Research advances on neurite outgrowth inhibitor B receptor

Neurite outgrowth inhibitor‐B (Nogo‐B) is a membrane protein which is extensively expressed in multiple organs, especially in endothelial cells and vascular smooth muscle cells of blood vessels and belongs to the reticulon protein family. Notably, its specific receptor, Nogo‐B receptor (NgBR), encoded by NUS1, has been implicated in many crucial cellular processes, such as cholesterol trafficking, lipid metabolism, dolichol synthesis, protein N‐glycosylation, vascular remodelling, angiogenesis, tumorigenesis and neurodevelopment. In recent years, accumulating studies have demonstrated the statistically significant changes of NgBR expression levels in human diseases, including Niemann‐Pick type C disease, fatty liver, congenital disorders of glycosylation, persistent pulmonary hypertension of the newborn, invasive ductal breast carcinoma, malignant melanoma, non‐small cell lung carcinoma, paediatric epilepsy and Parkinson's disease. Besides, both the in vitro and in vivo studies have shown that NgBR overexpression or knockdown contribute to the alteration of various pathophysiological processes. Thus, there is a broad development potential in therapeutic strategies by modifying the expression levels of NgBR.     

Arctigenin,a Natural Lignan Compound,Induces Apoptotic Death of Hepatocellular Carcinoma Cells via Suppression of PI3‐K/Akt Signaling

In this study, we explored the cytotoxic effects of arctigenin, a natural lignan compound, on human hepatocellular carcinoma (HCC) cells and check the involvement of phosphatidylinositol 3‐kinase (PI3‐K)/Akt signaling. HCC cells were treated with different concentrations of arctigenin and cell viability and apoptosis were assessed. Manipulating Akt signaling was used to determine its role in the action of arctigenin. Arctigenin significantly inhibited the viability of HCC cells in a concentration‐dependent manner. Arctigenin induced apoptosis and activation of caspase‐9 and ‐3. Overexpression of a constitutively active Akt mutant blocked arctigenin‐induced apoptosis. Combinational treatment with arctigenin and the PI3‐K inhibitor LY294002 significantly enhanced apoptosis. Arctigenin reduced the expression of Bcl‐xL, Mcl‐1, and survivin and the phosphorylation of mTOR and S6K, which were significantly reversed by overexpression of constitutively active Akt. This is the first report about the anticancer activity of arctigenin in HCC cells, which is mediated by inactivation of PI3‐K/Akt signaling.     

Expression of NgBR Is Highly Associated with Estrogen Receptor Alpha and Survivin in Breast Cancer

NgBR is a type I receptor with a single transmembrane domain and was identified as a specific receptor for Nogo-B. Our recent findings demonstrated that NgBR binds farnesylated Ras and recruits Ras to the plasma membrane, which is a critical step required for the activation of Ras signaling in human breast cancer cells and tumorigenesis. Here, we first use immunohistochemistry and real-time PCR approaches to examine the expression patterns of Nogo-B and NgBR in both normal and breast tumor tissues. Then, we examine the relationship between NgBR expression and molecular subtypes of breast cancer, and the roles of NgBR in estrogen-dependent survivin signaling pathway. Results showed that NgBR and Nogo-B protein were detected in both normal and breast tumor tissues. However, the expression of Nogo-B and NgBR in breast tumor tissue was much stronger than in normal breast tissue. The statistical analysis demonstrated that NgBR is highly associated with ER-positive/HER2-negative breast cancer. We also found that the expression of NgBR has a strong correlation with the expression of survivin, which is a well-known apoptosis inhibitor. The correlation between NgBR and survivin gene expression was further confirmed by real-time PCR. In vitro results also demonstrated that estradiol induces the expression of survivin in ER-positive T47D breast tumor cells but not in ER-negative MDA-MB-468 breast tumor cells. NgBR knockdown with siRNA abolishes estradiol-induced survivin expression in ER-positive T47D cells but not in ER-negative MDA-MB-468 cells. In addition, estradiol increases the expression of survivin and cell growth in ER-positive MCF-7 and T47D cells whereas knockdown of NgBR with siRNA reduces estradiol-induced survivin expression and cell growth. In summary, these results indicate that NgBR is a new molecular marker for breast cancer. The data suggest that the expression of NgBR may be essential in promoting ER-positive tumor cell proliferation via survivin induction in breast cancer.     

