GABARAPL1 is required for increased EGFR membrane expression during hypoxia

Identification of mitophagy-related genes in patients with acute myocardial infarction

Mitophagy is involved in acute myocardial infarction (AMI) process. However, the role of mitophagy-related genes (MRGs) in the AMI process is not well illustrated. We identified MRGs involved in AMI by bioinformatics analysis. The external datasets were employed for the validation of the MRGs, alongside the execution of cellular and animal experiments. Forty-five MRGs were detected, and machine learning identified the top four hub genes, namely ALDH2, ACSL1, IL1B, and GABARAPL1. Additionally, an external validation set was used to screen for three diagnostic markers (ACSL1, IL1B, and GABARAPL1) among these hub genes. Immune infiltration analysis revealed changes in the immune microenvironment among patients with AMI. Finally, the significant upregulation of ACSL1, IL1B, and GABARAPL1 in both cellular and animal models was confirmed. The occurrence of mitophagy was observed in the cell model through transmission electron microscopy (TEM). Our study demonstrated that ACSL1, IL1B, and GABARAPL1 possess potential biomarkers for AMI.

A new perspective on the autophagic and non-autophagic functions of the GABARAP protein family: a potential therapeutic target for human diseases

Mammalian autophagy-related protein Atg8, including the LC3 subfamily and GABARAP subfamily. Atg8 proteins play a vital role in autophagy initiation, autophagosome formation and transport, and autophagy-lysosome fusion. GABARAP subfamily proteins (GABARAPs) share a high degree of homology with LC3 family proteins, and their unique roles are often overlooked. GABARAPs are as indispensable as LC3 in autophagy. Deletion of GABARAPs fails autophagy flux induction and autophagy lysosomal fusion, which leads to the failure of autophagy. GABARAPs are also involved in the transport of selective autophagy receptors. They are engaged in various particular autophagy processes, including mitochondrial autophagy, endoplasmic reticulum autophagy, Golgi autophagy, centrosome autophagy, and dorphagy. Furthermore, GABARAPs are closely related to the transport and delivery of the inhibitory neurotransmitter γ-GABAA and the angiotensin II AT1 receptor (AT1R), tumor growth, metastasis, and prognosis. GABARAPs also have been confirmed to be involved in various diseases, such as cancer, cardiovascular disease, and neurodegenerative diseases. In order to better understand the role and therapeutic potential of GABARAPs, this article comprehensively reviews the autophagic and non-autophagic functions of GABARAPs, as well as the research progress of the role and mechanism of GABARAPs in cancer, cardiovascular diseases and neurodegenerative diseases. It emphasizes the significance of GABARAPs in the clinical prevention and treatment of diseases, and may provide new therapeutic ideas and targets for human diseases. GABARAP and GABARAPL1 in the serum of cancer patients are positively correlated with the prognosis of patients, which can be used as a clinical biomarker, predictor and potential therapeutic target.

GABARAPL1 is essential in extracellular vesicle cargo loading and metastasis development

BACKGROUND AND PURPOSE

Hypoxia is a common feature of tumours, associated with poor prognosis due to increased resistance to radio- and chemotherapy and enhanced metastasis development. Previously we demonstrated that GABARAPL1 is required for the secretion of extracellular vesicles (EV) with pro-angiogenic properties during hypoxia. Here, we explored the role of GABARAPL1+ EV in the metastatic cascade.

MATERIALS AND METHODS

GABARAPL1 deficient or control MDA-MB-231 cells were injected in murine mammary fat pads. Lungs were dissected and analysed for human cytokeratin 18. EV from control and GABARAPL1 deficient cells exposed to normoxia (21% O2) or hypoxia (O2 < 0.02%) were isolated and analysed by immunoblot, nanoparticle tracking analysis, high resolution flow cytometry, mass spectrometry and next-generation sequencing. Cellular migration and invasion were analysed using scratch assays and transwell-invasion assays, respectively.

