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J. Biol. Chem., Vol. 278, Issue 4, 2614-2623, January 24, 2003

This Article Full Text Full Text (PDF) All Versions of this Article: 278/4/2614    most recent M206241200v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Harris, T. J. C. Articles by Siu, C.-H. Search for Related Content PubMed PubMed Citation Articles by Harris, T. J. C. Articles by Siu, C.-H. Social Bookmarking                      What's this?

Cytoskeleton Interactions Involved in the Assembly and Function of Glycoprotein-80 Adhesion Complexes in Dictyostelium^*

Tony J. C. Harris^§¶, Amir Ravandi, Donald E. Awrey, and Chi-Hung Siu^§**

From the  Banting and Best Department of Medical Research and ^§ Department of Biochemistry, University of Toronto, Toronto, Ontario M5G 1L6, Canada and  Affinium Pharmaceuticals, Toronto, Ontario M5J 1V6, Canada

Adhesion complexes typically assemble from clustered receptors that link to the cytoskeleton via cytoplasmic adapter proteins. However, it is unclear how phospholipid-anchored adhesion molecules, such as the Dictyostelium receptor gp80, interact with the cytoskeleton. gp80 has been found to form adhesion complexes from raftlike membrane domains, which can be isolated as a Triton X-100-insoluble floating fraction (TIFF). We report here that the actin-binding protein ponticulin mediates TIFF-cytoskeleton interactions. Analysis of gp80-null cells revealed that these interactions were minimal in the absence of gp80. During development, gp80 was required to enhance these interactions as its adhesion complexes assembled. Whereas ponticulin and gp80 could partition independently into TIFF, gp80 was shown to recruit ponticulin to cell-cell contacts and to increase its partitioning into TIFF. However, these proteins did not co-immunoprecipitate. Furthermore, sterol sequestration abrogated the association of ponticulin with TIFF without affecting gp80, suggesting that sterols may mediate the interactions between ponticulin and gp80. In ponticulin-null cells, large gp80 adhesion complexes assembled in the absence of ponticulin despite the lack of cytoskeleton association. We propose that such nascent gp80 adhesion complexes produce expanded raftlike domains that recruit ponticulin and thereby establish stable cytoskeleton interactions to complete the assembly process.

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