Nitric-oxide production by murine mammary adenocarcinoma cells promotes tumor-cell invasiveness

Open Access
Publisher Website
Google Scholar
Abstract
The role of nitric oxide (NO) in tumor biology remains controversial and poorly understood. While a few reports indicate that the presence of NO in tumor cells or their micro‐environment is detrimental for tumor‐cell survival, and consequently their metastatic ability, a large body of data suggests that NO promotes tumor progression. The purpose of this study was to identify the source of NO in the spontaneously metastasizing C3‐L5 murine mammary‐adenocarcinoma model, the role of tumor‐derived NO in tumor‐cell invasiveness, and the mechanisms underlying the invasion‐stimulating effects of tumor‐derived NO. The source of NO was established by immunocytochemical localization of NO synthase (NOS) enzymes in C3‐L5 cells in vitro and transplanted tumors in vivo. An in vitro transwell Matrigel invasion assay was used to test the invasiveness of C3‐L5 cells in the presence or the absence of NO blocking agents or iNOS inducers (IFN‐γ and LPS). The mechanisms underlying the invasion‐stimulating effects of tumor‐derived NO were examined by measuring mRNA expression of matrix metalloproteinases (MMP)‐2 and ‐9, and tissue inhibitors of metalloproteinases (TIMP) 1, 2 and 3 in C3‐L5 cells in various experimental conditions. Results showed that C3‐L5 cells expressed high level of eNOS protein in vitro, and in vivo, both in primary and in metastatic tumors. C3‐L5 cells also expressed iNOS mRNA and protein when cultured in the presence of IFN‐γ and LPS. Constitutively produced NO promoted tumor‐cell invasiveness in vitro by down‐regulating TIMP 2 and TIMP 3. In addition, there was up‐regulation of MMP‐2, when extra NO was induced by IFN‐γ and LPS. In conclusion, NO produced by C3‐L5 cells promoted tumor‐cell invasiveness by altering the balance between MMP‐2 and its inhibitors TIMP‐2 and 3. Thus, our earlier observations of anti‐tumor and anti‐metastatic effects of NO inhibitors in vivo in this tumor model can be explained, at least in part, by reduced tumor‐cell invasiveness. Int. J. Cancer 81:889–896, 1999.
Keywords