p53-Mediated Mitochondrial Translocation of EI24 Triggered by ER Stress Plays an Important Role in Arsenic-Induced Liver Damage via Activating Mitochondrial Apoptotic Pathway

Chronic arsenic poisoning is a public health problem worldwide. In addition to skin lesions, the detrimental effect of arsenic poisoning on liver damage is one of the major issues. Our previous studies demonstrated that endoplasmic reticulum (ER) stress and p53 were associated with arsenic-induced liver damage. Literature has shown that EI24 is involved in hepatocyte hypertrophy; however, the underlying role and mechanism in arsenic-induced liver damage have not been fully elucidated. In this study, we explored the role of ER stress, p53, and EI24 as well as the regulatory relationship in arsenic poisoning populations and L-02 cells treated with distinct concentration NaAsO2 (2.5, 5, 10, and 20 μM). Results showed that as with arsenic dose increment, expression levels of ER stress key proteins GRP78, ATF4, and CHOP were significantly enhanced. Additionally, p53 expression in nucleus, p53 phosphorylation at Ser15 and Ser1392, and p53 acetylation at lys382 were significantly increased in NaAsO2-treated L-02 cells. ER stress inhibitor 4-phenylbutyric acid (4-PBA) decreased the expression of p53 phosphorylation at Ser 392, p53 acetylation at lys382, and p53 expression in nucleus. Additionally, in 5 μM NaAsO2 condition, p53 inhibitor pifithrin-α (PFT-α) aggravated 5 μM NaAsO2-induced GRP78, ATF4, and CHOP expressions, cell apoptosis, and protein-SH consumption. But in 20 μM NaAsO2 condition, PFT-α attenuated NaAsO2-induced cell apoptosis. Further results showed that 20 μM NaAsO2 facilitated translocation of EI24 from ER to mitochondrion and interaction with VDAC2, leading to activate mitochondrial apoptotic pathway, but not observed in the 5-μM NaAsO2 group. Moreover, PFT-α and 4-PBA inhibited 20 μM NaAsO2-induced EI24 expression in mitochondrion. Collectively, our results indicated that arsenic induced p53 activation via ER stress, under relatively low NaAsO2 concentration, NaAsO2-triggered p53 activation protected cells from apoptosis by alleviating ER stress. Another finding was that under relatively high NaAsO2 concentration, NaAsO2-activated p53 facilitated EI24 mitochondrial translocation and caused mitochondrial permeability increase, which represented a switch of p53 from a benefit role to pro-apoptosis function in NaAsO2-treated cells. The study contributed to in-depth understanding the mechanism of arsenic-induced liver damage and providing potential clues for following study.

Prognostic role and immune infiltration characteristics of EI24 in multiple cancer types

BACKGROUND

The autophagy-associated transmembrane protein EI24 is associated with cancer growth and patient survival. We aimed to explore the prognostic role and immune infiltration characteristics of EI24 at a pan-cancer level.

METHODS

We collected data from multiple databases to explore the expression and prognostic role of EI24 in various cancers. Correlations between EI24 expression and DNA methylation, RNA modification, tumor mutation burden (TMB), microsatellite instability (MSI), immune moderator, immune checkpoint-related genes, the tumor immune microenvironment, and clinicopathological characteristics were analyzed. Finally, immunohistochemistry and western blotting were performed to validate the protein levels of EI24 in different tumors.

RESULTS

Differential expression of EI24 was observed in most cancer types compared to non-cancerous tissues. EI24 showed a significant association with prognosis and may represent a new indicator of prognosis in patients with cancer. In most cancers, EI24 is closely associated with tumor immunity and interacts with various immune cells. Moreover, significant correlations were observed between EI24 expression and RNA modification, TMB, MSI, immune moderators, and immune checkpoint-related genes.

CONCLUSION

This study provides new insights into the functions and clinical value of EI24 in different tumors and suggests that EI24 may serve as a promising biomarker or therapeutic target for cancer management.