RESULTS

The number of pulmonary metastases derived from GABARAPL1 deficient tumours decreased by 84%. GABARAPL1 deficient cells migrate slower but display a comparable invasive capacity. Both normoxic and hypoxic EV contain proteins and miRNAs associated with metastasis development and, in line, increase cancer cell invasiveness. Although GABARAPL1 deficiency alters EV content, it does not alter the EV-induced increase in cancer cell invasiveness.

CONCLUSION

GABARAPL1 is essential for metastasis development. This is unrelated to changes in migration and invasion and suggests that GABARAPL1 or GABARAPL1+ EV are essential in other processes related to the metastatic cascade.

Unlocking the gate to GABARAPL2

GABARAPL2 was initially characterized for its involvement in protein transport and membrane fusion events, but has since gained notoriety for its role in autophagy. GABARAPL2 is frequently studied alongside its GABARAP subfamily members, GABARAP and GABARAPL1. Although functional redundancy exists among the subfamily members, a complex network of molecular interactions, physiological processes and pathologies can be primarily related to GABARAPL2. GABARAPL2 has a multifaceted role, ranging from cellular differentiation to intracellular degradation. Much of what we know about GABARAPL2 is gained through identifying its interacting partners-a list that is constantly growing. In this article, we review both the autophagy-dependent and autophagy-independent roles of GABARAPL2, and emphasize their implications for both health and disease.

Does GEC1 Enhance Expression and Forward Trafficking of the Kappa Opioid Receptor (KOR) via Its Ability to Interact with NSF Directly?

We reported previously that GEC1 (glandular epithelial cell 1), a member of microtubule-associated proteins (MAPs), interacted directly with the C-tail of KOR (KCT) and tubulin and enhanced cell surface expression of KOR in CHO cells by facilitating its trafficking along the export pathway. Two GEC1 analogs (GABARAP and GATE16) were also shown to increase KOR expression. In addition, to understand the underlying mechanism, we demonstrated that N-ethylmaleimide-sensitive factor (NSF), an essential component for membrane fusion, co-immunoprecipitated with GEC1 from brain extracts. In this study, using pull-down techniques, we have found that (1) GEC1 interacts with NSF directly and prefers the ADP-bound NSF to the ATP-bound NSF; (2) D1 and/or D2 domain(s) of NSF interact with GEC1, but the N domain of NSF does not; (3) NSF does not interact with KCT directly, but forms a protein complex with KCT via GEC1; (4) NSF and/or α-SNAP do not affect KCT-GEC1 interaction. Thus, GEC1 (vs the α-SNAP/SNAREs complex) binds to NSF in distinctive ways in terms of the ADP- or ATP-bound form and domains of NSF involved. In conclusion, GEC1 may, via its direct interactions with KOR, NSF, and tubulin, enhance trafficking and fusion of KOR-containing vesicles selectively along the export pathway, which leads to increase in surface expression of KOR. GABARAP and GATE16 may enhance KOR expression in a similar way.

Secretion of pro-angiogenic extracellular vesicles during hypoxia is dependent on the autophagy-related protein GABARAPL1

Tumour hypoxia is a hallmark of solid tumours and contributes to tumour progression, metastasis development and therapy resistance. In response to hypoxia, tumour cells secrete pro-angiogenic factors to induce blood vessel formation and restore oxygen supply to hypoxic regions. Extracellular vesicles (EVs) are emerging as mediators of intercellular communication in the tumour microenvironment. Here we demonstrate that increased expression of the LC3/GABARAP protein family member GABARAPL1, is required for endosomal maturation, sorting of cargo to endosomes and the secretion of EVs. Silencing GABARAPL1 results in a block in the early endosomal pathway and impaired secretion of EVs with pro-angiogenic properties. Tumour xenografts of doxycycline inducible GABARAPL1 knockdown cells display impaired vascularisation that results in decreased tumour growth, elevated tumour necrosis and increased therapy efficacy. Moreover, our data show that GABARAPL1 is expressed on the EV surface and targeting GABARAPL1+ EVs with GABARAPL1 targeting antibodies results in blockade of pro-angiogenic effects in vitro. In summary, we reveal that GABARAPL1 is required for EV cargo loading and secretion. GABARAPL1+ EVs are detectable and targetable and are therefore interesting to pursue as a therapeutic target.

