Cyclic AMP Regulation of Neutrophil Apoptosis Occurs via a Novel Protein Kinase A-independent Signaling Pathway

Abstract

The second messenger molecule cyclic AMP dramatically modulates the apoptotic program in a wide variety of cells, accelerating apoptosis in some and delaying the rate of apoptosis in others. Human neutrophil apoptosis, a process that regulates the fate and numbers of these potentially histotoxic cells in inflammatory sites, is profoundly delayed by the cell-permeable analog of cyclic AMP, dibutyryl-cAMP. We have investigated the mechanisms underlying cyclic AMP-mediated delay of neutrophil apoptosis, and we show that cyclic AMP inhibits loss of mitochondrial potential occurring during constitutive neutrophil apoptosis. Furthermore, we demonstrate that cyclic AMP also suppresses caspase activation in these inflammatory cells. Despite increasing protein kinase A activity, this kinase is unlikely to mediate the effect of cyclic AMP on apoptosis because blockade of protein kinase A activation did not influence the survival effects of cyclic AMP. Further investigation of the signaling mechanism demonstrated that the delay of apoptosis is independent of phosphoinositide 3-kinase and MAPK activation. Our results suggest cyclic AMP delays neutrophil apoptosis via a novel, reversible, and transcriptionally independent mechanism. We show that proteasome activity in the neutrophil is vitally involved in this process, and we suggest that a balance of pro-apoptotic and anti-apoptotic proteins plays a key role in the powerful ability of cyclic AMP to delay neutrophil death.

cAMP Dose-dependently Prevents Palmitate-induced Apoptosis by Both Protein Kinase A- and cAMP-Guanine Nucleotide Exchange Factor-dependent Pathways in β-Cells

“…Elevated levels of intracellular cAMP have been reported to protect various cell types including neutrophils, hepatocytes, and neuronal cells from apoptosis stimulated by various agents (3)(4)(5)(6). The mechanisms responsible for the protective action of cAMP against apoptosis include the synthesis of antiapoptotic proteins, inactivation of pro-apoptotic proteins, and activation of phoshatidylinositol 3-kinase-dependent Akt.…”

Synthesis and antibacterial activities of cadiolides A, B and C and analogues

“…Therefore, since the compounds 6c, 7c, 9 and 10 exerted the most relevant effects against human pathogens, they were primarily tested at 30 and 100 µM for potential cytotoxic effects in freshly isolated human neutrophils 10 by the use of two different approaches: the MTT (3[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) colorimetric assay 11 and by flow cytometry analysis 12,13 of cell apoptosis and survival. 14 Human neutrophils cell types have already been used for assaying the cytotoxic effects of different semi-synthetic alkaloids with antibacterial activity.…”

“…1 H NMR (300 MHz, CDCl 3 ): δ = 8.08 (s, 2H), 3.93 (s, 3H), 2.56 (s, 3H) ppm. 13 General Procedure for the synthesis of α-bromo-ketones 13b-c (Procedure B): To a stirred solution of acetophenones 11b-c (1 equiv.) in THF (30 mL) was added trimethylphenylammonium tribromide (1.05 equiv.)…”

“…1 H NMR (300 MHz, CDCl 3 ): δ = 9.86 (s, 1H), 8.02 (s, 2H), 3.96 (s, 3H) ppm. 13 C NMR (75 MHz, CDCl 3 ): δ = 188. 6, 159.3, 134.4, 134.1, 119.5, 61.0 ppm.…”

“…The protocol indicated by the manufacturer (FITC Annexin V Apoptosis Detection Kit I; BD Biosciences) was used as outlined previously. 13 Cells (1 x 10 4 ) were analyzed in a BD FACSVerse Flow Cytometer (BD Biosciences, San Jose, CA) and differentiated as early or viable apoptotic (annexin V+ and PI-), late apoptotic and/or necrotic (annexin V+ and PI+), and viable nonapoptotic (annexin V-and PI-) cells.…”