Calcium transients on the ER surface trigger liquid-liquid phase separation of FIP200 to specify autophagosome initiation sites

The mechanism that initiates autophagosome formation on the ER in multicellular organisms is elusive. Here, we showed that autophagy stimuli trigger Ca²⁺ transients on the outer surface of the ER membrane, whose amplitude, frequency, and duration are controlled by the metazoan-specific ER transmembrane autophagy protein EPG-4/EI24. Persistent Ca²⁺ transients/oscillations on the cytosolic ER surface in EI24-depleted cells cause accumulation of FIP200 autophagosome initiation complexes on the ER. This defect is suppressed by attenuating ER Ca²⁺ transients. Multi-modal SIM analysis revealed that Ca²⁺ transients on the ER trigger the formation of dynamic and fusion-prone liquid-like FIP200 puncta. Starvation-induced Ca²⁺ transients on lysosomes also induce FIP200 puncta that further move to the ER. Multiple FIP200 puncta on the ER, whose association depends on the ER proteins VAPA/B and ATL2/3, assemble into autophagosome formation sites. Thus, Ca²⁺ transients are crucial for triggering phase separation of FIP200 to specify autophagosome initiation sites in metazoans.

EI24 promotes cell adaption to ER stress by coordinating IRE1 signaling and calcium homeostasis

The endoplasmic reticulum (ER) is a subcellular organelle crucial for protein folding and calcium storage. Accumulation of unfolded proteins or calcium depletion causes ER stress. Deficiency of ER stress adaptation leads to apoptosis, which is associated with several human disorders. Here, we reveal that ER transmembrane protein EI24 promotes cell adaptation to ER stress by coordinating the IRE1 branch of the unfolded protein response (UPR) and calcium signaling. Under nonstressed conditions, EI24 binds to the kinase domain of IRE1 to inhibit its activation. Upon ER stress, EI24 disassociates from IRE1 to permit UPR activation, and meanwhile targets IP3R1 to prevent ER calcium depletion, which together promote cell adaptation to ER stress. EI24 knockout causes failure of ER stress adaptation and apoptosis. Thus, EI24 is a novel anti-apoptotic factor implicated in ER stress signaling.

miR‑483 promotes the development of colorectal cancer by inhibiting the expression level of EI24

MicroRNAs (miRs) serve an important role in cell differentiation, proliferation and apoptosis by negatively regulating gene expression at the transcriptional or post‑transcriptional level. EI24 autophagy associated transmembrane protein (EI24) is a tumor suppressor gene that serves an important role in the occurrence and development of digestive system tumors. However, little is known regarding the relationship between EI24 and the prognosis of patients with colorectal cancer (CRC). Our previous study confirmed EI24 as the target molecule of miR‑483, using reporter gene detection. Thus, the aim of the present study was to elucidate the effect of the abnormal expression of miR‑483 on the malignant phenotype of CRC through a series of cell function experiments and nude mice tumorigenicity experiments, and to determine the expression level of EI24, a downstream target gene of miR‑483, in CRC and its relationship with patient prognosis. In CRC tissues and cells, the expression level of miR‑483 was upregulated, while the expression level of EI24 was downregulated. Cell function tests such as MTT assay, cell cycle assay, colony formation assay, Migration and invasion assays and nude mice tumorigenicity experiments demonstrated that the overexpression of miR‑483 promoted the proliferation, invasion and metastasis of CRC. Moreover, the reverse transcription‑quantitative PCR results indicated that overexpression of miR‑483 inhibited the expression level of EI24. The relationship between the clinical data and immunohistochemical results from 183 patients with CRC and survival was examined. It was found that the expression level of EI24 was positively associated with the prognosis of patients. As a cancer‑promoting factor, miR‑483 enhances the proliferation, migration and invasion of CRC cells by reducing the expression level of EI24.

