Lipopolysaccharide-induced apoptosis of macrophages determines the up-regulation of concentrative nucleoside transporters Cnt1 and Cnt2 through tumor necrosis factor-alpha-dependent and -independent mechanisms.
In murine bone marrow macrophages, lipopolysaccharide (LPS) induces apoptosis through the autocrine production of tumor necrosis factor-alpha (TNF-alpha), as demonstrated by the fact that macrophages from TNF-alpha receptor I knock-out mice did not undergo early apoptosis. In these conditions LPS up-regulated the two concentrative high affinity nucleoside transporters here shown to be expressed in murine bone marrow macrophages, concentrative nucleoside transporter (CNT) 1 and 2, in a rapid manner that is nevertheless consistent with the de novo synthesis of carrier proteins. This effect was not dependent on the presence of macrophage colony-stimulating factor, although LPS blocked the macrophage colony-stimulating factor-mediated up-regulation of the equilibrative nucleoside transport system es. TNF-alpha mimicked the regulatory response of nucleoside transporters triggered by LPS, but macrophages isolated from TNF-alpha receptor I knock-out mice similarly up-regulated nucleoside transport after LPS treatment. Although NO is produced by macrophages after LPS treatment, NO is not involved in these regulatory responses because LPS up-regulated CNT1 and CNT2 transport activity and expression in macrophages from inducible nitric oxide synthase and cationic amino acid transporter (CAT) 2 knock-out mice, both of which lack inducible nitric oxide synthesis. These data indicate that the early proapoptotic responses of macrophages, involving the up-regulation of CNT transporters, follow redundant regulatory pathways in which TNF-alpha-dependent- and -independent mechanisms are involved. These observations also support a role for CNT transporters in determining extracellular nucleoside availability and modulating macrophage apoptosis.
Soler
C
C
Departament de Fisiologia (Biologia del Macròfag), Universitat de Barcelona, Barcelona, Spain.
Valdés
R
R
Garcia-Manteiga
J
J
Xaus
J
J
Comalada
M
M
Casado
F J
FJ
Modolell
M
M
Nicholson
B
B
MacLeod
C
C
Felipe
A
A
Celada
A
A
Pastor-Anglada
M
M
D000818:Animals; D017209:Apoptosis; D015152:Blotting, Northern; D015153:Blotting, Western; D001854:Bone Marrow Cells / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D002412:Cations; D053938:DNA Fragmentation / Q000187:drug effects; D005269:Femur / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology*; D008262:Macrophage Activation; D016173:Macrophage Colony-Stimulating Factor / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism*; D026901:Membrane Transport Proteins; D051379:Mice; D008807:Mice, Inbred BALB C; D018345:Mice, Knockout; D019001:Nitric Oxide Synthase / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II; D021381:Protein Transport; D012333:RNA, Messenger / Q000378:metabolism; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*; D015854:Up-Regulation
D002352:Carrier Proteins; D002412:Cations; D008070:Lipopolysaccharides; D026901:Membrane Transport Proteins; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; C065171:cif nucleoside transporter; D016173:Macrophage Colony-Stimulating Factor; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse