Characterization of an Intronic Promoter of a Cyclic Adenosine 3′,5′-Monophosphate (cAMP)-Specific Phosphodiesterase Gene that Confers Hormone and cAMP Inducibility

In the Sertoli cell, FSH stimulates transcription of a cAMP-phosphodiesterase (PDE) gene (PDE4D) and accumulation of corresponding mRNA and PDE protein. The regulation of this PDE gene is an important component of the desensitization state induced by this hormone. Given the ubiquitous nature of this regulation controlling cAMP levels, the molecular basis for the PDE4D induction was further investigated. FSH stimulation of the Sertoli cell causes the accumulation of only two of the four known PDE4D mRNAs (PDE4D1 and PDE4D2). The promoter controlling the expression of these two messages was identified and characterized. An EcoRI fragment containing a coding exon as well as 5'-upstream sequence of the PDE4D1/2 mRNA was isolated from rat genomic libraries and sequenced. No TATA box was identified, but GC-rich regions were present upstream of the putative translation start site. RNAse protection and PCR analysis indicated the presence of at least two distinct cap sites. This genomic region had promoter activity when transfected both in Sertoli and MA-10 cells. Deletion mutation indicated that basal promoter activity was contributed by regions upstream of both cap sites. Transcription from this promoter was activated by FSH and (Bu)2cAMP, and elements responsible for cAMP regulation were present upstream from the second cap site. These data demonstrate that an intronic promoter that is cAMP- and hormone-inducible directs the expression of these truncated PDE proteins.