The overexpression of P21-activated kinase 5 (PAK5) promotes paclitaxel-chemoresistance of epithelial ovarian cancer

Protein kinases are important regulators in biologic processes. Aberrant expression of protein kinases often causes diseases including cancer. In the present study, we found that the serine-arginine protein kinase 1 (SRPK1) might be involved in hepatocellular carcinoma (HCC) proliferation from a kinome screen using a loss-of-function approach. In clinical samples, SRPK1 was frequently up-regulated in HCCs as compared with adjacent non-tumor tissues at both mRNA and protein levels. Functional studies indicated that overexpression of wild-type SRPK1 promoted HCC cell proliferation, while forced expression of the kinase-dead mutant of SRPK1 or RNA interference against SRPK1 suppressed cell growth and malignancy as measured in soft agar assay. The kinase-dead mutant of SRPK1 also inhibited subcutaneous xenografts’ growth of HCC cells in nude mice. Furthermore, western bolt analysis showed overexpression of wild-type SRPK1 enhanced Akt phosphorylation and knockdown of SRPK1 by RNA interference attenuated Akt phosphorylation induced by epidermal growth factor. Meanwhile, overexpression of wild-type SRPK1 also induced a concurrent increase in the total tyrosine phosphorylation of phosphotidylinositol-3 kinase p110α subunit, indicating a functional link between SRPK1 and PI3K/Akt signaling. Our findings suggest that SRPK1 plays an oncogenic role and could be a potential therapeutic target in HCC.     

Interaction of the Hepatitis B Spliced Protein with Cathepsin B Promotes Hepatoma Cell Migration and Invasion

Hepatitis B spliced protein (HBSP) is involved in the pathogenicity and/or persistence of hepatitis B virus (HBV). Chronic HBV infection is one of the most important risk factors for the development of hepatocellular carcinoma (HCC). However, whether or not HBSP contributes to the progression of HBV-associated HCC remains unknown. This study reports that overexpression of HBSP in human hepatoma cells increased cell invasion and motility. Conversely, small interfering RNA (siRNA)-mediated knockdown of HBSP expression inhibited migration and invasion. By glutathione S-transferase (GST) pulldown, coimmunoprecipitation, and a mammalian two-hybrid assay, HBSP was found to directly interact with cathepsin B (CTSB). Similar to HBSP knockdown, knocking down CTSB also reduced cell migration and invasion. Furthermore, the HBSP-overexpressing hepatoma cells were shown to have increased expression and activity of matrix metalloproteinase-9 (MMP-9) and urokinase-type plasminogen activator (uPA), and overexpression of HBSP significantly enhanced tumor-induced vascularization of endothelial cells. In contrast, knockdown of either HBSP or CTSB by siRNA resulted in inhibition of the two proteolytic enzymes and of the in vitro angiogenesis. Expression of HBSP in the hepatoma cells appeared to activate the mitogen-activated protein kinase (MAPK) and Akt signaling pathway, as evidenced by increases in phosphorylation of p38, Jun N-terminal protein kinase (JNK), extracellular signal-regulated kinase (ERK), and Akt. Taken together, these findings imply that interaction of HBSP with CTSB may promote hepatoma cell motility and invasion and highlight new molecular mechanisms for HBSP-induced HCC progression that involve the secretion and activation of proteolytic enzymes, increased tumor-induced angiogenesis, and activation of the MAPK/Akt signaling, thereby leading to the aggressiveness of hepatoma cells.     

T‐LAK cell‐originated protein kinase is essential for the proliferation of hepatocellular carcinoma SMMC‐7721 cells

Hepatocellular carcinoma (HCC) is one of the most common malignancies worldwide and typically has poor prognosis. Like most cancers, altered gene expression was always associated with the induction and maintenance of HCC. Here, we reported that the expression level of T‐LAK cell‐originated protein kinase (TOPK) is significantly up‐regulated in human HCC samples and cell lines. The suppression of TOPK by short hairpin RNA in HCC cell line SMMC‐7721 caused cell cycle arrest and reduced cell growth and colony formation ability. Moreover, the tumor formation ability of the TOPK‐suppression cells was significantly impaired compared with the control cells in nude mice. In addition, the knockdown expression of TOPK reduced the AKT phosphorylation. Taken together, we unveiled a novel role of TOPK which acts as an important positive regulator in human HCC cell proliferation. Copyright © 2013 John Wiley & Sons, Ltd.     

