Macroautophagy/autophagy acts to promote homeostasis and is increasingly understood to selectively target cargo for degradation. The LC3-family of proteins mediate diverse yet distinct cargo ...recruitment to phagophores. However, what underlies specificity for cargo engagement among LC3 proteins is poorly understood. Using an unbiased protein interaction screen of LC3B and LC3C, we uncover a novel LC3C-endocytic-associated-pathway (LEAP) that recruits selective plasma membrane (PM) cargo to phagophores. We show LC3C but not LC3B localizes to peripheral endosomes and engages proteins that traffic between the PM, endosomes and autophagosomes. We establish that endocytic LC3C binds cargo internalized from the PM, including MET receptor tyrosine kinase and TFRC (transferrin receptor), and targets them toward autophagic degradation. These findings identify LEAP as an unexpected LC3C-dependent pathway, providing new understanding of selective coupling of PM signaling and autophagic degradation with important implications in cancer and other disease states.
Cancer cells adapt metabolically to proliferate under nutrient limitation. Here we used combined transcriptional-metabolomic network analysis to identify metabolic pathways that support ...glucose-independent tumor cell proliferation. We found that glucose deprivation stimulated re-wiring of the tricarboxylic acid (TCA) cycle and early steps of gluconeogenesis to promote glucose-independent cell proliferation. Glucose limitation promoted the production of phosphoenolpyruvate (PEP) from glutamine via the activity of mitochondrial PEP-carboxykinase (PCK2). Under these conditions, glutamine-derived PEP was used to fuel biosynthetic pathways normally sustained by glucose, including serine and purine biosynthesis. PCK2 expression was required to maintain tumor cell proliferation under limited-glucose conditions in vitro and tumor growth in vivo. Elevated PCK2 expression is observed in several human tumor types and enriched in tumor tissue from non-small-cell lung cancer (NSCLC) patients. Our results define a role for PCK2 in cancer cell metabolic reprogramming that promotes glucose-independent cell growth and metabolic stress resistance in human tumors.
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•Tumor cell metabolic flexibility enables glucose-independent cell proliferation•PCK2 helps generate glycolytic intermediates under low-glucose conditions•PCK2 expression is regulated by glucose and required for in vivo tumor growth•PCK2 expression is elevated in non-small-cell lung carcinoma (NSCLC)
Cancer cells adapt metabolically to maintain proliferation under nutrient limitation. Vincent et al. demonstrate that cancer cells can engage the early steps of gluconeogenesis—a process regulated by mitochondrial PEPCK (PCK2)—to generate biosynthetic intermediates required for tumor cell proliferation.
Abstract
Autophagy selectively targets cargo for degradation, yet mechanistic understanding remains incomplete. The ATG8-family plays key roles in autophagic cargo recruitment. Here by mapping the ...proximal interactome of ATG8-paralogs, LC3B and LC3C, we uncover a LC3C-Endocytic-Associated-Pathway (LEAP) that selectively recruits plasma-membrane (PM) cargo to autophagosomes. We show that LC3C localizes to peripheral endosomes and engages proteins that traffic between PM, endosomes and autophagosomes, including the SNARE-VAMP3 and ATG9, a transmembrane protein essential for autophagy. We establish that endocytic LC3C binds cargo internalized from the PM, including the Met receptor tyrosine kinase and transferrin receptor, and is necessary for their recruitment into ATG9 vesicles targeted to sites of autophagosome initiation. Structure-function analysis identified that LC3C-endocytic localization and engagement with PM-cargo requires the extended carboxy-tail unique to LC3C, the TBK1 kinase, and TBK1-phosphosites on LC3C. These findings identify LEAP as an unexpected LC3C-dependent pathway, providing new understanding of selective coupling of PM signalling with autophagic degradation.
Summary
Context
Although metabolic syndrome has been studied in patients with autonomous cortisol secretion, there are limited data for those with nonfunctioning adrenal incidentaloma (NFAI).
...Objective
To assess metabolic syndrome frequency in NFAI patients and controls without adrenal adenoma according to World Health Organization (WHO), National Cholesterol Education Program‐Adult Treatment Panel III (NCEP‐ATP III), American Association of Clinical Endocrinologists/American College of Endocrinology (AACE/ACE) and International Diabetes Federation (IDF) criteria.
Design
Retrospective and transversal study.
Patients
Seventy‐four NFAI and 90 controls were evaluated. NFAI diagnosis was established according to current guidelines. The control group was selected based on normal adrenal imaging examinations.
Measurements
Subjects were categorized by metabolic syndrome presence according to WHO, NCEP‐ATP III, AACE/ACE and IDF.
