Abstract
The regulation of phosphodiesterase-4 (PDE4) by various phospholipids was explored using PDE4s partially purified from U937 cells. Preincubation (5 min, 4 degrees C) of the large molecular weight PDE4 denoted "Peak 2 PDE4" with mixed phosphatidic acids (PAs) produced a 2-fold increase in its Vmax without changing its Km (approximately 2 microM) for cyclic AMP. This "activation" was not limited to PAs with specific fatty acid substituents: Synthetic PAs containing saturated and/or unsaturated fatty acids 16-20 carbons long produced similar effects. Lysophosphatidic acids (LPAs) and phosphatidylserines (PSs) also induced PDE4 activation, whereas phosphatidylcholines (PCs), phosphatidylethanolamines (PEs) and diacylglycerol did not. Antibodies to a peptide region near the PDE4 catalytic site specifically inhibited PA-induced activation. The data demonstrate that anionic phospholipids can act as non-essential activators of a leukocyte PDE4, and suggest biochemical crosstalk between phospholipid-dependent and cyclic AMP-dependent signalling pathways in human leukocytes.
MeSH terms
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3',5'-Cyclic-AMP Phosphodiesterases*
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Amino Acid Sequence
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Animals
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Antibody Formation
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Cyclic AMP / metabolism*
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Cyclic GMP / pharmacology
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Cyclic Nucleotide Phosphodiesterases, Type 4
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Enzyme Activation / drug effects
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Fatty Acids / analysis
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Humans
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Lymphoma, Large B-Cell, Diffuse / pathology
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Lysophospholipids / pharmacology
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Molecular Sequence Data
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Monocytes / drug effects*
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Monocytes / enzymology
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Neoplasm Proteins / metabolism
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Peptide Fragments / immunology
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Phosphatidic Acids / pharmacology
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Phosphatidylcholines / pharmacology
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Phospholipids / chemistry
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Phospholipids / pharmacology*
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Phosphoric Diester Hydrolases / chemistry
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Phosphoric Diester Hydrolases / immunology
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Phosphoric Diester Hydrolases / metabolism*
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Pyrrolidinones / pharmacology
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Rabbits
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Rolipram
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Structure-Activity Relationship
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Tumor Cells, Cultured / drug effects
Substances
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Fatty Acids
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Lysophospholipids
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Neoplasm Proteins
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Peptide Fragments
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Phosphatidic Acids
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Phosphatidylcholines
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Phospholipids
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Pyrrolidinones
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Cyclic AMP
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Phosphoric Diester Hydrolases
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3',5'-Cyclic-AMP Phosphodiesterases
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Cyclic Nucleotide Phosphodiesterases, Type 4
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Cyclic GMP
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Rolipram