HSP90α induces immunosuppressive myeloid cells in melanoma via TLR4 signaling

Abstract

Background Tumor cells modulate host immunity by secreting extracellular vesicles (EV) and soluble factors. Their interactions with myeloid cells lead to the generation of myeloid-derived suppressor cells (MDSC), which inhibit the antitumor function of T and NK cells. We demonstrated previously that EV derived from mouse and human melanoma cells induced immunosuppressive activity via increased expression of programmed cell death ligand 1 (PD-L1) on myeloid cells that was dependent on the heat-shock protein 90α (HSP90α) in EV. Here, we investigated whether soluble HSP90α could convert monocytes into MDSC. Methods CD14 monocytes were isolated from the peripheral blood of healthy donors, incubated with human recombinant HSP90α (rHSP90α) alone or in the presence of inhibitors of TLR4 signaling and analyzed by flow cytometry. Inhibition of T cell proliferation assay was applied to assess the immunosuppressive function of rHSP90α-treated monocytes. HSP90α levels were measured by ELISA in plasma of patients with advanced melanoma and correlated with clinical outcome. Results We found that the incubation of monocytes with rHSP90α resulted in a strong upregulation of PD-L1 expression, whereas reactive oxygen species (ROS) and nitric oxide (NO) production as well as the expression of arginase-1, ectoenzymes CD39 and CD73 remained unchanged. The PD-L1 upregulation was blocked by anti-TLR4 antibodies and a nuclear factor-κB inhibitor. rHSP90α-treated monocytes displayed the downregulation of HLA-DR expression and acquired the resistance to apoptosis. Moreover, these monocytes were converted into MDSC as indicated by their capacity to inhibit T cell proliferation, which was mediated by TLR4 signaling as well as PD-L1 and indoleamine 2,3-dioxygenase (IDO) 1 expression. Higher levels of HSP90α in plasma of patients with melanoma correlated with augmented PD-L1 expression on circulating monocytic (M)-MDSC. Patients with melanoma with high levels of HSP90α displayed shorter progression-free survival (PFS) on the treatment with immune checkpoint inhibitors (ICIs). Conclusion Our findings demonstrated that soluble rHSP90α increased the resistance of normal human monocytes to apoptosis and converted them into immunosuppressive MDSC via TLR4 signaling that stimulated PD-L1 and IDO-1 expression. Furthermore, patients with melanoma with high concentrations of HSP90α displayed increased PD-L1 expression on M-MDSC and reduced PFS after ICI therapy, suggesting HSP90α as a promising therapeutic target for overcoming immunosuppression in melanoma.

Nano-based formulations of curcumin: elucidating the potential benefits and future prospects in skin cancer

“…Heat shock protein (Hsp90) is considered one of the important cell stress response mediators that are upregulated in melanoma cells. There is strong evidence indicating a synergistic action of curcumin that augmented the anti-carcinogenic effect of the drug bortezomib via suppression of Hsp90 [51].…”

Dialog beyond the Grave: Necrosis in the Tumor Microenvironment and Its Contribution to Tumor Growth

“…Iannucci et al also showed recently that TLR4 can mediate inflammation by extracellular IFI16, a novel DAMP and TLR4 ligand, which is released from chronically inflamed tissue [ 138 ]. Several recent studies demonstrated the role of TLR4 in the creation of an immunosuppressive environment: by stimulating immunosuppressive myeloid cells [ 139 ], by small extracellular vesicles released from malignant cells [ 140 ], and by HMGB1 stimulation of TLR4 resulting in the production of immunosuppressive protein galectin-9 [ 127 ].…”

“…HSPs are also the key target proteins in novel cancer therapies (recently reviewed in [ 169 ]) since they may promote chemoresistance [ 170 , 171 ]. Moreover, HSP90α converts monocytes to immunosuppressive myeloid cells in melanoma through TLR4 signaling [ 139 ]. A recent study demonstrated that plasma HSP90α level can be used as a prognostic biomarker for hepatocellular carcinoma [ 172 ].…”

“…Moreover, overexpression of S100A6, S100A10, S100A11, S100A14, and S100A16 may impair the infiltration and cytolytic activity of cytotoxic lymphocytes in pancreatic cancer [ 156 ]. HP70 and HSP90α both induce the immunosuppressive effect of MDSCs [ 139 , 206 ].…”

Roles of the HIF-1α pathway in the development and progression of keloids

“…Toll-like receptor 4 (TLR4), a transmembrane protein, is widely expresses expressed in inflammatory cells, fibroblasts, and keratinocytes [ 80 ]. It binds to endogenous ligands, such as fibronectin and heat shock proteins, and to exogenous one ones, such as lipopolysaccharide [ 81 ]. Also, TLR4 has been showed to modulate intracellular signaling transduction via the adaptor protein myeloid differentiation factor 88 (MyD88) [ 82 ].…”