Editing Signal transduction (section)

====Integrins====
{{Main|Integrin}}
[[Image:Integrin sig trans overview.jpeg|450px|thumb|right|An overview of integrin-mediated signal transduction, adapted from Hehlgens ''et al.'' (2007).<ref name="hehlgans">{{Cite journal |vauthors=Hehlgans S, Haase M, Cordes N |date=January 2007 |title=Signalling via integrins: implications for cell survival and anticancer strategies |journal=Biochimica et Biophysica Acta (BBA) - Reviews on Cancer |volume=1775 |issue=1 |pages=163–80 |doi=10.1016/j.bbcan.2006.09.001 |pmid=17084981}}</ref>]]

Integrins are produced by a wide variety of cells; they play a role in cell attachment to other cells and the [[extracellular matrix]] and in the transduction of signals from extracellular matrix components such as [[fibronectin]] and [[collagen]]. Ligand binding to the extracellular domain of integrins changes the protein's conformation, clustering it at the cell membrane to initiate signal transduction. Integrins lack kinase activity; hence, integrin-mediated signal transduction is achieved through a variety of intracellular protein kinases and adaptor molecules, the main coordinator being [[integrin-linked kinase]].<ref name=hehlgans/> As shown in the adjacent picture, cooperative integrin-RTK signaling determines the timing of cellular survival, [[apoptosis]], [[cell growth|proliferation]], and [[Cellular differentiation|differentiation]].

Important differences exist between integrin-signaling in circulating blood cells and non-circulating cells such as [[epithelial cell]]s; integrins of circulating cells are normally inactive. For example, cell membrane integrins on circulating [[leukocytes]] are maintained in an inactive state to avoid epithelial cell attachment; they are activated only in response to stimuli such as those received at the site of an [[inflammation|inflammatory response]]. In a similar manner, integrins at the cell membrane of circulating [[platelets]] are normally kept inactive to avoid [[thrombosis]]. Epithelial cells (which are non-circulating) normally have active integrins at their cell membrane, helping maintain their stable adhesion to underlying stromal cells that provide signals to maintain normal functioning.<ref name="gilcrease">{{Cite journal |vauthors=Gilcrease MZ |date=March 2007 |title=Integrin signaling in epithelial cells |journal=Cancer Letters |volume=247 |issue=1 |pages=1–25 |doi=10.1016/j.canlet.2006.03.031 |pmid=16725254}}</ref>

In plants, there are no bona fide integrin receptors identified to date; nevertheless, several integrin-like proteins were proposed based on structural homology with the metazoan receptors.<ref>{{Cite journal |vauthors=Knepper C, Savory EA, Day B |date=May 2011 |title=Arabidopsis NDR1 is an integrin-like protein with a role in fluid loss and plasma membrane-cell wall adhesion |journal=Plant Physiology |volume=156 |issue=1 |pages=286–300 |doi=10.1104/pp.110.169656 |pmc=3091050 |pmid=21398259}}</ref> Plants contain integrin-linked kinases that are very similar in their primary structure with the animal ILKs. In the experimental model plant ''[[Arabidopsis thaliana]]'', one of the integrin-linked kinase genes, ''ILK1'', has been shown to be a critical element in the plant immune response to signal molecules from bacterial pathogens and plant sensitivity to salt and osmotic stress.<ref name="Brauer 1470–1484">{{Cite journal |display-authors=6 |vauthors=Brauer EK, Ahsan N, Dale R, Kato N, Coluccio AE, Piñeros MA, Kochian LV, Thelen JJ, Popescu SC |date=June 2016 |title=The Raf-like Kinase ILK1 and the High Affinity K+ Transporter HAK5 Are Required for Innate Immunity and Abiotic Stress Response |journal=Plant Physiology |volume=171 |issue=2 |pages=1470–84 |doi=10.1104/pp.16.00035 |pmc=4902592 |pmid=27208244}}</ref> ILK1 protein interacts with the high-affinity potassium transporter [[HAK5]] and with the calcium sensor CML9.<ref name="Brauer 1470–1484" /><ref>{{Cite journal |display-authors=6 |vauthors=Popescu SC, Popescu GV, Bachan S, Zhang Z, Seay M, Gerstein M, Snyder M, Dinesh-Kumar SP |date=March 2007 |title=Differential binding of calmodulin-related proteins to their targets revealed through high-density Arabidopsis protein microarrays |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=104 |issue=11 |pages=4730–5 |bibcode=2007PNAS..104.4730P |doi=10.1073/pnas.0611615104 |pmc=1838668 |pmid=17360592 |doi-access=free}}</ref>