HtrA4 regulates placental cell invasion. (A) Overexpression of HtrA4 stimulates placental cell invasion. Mock and HtrA4-HA-expressing JAR cells were plated in Matrigel-coated chambers for invasion analysis. Expression of HtrA4-HA was analyzed by immunoblotting with HA MAb (left). (B) HtrA4 knockdown suppresses placental cell invasion. BeWo cells stably expressing scrambled or HtrA4 shRNA were subjected to invasion analysis as described for panel A. Knockdown of HtrA4 expression in BeWo cells was analyzed by immunoblotting with HtrA4 Ab (left). (C) Proteolytic cleavage of fibronectin by HtrA4. Purified HtrA4-FLAG and HtrA4mt-FLAG proteins from culture medium of 293T cells transfected with pHtrA4-FLAG and pHtrA4mt-FLAG, respectively, were analyzed by immunoblotting with FLAG MAb (left). Fibronectin was incubated with increasing amounts of HtrA4-FLAG or HtrA4mt-FLAG at 37°C for 16 h. The reaction mixture was then subjected to immunoblotting with HtrA4 or fibronectin Ab. Of note, partial cleavage of HtrA4-FLAG, but not HtrA4mt-FLAG, in the reaction was detected (bottom).