RACK1 modulates apoptosis induced by sorafenib in HCC cells by interfering with the IRE1/XBP1 axis

Decoding the Role of O-GlcNAcylation in Hepatocellular Carcinoma

Post-translational modifications (PTMs) influence protein functionality by modulating protein stability, localization, and interactions with other molecules, thereby controlling various cellular processes. Common PTMs include phosphorylation, acetylation, ubiquitination, glycosylation, SUMOylation, methylation, sulfation, and nitrosylation. Among these modifications, O-GlcNAcylation has been shown to play a critical role in cancer development and progression, especially in hepatocellular carcinoma (HCC). This review outlines the role of O-GlcNAcylation in the development and progression of HCC. Moreover, we delve into the underlying mechanisms of O-GlcNAcylation in HCC and highlight compounds that target O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA) to improve treatment outcomes. Understanding the role of O-GlcNAcylation in HCC will offer insights into potential therapeutic strategies targeting OGT and OGA, which could improve treatment for patients with HCC.

ER stress signaling at the interphase between MASH and HCC

HCC is the most frequent primary liver cancer with an extremely poor prognosis and often develops on preset of chronic liver diseases. Major risk factors for HCC include metabolic dysfunction-associated steatohepatitis, a complex multifactorial condition associated with abnormal endoplasmic reticulum (ER) proteostasis. To cope with ER stress, the unfolded protein response engages adaptive reactions to restore the secretory capacity of the cell. Recent advances revealed that ER stress signaling plays a critical role in HCC progression. Here, we propose that chronic ER stress is a common transversal factor contributing to the transition from liver disease (risk factor) to HCC. Interventional strategies to target the unfolded protein response in HCC, such as cancer therapy, are also discussed.

RACK1 promotes autophagy via the PERK signaling pathway to protect against traumatic brain injury in rats

AIMS

Neuronal cell death is a primary factor that determines the outcome after traumatic brain injury (TBI). We previously revealed the importance of receptor for activated C kinase (RACK1), a multifunctional scaffold protein, in maintaining neuronal survival after TBI, but the specific mechanism remains unclear. The aim of this study was to explore the mechanism underlying RACK1-mediated neuroprotection in TBI.

METHODS

TBI model was established using controlled cortical impact injury in Sprague-Dawley rats. Genetic intervention and pharmacological inhibition of RACK1 and PERK-autophagy signaling were administrated by intracerebroventricular injection. Western blotting, coimmunoprecipitation, transmission electron microscopy, real-time PCR, immunofluorescence, TUNEL staining, Nissl staining, neurobehavioral tests, and contusion volume assessment were performed.

RESULTS

Endogenous RACK1 was upregulated and correlated with autophagy induction after TBI. RACK1 knockdown markedly inhibited TBI-induced autophagy, whereas RACK1 overexpression exerted the opposite effects. Moreover, RACK1 overexpression ameliorated neuronal apoptosis, neurological deficits, and cortical tissue loss after TBI, and these effects were abrogated by the autophagy inhibitor 3-methyladenine or siRNAs targeting Beclin1 and Atg5. Mechanistically, RACK1 interacted with PERK and activated PERK signaling. Pharmacological and genetic inhibition of the PERK pathway abolished RACK1-induced autophagy after TBI.

CONCLUSION

Our findings indicate that RACK1 protected against TBI-induced neuronal damage partly through autophagy induction by regulating the PERK signaling pathway.

Hepatocellular carcinoma cell-derived exosomal miR-21-5p promotes the polarization of tumor-related macrophages (TAMs) through SP1/XBP1 and affects the progression of hepatocellular carcinoma

BACKGROUND

Tumor-associated macrophages (TAMs) have unique functions in the development of hepatocellular carcinoma (HCC). The tumor microenvironment is in a complex state in chronic disease. As a major participant in tumor-associated inflammation, TAMs have a unique effect on promoting tumor cell proliferation, angiogenesis and immunosuppression. The in-depth study of TAMs has important scientific and clinical value and provides new ideas for the treatment of cancer.

METHODS

Bioinformatics analysis, dual-luciferase reporter assays, RT-qPCR and clinical samples were used to analyze the potential mechanism of the miR-21-5p/SP1/XBP1 molecular axis in HCC. In this study, miR-21-5p was highly expressed in HCC exosomes compared with normal hepatocyte exosomes, and HCC exosomes containing miR-21-5p promoted the proliferation and migration of HCC cells and inhibited cell apoptosis. In addition, this treatment promoted the M2 polarization of macrophages, induced the expression of transcription factor-specific protein 1 (SP1), and inhibited the expression of X-box binding protein 1 (XBP1). However, these expression trends were reversed after inhibition of miR-21-5p expression in exosomes of hepatoma cells, and the effects of exosomal miR-21-5p were partially restored after overexpression of SP1. Animal experiments also verified that exosomal miR-21-5p in HCC cells affected the expression level of the SP1/XBP1 protein and promoted M2 polarization of TAMs.

CONCLUSION

Exosomal miR-21-5p in HCC cells can affect the development of HCC cells by regulating SP1/XBP1 and promoting the M2 polarization of TAMs, thereby affecting the adverse prognostic response of HCC patients.

