Selective up-regulation of PDE1B2 upon monocyte-to-macrophage differentiation.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a major regulator of monocyte to macrophage differentiation. In both humans and mice, the main phenotype of decreased GM-CSF function is pulmonary proteinosis due to aberrant function of alveolar macrophages. Recently, this cytokine has been shown to up-regulate a cyclic nucleotide phosphodiesterase, PDE1B. Two PDE1B variants with unique N-terminal sequences, PDE1B1 and PDE1B2, have been identified. Here, we report that the previously uncharacterized PDE1B2 is selectively increased by GM-CSF by stimulation of transcription at a previously unknown transcriptional start site. Analysis of the exon and intron organization of the PDE1B gene reveals that PDE1B2 has a different N-terminal sequence because of a separate first exon that is located 11.5 kb downstream from the PDE1B1 first exon. By using 5'-RACE, alignment of EST sequences, and a luciferase-reporter system, we provide evidence that PDE1B2 has a separate transcriptional start site from PDE1B1 that can be activated by monocyte differentiation. Furthermore, IL-4 treatment in the presence of GM-CSF, which shifts the differentiation from a macrophage to a dendritic cell phenotype, suppresses the up-regulation of PDE1B2. Induction of PDE1B2 is also found in T cells upon activation by PHA. Therefore, PDE1B2 may have a regulatory role in multiple immune cell types. Last, characterization of the catalytic properties of recombinant PDE1B2 shows that it prefers cGMP over cAMP as a substrate and, thus, is likely to regulate cGMP in macrophages. Also, PDE1B2 has a nearly 3-fold lower EC(50) for activation by calmodulin than PDE1B1.

Differentiation of human monocytes in vitro with granulocyte-macrophage colony-stimulating factor and macrophage colony-stimulating factor produces distinct changes in cGMP phosphodiesterase expression.

The cytokines macrophage colony-stimulating factor (M-CSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF) promote differentiation of monocytes into macrophages with distinct phenotypes and unique functional abilities. In this report, we characterize how monocytes and macrophages differentiated from monocytes with M-CSF and GM-CSF regulate their cGMP levels by controlling which phosphodiesterases (PDEs) and guanylyl cyclases (GCs) are expressed. We find that PDE1B and PDE2A are expressed at low levels in monocytes, but are the major cGMP PDEs expressed in macrophages. M-CSF differentiation triggers increased expression of PDE1B and PDE2A, while GM-CSF causes a large increase only in PDE1B. Based on PDE expression, we identified THP-1 and U937 cell lines as possible models for studying the roles of PDE1B and PDE2A in macrophage function. We additionally characterized changes in expression of GCs upon differentiation. We found that GM-CSF differentiation triggers a small decrease in soluble guanylyl cyclase (sGC) and a large increase in GC-A, while M-CSF significantly decreases sGC.