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Regulation of mouse SP-B gene promoter by AP-1 family members
Z Sever-Chroneos1, C J Bachurski, C Yan
1Division of Pulmonary Biology, Children's Hospital Medical Center, Cincinnati, Ohio 45229, USA.
Abstract:
The regulatory role of activator protein-1 (AP-1) family members in mouse surfactant protein (SP) B (mSP-B) promoter function was assessed in the mouse lung epithelial cell line MLE-15. Expression of recombinant Jun B and c-Jun inhibited mSP-B promoter activity by 50-75%. Although c-Fos expression did not alter mSP-B transcription, Jun D enhanced mSP-B promoter activity and reversed inhibition of mSP-B by c-Jun or Jun B. A proximal AP-1 binding site (-18 to -10 bp) was identified that overlaps a thyroid transcription factor-1 binding site. Mutation of this proximal AP-1 site blocked both Jun B inhibition and Jun D enhancement and partially blocked c-Jun inhibition of promoter activity. Promoter deletion mutants were used to identify additional sequences mediating the inhibitory effects of c-Jun in the distal region from -397 to -253 bp. The AP-1 element in this distal site (-370 to -364 bp) is part of a composite binding site wherein AP-1, cAMP response element binding protein, thyroid transcription factor-1, and nuclear factor I interact. Point mutation of the distal AP-1 binding site partially blocked c-Jun-mediated inhibition of the SP-B promoter. Both stimulatory (Jun D) and inhibitory (c-Jun/Jun B) effects of AP-1 family members on mSP-B promoter activity are mediated by distinct cis-acting elements in the mSP-B 5'-flanking region.
Insights
Activator protein-1 (AP-1) family members regulate mouse surfactant protein B (mSP-B) promoter activity. Jun D enhances mSP-B transcription, while c-Jun and Jun B inhibit it, acting on distinct DNA elements.
Area of Science:
- Molecular Biology
- Gene Regulation
- Respiratory Physiology
Background:
- Surfactant protein B (SP-B) is crucial for lung function.
- The regulation of SP-B gene expression is complex and not fully understood.
- Activator protein-1 (AP-1) is a transcription factor family involved in various cellular processes.
Purpose of the Study:
- To investigate the role of AP-1 family members in regulating mouse SP-B (mSP-B) promoter activity.
- To identify specific AP-1 binding sites and their functional significance in mSP-B gene transcription.
Main Methods:
- Utilized the mouse lung epithelial cell line MLE-15.
- Employed promoter-reporter assays with wild-type and mutated mSP-B promoter constructs.
- Expressed recombinant AP-1 family members (Jun B, c-Jun, c-Fos, Jun D) to assess their effects on promoter activity.
- Analyzed promoter deletion mutants to map regulatory regions.
Main Results:
- Jun B and c-Jun significantly inhibited mSP-B promoter activity (50-75%).
- Jun D enhanced mSP-B promoter activity and counteracted inhibition by c-Jun or Jun B.
- A proximal AP-1 binding site (-18 to -10 bp) overlaps with a thyroid transcription factor-1 site and mediates effects of Jun B, Jun D, and partially c-Jun.
- A distal AP-1 element (-370 to -364 bp) within a composite binding site is also involved in c-Jun-mediated inhibition.
Conclusions:
- AP-1 family members differentially regulate mSP-B promoter activity through distinct cis-acting elements.
- Both stimulatory (Jun D) and inhibitory (c-Jun, Jun B) effects are mediated by specific DNA sequences in the mSP-B 5'-flanking region.
- The findings elucidate a novel regulatory mechanism for mSP-B gene expression involving AP-1 transcription factors.