A Downstream AP-1 Element Regulates In Vitro Lung Transcription from the Human Pulmonary Surfactant Protein B Promoter

We have used the human lung surfactant protein B (SP-B) gene as a template for in vitro transcription studies. Transcription factors were provided by nuclear extracts from a cultured line of human lung (type II-like) cells. Elements upstream of −50 had essentially no effect on the efficiency of the SP-B promoter in vitro. However, a deletion of the region from +8 to +8 reduced in vitro transcription by a factor of 10. The only factor whose binding was detected between +1 and +100 by footprinting, and between +12 and +38 by electrophoretic mobility shift analysis (EMSA), was a member of the AP-1 family. Mutation of 4 of 7 bases of the AP-1 site reduced transcription two-fold and ablated the AP-1 EMSA binding complex observed on the SP-B downstream region (+12 to +38). Competition with unlabeled AP-1 consensus oligonucleotide abolished the downstream footprint over the AP-1 site. Thus, the SP-B promoter is one of a very small class of RNA polymerase II promoters that are strongly dependent in vitro on sequence elements downstream of the transcription start site, and, in this case, the AP-1 consensus element and surrounding sequences.