Role of intracellular chloride in the reversible activation of neutrophil beta 2 integrins: a lesson from TNF stimulation.
The process of beta(2) integrin activation, which enhances the interaction of these heterodimers with ligands, plays a crucial role in the adherence-dependent neutrophilic polymorphonuclear leukocytes' (PMN) responses to TNF. Our previous observation, showing that a marked decrease of the high basal Cl(-) content (Cl(-)(i)) is an essential step in the TNF-induced activation of PMN, stimulated this study, which investigates the role of alterations of Cl(-)(i) in the activation of beta(2) integrins triggered by TNF. Here we show that TNF enhances the expression of activation-specific neoepitopes of beta(2) integrins, namely, epitope 24, a unique epitope present on all three leukocyte integrin alpha subunits, and epitope CBRM1/5, localized to the I domain on the alpha-chain of Mac-1 (CD11bCD18). Moreover, we demonstrate that the conformational changes underlying the expression of the neoepitopes are dependent on a drop in Cl(-)(i) because 1) inhibition of Cl(-)(i) decrease is invariably accompanied by inhibition of beta(2) integrin activation, 2) Cl(-)(i) decrease induced by means other than agonist stimulation, i.e., by placing PMN in Cl(-)-free buffers, activates beta(2) integrins, and 3) restoration of the original Cl(-)(i) levels is accompanied by deactivation of beta(2) integrins. We also show that Cl(-)(i) decrease is required for TNF-induced cytoplasmic alkalinization, but such a rise in pH(i) does not seem to be relevant for beta(2) integrin activation. The results of our study emphasize the role of Cl(-) as a new PMN "second messenger."
Menegazzi
R
R
Department of Physiology and Pathology, University of Trieste, Trieste, Italy. menego@fc.univ.trieste.it
Busetto
S
S
Cramer
R
R
Dri
P
P
Patriarca
P
P
D017920:Antiporters / Q000494:pharmacology; D002021:Buffers; D002084:Butylated Hydroxytoluene / Q000031:analogs & derivatives* / Q000494:pharmacology; D018821:CD18 Antigens / Q000737:chemistry / Q000378:metabolism*; D002448:Cell Adhesion / Q000502:physiology; D002712:Chlorides / Q000378:metabolism / Q000502:physiology*; D000939:Epitopes / Q000096:biosynthesis; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007424:Intracellular Fluid / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D018375:Neutrophil Activation / Q000187:drug effects; D009504:Neutrophils / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D011487:Protein Conformation; D014409:Tumor Necrosis Factor-alpha / Q000037:antagonists & inhibitors / Q000502:physiology*
D017920:Antiporters; D002021:Buffers; D018821:CD18 Antigens; D002712:Chlorides; D000939:Epitopes; D014409:Tumor Necrosis Factor-alpha; D002084:Butylated Hydroxytoluene; C013753:2-aminomethyl-4-t-butyl-6-iodophenol