Diminished PKC activity and decreased binding of transcription factors are involved in the impaired production of nitric oxide by macrophages from tumor-bearing mice
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- Published online on: March 1, 2005 https://doi.org/10.3892/ijmm.15.3.503
- Pages: 503-511
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Abstract
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-γ. 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-κB, 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 δ. Alterations in the binding activity of the transcription factors NF-κB 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.