EDITORIAL article Front. Physiol., 24 January 2022Sec. Respiratory Physiology and Pathophysiology Volume 12 - 2021 | https://doi.org/10.3389/fphys.2021.830285

Despite their putative importance in stress sensing, the specific integrin α-subunit(s) involved in cardiac hypertrophy has not been identified. Here, we show that α11 and syndecan-4 are critical and interdependent mediators of the hypertrophic response to increased LV afterload. We demonstrate in cells lacking both receptors an interdependent reduction in cell attachment to the major cardiac extracellular matrix components, suggesting that their interplay represents an important mechanism for stress sensing in cardiac cells.

Background Treatment of cancers has largely benefited from the development of immunotherapy. In particular, Chimeric Antigen Receptor (CAR) redirected T cells have demonstrated impressive efficacy against B-cell malignancies and continuous efforts are made to adapt this new therapy to solid tumors, where the immunosuppressive tumor microenvironment is a barrier for delivery. CAR T-cell validation relies on in vitro functional assays using monolayer or suspension cells and in vivo xenograft models in immunodeficient animals. However, the efficacy of CAR therapies remains difficult to predict with these systems, in particular when challenged against 3D organized solid tumors with highly intricate microenvironment. An increasing number of reports have now included an additional step in the development process in which redirected T cells are tested against tumor spheres. Results Here, we report a method to produce 3D structures, or cysts, out of a colorectal cancer cell line, Caco-2, which has the ability to form polarized spheroids as a validation tool for adoptive cell therapy in general. We used CD19CAR T cells to explore this method and we show that it can be adapted to various platforms including high resolution microscopy, bioluminescence assays and high-throughput live cell imaging systems. Conclusion We developed an affordable, reliable and practical method to produce cysts to validate therapeutic CAR T cells. The integration of this additional layer between in vitro and in vivo studies could be an important tool in the pre-clinical workflow of cell-based immunotherapy.

The biological effects of gamma radiation may exert damage beyond that of the individual through its deleterious effects on reproductive function. Impaired reproductive performance can result in reduced population size over consecutive generations. In a continued effort to investigate reproductive and heritable effects of ionizing radiation, we recently demonstrated adverse effects and genomic instability in progeny of parents exposed to gamma radiation. In the present study, genotoxicity and effects on the reproduction following subchronic exposure during a gametogenesis cycle to 60Co gamma radiation (27 days, 8.7 and 53 mGy/h, total doses 5.2 and 31 Gy) were investigated in the adult wild-type zebrafish (Danio rerio). A significant reduction in embryo production was observed one month after exposure in the 53 mGy/h exposure group compared to control and 8.7 mGy/h. One year later, embryo production was significantly lower in the 53 mGy/h group compared only to control, with observed sterility, accompanied by a regression of reproductive organs in 100% of the fish 1.5 years after exposure. Histopathological examinations revealed no significant changes in the testis in the 8.7 mGy/h group, while in 62.5% of females exposed to this dose rate the oogenesis was found to be only at the early previtellogenic stage. The DNA damage determined in whole blood, 1.5 years after irradiation, using a high throughput Comet assay, was significantly higher in the exposed groups (1.2 and 3-fold increase in 8.7 and 53 mGy/h females respectively; 3-fold and 2-fold increase in 8.7 and 53 mGy/h males respectively) compared to controls. A significantly higher number of micronuclei (4-5%) was found in erythrocytes of both the 8.7 and 53 mGy/h fish compared to controls. This study shows that gamma radiation at a dose rate of ≥ 8.7 mGy/h during gametogenesis causes adverse reproductive effects and persistent genotoxicity (DNA damage and increased micronuclei) in adult zebrafish.

