Extracellular HSP90α Induces MyD88-IRAK Complex-Associated IKKα/β-NF-κB/IRF3 and JAK2/TYK2 STAT-3 Signaling in Macrophages for Tumor-Promoting M2-Polarization

M2-polarization and the tumoricidal to tumor-promoting transition are commonly observed with tumor-infiltrating macrophages after interplay with cancer cells or/and other stroma cells. Our previous study indicated that macrophage M2-polarization can be induced by extracellular HSP90 alpha (eHSP90 alpha) secreted from endothelial-to-mesenchymal transition-derived cancer-associated fibroblasts. To extend the finding, we herein validated that eHSP90 alpha-induced M2-polarized macrophages exhibited a tumor-promoting activity and the promoted tumor tissues had significant increases in microvascular density but decreases in CD4(+) T-cell level. We further investigated the signaling pathways occurring in eHSP90 alpha-stimulated macrophages. When macrophages were exposed to eHSP90 alpha, CD91 and toll-like receptor 4 (TLR4) functioned as the receptor/co-receptor for eHSP90 alpha binding to recruit interleukin (IL)-1 receptor-associated kinases (IRAKs) and myeloid differentiation factor 88 (MyD88), and next elicited a canonical CD91/MyD88-IRAK1/4-I kappa B kinase alpha/beta (IKK alpha/beta)-nuclear factor- kappa B (NF-kappa B)/interferon regulatory factor 3 (IRF3) signaling pathway. Despite TLR4-MyD88 complex-associated activations of IKK alpha/beta, NF-kappa B and IRF3 being well-known as involved in macrophage M1-activation, our results demonstrated that the CD91-TLR4-MyD88 complex-associated IRAK1/4 IKK alpha/beta-NF-kappa B/IRF3 pathway was not only directly involved in M2-associated CD163, CD204, and IL-10 gene expressions but also required for downregulation of M1 inflammatory cytokines. Additionally, Janus kinase 2 (JAK2) and tyrosine kinase 2 (TYK2) were recruited onto MyD88 to induce the phosphorylation and activation of the transcription factor signal transducer and activator of transcription-3 (STAT-3). The JAK2/TYK2 STAT-3 signaling is known to associate with tumor promotion. In this study, the MyD88 JAK2/TYK2 STAT-3 pathway was demonstrated to contribute to eHSP90 alpha-induced macrophage M2-polarization by regulating the expressions of M1- and M2-related genes, proangiogenic protein vascular endothelial growth factor, and phagocytosis-interfering factor Sec22b.