Análise dos mecanismos moleculares envolvidos nos efeitos antitumorais da lipoxina em macrófagos associados ao tumor

Abstract

Macrophage population is heterogeneous, being able to acquire pro-inflammatory (M1) or anti-inflammatory (M2) profiles. In tumor microenvironments, macrophages can acquire tumor-promoting characteristics. These tumor-associated macrophages (TAM) exhibit an M2-like profile. Our group demonstrated that lipoxin (LX), an important lipid mediator, has antitumor effects by inhibiting the M2 profile in TAM. These actions are selective and specific in the modulation of the M2 profile of TAMs, since lipoxin does not alter other M2 phenotypes, suggesting that LX modulates these effects by different signaling pathways not yet studied. Thus, the objective of this study was to investigate the cellular and molecular mechanisms involved in the differential polarization of Mphi, as well as the effects of LX in the modulation of these mechanisms. To obtain TAMs, Mphi derived from human monocytes were incubated for 72 hours with conditioned medium of MV3, a human melanoma cell lineage. By western blotting assay we investigated the signaling pathways involved in Mphi polarization. Firstly, we have seen that LX decreases activation ERK pathway activation in TAMs and M2 and have no effect in M1 mphi. Besides that, LX enhances AKT phosphorylation in TAMs. We next analyze the involvement of VEGF, a classic pro-angiogenic factor, on the polarization of TAMs triggered by LX. We observed that LX does not interfere in the release of VEGF in TAMs. Interestingly, our results shown that lipoxin effect on the induction of an M1-like profile in TAMs is dependent on the actions of VEGF. We also observed that LX decreases VEGFR-1 phosphorylation and increases SHP-1 expression in TAMs, one of the major phosphatases found in tumors, suggesting that the effect of LX on modulation of VEGF effects in TAMs may be through down-regulation of VEGFR phosphorylation by SHP-1. Our results suggest that lipoxin, selectively, modifies the polarization of TAMs by modulating important macrophage-activated signaling pathways in the tumor microenvironment.