Cucurbitacin B induces apoptosis in colorectal cells through reactive oxygen species generation and endoplasmic reticulum stress pathways

Cucurbitacin B (CuB) is a member of the cucurbitacin family, which has shown potent anticancer pharmacological activity. Prolonged or severe endoplasmic reticulum stress (ERS) induces apoptosis; therefore, the present study investigated whether CuB may activate the ERS pathway to induce apoptosis. HT-29 and SW620 colorectal cancer (CRC) cells were treated with a range of concentrations of CuB for 48 h, and the viability and proliferation of cells were determined using Cell Counting Kit 8 (CCK8) and colony formation assays. Subsequently, the appropriate CuB concentration (5 µM) was selected for treatment of CRC cells for 48 h. Western blot analysis was used to measure the expression levels of ERS-related proteins, flow cytometry was used to evaluate apoptosis, the dichlorodihydrofluorescein diacetate fluorescent probe was used to detect reactive oxygen species (ROS) production, and the relationship between ROS and ERS was determined by western blot analysis. Furthermore, flow cytometry was used to evaluate apoptosis after treatment with the ERS inhibitor 4-phenylbutyric acid, the ROS inhibitor N-acetylcysteine and following knockdown of CHOP expression. In addition, western blot analysis was performed to measure Bax and Bcl2 protein expression levels, and a CCK8 assay was performed to evaluate the viability of cells following knockdown of CHOP. Notably, CuB treatment increased apoptosis and inhibited cell proliferation in CRC cell lines, and these effects were mediated by ROS and ROS-regulated activation of the PERK and XBP1 ERS pathways. In conclusion, CuB may induce apoptosis in HT-29 and SW620 CRC cells via ROS and ERS.

Crosstalk between endoplasmic reticulum stress and multidrug-resistant cancers: hope or frustration

Endoplasmic reticulum stress (ERS) is a kind of cell response for coping with hypoxia and other stresses. Pieces of evidence show that continuous stress can promote the occurrence, development, and drug resistance of tumors through the unfolded protein response. Therefore, the abnormal ac-tivation of ERS and its downstream signaling pathways not only can regulate tumor growth and metastasis but also profoundly affect the efficacy of antitumor therapy. Therefore, revealing the molecular mechanism of ERS may be expected to solve the problem of tumor multidrug resistance (MDR) and become a novel strategy for the treatment of refractory and recurrent tumors. This re-view summarized the mechanism of ERS and tumor MDR, reviewed the relationship between ERS and tumor MDR, introduced the research status of tumor tissue and ERS, and previewed the prospect of targeting ERS to improve the therapeutic effect of tumor MDR. This article aims to provide researchers and clinicians with new ideas and inspiration for basic antitumor treatment.

XBP1 as a novel molecular target to attenuate drug resistance in hepatocellular carcinoma

INTRODUCTION

Despite improvements in clinical management of hepatocellular carcinoma (HCC), prognosis remains poor with a 5-year survival rate less than 40%. Drug resistance in HCC makes it challenging to treat; therefore, it is imperative to develop new therapeutic strategies. Higher expression of X-box binding protein 1 (XBP1) in tumor cells is highly correlated with poor prognosis. In tumor cells, XBP1 modulates the unfolded protein response (UPR) to restore homeostasis in endoplasmic reticulum. Targeting XBP1 could be a promising therapeutic strategy to overcome HCC resistance and improve the survival rate of patients.

AREAS COVERED

This review provides the recent evidence that indicates XBP1 is involved in HCC drug resistance via DNA damage response, drug inactivation, and inhibition of apoptosis. In addition, the potential roles of XBP1 in inducing resistance in HCC cells were highlighted, and we showed how its inhibition could sensitize tumor cells to controlled cell death.

EXPERT OPINION

Due to the diversity in molecular mechanism of multidrug-resistance, targeting one specific pathway is inadequate. XBP1 inhibition could be a potential therapeutic target to overcome verity of resistance mechanisms. The main function of this transcription factor in HCC treatment response is an attractive area for further studies and should be discussed more.

Azithromycin suppresses TGF-β1-related epithelial-mesenchymal transition in airway epithelial cells via targeting RACK1

Transforming growth factor-β1 (TGF-β1) associated epithelial-mesenchymal transition (EMT) contributes to multiple respiration diseases via Smad or MAPKs pathway. Our previous study has demonstrated that the typical macrolide antibiotic, azithromycin (AZM) played a notable anti-EMT role in ovalbumin (OVA)-challenged mice. However, the precise mechanism of AZM on TGF-β1 mediated EMT in bronchial epithelial cells is still unclear. The purpose of this study was to elucidate whether azithromycin targeting RACK1 inhibits TGF-β1 mediated EMT in vitro. The results showed that AZM significantly inhibited the expression of RACK1 and the activation of the downstream JNK, ERK, and Smad3 signaling pathways, thereby suppressing the migration of bronchial epithelial cells and reversing the TGF-β1-induced EMT. The effect of AZM on TGF-β1 mediated EMT in vitro is dependent on the dose of AZM. Although RACK1 has been shown to regulate IRE1α expression with siRACK1 transfection, there was no direct interaction between IRE1α and AZM. On the contrary, weak interaction between AZM and RACK1 was predicted with molecular docking. In summary, AZM targets RACK1 to trigger downstream JNK, ERK, and Smad3 signaling pathways and is an effective anti-EMT drug for bronchial epithelial cells in a dose-dependent manner.

