Modulation of constitutive and delayed apoptosis by brefeldin A in human neutrophils

Glucose-6-phosphatase-β, implicated in a congenital neutropenia syndrome, is essential for macrophage energy homeostasis and functionality

Glucose-6-phosphatase-β (G6Pase-β or G6PC3) deficiency, also known as severe congenital neutropenia syndrome 4, is characterized not only by neutropenia but also by impaired neutrophil energy homeostasis and functionality. We now show the syndrome is also associated with macrophage dysfunction, with murine G6pc3(-/-) macrophages having impairments in their respiratory burst, chemotaxis, calcium flux, and phagocytic activities. Consistent with a glucose-6-phosphate (G6P) metabolism deficiency, G6pc3(-/-) macrophages also have a lower glucose uptake and lower levels of G6P, lactate, and ATP than wild-type macrophages. Furthermore, the expression of NADPH oxidase subunits and membrane translocation of p47(phox) are down-regulated, and G6pc3(-/-) macrophages exhibit repressed trafficking in vivo both during an inflammatory response and in pregnancy. During pregnancy, the absence of G6Pase-β activity also leads to impaired energy homeostasis in the uterus and reduced fertility of G6pc3(-/-) mothers. Together these results show that immune deficiencies in this congenital neutropenia syndrome extend beyond neutrophil dysfunction.

High levels of intracellular IL-4 are expressed in circulating apoptotic T cells in patients with tuberculosis and in community controls

Data concerning T helper cell phenotypes in response to Mycobacterium tuberculosis infection remain controversial. T lymphocyte intracellular interleukin-4 production in response to CD3 stimulation was determined by flow cytometry in 21 TB patients and 14 community controls. In supplementary experiments the association of interleukin-4 expression with apoptosis was investigated. A low percentage of CD4 T cells in both patients and controls expressed high levels of interleukin-4 (IL-4(high)). A larger subset of both CD4 and CD8 T cells of all subjects expressed low levels of intracellular IL-4 (IL-4(low)). Stimulated and unstimulated cells expressed IL-4(low) and IL-4(high). IL-4(low) percentages were lower in TB patients at diagnosis compared to controls while IL-4(high) percentages were higher in patients. Most IL-4(high) cells co-expressed active caspase-3, a marker for apoptosis. This co-expression was also shown in experimentally induced apoptotic Jurkat cells and peripheral blood neutrophils and monocytes. IL-4 levels may therefore not necessarily indicate a skewed Th cell phenotype, as our data suggest that IL-4 production by CD4 and CD8 T cells can occur constitutively in healthy controls with latent TB infection and in TB patients. Cellular IL-4 production may represent a normal cellular growth factor mechanism which is disturbed at the onset of apoptosis.

Apoptosis of human neutrophils induced by protein phosphatase 1/2A inhibition is caspase-independent and serine protease-dependent

Protein phosphatase (PP) activity is associated with the regulation of apoptosis in neutrophils. However, the underlying regulatory mechanism(s) in apoptosis remain unclear. The type of cell death induced by okadaic acid (OA), the inhibitor of PP1 and PP2A, is characterized by apoptotic morphological changes of the cells and annexin V-positive staining without DNA fragmentation. The apoptotic effects of OA and calyculin A on neutrophils were observed at concentrations ranging from 50 to 200 nM, or 10 to 50 nM, respectively. Cyclosporine A (a PP2B specific inhibitor), however, did not exhibit any pro-apoptotic effects. OA and calyculin A, but not cyclosporine A, exhibited significant effects on protein levels and on the electrophoretic mobility of Mcl-1. zVAD-fmk, a pancaspase inhibitor, failed to inhibit the effect of OA on the caspase-3 activity, procaspase-3 processing, and the apoptotic rate of neutrophils. However, 4-(2-aminoethyl) benzenesulfonylfluoride (AEBSF), a general serine protease inhibitor, significantly abrogated the OA-induced mobility shift in procaspase-3, caspase-3 activation, and the apoptotic morphological changes in neutrophils. Moreover, OA enhanced the serine protease activity of the neutrophils. The addition of the proteinase-3 protein increased the rate of neutrophil apoptosis, which was also blocked by AEBSF but not by zVAD-fmk. These results suggest that OA induces procaspase-3 processing but that OA-induced apoptosis is caspase-independent and serine protease-dependent.

