SUMMARY Prognostically relevant RNA expression states exist in pancreatic ductal adenocarcinoma (PDAC), but our understanding of their drivers, stability, and relationship to therapeutic response is limited. To examine these attributes systematically, we profiled metastatic biopsies and matched organoid models at single-cell resolution. In vivo , we identify a new intermediate PDAC transcriptional cell state and uncover distinct site- and state-specific tumor microenvironments (TMEs). Benchmarking models against this reference map, we reveal strong culture-specific biases in cancer cell transcriptional state representation driven by altered TME signals. We restore expression state heterogeneity by adding back in vivo -relevant factors and show plasticity in culture models. Further, we prove that non-genetic modulation of cell state can strongly influence drug responses, uncovering state-specific vulnerabilities. This work provides a broadly applicable framework for aligning cell states across in vivo and ex vivo settings, identifying drivers of transcriptional plasticity and manipulating cell state to target associated vulnerabilities.

Huntington's Disease (HD) is a neurodegenerative disease caused by poly-glutamine expansion in the Htt protein, resulting in Htt misfolding and cell death. Expression of the cellular protein folding and pro-survival machinery by heat shock transcription factor 1 (HSF1) ameliorates biochemical and neurobiological defects caused by protein misfolding. We report that HSF1 is degraded in cells and mice expressing mutant Htt, in medium spiny neurons derived from human HD iPSCs and in brain samples from patients with HD. Mutant Htt increases CK2α′ kinase and Fbxw7 E3 ligase levels, phosphorylating HSF1 and promoting its proteasomal degradation. An HD mouse model heterozygous for CK2α′ shows increased HSF1 and chaperone levels, maintenance of striatal excitatory synapses, clearance of Htt aggregates and preserves body mass compared with HD mice homozygous for CK2α′. These results reveal a pathway that could be modulated to prevent neuronal dysfunction and muscle wasting caused by protein misfolding in HD.

Neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, amyotrophic lateral sclerosis and prion-based neurodegeneration are associated with the accumulation of misfolded proteins, resulting in neuronal dysfunction and cell death. However, current treatments for these diseases predominantly address disease symptoms, rather than the underlying protein misfolding and cell death, and are not able to halt or reverse the degenerative process. Studies in cell culture, fruitfly, worm and mouse models of protein misfolding-based neurodegenerative diseases indicate that enhancing the protein-folding capacity of cells, via elevated expression of chaperone proteins, has therapeutic potential. Here, we review advances in strategies to harness the power of the natural cellular protein-folding machinery through pharmacological activation of heat shock transcription factor 1 — the master activator of chaperone protein gene expression — to treat neurodegenerative diseases.

Summary Heat Shock Transcription Factor 1 (HSF1) is an evolutionarily conserved transcription factor that protects cells from protein misfolding-induced stress and apoptosis. The mechanisms by which cytosolic protein misfolding leads to HSF1 activation have not been elucidated. Here we demonstrate that HSF1 is directly regulated by TRiC/CCT, a central ATP-dependent chaperonin complex that folds cytosolic proteins. A small molecule activator of HSF1, HSF1A, protects cells from stress-induced apoptosis, binds TRiC subunits in vivo and in vitro and inhibits TRiC activity without perturbation of ATP hydrolysis. Genetic inactivation or depletion of the TRiC complex results in human HSF1 activation and HSF1A inhibits the direct interaction between purified TRiC and HSF1 in vitro. These results demonstrate a direct regulatory interaction between the cytosolic chaperone machine and a critical transcription factor that protects cells from proteo-toxicity, providing a mechanistic basis for signaling perturbations in protein folding to a stress-protective transcription factor.

Morphine and other opiates mediate their effects through activation of the -opioid receptor (MOR), and regulation of the MOR has been shown to critically affect receptor responsiveness. Activation of the MOR results in receptor phosphorylation, ␤-arrestin recruitment, and internalization. This classical regulatory process can differ, depending on the ligand occupying the receptor. There are two forms of ␤-arrestin, ␤-arrestin1 and ␤-arrestin2 (also known as arrestin2 and arrestin3, respectively); however, most studies have focused on the consequences of recruiting ␤-arrestin2 specifically. In this study, we examine the different contributions of ␤-arrestin1-and ␤-arrestin2-mediated regulation of the MOR by comparing MOR agonists in cells that lack expression of individual or both ␤-arrestins. Here we show that morphine only recruits ␤-arrestin2, whereas the MOR-selective enkephalin [D-Ala 2 ,N-MePhe 4 ,Gly 5 -ol]enkephalin (DAMGO), recruits either ␤-arrestin. We show that ␤-arrestins are required for receptor internalization and that only ␤-arrestin2 can rescue morphine-induced MOR internalization, whereas either ␤-arrestin can rescue DAMGO-induced MOR internalization. DAMGO activation of the receptor promotes MOR ubiquitination over time. Interestingly, ␤-arrestin1 proves to be critical for MOR ubiquitination as modification does not occur in the absence of ␤-arrestin1 nor when morphine occupies the receptor. Moreover, the selective interactions between the MOR and ␤-arrestin1 facilitate receptor dephosphorylation, which may play a role in the resensitization of the MOR and thereby contribute to overall development of opioid tolerance.Morphine and other opiates are among the most clinically useful analgesics, and their actions are mediated largely through activation of -opioid receptors (MORs).3 As a G protein-coupled receptor (GPCR), the MOR is subject to regulation paradigms that include phosphorylation by GPCR kinases (GRKs) and subsequent interactions with ␤-arrestins (␤-arrestin1, also known as arrestin2, and ␤-arrestin2, also known as arrestin3). ␤-Arrestins can then initiate receptor internalization, which in turn can promote both receptor down-regulation and resensitization (1-3). ␤-Arrestins can also facilitate these regulatory events by scaffolding ubiquitination machinery, such as E3 ligases, to GPCRs, as has been shown for the ␤ 2 adrenergic receptor (␤ 2 AR), V2 vasopressin receptor, and the chemokine receptor (CXCR4) (4 -6), however this has not been demonstrated for the MOR. MOR regulation has been shown to be contingent upon the particular agonist acting at the receptor as morphine promotes different regulatory events than other opioid ligands, including the D-enkephalin analog, [D-Ala 2 ,N-Me-Phe 4 ,Gly 5 -ol]enkephalin (DAMGO), fentanyl, methadone, and etorphine, although all of these ligands are full agonists at the MOR with respect to G protein coupling (7). The difference between agonists was first recognized when Arden et al. (8) observed that although DAMGO promotes robust internalizatio...