The molecular mechanisms underlying the interdependence between intracellular trafficking and epithelial cell polarity are poorly understood. Here we show that inactivation of class III phosphatidylinositol-3-OH kinase (CIII-PI3K), which produces phosphatidylinositol-3-phosphate (PtdIns3P) on endosomes, disrupts epithelial organization. This is caused by dysregulation of endosomally localized Liver Kinase B1 (LKB1, also known as STK11), which shows delocalized and increased activity accompanied by dysplasia-like growth and invasive behaviour of cells provoked by JNK pathway activation. CIII-PI3K inactivation cooperates with RasV12 to promote tumour growth in vivo in an LKB1-dependent manner. Strikingly, co-depletion of LKB1 reverts these phenotypes and restores epithelial integrity. The endosomal, but not autophagic, function of CIII-PI3K controls polarity. We identify the CIII-PI3K effector, WD repeat and FYVE domain-containing 2 (WDFY2), as an LKB1 regulator in Drosophila tissues and human organoids. Thus, we define a CIII-PI3K-regulated endosomal signalling platform from which LKB1 directs epithelial polarity, the dysregulation of which endows LKB1 with tumour-promoting properties.

Colorectal cancer, encompassing colon and rectal cancer, arises from the epithelial lining of the large bowel. It is most prevalent in Westernised societies and is increasing in frequency as the world becomes more industrialised. Unfortunately, metastatic colorectal cancer is not cured by chemotherapy and the annual number of deaths caused by colorectal cancer, currently 700,000, is expected to rise. Our understanding of the contribution that genetic mutations make to colorectal cancer, although incomplete, is reasonably well advanced. However, it has only recently become widely appreciated that in addition to the ongoing accumulation of genetic mutations, chronic inflammation also plays a critical role in the initiation and progression of this disease. While a robust and tractable genetic model of colorectal cancer in zebrafish, suitable for pre-clinical studies, is not yet available, the identification of genes required for the rapid proliferation of zebrafish intestinal epithelial cells during development has highlighted a number of essential genes that could be targeted to disable colorectal cancer cells. Moreover, appreciation of the utility of zebrafish to study intestinal inflammation is on the rise. In particular, zebrafish provide unique opportunities to investigate the impact of genetic and environmental factors on the integrity of intestinal epithelial barrier function. With currently available tools, the interplay between epigenetic regulators, intestinal injury, microbiota composition and innate immune cell mobilisation can be analysed in exquisite detail. This provides excellent opportunities to define critical events that could potentially be targeted therapeutically. Further into the future, the use of zebrafish larvae as hosts for xenografts of human colorectal cancer tissue, while still in its infancy, holds great promise that zebrafish could one day provide a practical, preclinical personalized medicine platform for the rapid assessment of the metastatic potential and drug-sensitivity of patient-derived cancers.

Perfluorinated alkyl acids (PFAAs) are stable chemicals detected in tissue and serum from various species, including humans, and have been linked to adverse health outcomes. Experimental PFAA exposure in rodents has been associated with changes in mammary gland development. The estrogen receptor (ER)-negative human breast epithelial cell line, MCF-10A, can be grown as monolayer, but also has the ability to form three-dimensional acini in vitro, reflecting aspects of mammary glandular morphogenesis. Cells were exposed to five different PFAAs, perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), and perfluoroundecanoic acid (PFUnDA), both in monolayer and acini cultures. In monolayer cultures only the higher concentrations of PFOS, PFNA and PFDA (400-500μM) caused a significant increase in cell death, whereas PFOA and PFUnDA had no effect. Normal acini maturation was negatively impacted by PFOS, PFNA and PFDA already at the lowest concentration tested (0.6μM). Observed effects included loss of organization of the cell clusters and absence of a hollow lumen. Overall, this study demonstrated that PFAAs can interfere with cellular events related to normal development of glandular breast tissue through ER-independent mechanisms.

The 9th European Zebrafish Meeting took place recently in Oslo ( June 28–July 2, 2015). A total of 650 participants came to hear the latest research news focused on the zebrafish, Danio rerio, and to its distant evolutionary relative medaka, Oryzias latipes. The packed program included keynote and plenary talks, short oral presentations and poster sessions, workshops, and strategic discussions. The meeting was a great success and revealed dramatically how important the zebrafish in particular has become as a model system for topics, such as developmental biology, functional genomics, biomedicine, toxicology, and drug development. A new emphasis was given to its potential as a model for aquaculture, a topic of great economic interest to the host country Norway and for the future global food supply in general. Zebrafish husbandry as well as its use in teaching were also covered in separate workshops. As has become a tradition in these meetings, there was a well-attended Wellcome Trust Sanger Institute and ZFIN workshop focused on Zebrafish Genome Resources on the first day. The full EZM 2015 program with abstracts can be read and downloaded from the EZM 2015 Web site zebrafish2015.org.

