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The integrated stress response (ISR) is an essential stress-support pathway increasingly recognized as a determinant of tumorigenesis. Here we demonstrate that ISR is pivotal in lung adenocarcinoma (LUAD) development, the most common histological type of lung cancer and a leading cause of cancer death worldwide. Increased phosphorylation of the translation initiation factor eIF2 (p-eIF2α), the focal point of ISR, is related to invasiveness, increased growth, and poor outcome in 928 LUAD patients. Dissection of ISR mechanisms in KRAS -driven lung tumorigenesis in mice demonstrated that p-eIF2α causes the translational repression of dual specificity phosphatase 6 (DUSP6), resulting in increased phosphorylation of the extracellular signal-regulated kinase (p-ERK). Treatments with ISR inhibitors, including a memory-enhancing drug with limited toxicity, provides a suitable therapeutic option for KRAS -driven lung cancer insofar as they substantially reduce tumor growth and prolong mouse survival. Our data provide a rationale for the implementation of ISR-based regimens in LUAD treatment. The Integrated Stress Response (ISR) is a cytoprotective pathway upregulated in many cancers. Here the authors show that the activation of PERK/p-eIF2α arm of ISR enhances ERK phosphorylation through translation repression of DUSP6, thus resulting in KRAS-driven lung tumorigenesis.

Translation of mRNA is controlled by a whole host of tightly regulated processes. In this Focus Review, Piccirillo et al . describe how translational skewing can serve a key role in the immune system. Selective translational control of gene expression is emerging as a principal mechanism for the regulation of protein abundance that determines a variety of functions in both the adaptive immune system and the innate immune system. The translation-initiation factor eIF4E acts as a node for such regulation, but non-eIF4E mechanisms are also prevalent. Studies of 'translatomes' (genome-wide pools of translated mRNA) have facilitated mechanistic discoveries by identifying key regulatory components, including transcription factors, that are under translational control. Here we review the current knowledge on mechanisms that regulate translation and thereby modulate immunological function. We further describe approaches for measuring and analyzing translatomes and how such powerful tools can facilitate future insights on the role of translational control in the immune system.

The clinical benefits of pan-mTOR active-site inhibitors are limited by toxicity and relief of feedback inhibition of receptor expression. To address these limitations, we designed a series of compounds that selectively inhibit mTORC1 and not mTORC2. These ‘bi-steric inhibitors’ comprise a rapamycin-like core moiety covalently linked to an mTOR active-site inhibitor. Structural modification of these components modulated their affinities for their binding sites on mTOR and the selectivity of the bi-steric compound. mTORC1-selective compounds potently inhibited 4EBP1 phosphorylation and caused regressions of breast cancer xenografts. Inhibition of 4EBP1 phosphorylation was sufficient to block cancer cell growth and was necessary for maximal antitumor activity. At mTORC1-selective doses, these compounds do not alter glucose tolerance, nor do they relieve AKT-dependent feedback inhibition of HER3. Thus, in preclinical models, selective inhibitors of mTORC1 potently inhibit tumor growth while causing less toxicity and receptor reactivation as compared to pan-mTOR inhibitors. Design of a bivalent inhibitor containing an ATP-competitive moiety and rapamycin-modified FRB binding ligand that selectively inhibits mTORC1 results in potent and durable inhibition of 4EBP1 phosphorylation and cell proliferation in vitro and in vivo.

Pathological remodeling of the extracellular matrix (ECM) by fibroblasts leads to organ failure. Development of idiopathic pulmonary fibrosis (IPF) is characterized by a progressive fibrotic scarring in the lung that ultimately leads to asphyxiation; however, the cascade of events that promote IPF are not well defined. Here, we examined how the interplay between the ECM and fibroblasts affects both the transcriptome and translatome by culturing primary fibroblasts generated from IPF patient lung tissue or nonfibrotic lung tissue on decellularized lung ECM from either IPF or control patients. Surprisingly, the origin of the ECM had a greater impact on gene expression than did cell origin, and differences in translational control were more prominent than alterations in transcriptional regulation. Strikingly, genes that were translationally activated by IPF-derived ECM were enriched for those encoding ECM proteins detected in IPF tissue. We determined that genes encoding IPF-associated ECM proteins are targets for miR-29, which was downregulated in fibroblasts grown on IPF-derived ECM, and baseline expression of ECM targets could be restored by overexpression of miR-29. Our data support a model in which fibroblasts are activated to pathologically remodel the ECM in IPF via a positive feedback loop between fibroblasts and aberrant ECM. Interrupting this loop may be a strategy for IPF treatment.

