EMBO Journal最新文献

Somatostatin, released from δ-cells within pancreatic islets of Langerhans, is one of the most important negative regulators of islet hormone secretion. We find that islet δ-cells are positioned near, and release somatostatin onto, primary cilia of the other islet cell types, including insulin-secreting β-cells. Somatostatin activates ciliary somatostatin receptors, resulting in rapid lowering of the ciliary cAMP concentration which in turn promotes more sustained nuclear translocation of the cilia-dependent transcription factor GLI2 through a mechanism that operates in parallel with the canonical Hedgehog pathway and depends on ciliary Ca²⁺ signaling. We also find that primary cilia length is reduced in islets from human donors with type-2 diabetes, which is associated with a reduction in interactions between δ-cells and cilia. Our findings show that islet cell primary cilia constitute an important target of somatostatin action, which endows somatostatin with the ability to regulate islet cell function beyond acute suppression of hormone release.

The fast and transient induction of immediate early genes orchestrates the cellular response to various stimuli. These stimuli trigger phosphorylation cascades that promote immediate early gene transcription independent of de novo protein synthesis. Here we show that the same phosphorylation cascades also target the splicing machinery, inducing an analogous splicing switch that we call immediate early splicing (IES). We characterize hnRNPC2-controlled IES, which depends on the MEK-ERK pathway and the T cell-specific kinase PKCθ. This splicing switch mainly targets components of the translation machinery, such as mRNAs encoding ribosomal proteins and eIF5A. Inducing the eIF5A IES protein variant is by itself sufficient to reduce global translation, and consistently, we observe reduced de novo protein synthesis early after T cell activation. We suggest that immediate early splicing and the ensuing transient decrease in translation efficiency help to coordinate the extensive changes in gene expression during T cell activation. Together, these findings set a paradigm for fast and transient alternative splicing in the immediate cellular response to activation, and provide evidence for its functional relevance during T-cell stimulation.

One way cells control the speed and specificity of protein degradation is by regulating the activity of ubiquitin ligases. Upon proteotoxic stress in yeast, the intrinsically disordered protein Roq1 binds the ubiquitin ligase Ubr1 as a pseudosubstrate, thereby modulating the degradation of substrates of the N-degron pathway and promoting the elimination of misfolded proteins. The mechanism underlying this reprograming of Ubr1 is unknown. Here, we show that Roq1 controls Ubr1 by means of two cooperating multifunctional motifs. The N-terminal arginine and a short hydrophobic motif of Roq1 interact with Ubr1 as part of a heterobivalent binding mechanism. Via its N-terminal arginine, Roq1 regulates the ubiquitination of various N-degron substrates and folded proteins. Via its hydrophobic motif, Roq1 accelerates the ubiquitination of misfolded proteins. These findings reveal how a small, intrinsically disordered protein with a simple architecture engages parallel channels of communication to reprogram a functionally complex ubiquitin ligase.

Polyglucosans are glycogen molecules with overlong chains, which are hyperphosphorylated in the neurodegenerative Lafora disease (LD). Brain polyglucosan bodies (PBs) cause fatal neurodegenerative diseases including Lafora disease and adult polyglucosan body disease (ABPD), for which treatments, biomarkers, and good understanding of their pathogenesis are currently missing. Mutations in the genes for the phosphatase laforin or the E3 ubiquitin ligase malin can cause LD. By depleting PTG, an activator of the glycogen chain-elongating enzyme glycogen synthase (GYS1), in laforin- and malin-deficient LD mice, we show that abnormal glycogen chain lengths and not hyperphosphorylation underlie polyglucosan formation, and that polyglucosan bodies induce neuroinflammation. We provide evidence indicating that a small pool of overactive GYS1 contributes to glycogen insolubility in LD and APBD. In contrast to previous findings, metabolomics experiments using in situ-fixed brains reveal only modest metabolic changes in laforin-deficient mice. These changes are not replicated in malin-deficient or APBD mice, and are not normalized in rescued LD mice. Finally, we identify a pool of metabolically volatile malto-oligoglucans as a polyglucosan body- and neuroinflammation-associated brain energy source, and promising candidate biomarkers for LD and APBD, including malto-oligoglucans and the neurodegeneration marker CHI3L1/YKL40.

Maternal inheritance of mitochondrial DNA (mtDNA) is highly conserved in metazoans. While many species eliminate paternal mtDNA during late sperm development to foster maternal inheritance, the regulatory mechanisms governing this process remain elusive. Through a forward genetic screen in Drosophila, we identified 47 mutant lines exhibiting substantial retention of mtDNA in mature sperm. We mapped one line to poldip2, a gene predominantly expressed in the testis. Disruption of poldip2 led to substantial mtDNA retention in mature sperm and subsequent paternal transmission to progeny. Further investigation via imaging, biochemical analyses and ChIP assays revealed that Poldip2 is a mitochondrial matrix protein capable of binding mtDNA. Moreover, we showed that ClpX, the key component of a major mitochondrial protease, interacts with Poldip2 to co-regulate mtDNA elimination in Drosophila spermatids. This study sheds light on the mechanisms underlying mtDNA removal during spermatogenesis and underscores the pivotal role of this process in safeguarding maternal inheritance.

