Analysis of MsrB1 promoter function in breast cancer cell lines. (A) MCF7 and MDA-MB231 cells were transiently transfected with five promoter constructs ranging from nt -1276 (P-1403) to -38 (P-165) relative to transcription start site and extending to nt +127. Promoter fragments were inserted into the pGL3-Basic luciferase vector. Luciferase activity was measured as relative light units of firefly luciferase normalized with respect to protein concentration. Promoter activity is expressed as the magnitude of normalized luciferase activity relative to the pGL3-Basic promoterless negative control vector (pGL3). The results are reported as mean ± S.D. of at least five different experiments, in duplicate for each construct. (B) a schematic map of the deletion constructs excluding each Sp1 binding site is reported (Sp-1A, Sp-1B, Sp-1C, Sp-1D and Sp-1E).