Results
Age, gender, ethnicity, body mass index, smoking, menopause, statin and fibrate use were comparable between patients and controls. The frequency of prediabetes, dyslipidaemia and hypertension as well as waist circumference were significantly higher in the NFAI patients compared to the controls. The metabolic syndrome frequency in the NFAI group was significantly higher compared to the normal adrenal group: WHO: 69.2% × 31.0% (P < 0.001); NCEP‐ATP III: 81.7% × 44.9% (P < 0.001); AACE/ACE: 77.1% × 31.9% (P < 0.001); IDF: 78.6% × 45.5% (P < 0.001). Logistic regression analysis showed that NFAI was a predictor of metabolic syndrome according to WHO (P = 0.001), NCEP‐ATP III (P = 0.005) and AACE/ACE (P = 0.007).
Conclusions
Metabolic syndrome is frequently found in patients with NFAI, and this frequency is higher in NFAI patients than in those with normal adrenal imaging.
Triple-negative breast cancers (TNBCs) display a complex spectrum of mutations and chromosomal aberrations. Chromosome 5q (5q) loss is detected in up to 70% of TNBCs, but little is known regarding ...the genetic drivers associated with this event. Here, we show somatic deletion of a region syntenic with human 5q33.2–35.3 in a mouse model of TNBC. Mechanistically, we identify KIBRA as a major factor contributing to the effects of 5q loss on tumor growth and metastatic progression. Re-expression of KIBRA impairs metastasis in vivo and inhibits tumorsphere formation by TNBC cells in vitro. KIBRA functions co-operatively with the protein tyrosine phosphatase PTPN14 to trigger mechanotransduction-regulated signals that inhibit the nuclear localization of oncogenic transcriptional co-activators YAP/TAZ. Our results argue that the selective advantage produced by 5q loss involves reduced dosage of KIBRA, promoting oncogenic functioning of YAP/TAZ in TNBC.
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•Reduced KIBRA expression is associated with chr 5q loss in breast cancer•Restoring Kibra expression inhibits metastatic dissemination in mice•KIBRA impairs the self-renewal capacity of triple-negative breast cancer cells•KIBRA blocks mechanotransduction signals required for YAP/TAZ activation
Triple-negative breast cancers (TNBCs) frequently lose chromosome 5q. Using a TNBC mouse model with spontaneous loss of a syntenic region, Knight et al. identify KIBRA as a metastasis suppressor. Mechanistically, KIBRA suppresses RHOA activation, impairing nuclear translocation of the oncogenes YAP/TAZ, which drive metastatic and cancer stem cell-like behavior.
The basal breast cancer subtype is enriched for triple-negative breast cancer (TNBC) and displays consistent large chromosomal deletions. Here, we characterize evolution and maintenance of chromosome ...4p (chr4p) loss in basal breast cancer. Analysis of The Cancer Genome Atlas data shows recurrent deletion of chr4p in basal breast cancer. Phylogenetic analysis of a panel of 23 primary tumor/patient-derived xenograft basal breast cancers reveals early evolution of chr4p deletion. Mechanistically we show that chr4p loss is associated with enhanced proliferation. Gene function studies identify an unknown gene, C4orf19, within chr4p, which suppresses proliferation when overexpressed—a member of the PDCD10-GCKIII kinase module we name PGCKA1. Genome-wide pooled overexpression screens using a barcoded library of human open reading frames identify chromosomal regions, including chr4p, that suppress proliferation when overexpressed in a context-dependent manner, implicating network interactions. Together, these results shed light on the early emergence of complex aneuploid karyotypes involving chr4p and adaptive landscapes shaping breast cancer genomes.
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•Chr4p loss evolves early in TNBC•Chr4p loss enhances growth•C4orf19 (PGCKA1) tumor suppressor
Kuzmin et al. report that chromosome 4p loss evolves early in triple-negative breast cancer (TNBC) and is associated with enhanced proliferation. C4orf19 (PGCKA1) is a tumor suppressor. Certain regions, including chr4p, suppress proliferation when overexpressed, differentially implicating network rewiring. This study illuminates the early emergence of complex aneuploid karyotypes in TNBC.
Differential inclusion or skipping of microexons is an increasingly recognized class of alternative splicing events. However, the functional significance of microexons and their contribution to ...signaling diversity is poorly understood. The Met receptor tyrosine kinase (RTK) modulates invasive growth and migration in development and cancer. Here, we show that microexon switching in the Arf6 guanine nucleotide exchange factor cytohesin-1 controls Met-dependent cell migration. Cytohesin-1 isoforms, differing by the inclusion of an evolutionarily conserved three-nucleotide microexon in the pleckstrin homology domain, display differential affinity for PI(4,5)P
(triglycine) and PI(3,4,5)P
(diglycine). We show that selective phosphoinositide recognition by cytohesin-1 isoforms promotes distinct subcellular localizations, whereby the triglycine isoform localizes to the plasma membrane and the diglycine to the leading edge. These data highlight microexon skipping as a mechanism to spatially restrict signaling and provide a mechanistic link between RTK-initiated phosphoinositide microdomains and Arf6 during signal transduction and cancer cell migration.