Prognostic Autophagy-Related Genes of Gastric Cancer Patients on Chemotherapy

Background: Chemotherapy resistance based on fluorouracil and cisplatin is one of the most encountered postoperative clinical problems in patients diagnosed with gastric cancer (GC), resulting in poor prognosis. Aim of the Study: This study aimed to combine autophagy-related genes (ARGs) to investigate the susceptibility patients with GC to postoperative chemotherapy. Methods: Based on The Cancer Genome Atlas (TCGA) database, gene expression data for GC patients undergoing chemotherapy were integrated and analyzed. Prognostic genes were screened based on univariate and multivariate analysis regression analysis. Subjects were divided into high-risk and low-risk groups according to the median risk score. Kaplan-Meier method was used to evaluate OS and DFS. The accuracy of the prediction was determined by the subject operating characteristic curve analysis. In addition, stratified analyses based on different clinical variables was performed to assess the correlation between risk scores and clinical variables. Quantitative real-time (qRT) PCR was used to verify the expression of CXCR4 in GC tissues and cell lines. Results: A total of nine ARGs related to the prognosis of chemotherapy patients were screened out. Compared with normal gastric mucosa cell, CXCR4 showed elevated expression in GC and was significantly associated with survival. Based on GEO and TCGA databases, the model accurately predicted DFS and OS after chemotherapy. Conclusion: This study established prognostic markers based on nine genes, predicting that ARGs are related to chemotherapy susceptibility of GC patients, which can provide better individualized treatment regimens for clinical practice.

The functions of Atg8-family proteins in autophagy and cancer: linked or unrelated?

The Atg8-family proteins are subdivided into two subfamilies: the GABARAP and LC3 subfamilies. These proteins, which are major players of the autophagy pathway, present a conserved glycine in their C-terminus necessary for their association to the autophagosome membrane. This family of proteins present multiple roles from autophagy induction to autophagosome-lysosome fusion and have been described to play a role during cancer progression. Indeed, GABARAPs are described to be downregulated in cancers, and high expression has been linked to a good prognosis. Regarding LC3 s, their expression does not correlate to a particular tumor type or stage. The involvement of Atg8-family proteins during cancer, therefore, remains unclear, and it appears that their anti-tumor role may be associated with their implication in selective protein degradation by autophagy but might also be independent, in some cases, of their conjugation to autophagosomes. In this review, we will then focus on the involvement of GABARAP and LC3 subfamilies during autophagy and cancer and highlight the similarities but also the differences of action of each subfamily member.Abbreviations: AIM: Atg8-interacting motif; AMPK: adenosine monophosphate-associated protein kinase; ATG: autophagy-related; BECN1: beclin 1; BIRC6/BRUCE: baculoviral IAP repeat containing 6; BNIP3L/NIX: BCL2 interacting protein 3 like; GABARAP: GABA type A receptor-associated protein; GABARAPL1/2: GABA type A receptor associated protein like 1/2; GABRA/GABAA: gamma-aminobutyric acid type A receptor subunit; LAP: LC3-associated phagocytosis; LMNB1: lamin B1; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MTOR: mechanistic target of rapamycin kinase; PI4K2A/PI4KIIα: phosphatidylinositol 4-kinase type 2 alpha; PLEKHM1: plecktrin homology and RUN domain containing M1; PtdIns3K-C1: class III phosphatidylinositol 3-kinase complex 1; SQSTM1: sequestosome 1; ULK1: unc51-like autophagy activating kinase 1.

