Mus81 knockdown improves chemosensitivity of hepatocellular carcinoma cells by inducing S-phase arrest and promoting apoptosis through CHK1 pathway

RP11-789C1.1 inhibits gastric cancer cell proliferation and accelerates apoptosis via the ATR/CHK1 signaling pathway

BACKGROUND

Long non-coding RNAs (lncRNAs) plays an important role in the progression of gastric cancer (GC). Their involvement ranges from genetic regulation to cancer progression. However, the mechanistic roles of RP11-789C1.1 in GC are not fully understood.

METHODS

We identified the expression of lncRNA RP11-789C1.1 in GC tissues and cell lines by real-time fluorescent quantitative polymerase chain reaction. A series of functional experiments revealed the effect of RP11-789C1.1 on the proliferation of GC cells. In vivo experiments verified the effect of RP11-789C1.1 on the biological behavior of a GC cell line. RNA pull-down unveiled RP11-789C1.1 interacting proteins. Western blot analysis indicated the downstream pathway changes of RP11-789C1.1, and an oxaliplatin dosing experiment disclosed the influence of RP11-789C1.1 on the drug sensitivity of oxaliplatin.

RESULTS

Our results demonstrated that RP11-789C1.1 inhibited the proliferation of GC cells and promoted the apoptosis of GC cells. Mechanistically, RP11-789C1.1 inhibited checkpoint kinase 1 (CHK1) phosphorylation by binding ataxia-telangiectasia mutated and Rad3 related (ATR), a serine/threonine-specific protein kinase, promoted GC apoptosis, and mediated oxaliplatin sensitivity.

CONCLUSION

In general, we discovered a tumor suppressor molecule RP11-789C1.1 and confirmed its mechanism of action, providing a theoretical basis for targeted GC therapy.

MUS81 Inhibition Enhances the Anticancer Efficacy of Talazoparib by Impairing ATR/CHK1 Signaling Pathway in Gastric Cancer

MUS81 is a critical endonuclease involved in heterodimer formation with Eme1/Mms4 and an important DNA damage repair regulatory molecule. Our previous study suggested that MUS81 was overexpressed and its high expression was positively correlated with gastric cancer metastasis. However, the therapeutic potential of targeting MUS81 in gastric cancer requires further exploration. Therefore, in this study, the Cancer Genome Atlas (TCGA) data were analyzed and showed that MUS81 is a key regulator of cell cycle distribution and DNA damage repair in gastric cancer. In vitro and in vivo, MUS81 knockdown significantly enhanced the anticancer effect of the PARP inhibitor talazoparib. Mechanistically, MUS81 inhibition impaired the activation of the ATR/CHK1 cell cycle signaling pathway and promoted gastric cancer cells with talazoparib-induced DNA damage to continue mitosis. Moreover, addition of the bromodomain-containing protein 4 inhibitor AZD5153 increased the anticancer effect of talazoparib via MUS81 inhibition in gastric cancer cells, and this combination effect was largely impaired when MUS81 was knocked down. In conclusion, these data suggested that MUS81 regulated ATR/CHK1 activation, a key signaling pathway in the G2M checkpoint, and targeting MUS81 enhanced the antitumor efficacy of talazoparib. Therefore, AZD5153 combined with talazoparib may represent a promising therapeutic strategy for patients with MUS81 proficient gastric cancer.

Marine derivatives prevent wMUS81 in silico studies

The winged-helix domain of the methyl methanesulfonate and ultraviolet-sensitive 81 (wMUS81) is a potential cancer drug target. In this context, marine fungi compounds were indicated to be able to prevent wMUS81 structure via atomistic simulations. Eight compounds such as D197 (Tryptoquivaline U), D220 (Epiremisporine B), D67 (Aspergiolide A), D153 (Preussomerin G), D547 (12,13-dihydroxyfumitremorgin C), D152 (Preussomerin K), D20 (Marinopyrrole B) and D559 (Fumuquinazoline K) were indicated that they are able to prevent the conformation of wMUS81 via forming a strong binding affinity to the enzyme via perturbation approach. The electrostatic interaction is the dominant factor in the binding process of ligands to wMUS81. The residues Trp55, Arg59, Leu62, His63 and Arg69 were found to frequently form non-bonded contacts and hydrogen bonds to inhibitors. Moreover, the influence of the ligand D197, which formed the lowest binding free energy to wMUS81, on the structural change of enzyme was investigated using replica exchange molecular dynamics simulations. The obtained results indicated that D197, which forms a strong binding affinity, can modify the structure of wMUS81. Overall, the marine compounds probably inhibit wMUS81 due to forming a strong binding affinity to the enzyme as well as altering the enzymic conformation.

