Figure 5.

(A) The wild-type (wt) Mitf protein up-regulates the human cathepsin K promoter whereas Mitf^mi, Mitf^or, or Mitf^ce mutant proteins have no significant transactivation activity. The wild-type human cathepsin K promoter −928 bp to +2 luciferase reporter was transfected into MCF-7 cells in the presence of wild-type Mitf, Mitf^or, Mitf^mi, Mitf^ce, or a vector control. The transfections were performed in triplicate with bars indicating standard errors. (B and C) Mitf mutants, Mitf^or, and Mitf^mi, which cause osteopetrosis in animal models, decrease the ability of wild-type Mitf (B) and TFE3 (C) to transactivate the cathepsin K promoter. The wild-type human cathepsin K promoter −928 bp to +2 luciferase reporter was transfected into MCF-7 cells in the presence of wild-type Mitf (B) or TFE3 (C) plus mutant Mitf (Mitf^or, Mitf^mi, or Mitf^ce), or vector controls. The transfections were performed in triplicate with bars indicating standard errors. The data are presented as % wild-type Mitf or TFE3 activity on the human cathepsin K promoter after subtracting vector only control. * indicates statistically significant repression of wild-type Mitf or TFE3 function by mutant Mitf^or and Mitf^mi (P < 0.04), whereas the nonosteopetrotic allele Mitf^ce did not affect wild-type Mitf and TFE3 activities.