Extended Data Figure 1: Summary of the experimental design and findings.

a, Schematic of the experimental approach to address four key questions concerning the chaperome in cancer: (1) what are the molecular characteristics and composition of the chaperome in cancer; (2) what molecular factors drive chaperome networks to crosstalk in tumours; (3) what distinguishes the chaperomes of tumours that are sensitive to pharmacologic inhibition from those that are not; and (4) what are the characteristics of tumours that may benefit from chaperome therapy? To retain the endogenous proteome/chaperome make-up and function, we applied a variety of chemical biology tools and biochemical methods that retain native protein conformations and complexes. This approach minimally interferes with the system it interrogates, thus providing answers closer to the reality of disease. When applicable, data were validated by alternative and complementary methods, as indicated. This approach led to the discovery of a novel mechanism of tumour regulation. Specifically, we have identified and characterized the epichaperome, a modified chaperome network. Our data demonstrate that heterogeneous and stable, multimeric chaperome complexes nucleating on HSP90 and HSP70, and incorporating co-chaperones, isomerases, scaffolding proteins, and transport proteins, bring about the effective physical and functional integration of the chaperome machinery into the epichaperome. Chaperome rewiring into the epichaperome is fuelled by powerful transcription activators such as MYC. Only under conditions in which the chaperome becomes tightly integrated both functionally and physically to form the epichaperome are tumours addicted to individual chaperome members. The epichaperome is the survival mechanism for type 1 tumours; when the epichaperome is dismantled by ablation of a component chaperome, the chaperome network collapses leading to cell death. In contrast, in type 2 tumours in which the integration of the chaperome is only partial and most chaperome members function as insular communities, depletion of chaperome members only ‘locally’ compromises the chaperome, maintaining overall cellular survival. b, c, Therapeutic and diagnostic implications of the findings. We propose the epichaperome as a biomarker to stratify patients for chaperome therapy, such as HSP90 inhibitors. This work also provides several ways to measure the epichaperome in clinic, that is, a non-invasive imaging assay (PU-PET) for solid tumours, a flow cytometry assay based on PU-FITC for liquid tumours and a native protein separation and analysis for minute biopsy specimens (isoelectric focusing; NanoPro technique) (b). We also propose that HSP90 is a cancer target when integrated into the epichaperome. Thus, HSP90 inhibitors that are specific for HSP90 when part of the epichaperome would be preferred for clinical use. Non-discriminate pharmacological agents that target chaperome members regardless of whether they are in the epichaperome or are part of dynamic complexes, such as in normal cells, could lead to toxicities and a low therapeutic index. For example, GI and ocular toxicities have been associated with some HSP90 inhibitors and not others due to chronic HSP90 inhibition in these normal tissues.