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The stress response has been studied now for over 50 years and is known to have significance in the survival of organisms in a challenging environment and in the healthy development of all known descendants of the last common universal ancestor (LUCA). This meeting was concentrated mostly on the responses of cells and organisms to environmental and cell stress including the impact of thermal stress, which was a major theme throughout this meeting. One emphasis was on the deployment of the heat shock response that permits damage to proteins to be detected and responded to by the abundant synthesis of heat shock proteins (HSPs). Speakers and presenters of posters responded to the questions of how are the HSPs rapidly induced by stressors? By which mechanisms are they are regulated in the cell by protein-protein interactions or posttranslational modification? And, what are the consequences when these abundantly expressed proteins escape the confines of the cell and influence the extracellular microenvironment? Key among the questions was how does stress influence longevity and aging and what happens in terms of disease control (malignant, neurodegenerative) when stress responses become compromised? In this context, many presenters addressed the question of pharmacologically modifying the heat shock response and HSP functions and thus improving responses to a range of disease types. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s12192-018-00966-w) contains supplementary material, which is available to authorized users.

Elevated temperatures produce a wide range of effects in tumor bearing hosts and have been used in cancer therapy. At lower temperatures, in the fever range (FRH) direct tumor cell killing is minimal and cell inactivation is due to profound immune stimulation of a wide range of immune cells under FRH conditions. As temperatures increase above 41 °C, direct cell killing is observed and follows a time and temperature dependent course. Cell death in the “hyperthermia range” (42–47 °C) appears to be due to protein denaturation and is strongly enhanced by properties of the tumor microenvironment such as low glucose and reduced extracellular pH. All cells however possess a powerful resistance mechanism triggered by hyperthermia (thermotolerance), which is mediated by the induction of heat shock proteins (HSPs). HSPs possess molecular chaperone functions, can rapidly repair thermal damage to proteins and lead to thermotolerance. Above 50 °C a different mode of tumor eradication is seen, characterized by cell necrosis and tissue coagulation. The role of the tumor microenvironment in cell killing at these “ablation range” temperatures is not clear. Immune effects of hyperthermia may depend on the mode of cell death that is produced. In broad terms, apoptotic cell death is tolerogenic and absorption of apoptotic cell bodies by immune cells inhibits immunity. Hyperthermia range heating may lead to profound levels of apoptosis and its role in immunity is somewhat ambiguous. However, in the ablation range, cancer cell necrosis dominates and tumor specific immunity is observed, an effect that may play an important role in the outcome of treatment.

Extracellular molecular chaperones bind to a number of receptors including pattern recognition receptors, c-type lectins and scavenger receptor families. We have discussed the properties of two such receptors, the class F scavenger receptor SRECI and class H scavenger receptor stabilin-1. These receptors have, in common, the possession of extracellular domains containing multiple repeats of the EGF-like motif and the ability to bind HSPs. However, their regulatory properties are quite distinct. SRECI is an important receptor in the function of HSP vaccines and is able to mediate binding and endocytosis of HSP-peptide antigen complexes and to facilitate antigen cross presentation to T lymphocytes. Uptake of SRECI involves recruitment of the receptor to lipid raft domains and endocytosis, via the newly characterized GEEC compartment, prior to entry into early endosomes. Stabilin-1, by contrast, is localized largely to intracellular endosomes and the trans Golgi network (TGN). Although Stabilin-1 mediates internalization of HSPs, it does not appear to play an important role in antigen cross presentation and appears to be involved in other processes in response to extracellular molecular chaperones. Stabilin-1 is an unusual receptor in that it can mediate at least three processes in macrophages, including: (1) receptor-mediated endocytosis; (2) trafficking between the TGN and endosomal compartments and; (3) secretion through the lysosomal pathway. Possession of a range of HSP receptors may provide modulated responses to the molecular chaperones and is likely to impact on use of HSP based immunotherapy.

Heat shock proteins (HSP) have an essential role in the cytoplasm of all cells in mediating protein quality control. However, in addition to these molecular chaperone properties, HSP play additional extracellular roles as mediators of inflammation and immunity. Because of their lack of a signal sequence and exclusion from the classical secretion pathways, it was initially assumed that extracellular HSPs resulted from cell necrosis and release of cell contents. However, non-canonical protein secretion pathways have been described, and have been studied intensively for the cytokine interleukin-1b (IL-1b). At least four mechanisms have been described, including: (1) IL-1b entry into secretary lysosomes and secretion into the medium along with lysosomal enzymes; (2) shedding of microvesicles from the membrane that contain IL-1b; (3) release of IL-1b directly through the membrane bound to a conjectured secreted-protein-transporter and; (4) formation of multivesicular bodies containing IL-1b and MHC class II within recycling endosomes and release of IL-1b entrapped in exosomes enclosed within the vesicles. Each of these mechanisms may be operative in HSP secretion and there is particularly strong evidence for mechanisms (1) and (4), in which either free Hsp70 is released through the endolysosome pathway or HSPs are secreted in association with exosomes. HSPs released through these mechanisms have intercellular signalling properties and can regulate phagocytosis, T and NK cell activation and release of cytokines in the acute inflammatory response. We discuss triggering mechanisms for HSP release, the pathways involved in HSP traverse of lipid membranes and the physiological consequences of HSP secretion.