EI24 alleviates renal interstitial fibrosis through inhibition of epithelial-mesenchymal transition and fibroblast activation

Etoposide-induced 2.4 (EI24) exerts tumor suppressor activity through participating in cell apoptosis, autophagy, and inflammation. However, its role in renal diseases has not been elucidated. This study showed that the EI24 level decreased gradually in the kidneys of mice with unilateral ureteral obstruction (UUO) and in another fibrosis model induced by diabetic kidney disease. The overexpression of EI24 was used to investigate the possible role both in vivo and in vitro. The overexpression 1 day after UUO through tail vein injection alleviated the progression of renal interstitial fibrosis (RIF). EI24 inhibited epithelial-mesenchymal transition, excessive deposition of the extracellular matrix, and activation of fibroblasts. Furthermore, administration of EI24-overexpressing plasmids restrained the phosphorylation of nuclear factor-κB (NF-κB) and c-Jun kinase (JNK) through regulating the proteasome-dependent degradation of TRAF2, and then, inhibited the expression of downstream inflammation-associated cytokines (interleukin-6, tumor necrosis factor-α, and monocyte chemotactic protein-1) and infiltration of macrophages and neutrophils in mouse kidney after UUO. In conclusion, the data indicated that EI24, a novel anti-fibrosis regulator, was important in the progression of RIF.

Autophagy-related protein EI24 delays the development of pulmonary fibrosis by promoting autophagy

Etoposide-induced protein 2.4 (EI24) is an autophagy-associated protein and acts as a tumor suppressor. However, its role in tissue fibrosis remains unknown. Herein, a downregulation of EI24 levels in the lungs from mouse pulmonary fibrosis (PF) model and lung epithelial cells was observed in response to bleomycin (BLM) or transforming growth factor-β1 (TGF-β1). Then, the role of EI24 in PF was investigated through the upregulation of EI24 in vitro and in vivo. EI24 inhibited epithelial-mesenchymal transition (EMT) process and extracellular matrix (ECM) production in EI24-overexpressing cells after stimulation with BLM or TGF-β1. The overexpression of EI24 at 14 days after the establishment of the PF model through tail vein injection delayed the progression of PF. Moreover, the administration of EI24-overexpressing plasmid promoted the autophagy level in the lungs of the PF mouse model. In addition, the inhibition of autophagy by 3-methyladenine limited the role of EI24 in these processes. Thus, the current data indicated that EI24 attenuates PF through inhibition of EMT process and ECM production by promoting autophagy.

EI24 Inhibits Cell Proliferation and Drug Resistance of Esophageal Squamous Cell Carcinoma

Drug resistance, whether intrinsic or acquired, often leads to treatment failure in esophageal squamous cell carcinoma (ESCC). Clarifying the mechanism of drug resistance in ESCC has great significance for reversing drug resistance, as well as improving the prognosis of patients. Previously, we demonstrated that etoposide-induced 2.4-kb mRNA (EI24) is the target of miR-483-3p, which promoted the growth, migration, and drug resistance in ESCC, suggesting that EI24 participates in repressing the tumorigenesis and progression of ESCC. Here, we observed that EI24 was remarkably decreased in ESCC tissues. Moreover, its expression was directly linked to the prognosis of patients. We then confirmed that the forced overexpression of EI24 repressed cell growth and sensitized ESCC cells to chemotherapeutic agents, whereas EI24 silencing had the opposite effect. Furthermore, gene microarray and ingenuity pathway analysis (IPA) were performed to establish the potential mechanisms and indicated that EI24 exerts a tumor-suppressive role via suppressing the acute phase response signaling pathway or IL-1 signaling pathway in ESCC. Collectively, our data reveal that EI24 overexpression attenuates malignant phenotypes of ESCC and that it is a novel possible ESCC therapeutic target.

[WWP1 promotes cell proliferation in hepatocellular carcinoma through ubiquitin-degradation EI24]

