BIRC6 promotes hepatocellular carcinogenesis: interaction of BIRC6 with p53 facilitating p53 degradation

BIRC6 Modulates the Protein Stability of Axin to Regulate the Growth, Stemness, and Resistance of Renal Cancer Cells via the β-Catenin Pathway

The mechanism underlying the development of renal cell carcinoma (RCC) remains unclear, and effective prevention and therapeutic measures are lacking. BIRC6, a protein inhibitor of apoptosis, has attracted great interest. Our data indicated that overexpression of BIRC6 elevated cell growth, colony formation, migration, and invasion of cultured RCC cells, while siRNA knockdown of BIRC6 suppressed these processes. Additionally, BIRC6 was highly expressed in RCC clinical samples along with a downregulated level of Axin. Immunoprecipitation assays found that BIRC6 interacted with Axin and the two proteins colocalized within the cytoplasm of RCC cells. Overexpression of BIRC6 promoted the ubiquitination modification of Axin, while genetic knockdown of BIRC6 suppressed it. Furthermore, overexpression of BIRC6 significantly promoted the turnover of Axin, suggesting BIRC6's inhibitory effect on Axin protein stability. BIRC6 was also upregulated in cancer stem-like cells of RCC and increased the drug resistance of RCC cells against sunitinib. Western blotting assays showed that the overexpression of BIRC6 upregulated CXCR4 protein expression and activated the β-catenin pathway. Two cell lines were then constructed with BIRC6 overexpressed by lentiviruses. Pharmacological administration of a Wnt/β-catenin inhibitor, XAV-939, or genetic knockdown of β-catenin inhibited cell growth, tumor sphere formation, colony formation, migration, and invasion of BIRC6-overexpressed cells. In vivo administration of XAV-939 markedly suppressed the tumorigenesis of BIRC6-overexpressed RCC cells in nude mice. In conclusion, we propose that BIRC6 activates the β-catenin signaling pathway via mediating the ubiquitination and degradation of Axin, promoting the growth, stemness, and drug resistance of RCC cells. This project aims to elucidate the role of BIRC6 as a potential therapeutic target and provide new insights into the clinical treatment of RCC.

Molecular mechanisms underlying the BIRC6-mediated regulation of apoptosis and autophagy

Procaspase 9 is the initiator caspase for apoptosis, but how its levels and activities are maintained remains unclear. The gigantic Inhibitor-of-Apoptosis Protein BIRC6/BRUCE/Apollon inhibits both apoptosis and autophagy by promoting ubiquitylation of proapoptotic factors and the key autophagic protein LC3, respectively. Here we show that BIRC6 forms an anti-parallel U-shaped dimer with multiple previously unannotated domains, including a ubiquitin-like domain, and the proapoptotic factor Smac/DIABLO binds BIRC6 in the central cavity. Notably, Smac outcompetes the effector caspase 3 and the pro-apoptotic protease HtrA2, but not procaspase 9, for binding BIRC6 in cells. BIRC6 also binds LC3 through its LC3-interacting region, probably following dimer disruption of this BIRC6 region. Mutation at LC3 ubiquitylation site promotes autophagy and autophagic degradation of BIRC6. Moreover, induction of autophagy promotes autophagic degradation of BIRC6 and caspase 9, but not of other effector caspases. These results are important to understand how the balance between apoptosis and autophagy is regulated under pathophysiological conditions.

High USP32 expression contributes to cancer progression and is correlated with immune infiltrates in hepatocellular carcinoma

BACKGROUND

Ubiquitin-specific protease 32 (USP32) is a highly conserved gene that promotes cancer progression. However, its role in hepatocellular carcinoma (HCC) is not well understood. The aim of this project is to explore the clinical significance and functions of USP32 in HCC.

METHODS

The expression of USP32 in HCC was evaluated using data from TCGA, GEO, TISCH, tissue microarray, and human HCC samples from our hospital. Survival analysis, PPI analysis and GSEA analysis were performed to evaluate USP32-related clinical significance, key molecules and enrichment pathways. Using the ssGSEA algorithm and TIMER, we investigated the relationships between USP32 and immune infiltrates in the TME. Univariate and multivariate Cox regression analyses were then used to identify key USP32-related immunomodulators and constructed a USP32-related immune prognostic model. Finally, CCK8, transwell and colony formation assays of HCC cells were performed and an HCC nude mouse model was established to verify the oncogenic role of USP32.

RESULTS

USP32 is overexpressed in HCC and its expression is an independent predictive factor for outcomes of HCC patients. USP32 is associated with pathways related to cell behaviors and cancer signaling, and its expression is significantly correlated with the infiltration of immune cells in the TME. We also successfully constructed a USP32-related immune prognostic model using 5 genes. Wet experiments confirmed that knockdown of USP32 could repress the proliferation, colony formation and migration of HCC cells in vitro and inhibit tumor growth in vivo.

CONCLUSION

USP32 is highly expressed in HCC and closely correlates with the TME of HCC. It is a potential target for improving the efficacy of chemotherapy and developing new strategies for targeted therapy and immunotherapy in HCC.

Inhibition of XPO1 impairs cholangiocarcinoma cell proliferation by triggering p53 intranuclear accumulation

BACKGROUND

XPO1 mediates the nuclear export of several proteins, mainly tumor suppressors. KPT-330 (Selinexor) is a selective inhibitor of XPO1 that has demonstrated good therapeutic effects in hematologic cancers.

METHODS

We used TCGA and GTEx pan-cancer database to evaluate XPO1 mRNA expression in various tumors. Cell proliferation assay and colony formation assay were used to analyze the in vitro antitumor effects of XPO1 inhibitor KPT-330. Western blot was performed to explore the specific mechanisms.

RESULTS

We found that XPO1 was highly expressed across a range of cancers and associated with poor prognosis in hepatobiliary and pancreatic tumors. We revealed that the XPO1 inhibitor KPT-330 triggered the nuclear accumulation of the p53 protein and significantly disrupted the proliferation of cholangiocarcinoma cells. Mechanistically, the XPO1 inhibitor, KPT-330, reduced BIRC6 expression by inhibiting the PI3K/AKT pathway to decrease p53 degradation and improve its stability.

CONCLUSION

Therefore, XPO1 may be a potential therapeutic target in cholangiocarcinoma, mediated by its effects on KPT-330.

