Fibronectin (FN) matrix assembly is a multi-step process that involves binding to integrin receptors, FN-FN interactions and connections to the actin cytoskeleton. Ultimately, FN is converted into stable matrix fibrils that are detergent-insoluble. RGD-binding integrins such as α5β1 play a major role in the assembly of fibrillar FN. Here we show that α4β1 binding to the alternatively spliced V (IIICS) region of FN initiates an alternative assembly pathway. Activation of α4β1 with exogenous agents such as Mn2+ or a β1-stimulatory antibody TS2/16 was sufficient to induce initiation of FN fibrillogenesis by Ramos B lymphoma cells and by CHO(B2)α4 cells. Using recombinant FNs lacking specific sequences, we show that assembly is independent of the RGD sequence but requires the V25/CS-1 segment. Previously, we have characterized an activated recombinant FN (FNΔIII1-7) that rapidly forms detergent-insoluble multimers upon binding to α5β1 integrin. α4β1 also formed FNΔIII1-7 multimers without the aid of exogenous stimulants, suggesting that an activated form of FN can override the need for activation of the integrin. In contrast to assembly by α5β1, actin filaments remained largely cortical and no change in cell growth rate was observed with α4β1-mediated assembly. These results show that binding sites on FN other than the RGD sequence/synergy site and distant from the cell binding domain can promote FN assembly. Thus, there appear to be multiple, integrin-specific mechanisms for assembly of FN matrix.
|Original language||English (US)|
|Number of pages||8|
|Journal||Journal of Cell Science|
|State||Published - Jan 1 2000|
All Science Journal Classification (ASJC) codes
- Cell Biology