Cyclic AMP Regulation of Mouse Proline-Rich Protein Gene Expression: Isoproterenol Induction of AP-1 Transcription Factors in Parotid Glands

Proline-rich protein mRNAs are increased dramatically in the salivary glands of rats, mice, and hamsters upon treatment with the β-agonist isoproterenol. Sequence comparisons between mice and hamster proline-rich protein genes identified conserved regions upstream from the transcription start site. Reporter plasmids containing these 5′-flanking sequences from a mouse proline-rich protein gene, MP2, were constructed and tested for transcriptional regulation by cAMP. Transient transfection experiments in mouse L-M cells showed that the upstream region −702 to −322 bp relative to the transcription start site is sufficient to confer cAMP induction on a heterologous promoter. Multiple copies of the AP-1 sequence elements within this region (−625 to −551) mediate the cAMP transcriptional response of reporter gene expression in L-M cells. L-M cell nuclear proteins and purified human c-jun protein bind to these upstream elements as determined by DNase I footprint analysis. Nuclear proteins isolated from mouse parotid glands protected the consensus AP-1 binding site 5′-TGAGTCA-3′ (−592 to −586). The nuclear proteins interacting at this site were increased about sixfold in glands isolated from isoproterenol-treated mice when compared with glands from untreated mice. These results suggest that induction of AP-1 transcription factors in the parotid gland control the upregulation of some mouse salivary proline-rich proteins.