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Molecular complexity and dynamics of cell-matrix adhesions

Department of Molecular Cell Biology, The Weizmann Institute of Science, Rehovot 76100, Israel

View larger version (59K): [in a new window]   Fig. 1. A scheme summarizing known interactions between the various constituents of cell-matrix adhesions. Components that were found to be associated with cell-matrix adhesion sites are placed inside the internal green box, whereas additional selected proteins that affect matrix adhesions but were not reported to stably associate with them are placed in the external blue frame. The general property of each component is indicated by the color of its box, and the type of interaction between the components is indicated by the style and color of the interconnecting lines, as indicated at the legend. For further details about this scheme see Cell Science at a Glance in this issue (Zamir and Geiger, 2001).

View larger version (44K): [in a new window]   Fig. 2. The proposed domain structure and possible post-translational regulation of vinculin. (A) Scheme showing the primary structure of vinculin, annotated with the various binding domains and some secondary and tertiary structural information. Numbers near component boxes indicate the locations of specific binding sites along the polypeptide chain (starting from the N-terminus). (B) The regulation of vinculin-binding activities by conformational changes. The intramolecular interaction between the head and tail of vinculin leads to a ‘closed’ conformation and masks many of the binding sites. The interaction of vinculin with PtdIns(4,5)P2 may release this inhibitory head-tail interaction and unmask different binding sites. (C) A hypothetical model for the effect of vinculin activation on the formation and assembly of focal contacts. Inactive vinculin (left) cannot crosslink the various molecular partners. Upon activation by PtdIns(4,5)P2 (right), vinculin can bind to actin filaments and other focal contact components. Abbreviations: a, actin; F, FAK; I, integrins, pa, paxillin; r, profilin; t, talin; va, VASP; vi, vinculin.

View larger version (53K): [in a new window]   Fig. 3. Molecular diversity of focal contacts and fibrillar adhesions in human fibroblasts. The cells were fixed 24 hours after plating and double labeled for 5-integrin and v-integrin or for tensin and phosphotyrosine (PY). The right-hand images show, in a spectrum scale, the ratio between the two labeled components, calculated as previously described (Zamir et al., 1999). Note the contrast between the high 5/v and tensin/PY ratios in the fibrillar adhesions (indicated by their red color in the ratio image) and the lower ratio values in the focal contacts (indicated by their yellow color). Arrows and arrowheads indicate examples of focal contacts and fibrillar adhesions, respectively.

View larger version (65K): [in a new window]   Fig. 4. A hypothetical molecular model depicting the segregation of focal contacts and fibrillar adhesions. (A) Initial adhesions contain both 5ß1 integrin (bound primarily to fibronectin) and vß3 integrin (bound primarily to vitronectin). Both integrins are associated through different proteins with actin filaments and are subjected to actomyosin-driven contraction forces. (B) Since substrate-attached vitronectin forms a rigid matrix, vß3 integrin remains immobile despite the applied contraction force. In contrast, 5ß1 integrin is bound to a relatively soft fibronectin matrix and thus translocates centripetally owing to the actomyosin-driven pulling. The translocation of the fibronectin receptor can also stretch the fibronectin matrix and promote fibrillogenesis. Abbreviations: a, actin; , -actinin, F, FAK; fn, fibronectin; m, myosin II; P, parvin/actopaxin; pa, paxillin; ta, talin; te, tensin; vi, vinculin; vn, vitronectin; 51, 5ß1 integrin; v3, vß3 integrin.