Gα13 Switch Region 2 Binds to the Talin Head Domain and Activates αIIbβ3 Integrin in Human Platelets

Srinivasan, Subhashini; Schiemer, James; Zhang, Xiaowei; Chishti, Athar H.; Breton, Guy C. Le

doi:10.1074/jbc.m115.650978

Cited by 7 publications

(19 citation statements)

References 31 publications

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“…Furthermore, a single amino acid mutation of talin's head domain, M319A, increases integrin activation compared with both wild type fulllength GFP-talin and GFP-THD (15,31). Additionally, it was shown that the co-transfection of GFP-talin with G␣ 13 , but not SR2 mutants R227A or R232A, increased integrin activation (27). These observations suggest that GFP-talin is partially, if not completely, autoinhibited when overexpressed in this model cell system.…”

Section: G␣ 13 Sr2 Binds To F3 Lobe Within the Ferm Domain Ofmentioning

confidence: 62%

“…Previously, the G protein subunit G␣ 13 has been shown to engage its SR1 to directly bind to p115RhoGEF thus increasing RhoA activity leading to cytoskeletal rearrangements (25). Recently, our group reported that G␣ 13 SR2 (where SR2 is one of three conformationally sensitive switch regions present in G␣ subunits) directly binds to talin and thereby modulates platelet integrin ␣IIb␤3 activation (27). This finding provided the first evidence for a G␣ 13 /talin interaction and thus represented a novel regulatory pathway.…”

mentioning

confidence: 75%

“…Our previous work demonstrated that myristoylated SR2 peptide (G␣ 13 SR2 Pep ) inhibits platelet aggregation in response to all agonists tested (27). This global inhibition of platelet aggregation was attributed to inhibition of ␣IIb␤3 integrin activation (27).…”

Section: G␣ 13 Sr2 Binds To F3 Lobe Within the Ferm Domain Ofmentioning

confidence: 99%

“…Talin-Although our recent work reported direct binding of G␣ 13 SR2 to THD (27), the location of the G␣ 13 SR2-binding site within the THD domain remained unknown. The FERM domain of talin is composed of four distinct lobes: F0 (aa 1-83), F1 (aa 85-196), F2 (aa 208 -306), and F3 (310 -400), with flexible linker regions connecting each lobe.…”

Section: G␣ 13 Sr2 Binds To F3 Lobe Within the Ferm Domain Ofmentioning

confidence: 99%

“…Both the ␣ and ␤␥ subunits can interact with downstream molecules resulting in a signaling cascade. Although the switch regions are necessary for G protein activation, it is known that these regions also have a secondary function, which enables their specific recognition of the downstream effectors (25)(26)(27). Previously, the G protein subunit G␣ 13 has been shown to engage its SR1 to directly bind to p115RhoGEF thus increasing RhoA activity leading to cytoskeletal rearrangements (25).…”

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confidence: 99%

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Gα13 Switch Region 2 Relieves Talin Autoinhibition to Activate αIIbβ3 Integrin

Schiemer

Bohm

et al. 2016

Journal of Biological Chemistry

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Edited by Henrik DohlmanIntegrins function as bi-directional signaling transducers that regulate cell-cell and cell-matrix signals across the membrane. A key modulator of integrin activation is talin, a large cytoskeletal protein that exists in an autoinhibited state in quiescent cells. Talin is a large 235-kDa protein composed of an N-terminal 45-kDa FERM (4.1, ezrin-, radixin-, and moesin-related protein) domain, also known as the talin head domain, and a series of helical bundles known as the rod domain. The talin head domain consists of four distinct lobes designated as F0 -F3. Integrin binding and activation are mediated through the F3 region, a critically regulated domain in talin. Regulation of the F3 lobe is accomplished through autoinhibition via anti-parallel dimerization. In the anti-parallel dimerization model, the rod domain region of one talin molecule binds to the F3 lobe on an adjacent talin molecule, thus achieving the state of autoinhibition. Platelet functionality requires integrin activation for adherence and thrombus formation, and thus regulation of talin presents a critical node where pharmacological intervention is possible. A major mechanism of integrin activation in platelets is through heterotrimeric G protein signaling regulating hemostasis and thrombosis. Here, we provide evidence that switch region 2 (SR2) of the ubiquitously expressed G protein (G␣13) directly interacts with talin, relieves its state of autoinhibition, and triggers integrin activation. Biochemical analysis of G␣ 13 shows SR2 binds directly to the F3 lobe of talin's head domain and competes with the rod domain for binding. Intramolecular FRET analysis shows G␣ 13 can relieve autoinhibition in a cellular milieu. Finally, a myristoylated SR2 peptide shows demonstrable decrease in thrombosis in vivo. Altogether, we present a mechanistic basis for the regulation of talin through G␣ 13 .Integrins are transmembrane receptors that regulate dynamic cell/cell and cell/matrix interactions (1, 2). Environmental cues regulate a multitude of cellular processes through integrins, such as cell proliferation, shape, adhesion, and migration. Because of the well established importance of integrin signaling in hemostasis and thrombosis, the mechanisms of integrin regulation remain an area of intense investigation. Upon activation, platelet integrins switch from a low affinity to a high affinity state, thus permitting the binding to multivalent ligands such as von Willebrand factor and fibrinogen to enable clotting (3-7). The most abundant platelet integrin complex, ␣IIb␤3, is activated through the cytoskeletal protein talin (1, 8 -12). Talin is a large 235-kDa protein composed of an N-terminal 45-kDa FERM 2 domain, also known as the talin head domain (THD). THD is connected to a large rod domain composed of a series of ␣-helical bundles. The talin head domain consists of four distinct lobes or regions designated as F0 -F3. Integrin binding and activation are mediated through the F3 region, a critically regulated domain in talin. Regul...

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