MULTIPLE SPLICE VARIANTS OF PHOSPHODIESTERASE PDE4C CLONED FROM HUMANLUNG AND TESTIS

Four closely related cyclic-nucleotide specific phosphodiesterase (PDE 4) genes have been identified in both humans and rats: PDE4A, 4B, 4C a nd 4D. We have now cloned cDNAs for multiple splice variants of human PDE4C. Two splice variants, PDE4C-791 and PDE4C-426, were isolated fro m a fetal lung library. The longest open reading frame (ORF) of 791 am ino acids (aa) is encoded by PDE4C-791, which is similar to a recently described cDNA [Engels, P., Sullivan, M., Muller, T. and Lubbert, H. FEBS Lett. 358 (1995) 305-10], except that an alternative 5'-end seque nce upstream of the first methionine extends the PDE4C-791 ORF by 79 a a. The PDE4C-426 variant contains 3 insertions that are located 5' to the catalytic domain and encode several in-frame stop codons. The pred icted 426 aa protein initiates at a methionine 365 aa within PDE4C-791 . A baculovirus clone starting at this methionine expressed an enzymat ically active protein. Two additional splice variants, PDE4C-Delta 54 and PDE4C-Delta 109, were found in testis mRNA. PDE4C-Delta 54 contain ed a novel 5'-end region and a deletion of 162 nt; the predicted prote in deletes 54 aa from the amino-terminal region. The PDE4C-Delta 54 pr otein produced in baculovirus-infected cells was enzymatically active and sensitive to PDE4-specific inhibitors. The PDE4C-Delta 109 protein is similar to PDE4C-Delta 54 but has an additional 55 aa deleted in t he catalytic domain; it lacked enzymatic activity. Analysis of unclone d total mRNA from 4 tissue sources by polymerase chain reaction (PCR) confirmed the presence of mRNAs with the two deletions and three inser tions that we observed in cDNA clones. The PDE4C-Delta 54 variant was found only in testis and the 5'-extended region of PDE4C-791 was seen only in lung and the melanoma cell line G361. Hence, tissue-specific e xpression of various PDE4C isoforms should be considered in understand ing how these gene products modulate cellular responses to cAMP. (C) 1 997 Elsevier Science B.V.