Involvement of SEPT4_i1 in hepatocellular carcinoma: SEPT4_i1 regulates susceptibility to apoptosis in hepatocellular carcinoma cells

SEPT4 belongs to the Septin family with multiple functions in cell division, cytoskeletal organization and other processes. This study aims to investigate the relationship between SEPT4_i1 isoform and human hepatocellular carcinoma (HCC). We showed that over-expression of SEPT4_i1 in HCC cells was able to sensitize cells to serum starvation-induced apoptosis. By contrast, knockdown of SEPT4_i1 expression in HCC cells was able to rescue cells from apoptosis induced by serum deprivation and to promote cell growth. Expressional analysis of SEPT4_i1 in tumor tissues further revealed that SEPT4_i1 was significantly down-regulated in human HCC tissues. Taken together, these data suggests a tumor suppressor role of SEPT4_i1 in HCC through regulating HCC cell apoptosis.     

GRK2 negatively regulates IGF‐1R signaling pathway and cyclins' expression in HepG2 cells

G protein coupled receptor kinase 2 (GRK2) plays a central role in the regulation of a variety of important signaling pathways. Alternation of GRK2 protein level and activity casts profound effects on cell physiological functions and causes diseases such as heart failure, rheumatoid arthritis, and obesity. We have previously reported that overexpression of GRK2 has an inhibitory role in cancer cell growth. To further examine the role of GRK2 in cancer, in this study, we investigated the effects of reduced protein level of GRK2 on insulin‐like growth factor 1 receptor (IGF‐1R) signaling pathway in human hepatocellular carcinoma (HCC) HepG2 cells. We created a GRK2 knockdown cell line using a lentiviral vector mediated expression of GRK2 specific short hairpin RNA (shRNA). Under IGF‐1 stimulation, HepG2 cells with reduced level of GRK2 showed elevated total IGF‐1R protein expression as well as tyrosine phosphorylation of receptor. In addition, HepG2 cells with reduced level of GRK2 also demonstrated increased tyrosine phosphorylation of IRS1 at the residue 612 and increased phosphorylation of Akt, indicating a stronger activation of IGF‐1R signaling pathway. However, HepG2 cells with reduced level of GRK2 did not display any growth advantage in culture as compared with the scramble control cells. We further detected that reduced level of GRK2 induced a small cell cycle arrest at G2/M phase by enhancing the expression of cyclin A, B1, and E. Our results indicate that GRK2 has contrasting roles on HepG2 cell growth by negatively regulating the IGF‐1R signaling pathway and cyclins' expression. J. Cell. Physiol. 228: 1897–1901, 2013. © 2013 Wiley Periodicals, Inc.     

NgBR is essential for endothelial cell glycosylation and vascular development

NgBR is a transmembrane protein identified as a Nogo‐B‐interacting protein and recently has been shown to be a subunit required for cis‐prenyltransferase (cisPTase) activity. To investigate the integrated role of NgBR in vascular development, we have characterized endothelial‐specific NgBR knockout embryos. Here, we show that endothelial‐specific NgBR knockout results in embryonic lethality due to vascular development defects in yolk sac and embryo proper. Loss of NgBR in endothelial cells reduces proliferation and promotes apoptosis of the cells largely through defects in the glycosylation of key endothelial proteins including VEGFR2, VE‐cadherin, and CD31, and defective glycosylation can be rescued by treatment with the end product of cisPTase activity, dolichol phosphate. Moreover, NgBR functions in endothelial cells during embryogenesis are Nogo‐B independent. These data uniquely show the importance of NgBR and protein glycosylation during vascular development.     

Lanthionine synthetase C–like protein 2 (LanCL2) is a novel regulator of Akt

The serine/threonine protein kinase Akt controls a wide range of biochemical and cellular processes under the modulation of a variety of regulators. In this study, we identify the lanthionine synthetase C–like 2 (LanCL2) protein as a positive regulator of Akt activation in human liver cells. LanCL2 knockdown dampens serum- and insulin-stimulated Akt phosphorylation, whereas LanCL2 overexpression enhances these processes. Neither insulin receptor phosphorylation nor the interaction between insulin receptor substrate and phosphatidylinositide 3-kinase (PI3K) is affected by LanCL2 knockdown. LanCL2 also does not function through PP2A, a phosphatase of Akt. Instead, LanCL2 directly interacts with Akt, with a preference for inactive Akt. Moreover, we show that LanCL2 also binds to the Akt kinase mTORC2, but not phosphoinositide-dependent kinase 1. Whereas LanCL2 is not required for the Akt-mTORC2 interaction, recombinant LanCL2 enhances Akt phosphorylation by target of rapamycin complex 2 (mTORC2) in vitro. Finally, consistent with a function of Akt in regulating cell survival, LanCL2 knockdown increases the rate of apoptosis, which is reversed by the expression of a constitutively active Akt. Taken together, our findings reveal LanCL2 as a novel regulator of Akt and suggest that LanCL2 facilitates optimal phosphorylation of Akt by mTORC2 via direct physical interactions with both the kinase and the substrate.     

