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J. Biol. Chem., Vol. 282, Issue 44, 32442-32452, November 2, 2007

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The Involvement of Abl and PTP61F in the Regulation of Abi Protein Localization and Stability and Lamella Formation in Drosophila S2 Cells^*

Chiu-Hui Huang, Tzu-Yang Lin, Rong-Long Pan, and Jyh-Lyh Juang^¶1

From the Division of Molecular and Genomic Medicine, National Health Research Institutes, Zhunan, Miaoli 35053, Taiwan, the Department of Life Science, National Tsing Hua University, Hsinchu 30043, Taiwan, and the ^¶Graduate Institute of Life Sciences, National Defense Medical Center, Taipei 11490, Taiwan

Most aspects of cellular events are regulated by a series of protein phosphorylation and dephosphorylation processes. Abi (Abl interactor protein) functions as a substrate adaptor protein for Abl and a core member of the WAVE complex, relaying signals from Rac to Arp2/3 complex and regulating actin dynamics. It is known that the recruitment of Abi into the lamella promotes polymerization of actin, although how it does this is unclear. In this study, we found PTP61F, a Drosophila homolog of mammalian PTP1B, can reverse the Abl phosphorylation of Abi and colocalizes with Abi in Drosophila S2 cells. Abi can be translocalized from the cytosol to the cell membrane by either increasing Abl or reducing endogenous PTP61F. This reciprocal regulation of Abi phosphorylation is also involved in modulating Abi protein level, which is thought to affect the stability of the WAVE complex. Using mass spectrometry, we identified several important tyrosine phosphorylation sites in Abi. We compared the translocalization and protein half-life of wild type (wt) and phosphomutant Abi and their abilities to restore the lamellipodia structure of the Abi-reduced cells. We found the phosphomutant to have reduced ability to translocalize and to have a protein half-life shorter than that of wt Abi. We also found that although the wt Abi could fully restore the lamellipodia structure, the phosphomutant could not. Together, these findings suggest that the reciprocal regulation of Abi phosphorylation by Abl and PTP61F may regulate the localization and stability of Abi and may regulate the formation of lamella.

Received for publication, March 26, 2007 , and in revised form, August 29, 2007.

^* This work was supported by the National Health Research Institutes and the National Science Council (NSC95-2311-B-400-001-MY3). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence should be addressed: Division of Molecular and Genomic Medicine, National Health Research Institutes, 35 Keyan Rd., Zhunan Town, Miaoli County 35053, Taiwan. Tel.: 886-37-246166, Ext. 35308; Fax: 886-37-586459; E-mail: juang{at}nhri.org.tw.

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