Diminished PKC activity and decreased binding of transcription factors are involved in the impaired production of nitric oxide by macrophages from tumor-bearing mice.
In previous studies we have shown that peritoneal macrophages (PEM) from mammary tumor-bearing BALB/c mice (T-PEM) display a diminished ability to lyse tumor cells upon stimulation with LPS, a phenomenon that is associated to a lower production of nitric oxide, and that is reverted upon costimulation with IFN-gamma. The reduced lytic activity and NO production displayed by T-PEM upon LPS activation were earlier shown by us to be due to a diminished transcription of the inducible nitric oxide synthase (iNOS) gene. In the present study, we have investigated the participation of possible signaling molecules and transcription factors - PKC, NF-kappaB, C/EBP and IRF-1 - in the downregulation of NO production in LPS-activated T-PEM. It was found that PKC activity was greatly reduced in T-PEM as compared to normal macrophages, and did not respond to activation. Interestingly, the different PKC isozyme levels were not significantly altered in T-PEM, with the exception of PKC delta. Alterations in the binding activity of the transcription factors NF-kappaB and C/EBP appeared to be involved in the reduced transcription of iNOS previously observed in T-PEM after LPS activation. These results provide evidence that reductions in iNOS transcription secondary to alterations in cell signaling may be responsible for the diminished capacity of macrophages of LPS-activated tumor-bearers to produce NO and lyse tumor targets.
Di Napoli
Michael R
MR
Department of Microbiology and Immunology, University of Miami School of Medicine and the Sylvester Comprehensive Cancer Center, Miami, FL 33136, USA.
Torroella-Kouri
Marta
M
Perry
Giselle
G
Lopez
Diana M
DM
D000818:Animals; D022762:CCAAT-Enhancer-Binding Proteins / Q000378:metabolism; D024202:Electrophoretic Mobility Shift Assay; D007371:Interferon-gamma / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000494:pharmacology; D008264:Macrophages / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D016328:NF-kappa B / Q000378:metabolism; D009368:Neoplasm Transplantation; D009369:Neoplasms / Q000378:metabolism* / Q000473:pathology; D009569:Nitric Oxide / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000235:genetics; D052247:Nitric Oxide Synthase Type II; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D011493:Protein Kinase C / Q000378:metabolism*; D051745:Protein Kinase C-delta; D020218:Response Elements / Q000235:genetics; D014157:Transcription Factors / Q000378:metabolism*
D022762:CCAAT-Enhancer-Binding Proteins; D008070:Lipopolysaccharides; D016328:NF-kappa B; D014157:Transcription Factors; D009569:Nitric Oxide; D007371:Interferon-gamma; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse; C497259:Prkcd protein, mouse; D011493:Protein Kinase C; D051745:Protein Kinase C-delta