Objective: To screen the interaction proteins of WW domain containing protein 1 (WWP1), and explore the effects of WWP1 and etoposide induced 24 (EI24) on cell proliferation in hepatocellular carcinoma (HCC). Methods: Yeast two-hybrid screening system was used to identify the interaction proteins of WWP1. The interaction was further validated by co-immunoprecipitation. WWP1 and EI24 stably over-expressing or deleted HepG2 cells were established by using the lentivirus transduction method. Colony forming assay and cell counting kit-8 (CCK8) assay were performed to identify the effects of WWP1 and EI24 on cell proliferation. In addition, the role of WWP1 in the tumorigenicity of liver cancer in vivo was examined by subcutaneous injection of different level of WWP1 expressed HepG2 into nude mice. Results: WWP1 can interact with EI24 and ubiquitin-degrade EI24 protein. The WWP1 and EI24 over-expressing or deleted HepG2 cell lines were successfully generated. Overexpression of WWP1 decreased while knockdown of WWP1 increased the protein level of EI24. The results of CCK-8 assay showed that the relative proliferation activities of WWP1 overexpressed (WWP1-OE) group and WWP1 knockdown (shWWP1) group on 36 hours were (347.00±8.15)% and (187.08±4.86)%, respectively, significantly different from (270.33±15.01)% of control group (both P<0.05). The relative proliferation activities of EI24 overexpressed (EI24-OE) group and EI24 knockdown (shEI24) group on 36 hours were (183.75±8.11)% and (317.33±9.60)%, respectively, significantly different from (270.33±15.01) % of control group (both P<0.05). The results of colony formation assay showed that the colony numbers of control group, WWP1-OE group and shWWP1 group were (52±7)/visual field (VF), (76±4)/VF, (19±3)/VF, respectively. Overexpression of WWP1 significantly increased while knockdown of WWP1 significantly decreased the colon formation ability of HepG2 cells (both P<0.05). The colon number of control group, EI24-OE group and shEI24 group were (38±4)/VF, (10±3)/VF, (69±7)/VF, respectively. Overexpression of EI24 significantly decreased while knockdown of EI24 significantly increased the colony formation ability of HepG2 cells (both P<0.05). The results of xenograft mice model showed that the tumor volumes of control, WWP1-OE, and shWWP1 group were (1 400.00±43.71)mm(3,) (2 636.67±290.45) mm(3) and (642.17±36.00)mm(3,) respectively, with significant differences (P<0.05). The tumor weight for these three groups were (1.23±0.08)g, (2.05±0.17)g, and (0.88±0.09)g, respectively, with significant differences (P<0.05). The tumor volumes of control, EI24-OE, and shEI24 group were (1 245.17±93.10)mm(3,) (662.17±60.88)mm(3) and (1 986.67±226.75)mm(3) respectively, with significant differences (P<0.05). The tumor weight for these three groups were (1.15±0.04)g, (0.85±0.02)g and (1.73±0.05)g respectively, with significant difference (P<0.05). Conclusion: WWP1 promote the cell proliferation of liver cancer through ubiquitin-degradation of EI24.

EI24, as a Component of Autophagy, Is Involved in Pancreatic Cell Proliferation

Autophagy is a highly conserved cellular process in which cytoplasmic materials are degraded and recycled as energy sources when nutrient supplies are lacking. Established tumor cells require autophagy for cell growth and tumor promotion. In particular, the survival of pancreatic tumor cells appears to be strongly dependent on autophagy, referred to as autophagy addiction. This dependency of pancreatic tumor cells on autophagy may be a candidate target for pancreatic tumor therapy. EI24 (etoposide-induced gene 2.4 kb; PIG8, p53-induced gene 8) acts as a tumor suppressor, inhibiting cell growth and inducing apoptosis in breast, cervical, and prostate cancer cells. However, recent papers have reported that EI24 is an essential component of the autophagy pathway. This newly discovered role of EI24 as a component of autophagy may act as a tumor promoter, which is contradictory to its known role as a tumor suppressor. We investigated the role of EI24 as a component of autophagy in pancreatic tumor cell proliferation. Here, we demonstrated that knockdown of EI24 using siRNA in pancreatic tumor cells led to impaired autophagy at a late step (increase in LC3-II and accumulation of p62 and autolysosomes). EI24 deficiency in pancreatic tumor cell lines inhibited cell proliferation. We confirmed that loss of EI24 inhibited pancreatic cell proliferation using the CRISPR-Cas9 system. However, loss of EI24 in other cell lines did not affect cell proliferation. Taken together, our results suggest that EI24 acts as a tumor promoter in pancreatic tumor cells, and studying the role of EI24 in reference to its cellular context may lead to a useful therapeutic target.