Breast Cancer Metastasis Suppressor 1 Regulates Hepatocellular Carcinoma Cell Apoptosis via Suppressing Osteopontin Expression

Breast cancer metastasis suppressor 1 (BRMS1) was originally identified as an active metastasis suppressor in human breast cancer. Loss of BRMS1 expression correlates with tumor progression, and BRMS1 suppresses several steps required for tumor metastasis. However, the role of BRMS1 in hepatocellular carcinoma (HCC) remains elusive. In this study, we found that the expression level of BRMS1 was significantly down-regulated in HCC tissues. Expression of BRMS1 in SK-Hep1 cells did not affect cell growth under normal culture conditions, but sensitized cells to apoptosis induced by serum deprivation or anoikis. Consistently, knockdown of endogenous BRMS1 expression in Hep3B cells suppressed cell apoptosis. We identified that BRMS1 suppresses osteopontin (OPN) expression in HCC cells and that there is a negative correlation between BRMS1 and OPN mRNA expression in HCC tissues. Moreover, knockdown of endogenous OPN expression reversed the anti-apoptosis effect achieved by knockdown of BRMS1. Taken together, our results show that BRMS1 sensitizes HCC cells to apoptosis through suppressing OPN expression, suggesting a potential role of BRMS1 in regulating HCC apoptosis and metastasis.     

Enhanced NOLC1 promotes cell senescence and represses hepatocellular carcinoma cell proliferation by disturbing the organization of nucleolus

The nucleolus is a key organelle that is responsible for the synthesis of rRNA and assembly of ribosomal subunits, which is also the center of metabolic control because of the critical role of ribosomes in protein synthesis. Perturbations of rRNA biogenesis are closely related to cell senescence and tumor progression; however, the underlying molecular mechanisms are not well understood. Here, we report that cellular senescence‐inhibited gene (CSIG) knockdown up‐regulated NOLC1 by stabilizing the 5′UTR of NOLC1 mRNA, and elevated NOLC1 induced the retention of NOG1 in the nucleolus, which is responsible for rRNA processing. Besides, the expression of NOLC1 was negatively correlated with CSIG in the aged mouse tissue and replicative senescent 2BS cells, and the down‐regulation of NOLC1 could rescue CSIG knockdown‐induced 2BS senescence. Additionally, NOLC1 expression was decreased in human hepatocellular carcinoma (HCC) tissue, and the ectopic expression of NOLC1 repressed the proliferation of HCC cells and tumor growth in a HCC xenograft model.     

Functional analysis of α1,3/4-fucosyltransferase VI in human hepatocellular carcinoma cells

The α1,3/4-fucosyltransferases (FUT) subfamily are key enzymes in cell surface antigen synthesis during various biological processes. A novel role of FUTs in tumorigenesis has been discovered recently, however, the underlying mechanism remains largely unknown. Here, we characterized FUT6, a member of α1,3/4-FUT subfamily, in human hepatocellular carcinoma (HCC). In HCC tissues, the expression levels of FUT6 and its catalytic product SLe(x) were significantly up-regulated. Overexpression of FUT6 in HCC cells enhanced S-phase cell population, promoted cell growth and colony formation ability. Moreover, subcutaneously injection of FUT6-overexpressing cells in nude mice promoted cell growth in vivo. In addition, elevating FUT6 expression markedly induced intracellular Akt phosphorylation, and suppressed the expression of the cyclin-dependent kinases inhibitor p21. Bath application of the PI3K inhibitor blocked FUT6-induced Akt phosphorylation, p21 suppression and cell proliferation. Our results suggest that FUT6 plays an important role in HCC growth by regulating the PI3K/Akt signaling pathway.     

