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Molecular mechanisms regulating TNF-alpha production by tumor-associated macrophages
S T Dougherty1, C J Eaves, W H McBride
1Terry Fox Laboratory, BC Cancer Agency, Vancouver, British Columbia, Canada.
Abstract:
The molecular mechanisms that regulate the production and/or functional activity of intratumoral tumor necrosis factor-alpha (TNF-alpha) remain poorly defined. To begin to address this issue we have examined the level of TNF-alpha mRNA and protein produced by macrophages present within immunogenic Fsa-R and non-immunogenic Fsa-N tumors grown in syngeneic Lps(d) C3H/HeJ and Lps(n) C3H/HeN mice. The results obtained indicate that macrophages isolated from tumors grown in Lps(d) C3H/HeJ mice express 5-10-fold less TNF-alpha than equivalent cells present in tumors grown in Lps(n) C3H/HeN mice. These data suggest that the mechanisms that operate within the tumor microenvironment to induce the production of TNF-alpha act, at least in part, via the same signal transduction pathway that is defective in Lps(d) C3H/HeJ mice. Interestingly, despite such differences in TNF-alpha production, tumors inoculated into C3H/HeJ and C3H/HeN mice grew at a similar rate and contained an almost identical proportion of macrophages. Moreover, tumor cells purified from tumors grown in C3H/HeJ and C3H/HeN mice produced similar quantities of the TNF-alpha-inducible cytokine GM-CSF. Thus, although differences in the level of TNF-alpha produced within tumors grown in C3H/HeN and C3H/HeJ mice are readily demonstrable, such differences appear to have little direct impact on the outcome of tumor growth.
Insights
Tumor microenvironment macrophages produce less tumor necrosis factor-alpha (TNF-alpha) in C3H/HeJ mice due to a defective signaling pathway. This reduced TNF-alpha did not impact tumor growth rate or GM-CSF production.
Area of Science:
- Immunology
- Cancer Biology
- Molecular Mechanisms
Background:
- Intratumoral tumor necrosis factor-alpha (TNF-alpha) production and activity are poorly understood.
- Macrophages are key immune cells within the tumor microenvironment.
- Genetic variations in mice (Lps(d) C3H/HeJ vs. Lps(n) C3H/HeN) influence immune responses.
Purpose of the Study:
- To investigate the regulation of intratumoral TNF-alpha production.
- To compare TNF-alpha levels in macrophages from different tumor models and mouse strains.
- To determine the impact of TNF-alpha differences on tumor growth and cytokine production.
Main Methods:
- Isolation and analysis of macrophages from immunogenic (Fsa-R) and non-immunogenic (Fsa-N) tumors grown in C3H/HeJ and C3H/HeN mice.
- Quantification of TNF-alpha mRNA and protein levels.
- Assessment of tumor growth rates and macrophage infiltration.
- Measurement of granulocyte-macrophage colony-stimulating factor (GM-CSF) production by tumor cells.
Main Results:
- Macrophages from tumors in Lps(d) C3H/HeJ mice produced 5-10 fold less TNF-alpha compared to those in Lps(n) C3H/HeN mice.
- The reduced TNF-alpha production in C3H/HeJ mice is likely due to a defect in the same signal transduction pathway affected by LPS.
- Despite TNF-alpha level differences, tumor growth rates, macrophage proportions, and GM-CSF production were similar across both mouse strains.
Conclusions:
- The tumor microenvironment utilizes specific signaling pathways to induce TNF-alpha production, partially via pathways defective in Lps(d) C3H/HeJ mice.
- Differences in intratumoral TNF-alpha levels between C3H/HeN and C3H/HeJ mice do not significantly affect tumor growth outcomes.
- Further research is needed to elucidate the precise role of TNF-alpha in modulating tumor progression.