Oral Squamous Cell Carcinoma: The Role of BIRC6 Serum Level

Background

Different factors are involved in the incidence, etiology, metastasis, diagnosis, and treatment of oral squamous cell carcinoma, including apoptosis inhibitor proteins. Baculoviral IAP repeat containing protein 6 (BIRC6) is one of the apoptosis inhibitor proteins contributing to cancer cells' survival in many cancer types with diagnostic and treatment importance. This study is aimed at assessing the serum level of BIRC6 in oral squamous cell carcinoma.

Materials and Methods

In this retrospective cross-sectional study, 60 serum samples were collected from 45 male and 15 female patients with a mean age of 61 years as the case group and 28 serum samples of healthy people as a control group. The serum samples were analyzed using a commercial sandwich ELISA kit.

Results

There were no significant differences between BIRC6 serum levels in patients and healthy subjects. Moreover, we did not observe any significant relationships between BIRC6 serum levels and the patients' demographic or clinical characteristics.

Conclusions

There was no significant difference in serum BIRC6 levels in patients with oral squamous cell carcinoma and healthy individuals. Its use in determining the prognosis of squamous cell carcinoma or considering it a determinant marker in this type of cancer may not have a place. More in-depth studies for evaluating BIRC6 serum levels in oral squamous cell carcinoma patients are recommended for better insight into this protein's role in diagnosing, progression, and prognosis of the disease.

The Zebrafish Antiapoptotic Protein BIRC2 Promotes Edwardsiella piscicida Infection by Inhibiting Caspases and Accumulating p53 in a p53 Transcription-Dependent and -Independent Manner

IAPs (inhibitors of apoptosis) are endogenous caspase inhibitors with multiple biological activities. In the present study, we show functional characteristics of antiapoptotic protein BIRC2 (cIAP1) in response to Edwardsiella piscicida infection. Overexpression of BIRC2 in zebrafish larvae promoted the proliferation of E. piscicida, leading to a decreased larvae survival. The expression levels of caspases including casp3, casp8, and casp9 were significantly inhibited by BIRC2 overexpression in the case of E. piscicida infection. Treatment of zebrafish larvae microinjected with BIRC2 with the caspase activator PAC-1 completely blocked the negative regulation of BIRC2 on the E. piscicida infection, with the reduced inhibition on the casp3 and without inhibition on casp8 and casp9. In contrast to the regulation of BIRC2 on the caspases, BIRC2 overexpression significantly induced the expression of p53, especially at 24 hpi. In addition to the cytoplasmic p53 expression, BIRC2 overexpression also induced the expression of the nuclear p53 protein. Further analysis demonstrated that BIRC2 could interact and colocalize with p53 in the cytoplasm. The numbers of E. piscicida in larvae overexpressed with BIRC2 and treated with pifithrin-μ (an inhibitor of mitochondrial p53) or pifithrin-α (an inhibitor of p53 transactivation) were lower than those of larvae without pifithrin-μ or pifithrin-α treatment. Critically, the p53 inactivators pifithrin-μ and pifithrin-α had no significant effect on larval survival, but completely rescued larval survival for zebrafish microinjected with BIRC2 in the case of E. piscicida infection. Collectively, the present study suggest that piscine BIRC2 is a negative regulator for antibacterial immune response in response to the E. piscicida infection via inhibiting caspases, and accumulating p53 in a p53 transcription-dependent and -independent manner.

Overexpression of BIRC6 driven by EGF-JNK-HECTD1 signaling is a potential therapeutic target for triple-negative breast cancer

Triple-negative breast cancer (TNBC) is an aggressive and highly lethal disease. The lack of targeted therapies and poor patient outcome have fostered efforts to discover new molecular targets to treat patients with TNBC. Here, we showed that baculoviral IAP repeat containing 6 (BIRC6) is overexpressed and positively correlated with epidermal growth factor (EGF) receptor (EGFR) in TNBC cells and tissues and that BIRC6 overexpression is associated with poor patient survival. Mechanistic studies revealed that BIRC6 stability is increased by EGF-JNK signaling, which prevents ubiquitination and degradation of BIRC6 mediated by the E3 ubiquitin ligase HECTD1. BIRC6 in turn decreases SMAC expression by inducing the ubiquitin-proteasome pathway, thereby antagonizing apoptosis and promoting the proliferation, colony formation, tumorsphere formation, and tumor growth capacity of TNBC cells. Therapeutically, the PEGylated cationic lipid nanoparticle (pCLN)-assisted delivery of BIRC6 small interfering RNA (siRNA) efficiently silences BIRC6 expression in TNBC cells, thus suppressing TNBC cell growth in vitro and in vivo, and its antitumor activity is significantly superior to that of the EGFR inhibitor gefitinib. Our findings identify an important regulatory mechanism of BIRC6 overexpression and provide a potential therapeutic option for treating TNBC.

Silencing circ‑BIRC6 inhibits the proliferation, invasion, migration and epithelial‑mesenchymal transition of bladder cancer cells by targeting the miR‑495‑3p/XBP1 signaling axis

Circular RNAs (circRNAs) regulate gene expression by acting as a 'sponge' for microRNAs (miRs) and play crucial roles in tumorigenesis, including in bladder cancer (BC). circRNA‑baculoviral IAP repeat‑containing 6 (circ‑BIRC6) has been reported to participate in the pathogenesis of several cancer types. The present study aimed to elucidate the roles and potential mechanisms of circ‑BIRC6 in the progression of BC. circ‑BIRC6 expression levels in BC cell lines were determined using reverse transcription‑quantitative PCR. Following circ‑BIRC6 knockdown, cell proliferation, invasion and migration were detected using Cell Counting Kit‑8, colony formation, Transwell and wound healing assays, respectively. Western blotting was also conducted to evaluate the expression levels of X‑box binding protein 1 (XBP1) and epithelial‑mesenchymal transition (EMT)‑associated proteins. In addition, rescue experiments were performed using by transfecting a miR‑495‑3p inhibitor into T24 cells following circ‑BIRC6 knockdown. The interactions between circ‑BIRC6, miR‑495‑3p and XBP1 was verified using dual luciferase reporter assays. Moreover, T24 cells with circ‑BIRC6 knockdown and miR‑495‑3p inhibitor transfection were used for the tumor‑bearing experiment. Tumor growth was observed and Ki‑67 expression was determined using immunohistochemistry. The results demonstrated that circ‑BIRC6 expression was upregulated in BC cell lines. Moreover, circ‑BIRC6 knockdown notably attenuated the proliferation, invasion, migration and EMT of BC cells, which was blocked by the miR‑495‑3p inhibitor. It was also identified that circ‑BIRC6 sponged miR‑495‑3p to regulate XBP1 expression. In addition, results from the xenograft experiments indicated that the knockdown of circ‑BIRC6 and miR‑495‑3p expression significantly inhibited tumor growth. It was also found that the expression levels of XBP1, Ki‑67 and EMT‑associated proteins in tumor tissues of the co‑transfection group were markedly restored compared with the circ‑BIRC6 knockdown group. In conclusion, these findings demonstrated that circ‑BIRC6 knockdown suppressed BC tumorigenesis and progression via regulation of the miR‑495‑3p/XBP1 signaling axis, offering a promising therapeutic target for the treatment of BC.

