Figure 4.

Endogenous SMAD can bind to the SBE in response to TGF-β. Whole-cell extracts from HaCaT cells that were untreated or treated with TGF-β for 1 h were incubated with the 16-bp probe in a gel mobility shift assay shown in A and B. (A) Antibodies against Smad2/Smad3 or Smad4 can cause supershift of the TGF-β-inducible DNA–protein complex. (B) Specific competitor refers to an oligo with mutated flanking sequence but containing intact 8-bp SBE. Nonspecific competitor refers to an oligo with a 2-bp mutation in the GTCT sequence of the SBE. (C) HaCaT cells were untreated or treated with TGF-β for various times and then analyzed for SBE-binding activity in a gel mobility shift assay.