In the present work, we showed that: (1) Sp1 is essential for the human MsrB1 promoter activity; (2) despite having all of the usual characteristics of a ubiquitously expressed "housekeeping" gene, MsrB1 is regulated differently among breast carcinoma cells; and (3) treatment with DNA methyltransferase inhibitor 5-Aza-dC induced MsrB1 gene expression in the highly metastatic MDA-MB231 cells. Here, SP1 is linked to breast carcinoma.