Morphological changes and functional circRNAs screening of rabbit skeletal muscle development

BACKGROUND

The temporal expression pattern of circular RNAs (circRNAs) across developmental stages is essential for skeletal muscle growth and functional analysis. However, there are few analyses on the potential functions of circRNAs in rabbit skeletal muscle development.

RESULTS

Initially, the paraffin sections showed extremely significant differences in the diameter, number, area and density of skeletal muscle fibers of the fetus, child, adult rabbit hind legs (P < 0.01). Then, RNA-seq libraries of these three stages were constructed. A total of 481 differentially expressed circRNAs (DE-circRNAs) and 5,658 differentially expressed genes (DEGs) were identified. Subsequently, DE-circRNAs, whose host genes were DEGs or non-DEGs, were analyzed by GO respectively. In the fetus vs. child group, up-regulated DE-circRNAs (whose host genes were DEGs) were related to muscle fiber structure, and down-regulated ones were related to mitosis. The up-regulated DE-circRNAs (whose host genes were non-DEGs) were involved in enzyme activity, methylation and glycosylation, and the down-regulated ones were involved in mitosis and catabolism. In the fetus vs. adult group, the up-regulated DE-circRNAs (whose host genes were DEGs) were related to skeletal muscle basic structure, and the down-regulated ones were also associated with cell proliferation. But the up-regulated DE-circRNAs (whose host genes were non-DEGs) were connected with regulation of histone ubiquitination, chromatin and organelles. The down-regulated DE-circRNAs were connected with the catabolism processes. In addition, novel_circ_0022663 and novel_circ_0005489, which might have coding potential, and novel_circ_0004210 and novel_circ_0001669, which might have miRNA sponge capability, were screened out.

CONCLUSIONS

In this study, hind leg muscles of fetus, child and adult rabbits were collected for paraffin section and RNA-seq to observe the structural changes of skeletal muscle and obtain circRNA expression profiles at different stages. These data provided a catalog of circRNAs related to muscle development in New Zealand rabbits, allowing us to better understand the functional transitions in mammalian muscle development.

The Molecular Basis of Ubiquitin-Conjugating Enzymes (E2s) as a Potential Target for Cancer Therapy

Ubiquitin-conjugating enzymes (E2s) are one of the three enzymes required by the ubiquitin-proteasome pathway to connect activated ubiquitin to target proteins via ubiquitin ligases. E2s determine the connection type of the ubiquitin chains, and different types of ubiquitin chains regulate the stability and activity of substrate proteins. Thus, E2s participate in the regulation of a variety of biological processes. In recent years, the importance of E2s in human health and diseases has been particularly emphasized. Studies have shown that E2s are dysregulated in variety of cancers, thus it might be a potential therapeutic target. However, the molecular basis of E2s as a therapeutic target has not been described systematically. We reviewed this issue from the perspective of the special position and role of E2s in the ubiquitin-proteasome pathway, the structure of E2s and biological processes they are involved in. In addition, the inhibitors and microRNAs targeting E2s are also summarized. This article not only provides a direction for the development of effective drugs but also lays a foundation for further study on this enzyme in the future.

Tumor Suppressor Protein p53 and Inhibitor of Apoptosis Proteins in Colorectal Cancer-A Promising Signaling Network for Therapeutic Interventions

Simple Summary

Tumor suppressor 53 (p53) is a multifunctional protein that regulates cell cycle, DNA repair, apoptosis and metabolic pathways. In colorectal cancer (CRC), mutations of the gene occur in 60% of patients and are associated with a more aggressive tumor phenotype and resistance to anti-cancer therapy. In addition, inhibitor of apoptosis (IAP) proteins are distinguished biomarkers overexpressed in CRC that impact on a diverse set of signaling pathways associated with the regulation of apoptosis/autophagy, cell migration, cell cycle and DNA damage response. As these mechanisms are further firmly controlled by p53, a transcriptional and post-translational regulation of IAPs by p53 is expected to occur in cancer cells. Here, we aim to review the molecular regulatory mechanisms between IAPs and p53 and discuss the therapeutic potential of targeting their interrelationship by multimodal treatment options.

Abstract

Despite recent advances in the treatment of colorectal cancer (CRC), patient’s individual response and clinical follow-up vary considerably with tumor intrinsic factors to contribute to an enhanced malignancy and therapy resistance. Among these markers, upregulation of members of the inhibitor of apoptosis protein (IAP) family effects on tumorigenesis and radiation- and chemo-resistance by multiple pathways, covering a hampered induction of apoptosis/autophagy, regulation of cell cycle progression and DNA damage response. These mechanisms are tightly controlled by the tumor suppressor p53 and thus transcriptional and post-translational regulation of IAPs by p53 is expected to occur in malignant cells. By this, cellular IAP1/2, X-linked IAP, Survivin, BRUCE and LIVIN expression/activity, as well as their intracellular localization is controlled by p53 in a direct or indirect manner via modulating a multitude of mechanisms. These cover, among others, transcriptional repression and the signal transducer and activator of transcription (STAT)3 pathway. In addition, p53 mutations contribute to deregulated IAP expression and resistance to therapy. This review aims at highlighting the mechanistic and clinical importance of IAP regulation by p53 in CRC and describing potential therapeutic strategies based on this interrelationship.

