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Blood, 21 May 2009, Vol. 113, No. 21, pp. 5304-5313.
Prepublished online as a Blood First Edition Paper on March 18, 2009; DOI 10.1182/blood-2008-07-169136.
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Submitted July 17, 2008
Accepted February 21, 2009
Integrin-linked kinase associated with integrin activation
Shigenori Honda*, Hiroko Shirotani-Ikejima, Seiji Tadokoro, Yusuke Maeda, Taroh Kinoshita, Yoshiaki Tomiyama, and Toshiyuki Miyata
National Cardiovascular Center Research Institute, Osaka, Japan
Department of Hematology and Oncology, Osaka University Graduate School of Medicine, Osaka, Japan
Research Institute for Microbial Diseases, Osaka University, Osaka, Japan
* Corresponding author; email: shige{at}ri.ncvc.go.jp.
Platelet integrin IIb 3 activation is tightly controlled by intracellular signaling pathways, and several molecules including talin have been identified as critical for IIb 3 activation. However, the whole pathway associated with IIb 3 activation remains to be determined. To address this issue, we established a Chinese hamster ovary cell line (parental cells) that expresses constitutively activated chimeric integrin IIb 6B 3, and then obtained mutant cells expressing inactivated IIb 6B 3 by genome-wide mutagenesis. We have performed expression cloning to isolate signaling molecules responsible for integrin activation in the mutant cells. We show that integrin-linked kinase (ILK) complements defective integrin activation in the mutant cells. ILK mRNAs in the mutant cells contained two nonsense mutations, R317X and W383X, in a compound heterozygous state, resulting in a complete loss of ILK expression. Moreover, the mutant cells showed partially impaired activation of endogenous 1 integrins. Knockdown of ILK in parental cells suppressed the activated state of IIb 6B 3. However, ILK overexpression did not rescue the impaired integrin activation in talin knocked-down parental cells, whereas overexpression of talin-F3, a subdomain of the talin head domain restored the function. Our present data suggest that ILK contributes to inside-out integrin activation.

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[Abstract]
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