Effect of EI24 expression on the tumorigenesis of ApcMin/+ colorectal cancer mouse model

Etoposide-induced 2.4 kb transcript (EI24, also known as PIG8) is a p53 target gene involved in cell growth suppression and apoptosis and known to be frequently altered in human cancers. Although EI24 expression is decreased in various cancers and is associated with colorectal cancer progression and metastasis, the physiological function of EI24 in colorectal cancer is yet unclear. We generated an Ei24 conditional transgenic (Tg) mouse to study the therapeutic effects of Ei24 in vivo and evaluated whether Ei24 plays a role of a tumor suppressor using Ei24 Tg mouse crossed with Apc^Min/+ mouse, which develops multiple intestinal adenomas. The overexpression of Ei24 failed to cause any notable difference in the number of polyps, lengths of the intestine and spleen, and survival rate between Apc^Min/+ and Apc^Min/+Ei24 Tg mice. Ei24 plays no significant role in colon cancer caused by the substitutional mutation of Apc in mice. Therefore, our result dismisses the hypothesized direct link between Apc^Min/+ mutation and Ei24 expression in colorectal cancer model.

Emerging Paradigm of Crosstalk between Autophagy and the Ubiquitin-Proteasome System

Cellular protein homeostasis is maintained by two major degradation pathways, namely the ubiquitin-proteasome system (UPS) and autophagy. Until recently, the UPS and autophagy were considered to be largely independent systems targeting proteins for degradation in the proteasome and lysosome, respectively. However, the identification of crucial roles of molecular players such as ubiquitin and p62 in both of these pathways as well as the observation that blocking the UPS affects autophagy flux and vice versa has generated interest in studying crosstalk between these pathways. Here, we critically review the current understanding of how the UPS and autophagy execute coordinated protein degradation at the molecular level, and shed light on our recent findings indicating an important role of an autophagy-associated transmembrane protein EI24 as a bridging molecule between the UPS and autophagy that functions by regulating the degradation of several E3 ligases with Really Interesting New Gene (RING)-domains.

MicroRNA-455-3p promotes invasion and migration in triple negative breast cancer by targeting tumor suppressor EI24

Lacking of treatment methods for the patients with triple negative breast cancer (TNBC) underscores the pivotal needs to further understand its biology as well as to find better biomarkers and develop novel therapeutic strategies. Increasing evidences support that aberrantly expressed microRNAs (miRNAs) are involved in tumorigenesis and may serve as biomarkers for diagnostic and prognostic purposes of various cancers. In current study, we found that miR-455-3p and miR-196a-5p were intensively overexpressed in TNBC compared with the hormone receptor (HR) positive breast cancer whereas miR-425-5p was down-regulated by miRNA microarray analysis. qRT-PCR analysis confirmed that the expression of miR-455-3p in TNBC cell lines MDA-MB-231 and MDA-MB-468 was higher than that in HR positive breast cancer cell line MCF-7(p<0.01). Functional experiments in vitro showed that miR-455-3p enhanced cell proliferative, invasive and migrational abilities in TNBC cell lines. miRNA targets prediction showed SMAD2, LTBR and etoposide induced 2.4 (EI24) were potential target genes of miR-455-3p, and then it was confirmed by qRT-PCR assay. Dual luciferase reporter assay showed the specific binding of miR-455-3p to 3′ UTR of EI24 in TNBC. Then we found miR-455-3p inhibited the EI24 expression at the levels of mRNA and protein. Through small interfering RNA (siRNA) targeting EI24 gene, there were strengthened capabilities of invasion and migration of TNBC cells, and increased expression of EI24 had the inverse effects. In conclusion, the data suggest that miRNA455-3p promotes invasion and migration by targeting tumor suppressor EI24 and might be a potential prognostic biomarker and therapeutic target in TNBC.