[Effect of small interfering RNA-mediated BIRC6 silencing on apoptosis and autophagy of renal cancer 786-O cells]

OBJECTIVE

To study the expression of BIRC6 in renal cancer tissues and investigate the effect of BIRC6 silencing on apoptosis and autophagy of 786-O cells.

METHODS

Twenty surgical specimens of renal cancer tissues and adjacent renal tissues were collected from Meizhou People's Hospital between February, 2016 and December, 2018 for detection of BIRC6 protein expression using immunohistochemistry. Renal cancer 786-O cells were transfected with a control small interfering RNA (siRNA) or BIRC6 siRNA via lipofectamine 2000, and the changes in cell proliferation and apoptosis following 5-FU treatment were assessed using CCK8 assay and flow cytometry; the expressions of autophagy-related proteins Beclin and LC3A/B were detected by Western blotting.

RESULTS

The expression of BIRC6 protein was significantly higher in renal cancer tissues than in the adjacent renal tissues. Western blotting showed that siRNA-mediated silencing of BIRC6 significantly lowered the expression of BIRC6 in 786-O cells. In the cells with BIRC6 silencing, treatment with 12.5, 25, 50, 100 and 200 μg/mL 5-FU resulted in significantly higher proliferation inhibition rates than in the cells transfected with the control siRNA (P < 0.01). BIRC6 silencing also significantly increased the apoptosis rate of 786-O cells following 5-FU treatment (P < 0.01). The results of Western blotting showed that BIRC6 silencing significantly lowered the protein expressions of Beclin and LC3A/B in 786-O cells.

CONCLUSIONS

Interference of BIRC6 mediated by siRNA can inhibit autophagy and promote 5-FU-induced apoptosis to enhance the sensitivity of 786-O cells to 5-FU.

Circular RNAs: Emerging Role in Cancer Diagnostics and Therapeutics

Circular RNAs (circRNAs) are rapidly coming to the fore as major regulators of gene expression and cellular functions. They elicit their influence via a plethora of diverse molecular mechanisms. It is not surprising that aberrant circRNA expression is common in cancers and they have been implicated in multiple aspects of cancer pathophysiology such as apoptosis, invasion, migration, and proliferation. We summarize the emerging role of circRNAs as biomarkers and therapeutic targets in cancer.

CAPS1 Suppresses Tumorigenesis in Cholangiocarcinoma

BACKGROUND

CAPS1 (calcium-dependent activator protein for secretion) is a multi-domain protein involved in regulating exocytosis of synaptic vesicles and dense-core vesicles. However, the expression and function of CAPS1 in cholangiocarcinoma (CCA) remains unclear. In the present study, we explored the role of CAPS1 in CCA carcinogenesis.

METHODS

CAPS1 expression was explored using western blotting and immunohistochemistry in four CCA cell lines and clinical samples from 90 cases of CCA. The clinical significance of CAPS1 was analyzed. The biological function of CAPS1 in CCA cells was detected in vitro and in vivo. The underlying mechanism of CAPS1 function was explored by detecting the expression of critical molecules in its associated signaling pathways. The mechanism of CAPS1 downregulation in tumor tissues was explored using in silico prediction and luciferase reporter assays.

RESULTS

CAPS1 expression was reduced in CCA cell lines and human tumor tissues. Loss of CAPS1 in tumor tissues was closely associated with poor prognosis of patients with CCA. Moreover, CAPS1 expression correlated significantly with tumor-node-metastasis stage, lymph node metastasis, and vascular invasion. Lentivirus-mediated CAPS1 overexpression substantially prevented clone formation, cell proliferation, and cell cycle progression. CAPS1 overexpression also suppressed carcinogenesis in nude mice. Mechanistically, CAPS1 overexpression greatly accelerated the ERK and p38 MAPK signal pathways. In addition, microRNA miR-30e-5p negatively regulated CAPS1 expression.

CONCLUSION

These data showed that CAPS1 functions as a tumor suppressor in CCA. Reduced CAPS1 expression could indicate poor prognosis of patients with CCA.

MALAT1 knockdown inhibits prostate cancer progression by regulating miR-140/BIRC6 axis

BACKGROUND

Prostate cancer (PCa) is the second most common cancer among men globally. Long non-coding RNA metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) has been reported to be implicated in tumorigenesis and progression of PCa. However, the pathogenesis of MALAT1 in PCa has not been thoroughly elaborated.

METHODS

RT-qPCR assay was conducted to measure expression of MALAT1, microRNA-140 (miR-140) and Baculoviral IAP repeat containing 6 (BIRC6) mRNA. Protein expression of BIRC6 was detected by western blot assay. Cell proliferative ability was assessed by MTS and Edu retention assays. Cell migratory and invasive abilities were evaluated by wound healing assay and Transwell invasion assay, respectively. Cell apoptotic rate was examined using a flow cytometry. The interaction between miR-140 and MALAT1 or BIRC6 3'UTR was explored by luciferase, RNA immunoprecipitation (RIP) and RNA pull down assays. Xenograft models of PCa were established to further explore the role and molecular mechanism of MALAT in PCa tumorigenesis in vivo.

RESULTS

MALAT1 and BIRC6 were highly expressed in human PCa tumor tissues and cell lines. MALAT1 or BIRC6 knockdown inhibited cell proliferation, migration and invasion and induced cell apoptosis in PCa. MiR-140 could directly bind with MALAT1 or BIRC6 3'UTR. Moreover, MALAT1 knockdown inhibited BIRC mRNA and protein expression through upregulating miR-140 in PCa cells. Additionally, MALAT1 knockdown inhibited PCa xenograft tumor growth by regulating miR-140/BIRC6 axis in vivo.

CONCLUSION

MALAT1 knockdown hindered PCa progression by regulating miR-140/BIRC6 axis in vitro and in vivo, hinting the potential value of MALAT1 in the management of PCa.