Oxygen Deprivation Modulates EGFR and PD-L1 in Squamous Cell Carcinomas of the Head and Neck

Abundance and signaling of the epidermal growth factor receptor (EGFR) and programmed cell death protein ligand 1 (PD-L1) in head and neck squamous cell carcinoma (HNSCC) are not only genetically determined but are also subject to the traits of the tumor microenvironment, which has hitherto not been clarified completely. We investigated the impact of hypoxia on the EGFR system and on PD-L1 in six HPV negative HNSCC cell lines in vitro and in FaDu xenografts in vivo. Protein levels of EGFR, AKT, pAKT, ERK1/2, pERK1/2, CA IX, cleaved PARP (apoptosis), LC3B (autophagy), and PD-L1 were quantified by western blot after oxygen deprivation or CoCl₂, staurosporine, and erlotinib treatment. In FaDu xenograft tumors the expression of EGFR, CA IX andCD34 staining were analyzed. Reduced oxygen supply strongly downregulated EGFR protein levels and signaling in FaDu cells in vitro and in vivo, and a transient downregulation of EGFR signaling was found in three other HNSCC cell lines. PD-L1 was affected by oxygen deprivation in only one HNSCC cell line showing increased protein amounts. The results of this study indicate a significant impact of the traits of the tumor microenvironment on crucial molecular targets of cancer therapies with high clinical relevance for therapy resistance and response in HNSCC.

Deficiency of GABARAP but not its Paralogs Causes Enhanced EGF-induced EGFR Degradation

The γ-aminobutyric acid type A receptor-associated protein (GABARAP) and its close paralogs GABARAPL1 and GABARAPL2 constitute a subfamily of the autophagy-related 8 (Atg8) protein family. Being associated with a variety of dynamic membranous structures of autophagic and non-autophagic origin, Atg8 proteins functionalize membranes by either serving as docking sites for other proteins or by acting as membrane tethers or adhesion factors. In this study, we describe that deficiency for GABARAP alone, but not for its close paralogs, is sufficient for accelerated EGF receptor (EGFR) degradation in response to EGF, which is accompanied by the downregulation of EGFR-mediated MAPK signaling, altered target gene expression, EGF uptake, and EGF vesicle composition over time. We further show that GABARAP and EGFR converge in the same distinct compartments at endogenous GABARAP expression levels in response to EGF stimulation. Furthermore, GABARAP associates with EGFR in living cells and binds to synthetic peptides that are derived from the EGFR cytoplasmic tail in vitro. Thus, our data strongly indicate a unique and novel role for GABARAP during EGFR trafficking.

Iron deficiency-induced loss of skeletal muscle mitochondrial proteins and respiratory capacity; the role of mitophagy and secretion of mitochondria-containing vesicles

Iron homeostasis is essential for mitochondrial function, and iron deficiency has been associated with skeletal muscle weakness and decreased exercise capacity in patients with different chronic disorders. We hypothesized that iron deficiency-induced loss of skeletal muscle mitochondria is caused by increased mitochondrial clearance. To study this, C2C12 myotubes were subjected to the iron chelator deferiprone. Mitochondrial parameters and key constituents of mitophagy pathways were studied in presence or absence of pharmacological autophagy inhibition or knockdown of mitophagy-related proteins. Furthermore, it was explored if mitochondria were present in extracellular vesicles (EV). Iron chelation resulted in an increase in BCL2/Adenovirus E1B 19 kDa protein-interacting protein 3 (BNIP3) and BNIP3-like gene and protein levels, and the appearance of mitochondria encapsulated by lysosome-like vesicular structures in myotubes. Moreover, mitochondria were secreted via EV. These changes were associated with cellular mitochondrial impairments. These impairments were unaltered by autophagy inhibition, knockdown of mitophagy-related proteins BNIP3 and BNIP3L, or knockdown of their upstream regulator hypoxia-inducible factor 1 alpha. In conclusion, mitophagy is not essential for development of iron deficiency-induced reductions in mitochondrial proteins or respiratory capacity. The secretion of mitochondria-containing EV could present an additional pathway via which mitochondria can be cleared from iron chelation-exposed myotubes.