Invadopodia are specialized membrane protrusions that support degradation of extracellular matrix (ECM) by cancer cells, allowing invasion and metastatic spread. Although early stages of invadopodia ...assembly have been elucidated, little is known about maturation of invadopodia into structures competent for ECM proteolysis. The localized conversion of phosphatidylinositol(3,4,5)-triphosphate and accumulation of phosphatidylinositol(3,4)-bisphosphate at invadopodia is a key determinant for invadopodia maturation. Here we investigate the role of the 5'-inositol phosphatase, SHIP2, and reveal an unexpected scaffold function of SHIP2 as a prerequisite for invadopodia-mediated ECM degradation. Through biochemical and structure-function analyses, we identify specific interactions between SHIP2 and Mena, an Ena/VASP-family actin regulatory protein. We demonstrate that SHIP2 recruits Mena, but not VASP, to invadopodia and that disruption of SHIP2-Mena interaction in cancer cells leads to attenuated capacity for ECM degradation and invasion in vitro, as well as reduced metastasis in vivo. Together, these findings identify SHIP2 as a key modulator of carcinoma invasiveness and a target for metastatic disease.
Background
Preserved skeletal muscle is essential for the maintenance of healthy bone. Loss of bone mineral density (BMD) and muscle strength, considered a predictor of BMD, have been demonstrated in ...patients with cirrhosis, but they are poorly studied in chronic hepatitis C (CHC) without cirrhosis. Thus, we aimed to evaluate the prevalence of low BMD and its association with body composition, muscle strength, and nutritional status in CHC.
Methods
One hundred and four subjects mean age, 50.5 ± 11.3 years; 75.0% males; 67.3% non‐cirrhotic; and 32.7% with compensated cirrhosis with CHC, prospectively, underwent scanning of the lean tissue, appendicular skeletal muscle mass (ASM), fat mass, lumbar spine, hip, femoral neck, and whole‐body BMD by dual‐energy X‐ray absorptiometry. Muscle strength was assessed by dynamometry. Sarcopenia was defined by the presence of both low, ASM/height2 (ASMI) and low muscle strength according to the European Working Group on Sarcopenia in Older People criteria. The cut‐off points for low ASMI and low muscle strength, for women and men, were < 5.45 and < 7.26 kg/m2 and < 20 and < 30 kg, respectively. According to the adopted World Health Organization criteria in men aged > 50 years, the T‐score of osteopenia is between −1.0 and −2.49 standard deviation (SD) below the young average value and of osteoporosis is ≥−2.5 SD below the young normal mean for men, and the Z‐score of low bone mass is ≤−2.0 SD below the expected range in men aged < 50 years and women in the menacme. Nutritional status evaluation was based on the Controlling Nutritional Status score.
Results
Low BMD, low muscle strength, pre‐sarcopenia, sarcopenia, and sarcopenic obesity were observed in 34.6% (36/104), 27.9% (29/104), 14.4% (15/104), 8.7% (9/104), and 3.8% (4/104) of the patients, respectively. ASMI was an independent predictor of BMD (P < 0.001). Sarcopenia was independently associated with bone mineral content (P = 0.02) and malnutrition (P = 0.01). In 88.9% of the sarcopenic patients and in all with sarcopenic obesity, BMI was normal. The mid‐arm muscle circumference was positively correlated with ASMI (r = 0.88; P < 0.001).
Conclusions
This is the first study to demonstrate that ASM is an independent predictor of BMD in CHC. Mid‐arm muscle circumference coupled with handgrip strength testing should be incorporated into routine clinical practice to detect low muscle mass, which may be underdiagnosed when only BMI is used. These findings may influence clinical decision‐making and contribute to the development of effective strategies to screen the musculoskeletal abnormalities in CHC patients, independently of the stage of the liver disease.
Differential inclusion or skipping of microexons is an increasingly recognized class of alternative splicing events. However, the functional significance of microexons and their contribution to ...signaling diversity is poorly understood. The Met receptor tyrosine kinase (RTK) modulates invasive growth and migration in development and cancer. Here, we show that microexon switching in the Arf6 guanine nucleotide exchange factor cytohesin-1 controls Met-dependent cell migration. Cytohesin-1 isoforms, differing by the inclusion of an evolutionarily conserved three-nucleotide microexon in the pleckstrin homology domain, display differential affinity for PI(4,5)P2 (triglycine) and PI(3,4,5)P3 (diglycine). We show that selective phosphoinositide recognition by cytohesin-1 isoforms promotes distinct subcellular localizations, whereby the triglycine isoform localizes to the plasma membrane and the diglycine to the leading edge. These data highlight microexon skipping as a mechanism to spatially restrict signaling and provide a mechanistic link between RTK-initiated phosphoinositide microdomains and Arf6 during signal transduction and cancer cell migration.
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