Synergistic antitumor activity of sorafenib and MG149 in hepatocellular carcinoma cells

Advanced hepatocellular carcinoma (HCC) is among the most challenging cancers to overcome, and there is a need for better therapeutic strategies. Among the different cancer drugs that have been used in clinics, sorafenib is considered the standard first-line drug for advanced HCC. Here, to identify a chemical compound displaying a synergistic effect with sorafenib in HCC, we screened a focused chemical library and found that MG149, a histone acetyltransferase inhibitor targeting the MYST family, exhibited the most synergistic anticancer effect with sorafenib on HCC cells. The combination of sorafenib and MG149 exerted a synergistic anti-proliferation effect on HCC cells by inducing apoptotic cell death. We revealed that cotreatment with sorafenib and MG149 aggravated endoplasmic reticulum (ER) stress to promote the death of HCC cells rather than adaptive cell survival. In addition, combined treatment with sorafenib and MG149 significantly increased the intracellular levels of unfolded proteins and reactive oxygen species, which upregulated ER stress. Collectively, these results suggest that MG149 has the potential to improve the efficacy of sorafenib in advanced HCC via the upregulation of cytotoxic ER stress. [BMB Reports 2022; 55(10): 506-511].

Hepatic RACK1 deletion disturbs lipid and glucose homeostasis independently of insulin resistance

Receptor for activated C kinase 1 (RACK1) is a versatile protein involved in multiple biological processes. In a previous study by Zhao et al., hepatic RACK1 deletion in mice led to an inhibition of autophagy, blocked autophagy-dependent lipolysis, and caused steatosis. Using the same mouse model (RACK1hep-/-), we revealed new roles of RACK1 in maintaining bile acid homeostasis and hepatic glucose uptake, which further affected circulatory lipid and glucose levels. To be specific, even under hepatic steatosis, the plasma lipids were generally reduced in RACK1hep-/- mouse, which was due to the suppression of intestinal lipid absorption. Accordingly, a decrease in total bile acid level was found in RACK1hep-/- livers, gallbladders, and small intestine tissues, and specific decrease of 12-hydroxylated bile acids was detected by liquid chromatography-mass spectrometry. Consistently, reduced expression of CYP8B1 was found. A decrease in hepatic glycogen storage was also observed, which might be due to the inhibited glucose uptake by GLUT2 insufficiency. Interestingly, RACK1-KO-inducing hepatic steatosis did not raise insulin resistance (IR) nor IR-inducing factors like endoplasmic reticulum stress and inflammation. In summary, this study uncovers that hepatic RACK1 might be required in maintaining bile acid homeostasis and glucose uptake in hepatocytes. This study also provides an additional case of hepatic steatosis disassociation with insulin resistance.

Broad Transcriptomic Impact of Sorafenib and Its Relation to the Antitumoral Properties in Liver Cancer Cells

Simple Summary

Hepatocellular carcinoma (HCC) is the fourth most frequent cause of cancer-related mortality worldwide. While ablation, resection and orthotopic liver transplantation are indicated at an early stage of the disease, Sorafenib (Sfb) is the current most administrated first-line treatment for advanced HCC, even though its therapeutic benefit is limited due to the appearance of resistance. Deep knowledge on the molecular consequences of Sfb-treatment is essentially required for optimizing novel therapeutic strategies to improve the outcomes for patients with advanced HCC. In this study, we analyzed differential gene expression changes in two well characterized liver cancer cell lines upon a Sfb-treatment, demonstrating that both lines responded similarly to the treatment. Our results provide valuable information on the molecular action of Sfb on diverse cellular fundamental processes such as DNA repair, translation and proteostasis and identify rationalization issues that could provide a different therapeutic perspective to Sfb.

Abstract

Hepatocellular carcinoma (HCC) is one of the most frequent and essentially incurable cancers in its advanced stages. The tyrosine kinase inhibitor Sorafenib (Sfb) remains the globally accepted treatment for advanced HCC. However, the extent of its therapeutic benefit is limited. Sfb exerts antitumor activity through its cytotoxic, anti-proliferative and pro-apoptotic roles in HCC cells. To better understand the molecular mechanisms underlying these effects, we used RNA sequencing to generate comprehensive transcriptome profiles of HepG2 and SNU423, hepatoblastoma- (HB) and HCC-derived cell lines, respectively, following a Sfb treatment at a pharmacological dose. This resulted in similar alterations of gene expression in both cell lines. Genes functionally related to membrane trafficking, stress-responsible and unfolded protein responses, circadian clock and activation of apoptosis were predominantly upregulated, while genes involved in cell growth and cycle, DNA replication and repair, ribosome biogenesis, translation initiation and proteostasis were downregulated. Our results suggest that Sfb causes primary effects on cellular stress that lead to upregulation of selective responses to compensate for its negative effect and restore homeostasis. No significant differences were found specifically affecting each cell line, indicating the robustness of the Sfb mechanism of action despite the heterogeneity of liver cancer. We discuss our results on terms of providing rationalization for possible strategies to improve Sfb clinical outcomes.