Lysosomal Pathways and Autophagy Distinctively Control Endothelial Cell Behavior to Affect Tumor Vasculature

Cancer cell-stromal cell crosstalk is orchestrated by a plethora of ligand-receptor interactions generating a tumor microenvironment (TME) which favors tumor growth. The high pro-angiogenic nature of the TME perpetuates the chaotic network of structurally immature, low pericyte-covered vessels characteristic of the tumor vasculature. We previously demonstrated that chloroquine (CQ) -a lysosomotropic agent used as first-generation autophagy blocker in clinical trials- induced tumor vessel normalization and reduced tumor hypoxia. CQ improved both vessel structure and maturation, whereas the conditional knockout of the crucial autophagy gene Atg5 in endothelial cells (ECs) did not, thus highlighting a potential differential role for EC-associated autophagy and the lysosomes in pathological tumor angiogenesis. However, how CQ or ATG5-deficiency in ECs affect angiogenic signals regulating EC-pericyte interface and therefore vessel maturation, remains unknown. Here, we show that in ECs CQ constrained VEGF-A-mediated VEGF receptor (VEGFR)2 phosphorylation, a driver of angiogenic signaling. In the presence of CQ we observed increased expression of the decoy receptor VEGFR1 and of a lower molecular weight form of VEGFR2, suggesting receptor cleavage. Consequently, VEGF-A-driven EC spheroid sprouting was reduced by CQ treatment. Furthermore, CQ significantly affected the transcription and secretion of platelet-derived growth factor (PDGF)-AB/BB (upregulated) and Endothelin-1 (EDN1, downregulated), both modulators of perivascular cell (PC) behavior. In contrast, silencing of ATG5 in ECs had no effect on VEGFR2 to VEGFR1 ratio nor on PDGFB and EDN1 expression. Accordingly, mice harboring B16F10 melanoma tumors treated with CQ, displayed both an increased number of αSMA⁺ PCs covering tumor vessels and co-expressed PDGF receptor-β, enabling PDGF ligand dependent recruitment. Moreover, upon CQ treatment the tumoral expression of angiopoietin-1 (Angpt1), which retains mural cells, and induces vessel stabilization by binding to the EC-localized cognate receptor (TIE2), was increased thus supporting the vessel normalization function of CQ. These features associated with improved tumor vasculature were not phenocopied by the specific deletion of Atg5 in ECs. In conclusion, this study further unravels endothelial cell autonomous and non-autonomous mechanisms by which CQ “normalizes” the intercellular communication in the tumor vasculature independent of autophagy.

Hypoxia-induced autophagy promotes EGFR loss in specific cell contexts, which leads to cell death and enhanced radiosensitivity

Treatment failure through radioresistance of tumors is associated with activation of the epidermal growth factor receptor (EGFR). Tumor cell proliferation, DNA-repair, hypoxia and metastases-formation are four mechanisms in which EGFR signaling has an important role. However, the effect of hypoxia on EGFR expression is still controversial. In this study, we demonstrated that hypoxia enhanced EGFR expression and sustained cell survival in SiHa, CAL 27 and A549 cells at both low and high cell desnities, while in MCF-7, MDA-MB-231 and HeLa cells, EGFR and cell survival were regulated by hypoxic treatment in a cell-density dependent manner: upregulated at low cell density and downregulated at high cell density. In MCF-7 and HeLa xenografts in nude mice, EGFR expression varied inversely with the pimonidazole level that was used as an indicator of hypoxia, accordant with the effect of hypoxia at high cell density in vitro. Hypoxia induced more remarkable cell autophagy at high cell density than at low cell density. Autophagy inhibitor 3MA, rather than proteasome inhibitor MG132 inhibited hypoxia-mediated EGFR loss and shifted cell death to cell survival in HeLa cells. The MCF7 cells' sensitivity to ionizing radiation (IR) under hypoxia was also conditional on the cell densities when the hypoxia treatment was introduced, inversely associated with the expression levels of EGFR. Altogether, hypoxia can decrease EGFR expression in some cell lines by enhancing autophagy at high cell density, leading to cell death and hypersensitivity to radiotherapy. This study may help to understand how hypoxia influences EGFR expression and radiosensitivity.

