Cells live in a chemical environment and are able to orient towards chemical cues. Unicellular haploid fungal cells communicate by secreting pheromones to reproduce sexually. In the yeast models ...Saccharomyces cerevisiae and Schizosaccharomyces pombe, pheromonal communication activates similar pathways composed of cognate G-protein-coupled receptors and downstream small GTPase Cdc42 and MAP kinase cascades. Local pheromone release and sensing, at a mobile surface polarity patch, underlie spatial gradient interpretation to form pairs between two cells of distinct mating types. Concentration of secretion at the point of cell-cell contact then leads to local cell wall digestion for cell fusion, forming a diploid zygote that prevents further fusion attempts. A number of asymmetries between mating types may promote efficiency of the system. In this review, we present our current knowledge of pheromone signaling in the two model yeasts, with an emphasis on how cells decode the pheromone signal spatially and ultimately fuse together. Though overall pathway architectures are similar in the two species, their large evolutionary distance allows to explore how conceptually similar solutions to a general biological problem can arise from divergent molecular components.
•Divergent GPCR-MAPK signaling architectures result in conceptually similar mating strategies.•Pheromone communication between yeast cells occurs through local polarity patches.•Local cell wall digestion for cell-cell fusion relies on focusing of secretion.•Asymmetries between mating partners may increase mating efficiency.•Cell type-specific factors combine in zygotes to block further mating attempts.
Proteolytic cleavage and release from the cell surface of membrane-tethered ligands is an important mechanism of regulating intercellular signalling. TACE is a major shedding protease, responsible ...for the liberation of the inflammatory cytokine TNFα and ligands of the epidermal growth factor receptor. iRhoms, catalytically inactive members of the rhomboid-like superfamily, have been shown to control the ER-to-Golgi transport and maturation of TACE. Here, we reveal that iRhom2 remains associated with TACE throughout the secretory pathway, and is stabilised at the cell surface by this interaction. At the plasma membrane, ERK1/2-mediated phosphorylation and 14-3-3 protein binding of the cytoplasmic amino-terminus of iRhom2 alter its interaction with mature TACE, thereby licensing its proteolytic activity. We show that this molecular mechanism is responsible for triggering inflammatory responses in primary mouse macrophages. Overall, iRhom2 binds to TACE throughout its lifecycle, implying that iRhom2 is a primary regulator of stimulated cytokine and growth factor signalling.
Many intercellular signals are synthesised as transmembrane precursors that are released by proteolytic cleavage ('shedding') from the cell surface. ADAM17, a membrane-tethered metalloprotease, is ...the primary shedding enzyme responsible for the release of the inflammatory cytokine TNFα and several EGF receptor ligands. ADAM17 exists in complex with the rhomboid-like iRhom proteins, which act as cofactors that regulate ADAM17 substrate shedding. Here we report that the poorly characterised FERM domain-containing protein FRMD8 is a new component of the iRhom2/ADAM17 sheddase complex. FRMD8 binds to the cytoplasmic N-terminus of iRhoms and is necessary to stabilise iRhoms and ADAM17 at the cell surface. In the absence of FRMD8, iRhom2 and ADAM17 are degraded via the endolysosomal pathway, resulting in the reduction of ADAM17-mediated shedding. We have confirmed the pathophysiological significance of FRMD8 in iPSC-derived human macrophages and mouse tissues, thus demonstrating its role in the regulated release of multiple cytokine and growth factor signals.
Centrioles organise centrosomes and cilia, and these organelles have an important role in many cell processes. In flies, the centriole protein Ana1 is required for the assembly of functional ...centrosomes and cilia. It has recently been shown that Cep135 (also known as Bld10) initially recruits Ana1 to newly formed centrioles, and that Ana1 then recruits Asl (known as Cep152 in mammals) to promote the conversion of these centrioles into centrosomes. Here, we show that ana1 mutants lack detectable centrosomes in vivo, that Ana1 is irreversibly incorporated into centrioles during their assembly and appears to play a more important role in maintaining Asl at centrioles than in initially recruiting Asl to centrioles. Unexpectedly, we also find that Ana1 promotes centriole elongation in a dose-dependent manner: centrioles are shorter when Ana1 dosage is reduced and are longer when Ana1 is overexpressed. This latter function of Ana1 appears to be distinct from its role in centrosome and cilium function, as a GFP-Ana1 fusion lacking the N-terminal 639 amino acids of the protein can support centrosome assembly and cilium function but cannot promote centriole over-elongation when overexpressed.
