Phosphoinositides are a minor group of membrane-associated phospholipids that are transiently generated on the cytoplasmic leaflet of many organelle membranes and the plasma membrane. There are seven ...functionally distinct phosphoinositides, each derived via the reversible phosphorylation of phosphatidylinositol in various combinations on the inositol ring. Their generation and termination is tightly regulated by phosphatidylinositol-kinases and –phosphatases. These enzymes can function together in an integrated and coordinated manner, whereby the phosphoinositide product of one enzyme may subsequently serve as a substrate for another to generate a different phosphoinositide species. This regulatory mechanism not only enables the transient generation of phosphoinositides on membranes, but also more complex sequential or bidirectional conversion pathways, and phosphoinositides can also be transferred between organelles via membrane contacts. It is this capacity to fine-tune phosphoinositide signals that makes them ideal regulators of membrane organization and dynamics, through their recruitment of signalling, membrane altering and lipid transfer proteins. Research spanning several decades has provided extensive evidence that phosphoinositides are major gatekeepers of membrane organization, with roles in endocytosis, exocytosis, autophagy, lysosome dynamics, vesicular transport and secretion, cilia, inter-organelle membrane contact, endosome maturation and nuclear function. By contrast, there has been remarkably little known about the role of phosphoinositides at mitochondria – an enigmatic and major knowledge gap, with challenges in reliably detecting phosphoinositides at this site.
Here we review recent significant breakthroughs in understanding the role of phosphoinositides in regulating mitochondrial dynamics and metabolic function.
Macroautophagy/autophagy occurs basally under nutrient-rich conditions in most mammalian cells, contributing to protein and organelle quality control, and protection against aging and ...neurodegeneration. During autophagy, lysosomes are heavily utilized via their fusion with autophagosomes and must be repopulated to maintain autophagic degradative capacity. During starvation-induced autophagy, lysosomes are generated via
biogenesis under the control of TFEB (transcription factor EB), or by the recycling of autolysosome membranes via autophagic lysosome reformation (ALR). However, these lysosome repopulation processes do not operate under nutrient-rich conditions. In our recent study, we identify a sequential phosphoinositide conversion pathway that enables lysosome repopulation under nutrient-rich conditions to facilitate basal autophagy. Phosphatidylinositol-3,4-bisphosphate (PtdIns3,4P
) signals generated downstream of phosphoinositide 3-kinase alpha (PI3Kα) during growth factor stimulation are converted to phosphatidylinositol-3-phosphate (PtdIns3P) on endosomes by INPP4B (inositol polyphosphate-4-phosphatase type II B). We show that PtdIns3P is retained as endosomes mature into endolysosomes, and serves as a substrate for PIKFYVE (phosphoinositide kinase, FYVE-type zinc finger containing) to generate phosphatidylinositol-3,5-bisphosphate (PtdIns3,5P
) to promote SNX2-dependent lysosome reformation, basal autophagic flux and protein aggregate degradation. Therefore, endosome maturation couples nutrient signaling to lysosome repopulation during basal autophagy by delivering PI3Kα-derived PtdIns3P to endolysosomes for PtdIns(3,5)P
-dependent lysosome reformation.
ALR: autophagic lysosome reformation; INPP4B: inositol polyphosphate-4-phosphatase type II B; PI3Kα: phosphoinositide 3-kinase alpha; PIKFYVE: phosphoinositide kinase FYVE-type zinc finger containing; PtdIns3P: phosphatidylinositol-3-phosphate; PtdIns(3,4)P
: phosphatidylinositol-3,4-bisphosphate; PtdIns(3,5)P
phosphatidylinositol-3,5-bisphosphate; SNX2 sorting nexin 2; PIK3C3/VPS34 phosphatidylinositol 3-kinase catalytic subunit type 3.
