TRANSCRIPTIONAL REGULATION OF THE LYSOZYME GENE IN AIRWAY GLAND SEROUS CELLS

Lysozyme is expressed in serous, but not mucous, cells of the tracheob ronchial glands and thereby constitutes a marker of the serous cell li neage in these glands. To identify DNA regulatory elements and transcr iption factors mediating the commitment of progenitor cells to the ser ous cell lineage, we have characterized the regulatory activity and DN A-protein interactions of the 5'-flanking region of the bovine lysozym e gene lys 5a. Results obtained from these studies indicate that altho ugh approximately 94 bp of 5' flanking DNA are necessary for high leve l expression in transient transfection assays, an evolutionarily conse rved promoter within 66 bp of the transcription start site is sufficie nt to confer serous cell-specific expression. Farther upstream, within 6.1 kb of the 5' flanking region, are 4 silencers. Analysis of the se rous cell-specific lysozyme promoter by electrophoretic mobility shift assay (EMSA) revealed the presence of binding sites for 3 serous cell nuclear proteins, designated LSF1, LSF2 and LSF3. Binding of LSF2 and LSF3 was localized to a 20-mer subdomain (-50/-30) of the cell-specif ic promoter using binding competition assays. More accurate identifica tion of the protein binding site(s) was achieved through the use of mu tagenesis, which implicated the motif 5'AAGGAAT 3' (-46/-40) in both p rotein binding and serous cell-specific transcriptional activity. This motif has previously been identified as a binding site for ets protei n transcription factors, suggesting that serous cell-specific regulati on of lys 5a transcription is partly controlled by the binding of ets- like protein(s) to the motif 5'AGGAAGT3'. (C) 1996 Wiley-Liss, Inc.