Ubiquitin specific peptidase 5 mediates Histidine‐rich protein Hpn induced cell apoptosis in hepatocellular carcinoma through P14‐P53 signaling

Hpn is a small histidine‐rich cytoplasmic protein from Helicobacter pylori and has been recognized as a high‐risk factor for several cancers including gastric cancer, colorectal cancer, and MALT lymphoma. However, the relationship between Hpn and cancers remains elusive. In this study, we discovered that Hpn protein effectively suppressed cell growth and induced apoptosis in hepatocellular carcinoma (HCC). A two‐dimensional gel electrophoresis and mass spectrometry‐based comparative proteomics was performed to find the molecular targets of Hpn in HCC cells. It was identified that twelve proteins were differentially expressed, with USP5 being one of the most significantly downregulated protein. The P14^ARF‐P53 signaling was activated by USP5 knockdown in HCC cells. Furthermore, USP5 overexpression significantly rescued the suppressive effect of Hpn on the viability of HCC cells. In conclusion, our study suggests that Hpn plays apoptosis‐inducing roles through suppressing USP5 expression and activating the P14^ARF‐P53 signaling. Therefore, Hpn may be a potential candidate for developing novel anti‐HCC drugs.     

Perifosine induces cell cycle arrest and apoptosis in human hepatocellular carcinoma cell lines by blockade of Akt phosphorylation

Hepatocellular carcinoma (HCC) is one of the most common solid cancers, representing the third cause of cancer-related death among cirrhotic patients. Treatment of advanced HCC has become a very active area of research. Perifosine, a new synthetic alkylphospholipid Akt inhibitor, has shown anti-tumor activity by inhibition of Akt phosphorylation. In this study, the effect of perifosine on the cell proliferation and apoptosis in hepatoma cells has been investigated. Cell growth inhibition was detected by MTT assay, cell cycle was analyzed by flow cytometry, AnnexinV-FITC apoptosis detection kit was used to detect cell apoptosis, and protein expression was examined by Western blotting analysis. Our present studies showed that Akt phosphorylation was inhibited by perifosine in HepG2 and Bel-7402 human hepatocellular carcinoma cells. Perifosine inhibited the growth of HepG2 cells and Bel-7402 cells in a dose-dependent manner, and arrested cell cycle progression at the G₂ phase. Apoptosis induction became more effective with increasing perifosine concentration. The caspase cascade and its downstream effectors, Poly (ADP-ribose) polymerase (PARP), were also activated simultaneously upon perifosine treatment. The proapoptotic effect of perifosine was in part depending on regulation of the phosphorylation level of ERK and JNK. Perifosine cotreatment substantially increased cytotoxic effects of cisplatin in HepG2 cells. Down-regulating the expression of Bcl-2 and up-regulating the level of Bax may be the potential mechanism for this synergistic effect. Our findings suggest that the small molecule Akt inhibitor perifosine shows substantial anti-tumor activity in human hepatoma cancer cell lines, and is a good candidate for treatment combinations with classical cytostatic compounds in hepatocellular carcinoma.     

Resveratrol suppresses the proliferation of breast cancer cells by inhibiting fatty acid synthase signaling pathway

In breast cancer cells, overexpression of human epidermal growth factor receptor 2 (HER2) increases the translation of fatty acid synthase (FASN) by altering the activity of PI3K/Akt signaling pathways. Cancer chemotherapy causes major side effects and is not effective enough in slowing down the progression of the disease. Earlier studies showed a role for resveratrol in the inhibition of FASN, but the molecular mechanisms of resveratrol-induced inhibition are not known. In the present study, we examined the novel mechanism of resveratrol on Her2-overexpressed breast cancer cells.The effect of resveratrol on the growth of breast cancer cells was assessed as percent cell viability by cytotoxicity-based MTT assay and the induction of apoptosis was determined by cell-death detection ELISA and flow cytometric analysis of Annexin-V–PI binding. Western immunobloting was used to detect signaling events in human breast cancer (SKBR-3) cells.Data showed that resveratrol-mediated down-regulation of FASN and HER2 genes synergistically induced apoptotic death in SKBR-3 cells. This concurrently caused a prominent up-regulation of PEA3, leads to down-regulation of HER2 genes. Resveratrol also alleviated the PI3K/Akt/mTOR signaling by down-regulation of Akt phosphorylation and up-regulation of PTEN expression.These findings suggest that resveratrol alters the cell cycle progression and induce cell death via FASN inhibition in HER2 positive breast cancer.     