Drug Resistance and Endoplasmic Reticulum Stress in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most common and deadly cancers worldwide. It is usually diagnosed in an advanced stage and is characterized by a high intrinsic drug resistance, leading to limited chemotherapeutic efficacy and relapse after treatment. There is therefore a vast need for understanding underlying mechanisms that contribute to drug resistance and for developing therapeutic strategies that would overcome this. The rapid proliferation of tumor cells, in combination with a highly inflammatory microenvironment, causes a chronic increase of protein synthesis in different hepatic cell populations. This leads to an intensified demand of protein folding, which inevitably causes an accumulation of misfolded or unfolded proteins in the lumen of the endoplasmic reticulum (ER). This process is called ER stress and triggers the unfolded protein response (UPR) in order to restore protein synthesis or—in the case of severe or prolonged ER stress—to induce cell death. Interestingly, the three different arms of the ER stress signaling pathways have been shown to drive chemoresistance in several tumors and could therefore form a promising therapeutic target. This review provides an overview of how ER stress and activation of the UPR contributes to drug resistance in HCC.

Inhibition of Fam114A1 protects melanocytes from apoptosis through higher RACK1 expression

Fam114A1 is a gene closely related to the development of nerve cells, melanocytes, and nerve cells that originate from the neural crest of the embryonic ectoderm. Recent studies showed that Fam114A1 has a role in the occurrence of ankylosing myelitis spondylitis and autoimmune enteritis; still, its cellular function remains poorly understood. In this study, we investigated the effect of Fam114A1 on the biological activity of melanocytes. We found that the expression of Fam114A1 in vitiligo melanocytes (MCV-L, MCV-N, PI3V) was higher than that in normal melanocytes, and the biological function of melanocytes was significantly affected when the Fam114A1 gene was silenced. Inhibition of Fam114A1 increased proliferation, migration, and melanin synthesis proteins, decreased apoptosis, while its overexpression reversed this process. Mechanistically, we discovered that RACK1 is a target protein of Fam114A1 and that RACK1 can be negatively regulated by Fam114A1. Further study showed that Fam114A1 inhibition could not protect melanocytes from apoptosis once the expression of RACK1 protein was silenced. In summary, Fam114A1 is an effective regulatory protein for regulating the function of melanocytes. Inhibition Fam114A1 protects melanocytes from apoptosis through increasing RACK1.

RCN1 induces sorafenib resistance and malignancy in hepatocellular carcinoma by activating c-MYC signaling via the IRE1α-XBP1s pathway

The increasing incidence of hepatocellular carcinoma (HCC) is of great concern globally, but the molecular pathogenesis of these tumors remains unclear. Sorafenib is a first-line drug for the treatment of advanced HCC. However, the efficacy of sorafenib in improving patient survival is limited, and most patients inevitably develop resistance to this drug. Recent studies have demonstrated that the activation of the IRE1α–XBP1s pathway might play a protective role in the response to sorafenib and contribute to malignancy in HCC. Here, we found that RCN1, an endoplasmic reticulum resident protein, is significantly upregulated in sorafenib-resistant HCC cells and promotes tumor progression. Our analysis showed that RCN1 may be an independent predictor of tumor recurrence and overall survival. Mechanistically, RCN1 promotes the dissociation of GRP78 from IRE1α in sorafenib-resistant cells by interacting with GRP78 through its EFh1/2 domain. Subsequently, the IRE1α–XBP1s pathway, a branch of the unfolded protein response, is sustainably activated. Interestingly, IRE1α–XBP1s pathway activity is required for c-MYC signaling, one of the most highly activated oncogenic pathways in HCC. These results suggest that RCN1-targeted therapy might be a feasible strategy for the treatment of HCC.

Endoplasmic reticulum stress: Multiple regulatory roles in hepatocellular carcinoma

BACKGROUND

Endoplasmic reticulum (ER) stress is a basic cellular stress response that maintains cellular protein homeostasis under endogenous or exogenous stimuli, which depends on the stimulus, its intensity, and action time. The ER produces a corresponding cascade reaction for crosstalk of adaptive and/or pro-death regulation with other organelles. Hepatocellular carcinoma(HCC) is one of the most common malignant solid tumors with an extremely poor prognosis. Viral hepatitis infection, cirrhosis, and steatohepatitis are closely related to the occurrence and development of HCC, and ER stress has gradually been shown to be a major mechanism. Moreover, an increasing need for protein and lipid products and relative deficiencies of oxygen and nutrients for rapid proliferation and endoplasmic reticulum stress are undoubtedly involved. Therefore, to fully and comprehensively understand the regulatory role of endoplasmic reticulum stress in the occurrence and progression of HCC is of vital importance to explore its pathogenesis and develop novel anti-cancer strategies.