Autophagy depends on the repopulation of lysosomes to degrade intracellular components and recycle nutrients. How cells co‐ordinate lysosome repopulation during basal autophagy, which occurs ...constitutively under nutrient‐rich conditions, is unknown. Here, we identify an endosome‐dependent phosphoinositide pathway that links PI3Kα signaling to lysosome repopulation during basal autophagy. We show that PI3Kα‐derived PI(3)P generated by INPP4B on late endosomes was required for basal but not starvation‐induced autophagic degradation. PI(3)P signals were maintained as late endosomes matured into endolysosomes, and served as the substrate for the 5‐kinase, PIKfyve, to generate PI(3,5)P2. The SNX‐BAR protein, SNX2, was recruited to endolysosomes by PI(3,5)P2 and promoted lysosome reformation. Inhibition of INPP4B/PIKfyve‐dependent lysosome reformation reduced autophagic clearance of protein aggregates during proteotoxic stress leading to increased cytotoxicity. Therefore under nutrient‐rich conditions, PI3Kα, INPP4B, and PIKfyve sequentially contribute to basal autophagic degradation and protection from proteotoxic stress via PI(3,5)P2‐dependent lysosome reformation from endolysosomes. These findings reveal that endosome maturation couples PI3Kα signaling to lysosome reformation during basal autophagy.
Synopsis
Autophagy is an adaptive response to nutrient‐poor conditions, but also regulates cells under more normal conditions. Here, sequential phosphoinositide conversion is found to mediate lysosome reformation necessary for autophagic degradation and protein aggregate clearance under nutrient‐rich conditions.
PI3Kα‐derived PI(3)P generated by INPP4B on late endosomes is required for basal but not starvation‐induced autophagic degradation.
PI(3)P is maintained on late endosomes as they mature into endolysosomes, where they act as a substrate for PI(3,5)P2 generation by PIKfyve.
PI(3,5)P2 recruits the SNX‐BAR protein SNX2 to drive lysosome reformation from endolysosomes.
Inactivation of INPP4B/PIKfyve‐dependent lysosome reformation reduces autophagic clearance of protein aggregates during proteotoxic stress, causing cell death.
Sequential phosphoinositide conversion by PI3Kα, INPP4B and PIKfyve is necessary for autophagic degradation and protein aggregate clearance under nutrient‐rich conditions.
Despite significant progress, our understanding of how specific oncogenes transform cells is still limited and likely underestimates the complexity of downstream signalling events. To address this ...gap, we use mass spectrometry-based chemical proteomics to characterize the global impact of an oncogene on the expressed kinome, and then functionally annotate the regulated kinases. As an example, we identify 63 protein kinases exhibiting altered expression and/or phosphorylation in Src-transformed mammary epithelial cells. An integrated siRNA screen identifies nine kinases, including SGK1, as being essential for Src-induced transformation. Accordingly, we find that Src positively regulates SGK1 expression in triple negative breast cancer cells, which exhibit a prominent signalling network governed by Src family kinases. Furthermore, combined inhibition of Src and SGK1 reduces colony formation and xenograft growth more effectively than either treatment alone. Therefore, this approach not only provides mechanistic insights into oncogenic transformation but also aids the design of improved therapeutic strategies.
Mutations in inositol polyphosphate 5-phosphatase E (INPP5E) cause the ciliopathies known as Joubert and MORM syndromes; however, the role of INPP5E in ciliary biology is not well understood. Here, ...we describe an interaction between INPP5E and AURKA, a centrosomal kinase that regulates mitosis and ciliary disassembly, and we show that this interaction is important for the stability of primary cilia. Furthermore, AURKA phosphorylates INPP5E and thereby increases its 5-phosphatase activity, which in turn promotes transcriptional downregulation of AURKA, partly through an AKT-dependent mechanism. These findings establish the first direct link between AURKA and phosphoinositide signaling and suggest that the function of INPP5E in cilia is at least partly mediated by its interactions with AURKA.
Neurological worsening and recurrent stroke contribute substantially to morbidity associated with transient ischemic attacks and strokes (TIA-S).
To determine predictors of early recurrent ...cerebrovascular events (RCVEs) among patients with TIA-S and National Institutes of Health Stroke Scale scores of 0 to 3.
