Direct Thy-1/αVβ3 integrin interaction mediates neuron to astrocyte communication

Abstract

Thy-1 is an abundant neuronal glycoprotein of poorly defined function. We recently provided evidence indicating that Thy-1 clusters a beta3-containing integrin in astrocytes to induce tyrosine phosphorylation, RhoA activation and the formation of focal adhesions and stress fibers. To date, the alpha subunit partner of beta3 integrin in DI TNC1 astrocytes is unknown. Similarly, the ability of neuronal, membrane-bound Thy-1 to trigger astrocyte signaling via integrin engagement remains speculation. Here, evidence that alphav forms an alphavbeta3 heterodimer in DI TNC1 astrocytes was obtained. In neuron-astrocyte association assays, the presence of either anti-alphav or anti-beta3 integrin antibodies reduced cell-cell interaction demonstrating the requirement of both integrin subunits for this association. Moreover, anti-Thy-1 antibodies blocked stimulation of astrocytes by neurons but not the binding of these two cell types. Thus, neuron-astrocyte association involved binding between molecular components in addition to the Thy-1-integrin; however, the signaling events leading to focal adhesion formation in astrocytes depended exclusively on the latter interaction. Additionally, wild-type (RLD) but not mutated (RLE) Thy-1 was shown to directly interact with alphavbeta3 integrin by Surface Plasmon Resonance analysis. This interaction was promoted by divalent cations and was species-independent. Together, these results demonstrate that the alphavbeta3 integrin heterodimer interacts directly with Thy-1 present on neuronal cells to stimulate astrocytes.

Neuronal Thy-1 induces astrocyte adhesion by engaging syndecan-4 in a cooperative interaction with αvβ3 integrin that activates PKCα and RhoA

“…Findings from this laboratory have implicated Thy-1 membrane glycoprotein (Thy-1) -a small glycosyl phosphatidylinositolanchored protein and member of the immunoglobulin superfamily that is abundantly expressed on the neuronal surface -in binding to and clustering of αvβ3 integrin on astrocytes, as well as triggering the assembly of FAs and SFs (Hermosilla et al, 2008;Leyton et al, 2001) through the activation of RhoA and ROCK (Avalos et al, 2004;Avalos et al, 2002). These events require αvβ3 integrin in order to respond to Thy-1 stimulation, since mutation of the Thy-1-integrin-binding motif (RLD to RLE) prevents its ability to rapidly induce FA and SF formation in these cells (Hermosilla et al, 2008;Leyton et al, 2001).…”

“…These events require αvβ3 integrin in order to respond to Thy-1 stimulation, since mutation of the Thy-1-integrin-binding motif (RLD to RLE) prevents its ability to rapidly induce FA and SF formation in these cells (Hermosilla et al, 2008;Leyton et al, 2001). However, neuron-toastrocyte adhesion is only partially inhibited by recombinant Thy-1-Fc protein, antibodies to αvβ3 integrin or RGD-like peptides, suggesting that receptors other than αvβ3 integrin might be implicated in the association of Thy-1 with astrocytes (Hermosilla et al, 2008;Leyton et al, 2001). Interestingly, direct Thy-1 interaction with sulfated glycans, as well as the functional consequences of Thy-1-dependent thymo-epithelial cell adhesion have been reported (Hueber et al, 1992).…”

Dynamic catch of a Thy-1–α5β1+syndecan-4 trimolecular complex

“…Thy-1 (CD90) is a heavily N-glycosylated single v-type immunoglobulin (Ig) domaincontaining glycoprotein, probably of primordial origin within the immunoglobulin superfamily 2 . It is linked to the outer leaflet of the plasma membrane via a carboxy-terminal glycophosphatidylinositol anchor, where it binds integrins in a variety of tissue-specific contexts, including a M b 2 (Mac-1) on leukocytes 3,4 , a v b 3 on melanoma cells 5 and neurons 6,7 , and a v b 5 on lung fibroblasts 8 . For a full review, see ref.…”

“…9. Binding to a v integrins is mediated by Thy-1's Arg-Leu-Asp (RLD) motif, as mutation to non-functional Arg-Leu-Glu abolishes binding [6][7][8] . Thy-1 also binds heparin sulphate proteoglycans (HSPGs), including syndecan-4 (Syn4), through a conserved polycationic motif in the C-C' strand loop motif 7,10 .…”

Conformational coupling of integrin and Thy-1 regulates Fyn priming and fibroblast mechanotransduction

“…Thy-1 binds inactive α v β 3 integrin in cis, enabling integrin-mediated membrane raft recruitment to FAs Thy-1 is known to support integrin-mediated transcellular adhesion in a variety of tissue-specific contexts via α v β 3 (Leyton et al, 2001;Saalbach et al, 2005;Hermosilla et al, 2008), α v β 5 (Zhou et al, 2010), and α 5 β 1 (Fiore et al, 2014). We found that Thy-1 coimmunoprecipitates with α v integrins in conditions that discourage cell-cell interactions and in greater amounts in the absence of cell-matrix adhesion (i.e., suspension; Fig.…”