METHODOLOGY

We searched for relevant publications in the PubMed databases using the keywords "Endoplasmic reticulum stress", "hepatocellular carcinoma" in last five years,and present an overview of the current knowledge that links ER stress and HCC, which includes carcinogenesis, progression, and anti-cancer strategies, and propose directions of future research.

RESULT

ER stress were confirmed to be multiple regulators or effectors of cancer, which also be confirmed to drive tumorigenesis and progression of HCC. Targeting ER stress signaling pathway and related molecules could play a critical role for anti-HCC and has become a research hotspot for anti-cancer in recent years.

CONCLUSION

ER stress are critical for the processes of the tumorigenesis and progression of tumors. For HCC, ER stress was associated with tumorigenesis, development, metastasis, angiogenesis and drug resistance, targeting ER stress has emerged as a potential anti-tumor strategy.

Exploring the Role of Endoplasmic Reticulum Stress in Hepatocellular Carcinoma through mining of the Human Protein Atlas

Simple Summary

Hepatocellular carcinoma is a highly deadly primary liver cancer. It is usually diagnosed at a late stage, when therapeutic options are scarce, and the lack of predictive biomarkers poses a challenge for early detection. A known hallmark of hepatocellular carcinoma is the accumulation of misfolded proteins in the endoplasmic reticulum (ER), known as ER-stress. Growing experimental evidence suggests that ER-stress is involved in liver cancer initiation and progression. However, it remains unclear if ER-stress markers can be used as therapeutic targets or biomarkers for patients with liver cancer. In this study, we evaluated the prognostic value of proteins involved in managing ER-stress in liver cancer by mining a publicly available patient-derived database, the Human Protein Atlas. We thereby identified 44 ER-stress-associated proteins as prognostic markers in liver cancer. Furthermore, we discussed the expression of these markers in relation to disease stage, age, sex, ethnicity, and tissue localization.

Abstract

Endoplasmic reticulum (ER) stress and actors of unfolded protein response (UPR) have emerged as key hallmarks of hepatocarcinogenesis. Numerous reports have shown that the main actors in the UPR pathways are upregulated in HCC and contribute to the different facets of tumor initiation and disease progression. Furthermore, ER-stress inducers and inhibitors have shown success in preclinical HCC models. Despite the mounting evidence of the UPR’s involvement in HCC pathogenesis, it remains unclear how ER-stress components can be used safely and effectively as therapeutic targets or predictive biomarkers for HCC patients. In an effort to add a clinical context to these findings and explore the translational potential of ER-stress in HCC, we performed a systematic overview of UPR-associated proteins as predictive biomarkers in HCC by mining the Human Protein Atlas database. Aside from evaluating the prognostic value of these markers in HCC, we discussed their expression in relation to patient age, sex, ethnicity, disease stage, and tissue localization. We thereby identified 44 UPR-associated proteins as unfavorable prognostic markers in HCC. The expression of these markers was found to be higher in tumors compared to the stroma of the hepatic HCC patient tissues.

PERK/ATF4-Dependent ZFAS1 Upregulation Is Associated with Sorafenib Resistance in Hepatocellular Carcinoma Cells

Sorafenib, a multi-kinase inhibitor, is the first-line treatment for advanced hepatocellular carcinoma (HCC) patients. However, this drug only provides a short improvement of patients' overall survival, and drug resistance is commonly developed. Thus, the identification of resistant factor(s) or biomarker(s) is needed to develop more efficient therapeutic strategies. Long, non-coding RNAs (lncRNAs) have recently been viewed as attractive cancer biomarkers and drive many important cancer phenotypes. A lncRNA, ZFAS1 (ZNFX1 antisense RNA 1) has been found to promote HCC metastasis. This study found that sorafenib induced ZFAS1 expression specifically in sorafenib-resistant HCC cells. Although ZFAS1 knockdown did not restore the sensitivity of HCC cells to sorafenib, its expression may act as a resistant biomarker for sorafenib therapy. Bioinformatics analysis predicted that sorafenib tended to induce pathways related to endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) in sorafenib-resistant HCC cells. In vitro experimental evidence suggested that sorafenib induced protein kinase RNA-like ER kinase (PERK)/activating transcription factor 4 (ATF4)-dependent ZFAS1 expression, and sorafenib resistance could be overcome by PERK/ATF inhibitors. Therefore, PERK/ATF4/ZFAS1 signaling axis might be an attractive therapeutic and prognostic biomarker for sorafenib therapy in HCC.

Circ_0006168 Promotes the Migration, Invasion and Proliferation of Esophageal Squamous Cell Carcinoma Cells via miR-516b-5p-Dependent Regulation of XBP1

Background

Circular RNAs (circRNAs) exert important roles in carcinogenesis. Here, we aimed to uncover the working mechanism of circ_0006168 in esophageal squamous cell carcinoma (ESCC) development.

