CONICET | Buscador de Institutos y Recursos Humanos

Toll-like receptors (TLRs) are expressed not only in immune cells but also in cancer cells, where they play a highly controversial role. TLRs recognize not only microbial components, but also endogenous molecules released by stressed cells. All TLRs, except TLR3, use the adaptor molecule MyD88 to initiate the signaling cascade. In this work, we set up an experimental strategy to investigate the role of MyD88 signaling pathway in the proliferation of tumor cells in vivo, where only endogenous ligands present in the tumor microenvironment could activate it. To this end, we generated a stably transfected murine melanoma cells (B16) expressing a plasmid that express the protein Cherry (B16 Cherry). Then, we induced chimeric tumors, inoculating syngeneic animals with an equal number of B16 Cherry and B16 cells in which the expression of MyD88 was silenced (B16shMyD88) and that also expressed GFP. As control, tumors composed by B16 Cherry and B16 cells expressing GFP and shRNA for Luciferase (B16shLuc) were analysed. In this way, it was possible to compare growth of both cell lines, in a situation in which both cell types are exposed in vivo to the same conditions. The proliferation of each cell line was first tested in vitro by the MTT assay and no significant differences were found. In contrast, when each cell line was injected in vivo separately, an increased tumor growth was observed in tumors induced with B16shMyD88 cells, in either C57BL/6 or nude mice. Also, chimeric tumors composed by B16Cherry-B16shMyD88 cells showed an increased tumor growth compared to tumors composed by B16Cherry-B16shLuc. When immunofluorescent cells in tumor tissues were quantified, a higher number of B16shMyD88 cells were found. These results could support that in vivo, the activation of MyD88 pathway promotes a decrease in tumor cell proliferation. Our hypothesis suggests that an endogenous ligand may activate MyD88-dependent pathway and thus produce the observed changes.