GABARAPL1 acts as a potential marker and promotes tumor proliferation and metastasis in triple negative breast cancer

GABAA-receptor-associated protein like-1 (GABARAPL1) is involved in a variety of cancers. The purpose of this study was to investigate the expression, prognostic roles and functions of GABARAPL1 in triple negative breast cancer (TNBC). Quantitative real-time PCR (qRT-PCR) showed that GABARAPL1 was up regulated in both TNBC cell lines and clinical TNBC tissues. High GABARAPL1 expression level was associated with shorter overall survival (OS) and disease free survival (DFS). Furthermore, inhibition of GABARAPL1 suppressed cell proliferation, tumorigenesis, invasion and metastasis, and induced cell apoptosis. We found that metadherin (MTDH) was a downstream target of GABARAPL1. Inhibition of GABARAPL1 suppressed the mRNA and protein expression of MTDH, and overexpression of MTDH could reverse the effects of GABARAPL1 inhibition, which meant GABARAPL1 performed its function partly through MTDH. Our findings demonstrate that GABARAPL1 acts as a tumor promoter in TNBC partly through MTDH. Targeting at GABARAPL1 could be a potential therapeutic strategy for TNBC.

Direct binding to GABARAP family members is essential for HIV-1 Nef plasma membrane localization

HIV-1 Nef is an important pathogenic factor for HIV/AIDS pathogenesis. Studies have shown that the association of Nef with the inner leaflet of the plasma membrane and with endocytic and perinuclear vesicles is essential for most activities of Nef. Using purified recombinant proteins in pull-down assays and by co-immunoprecipitation assays we demonstrate that Nef binds directly and specifically to all GABARAP family members, but not to LC3 family members. Based on nuclear magnetic resonance (NMR) experiments we showed that Nef binds to GABARAP via two surface exposed hydrophobic pockets. S53 and F62 of GABARAP were identified as key residues for the interaction with Nef. During live-cell fluorescence microscopy an accumulation of Nef and all GABARAP family members in vesicular structures throughout the cytoplasm and at the plasma membrane was observed. This plasma membrane accumulation was significantly reduced after knocking down GABARAP, GABARAPL1 and GABARAPL2 with respective siRNAs. We identified GABARAPs as the first known direct interaction partners of Nef that are essential for its plasma membrane localization.

Autophagy-Dependent Secretion: Contribution to Tumor Progression

Autophagy is best known as a lysosomal degradation and recycling pathway to maintain cellular homeostasis. During autophagy, cytoplasmic content is recognized and packed in autophagic vacuoles, or autophagosomes, and targeted for degradation. However, during the last years, it has become evident that the role of autophagy is not restricted to degradation alone but also mediates unconventional forms of secretion. Furthermore, cells with defects in autophagy apparently are able to reroute their cargo, like mitochondria, to the extracellular environment; effects that contribute to an array of pathologies. In this review, we discuss the current knowledge of the physiological roles of autophagy-dependent secretion, i.e., the effect on inflammation and insulin/hormone secretion. Finally, we focus on the effects of autophagy-dependent secretion on the tumor microenvironment (TME) and tumor progression. The autophagy-mediated secreted factors may stimulate cellular proliferation via auto- and paracrine signaling. The autophagy-mediated release of immune modulating proteins changes the immunosuppresive TME and may promote an invasive phenotype. These effects may be either direct or indirect through facilitating formation of the mobilized vesicle, aid in anterograde trafficking, or alterations in homeostasis and/or autonomous cell signaling.