Negative regulation of autophagy by UBA6-BIRC6-mediated ubiquitination of LC3

Although the process of autophagy has been extensively studied, the mechanisms that regulate it remain insufficiently understood. To identify novel autophagy regulators, we performed a whole-genome CRISPR/Cas9 knockout screen in H4 human neuroglioma cells expressing endogenous LC3B tagged with a tandem of GFP and mCherry. Using this methodology, we identified the ubiquitin-activating enzyme UBA6 and the hybrid ubiquitin-conjugating enzyme/ubiquitin ligase BIRC6 as autophagy regulators. We found that these enzymes cooperate to monoubiquitinate LC3B, targeting it for proteasomal degradation. Knockout of UBA6 or BIRC6 increased autophagic flux under conditions of nutrient deprivation or protein synthesis inhibition. Moreover, UBA6 or BIRC6 depletion decreased the formation of aggresome-like induced structures in H4 cells, and α-synuclein aggregates in rat hippocampal neurons. These findings demonstrate that UBA6 and BIRC6 negatively regulate autophagy by limiting the availability of LC3B. Inhibition of UBA6/BIRC6 could be used to enhance autophagic clearance of protein aggregates in neurodegenerative disorders.

Oncogenic role of phospholipase C-γ1 in progression of hepatocellular carcinoma

AIM

Phospholipase C-γ1 (PLCG1) was previously found to be involved in a variety of oncogenic behaviors such as cell motility, cell proliferation, cell migration, and invasion. However, its function in hepatocellular carcinoma (HCC) was unknown. Here, we explored the expression pattern and function of PLCG1 in HCC progression.

METHODS

Expression of PLCG1 was examined by western blotting in hepatoma cells and human tumor tissues. Expression was also detected by immunohistochemistry in 150 HCC clinical samples, and its clinical significance was analyzed. The influence of PLCG1 on HCC carcinogenesis were determined in vitro and in vivo. The underlying mechanisms were explored by detecting the expression of critical molecules of signaling pathways.

RESULTS

The results showed that PLCG1 was overexpressed in hepatoma cell lines and clinical HCC tissues. Increased PLCG1 expression in tumor tissues was remarkably correlated with poor clinical features of HCC. Patients with positive PLCG1 expression in tumor tissues had shorter overall survival and relapse-free survival. Phospholipase C gamma 1 could substantially promote cell proliferation, anchor growth, and cell invasion in vitro. The in vivo study showed that inhibition of PLCG1 in hepatoma cells significantly repressed tumor growth in nude mice. Furthermore, we showed that PLCG1 might exert its function by activating the mitogen-activated protein kinase and nuclear factor-κB signaling pathways.

CONCLUSION

Our data indicated that PLCG1 could act as an oncogene in HCC carcinogenesis and could serve as a valuable prognostic marker and potential therapeutic target for HCC.

Linc01194 acts as an oncogene in colorectal carcinoma and is associated with poor survival outcome

Background

The incidence of colorectal cancer ranks among the top three malignant tumors, attributing to more than 50,000 deaths in the United States every year. Survival rate is directly correlated with TNM stage at diagnosis, and identifying the molecules involved in the cancer development process will provide directions to better investigate the mechanisms of colorectal cancer.

Materials and methods

Bioinformatics analysis of differentially expressed long noncoding RNAs (lncRNAs), survival analysis, cell proliferation assay, migration assay, and Western blot analysis were performed.

Results

Fifty-one lncRNAs were identified between the early stage and late-stage groups. In the survival analysis, we found that Linc01194 is correlated with poor survival of colon cancer patients. In addition, by suppressing the expression of Linc01194 in colon cancer cell lines, cell proliferation and migration were inhibited. Western blot showed that N-cadherin and vimentin were downregulated, whereas E-cadherin was upregulated indicating that the process of epithelial–mesenchymal transition (EMT) was restrained.

Conclusion

Linc01194 promotes the proliferation and migration ability of colon cancer cells by activating EMT. It acts as an oncogene in colorectal carcinoma and is associated with worse survival outcome.

TREM2 acts as a tumor suppressor in hepatocellular carcinoma by targeting the PI3K/Akt/β-catenin pathway

Triggering receptor expressed on myeloid cells 2 (TREM2) is involved in nonmalignant pathological processes. However, TREM2’s function in malignant diseases, especially in hepatocellular carcinoma (HCC) remains unknown. In the present study, we report that TREM2 is a novel tumor suppressor in HCC. TREM2 expression was obviously decreased in hepatoma cells (especially metastatic HCC cells), and in most human HCC tissues (especially extrahepatic metastatic tumors). Reduced tumor TREM2 expression was correlated with poor prognosis of HCC patients, and with aggressive pathological features (BCLC stage, tumor size, tumor encapsulation, vascular invasion, and tumor differentiation). TREM2 knockdown substantially promoted cell growth, migration, and invasion in vitro and in vivo, while TREM2 overexpression produced the opposite effect. TREM2 suppressed HCC metastasis by inhibiting epithelial-mesenchymal transition, accompanied by abnormal expression of epithelial and mesenchymal markers. Further study revealed that downregulation of TREM2 in HCC was regulated by miR-31-5p. Moreover, by directly interacting with β-catenin, TREM2 attenuated oncogenic and metastatic behaviors by inhibiting Akt and GSK3β phosphorylation, and activating β-catenin. TREM2 suppressed carcinogenesis and metastasis in HCC by targeting the PI3K/Akt/β-catenin pathway. Thus, we propose that TREM2 may be a candidate prognostic biomarker in malignant diseases and TREM2 restoration might be a prospective strategy for HCC therapy.

MiR-204 acts as a potential therapeutic target in acute myeloid leukemia by increasing BIRC6-mediated apoptosis

Acute myeloid leukemia (AML) is one of the most common hematological malignancies all around the world. MicroRNAs have been determined to contribute various cancers initiation and progression, including AML. Although microRNA-204 (miR-204) exerts anti-tumor effects in several kinds of cancers, its function in AML remains unknown. In the present study, we assessed miR-204 expression in AML blood samples and cell lines. We also investigated the effects of miR-204 on cellular function of AML cells and the underlying mechanisms of the action of miR-204. Our results showed that miR-204 expression was significantly downregulated in AML tissues and cell lines. In addition, overexpression of miR-204 induced growth inhibition and apoptosis in AML cells, including AML5, HL-60, Kasumi-1 and U937 cells. Cell cycle analysis further confirmed an augmentation in theapoptotic subG1 population by miR-204 overexpression. Mechanistically, baculoviral inhibition of apoptosis protein repeat containing 6 (BIRC6) was identified as a direct target of miR-204. Enforcing miR-204 expression increased the luciferase activity and expression of BIRC6, as well as p53 and Bax expression. Moreover, restoration of BIRC6 reversed the pro-apoptotic effects of miR-204 overexpression in AML cells. Taken together, this study demonstrates that miR-204 causes AML cell apoptosis by targeting BIRC6, suggesting miR-204 may play an anti-carcinogenic role in AML and function as a novel biomarker and therapeutic target for the treatment of this disease.

