Abstract
The cAMP-specific phosphodiesterase-4 (PDE4) gene family is the target of several potential selective therapeutic inhibitors. The four PDE4 genes generate several distinct protein-coding isoforms through the use of alternative promoters and 5′-coding exons. Using mouse transcripts, we identified a novel, super-short isoform of human PDE4B encoding a novel 5′ terminus, which we label PDE4B5. The protein-coding region of the novel 5′ exon is conserved across vertebrates, chicken, zebrafish, and fugu. Reverse-transcription-polymerase chain reaction (PCR) and quantitative (PCR) measurements show that this isoform is brain-specific. The novel protein is 58 ± 2 kDa; it has cAMP hydrolyzing enzymatic activity and is inhibited by PDE4-selective inhibitors rolipram and cilomilast (Ariflo). Confocal and subcellular fractionation analyses show that it is distributed predominantly and unevenly within the cytosol. The 16 novel N-terminal residues of PDE4B5 are identical to the 16 N-terminal residues of the super-short isoform of PDE4D (PDE4D6), which is also brain-specific. PDE4B5 is able to bind the scaffold protein DISC1, whose gene has been linked to schizophrenia. Microarray expression profiling of the PDE4 gene family shows that specific PDE4 genes are enriched in muscle and blood fractions; however, only by monitoring the individual isoforms is the brain specificity of the super-short PDE4D and PDE4B isoforms revealed. Understanding the distinct tissue specificity of PDE4 isoforms will be important for understanding phosphodiesterase biology and opportunities for therapeutic intervention.
Footnotes
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M.D.H. was supported by the Medical Research Council (UK) (G8604010).
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.107.122218.
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ABBREVIATIONS: PDE, phosphodiesterase; UCR, upstream conserved regions; RT, reverse transcription; PCR, polymerase chain reaction; SDS, sodium dodecyl sulfate; PAGE, polyacrylamide gel electrophoresis; ORF, open reading frame; DISC1, disrupted in schizophrenia 1; PBS, phosphate-buffered saline; DMSO, dimethyl sulfoxide; EST, expressed sequence tag; nt, nucleotide(s); fl-DISC1, full-length 100-kDa DISC1.
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↵1 Current affiliation: Genentech, Inc., South San Francisco, California.
- Received March 2, 2007.
- Accepted May 21, 2007.
- The American Society for Pharmacology and Experimental Therapeutics
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