ABSTRACT
First Person is a series of interviews with the first authors of a selection of papers published in Journal of Cell Science, helping researchers promote themselves alongside their papers. ...Boris Sieber and Fangfang Lu are co-first authors on ‘ iRhom2 regulates ERBB signalling to promote KRAS-driven tumour growth of lung cancer cells’, published in JCS. Boris is a postdoc in the lab of Sophie Martin at University of Lausanne, Lausanne, Switzerland, investigating the regulation of Ras signalling and the MAPK cascade upon receptor activation. Fangfang is a PhD student in the lab of Matthew Freeman at University of Oxford, Oxford, UK, investigating control of cell signalling and its implications in health and diseases.
Dysregulation of the ERBB/EGFR signalling pathway causes multiple types of cancer. Accordingly, ADAM17, the primary shedding enzyme that releases and activates ERBB ligands, is tightly regulated. It ...has recently become clear that iRhom proteins, inactive members of the rhomboid-like superfamily, are regulatory cofactors for ADAM17. Here, we show that oncogenic KRAS mutants target the cytoplasmic domain of iRhom2 (also known as RHBDF2) to induce ADAM17-dependent shedding and the release of ERBB ligands. Activation of ERK1/2 by oncogenic KRAS induces the phosphorylation of iRhom2, recruitment of the phospho-binding 14-3-3 proteins, and consequent ADAM17-dependent shedding of ERBB ligands. In addition, cancer-associated mutations in iRhom2 act as sensitisers in this pathway by further increasing KRAS-induced shedding of ERBB ligands. This mechanism is conserved in lung cancer cells, where iRhom activity is required for tumour xenograft growth. In this context, the activity of oncogenic KRAS is modulated by the iRhom2-dependent release of ERBB ligands, thus placing the cytoplasmic domain of iRhom2 as a central component of a positive feedback loop in lung cancer cells. This article has an associated First Person interview with the first authors of the paper.
My first project focuses upon the regulation of TACE by oncogenic stimulation. TACE (for TNFα-activating enzyme) is a major regulator of numerous cell signalling pathways, including epidermal growth ...factor receptor (EGFR) signalling. TACE acts at the plasma membrane to release signalling factors into the extracellular medium. iRhom1 and iRhom2 are multi-pass membrane proteins that belong to the rhomboid-like superfamily, and they are the ultimate regulators of TACE activity. It has been recently discovered that the phosphorylation of iRhom2 is required for the stimulated activity of TACE at the plasma membrane. However, whether iRhom phosphorylation is crucial in other pathological contexts is unknown. In addition, the role of iRhom1 phosphorylation in TACE activation remains unstudied. I have demonstrated that the phosphorylation of iRhom1 is required for TACE activity upon pharmacological stimulation. Therefore, the mechanism of TACE activation is conserved between iRhom1 and iRhom2. To study the role of iRhom phosphorylation in cancer, the role of the central proto-oncogenes Ras was investigated. Oncogenic KRas and HRas stimulate TACE activity, which demonstrates the conserved role of Ras proteins in stimulating the release of EGFR ligands by TACE. The reconstitution of double knockout (DKO) cells with iRhom2, but not with iRhom1 supports KRas-induced shedding. The specificity towards iRhom2 therefore constitutes a characteristic feature of oncogenic stimulation of TACE activity. Importantly, I have shown KRas-induced shedding requires iRhom2 phosphorylation and recruitment of the phospho-binding proteins 14-3-3. To assess the importance of these findings in lung cancer, the expression of iRhoms was genetically removed in non-small-cell lung cancer cells, thereby allowing me to test the requirement of iRhom2 phosphorylation for in vivo tumourigenesis. My second project concerns another regulatory function of iRhoms: the degradation of EGFR ligands. Before being cleaved off at the plasma membrane, EGFR ligands are produced as single-pass transmembrane proteins in the endoplasmic reticulum. It was discovered that iRhoms induce the degradation of EGFR ligands by the proteasome. The role of iRhoms as negative regulators of EGFR ligands is conserved in Drosophila and in mammalian cells. However, the molecular mechanism by which iRhoms destabilise EGFR ligands was unknown. I established a system in human cells and confirmed that ectopic iRhom expression triggers dose-dependent degradation of EGF. I found that the two degradation machineries of the cell support iRhom-driven degradation: the proteasome and the lysosome. Focussing on lysosomal degradation, I found that iRhoms drive EGF to lysosomal degradation directly from the ER, suggesting that this constitutes an ER-phagy route. Importantly, I found a requirement for the autophagy core protein Beclin-1 in this process. Finally, I attempted to determine the requirement of endogenous iRhoms in the degradation of EGF. Although I found an upregulation in EGF protein in iRhom-depleted cells, further validation with iRhom depletion and genetic ablation of iRhom1/2 by CRISPR/Cas9 highlighted technical issues with my approach. Therefore, further work is required to establish the involvement of endogenous iRhoms in EGF degradation.
