Loss of Elp3 blocks intestinal tuft cell differentiation via an mTORC1-Atf4 axis.

peer reviewedIntestinal tuft cells are critical for anti-helminth parasite immunity because they produce IL-25, which triggers IL-13 secretion by activated group 2 innate lymphoid cells (ILC2s) to expand both goblet and tuft cells. We show that epithelial Elp3, a tRNA-modifying enzyme, promotes tuft cell differentiation and is consequently critical for IL-25 production, ILC2 activation, goblet cell expansion and control of Nippostrongylus brasiliensis helminth infection in mice. Elp3 is essential for the generation of intestinal immature tuft cells and for the IL-13-dependent induction of glycolytic enzymes such as Hexokinase 1 and Aldolase A. Importantly, loss of epithelial Elp3 in the intestine blocks the codon-dependent translation of the Gator1 subunit Nprl2, an mTORC1 inhibitor, which consequently enhances mTORC1 activation and stabilizes Atf4 in progenitor cells. Likewise, Atf4 overexpression in mouse intestinal epithelium blocks tuft cell differentiation in response to intestinal helminth infection. Collectively, our data define Atf4 as a negative regulator of tuft cells and provide insights into promotion of intestinal type 2 immune response to parasites through tRNA modifications

Elp3-mediated codon-dependent translation promotes mTORC2 activation and regulates macrophage polarization.

peer reviewedMacrophage polarization is a process whereby macrophages acquire distinct effector states (M1 or M2) to carry out multiple and sometimes opposite functions. We show here that translational reprogramming occurs during macrophage polarization and that this relies on the Elongator complex subunit Elp3, an enzyme that modifies the wobble uridine base U34 in cytosolic tRNAs. Elp3 expression is downregulated by classical M1-activating signals in myeloid cells, where it limits the production of pro-inflammatory cytokines via FoxO1 phosphorylation, and attenuates experimental colitis in mice. In contrast, alternative M2-activating signals upregulate Elp3 expression through a PI3K- and STAT6-dependent signaling pathway. The metabolic reprogramming linked to M2 macrophage polarization relies on Elp3 and the translation of multiple candidates, including the mitochondrial ribosome large subunit proteins Mrpl3, Mrpl13, and Mrpl47. By promoting translation of its activator Ric8b in a codon-dependent manner, Elp3 also regulates mTORC2 activation. Elp3 expression in myeloid cells further promotes Wnt-driven tumor initiation in the intestine by maintaining a pool of tumor-associated macrophages exhibiting M2 features. Collectively, our data establish a functional link between tRNA modifications, mTORC2 activation, and macrophage polarization

Wobble tRNA modification and hydrophilic amino acid patterns dictate protein fate.

peer reviewedRegulation of mRNA translation elongation impacts nascent protein synthesis and integrity and plays a critical role in disease establishment. Here, we investigate features linking regulation of codon-dependent translation elongation to protein expression and homeostasis. Using knockdown models of enzymes that catalyze the mcm(5)s(2) wobble uridine tRNA modification (U(34)-enzymes), we show that gene codon content is necessary but not sufficient to predict protein fate. While translation defects upon perturbation of U(34)-enzymes are strictly dependent on codon content, the consequences on protein output are determined by other features. Specific hydrophilic motifs cause protein aggregation and degradation upon codon-dependent translation elongation defects. Accordingly, the combination of codon content and the presence of hydrophilic motifs define the proteome whose maintenance relies on U(34)-tRNA modification. Together, these results uncover the mechanism linking wobble tRNA modification to mRNA translation and aggregation to maintain proteome homeostasis