Down-regulation of EGFL8 regulates migration, invasion and apoptosis of hepatocellular carcinoma through activating Notch signaling pathway

BACKGROUND

Our previous studies have reported the down-regulation of EGFL8 correlates to the development and prognosis of colorectal and gastric cancer. The present study is carried out to explore the expression pattern and role of EGFL8 in hepatocellular carcinoma (HCC).

METHODS AND MATERIALS

EGFL8 expression in 102 cases of HCC tissues matched with adjacent non-tumorous liver tissues, a normal liver cell line and three liver cancer cell lines with different metastatic capacity was detected by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and Western blot. Moreover, the clinicopathological features and prognosis of HCC patients were correlated with expression of EGFL8. Subsequently, the gain-and loss-of-function experiments were carried out to investigate the biological function of EGFL8 in HCC. We also used N-[N-(3,5-Difluorophenacetyl-L-alanyl)]-(S)- phenylglycine t-butyl ester (DAPT), an inhibitor for Notch signaling pathway, in these experiments to verify the involvement of Notch signaling pathway in the effects of EGFL8. Additionally, a mouse model was established to investigate the effect of EGFL8 on metastasis of HCC cells. The expression of Notch signaling pathway in HCC cells and xenograft mouse tumors were detected by Western blot and immunohistochemistory.

RESULTS

The expression of EGFL8 was significantly decreased in HCC tissues and cell lines and EGFL8 down-regulation correlated to multiple nodules, vein invasion, high TNM stage and poor prognosis of HCC. Interestingly, the expression levels of EGFL8 in three liver cancer cell lines were negatively associated with their metastatic capacity. In vitro and in vivo experiments indicated that EGFL8 obviously suppressed metastasis and invasion of HCC cells but slightly promoted apoptosis. Meanwhile, the expression of Notch signaling pathway was obviously suppressed in EGFL8 overexpressed HCCLM3 cells and xenograft mouse tumors generated from these cells but markedly elevated in EGFL8 depleted Hep3B cells. Furthermore, the up-regulated expression of Notch signaling pathway and effects induced by EGFL8 knockdown in Hep3B cells could be counteracted by DAPT treatment.

CONCLUSION

The down-regulation of EGFL8 was correlated to progression and poor prognosis of HCC and regulates HCC cell migration, invasion and apoptosis through activating the Notch signaling pathway, suggesting EGFL8 as a novel therapeutic target and a potential prognostic marker for HCC.

Computational investigation of possible inhibitors of the winged-helix domain of MUS81

The methyl methanesulfonate and ultraviolet sensitive 81 (MUS81) is a structure-specific endonuclease that is highly conserved in eukaryotes and essential for homologous recombination repair. The winged-helix domain at the N-terminus of MUS81 (wMUS81) can bind DNA substrates and regulate the endonuclease activity. The repression of MUS81 activity could enhance the sensitivity to antitumor compounds of different tumour cells. Thus, MUS81 is a potential therapeutic target in cancer therapy. However, specific inhibitors of MUS81 have remained elusive. Here, for the first time, we attempt to discover the compounds disrupting the wMUS81 activity. The binding affinity of available drugs to wMUS81 was first estimated by molecular docking. pK_a values were taken into consideration to eliminate unlikely protonation states of the ligands. Top-lead compounds were then estimated the binding affinity using the fast pulling ligand simulations. Finally, the free energy perturbation method accurately defined the absolute binding free energy of the top four ligands, revealing the most potential inhibitors of wMUS81 including simeprevir and nilotinib. Binding of simeprevir destabilizes the β-hairpin region of wMUS81, likely disturbing the wMUS81 function. The van der Waals free binding energy majorly modulates the ligand-binding mechanism. The two conserved residues Leu189 and Arg196 are likely important in monitoring the interacting process of simeprevir to wMUS81.

