Physiological activation of human neutrophils down-regulates CD53 cell surface antigen

Abstract

Tetraspanin transmembrane proteins have a metastasis suppressor effect by acting as cell motility brakes in tumor cells. CD53 is a panleukocyte antigen that belongs to the tetra-span superfamily. Human neutrophils express high levels of CD53. We tested the hypothesis that this antigen level changes when cells are activated. Treatment of human neutrophils with their physiological activators, tumor necrosis factor ␣ or platelet-activating factor, resulted in down-regulation of this antigen from the cell surface, as assessed by immunofluorescence flow cytometry. Similar responses were observed when neutrophils were stimulated with chemotactic N-formyl-methionyl-leucyl-phenylalanine, phorbol ester, or the calcium ionophore ionomycin. The CD53 antigen down-regulation upon neutrophil stimulation was further confirmed by immunoblotting analysis and was not correlated with a change in the level of CD53 transcripts. This CD53 antigen down-regulation paralleled that of CD43 and CD44 antigens in these cells, despite their different protein structure. The down-regulation of the three antigens CD53, CD43, and CD44 could be inhibited by phenylmethylsulfonyl fluoride, suggesting that CD53 antigen down-regulation is the result of the activation of a proteolytic mechanism. Down-regulation of CD53 antigen level, as a result of cellular stimulation, might play a role in the different aspects of neutrophil biology, by modulating its interactions on the cell surface.

Alkyl-lysophospholipid Accumulates in Lipid Rafts and Induces Apoptosis via Raft-dependent Endocytosis and Inhibition of Phosphatidylcholine Synthesis

“…However, after 30 min the uptake of ALP leveled off in S49 AR cells but not in S49 cells. Because the uptake of ALP in S49 cells does not reach saturation, it is unlikely that it would be mediated by a receptor (like that for PAF), which agrees with other reports (1,15,17). Instead, we envision that ALP, because of its single long alkyl chain, easily inserts into the outer leaflet of the plasma membrane lipid bilayer, prior to and/or during internalization.…”

“…The synthetic alkyl-lysophospholipid (ALP), 1 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine (Et-18-OCH 3 ; Edelfosine), is a selective antitumor agent, known to induce apoptosis in various cell types (1,2). Unlike most conventional chemotherapeutic drugs, ALP does not target the DNA but acts at the level of cell membranes.…”

“…We questioned how ALP can reach this intracellular target from outside the cell and how this subsequently initiates apoptosis. There are reports on uptake of ALP correlating with apoptosis induction (1,14). However, the mechanism by which ALP is internalized has remained uncertain.…”

“…ALP is not taken up via a specific receptor (such as for the structurally related plateletactivating factor or lyso-PC) (1,(15)(16)(17). Some investigators argue that endocytosis is not a major pathway by which ALP is taken up (1,14,18), whereas others reach the opposite conclusion (15,19). To address this issue in more detail, we investigated the uptake and action of ALP in S49 cells in comparison with an ALP-resistant variant cell line S49 AR .…”

Lipid nanoparticles for alkyl lysophospholipid edelfosine encapsulation: Development and in vitro characterization

“…Phase I studies have shown a good tolerability of the drug but with haematological and systemic side effects [1,2]. However, although edelfosine has been shown to exert potent antineoplastic effects in vitro [3,4], the antitumor activity in phase II clinical studies has been only moderate [5]. Moreover, ALPs show manifold biological effects in addition to their antineoplastic actions, including an antiparasitic effect on Leishmania [6] as well as an inhibition of the cell membrane phospholipid turnover [7] and a potent inhibition of neovascularization [8], protein kinase C and Na + /K + -ATPase [9].…”