Smad4-dependent TGFβ induction of the LAMA3 promoter is mediated via an SBE and downstream AP1 sites. Normalized promoter activity of LAMA3 in Smad4-negative, Smad4-reexpressing and TGFβ-treated Smad4-positive SW480 and BxPC3 carcinoma cells as well as TGFβ-untreated and -treated Smad4-positive LT97 cells. Point mutations were introduced using the Quick-Change Site directed mutagenesis kit (Stratagene). Bars show the mean value of three approaches with the standard error of the mean. Mutational inactivation of the SBE site at -1.5 kb did not affect the Smad4-dependent increase of constitutive activity but reduced the TGFβ response to approximately half in all three cell lines tested (b). A mutation construct with all three AP1 sites mutated displayed a reduction of basal promoter activity (c). The reduction was moderate in SW480 cells and very pronounced in LT97 and BxPC3 cells. When both, mutation of the SBE site and mutation of the AP1 sites, were combined the TGFβ response was completely abolished (d).