Sestrin 2 confers primary resistance to sorafenib by simultaneously activating AKT and AMPK in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the malignancy derived from normal hepatocytes with increasing incidence and extremely poor prognosis worldwide. The only approved first‐line systematic treatment agent for HCC, sorafenib, is capable to effectively improve advanced HCC patients’ survival. However, it is gradually recognized that the therapeutic response to sorafenib could be drastically diminished after short‐term treatment, defined as primary resistance. The present study is aimed to explore the role of stress‐inducible protein Sestrin2 (SESN2), one of the most important sestrins family members, in sorafenib primary resistance. Herein, we initially found that SESN2 expression was significantly up‐regulated in both HCC cell lines and tissues compared to normal human hepatocytes and corresponding adjacent liver tissues, respectively. In addition, SESN2 expression was highly correlated with sorafenib IC₅₀ of HCC cell lines. Thereafter, we showed that sorafenib treatment resulted in an increase of SESN2 expression and the knockdown of SESN2 exacerbated sorafenib‐induced proliferation inhibition and cell apoptosis. Further mechanistic study uncovered that SESN2 deficiency impaired both AKT and AMPK phosphorylation and activation after sorafenib treatment. Moreover, the correlations between SESN2 expression and both phosphor‐AKT and phosphor‐AMPK expression were illustrated in HCC tissues. Taken together, our study demonstrates that SESN2 activates AKT and AMPK signaling as a novel mechanism to induce sorafenib primary resistance in HCC.

LAMP3 plays an oncogenic role in osteosarcoma cells partially by inhibiting TP53

BACKGROUND

Osteosarcoma (OS) is a common malignant tumor that predominantly occurs in adolescents. Its most common metastasis is to the lungs. As shown in our earlier study, lysosome-associated membrane glycoprotein 3 (LAMP3) is highly upregulated in metastatic OS. However, its role in the regulation of OS cell viability and apoptosis remains unknown.

METHODS

We knocked down and overexpressed LAMP3 in OS cells and assessed the cell viability and apoptosis. Then, we investigated the expression of apoptosis-associated genes to identify the downstream gene(s) of LAMP3.

RESULTS

Knockdown of LAMP3 significantly inhibited OS cell viability and promoted apoptosis. TP53, which is involved in the apoptosis pathway, was found to be highly upregulated after knockdown of LAMP3. Overexpression of LAMP3 significantly increased cell viability and abrogated apoptosis. Importantly, subsequent knockdown of TP53 partially suppressed the increased OS cell apoptosis induced by the inhibition of LAMP3, suggesting that TP53 is a key functional downstream gene of LAMP3.

CONCLUSIONS

Our findings suggest that LAMP3 promotes OS cell viability and survival by regulating TP53 expression.

Renal inhibition of miR-181a ameliorates 5-fluorouracil-induced mesangial cell apoptosis and nephrotoxicity

The development of nephrotoxicity largely limits the clinical use of chemotherapy. MiRNAs are able to target various genes and involved in the regulation of diverse cellular processes, including cell apoptosis and death. Our study showed that miR-181a expression was significantly increased after 5-fluorouracil (5-FU) treatment in renal mesangial cells and kidney tissue, which was associated with decreased baculoviral inhibition of apoptosis protein repeat-containing 6 (BIRC6) expression and increased apoptotic rate. Enforced miR-181a expression enhanced 5-FU-induced p53-dependent mitochondrial apoptosis, including declined Bcl-2/Bax ratio, loss of mitochondrial membrane potential, cytochrome c release, and caspase-9 and caspase-3 activation. However, inhibition of miR-181a was associated with reduced p53-mediated mitochondrial apoptosis induced by 5-FU. Moreover, miR-181a increased BIRC6 downstream gene p53 protein expression and transcriptional activity by reducing ubiquitin-mediated protein degradation. We found that miR-181a directly targeted 3'-UTR of BIRC6 mRNA and negatively regulated BIRC6 expression. In vivo study, knockdown of miR-181a with adeno-associated virus harboring miR-181a-tough decoy attenuated 5-FU-induced renal cell apoptosis, inflammation and kidney injury. In conclusion, these results demonstrate that miR-181a increases p53 protein expression and transcriptional activity by targeting BIRC6 and promotes 5-FU-induced apoptosis in mesangial cells. Inhibition of miR-181a ameliorates 5-FU-induced nephrotoxicity, suggesting that miR-181a may be a novel therapeutic target for nephrotoxicity treatment during chemotherapy.

The IAP family member BRUCE regulates autophagosome-lysosome fusion

Autophagy has an important role in cellular homeostasis by degrading and recycling cytotoxic components. Ubiquitination is known to target cargoes for autophagy; however, key components of this pathway remain elusive. Here we performed an RNAi screen to uncover ubiquitin modifiers that are required for starvation-induced macroautophagy in mammalian cells. Our screen uncovered BRUCE/Apollon/Birc6, an IAP protein, as a new autophagy regulator. Depletion of BRUCE leads to defective fusion of autophagosomes and lysosomes. Mechanistically, BRUCE selectively interacts with two ATG8 members GABARAP and GABARAPL1, as well as with Syntaxin 17, which are all critical regulators of autophagosome–lysosome fusion. In addition, BRUCE colocalizes with LAMP2. Interestingly, a non-catalytic N-terminal BRUCE fragment that is sufficient to bind GABARAP/GABARAPL1 and Syntaxin 17, and to colocalize with LAMP2, rescues autolysosome formation in Bruce^−/− cells. Thus, BRUCE promotes autolysosome formation independently of its ubiquitin-conjugating activity and is a regulator of both macroautophagy and apoptosis.

The inhibitor of apoptosis (IAP) protein, BRUCE is known to ubiquitinate apoptosis regulators for proteasomal degradation. Here the authors show that BRUCE provides a bridge between LAMP2 on lysosomes and Atg8 family proteins on autophagosomes to support autophagosome-lysosome fusion.

