Heat shock-induced dendritic cell maturation is coupled by transient aggregation of ubiquitinated proteins independently of heat shock factor 1 or inducible heat shock protein 70

The transition of dendritic cells (DCs) from immature to mature states is critical for the optimal priming of the adaptive immune response. This highly regulated process is accompanied by structural and functional alterations of DCs, including rapid and dramatic redistributions of MHC class I and class II molecules to cell surfaces, nuclear translocation of NF-kappaB,and transient appearance of dendritic cell aggresome-like induced structures (DALIS) in the cytosol. We have previously found that DCs can be matured by a non-inflammatory stress stimulation, i.e., heat shock. In this study, we examined if thermomanipulation could induce DALIS formation. We found that heat shock of DCs, but not of other cell types, led to the appearance of aggresome-like structures that were structurally indistinguishable from DALIS induced by lipopolysaccharide (LPS). Furthermore, the induction of DALIS in DCs by heat, but not by LPS, correlated with the increased ability of DCs to cross-present exogenous antigens to MHC I. Since the canonical biochemical response to heat shock is the induction of heat shock proteins (HSP) by heat shock factors (Hsf), we studied the contribution of both HSP and Hsf in heat shock-mediated DALIS formation using gene knockout mice. We demonstrated that neither inducible HSP70 nor the major mammalian heat shock transcription factor Hsf1 was involved in the formation of DALIS. Our results highlighted the important roles of heat shock in modulating the function of DCs, and they further suggested that heat-mediated immune regulation can be uncoupled from heat shock response.