Surfactant protein A (SP-A) is selectively synthesized in subsets of cells
lining the respiratory epithelium, where its expression is regulated by var
ious transcription factors including thyroid transcription factor-1 (TTF-1)
, Cell-specific transcription of the mouse SP-A promoter is mediated by bin
ding of TTF-1 at four distinct cis-active sites located in the 5'-flanking
region of the gene, Mutation of TTF-1-binding sites (TBE) 1, 3, and 4 in co
mbination markedly decreased transcriptional activity of SP-A promoter-chlo
ramphenicol acetyltransferase constructs containing SP-A gene sequences fro
m -256 to +45, In contrast, the same mutations enhanced transcriptional act
ivity in constructs containing additional 5' SP-A sequences from -399 to +4
5 suggesting that cis-acting elements within the region -399 to -256 influe
nce effects of TTF-1 on SP-A promoter activity. A consensus Myb-binding sit
e was identified within the region, located at positions -380 to -371 in th
e mouse gene. Mutation of the Myb-binding site decreased activity of SP-A p
romoter constructs in MLE-15 cells. MLE-15 cells, a cell line expressing SP
-A mRNA, also expressed B-Myb. B-Myb bound to the MBS in the SP-A gene as a
ssessed by electrophoretic mobility shift assay. While co-transfection of H
eLa cells with a E-Myb expression plasmid activated the transfected SP-A pr
omoter about 3-fold, co-transfection of B-myb with cyclin A and cdk-2, to e
nhance phosphorylation of B-Myb, increased transcriptional activity of SP-A
constructs approximately 20-fold. Taken together, the data support activat
ion of SP-A gene promoter activity by E-Myb which acts at a cis-acting elem
ent in the SP-A gene.