The role and regulation of nitric oxide in macrophage-mediated tumoricidal activity in a murine mammary adenocarcinoma system

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)


Microbiology and Immunology

First Committee Member

Diana M. Lopez - Committee Chair


Nitric oxide (NO) is a major tumoricidal effector molecule produced by activated macrophages. Upon stimulation with (lipopolysaccharide) LPS, peritoneal-elicited macrophages (PEM) from mammary tumor-bearing mice (T-PEM) displayed a diminished ability to lyse tumor cells due to reduced NO production. In contrast, when stimulated with LPS and (interferon-gamma) IFN-$\gamma$, T-PEM performed these functions at normal levels. Further studies revealed that the deficiencies in NO production and cytolytic activity became more pronounced with tumor progression and were most profound in tumor-associated macrophages (TAM), which were unable to recover these functions even with IFN-$\gamma.$ However, TAM did maintain the ability to produce TNF-$\alpha$ and IL-6. The alterations in cytolytic activity and NO production by tumor-bearers' macrophages were due to reduced transcription of the inducible nitric oxide synthase (iNOS) gene. Additionally, TAM displayed minimal induction of the IFN-$\gamma$-inducible gene mGBP-1 and failed to transcribe the developmentally regulated gene lysozyme, suggesting that the maturational state of these cells participates in their unresponsiveness. Further, tumor-derived phosphatidyl serine was implicated in the majority of the changes noted in tumor-bearers' macrophages, and may have exerted its effect through dysregulations of signal transduction. Alterations in the activity of PKC and in the binding of NF-$\kappa$B to the NF-$\kappa$Bd site of the iNOS promoter appeared to be involved in the reduced transcription of iNOS in T-PEM. The addition of IFN-$\gamma$ led to increased rates of iNOS transcription, but did not significantly increase PKC activity or NF-$\kappa$B binding. Rather, IFN-$\gamma$ was able to bypass these defects through an independent signaling pathway that enhanced iNOS induction through the binding of IFN-$\gamma$-inducible nuclear factors to interferon-responsive elements within the iNOS promoter. The results described demonstrate maturational and spacial differences in the functional suppression of macrophages from tumor-bearing mice and, further, implicate tumor-derived phosphatidyl serine in these impairments. Moreover, these data provide evidence that reductions in iNOS transcription secondary to alterations in cell signaling are responsible for the diminished capacity of tumor-bearers' macrophages to produce NO and lyse tumor targets.


Biology, Molecular; Health Sciences, Immunology; Health Sciences, Oncology

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