A retrospective cohort study was conducted at 2 tertiary care centers (Columbia University Medical Center, New York, New York, and Tulane University Medical Center, New Orleans, Louisiana) between January 1, 2010, and December 31, 2014. All patients with neurologist-diagnosed TIA-S with a National Institutes of Health Stroke Scale score of 0 to 3 who presented to the emergency department were included.
The primary outcome (adjudicated by 3 vascular neurologists) was RCVE: neurological deterioration in the absence of a medical explanation or recurrent TIA-S during hospitalization.
Of the 1258 total patients, 1187 had no RCVEs and 71 had RCVEs; of this group, 750 patients (63.2%) and 39 patients (54.9%), respectively, were aged 60 years or older. There were 505 patients with TIA-S at Columbia University; 31 (6.1%) had RCVEs (15 patients had neurological deterioration only, 11 had recurrent TIA-S only, and 5 had both). The validation cohort at Tulane University consisted of 753 patients; 40 (5.3%) had RCVEs (24 patients had neurological deterioration only and 16 had both). Predictors of RCVE in multivariate models in both cohorts were infarct on neuroimaging (computed tomographic scan or diffusion-weighted imaging sequences on magnetic resonance imaging) (Columbia University: not applicable and Tulane University: odds ratio, 1.75; 95% CI, 0.82-3.74; P = .15) and large-vessel disease etiology (Columbia University: odds ratio, 6.69; 95% CI, 3.10-14.50 and Tulane University: odds ratio, 8.13; 95% CI, 3.86-17.12; P < .001). There was an increase in the percentage of patients with RCVEs when both predictors were present. When neither predictor was present, the rate of RCVE was extremely low (up to 2%). Patients with RCVEs were less likely to be discharged home in both cohorts.
In patients with minor stroke, vessel imaging and perhaps neuroimaging parameters, but not clinical scores, were associated with RCVEs in 2 independent data sets. Prospective studies are needed to validate these predictors.
•Uveitis is a heterogeneous collection of diseases.•Despite the heterogeneity of uveitis, specific RNA transcripts expressed by cells in peripheral blood as well as pathways involving multiple genes ...are common to different forms of uveitis.•The shared expression of mRNA from different forms of uveitis is consistent with a prior publication based on peripheral blood and thus independently validated.•Transcripts that are implicated in multiple forms of uveitis could suggest therapeutic targets that could benefit multiple forms of uveitis.
Uveitis is a heterogeneous collection of diseases. We tested the hypothesis that despite the diversity of uveitides, there could be common mechanisms shared by multiple subtypes, and that evidence of these common mechanisms may be detected as gene expression profiles in whole blood.
Cohort study.
Ninety subjects with uveitis including axial spondyloarthritis (n = 17), sarcoidosis (n = 13), inflammatory bowel disease (n = 12), tubulointerstitial nephritis with uveitis (n = 10), or idiopathic uveitis (n = 38) as well as 18 healthy controls were enrolled, predominantly at Oregon Health & Science University. RNA-Seq data generated from peripheral, whole blood identified 19,859 unique transcripts. We analyzed gene expression pathways via Kyoto Encyclopedia of Genes and Genomes and Gene Ontology (GO). We validated our list of upregulated genes by comparison to a previously published study on peripheral blood gene expression among 50 subjects with diverse forms of uveitis.
Both the Kyoto Encyclopedia of Genes and Genomes and GO analysis identified multiple shared pathways or GO terms with a P value of <.0001. Almost all pathways related to the immune response and/or response to an infection. A total of 119 individual transcripts were upregulated by at least 1.5-fold and false discovery rate <.05, and 61 were downregulated by similar criteria. Comparing mRNA from our study with a false discovery rate <.05 and the prior report, we identified 10 common gene transcripts: ICAM1, IL15RA, IL15, IRF1, IL10RB, GSK3A, TYK2, MEF2A, MEF2B, and MEF2D.
Many forms of uveitis share overlapping mechanisms. These data support the concept that a single therapeutic approach could benefit diverse forms of this disease.
Women in cancer research Mitchell, Christina A; Roussel, Martine F; Walsh, Leonie ...