A fundamental question is how autophagosome formation is regulated. Here we show that the PX domain protein HS1BP3 is a negative regulator of autophagosome formation. HS1BP3 depletion increased the formation of LC3-positive autophagosomes and degradation of cargo both in human cell culture and in zebrafish. HS1BP3 is localized to ATG16L1- and ATG9-positive autophagosome precursors and we show that HS1BP3 binds phosphatidic acid (PA) through its PX domain. Furthermore, we find the total PA content of cells to be significantly upregulated in the absence of HS1BP3, as a result of increased activity of the PA-producing enzyme phospholipase D (PLD) and increased localization of PLD1 to ATG16L1-positive membranes. We propose that HS1BP3 regulates autophagy by modulating the PA content of the ATG16L1-positive autophagosome precursor membranes through PLD1 activity and localization. Our findings provide key insights into how autophagosome formation is regulated by a novel negative-feedback mechanism on membrane lipids.

The 9th European Zebrafish Meeting took place recently in Oslo (June 28-July 2, 2015). A total of 650 participants came to hear the latest research news focused on the zebrafish, Danio rerio, and to its distant evolutionary relative medaka, Oryzias latipes. The packed program included keynote and plenary talks, short oral presentations and poster sessions, workshops, and strategic discussions. The meeting was a great success and revealed dramatically how important the zebrafish in particular has become as a model system for topics, such as developmental biology, functional genomics, biomedicine, toxicology, and drug development. A new emphasis was given to its potential as a model for aquaculture, a topic of great economic interest to the host country Norway and for the future global food supply in general. Zebrafish husbandry as well as its use in teaching were also covered in separate workshops. As has become a tradition in these meetings, there was a well-attended Wellcome Trust Sanger Institute and ZFIN workshop focused on Zebrafish Genome Resources on the first day. The full EZM 2015 program with abstracts can be read and downloaded from the EZM 2015 Web site zebrafish2015.org .

Previously, we have shown that the phosphoinositide metabolizing enzymes PIKfyve (phosphoinositide 5-kinase, FYVE finger containing) and MTMR3 (myotubularin-related protein 3), together with their lipid product PtdIns5P, are important for migration of normal human fibroblasts. As these proteins are a kinase and a phosphatase respectively, and thereby considered druggable, we wanted to test their involvement in cancer cell migration and invasion. First, we showed that PIKfyve and MTMR3 are expressed in most cancer cells. Next, we demonstrated that depletion of PIKfyve or MTMR3 resulted in decreased velocity in three different cancer cell lines by using new software for cell tracking. Inhibition of the enzymatic activity of PIKfyve by the inhibitor YM201636 also led to a strong reduction in cell velocity. Mechanistically, we show that PIKfyve and MTMR3 regulate the activation of the Rho family GTPase Rac1. Further experiments also implicated PtdIns5P in the activation of Rac1. The results suggest a model for the activation of Rac1 in cell migration where PIKfyve and MTMR3 produce PtdIns5P on cellular membranes which may then serve to recruit effectors to activate Rac1. Finally, in an invasion assay, we demonstrate that both PIKfyve and MTMR3 are implicated in invasive behaviour of cancer cells. Thus PIKfyve and MTMR3 could represent novel therapeutic targets in metastatic cancer.

