Tax-induced c-Jun interacts with Smad3 and abrogates Smad3 DNA binding activity.

(A) Nuclear extracts from TGF-β1–stimulated HepG2 cells transfected with the Tax expression vector, empty vector (control), or increasing doses of c-Jun expression vector (c-Jun 0.5, 4) were used with the³²P-labeled probe containing 3 CAGA boxes for EMSA. (B) Cos-7 cells were transfected with the indicated combination of HA-c-Jun, Myc-Smad3 (top panel), and Tax expression vectors (bottom panel) and were subjected to immunoprecipitation by using an anti-Myc antibody. The expression of Tax or Smad3 was detected by immunoblot by using an anti-Tax or an anti-Myc antibody before immunoprecipitation. (C) Nuclear extracts, from TGF-β1–stimulated (+) or not (−) HepG2 cells transfected with the indicated expression vectors (empty vector [control]), Tax alone (Tax), or associated with an antisense c-Jun (Tax/AS c-Jun) or a dominant-negative JNK (Tax/JNK-(K-R)) expression vectors were used with the ³²P-labeled probe containing 3 CAGA boxes for EMSA.