Vascular pericytes, an important cellular component in the tumor microenvironment, are often associated with tumor vasculatures, and their functions in cancer invasion and metastasis are poorly understood. Here we show that PDGF-BB induces pericyte–fibroblast transition (PFT), which significantly contributes to tumor invasion and metastasis. Gain- and loss-of-function experiments demonstrate that PDGF-BB-PDGFRβ signaling promotes PFT both in vitro and in in vivo tumors. Genome-wide expression analysis indicates that PDGF-BB–activated pericytes acquire mesenchymal progenitor features. Pharmacological inhibition and genetic deletion of PDGFRβ ablate the PDGF-BB–induced PFT. Genetic tracing of pericytes with two independent mouse strains, TN-AP-CreERT2:R26R-tdTomato and NG2-CreERT2:R26R-tdTomato, shows that PFT cells gain stromal fibroblast and myofibroblast markers in tumors. Importantly, coimplantation of PFT cells with less-invasive tumor cells in mice markedly promotes tumor dissemination and invasion, leading to an increased number of circulating tumor cells and metastasis. Our findings reveal a mechanism of vascular pericytes in PDGF-BB–promoted cancer invasion and metastasis by inducing PFT, and thus targeting PFT may offer a new treatment option of cancer metastasis.

Despite the success of therapies targeting oncogenes in cancer, clinical outcomes are limited by residual disease that ultimately results in relapse. This residual disease is often characterized by non-genetic adaptive resistance, that in melanoma is characterised by altered metabolism. Here, we examine how targeted therapy reprograms metabolism in BRAF-mutant melanoma cells using a genome-wide RNA interference (RNAi) screen and global gene expression profiling. Using this systematic approach we demonstrate post-transcriptional regulation of metabolism following BRAF inhibition, involving selective mRNA transport and translation. As proof of concept we demonstrate the RNA processing kinase U2AF homology motif kinase 1 (UHMK1) associates with mRNAs encoding metabolism proteins and selectively controls their transport and translation during adaptation to BRAF-targeted therapy. UHMK1 inactivation induces cell death by disrupting therapy induced metabolic reprogramming, and importantly, delays resistance to BRAF and MEK combination therapy in multiple in vivo models. We propose selective mRNA processing and translation by UHMK1 constitutes a mechanism of non-genetic resistance to targeted therapy in melanoma by controlling metabolic plasticity induced by therapy. Different adaptive mechanisms have been reported to reduce the efficacy of mutant BRAF inhibition in melanoma. Here, the authors show BRAF inhibition induces the translational regulation of metabolic genes leading to acquired therapy resistance.

G3BP-1 and -2 (hereafter referred to as G3BP) are multifunctional RNA-binding proteins involved in stress granule (SG) assembly. Viruses from diverse families target G3BP for recruitment to replication or transcription complexes in order to block SG assembly but also to acquire pro-viral effects via other unknown functions of G3BP. The Old World alphaviruses, including Semliki Forest virus (SFV) and chikungunya virus (CHIKV) recruit G3BP into viral replication complexes, via an interaction between FGDF motifs in the C-terminus of the viral non-structural protein 3 (nsP3) and the NTF2-like domain of G3BP. To study potential proviral roles of G3BP, we used human osteosarcoma (U2OS) cell lines lacking endogenous G3BP generated using CRISPR-Cas9 and reconstituted with a panel of G3BP1 mutants and truncation variants. While SFV replicated with varying efficiency in all cell lines, CHIKV could only replicate in cells expressing G3BP1 variants containing both the NTF2-like and the RGG domains. The ability of SFV to replicate in the absence of G3BP allowed us to study effects of different domains of the protein. We used immunoprecipitation to demonstrate that that both NTF2-like and RGG domains are necessary for the formation a complex between nsP3, G3BP1 and the 40S ribosomal subunit. Electron microscopy of SFV-infected cells revealed that formation of nsP3:G3BP1 complexes via the NTF2-like domain was necessary for clustering of cytopathic vacuoles (CPVs) and that the presence of the RGG domain was necessary for accumulation of electron dense material containing G3BP1 and nsP3 surrounding the CPV clusters. Clustered CPVs also exhibited localised high levels of translation of viral mRNAs as detected by ribopuromycylation staining. These data confirm that G3BP is a ribosomal binding protein and reveal that alphaviral nsP3 uses G3BP to concentrate viral replication complexes and to recruit the translation initiation machinery, promoting the efficient translation of viral mRNAs.