Methods

Western blot assay and real-time quantitative polymerase chain reaction (RT-qPCR) were used to determine protein and RNA expression, respectively. Wound healing assay and transwell migration assay were performed to assess cell migration ability, whereas cell invasion ability was evaluated by transwell invasion assay. 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and colony formation assay were utilized to analyze cell proliferation ability. Xenograft tumor model was utilized to assess the role of X-box binding protein 1 (XBP1) in xenograft tumor growth in vivo. Dual-luciferase reporter assay, RNA immunoprecipitation (RIP) assay and RNA pull down assay were used to verify intermolecular interactions.

Results

XBP1 silencing suppressed the migration, invasion and proliferation of ESCC cells in vitro and restrained the xenograft tumor growth in vivo. MicroRNA-516b-5p (miR-516b-5p) interacted with the 3ʹ untranslated region (3ʹUTR) of XBP1 in ESCC cells. MiR-516b-5p overexpression inhibited the proliferation and motility of ESCC cells. MiR-516b-5p was a molecular target of circ_0006168 in ESCC cells. The interference of circ_0006168 restrained the motility and proliferation of ESCC cells. Circ_0006168 acted as miR-516b-5p sponge to up-regulate XBP1 expression in ESCC cells. MiR-516b-5p silencing or the accumulation of XBP1 largely rescued the proliferation ability and motility in circ_0006168-silenced ESCC cells.

Conclusion

In conclusion, circ_0006168 contributed to ESCC development through promoting the proliferation and motility of ESCC cells via mediating miR-516b-5p/XBP1 axis.

Molecular Changes in Tissue Proteome during Prostate Cancer Development: Proof-of-Principle Investigation

(1) Background: Prostate cancer (PCa) is characterized by high heterogeneity. The aim of this study was to investigate molecular alterations underlying PCa development based on proteomics data. (2) Methods: Liquid chromatography coupled to tandem mass spectrometry was conducted for 22 fresh-frozen tissue specimens from patients with benign prostatic hyperplasia (BPH, n = 5) and PCa (n = 17). Mann Whitney test was used to define significant differences between the two groups. Association of protein abundance with PCa progression was evaluated using Spearman correlation, followed by verification through investigating the Prostate Cancer Transcriptome Atlas. Functional enrichment and interactome analysis were carried out using Metascape and String. (3) Results: Proteomics analysis identified 1433 proteins, including 145 proteins as differentially abundant between patients with PCa and BPH. In silico analysis revealed alterations in several pathways and hallmarks implicated in metabolism and signalling, represented by 67 proteins. Among the latter, 21 proteins were correlated with PCa progression at both the protein and mRNA levels. Interactome analysis of these 21 proteins predicted interactions between Myc proto-oncogene (MYC) targets, protein processing in the endoplasmic reticulum, and oxidative phosphorylation, with MYC targets having a central role. (4) Conclusions: Tissue proteomics allowed for characterization of proteins and pathways consistently affected during PCa development. Further validation of these findings is required.

Decomposition profile data analysis of multiple drug effects identifies endoplasmic reticulum stress-inducing ability as an unrecognized factor

Chemicals have multiple effects in biological systems. Because their on-target effects dominate the output, their off-target effects are often overlooked and can sometimes cause dangerous adverse events. Recently, we developed a novel decomposition profile data analysis method, orthogonal linear separation analysis (OLSA), to analyse multiple effects. In this study, we tested whether OLSA identified the ability of drugs to induce endoplasmic reticulum (ER) stress as a previously unrecognized factor. After analysing the transcriptome profiles of MCF7 cells treated with different chemicals, we focused on a vector characterized by well-known ER stress inducers, such as ciclosporin A. We selected five drugs predicted to be unrecognized ER stress inducers, based on their inducing ability scores derived from OLSA. These drugs actually induced X-box binding protein 1 splicing, an indicator of ER stress, in MCF7 cells in a concentration-dependent manner. Two structurally different representatives of the five test compounds exhibited similar results in HepG2 and HuH7 cells, but not in PXB primary hepatocytes derived from human-liver chimeric mice. These results indicate that our decomposition strategy using OLSA uncovered the ER stress-inducing ability of drugs as an unrecognized effect, the manifestation of which depended on the background of the cells.

Rack1 mediates Src binding to drug transporter P-glycoprotein and modulates its activity through regulating Caveolin-1 phosphorylation in breast cancer cells

The failure of chemotherapy and the emergence of multidrug resistance (MDR) are the major obstacles for effective therapy in locally advanced and metastatic breast cancer. Overexpression of the drug transporter P-glycoprotein (P-gp) in cancer cells is one of the main causes of MDR due to its ability to efflux anticancer drugs out of cells. Although the signaling node that regulates the expression of P-gp has been intensively investigated; the regulatory mechanism underlying P-gp transport activity remains obscure. Herein, we reported that Rack1 and tyrosine kinase Src confer drug resistance through modulating the transport function of P-gp without altering its protein level. We provide evidences that Rack1 and Src regulate P-gp activity by modulating caveolin-1 (Cav1) phosphorylation. Importantly, Rack1 acts as a signaling hub and mediates Src binding to P-gp, thereby facilitating the phosphorylation of Cav1 by Src and abolishing the inhibitory effect of Cav1 on P-gp. Taken together, our results demonstrate the pivotal roles of Rack1 and Src in modulating P-gp activity in drug-resistant cells. Our findings also provide novel insights into the mechanism regulating P-gp transport activity. Rack1 may represent a new target for the development of effective therapies for reversing drug resistance.