Centriole assembly requires a small number of conserved proteins. The precise pathway of centriole assembly has been difficult to study, as the lack of any one of the core assembly proteins-Plk4, ...Ana2/STIL, Sas-6, Sas-4/CPAP or Asl/Cep152-leads to the absence of centrioles. Here we use Sas-6/Ana2 Particles (SAPs) as a new model to probe the pathway of centriole and centrosome assembly. SAPs form in Drosophila eggs/embryos when Sas-6 and Ana2 are overexpressed. SAP assembly requires Sas-4, but not Plk4, while Asl helps to initiate SAP assembly, but is not required for SAP growth. Although not centrioles, SAPs recruit and organize many centriole and centrosome components, nucleate microtubules, organise actin structures and compete with endogenous centrosomes to form mitotic spindle poles. SAPs require Asl/Cep152 to efficiently recruit pericentriolar material (PCM), but Spd-2/Cep192 can promote some PCM assembly independently of Asl/Cep152. These observations provide new insights into the pathways of centriole and centrosome assembly.
Centriole assembly requires a small number of conserved proteins. The precise pathway of centriole assembly has been difficult to study, as the lack of any one of the core assembly proteins Plk4, ...Ana2 (the homologue of mammalian STIL), Sas-6, Sas-4 (mammalian CPAP) or Asl (mammalian Cep152) leads to the absence of centrioles. Here, we use Sas-6 and Ana2 particles (SAPs) as a new model to probe the pathway of centriole and centrosome assembly. SAPs form in
eggs or embryos when Sas-6 and Ana2 are overexpressed. SAP assembly requires Sas-4, but not Plk4, whereas Asl helps to initiate SAP assembly but is not required for SAP growth. Although not centrioles, SAPs recruit and organise many centriole and centrosome components, nucleate microtubules, organise actin structures and compete with endogenous centrosomes to form mitotic spindle poles. SAPs require Asl to efficiently recruit pericentriolar material (PCM), but Spd-2 (the homologue of mammalian Cep192) can promote some PCM assembly independently of Asl. These observations provide new insights into the pathways of centriole and centrosome assembly.
Poor sleep quality and physical inactivity are known risk factors for depressive symptoms. Yet, whether these factors differently contribute to depressive symptoms and whether they interact with one ...another remains unclear. Here, we examined how sleep quality and physical activity influence depressive symptoms in 79,274 adults 50 years of age or older (52.4% women) from the Survey of Health, Aging and Retirement in Europe (SHARE) study. Sleep quality (poor vs. good), physical activity (inactive vs. active), and depressive symptoms (0 to 12 score) were repeatedly collected (7 waves of data collection) between 2004 and 2017. Results showed that sleep quality and physical activity were associated with depressive symptoms. Specifically, participants with poorer sleep quality reported more depressive symptoms than participants with better sleep quality (b = 1.85, 95% CI = 1.83–1.86, p < .001). Likewise, compared to physically active participants, physically inactive participants reported more depressive symptoms (b = 0.44, 95% CI = 0.42–0.45, p < .001). Moreover, sleep quality and physical activity showed an interactive association with depressive symptoms (b = 0.17, 95% CI = 0.13–0.20, p < .001). The negative association between poor sleep quality and higher depressive symptoms was stronger in physically inactive than active participants. These findings suggest that, in adults 50 years of age or older, both poor sleep quality and physical inactivity are related to an increase in depressive symptoms. Moreover, the detrimental association between poor sleep quality and depressive symptoms is amplified in physically inactive individuals.
•European large-scale sample of non-institutionalized adults 50 years of age or older.•Physical inactivity and poor sleep quality contribute to higher depressive symptoms.•Physical inactivity and poor sleep quality interact to predict depressive symptoms.•Physical inactivity strengthens the association between poor sleep quality and depressive symptoms.•Physical activity and sleep quality are essential to older adults' mental health.
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