The human MBN promoter harbors conserved PU.1, C/EBP, and Myb binding sites: importance for MBN expression and down-regulation in ATRA-induced PLB-985 cells.
(A) Sequence homology between human and murine MBN promoters. Both strands were sequenced. The numbering is relative to the human transcription initiation site. The TATA box is underlined; the CG element as well as the PU.1, C/EBP, and Myb binding sites are boxed. (B) Comparison of the human and murine putative PU.1, C/EBP, and Myb binding sites with their consensus binding sites. The C/EBP site is in the reverse orientation. (C) ATRA affects MBN promoter activity. The pMBN 5′ deletion promoter mutants were fused to the CAT gene (i). PLB-985 cells were transfected with 20 μg each of the indicated MBN 5′ deletion mutants and cultured with or without ATRA (10−6 M). CAT activity was measured after normalization to the luciferase internal control (ii). The graph on the left shows untreated (−ATRA, ░) and ATRA-treated (+ATRA, ▪) cells. CAT activities presented for each pMBN construct were calculated relative to the pMBN-658. On the right are calculated −ATRA/+ATRA ratios as well as standard errors for each construct.
