrinology and Metabolism | volume = 86 | issue = 5 | pages = 2104–10 | date = May 2001 | pmid = 11344214 | doi = 10.1210/jcem.86.5.7472 | doi-access = free }}</ref>
* [[Tenascin C|TNC]],<ref name="pmid7499434">{{cite journal | vauthors = Chung CY, Zardi L, Erickson HP | title = Binding of tenascin-C to soluble fibronectin and matrix fibrils | journal = The Journal of Biological Chemistry | volume = 270 | issue = 48 | pages = 29012–7 | date = Dec 1995 | pmid = 7499434 | doi = 10.1074/jbc.270.48.29012 | doi-access = free }}</ref> and
* [[TRIB3]].<ref name="pmid18276110">{{cite journal | vauthors = Zhou Y, Li L, Liu Q, Xing G, Kuai X, Sun J, Yin X, Wang J, Zhang L, He F | title = E3 ubiquitin ligase SIAH1 mediates ubiquitination and degradation of TRB3 | journal = Cellular Signalling | volume = 20 | issue = 5 | pages = 942–8 | date = May 2008 | pmid = 18276110 | doi = 10.1016/j.cellsig.2008.01.010 }}</ref>

== See also ==
* [[Fetal fibronectin]]
* [[Fibronectin type I domain]]
* [[Fibronectin type II domain]]
* [[Fibronectin type III domain]]
* [[Monobody]], an engineered antibody mimetic based on the structure of the fibronectin type III domain
* [[Substrate adhesion molecules]]

== References ==
{{Reflist|2}}

== Further reading ==
{{refbegin | 2}}
* {{cite journal | vauthors = ffrench-Constant C | title = Alternative splicing of fibronectin--many different proteins but few different functions | journal = Experimental Cell Research | volume = 221 | issue = 2 | pages = 261–71 | date = Dec 1995 | pmid = 7493623 | doi = 10.1006/excr.1995.1374 }}
* {{cite journal | vauthors = Snásel J, Pichová I | title = The cleavage of host cell proteins by HIV-1 protease | journal = Folia Biologica | volume = 42 | issue = 5 | pages = 227–30 | year = 1997 | pmid = 8997639 | doi = 10.1007/BF02818986 | s2cid = 7617882 }}
* {{cite journal | vauthors = Schor SL, Schor AM | title = Phenotypic and genetic alterations in mammary stroma: implications for tumour progression | journal = Breast Cancer Research | volume = 3 | issue = 6 | pages = 373–9 | year = 2003 | pmid = 11737888 | pmc = 138703 | doi = 10.1186/bcr325 | doi-access = free }}
* {{cite journal | vauthors = Przybysz M, Katnik-Prastowska I | title = [Multifunction of fibronectin] | language = pl | journal = Postȩpy Higieny I Medycyny Doświadczalnej | volume = 55 | issue = 5 | pages = 699–713 | year = 2002 | pmid = 11795204 |trans-title=Multifunction of fibronectin }}
* {{cite journal | vauthors = Rameshwar P, Oh HS, Yook C, Gascon P, Chang VT | title = Substance p-fibronectin-cytokine interactions in myeloproliferative disorders with bone marrow fibrosis | journal = Acta Haematologica | volume = 109 | issue = 1 | pages = 1–10 | year = 2003 | pmid = 12486316 | doi = 10.1159/000067268 | s2cid = 25830801 }}
* {{cite journal | vauthors = Cho J, Mosher DF | title = Role of fibronectin assembly in platelet thrombus formation | journal = Journal of Thrombosis and Haemostasis | volume = 4 | issue = 7 | pages = 1461–9  | date = Jul 2006 | pmid = 16839338 | doi = 10.1111/j.1538-7836.2006.01943.x | s2cid = 24109462 | doi-access = free }}
* {{cite journal | vauthors = Schmidt DR, Kao WJ | title = The interrelated role of fibronectin and interleukin-1 in biomaterial-modulated macrophage function | journal = Biomaterials | volume = 28 | issue = 3 | pages = 371–82  | date = Jan 2007 | pmid = 16978691 | doi = 10.1016/j.biomaterials.2006.08.041 }}
* {{cite book | vauthors = Dallas SL, Chen Q, Sivakumar P | chapter = Dynamics of assembly and reorganization of extracellular matrix proteins | title = Current Topics in Developmental Biology | volume = 75 | pages = 1–24 | year = 2006 | pmid = 16984808 | doi = 10.1016/S0070-2153(06)75001-3 | isbn = 9780121531751 }}
{{refend}}

== External links ==
* [https://www.callutheran.edu/BioDev/omm/fibro/fibro.htm Fibronectin, an Extracellular Adhesion Molecule]
* {{usurped|1=[https://web.archive.org/web/20220310184309/http://macromoleculeinsights.com/fibronectin.php The Fibronectin Protein]}}
* {{MeshName|Fibronectin}}
* [https://web.archive.org/web/20101128081517/https://nethingham.org/FN2009/intro/ Fibronectin molecular interactions]
* {{PDBe-KB2|P02751|Human Fibronectin}}
* {{PDBe-KB2|P11276|Mouse Fibronectin}}

{{PDB Gallery|geneid=2335}}
{{Globulins}}

[[Category:Glycoproteins]]
[[Category:Diagnostic obstetrics and gynaecology]]
[[Category:Extracellular matrix proteins]]