Although phosphatidylinositol 5-phosphate (PtdIns5P) is present in many cell types and its biogenesis is increased by diverse stimuli, its precise cellular function remains elusive. Here we show that PtdIns5P levels increase when cells are stimulated to move and we find PtdIns5P to promote cell migration in tissue culture and in a Drosophila in vivo model. First, class III phosphatidylinositol 3-kinase, which produces PtdIns3P, was shown to be involved in migration of fibroblasts. In a cell migration screen for proteins containing PtdIns3P-binding motifs, we identified the phosphoinositide 5-kinase PIKfyve and the phosphoinositide 3-phosphatase MTMR3, which together constitute a phosphoinositide loop that produces PtdIns5P via PtdIns(3,5)P(2). The ability of PtdIns5P to stimulate cell migration was demonstrated directly with exogenous PtdIns5P and a PtdIns5P-producing bacterial enzyme. Thus, the identified phosphoinositide loop defines a new role for PtdIns5P in cell migration.

Recent evidence implicates the endosomal sorting complex required for transport (ESCRT) in the regulation of epithelial polarity in Drosophila melanogaster, but the mechanisms responsible for this action remain unclear. Here we show that ESCRTs determine cell orientation during directed migration in human fibroblasts. We find that endosomal retention of α5β1 integrin and its downstream signaling effector Src in ESCRT-depleted cells is accompanied by the failure to activate myosin light chain kinase (MLCK), which thereby cannot phosphorylate myosin regulatory light chain (MRLC). Using this mechanism, ESCRT-depleted fibroblasts fail to orient their Golgi complex to undergo directional migration and show impaired focal adhesion turnover and increased spreading on fibronectin. Consistent with these findings, expression of a phosphomimetic mutant of MRLC in ESCRT-depleted cells restores normal phenotypes during cell spreading and orientation of the Golgi. These results suggest that, through their role in regulating integrin trafficking, ESCRTs regulate phosphorylation of MRLC and, subsequently, Golgi orientation and cell spreading.

