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Increased Intracellular, Cell Surface, and Secreted Inducible Heat Shock Protein 70 Responses Are Triggered during the Monocyte to Dendritic Cell (DC) Transition by Cytokines Independently of Heat Stress and Infection and May Positively Regulate DC Growth¹

Department of Biology, Farmingdale State College, State University of New York, Farmingdale, NY 11735

Physiologic triggers and functional consequences of endogenous heat shock protein (HSP) responses in dendritic cells (DC) are poorly defined. In this study, we show that even in the absence of heat stress and infection, a specific cohort of DC/proinflammatory cytokines (IL-4-IL-13/IL-6/GM-CSF) institutes an enhanced inducible (i)HSP70 intracellular and extracellular response in human monocyte-derived DC, especially during the monocyte to DC transition. Interestingly, whereas heat stress alone initiated an intracellular iHSP70 response in monocyte DC precursors, it did not promote cell surface or secreted iHSP70 responses, both of which were induced by cytokines independently of heat. The cytokine-induced iHSP70 response, which did not occur in lymphocytes, or monocytes-macrophages generated with M-CSF, was instituted within 48 h of cytokine exposure, and peaked upon commitment to DC growth at 72 h. Although a return to baseline levels was noted after this period, a distinct rise in iHSP70 occurred again during terminal DC maturation. Chemical inhibition of the iHSP70 response with either triptolide or KNK-437 was coupled with inhibition of DC differentiation and yielded cells displaying features of monocytes-macrophages. Exogenously supplied riHSP70 amplified events associated with cytokine-advanced DC differentiation/maturation, most notably the up-regulation of antiapoptotic proteins (Bcl-x_L). Engaging the HSP receptor CD40 with CD40L produced identical results as extracellular riHSP70, and, moreover, an enhanced iHSP70 response. Thus, distinct iHSP70 and HSP receptor-mediated responses are triggered by cytokines irrespective of heat stress and infection in monocyte-derived DC and may function to positively regulate monocyte-derived DC, especially during critical periods of their growth.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ This work was supported in part by grants from the National Arthritis Foundation, National Institutes of Health Grant R03AR05396601 (awarded to F.S.-S.), and resources from the Department of Veterans Affairs Medical Center (Northport, NY).

² Address correspondence and reprint requests to Dr. Frances Santiago-Schwarz, Department of Biology, Farmingdale State College, State University of New York, Farmingdale, NY 11735. E-mail address: santiaf{at}Farmingdale.edu

³ Abbreviations used in this paper: HSP, heat shock protein; DC, dendritic cell; IF, immunofluorescence; iHSP, inducible HSP; MFI, mean fluorescence intensity; MNC, mononuclear cell; NHS, normal human serum; RA, rheumatoid arthritis; HSF, heat shock factor.

⁴ The online version of this article contains supplemental material.