Some of the anti-neoplastic effects of anthracyclines in mice originate from the induction of innate and T cell-mediated anticancer immune responses. Here we demonstrate that anthracyclines stimulate the rapid production of type I interferons (IFNs) by malignant cells after activation of the endosomal pattern recognition receptor Toll-like receptor 3 (TLR3). By binding to IFN-α and IFN-β receptors (IFNARs) on neoplastic cells, type I IFNs trigger autocrine and paracrine circuitries that result in the release of chemokine (C-X-C motif) ligand 10 (CXCL10). Tumors lacking Tlr3 or Ifnar failed to respond to chemotherapy unless type I IFN or Cxcl10, respectively, was artificially supplied. Moreover, a type I IFN-related signature predicted clinical responses to anthracycline-based chemotherapy in several independent cohorts of patients with breast carcinoma characterized by poor prognosis. Our data suggest that anthracycline-mediated immune responses mimic those induced by viral pathogens. We surmise that such 'viral mimicry' constitutes a hallmark of successful chemotherapy.

The small heat shock proteins (sHsps) from human (Hsp27) and mouse (Hsp25) form large oligomers which can act as molecular chaperones in vitro and protect cells from heat shock and oxidative stress when overexpressed. In addition, mammalian sHsps are rapidly phosphorylated by MAPKAP kinase 2/3 at two or three serine residues in response to various extracellular stresses. Here we analyze the effect of sHsp phosphorylation on its quaternary structure, chaperone function, and protection against oxidative stress. We show that in vitro phosphorylation of recombinant sHsp as well as molecular mimicry of Hsp27 phosphorylation lead to a significant decrease of the oligomeric size. We demonstrate that both phosphorylated sHsps and the triple mutant Hsp27-S15D,S78D,S82D show significantly decreased abilities to act as molecular chaperones suppressing thermal denaturation and facilitating refolding of citrate synthase in vitro. In parallel, Hsp27 and its mutants were analyzed for their ability to confer resistance against oxidative stress when overexpressed in L929 and 13.S.1.24 cells. While wild type Hsp27 confers resistance, the triple mutant S15D,S78D,S82D cannot protect against oxidative stress effectively. These data indicate that large oligomers of sHsps are necessary for chaperone action and resistance against oxidative stress whereas phosphorylation down-regulates these activities by dissociation of sHsp complexes to tetramers. Small heat shock proteins (sHsps)1 are constitutively expressed in virtually all organisms and exhibit a monomeric molecular mass of 15-42 kDa (for a recent review see Ref. 1). Within the cell they can form oligomeric complexes of up to 1 MDa (2). Overexpression of different mammalian sHsps increases cellular thermoresistance to a significant degree (3, 4). sHsps can, furthermore, function in different, seemingly unrelated processes like RNA stabilization (5), interaction with the cytoskeleton (6, 7), or apoptosis (8, 9). In vitro sHsps act as molecular chaperones preventing unfolded proteins from irreversible aggregation (10 -12) and, in cooperation with other factors, e.g. Hsp70 and ATP, facilitating productive refolding of unfolded proteins (13,14).In mammalian cells certain sHsps, e.g. mouse Hsp25 or human Hsp27, form a converging element of the cellular stress response since they show both a stress-induced increase in expression and phosphorylation. Under heat shock conditions increased phosphorylation can be detected after several minutes while changes in expression are detected after several hours (15). The rapid stress-induced phosphorylation is the result of stimulation of the p38 MAP kinase cascade and subsequent activation of MAPKAP kinases 2 and 3 which directly phosphorylate mammalian sHsps (16, 17) at several distinct sites (18,19). Since sHsp phosphorylation and stress-induced expression show different kinetics, it is assumed that phosphorylation of the pre-existing constitutively expressed sHsps is a first phase of the stress response while the elevated expression at a time w...

Expression of small stress proteins (shsp) enhances the survival of mammalian cells exposed to heat or oxidative injuries. Recently, we have shown that the expression of shsp from different species, such as human hsp27, Drosophila hsp27 or human alphaB‐crystallin protected murine L929 cells against cell death induced by tumor necrosis factor (TNFalpha), hydrogen peroxide or menadione. Here, we report that, in growing L929 cell lines, the presence of these shsp decreased the intracellular level of reactive oxygen species (ROS). shsp expression also abolished the burst of intracellular ROS induced by TNFalpha. Several downstream effects resulting from the TNFalpha‐mediated ROS increment, such as NF‐kappaB activation, lipid peroxidation and protein oxidation, were inhibited by shsp expression. We also report that the expression of these different shsp raised the total glutathione level in both L929 cell lines and transiently transfected NIH 3T3‐ras cells. This phenomenon was essential for the shsp‐mediated decrease in ROS and resistance against TNFalpha. Our results therefore suggest that the protective activity shared by human hsp27, Drosophila hsp27 and human alphaB‐crystallin against TNFalpha‐mediated cell death and probably other types of oxidative stress results from their conserved ability to raise the intracellular concentration of glutathione.