Radiotherapy is under investigation for its ability to enhance responses to immunotherapy. However, the mechanisms by which radiation induces anti-tumour T cells remain unclear. We show that the DNA ...exonuclease Trex1 is induced by radiation doses above 12-18 Gy in different cancer cells, and attenuates their immunogenicity by degrading DNA that accumulates in the cytosol upon radiation. Cytosolic DNA stimulates secretion of interferon-β by cancer cells following activation of the DNA sensor cGAS and its downstream effector STING. Repeated irradiation at doses that do not induce Trex1 amplifies interferon-β production, resulting in recruitment and activation of Batf3-dependent dendritic cells. This effect is essential for priming of CD8
T cells that mediate systemic tumour rejection (abscopal effect) in the context of immune checkpoint blockade. Thus, Trex1 is an upstream regulator of radiation-driven anti-tumour immunity. Trex1 induction may guide the selection of radiation dose and fractionation in patients treated with immunotherapy.
Translation initiation of most mammalian mRNAs is mediated by a 5' cap structure that binds eukaryotic initiation factor 4E (eIF4E). However, inactivation of eIF4E does not impair translation of many ...capped mRNAs, suggesting an unknown alternate mechanism may exist for cap-dependent but eIF4E-independent translation. We show that DAP5, an eIF4GI homolog that lacks eIF4E binding, utilizes eIF3d to facilitate cap-dependent translation of approximately 20% of mRNAs. Genome-wide transcriptomic and translatomic analyses indicate that DAP5 is required for translation of many transcription factors and receptor capped mRNAs and their mRNA targets involved in cell survival, motility, DNA repair and translation initiation, among other mRNAs. Mass spectrometry and crosslinking studies demonstrate that eIF3d is a direct binding partner of DAP5. In vitro translation and ribosome complex studies demonstrate that DAP5 and eIF3d are both essential for eIF4E-independent capped-mRNA translation. These studies disclose a widespread and previously unknown mechanism for cap-dependent mRNA translation by DAP5-eIF3d complexes.
Cancer cell plasticity enables cell survival in harsh physiological environments and fate transitions such as the epithelial-to-mesenchymal transition (EMT) that underlies invasion and metastasis. ...Using genome-wide transcriptomic and translatomic studies, an alternate mechanism of cap-dependent mRNA translation by the DAP5/eIF3d complex is shown to be essential for metastasis, EMT, and tumor directed angiogenesis. DAP5/eIF3d carries out selective translation of mRNAs encoding EMT transcription factors and regulators, cell migration integrins, metalloproteinases, and cell survival and angiogenesis factors. DAP5 is overexpressed in metastatic human breast cancers associated with poor metastasis-free survival. In human and murine breast cancer animal models, DAP5 is not required for primary tumor growth but is essential for EMT, cell migration, invasion, metastasis, angiogenesis, and resistance to anoikis. Thus, cancer cell mRNA translation involves two cap-dependent mRNA translation mechanisms, eIF4E/mTORC1 and DAP5/eIF3d. These findings highlight a surprising level of plasticity in mRNA translation during cancer progression and metastasis.
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•Two cap-dependent mRNA translation mechanisms promote tumor progression•eIF4E/mTORC1 is required for cancer cell proliferation and survival•DAP5/eIF3d is required for the cancer cell EMT, cell migration, and metastasis•Inhibition of DAP5 strongly reduces metastasis and survival of metastases
Alard et al. show that cancer cell mRNA translation involves two distinct cap-dependent mRNA translation mechanisms, one directed by canonical eIF4E/mTORC1 and the other by specialized DAP5/eIF3d. A surprising level of plasticity exists in mRNA translation during cancer progression and metastasis.
Cancer‐associated fibroblasts (CAFs) are considered the most abundant type of stromal cells in pancreatic ductal adenocarcinoma (PDAC), playing a critical role in tumour progression and ...chemoresistance; however, a druggable target on CAFs has not yet been identified. Here we report that focal adhesion kinase (FAK) activity (evaluated based on 397 tyrosine phosphorylation level) in CAFs is highly increased compared to its activity in fibroblasts from healthy pancreas. Fibroblastic FAK activity is an independent prognostic marker for disease‐free and overall survival of PDAC patients (cohort of 120 PDAC samples). Genetic inactivation of FAK within fibroblasts (FAK kinase‐dead, KD) reduces fibrosis and immunosuppressive cell number within primary tumours and dramatically decreases tumour spread. FAK pharmacologic or genetic inactivation reduces fibroblast migration/invasion, decreases extracellular matrix (ECM) expression and deposition by CAFs, modifies ECM track generation and negatively impacts M2 macrophage polarization and migration. Thus, FAK activity within CAFs appears as an independent PDAC prognostic marker and a druggable driver of tumour cell invasion.
Synopsis
Understanding how cancer‐associated fibroblasts (CAFs) promote PDAC progression is of major interest given the poor prognosis of patients. This study identifies a druggable key regulator of CAF‐induced tumour cell metastasis and a prognostic factor: the protein Focal Adhesion Kinase (FAK).