LC3/GABARAP family proteins: autophagy-(un)related functions

From yeast to mammals, autophagy is an important mechanism for sustaining cellular homeostasis through facilitating the degradation and recycling of aged and cytotoxic components. During autophagy, cargo is captured in double-membraned vesicles, the autophagosomes, and degraded through lysosomal fusion. In yeast, autophagy initiation, cargo recognition, cargo engulfment, and vesicle closure is Atg8 dependent. In higher eukaryotes, Atg8 has evolved into the LC3/GABARAP protein family, consisting of 7 family proteins [LC3A (2 splice variants), LC3B, LC3C, GABARAP, GABARAPL1, and GABARAPL2]. LC3B, the most studied family protein, is associated with autophagosome development and maturation and is used to monitor autophagic activity. Given the high homology, the other LC3/GABARAP family proteins are often presumed to fulfill similar functions. Nevertheless, substantial evidence shows that the LC3/GABARAP family proteins are unique in function and important in autophagy-independent mechanisms. In this review, we discuss the current knowledge and functions of the LC3/GABARAP family proteins. We focus on processing of the individual family proteins and their role in autophagy initiation, cargo recognition, vesicle closure, and trafficking, a complex and tightly regulated process that requires selective presentation and recruitment of these family proteins. In addition, functions unrelated to autophagy of the LC3/GABARAP protein family members are discussed.-Schaaf, M. B. E., Keulers, T. G, Vooijs, M. A., Rouschop, K. M. A. LC3/GABARAP family proteins: autophagy-(un)related functions.

Nuclear EGFR renders cells radio-resistant by binding mRNA species and triggering a metabolic switch to increase lactate production

BACKGROUND AND PURPOSE

EGFR is translocated into the cell nucleus in response to irradiation, where it is involved in regulation of radio-sensitivity. The aim of this study is to elucidate the functional role of nuclear EGFR.

MATERIAL AND METHODS

To identify EGFR-bound nuclear proteins and mRNAs, Maldi-TOF analysis and mRNA gene arrays were used. Complex formation of proteins was shown by confocal microscopy, immunoprecipitation and Western blotting. The effect of EGFR binding to mRNAs was exhibited by quantitative RT-PCR. Cellular endpoints were shown by Western blotting, mitochondrial mass quantification, lactate quantification and clonogenic survival assays.

RESULTS

Maldi-TOF analysis of proteins bound to nuclear EGFR in response to irradiation showed colocalization with Lamin A and heterogeneous nuclear ribonucleoproteins. Confocal microscopy and Western blotting confirmed this colocalization. Both Lamin A and heterogeneous nuclear ribonucleoproteins are involved in mRNA processing. To support a role of nEGFR in this context after irradiation, we isolated EGFR-bound mRNA and observed an EGFR kinase-dependent mRNA stabilizing effect. With the help of DNA microarrays, we identified mRNAs associated with the Warburg effect that were bound to nuclear EGFR. In this context, we observed radiation-induced HIF1α expression, which triggers inhibition of pyruvate dehydrogenase and blocks the tricarboxylic acid cycle. Consequently, we detected mitophagy and increased lactate production, which is associated with increased treatment resistance. Reduction of nEGFR decreased radiation-induced expression of Hif1α and lactate production.

CONCLUSIONS

We showed that nuclear EGFR selectively binds and stabilizes mRNA involved in the Warburg effect in response to irradiation. As a consequence, cells switch from aerobic to anaerobic glucose metabolism, which can be prevented by HIF1α inhibitor BAY87-2243, Dasatinib, Erlotinib or EGFR siRNA.