TLR4 interaction with LPS in glioma CD133+ cancer stem cells induces cell proliferation, resistance to chemotherapy and evasion from cytotoxic T lymphocyte-induced cytolysis

Abstract

Despite advances in treatment modalities, 5-year survival among glioma patients remains poor. Glioma cancer stem cells (CSCs) exhibit high tumorigenic activity and are associated with resistance to treatment and tumor recurrence. Because overexpression of toll-like receptor 4 (TLR4) correlated with cancer development, we investigated LPS-induced TLR4 signaling in glioma CD133-positive (CD133+) CSCs. The proliferation of CD133+ CSCs isolated from CSCs derived from the U251 and SF295 glioma cell lines and from human glioma samples was upregulated on a time- and concentration-dependent basis by LPS stimulation, with increases in CD133, NANOG, and NESTIN mRNA and protein levels. Also elevated was cytokine expression, which was coupled to phosphorylation of mitogen-activated protein kinase, and activation of cyclins and cyclin-dependent kinase complexes. TLR4 knockdown reduced LPS-induced CD133+ CSC proliferation, whereas Adriamycin-induced CD133+ CSC apoptosis was moderately inhibited by treatment with LPS, implying a protective effect of LPS. The capacity of glioma CD133+ CSC-reactive cytotoxic T lymphocyte to selectively kill CD133+ CSCs was reduced by LPS, and this effect was not apparent after TLR4 knockdown in CD133+ CSCs. These data suggest TLR4 signaling is a factor in CD133+ CSC immune evasion, and thus disruption of TLR4 signaling is a potential therapeutic strategy in glioma.

TLR4-Induced Inflammation Is a Key Promoter of Tumor Growth, Vascularization, and Metastasis

“…Among multiple LPS-induced cytokines in cancer cells are particularly important angiogenic factor VEGF-A [55,60,181], immunosuppressive TGF-beta [60,182], and a variety of chemokines recruiting BM-derived myeloid cells [34,178] that promote tumor progression through their own mechanisms. On a cellular level, TLR4 activation increases tumor cell proliferation [69,177,183], migration [64,175], invasion [159], and survival [58,176,184] that collectively results in resistance to therapy [58,61,69,136,183]. Some studies also reported increased stemness due to expansion of cancer stem cells [153,183].…”

“…On a cellular level, TLR4 activation increases tumor cell proliferation [69,177,183], migration [64,175], invasion [159], and survival [58,176,184] that collectively results in resistance to therapy [58,61,69,136,183]. Some studies also reported increased stemness due to expansion of cancer stem cells [153,183]. Additional effects include induction of epithelial-mesenchymal transition (EMT) [66,180] and evasion of immunosurveillance [183], both of which might reflect TLR4activated macrophage properties enabling tissue repair and resilience against pathogen-produced toxins.…”

Receptor do tipo Toll 4 dentre os TLRs de membrana plasmática possui um papel na malignidade de astrocitomas

“…The presence of TLR4 has been previously described in GBM, particularly in CD133 + tumor stem cells [38,39], and also in GBM cell lineages A172, U87MG [3,40,41], and U251 [42]. Such TLR4 positivity conferred a proliferative phenotype to these tumor cells [38,42]. Furthermore, the presence of TLR2 was also detected in murine GL261 glioma cell line, and the activation of this receptor leads to an invasive and migratory profile of the tumor cells [43].…”

“…Moreover, an associated expression of these receptors were observed in GBM cases, suggesting their role in tumor aggressiveness. The presence of TLR4 has been previously described in GBM, particularly in CD133 + tumor stem cells [38,39], and also in GBM cell lineages A172, U87MG [3,40,41], and U251 [42]. Such TLR4 positivity conferred a proliferative phenotype to these tumor cells [38,42].…”

“…In the beginning of the neoplastic transformation, microglia induce tumor cells apoptosis. Some tumor cells are capable to evade the immune system and alter microglia functions to support tumor growth (38).…”