Correspondence11 December 2012free access Antibody crossreactivity between the tumour suppressor PHLPP1 and the proto-oncogene β-catenin Viola H Lobert Viola H Lobert Centre for Cancer Biomedicine, Faculty of Medicine, Oslo University Hospital, Oslo, Norway Department of Biochemistry, Institute for Cancer Research, Oslo University Hospital, Norway Institute for Cancer Research and Molecular Medicine, Norwegian University of Science and Technology, Trondheim, Norway Search for more papers by this author Jarle Bruun Jarle Bruun Centre for Cancer Biomedicine, Faculty of Medicine, Oslo University Hospital, Oslo, Norway Department of Cancer Prevention, Institute for Cancer Research, Oslo University Hospital, Norway Search for more papers by this author Hilde Abrahamsen Hilde Abrahamsen Centre for Cancer Biomedicine, Faculty of Medicine, Oslo University Hospital, Oslo, Norway Department of Biochemistry, Institute for Cancer Research, Oslo University Hospital, Norway Search for more papers by this author Ragnhild A Lothe Ragnhild A Lothe Centre for Cancer Biomedicine, Faculty of Medicine, Oslo University Hospital, Oslo, Norway Department of Cancer Prevention, Institute for Cancer Research, Oslo University Hospital, Norway Search for more papers by this author Harald Stenmark Harald Stenmark Centre for Cancer Biomedicine, Faculty of Medicine, Oslo University Hospital, Oslo, Norway Department of Biochemistry, Institute for Cancer Research, Oslo University Hospital, Norway Institute for Cancer Research and Molecular Medicine, Norwegian University of Science and Technology, Trondheim, Norway Search for more papers by this author Matthias Kolberg Matthias Kolberg Centre for Cancer Biomedicine, Faculty of Medicine, Oslo University Hospital, Oslo, Norway Department of Cancer Prevention, Institute for Cancer Research, Oslo University Hospital, Norway Search for more papers by this author Coen Campsteijn Coen Campsteijn Centre for Cancer Biomedicine, Faculty of Medicine, Oslo University Hospital, Oslo, Norway Department of Biochemistry, Institute for Cancer Research, Oslo University Hospital, Norway Search for more papers by this author Viola H Lobert Viola H Lobert Centre for Cancer Biomedicine, Faculty of Medicine, Oslo University Hospital, Oslo, Norway Department of Biochemistry, Institute for Cancer Research, Oslo University Hospital, Norway Institute for Cancer Research and Molecular Medicine, Norwegian University of Science and Technology, Trondheim, Norway Search for more papers by this author Jarle Bruun Jarle Bruun Centre for Cancer Biomedicine, Faculty of Medicine, Oslo University Hospital, Oslo, Norway Department of Cancer Prevention, Institute for Cancer Research, Oslo University Hospital, Norway Search for more papers by this author Hilde Abrahamsen Hilde Abrahamsen Centre for Cancer Biomedicine, Faculty of Medicine, Oslo University Hospital, Oslo, Norway Department of Biochemistry, Institute for Cancer Research, Oslo University Hospital, Norway Search for more papers by this author Ragnhild A Lothe Ragnhild A Lothe Centre for Cancer Biomedicine, Faculty of Medicine, Oslo University Hospital, Oslo, Norway Department of Cancer Prevention, Institute for Cancer Research, Oslo University Hospital, Norway Search for more papers by this author Harald Stenmark Harald Stenmark Centre for Cancer Biomedicine, Faculty of Medicine, Oslo University Hospital, Oslo, Norway Department of Biochemistry, Institute for Cancer Research, Oslo University Hospital, Norway Institute for Cancer Research and Molecular Medicine, Norwegian University of Science and Technology, Trondheim, Norway Search for more papers by this author Matthias Kolberg Matthias Kolberg Centre for Cancer Biomedicine, Faculty of Medicine, Oslo University Hospital, Oslo, Norway Department of Cancer Prevention, Institute for Cancer Research, Oslo University Hospital, Norway Search for more papers by this author Coen Campsteijn Coen Campsteijn Centre for Cancer Biomedicine, Faculty of Medicine, Oslo University Hospital, Oslo, Norway Department of Biochemistry, Institute for Cancer Research, Oslo University Hospital, Norway Search for more papers by this author Author Information Viola H Lobert1,2,3, Jarle Bruun1,4, Hilde Abrahamsen1,2, Ragnhild A Lothe1,4, Harald Stenmark1,2,3, Matthias Kolberg1,4 and Coen Campsteijn1,2 1Centre for Cancer Biomedicine, Faculty of Medicine, Oslo University Hospital, Oslo, Norway 2Department of Biochemistry, Institute for Cancer Research, Oslo University Hospital, Norway 3Institute for Cancer Research and Molecular Medicine, Norwegian University of Science and Technology, Trondheim, Norway 4Department of Cancer Prevention, Institute for Cancer Research, Oslo University Hospital, Norway EMBO Reports (2013)14:10-11https://doi.org/10.1038/embor.2012.188 There is a Correspondence (June 2013) associated with this Correspondence. PDFDownload PDF of article text and main figures. ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InMendeleyWechatReddit Figures & Info During recent years, the PH domain leucine-rich repeat protein phosphatase 1 (PHLPP1) has received increasing attention as a tumour suppressor that functions by dephosphorylating and antagonizing the survival-promoting protein kinases AKT, PKC and S6K1 [1]. Previous studies reported that PHLPP1 co-localizes with the tumour suppressor Scribble at cell–cell contacts [2], its expression is lost in colorectal cancer tumours [3] and it correlates with expression of PTEN, a tumour suppressor phosphatase that functions as a negative regulator upstream from AKT [2,4]. We warn that the PHLPP1 antibodies used in these studies (Bethyl IHC-00382 and A300-660A) crossreact strongly with β-catenin, a proto-oncogene product known to localize to adherens junctions. When probing Caco-2 whole cell lysates (WCLs) for PHLPP1 with commonly used commercial PHLPP1 antibodies (Bethyl IHC-00382 and A300-660A—different types of the same antibody), we observed an additional prominent immunoreactive band around 90 kDa (Fig 1C), which was still apparent on PHLPP1 immunoprecipitation using the same antibodies (Fig 1A). In contrast with full length PHLPP1, the 90 kDa band was not responsive to siRNA-mediated knockdown of PHLPP1 (Fig 1A,C), arguing against a PHLPP1 variant and suggesting it reflected antibody crossreactivity. To characterize further this putative crossreactivity, we used stable isotope labelling in cell culture and performed quantitative tandem mass spectrometry on PHLPP1 immunoprecipitates (Fig 1A). The oncogenic WNT-signalling component β-catenin was identified as the most prominent specifically purified protein—37.5% sequence coverage compared with 4.5% for PHLPP1; data not shown—having a reported molecular weight of 90 kDa. Indeed, β-catenin comigrated with the PHLPP1 antibody crossreactivity in WCL and PHLPP1 immunoprecipitates (Fig 1B,C). Conversely, the PHLPP1 antibody strongly recognized a 90 kDa species in β-catenin immunoprecipitates, (Fig 1B) further substantiating β-catenin as the underlying crossreactivity. To exclude alternative explanations, we performed siRNA-mediated knockdown of PHLPP1 and β-catenin. PHLPP1 antibody crossreactivity at 90 kDa was strongly reduced after β-catenin knockdown without affecting full-length PHLPP1 levels (Fig 1C). β-catenin levels in PHLPP1 immunoprecipitates were not affected by PHLPP1 knockdown (Fig 1B). This argued against a prominent physiological direct association of PHLPP1 and β-catenin and thus explained the immunoreactivity (Fig 1A). Our observations were reproducible in other cell lines (HeLa and 293T), excluding the existence of Caco-2-specific artefacts. Figure 1.PH domain leucine-rich repeat protein phosphatase 1 antibodies crossreact with β-catenin. (A) Characterization of immunoreactivity of the PH domain leucine-rich repeat protein phosphatase 1 (PHLPP1) antibody Bethyl A300-660A indicates the presence of an additional prominent 90 kDa immunoreactivity as indicated with an asterisk. For quantitative mass spectrometry, Caco-2 cells were labelled with light (L, K0R0) or heavy (H, K6R10) isotopes for seven days and lysates were used for control (IgG) or A300-660A immunoprecipitation. Immunoprecipitates were pooled and processed for mass spectrometry (see text). (B) Crossreactivity of A300-660A with β-catenin. Caco-2 cells were transfected with control PHLPP1 or β-catenin siRNAs. Lysates were subjected to immunoprecipitation with control IgGs, PHLPP1 (A300-660A) or β-catenin (BD Biosciences, 610154) antibodies, and immunoblots were probed with the same antibodies. Bottom panel; dual colour visualization of the same blot, scanned by using the Odyssey dual colour imaging system with PHLPP1 in red and β-catenin in green as indicated. (C) PHLPP1 antibodies A300-660A (left panel) and IHC-00382 (right panel) show the same immunoreactivity in whole cell lysates. siRNA treatment of Caco-2 cells indicates that the 90 kDa crossreactivity (asterisk) is highly sensitive to β-catenin knockdown but not to PHLPP1 knockdown, with β-actin used as a loading control. (D) Immunostaining by using methanol fixation of PHLPP1 (IHC-00382) and β-catenin (BD Biosciences, 610154) in β-catenin-depleted Caco-2 cells. Asterisks indicate successfully depleted cells. Scale bar, 10 μm. Immunohistochemical staining of PHLPP1, by using PHLPP1 (IHC-00382) and β-catenin (BD Biosciences, 610154) antibodies in colorectal tumours, shows plasma membrane staining (E) and nuclear staining (F). Download figure Download PowerPoint