Smurf2, an E3 ubiquitin ligase, interacts with PDE4B and attenuates liver fibrosis through miR-132 mediated CTGF inhibition

We previously reported that Smad ubiquitin regulatory factor 2 (Smurf2) activity was decreased in human fibrotic livers. Here, we overexpressed Smurf2 in livers of transgenic mice and observed inhibited collagen deposition and hepatic stellate cell activation in fibrotic model induced by carbon tetrachloride treatment or bile duct ligation. Hepatic Smurf2 overexpression also inhibited the production of connective tissue growth factor (CTGF), a central mediator of liver fibrosis. Using miRNA array and bioinformatics analyses, we identified miR-132 as a mediator of this inhibitory effect. miR-132 directly targets the 3'-untranslated region of CTGF and was transcriptionally upregulated by cAMP-PKA-CREB signaling. In addition, Smurf2 activated cAMP-PKA-CREB pathway by interacting with phosphodiesterase 4B (PDE4B) and facilitating its degradation. Thus, we have demonstrated a previously unrecognized anti-fibrotic pathway controlled by Smurf2.

Revealing protein networks and gene-drug connectivity in cancer from direct information

The connection between genetic variation and drug response has long been explored to facilitate the optimization and personalization of cancer therapy. Crucial to the identification of drug response related genetic features is the ability to separate indirect correlations from direct correlations across abundant datasets with large number of variables. Here we analyzed proteomic and pharmacogenomic data in cancer tissues and cell lines using a global statistical model connecting protein pairs, genes and anti-cancer drugs. We estimated this model using direct coupling analysis (DCA), a powerful statistical inference method that has been successfully applied to protein sequence data to extract evolutionary signals that provide insights on protein structure, folding and interactions. We used Direct Information (DI) as a metric of connectivity between proteins as well as gene-drug pairs. We were able to infer important interactions observed in cancer-related pathways from proteomic data and predict potential connectivities in cancer networks. We also identified known and potential connections for anti-cancer drugs and gene mutations using DI in pharmacogenomic data. Our findings suggest that gene-drug connections predicted with direct couplings can be used as a reliable guide to cancer therapy and expand our understanding of the effects of gene alterations on drug efficacies.

BIRC6 mediates imatinib resistance independently of Mcl-1

Baculoviral IAP repeat containing 6 (BIRC6) is a member of the inhibitors of apoptosis proteins (IAPs), a family of functionally and structurally related proteins that inhibit apoptosis. BIRC6 has been implicated in drug resistance in several different human cancers, however mechanisms regulating BIRC6 have not been extensively explored. Our phosphoproteomic analysis of an imatinib-resistant chronic myelogenous leukemia (CML) cell line (MYL-R) identified increased amounts of a BIRC6 peptide phosphorylated at S480, S482, and S486 compared to imatinib-sensitive CML cells (MYL). Thus we investigated the role of BIRC6 in mediating imatinib resistance and compared it to the well-characterized anti-apoptotic protein, Mcl-1. Both BIRC6 and Mcl-1 were elevated in MYL-R compared to MYL cells. Lentiviral shRNA knockdown of BIRC6 in MYL-R cells increased imatinib-stimulated caspase activation and resulted in a ~20-25-fold increase in imatinib sensitivity, without affecting Mcl-1. Treating MYL-R cells with CDK9 inhibitors decreased BIRC6 mRNA, but not BIRC6 protein levels. By contrast, while CDK9 inhibitors reduced Mcl-1 mRNA and protein, they did not affect imatinib sensitivity. Since the Src family kinase Lyn is highly expressed and active in MYL-R cells, we tested the effects of Lyn inhibition on BIRC6 and Mcl-1. RNAi-mediated knockdown or inhibition of Lyn (dasatinib/ponatinib) reduced BIRC6 protein stability and increased caspase activation. Inhibition of Lyn also increased formation of an N-terminal BIRC6 fragment in parallel with reduced amount of the BIRC6 phosphopeptide, suggesting that Lyn may regulate BIRC6 phosphorylation and stability. In summary, our data show that BIRC6 stability is dependent on Lyn, and that BIRC6 mediates imatinib sensitivity independently of Mcl-1 or CDK9. Hence, BIRC6 may be a novel target for the treatment of drug-resistant CML where Mcl-1 or CDK9 inhibitors have failed.

Inducing death in tumor cells: roles of the inhibitor of apoptosis proteins

The heterogeneous group of diseases collectively termed cancer results not just from aberrant cellular proliferation but also from a lack of accompanying homeostatic cell death. Indeed, cancer cells regularly acquire resistance to programmed cell death, or apoptosis, which not only supports cancer progression but also leads to resistance to therapeutic agents. Thus, various approaches have been undertaken in order to induce apoptosis in tumor cells for therapeutic purposes. Here, we will focus our discussion on agents that directly affect the apoptotic machinery itself rather than on drugs that induce apoptosis in tumor cells indirectly, such as by DNA damage or kinase dependency inhibition. As the roles of the Bcl-2 family have been extensively studied and reviewed recently, we will focus in this review specifically on the inhibitor of apoptosis protein (IAP) family. IAPs are a disparate group of proteins that all contain a baculovirus IAP repeat domain, which is important for the inhibition of apoptosis in some, but not all, family members. We describe each of the family members with respect to their structural and functional similarities and differences and their respective roles in cancer. Finally, we also review the current state of IAPs as targets for anti-cancer therapeutics and discuss the current clinical state of IAP antagonists.

Expression and clinical significance of Apollon in renal carcinoma

Apollon, namely baculoviral inhibitor of apoptosis proteins (IAP) repeat containing 6, is an unusually large member of the IAP family, and may be important in oncogenesis. The aim of the present study was to assess the association between renal carcinoma (RC) and Apollon expression, and to highlight the link between Apollon expression and the occurrence, development and prognosis of RC. Apollon expression was detected by immunohistochemistry, western blotting and reverse transcription-quantitative polymerase chain reaction in RC tissues, adjacent non-cancerous tissues and paired normal tissues, respectively, in order to analyze the association between Apollon expression and clinicopathological features of RC. Kaplan-Meier survival estimate was used to assess the prognostic significance. It was observed that Apollon expression was higher in carcinoma tissues than in adjacent non-cancerous tissues and normal control tissues at the protein and messenger RNA level (P<0.001). There was a significant difference in T-stage (P=0.006), nodal involvement (P=0.007) and tumor-node-metastasis-stage (P=0.035) in patients categorized according to different Apollon expression levels. A prognostic significance of Apollon was also identified by the Kaplan-Meier method. The results of the present study indicate that Apollon expression is associated with the biological characteristics of renal cancer, and is potentially a valuable predictor and novel target for RC.

