Figure 6.

Bacterial toxins that act on Rho and Rho mutants modulate the activity of the tyrosinase promoter. (A) B16 cells were cotransfected with the 2.2 MT-luc reporter plasmid together with an empty expression vector or a plasmid encoding the C3 exoenzyme (pEF-C3) and then incubated in the absence (NS) or in the presence of 20 μM forskolin for 48 h (FK). When indicated, CNF-1 was added. (B) B16 cells were cotransfected with either an empty expression vector or with a constitutive active version of Rho (Rho-V14) or a dominant negative Rho mutant (Rho-N19); in each case cells were left in growing medium (NS) or treated with forskolin (FK) for 48 h. Forty-eight hours after transfection, soluble extracts were harvested and assayed for luciferase activity. Data are expressed in fold stimulation of the basal tyrosinase activity in each transfection case. Data are means ± SE of five experiments performed in triplicate.