Nature reviews. Cancer,
10/2019, Letnik:
19, Številka:
10
Journal Article
Recenzirano
Odprti dostop
Gender inequality in science is a real issue, and without frank and open discussions leading to positive action it is likely to remain so. In February 2019, Nature Reviews Cancer was kindly invited ...to be part of a 'Women in Science Mentoring' panel discussion, which took place at the Lorne Cancer Conference in Victoria, Australia. Inspired by the scientific career paths and experiences of the women on the panel, we decided to share their stories with our readers in this Viewpoint article, along with their opinions on how men and women must equally take responsibility for supporting and empowering female scientists. To this end, we hope we might contribute in some small way to highlighting a few of the issues surrounding gender bias in cancer research, as well as science more generally, and show our commitment to ensuring gender diversity within the journal.
An ongoing challenge in cancer is the management of primary and metastatic brain malignancies. This is partly due to restrictions of the blood-brain barrier and their unique microenvironment. These ...challenges are most evident in cancers such as lymphoma and melanoma, which are typically responsive to treatment in systemic locations but resistant when established in the brain. We propose interleukin-1 receptor-associated kinase-4 (IRAK-4) as a potential target across these diseases and describe the activity and mechanism of oral IRAK-4 inhibitor CA-4948.
Human primary central nervous system lymphoma (PCNSL) and melanoma brain metastases (MBM) samples were analyzed for expression of IRAK-4 and downstream transcription pathways. We next determined the central nervous system (CNS) applicability of CA-4948 in naïve and tumor-bearing mice using models of PCNSL and MBM. The mechanistic effect on tumors and the tumor microenvironment was then analyzed.
Human PCNSL and MBM have high expression of IRAK-4, IRAK-1, and nuclear factor kappa B (NF-κB). This increase in inflammation results in reflexive inhibitory signaling. Similar profiles are observed in immunocompetent murine models. Treatment of tumor-bearing animals with CA-4948 results in the downregulation of mitogen-activated protein kinase (MAPK) signaling in addition to decreased NF-κB. These intracellular changes are associated with a survival advantage.
IRAK-4 is an attractive target in PCNSL and MBM. The inhibition of IRAK-4 with CA-4948 downregulates the expression of important transcription factors involved in tumor growth and proliferation. CA-4948 is currently being investigated in clinical trials for relapsed and refractory lymphoma and warrants further translation into PCNSL and MBM.
Epithelia are active materials where mechanical tension governs morphogenesis and homeostasis. But how that tension is regulated remains incompletely understood. We now report that caveolae control ...epithelial tension and show that this is necessary for oncogene-transfected cells to be eliminated by apical extrusion. Depletion of caveolin-1 (CAV1) increased steady-state tensile stresses in epithelial monolayers. As a result, loss of CAV1 in the epithelial cells surrounding oncogene-expressing cells prevented their apical extrusion. Epithelial tension in CAV1-depleted monolayers was increased by cortical contractility at adherens junctions. This reflected a signaling pathway, where elevated levels of phosphoinositide-4,5-bisphosphate (PtdIns(4,5)P2) recruited the formin, FMNL2, to promote F-actin bundling. Steady-state monolayer tension and oncogenic extrusion were restored to CAV1-depleted monolayers when tension was corrected by depleting FMNL2, blocking PtdIns(4,5)P2, or disabling the interaction between FMNL2 and PtdIns(4,5)P2. Thus, caveolae can regulate active mechanical tension for epithelial homeostasis by controlling lipid signaling to the actin cytoskeleton.
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•Caveolae influence contractile tension in epithelial monolayers•Caveolin-1 depletion enhances epithelial tension via PtdIns(4,5)P2 signaling•Elevated epithelial tension inhibits oncogenic cell extrusion
Teo et al. report that caveolae can regulate epithelial contractility by lipid signaling. Caveolin-1 depletion enhanced phosphoinositide-4,5- bisphosphate (PtdIns(4,5)P2) levels to recruit FMNL2, which stabilizes F-actin and increases tension at adherens junctions. Elevated epithelial tension disrupts the elimination of oncogene-expressing cells by apical extrusion.
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