Overexpression of Aurora-A enhances invasion and matrix metalloproteinase-2 expression in esophageal squamous cell carcinoma cells

Esophageal squamous cell carcinoma (ESCC) is one of the most aggressive cancers, and metastasis is the principal cause of death in ESCC patients. It has been shown that amplification and overexpression of mitotic serine/threonine kinase Aurora-A occur in several types of human tumors, including ESCC. Moreover, increase in expression levels of Aurora-A has been predicted to correlate with the grades of tumor differentiation and invasive capability. However, the mechanisms by which Aurora-A mediates its invasive effects still remain elusive. In this article, we showed that Aurora-A overexpression significantly increased cell migration and invasion as well as secretion and expression of matrix metalloproteinase-2 (MMP-2). Conversely, siRNA-mediated knockdown of Aurora-A expression in human ESCC cells led to inhibition of cell invasiveness as well as secretion and expression of MMP-2. In addition, Aurora-A overexpression increased phosphorylation levels of p38 mitogen-activated protein kinase (MAPK) and Akt, and the knockdown of Aurora-A by siRNA decreased the activity of p38 MAPK and Akt. Moreover, the blocking of the activity of above kinases using chemical inhibitors suppressed the ability of Aurora-A to induce MMP-2 secretion and expression as well as cell invasion. These data show that overexpression of Aurora-A contributes to the malignancy development of ESCC by enhancing tumor cell invasion as well as MMP-2 activity and expression, which can occur through signaling pathways involving p38 MAPK and Akt protein kinases. Taken together, these studies provide a molecular basis for promoting the role of Aurora-A in malignancy development of ESCC.     

Angiopoietin-2, an angiogenic regulator, promotes initial growth and survival of breast cancer metastases to the lung through the integrin-linked kinase (ILK)-AKT-B cell lymphoma 2 (Bcl-2) pathway

The early onsets of breast cancer metastasis involve cell retention, survival, and resistant to apoptosis and subsequent growth at target vascular beds and tissues in distant organs. We previously reported that angiopoietin-2 (Ang2), an angiogenic regulator stimulates MCF-7 breast tumor metastasis from their orthotopic sites to distant organs through the α(5)β(1) integrin/integrin-linked kinase (ILK)/Akt pathway. Here, by using an experimental tumor metastasis model and in vitro studies, we further dissect the underlying mechanism by which Ang2 promotes the initial growth and survival of MCF-7 breast cancer metastasis in the lung of animals. We show that Ang2 increases cell survival and suppresses cell apoptosis through ILK-induced phosphorylation of Akt1, Akt2, and up-regulation of Bcl-2 in breast cancer cells. Inhibition of ILK, Akt1, and Akt2, and their effector Bcl-2 diminishes Ang2-stimulated breast cancer cell survival and Ang2-attenuated apoptosis in vitro, and initial survival and growth of breast cancer metastasis in the lung of animals. Additionally, siRNA knockdown of endogenous Ang2 in three human metastatic breast cancer cell lines also inhibits phosphorylation of Akt, expression of Bcl-2, and tumor cell survival, migration, and increases cell apoptosis. Since increased expression of Ang2 correlates with elevated potential of human breast cancer metastasis in clinic, our data underscore the importance that up-regulated Ang2 not only stimulates breast cancer growth and metastasis at late stages of the process, but is also critical at the initiating stages of metastases onset, thereby suggesting Ang2 as a promising therapeutic target for treating patients with metastatic breast cancer.     

Tripartite motif protein 25 is associated with epirubicin resistance in hepatocellular carcinoma cells via regulating PTEN/AKT pathway

Tripartite motif protein 25 (TRIM25) expression was altered in various human cancers. Herein, we found that the expression of TRIM25 was elevated in hepatocellular carcinoma (HCC) tissues and cell lines. Knockdown of TRIM25 increased the sensitivity of HCC HepG2 cells to epirubicin (EPI), as indicated by reduced cell viability, enhanced cell apoptosis, and downregulated P‐glycoprotein (P‐gp) and multiple drug‐resistance protein 1 (MRP1). Moreover, TRIM25 knockdown strengthened the effects of EPI on phosphatase and tensin homolog (PTEN) and phosphorylated (p)‐AKT. However, overexpression of TRIM25 exerted an opposite effect, weakening the sensitivity of Huh7 to EPI, and obviously increasing PTEN and reducing p‐AKT. Most important, all the changes induced by TRIM25 overexpression in Huh7 were reversed with additional treatment of LY294002 (an AKT pathway inhibitor). Notably, coimmunoprecipitation experiments confirmed the interaction between TRIM25 and PTEN. Knockdown of TRIM25 resulted in reduced ubiquitination of PTEN protein. Collectively, our data suggested that TRIM25 enhanced EPI resistance via modulating PTEN/AKT pathway, and targeting TRIM25 may enhance the sensitivity of HCC cells toward chemotherapy drugs.