The mechanisms that govern organelle adaptation and remodelling remain poorly defined. The endo-lysosomal system degrades cargo from various routes, including endocytosis, phagocytosis, and autophagy. For phagocytes, endosomes and lysosomes (endo-lysosomes) are kingpin organelles because they are essential to kill pathogens and process and present antigens. During phagocyte activation, endo-lysosomes undergo a morphological transformation, going from a collection of dozens of globular structures to a tubular network in a process that requires the phosphatidylinositol-3-kinase-AKT-mechanistic target of rapamycin (mTOR) signalling pathway. Here, we show that the endo-lysosomal system undergoes an expansion in volume and holding capacity during phagocyte activation within 2 h of lipopolysaccharides (LPS) stimulation. Endo-lysosomal expansion was paralleled by an increase in lysosomal protein levels, but this was unexpectedly largely independent of the transcription factor EB (TFEB) and transcription factor E3 (TFE3), which are known to scale up lysosome biogenesis. Instead, we demonstrate a hitherto unappreciated mechanism of acute organelle expansion via mTOR Complex 1 (mTORC1)-dependent increase in translation, which appears to be mediated by both S6Ks and 4E-BPs. Moreover, we show that stimulation of RAW 264.7 macrophage cell line with LPS alters translation of a subset but not all of mRNAs encoding endo-lysosomal proteins, thereby suggesting that endo-lysosome expansion is accompanied by functional remodelling. Importantly, mTORC1-dependent increase in translation activity was necessary for efficient and rapid antigen presentation by dendritic cells. Collectively, we identified a previously unknown and functionally relevant mechanism for endo-lysosome expansion that relies on mTORC1-dependent translation to stimulate endo-lysosome biogenesis in response to an infection signal.

Translational regulation plays a critical role in the control of cell growth and proliferation. A key player in translational control is eIF4E, the mRNA 5' cap-binding protein. Aberrant expression of eIF4E promotes tumorigenesis and has been implicated in cancer development and progression. The activity of eIF4E is dysregulated in cancer. Regulation of eIF4E is partly achieved through phosphorylation. However, the physiological significance of eIF4E phosphorylation in mammals is not clear. Here, we show that knock-in mice expressing a nonphosphorylatable form of eIF4E are resistant to tumorigenesis in a prostate cancer model. By using a genome-wide analysis of translated mRNAs, we show that the phosphorylation of eIF4E is required for translational up-regulation of several proteins implicated in tumorigenesis. Accordingly, increased phospho-eIF4E levels correlate with disease progression in patients with prostate cancer. Our findings establish eIF4E phosphorylation as a critical event in tumorigenesis. These findings raise the possibility that chemical compounds that prevent the phosphorylation of eIF4E could act as anticancer drugs.

Pancreatic ductal adenocarcinoma (PDA) is a lethal malignancy with limited treatment options. Although metabolic reprogramming is a hallmark of many cancers, including PDA, previous attempts to target metabolic changes therapeutically have been stymied by drug toxicity and tumour cell plasticity. Here, we show that PDA cells engage an eIF4F-dependent translation program that supports redox and central carbon metabolism. Inhibition of the eIF4F subunit, eIF4A, using the synthetic rocaglate CR-1-31-B (CR-31) reduced the viability of PDA organoids relative to their normal counterparts. In vivo, CR-31 suppresses tumour growth and extends survival of genetically-engineered murine models of PDA. Surprisingly, inhibition of eIF4A also induces glutamine reductive carboxylation. As a consequence, combined targeting of eIF4A and glutaminase activity more effectively inhibits PDA cell growth both in vitro and in vivo. Overall, our work demonstrates the importance of eIF4A in translational control of pancreatic tumour metabolism and as a therapeutic target against PDA. Metabolic reprogramming is a hallmark of pancreatic ductal adenocarcinoma (PDA). Here, the authors show that in PDA cells redox and central carbon metabolism are driven by an eIF4F dependent translation program, and combined targeting of eIF4A and glutaminase can impact PDA proliferation.