Elongator is a tRNA-modifying complex that regulates protein translation. Recently, a moonlighting function of Elongator has been identified in regulating the polarization of the microtubule cytoskeleton during asymmetric cell division. Elongator induces symmetry breaking of the anaphase midzone by selectively stabilizing microtubules on one side of the spindle, contributing to the downstream polarized segregation of cell-fate determinants, and therefore to cell fate determination. Here, we investigate how Elongator controls microtubule dynamics. Elongator binds both to the tip of microtubules and to free GTP-tubulin heterodimers using two different subcomplexes, Elp123 and Elp456, respectively. We show that these activities must be coupled for Elongator to decrease the tubulin critical concentration for microtubule elongation. As a consequence, Elongator increases the growth speed and decreases the catastrophe rate of microtubules. Surprisingly, the Elp456 subcomplex binds to tubulin tails and has strong selectivity towards polyglutamylated tubulin. Hence, microtubules assembled by Elongator become selectively enriched with polyglutamylated tubulin, as observed in vitro, in mouse and Drosophila cell lines, as well as in vivo in Drosophila Sensory Organ Precursor cells. Therefore, Elongator rewrites the tubulin code of growing microtubules, placing it at the core of cytoskeletal dynamics and polarization during asymmetric cell division.

Cancers display cellular, genetic and epigenetic heterogeneity, complicating disease modeling. Multiple cell states defined by gene expression have been described in lung adenocarcinoma (LUAD). However, the functional contributions of cell state and the regulatory programs that control chromatin and gene expression in the early stages of tumor initiation are not well understood. Using single-cell RNA and ATAC sequencing in Kras/p53-driven tumor organoids, we identified two major cellular states: one more closely resembling alveolar type 2 (AT2) cells (SPC-high), and the other with epithelial-mesenchymal-transition (EMT)-associated gene expression (Hmga2-high). Each state exhibited distinct transcription factor networks, with SPC-high cells associated with TFs regulating AT2 fate and Hmga2-high cells enriched in Wnt- and NFκB-related TFs. CD44 was identified as a marker for the Hmga2-high state, enabling functional comparison of the two populations. Organoid assays and orthotopic transplantation revealed that SPC-high, CD44-negative cells exhibited higher tumorigenic potential within the lung microenvironment. These findings highlight the utility of organoids in understanding chromatin regulation in early tumorigenesis and identifying novel early-stage therapeutic targets in Kras-driven LUAD.

Aneuploidy is prevalent in cancer and associates with fitness advantage and poor patient prognosis. Yet, experimentally induced aneuploidy initially leads to adverse effects and impaired proliferation, suggesting that cancer cells must adapt to aneuploidy. We performed in vitro evolution of cells with extra chromosomes and obtained cell lines with improved proliferation and gene expression changes congruent with changes in aneuploid cancers. Integrated analysis of cancer multi-omics data and model cells revealed increased expression of DNA replicative and repair factors, reduced genomic instability, and reduced lysosomal degradation. We identified E2F4 and FOXM1 as transcription factors strongly associated with adaptation to aneuploidy in vitro and in cancers and validated this finding. The adaptation to aneuploidy also coincided with specific copy number aberrations that correlate with poor patient prognosis. Chromosomal engineering mimicking these aberrations improved aneuploid cell proliferation, while loss of previously present extra chromosomes impaired it. The identified common adaptation strategies suggest replication stress, genomic instability, and lysosomal stress as common liabilities of aneuploid cancers.

Although inflammation has been widely associated with cancer development, how it affects the outcomes of immunotherapy and chemotherapy remains incompletely understood. Here, we show that CKLF-like MARVEL transmembrane domain-containing member 4 (CMTM4) is highly expressed in multiple human and murine cancer types including Lewis lung carcinoma, triple-negative mammary cancer and melanoma. In lung carcinoma, loss of CMTM4 significantly reduces tumor growth and impairs NF-κB, mTOR, and PI3K/Akt pathway activation. Furthermore, we demonstrate that CMTM4 can regulate epidermal growth factor (EGF) signaling post-translationally by promoting EGFR recycling and preventing its Rab-dependent degradation. Consequently, CMTM4 knockout sensitizes human lung tumor cells to EGFR inhibitors. In addition, CMTM4 knockout tumors stimulated with EGF show a decreased ability to produce inflammatory cytokines including granulocyte colony-stimulating factor (G-CSF), leading to decreased recruitment of polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) and therefore establishing a less suppressive tumor immune environment in both lung and mammary cancers. We also present evidence indicating that CMTM4-targeting siRNA-loaded liposomes reduce lung tumor growth in vivo and prolong animal survival. Knockout of CMTM4 enhances immune checkpoint blockade or chemotherapy to further reduce lung tumor growth. These data suggest that CMTM4 represents a novel target for the inhibition of tumor inflammation, and improvement of the immune response and tumor drug sensitivity.

L-arginine is the most nitrogen-rich amino acid, acting as a key precursor for the synthesis of nitrogen-containing metabolites and an essential intermediate in the clearance of excess nitrogen. Arginine's side chain possesses a guanidino group which has unique biochemical properties, and plays a primary role in nitrogen excretion (urea), cellular signaling (nitric oxide) and energy buffering (phosphocreatine). The post-translational modification of protein-incorporated arginine by guanidino-group methylation also contributes to epigenetic gene control. Most human cells do not synthesize sufficient arginine to meet demand and are dependent on exogenous arginine. Thus, dietary arginine plays an important role in maintaining health, particularly upon physiologic stress. How cells adapt to changes in extracellular arginine availability is unclear, mostly because nearly all tissue culture media are supplemented with supraphysiologic levels of arginine. Evidence is emerging that arginine-deficiency can influence disease progression. Here, we review new insights into the importance of arginine as a metabolite, emphasizing the central role of mitochondria in arginine synthesis/catabolism and the recent discovery that arginine can act as a signaling molecule regulating gene expression and organelle dynamics.