Fig. 1.

KRT5 promoter reporter constructs effectively mark P4-inducible CK5⁺ breast cancer cells. a SCC-15 squamous carcinomas cells, and T47D and MCF7 breast cancer cells, were transiently transfected with a fragment of the human KRT5 promoter (K5p) fused to luciferase (K5pLuc) and treated with vehicle control (EtOH), 100 nM P4 (T47D), or 10 nM E2 + 100 nM P4 (MCF7) for 24 h (SCC-15 were treated with vehicle only). Data shown as fold induction normalized to empty vector. *p < 0.05, **p < 0.01, one-way ANOVA/Tukey post test. b Immunofluorescence for CK5 (red) and GFP (green) in T47D cells stably transduced with K5pGFP virus (T47D^K5pGFP) and treated with vehicle (EtOH), 100 nM P4, or 100 nM P4 + 1 μM RU486 for 24 h. Representative fields of cells are shown for CK5, GFP, and merged images plus DAPI counterstaining. Scale bar, 50 μm. c T47D^K5pGFP cells were treated as in b and extracts prepared and analyzed by Western blot with antibodies against GFP, CK5, PR, or β-actin. GFP and CK5 bands were undetectable by quantitation in EtOH, RU486, or P4 + RU486 lanes, with a relative density of 1.47 and 1.19 (normalized to β-actin), respectively, in the P4-treated sample