Fig. 4. Localization of FA proteins to the SßX receptor in cells spreading on collagen IV. (A) Cells expressing SßX-ßcyt were allowed to spread on collagen IV and stained for the SßX receptor (anti-₁ integrin) and with antibodies to either paxillin pY118 or FAK pY397. (B) Cells expressing SßX-ßcyt transiently transfected with either Cas-GFP or GFP-FAK were allowed to spread on fibronectin (FN) or collagen IV (CN) and stained for F-actin with Rhodamine-Phalloidin. Spreading on fibronectin indicates that Cas-GFP was able to localize to FAs generated with wild-type integrins whereas cells transfected with GFP-FAK verify that transiently transfected fluorescently tagged FA protein constructs were able to localize to radial FA-like structures formed by SßX cells on collagen IV. SßX-ßcyt (C) or SW1 (D) cells were transiently transfected with GFP-talin, allowed to spread on collagen IV and stained for the chimeric receptors. Lower panels in C are a higher magnification of the regions outlined in images of the whole cell. Talin, paxillin and FAK, but not Cas, localize to FA-like structures formed with SßX cells on collagen IV.