In recent years, it has been hypothesised that a new signalling system may exist in vertebrates in which secreted molecular chaperones form a dynamic continuum between the cellular stress response and corresponding homeostatic physiological mechanisms. This hypothesis seems to be supported by the finding that many molecular chaperones are released from cells and act as extracellular signals for a range of cells. However, this nascent field of biological research seems to suffer from an excessive criticism that the biological activities of molecular chaperones are due to undefined components of the microbial expression hosts used to generate recombinant versions of these proteins. In this article, a number of the proponents of the cell signalling actions of molecular chaperones take this criticism head-on. They show that sufficient evidence exists to support fully the hypothesis that molecular chaperones have cell-cell signalling actions that are likely to be part of the homeostatic mechanism of the vertebrate.

Recent studies of heat shock protein-mediated modulation of the inflammatory and immune responses suggest its involvement in host responses to infection. In addition, during infection, the mammalian host is faced with the interaction of the heat shock responses of two competing organisms. Indeed, both mammalian and pathogenic heat shock proteins bind to host cells where they can signal danger, mediate inflammation and influence immune cell function. These overlapping repertoires of stress proteins may thus participate in determining the outcome of pathogenic infections by their abilities to take part in, work to prevent, or resolve infection. In this account, we have examined the role of heat shock proteins largely from the point of view of the mammalian host during the infection by non-viral microorganisms. When assessing the role of heat shock proteins in infection, a number of issues must be unraveled. The first is the relative roles of intracellular and extracellular mammalian heat shock proteins in pro- or anti-inflammatory processes. It is thus apparent that the intracellular heat shock proteins, heat shock transcription factor1 (HSF1) and the heat shock response (HSR) influence the infection of mammals by pathogenic organisms. The HSR and intracellular heat shock proteins protect against severe sepsis and fever as demonstrated in experiments using Hsp70 and HSF1 knockout mice. However, in addition, heat shock protein in the extracellular spaces may be involved in earlier phases of infection, in processes such as in complement activation, microorganism engulfment by phagocytes, cytokine secretion and immune responses to pathogens.

The hsp70 gene family encode molecular chaperones intrinsic to cellular life and essential for cell survival (Georgopolis and Welch, 1993; Lindquist and Craig, 1988). The essential intracellular functions of the hsp70 genes are in protein folding and protection from cell death pathways. Each Hsp70 family member contains two major functional domains, a C-terminal peptide binding domain and an Nterminal ATPase domain that controls the opening and closing of the peptide binding domain (see review (Bukau and Horwich, 1998; Bukau et al., 2006)). These two domains mediate the immune properties of Hsp70, permitting the acquisition of cellular antigens and their delivery to immune effector cells (Calderwood et al., 2005b; Noessner et al., 2002; Srivastava and Amato, 2001). There are at least 12 members of the human hsp70 gene family members, including proteins expressed in cytoplasm, endoplasmic reticulum and mitochondria (Bukau and Horwich, 1998; Lindquist and Craig, 1988; Tang et al., 2005). In addition, cells possess both constitutive cytoplasmic Hsp70 members (such as human HSC73) and members induced by stress (HSP72) (Schlessinger, 1994; Tang et al., 2005). Hsp70 becomes dysregulated in cancer and the elevated Hsp70 levels that ensue protect emerging cancer cells from the triggering of programmed cell death that accompanies many of the steps in transformation, while also creating an opportunity for immune attack (Calderwood et al., 2007; Calderwood et al., 2006; Ciocca and Calderwood, 2005; Clark and Menoret, 2001; Cornford et al., 2000; Nylandsted et al., 2000; Tang et al., 2005) (Also see Ciocca et al, Chapter 2, this volume). Many studies now suggest that Hsp70, through its ability to bind peptide antigens is a major factor linking the tumor phenotype, with its accompanying expression of mutated and overexpressed

The heat shock response (HSR) and the acute inflammatory response (APR) are both key homeostatic mechanisms for resisting extracellular insult. There is evolving understanding regarding the relationship between these two responses. Activation of the HSR exerts some pro-inflammatory effects when HSP are released during cell insult and such extracellular HSP induce cytokine release in inflammatory and immune modulating cells. However, the intracellular mediators of the HSR including the transcription factor heat shock factor 1 (HSF1) and the HSP have profoundly anti-inflammatory effects. HSF1 can be induced by the elevated temperatures encountered in inflamed tissues and in fever as well as by anti-inflammatory prostaglandins. Such activated HSF1 represses cytokine release both directly by inhibiting nuclear factor of interleukin 6 (NF-IL6) and indirectly when elevated HSP inhibit the potent inflammatory factor NF-kB. Reciprocal effects are observed on activation of the APR which leads to inhibition of HSF1 through stimulation of inactivating phosphorylation events involving the mitogen activated kinase (MAPK) pathways. Activation of the HSR thus constitutes a feedback regulatory mechanism for the APR and limits the lethal over stimulation of cytokine release which may occur during infection. However, in order for rapid activation of the APR, mechanisms also exist for HSF1 repression, permitting controlled activation of the response during infection

Heat shock proteins (Hsp) participate in many events related to cancer as molecular chaperones, starting from the very beginning of carcinogenesis. Several etiological factors involve the Hsp family in their mechanisms of action, including oncogenic viruses, hereditary and non hereditary alterations in tumor suppressors or oncoproteins, hypermethylation, radiation and carcinogenic agents. All of them produce changes in the Hsp response with consequences in cell proliferation, differentiation, inflammation, apoptosis, DNA repair, angiogenesis, metastasis, and drug resistance and in the immunological response mounted by the host. In this chapter we will examine the participation of the Hsp response in tumor cell transformation, either by up-regulation or down-regulation of specific Hsp. This can explain the variations in Hsp expression found in pre-neoplastic and neoplastic human tumors in different tissues and organs. These variations have important clinical consequences in cancer progression, and the exploitation of such knowledge may improve anticancer treatment strategies