Fig. 5.

TGF-β induces downregulation of I-κB-α protein in SMAD4-null (−SMAD4) but not SMAD4-restored (+SMAD4) pancreatic cancer cells. Parental BxPc-3 cells were transfected with either an empty plasmid or wild-type SMAD4 construct. Twenty-four hours after transfection, cells were treated with TGF-β for 48 h. Cell lysates were subjected to electrophoresis through 7.5% SDS-polyacrylamide gels and transferred to PVDF membranes. Membranes were probed with an antibody specific for the I-κB-α. GAPDH was used as an internal standard. In the parental cells, TGF-β significantly induced removal of I-κB-α starting at 3 h and lasted for 24 h after treatment. Protein levels of I-κB-α exceeded the basal level 48 h after treatment. On the other hand, TGF-β induces upregulation of I-κB-α protein 1 h after treatment in the SMAD4-restored cells.