These results raise concern for the potential contaminating effects of β-catenin, a known membrane-targeted factor, for localization studies of PHLPP1. Indeed, in confluent Caco-2 cells, we observed complete co-localization of PHLPP1 (IHC-00382) with β-catenin by immunofluorescence (Fig 1D). Strikingly, cells in which β-catenin levels had been depleted by siRNA (as indicated with an asterisk in Fig 1) lost PHLPP1 staining at cell–cell contact, whereas PHLPP1 staining remained prominent in cells that had poor β-catenin knockdown. Immunohistochemical staining of PHLPP1 and β-catenin within 5 μm sections of each other, from a tissue microarray of primary colorectal carcinomas (n = 742; [5]), revealed a similar staining pattern with the two antibodies (Fig 1E) and, correspondingly, a non-physiologically strong correlation between PHLPP1 and β-catenin on membranes (p-value 2 × 10−64; Fig 1E) and in nuclear staining (p-value 1 × 10−14; Fig 1F). Collectively, these results confirm the strong crossreactivity of PHLPP1 antibodies Bethyl IHC-00382 and A300-660A with β-catenin, making it impossible to conclude the intracellular localization of PHLPP1 using these antibodies. Although the cause of crossreactivity remains uncertain, we note that the PHLPP1-derived antigen used for immunization bears substantial sequential homology to the carboxyl terminus of β-catenin—74% similarity over eight amino acids. As in situ analysis of the expression of potential biomarkers in patient tumours is used to correlate expression or localization with patient survival, it is important that the antibodies used in such studies are specific for the protein of interest. Given the localization of β-catenin and its implication in a wide variety of tumours, including those that are the focus of PHLPP1 studies, our observations strongly warn against the use of the antibodies Bethyl IHC-00382 and A300-660A in studies probing PHLPP1 function and inferring prognostic value to cellular PHLPP1 dynamics in tumour progression. Acknowledgements We thank Bernd Thiede and Magnus Arntzen (The Biotechnology Centre of Oslo, Norway) for help with mass spectrometry experiments. Conflict of Interest The authors declare that they have no conflict of interest. Biography Viola H Lobert, Jarle Bruun, Hilde Abrahamsen, Ragnhild A Lothe, Harald Stenmark, Matthias Kolberg and Coen Campsteijn are at the Centre for Cancer Biomedicine, Faculty of Medicine, Oslo University Hospital, Oslo, Norway. E-mail: [email protected]Viola H Lobert, Hilde Abrahamsen, Harald Stenmark and Coen Campsteijn are also at the Department of Biochemistry, Institute for Cancer Research, Oslo University Hospital, Norway.Viola H Lobert and Harald Stenmark are additionally at the Institute for Cancer Research and Molecular Medicine, Norwegian University of Science and Technology, Trondheim, Norway.Jarle Bruun, Ragnhild A Lothe and Matthias Kolberg are also at the Department of Cancer Prevention, Institute for Cancer Research, Oslo University Hospital, Norway. 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Ligand‐mediated lysosomal degradation of growth factor receptors, mediated by the endosomal sorting complex required for transport (ESCRT) machinery, is a mechanism that attenuates the cellular response to growth factors. In this article, we present a novel regulatory mechanism that involves ligand‐mediated degradation of a key component of the sorting machinery itself. We have investigated the endosomal localization of subunits of the four ESCRTs—Hrs (ESCRT‐0), Tsg101 (ESCRT‐I), EAP30/Vps22 (ESCRT‐II) and charged multivesicular body protein 3/Vps24 (ESCRT‐III). All the components were detected on the limiting membrane of multivesicular endosomes (MVEs). Surprisingly, however, Tsg101 and other ESCRT‐I subunits were also detected within intraluminal vesicles (ILVs) of MVEs. Tsg101 was sequestered along with cargo during endosomal sorting into ILVs and further degraded in lysosomes. Importantly, ESCRT‐mediated downregulation of two distinct cargoes, epidermal growth factor receptor (EGFR) and connexin43, mutually made cells refractory to degradation of the other cargo. Our observations indicate that the degradation of a key ESCRT component along with cargo represents a novel feedback control of endosomal sorting by preventing collateral degradation of cell surface receptors following stimulation of one specific pathway.

The endosomal sorting complex required for transport (ESCRT) machinery has been implicated in the regulation of endosomal sorting, cell division, viral budding, autophagy, and cell signaling. Here, we review recent evidence that implicates ESCRTs in cell polarity and cell migration, and discuss the potential role of ESCRTs as tumor suppressors.