Membrane trafficking of the human organic anion-transporting polypeptide C (hOATPC)

INTRODUCTION

The human organic anion transporting polypeptide C (OATPC) is one of the major transport proteins involved in the enterohepatic circulation of bile salts and plays an important role in vectorial transport of organic anions and drugs across hepatocytes.

MATERIALS AND METHODS

In this study, the effects of biological reagents on the membrane localization of OATPC were investigated by confocal microscopy and estrone-3-sulfate transport.

RESULTS

Our results demonstrated that the functional membrane expression of fluorescent chimera OATPC-GFP was achieved in non-polarized (COS7 and HEK293) and polarized (MDCK) cells. Both brefeldin A (a Golgi complex disruptor) and bafilomycin A1 (an inhibitor of vacuolar H+-ATPase) treatment significantly decreased the polarized membrane trafficking and markedly reduced the uptake of estrone-3-sulfate ( approximately 40-90%) in OATPC-GFP transfected cells, suggesting that membrane sorting of hOATPC-GFP was mediated by Golgi complex and vacuolar H+-ATPase-related vesicle transport pathways. Treatment with 8-Br-cAMP (a cAMP analog) stimulated OATPC-GFP membrane localization and enhanced estrone-3-sulfate uptake by approximately 20%. The protein kinase A (PKA) inhibitors (H89 and KT5720), but not a PKG inhibitor, blocked the polarized membrane expression of OATPC-GFP and reduced estrone-3-sulfate transport activity. The simultaneous treatment of cells with PKA activator/inhibitor and bafilomycin A1 demonstrated that bafilomycin A1 did not change the effects of 8-Br-cAMP and H89 on the membrane localization of OATPC-GFP compared with the use of 8-Br-cAMP and H89 alone.

DISCUSSION

These data suggest that a cAMP-PKA sensitive membrane sorting pathway for OATPC-GFP is independent of the vacuolar H+-ATPase associated (bafilomycin A1 sensitive) vesicle mediated membrane sorting pathway. In contrast, with combined treatment with brefeldin A, neither the PKA-activator (8-Br-cAMP) nor the inhibitor (H89) further altered the plasma membrane expression and transport activity of OATPC-GFP compared with brefeldin A treatment alone. These data suggest that the cAMP-PKA regulation of OATPC membrane expression involves the Golgi complex. When the Golgi apparatus was disrupted by brefeldin A treatment, the effects of cAMP-PKA on the Golgi-to-basolateral surface sorting process of OATPC was also diminished. In summary, the plasma membrane localization of human OATPC is mediated by Golgi complex and vacuolar H+-ATPase vesicle mediated membrane sorting pathways. cAMP-PKA regulates sorting process through the Golgi complex but not the vacuolar H+-ATPase associated vesicular pathway.

Pro-apoptotic effect of high concentrations of histamine on human neutrophils

Histamine receptors are expressed on neutrophils, and therefore, are likely to modulate neutrophil function. In this study, we investigated whether histamine modulates human neutrophil survival. Neutrophils were found to rapidly undergo spontaneous apoptosis upon culture in vitro and this was accelerated by high concentrations of histamine. Moreover, the percentage of apoptotic neutrophils was also markedly increased by treating with 10 mM histamine in the presence of inflammatory mediators, such as lipopolysaccharide (LPS), granulocyte macrophage-colony stimulating factor (GM-CSF), dibutyryl-cAMP (db-cAMP), or dexamethasone. Histamine-induced neutrophil apoptosis was inhibited by pyrilamine, a histamine receptor 1 antagonist, and by ranitidine, a selective histamine receptor 2 antagonist. In addition, diphenylene iodonium (DPI), an inhibitor of NADPH-oxidase, significantly blocked the apoptotic effect of histamine. Moreover, the induction of apoptosis by histamine was almost completely inhibited by zVAD-fmk, a pan-caspase inhibitor. In addition, immunoblotting showed that histamine induced the proteolytic activation of procaspase-3 in cell lysates treated with histamine. And, the protein kinase C (PKC)-delta inhibitor, rottlerin (5 microM) significantly blocked the apoptotic effect of histamine, though the cleavage of PKC-delta in 20 h cultured neutrophils was increased by histamine. However, an inhibitor of conventional PKC, Go6976 (100 nM) and a p38 mitogen-activated protein kinase inhibitor, SB203580 (10 microM), failed to block histamine-induced neutrophil apoptosis. These results suggest that high concentrations of histamine in local inflammatory and allergic lesions induce neutrophil apoptosis, and that this histamine-induced apoptosis is mediated by caspase activation and PKC-delta signaling.