Figure 5.

Integrin-α5 and -β3 are required at different stages of FN fibrillogenesis. (A) Immunostaining of CAFs on 2D coverslips for integrins α5 and αvβ3 (green) and FN (magenta). F-actin was stained with phalloidin-rhodamine (red), and DNA was stained with DAPI (blue). Bar, 40 µm. (B) Maximum intensity projections of CAFs in 3D collagen matrices immunostained for integrin-αvβ3 (green) and FN (magenta). Collagen was acquired using second harmonic generation (cyan). Bars: (main image) 40 µm; (magnified image) 10 µm. (C) Immunostaining of CAFs 2 h after plating for integrin-α5 or -αvβ3 (green) and FN (magenta). F-actin was stained with phalloidin-rhodamine (red), and DNA was stained with DAPI (blue). Bar, 20 µm. (A–C) Magnified regions are represented by white squares. (D) Model: CAFs present in the collagen I–rich tumor stroma secrete FN. (Top) Contractile forces exerted by CAFs align the ECM and activate αvβ3 at the sites of focal adhesions. (Bottom) αvβ3 activation leads to the formation of fibrillar adhesions and FN fibrillogenesis.