CAPS1 Negatively Regulates Hepatocellular Carcinoma Development through Alteration of Exocytosis-Associated Tumor Microenvironment

The calcium-dependent activator protein for secretion 1 (CAPS1) regulates exocytosis of dense-core vesicles (DCVs) in neurons and neuroendocrine cells. The role of CAPS1 in cancer biology remains unknown. The purpose of this study was to investigate the role of CAPS1 in hepatocellular carcinoma (HCC). We determined the levels of CAPS1 in eight hepatoma cell lines and 141 HCC specimens. We evaluated the prognostic value of CAPS1 expression and its association with clinical parameters. We investigated the biological consequences of CAPS1 overexpression in two hepatoma cell lines in vitro and in vivo. The results showed that loss of CAPS1 expression in HCC tissues was markedly correlated with aggressive tumor phenotypes, such as high-grade tumor node metastasis (TNM) stage (p = 0.003) and absence of tumor encapsulation (p = 0.016), and was associated with poor overall survival (p = 0.008) and high recurrence (p = 0.015). CAPS1 overexpression inhibited cell proliferation and migration by changing the exocytosis-associated tumor microenvironment in hepatoma cells in vitro. The in vivo study showed that CAPS1 overexpression inhibited xenograft tumor growth. Together, these results identified a previously unrecognized tumor suppressor role for CAPS1 in HCC development.

BIRC6 Targeting as Potential Therapy for Advanced, Enzalutamide-Resistant Prostate Cancer

Purpose: Enzalutamide resistance has emerged as a major problem in the management of castration-resistant prostate cancer (CRPC). Research on therapy resistance of CRPCs has primarily focused on the androgen receptor pathway. In contrast, there is limited information on antiapoptotic mechanisms that may facilitate the treatment resistance. The inhibitor of apoptosis proteins (IAP) family is well recognized for its role in promoting treatment resistance of cancers by inhibiting drug-induced apoptosis. Here, we examined whether BIRC6, an IAP family member, has a role in enzalutamide resistance of CRPCs and could provide a therapeutic target for enzalutamide-resistant CRPC.Experimental Design: Use of enzalutamide-resistant CRPC models: (i) the transplantable, first high-fidelity LTL-313BR patient-derived enzalutamide-resistant CRPC tissue xenograft line showing primary enzalutamide resistance, (ii) MR42D and MR49F CRPC cells/xenografts showing acquired enzalutamide resistance. Specific BIRC6 downregulation in these models was produced using a BIRC6-targeting antisense oligonucleotide (ASO-6w2). Gene expression was determined by qRT-PCR and gene expression profiling. Molecular pathways associated with growth inhibition were assessed via gene enrichment analysis.Results: Of eight IAPs examined, BIRC6 was the only one showing elevated expression in both enzalutamide-resistant CRPC models. Treatment with ASO-6w2 markedly suppressed growth of LTL-313BR xenografts and increased tumor apoptosis without inducing major host toxicity. Pathway enrichment analysis indicated that GPCR and matrisome signaling were the most significantly altered pathways. Furthermore, ASO-6w2 inhibited expression of prosurvival genes that were upregulated in the LTL-313BR line.Conclusions:BIRC6 targeting inhibited the growth of enzalutamide-resistant CRPC models and may represent a new option for clinical treatment of advanced, enzalutamide-resistant prostate cancer. Clin Cancer Res; 23(6); 1542-51. ©2016 AACR.

Expression and clinical significance of Apollon in esophageal squamous cell carcinoma

Apollon, an unusually large member of the inhibitors of apoptosis protein family, may be important for oncogenesis development. The aim of the present study was to assess the association between esophageal squamous cell carcinoma (ESCC) and Apollon expression levels, and to highlight the association between Apollon and the occurrence, development and prognosis of ESCC. Apollon expression was detected by immunohistochemical staining and reverse transcription-quantitative polymerase chain reaction in ESCC tissues, adjacent non-cancerous tissues and paired normal tissues respectively, in order to analyze the association between Apollon expression and the clinicopathological features of ESCC. Survival analysis was used to assess the prognostic significance of Apollon expression. It was determined that the mRNA and protein expression levels of Apollon were significantly higher in the carcinoma tissues compared with the adjacent non-cancerous tissues and normal control tissues (P<0.001). There was a significant difference in lymph node involvement and the tumor, nodes, and metastases stage in patients categorized according to different Apollon expression levels. The prognostic significance of Apollon was also determined using the log-rank method. The overexpression of Apollon was associated with shorter overall survival and disease-free survival rates. The present study indicates that Apollon expression is associated with the biological characteristics of ESCC, and may be a valuable prognostic factor and a novel chemotherapeutic target for ESCC treatment.

Downregulation of miR-129-2 by promoter hypermethylation regulates breast cancer cell proliferation and apoptosis

Aberrant expression of the miR-129 family has been found in several types of cancer, yet its expression and potential biologic role in breast cancer remain largely unknown. In the present study, we found that miR-129-2 was consistently downregulated in the breast cancer specimens and cell lines. Overexpression of miR-129-2-3p markedly suppressed breast cancer cell proliferation and induced its apoptosis. In addition, a luciferase reporter assay revealed that miR-129-2-3p suppressed BCL2L2 expression. Furthermore, BCL2L2 was able to reverse miR-129-2-3p-mediated cell apoptosis, indicating that BCL2L2 plays a crucial role in mediating the tumor-suppressive role of miR-129-2-3p. Moreover, bisulfite DNA sequencing PCR (BSP) analysis identified that promoter hypermethylation was responsible for the downregulation of miR-129-2 in breast cancer. Collectively, our findings indicate that miR-129-2 is downregulated in breast cancer cells by promoter hypermethylation. Moreover, downregulation of miR-129-2 results in BCL2L2 overexpression and disease progression in breast cancer patients.