FAK activity within CAFs was an independent prognostic marker for Disease Free Survival (DFS) and Overall Survival (OS) in a cohort of 120 PDAC patients.
Activation of FAK within CAFs did not necessarily impact tumour growth, but favored tumour spread in vivo.
Fibroblastic FAK activity promoted extracellular matrix (ECM) track formation used by tumor cells to invade, and MCP‐1 secretion leading to M2 macrophage recruitment to primary tumor site.
Specific FAK inactivation within CAFs “normalized” the tumor stroma (decreased fibrosis and pro‐tumor immunity) and drastically decreased spontaneous metastasis.
PDAC patients may benefit from treatment with FAK kinase inhibitor (already clinically available) through the inhibition of the deleterious pro‐metastatic action of CAFs.
Understanding how cancer‐associated fibroblasts (CAFs) promote PDAC progression is of major interest given the poor prognosis of patients. This study identifies a druggable key regulator of CAF‐induced tumour cell metastasis and a prognostic factor: the protein Focal Adhesion Kinase (FAK).
The 4G family of eukaryotic mRNA translation initiation factors is composed of three members (eIF4GI, eIF4GII, and DAP5). Their specific roles in translation initiation are under intense ...investigations, but how their respective intracellular amounts are controlled remains poorly understood. Here we show that eIF4GI and eIF4GII exhibit much shorter half-lives than that of DAP5. Both eIF4GI and eIF4GII proteins, but not DAP5, contain computer-predicted PEST motifs in their N-termini conserved across the animal kingdom. They are both sensitive to degradation by the proteasome. Under normal conditions, eIF4GI and eIF4GII are protected from proteasomal destruction through binding to the detoxifying enzyme NQO1 NAD(P)H:quinone oxidoreductase. However, when cells are exposed to oxidative stress both eIF4GI and eIF4GII, but not DAP5, are degraded by the proteasome in an N-terminal-dependent manner, and cell viability is more compromised upon silencing of DAP5. These findings indicate that the three eIF4G proteins are differentially regulated by the proteasome and that persistent DAP5 plays a role in cell survival upon oxidative stress.
The majority of breast cancers expresses the estrogen receptor (ER
) and is treated with anti-estrogen therapies, particularly tamoxifen in premenopausal women. However, tamoxifen resistance is ...responsible for a large proportion of breast cancer deaths. Using small molecule inhibitors, phospho-mimetic proteins, tamoxifen-sensitive and tamoxifen-resistant breast cancer cells, a tamoxifen-resistant patient-derived xenograft model, patient tumor tissues, and genome-wide transcription and translation studies, we show that tamoxifen resistance involves selective mRNA translational reprogramming to an anti-estrogen state by
and other mRNAs. Tamoxifen-resistant translational reprogramming is shown to be mediated by increased expression of eIF4E and its increased availability by hyperactive mTOR and to require phosphorylation of eIF4E at Ser209 by increased MNK activity. Resensitization to tamoxifen is restored only by reducing eIF4E expression or mTOR activity and also blocking MNK1 phosphorylation of eIF4E. mRNAs specifically translationally up-regulated with tamoxifen resistance include
, which inhibits ER signaling and estrogen responses and promotes breast cancer metastasis. Silencing
significantly restores tamoxifen sensitivity. Tamoxifen-resistant but not tamoxifen-sensitive patient ER
breast cancer specimens also demonstrate strongly increased MNK phosphorylation of eIF4E. eIF4E levels, availability, and phosphorylation therefore promote tamoxifen resistance in ER
breast cancer through selective mRNA translational reprogramming.
The MNK1 protein kinase is directly activated by the MAPK pathway and is specifically expressed in pancreatic acinar cells. Both the MNK1 kinase and the MAPK pathway are required for response to ...pancreatitis, suggesting that their pharmacological targeting would be of therapeutic interest. Because the mRNA cap-binding protein and translation initiation factor eIF4E is the major known MNK1 substrate, one could anticipate that the protective function of MNK1 in pancreatitis is mediated by eIF4E phosphorylation.
Acute pancreatitis was induced by the intraperitoneal administration of cerulein in wild-type mice and in transgenic mice carrying two non-phosphorylatable Eif4e alleles. The expression and phosphorylation of proteins of the MNK1-eIF4E pathway was visualized by western-blotting. The severity of pancreatitis was monitored by the measure of serum amylase levels and by histopathology and immunohistochemistry using apoptosis and immune infiltrate markers.
Despite a strong induction in MNK1 kinase activity in both wild-type and transgenic mice, precluding eIF4E phosphorylation has no impact on the severity of acute pancreatitis. Serum amylase is equally induced in both mouse genotypes and neither acinar cell apoptosis nor immune infiltrate is exacerbated.
eIF4E phosphorylation is not required for response to pancreatitis indicating that the acinar-cell-specific MNK1 kinase acts in acute pancreatitis via another substrate.
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