RACK1 Acts as a Potential Tumor Promoter in Colorectal Cancer

BACKGROUND

The receptor of activated protein kinase C 1 (RACK1) promotes the progression and invasion of several cancers. However, the role of RACK1 in the pathogenesis of colorectal cancer (CRC) has not been clearly defined. Herein, we aimed to investigate the biological role of RACK1 in CRC.

MATERIALS AND METHODS

The Cancer Genome Atlas (TCGA) and the Gene Expression Omnibus (GEO) dataset were searched, and the expression of RACK1 in CRC tissues and adjacent normal tissues was evaluated. Immunohistochemical staining was performed to detect the expression of RACK1 in human CRC, adenoma, and normal tissues. Western blotting was used to detect the expression of RACK1 in human CRC cell lines. Functional assays, such as BrdU, colony formation, and wound healing and transwell invasion assays, were used to explore the biological role of RACK1 in CRC.

RESULTS

RACK1 was upregulated in CRC tissues compared with its expression in adjacent normal tissues in TCGA and the GEO dataset (P < 0.05). Moreover, RACK1 was significantly overexpressed in CRC and adenoma tissues compared with its expression in normal tissues (P < 0.05). Loss-of-function experiments showed that RACK1 promoted cell proliferation, migration, and invasion in vitro.

CONCLUSIONS

Our data indicated that RACK1, as an oncogene, markedly promoted the progression of CRC, which suggested that RACK1 is a potential therapeutic target for CRC management.

Glucocorticoid-activated IRE1α/XBP-1s signaling: an autophagy-associated protective pathway against endotheliocyte damage

Glucocorticoid-induced endothelial injury has been reported in several diseases. Although there are several theories, the exact mechanism underlying the role of glucocorticoids in this process remains unclear. Autophagy has been reported to occur as a response to different stimuli and can affect cell survival and function. In this study, we found that glucocorticoids induced apoptosis and endoplasmic reticulum (ER) stress in endotheliocytes. Furthermore, we discovered that glucocorticoids induced autophagy in these cells and the inositol requiring protein 1 (IRE1α)/X-box binding protein 1s (XBP-1s) axis, one of the downstream signaling pathways of ER stress, was associated with the glucocorticoid-induced autophagy. The autophagy partly protected endotheliocytes from glucocorticoid-induced apoptosis and inhibition of proliferation. In conclusion, glucocorticoid-induced endoplasmic reticulum stress activated the IRE1α/XBP-1s signaling and induced autophagy, which, in turn, played a protective role in endotheliocyte survival and proliferation, avoiding further cellular damage caused by glucocorticoids.

Ribosomal proteins: insight into molecular roles and functions in hepatocellular carcinoma

Ribosomes, which are important sites for the synthesis of proteins related to expression and transmission of genetic information in humans, have a complex structure and diverse functions. They consist of a variety of ribosomal proteins (RPs), ribosomal RNAs (rRNAs) and small nucleolar RNAs. Owing to the involvement of ribosomes in many important biological processes of cells, their major components, rRNAs and RPs, have an important role in human diseases, including the initiation and evolvement of malignancies. However, the main mechanisms underlying the involvement of ribosomes in cancer remain unclear. This review describes the crucial role of ribosomes in various common malignant tumors; in particular, it examines the effects of RPs, including S6, the receptor for activated C-kinase and RPS15A, on the development and progression of hepatocellular carcinoma.

Endoplasmic reticulum stress signaling and chemotherapy resistance in solid cancers

The unfolded protein response (UPR) is an adaptive cellular program used by eukaryotic cells to cope with protein misfolding stress. During tumor development, cancer cells are facing intrinsic (oncogene activation) and extrinsic (limiting nutrient or oxygen supply) challenges, with which they must cope to survive. Moreover, chemotherapy represents an additional extrinsic challenge that cancer cells are facing and to which they adapt in the case of resistance. As of today, resistance to chemotherapy and targeted therapies is one of the important issues that oncologists have to deal with for treating cancer patients. In this review, we first describe the key molecular mechanisms controlling the UPR and their implication in solid cancers. Then, we review the literature that connects cancer chemotherapy resistance mechanisms and activation of the UPR. Finally, we discuss the possible applications of targeting the UPR to bypass drug resistance.

RACK1 promotes radiation resistance in esophageal cancer via regulating AKT pathway and Bcl-2 expression

RACK1 is a seven Trp-Asp 40 repeat protein, which interacts with a wide range of kinases and proteins. RACK1 plays an important role in the proliferation and progression of various cancers. The aim of this study is to detect the role of RACK1 in the radioresistance in esophageal cancer. The results indicated that downregulation of RACK1 reduced the colony formation ability, proliferation ability and resistance of cells to radiation effection through regulating the radiation-related proteins including pAKT, Bcl-2 and Bim; whereas upregulation of RACK1 promoted the ability and radioresistance of ESCC cells. Our findings suggest that RACK1 promotes proliferation and radioresistance in ESCC cells by activating the AKT pathway, upregulating Bcl-2 expression and downregulating protein levels of Bim. Our study fills in gaps in the field of RACK1 and radiation resistance and may provide new possibilities for improving strategies of radiotherapy in esophageal cancer.