Functional characterization of EI24-induced autophagy in the degradation of RING-domain E3 ligases

Historically, the ubiquitin-proteasome system (UPS) and autophagy pathways were believed to be independent; however, recent data indicate that these pathways engage in crosstalk. To date, the players mediating this crosstalk have been elusive. Here, we show experimentally that EI24 (EI24, autophagy associated transmembrane protein), a key component of basal macroautophagy/autophagy, degrades 14 physiologically important E3 ligases with a RING (really interesting new gene) domain, whereas 5 other ligases were not degraded. Based on the degradation results, we built a statistical model that predicts the RING E3 ligases targeted by EI24 using partial least squares discriminant analysis. Of 381 RING E3 ligases examined computationally, our model predicted 161 EI24 targets. Those targets are primarily involved in transcription, proteolysis, cellular bioenergetics, and apoptosis and regulated by TP53 and MTOR signaling. Collectively, our work demonstrates that EI24 is an essential player in UPS-autophagy crosstalk via degradation of RING E3 ligases. These results indicate a paradigm shift regarding the fate of E3 ligases.

miR-483-3p plays an oncogenic role in esophageal squamous cell carcinoma by targeting tumor suppressor EI24

microRNAs (miRNAs), through negatively regulating their target genes, influence the development and progression of many cancers. Previously, we found miR-483 was overexpressed in esophageal squamous cell carcinoma (ESCC) tissues, and its overexpression was negatively correlated with the prognosis and positively correlated with multidrug resistance of ESCC, but whether it could affect the biological role of proliferation and migration in ESCC cell lines is unknown. In the present study, we found miR-483-3p was overexpressed in ESCC cell lines as compared with the normal esophageal squamous epithelial cell line. Functional experiments in vitro showed that miR-483-3p could promote the proliferation, migration, transformation of cell cycle from G1 phase to G2 phase of ESCC cells and could inhibit cells' sensitivity to chemotherapy drugs. Nude mouse tumorigenicity assay indicated that miR-483-3p could promote the growth of ESCC cells in vivo. Western blot assay showed that ectopic expression of miR-483-3p in ESCC cells could downregulate the protein level of etoposide induced 2.4 (EI24), which is a tumor suppressor and has not been reported in ESCC. Luciferase reporter assay demonstrated that EI24 was a direct target of miR-483-3p. Collectively, our study demonstrated that miR-483-3p could promote ESCC progression at least in part through directly targeting EI24, supplying a potential strategy for miRNA-based ESCC therapy.

Reduced expression of EI24 confers resistance to gefitinib through IGF-1R signaling in PC9 NSCLC cells

OBJECTIVES

Lung cancer is the commonly diagnosed cancer and is the leading cause of cancer-related mortality worldwide. The most prevalent form of lung cancer is NSCLC, comprising 80% of all lung cancer cases, and epidermal growth factor receptor (EGFR) is frequently mutated in NSCLC. EI24 is a p53-responsive gene and plays an important role in tumor suppression. In the current study, we found that reduced expression of EI24 conferred resistance to EGFR-tyrosine-kinase inhibitor (TKI) in NSCLC cells.

MATERIALS AND METHODS

The correlation between EI24 expression and EGFR-TKI drug resistance in EGFR-driven tumors were determined from microarray datasets. The phospho-protein expression profiles of receptor tyrosine kinases and protein kinases were examined using antibody arrays method in PC9 cells expressing shRNAs targeting EI24 and gefitinib-resistant PC9-GR cells expressing exogenous EI24.

RESULTS AND CONCLUSIONS

The EGFR-TKI resistant clones had reduced expression of EI24 mRNA compared to the sensitive clones, and EI24 knockdown rendered sensitive cells resistant to EGFR-TKI. Receptor tyrosine kinase screening revealed the involvement of a kinase switch in EI24-mediated regulation of drug sensitivity. We found that EI24 modulates the insulin growth factor-1 receptor (IGF-1R) pathway through the induction of IGF-1. Combination treatment with EGFR and IGF-1R inhibitors significantly reduced the viability of EI24 knockdown-induced resistant cell lines compared to single-agent treatments. We also showed that low EI24 and high IGF-1R expressions in lung cancer patients were correlated with reduced overall survival. Taken together, these results suggest a potential role for EI24 as a biomarker of drug resistance, and indicate that combination therapy with EGFR and IGF-1R inhibitors would be effective in NSCLC patients with low EI24 expression.