The cDNA of a human lymphocyte cyclic-AMP phosphodiesterase (PDE IV) reveals a multigene family

Abstract Five protein families are needed to encompass the diversity of cyclic-AMP (cAMP) phosphodiesterases (PDE). Family IV PDEs (PDE IV) specifically hydrolyze cAMP with a low K m , and are selectively inhibited by rolipram (Rp) and related drugs. Cloned cDNAs from rat (r) suggest that the PDE IV family comprises four distinct members, designated A, B, C and D. Using RNA from a human lymphocytic B-cell line (43D-Cl 2 ), we have isolated a 3.8-kb cDNA by lowstringency screening using a rat PDE IV member B ( r - PDE IV b ) probe. Expression of the human (h) cDNA in Escherichia coli results in cAMP-specific PDE activity that is Rp sensitive. A single large open reading frame (ORF) predicts a 564-amino-acid protein with 92.9% identity to r-PDE IVs; at the nucleotide level the identity is 86.3%. This h - PDE IV b clone, HPB106, differs from a related cDNA clone isolated by others from h-monocytes [Livi et al., Mol. Cell. Biol. 10 (1990) 2678–2686]. Our analysis identifies the monocyte clone with r - PDE IV a . Southern blots using a 1.2-kb h - PDE IV b probe at low stringency suggest the presence of additional uncloned human PDE IV family members. Analysis of genomic Southern blots using short specific probes from the h - PDE IV a and h - PDE IV b cDNAs indicates that distinct genes encode these two PDE IV family members. RNA from fractionated normal human leukocytes shows major specific messages of 3.0 and 4.6 kb for h-PDE IV a and 3.7 kb for h-PDE IV b . Comparison of our cDNA clones, and PCR analysis of cellular mRNA, suggests that alternative 5'-end sequences of h-PDE IV b are utilized. These results demonstrate a phenomenal complexity in the expression of human PDE IV s which suggests that unique PDE IV isozymes may control cAMP concentrations in cells.