Petrich, B. G. et al. Talin is required for integrin-mediated platelet function in hemostasis and thrombosis. J. Exp. Med. 204, 3103-3111

Department of Medicine, University of California, San Diego, La Jolla, CA 92093, USA.
Journal of Experimental Medicine (Impact Factor: 12.52). 01/2008; 204(13):3103-11. DOI: 10.1084/jem.20071800
Source: PubMed


Integrins are critical for hemostasis and thrombosis because they mediate both platelet adhesion and aggregation. Talin is an integrin-binding cytoplasmic adaptor that is a central organizer of focal adhesions, and loss of talin phenocopies integrin deletion in Drosophila. Here, we have examined the role of talin in mammalian integrin function in vivo by selectively disrupting the talin1 gene in mouse platelet precursor megakaryocytes. Talin null megakaryocytes produced circulating platelets that exhibited normal morphology yet manifested profoundly impaired hemostatic function. Specifically, platelet-specific deletion of talin1 led to spontaneous hemorrhage and pathological bleeding. Ex vivo and in vitro studies revealed that loss of talin1 resulted in dramatically impaired integrin alphaIIbbeta3-mediated platelet aggregation and beta1 integrin-mediated platelet adhesion. Furthermore, loss of talin1 strongly inhibited the activation of platelet beta1 and beta3 integrins in response to platelet agonists. These data establish that platelet talin plays a crucial role in hemostasis and provide the first proof that talin is required for the activation and function of mammalian alpha2beta1 and alphaIIbbeta3 integrins in vivo.

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Available from: Patrizia Marchese, Jul 18, 2014
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    • "∼73%) corresponded to genes that were not differentially expressed in FL-MKRunx1−/− compared to FL-MKRunx1L/L. This subset of co-bound non-responsive genes contained several genes with major roles in MK development and platelet biogenesis including the TFs Srf [25], [26] and Zfpm1/Fog1 [27], the transcriptional repressor Gfi1b [28], the myosin heavy chain Myh9 [29], the glycoprotein 1b alpha (Gp1ba) [30] and the cytoskeletal protein Tln1 [31] (Figure 4). Runx1 may be involved in transcription regulation of these genes during preceding or subsequent stages of MK differentiation and platelet formation. "
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    ABSTRACT: RUNX1 transcription factor (TF) is a key regulator of megakaryocytic development and when mutated is associated with familial platelet disorder and predisposition to acute myeloid leukemia (FPD-AML). We used mice lacking Runx1 specifically in megakaryocytes (MK) to characterized Runx1-mediated transcriptional program during advanced stages of MK differentiation. Gene expression and chromatin-immunoprecipitation-sequencing (ChIP-seq) of Runx1 and p300 identified functional Runx1 bound MK enhancers. Runx1/p300 co-bound regions showed significant enrichment in genes important for MK and platelet homeostasis. Runx1 occupied genomic regions were highly enriched in RUNX and ETS motifs and to a lesser extent in GATA motif. Megakaryocytic specificity of Runx1/P300 bound enhancers was validated by transfection mutagenesis and Runx1/P300 co-bound regions of two key megakaryocytic genes Nfe2 and Selp were tested by in vivo transgenesis. The data provides the first example of genome wide Runx1/p300 occupancy in maturating primary FL-MK, unravel the Runx1-regulated program controlling MK maturation in vivo and identify a subset of its bona fide regulated genes. It advances our understanding of the molecular events that upon RUNX1mutations in human lead to the predisposition to familial platelet disorders and FPD-AML.
    PLoS ONE 05/2013; 8(5):e64248. DOI:10.1371/journal.pone.0064248 · 3.23 Impact Factor
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    • "Disruption of this interaction by mutation results in the constitutive activation of the affected αIIbβ3 heterodimers expressed in CHO and 293T cells [4], [7], [8]. Agonist-induced physiologic disruption of this interaction appears to be caused by the binding of talin [9], Kindlin [10] or other proteins [1], [11] to the cytoplasmic domain of β3. "
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    PLoS ONE 10/2012; 7(10):e47356. DOI:10.1371/journal.pone.0047356 · 3.23 Impact Factor
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    • "Thus, whereas changes in cell surface β1 integrin expression may take many minutes when regulated by receptor cycling and hours when regulated by transcription, integrin activation can take place within seconds, theoretically placing tumor cells at a relative advantage in metastatic tumor formation. Inside-out integrin signaling has been studied primarily in blood cells where β2 [36] and β3 integrin activation [37]–[39] are required for normal leukocyte trafficking and platelet aggregation, respectively. While β1 integrins are also subject to inside-out regulation in platelets [39]–[41], the role of β1 integrin activation in non-hematopoietic cells, and solid tumor cells in particular, remains to be clarified. "
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    ABSTRACT: After neoplastic cells leave the primary tumor and circulate, they may extravasate from the vasculature and colonize tissues to form metastases. β1 integrins play diverse roles in tumorigenesis and tumor progression, including extravasation. In blood cells, activation of β1 integrins can be regulated by "inside-out" signals leading to extravasation from the circulation into tissues. However, a role for inside-out β1 activation in tumor cell metastasis is uncertain. Here we show that β1 integrin activation promotes tumor metastasis and that activated β1 integrin may serve as a biomarker of metastatic human melanoma. To determine whether β1 integrin activation can influence tumor cell metastasis, the β1 integrin subunit in melanoma and breast cancer cell lines was stably knocked down with shRNA and replaced with wild-type or constitutively-active β1. When tumor cells expressing constitutively-active β1 integrins were injected intravenously into chick embryos or mice, they demonstrated increased colonization of the liver when compared to cells expressing wild-type β1 integrins. Rescue expression with mutant β1 integrins revealed that tumor cell extravasation and hepatic colonization required extracellular ligand binding to β1 as well as β1 interaction with talin, an intracellular mediator of integrin activation by the Rap1 GTPase. Furthermore, shRNA-mediated knock down of talin reduced hepatic colonization by tumor cells expressing wild-type β1, but not constitutively-active β1. Overexpression in tumor cells of the tumor suppressor, Rap1GAP, inhibited Rap1 and β1 integrin activation as well as hepatic colonization. Using an antibody that detects activated β1 integrin, we found higher levels of activated β1 integrins in human metastatic melanomas compared to primary melanomas, suggesting that activated β1 integrin may serve as a biomarker of invasive tumor cells. Altogether, these studies establish that inside-out activation of β1 integrins promotes tumor cell extravasation and colonization, suggesting diagnostic and therapeutic approaches for targeting of β1 integrin signaling in neoplasia.
    PLoS ONE 10/2012; 7(10):e46576. DOI:10.1371/journal.pone.0046576 · 3.23 Impact Factor
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