Hepatitis B virus X protein and endoplasmic reticulum stress

Persistent hepatitis B virus (HBV) infection is closely related to chronic hepatitis, cirrhosis and liver cancer. China is a country with a high prevalence of HBV infection, where the infection rate is up to 60%-70%, bringing great threat and harm to public health. What's worse is that HBV infection is the main etiology factor of primary hepatocellular carcinoma (HCC). However, the underlying mechanisms of virus-induced tumor formation remain controversial. Numerous studies indicate that HBV X protein (HBx) plays a prominent role in HBV-induced liver cell damage, hepatitis, liver fibrosis and malignant transformation, and is related to liver cancer induced by environmental exposure factors. As a multifunctional regulatory protein, HBx regulates a variety of cell signal transduction pathways, including the endoplasmic reticulum (ER) stress response. ER stress refers to the dysfunction of the ER, and misfolded or unfolded proteins gather in the ER. It is noteworthy that the expression of HBx can induce or effect ER stress, although the molecular mechanism remains unclear. This review summarizes the role of HBx in ER stress pathways, providing clues for the liver injury induced by HBV infection.

Netrin-1 Protects Hepatocytes Against Cell Death Through Sustained Translation During the Unfolded Protein Response

BACKGROUND & AIMS

Netrin-1, a multifunctional secreted protein, is up-regulated in cancer and inflammation. Netrin-1 blocks apoptosis induced by the prototypical dependence receptors deleted in colorectal carcinoma and uncoordinated phenotype-5. Although the unfolded protein response (UPR) triggers apoptosis on exposure to stress, it first attempts to restore endoplasmic reticulum homeostasis to foster cell survival. Importantly, UPR is implicated in chronic liver conditions including hepatic oncogenesis. Netrin-1's implication in cell survival on UPR in this context is unknown.

METHODS

Isolation of translational complexes, determination of RNA secondary structures by selective 2'-hydroxyl acylation and primer extension/dimethyl sulfate, bicistronic constructs, as well as conventional cell biology and biochemistry approaches were used on in vitro-grown hepatocytic cells, wild-type, and netrin-1 transgenic mice.

RESULTS

HepaRG cells constitute a bona fide model for UPR studies in vitro through adequate activation of the 3 sensors of the UPR (protein kinase RNA-like endoplasmic reticulum kinase (PERK)), inositol requiring enzyme 1α (IRE1α), and activated transcription factor 6 (ATF6). The netrin-1 messenger RNA 5'-end was shown to fold into a complex double pseudoknot and bear E-loop motifs, both of which are representative hallmarks of related internal ribosome entry site regions. Cap-independent translation of netrin 5' untranslated region-driven luciferase was observed on UPR in vitro. Unlike several structurally related oncogenic transcripts (l-myc, c-myc, c-myb), netrin-1 messenger RNA was selected for translation during UPR both in human hepatocytes and in mice livers. Depletion of netrin-1 during UPR induces apoptosis, leading to cell death through an uncoordinated phenotype-5A/C-mediated involvement of protein phosphatase 2A and death-associated protein kinase 1 in vitro and in netrin transgenic mice.

CONCLUSIONS

UPR-resistant, internal ribosome entry site-driven netrin-1 translation leads to the inhibition of uncoordinated phenotype-5/death-associated protein kinase 1-mediated apoptosis in the hepatic context during UPR, a hallmark of chronic liver disease.

LB-100 sensitizes hepatocellular carcinoma cells to the effects of sorafenib during hypoxia by activation of Smad3 phosphorylation

Hepatocellular carcinoma (HCC) is a common cancer with poor prognosis. The multikinase inhibitor sorafenib is the only clinically proved systematic treatment for HCC. However, few patients respond to sorafenib. Hypoxic microenvironments contribute to sorafenib resistance. LB-100, a serine/threonine protein phosphatase 2A (PP2A) inhibitor was previously found to be a chemosensitizer in HCC. Here, we tested whether LB-100 could sensitize HCC to the effects of sorafenib. Intriguingly, LB-100 enhanced the effects of sorafenib in HCC cells only during hypoxic environments. LB-100 dramatically increased intracellular p-Smad3 level, which was responsible for the effect of LB-100 as a sensitizer. LB-100 downregulated Bcl-2 expression and enhanced sorafenib-induced apoptosis in HCC cells. We further proved that PP2A mediated LB-100-induced p-Smad3 overexpression. In addition, p38 mitogen-activated protein kinase pathway was activated in hypoxic conditions, and enhanced p-Smad3-dependent Bcl-2 inhibition and consequent apoptosis. In conclusion, LB-100 sensitized HCC cells to sorafenib in hypoxic environments. This effect was mediated by inactivation of PP2A, resulting in enhanced level of p-Smad3. Increased p-Smad3 downregulated Bcl-2, causing increased apoptosis of HCC cells.