NF-κB, stem cells and breast cancer: the links get stronger

Self-renewing breast cancer stem cells are key actors in perpetuating tumour existence and in treatment resistance and relapse. The molecular pathways required for their maintenance are starting to be elucidated. Among them is the transcription factor NF-κB, which is known to play critical roles in cell survival, inflammation and immunity. Recent studies indicate that mammary epithelial NF-κB regulates the self-renewal of breast cancer stem cells in a model of Her2-dependent tumourigenesis. We will describe here the NF-κB-activating pathways that are involved in this process and in which progenitor cells this transcription factor is actually activated

EGFR and NF-kB: partners in cancer

Oncogenic proteins cooperate to promote tumor development and progression by sustaining cell proliferation, survival and invasiveness. Constitutive EGFR and NF-kappaB activities are seen in multiple solid tumors and combine to provide oncogenic signals to cancer cells. Understanding how these oncogenic pathways are connected is critical, given their role in intrinsic or acquired resistance to targeted anti-cancer therapies. We review molecular mechanisms by which both EGFR- and NF-kappaB-dependent pathways establish positive loops to increase their oncogenic potential. We also describe how NF-kappaB promotes resistance to EGFR inhibitors

NF-κB Signaling in Ex-Vivo Mouse Intestinal Organoids.

peer reviewedWe describe here a protocol to assess NF-κB activation in ex-vivo organoids generated from mouse intestinal crypts. These structures are maintained in culture as crypt-villus forming organoids. These ex-vivo organoids maintain both self-renewal and multilineage differentiation overtime. We also describe the generation of ex-vivo organoids from Apc-mutated mouse intestinal crypts. Both wild-type and Apc-mutated organoids respond very well to NF-κB-activating signals such as TNFα but not to LPS. The kinetic of NF-κB activation in response to these signals in ex-vivo intestinal organoids is very similar to what we see in 2D cell lines. This protocol provides investigators a powerful tool to assess NF-κB activation in both healthy and transformed intestinal epitheliums maintained in culture as 3D structures

HC gp-39 gene is upregulated in glioblastomas.

Public databases of the Cancer Genome Anatomy Project were used to quantify the relative gene expression levels in glioblastoma multiforme (GBM) and normal brain by Serial Analysis of Gene Expression (SAGE). Analysis revealed HC gp-39 among the genes with the most pronounced changes of expression in tumor cells. Northern hybridization confirmed the results of computer analysis and showed that enhanced expression of the HC gp-39 gene was mainly in GBMs and occasionally in anaplastic astrocytomas. Neither SAGE nor Northern analysis revealed the presence of HC gp-39 mRNA in the glioblastoma cell line, thus the detection of increased quantities of this mRNA in GBMs may be associated with activated macrophages. Since the numbers of infiltrating macrophages and small vessel density are higher in glioblastomas than in anaplastic astrocytomas or astrocytomas, the HC gp-39 gene can be used as a molecular marker in the analysis of malignant progression of astrocytic gliomas

Reduction of the transcription level of the mitochondrial genome in human glioblastoma.

Screening of human fetal brain cDNA library by glioblastoma (GB) and normal human brain total cDNA probes revealed 80 differentially hybridized clones. Hybridization of the DNA from selected clones and the same cDNA probes confirmed this difference for 38 clones, of which eight clones contained Alu-repeat inserts with increased levels in GB. Thirty clones contained cDNAs corresponding to mitochondrial genes for ATP synthase subunit 6 (ATP6), cytochrome c oxidase subunit II (COXII), cytochrome c oxidase subunit III (COXIII), NADH dehydrogenase subunit 1 (ND1), NADH dehydrogenase subunit 4 (ND4), and mitochondrial 12S rRNA. The levels of all these mitochondrial transcripts were decreased in glioblastomas as compared to tumor-adjacent histologically normal brain. Earlier we found the same for cytochrome c oxidase subunit I (COXI) Serial Analysis of Gene Expression (SAGE) showed lower content of the tags for all mitochondrial genes in GB SAGE libraries and together with our experimental data could serve as evidence of general inactivation of the mitochondrial genome in glioblastoma--the most malignant and abundant form of human brain tumor