Melatonin sensitises shikonin-induced cancer cell death mediated by oxidative stress via inhibition of the SIRT3/SOD2-AKT pathway

Recent research suggests that melatonin (Mel), an endogenous hormone and natural supplement, possesses anti-proliferative effects and can sensitise cells to anti-cancer therapies. Although shikonin (SHK) also possesses potential anti-cancer properties, the poor solubility and severe systemic toxicity of this compound hinders its clinical usage. In this study, we combined Mel and SHK, a potentially promising chemotherapeutic drug combination, with the aim of reducing the toxicity of SHK and enhancing the overall anti-cancer effects. We demonstrate for the first time that Mel potentiates the cytotoxic effects of SHK on cancer cells by inducing oxidative stress via inhibition of the SIRT3/SOD2-AKT pathway. Particularly, Mel-SHK treatment induced oxidative stress, increased mitochondrial calcium accumulation and reduced the mitochondrial membrane potential in various cancer cells, leading to apoptosis. This drug combination also promoted endoplasmic reticulum (ER) stress, leading to AKT dephosphorylation. In HeLa cells, Mel-SHK treatment reduced SIRT3/SOD2 expression and SOD2 activity, while SIRT3 overexpression dramatically reduced Mel-SHK-induced oxidative stress, ER stress, mitochondrial dysfunction and apoptosis. Hence, we propose the combination of Mel and SHK as a novel candidate chemotherapeutic regimen that targets the SIRT3/SOD2-AKT pathway in cancer.

Germline Mutation in MUS81 Resulting in Impaired Protein Stability is Associated with Familial Breast and Thyroid Cancer

Multiple primary thyroid cancer (TC) and breast cancer (BC) are commonly diagnosed, and the lifetime risk for these cancers is increased in patients with a positive family history of both TC and BC. Although this phenotype is partially explained by TP53 or PTEN mutations, a significant number of patients are negative for these alterations. We judiciously recruited patients diagnosed with BC and/or TC having a family history of these tumors and assessed their whole-exome sequencing. After variant prioritization, we selected MUS81 c.1292G>A (p.R431H) for further investigation. This variant was genotyped in a healthy population and sporadic BC/TC tissues and investigated at the protein level and cellular models. MUS81 c.1292G>A was the most frequent variant (25%) and the strongest candidate due to its function of double-strand break repair. This variant was confirmed in four relatives from two families. MUS81 p.R431H protein exhibited lower expression levels in tumors from patients positive for the germline variant, compared with wild-type BC, and normal breast and thyroid tissues. Using cell line models, we showed that c.1292G>A induced protein instability and affected DNA damage response. We suggest that MUS81 is a novel candidate involved in familial BC/TC based on its low frequency in healthy individuals and proven effect in protein stability.

B7-H3 promotes the cell cycle-mediated chemoresistance of colorectal cancer cells by regulating CDC25A

Colorectal cancer (CRC) is one of the most common malignancies, and chemoresistance is one of the key obstacles in the clinical outcome. Here, we studied the function of B7-H3 in regulating cell cycle-mediated chemoresistance in CRC. The ability of B7-H3 in regulating chemoresistance was investigated via cell viability, clonogenicity, apoptosis and cycle analysis in vitro. Moreover, the role of B7-H3/CDC25A axis in regulating chemoresistance in vivo in the xenograft tumor models by intraperitoneal injection of oxaliplatin (L-OHP) and CDC25A inhibitors. The correlation between B7-H3 and CDC25A was examined in the CRC patients by immunohistochemistry (IHC) and pathological analyses. We found that B7-H3 could effectively enhance the resistance to a chemotherapeutic drug (oxaliplatin or 5-fluorouracil) via CDC25A. B7-H3 regulated the expression of CDC25A by the STAT3 signaling pathway in CRC cells. Furthermore, overexpression of B7-H3 enhanced chemoresistance by reducing the G2/M phase arrest in a CDC25A-dependent manner. Silencing CDC25A or treatment with CDC25A inhibitor could reverse the B7-H3-induced chemoresistance of cancer cells. Moreover, both B7-H3 and CDC25A were significantly upregulated in CRC samples compared with normal adjacent tissues and that the levels correlated with tumor stage. CDC25A was positively correlated with B7-H3 expression in this cohort. Taken together, our findings provide an alternative mechanism by which CRC cells can acquire chemoresistance via the B7-H3/CDC25A axis.

A yeast phenomic model for the influence of Warburg metabolism on genetic buffering of doxorubicin

BACKGROUND

The influence of the Warburg phenomenon on chemotherapy response is unknown. Saccharomyces cerevisiae mimics the Warburg effect, repressing respiration in the presence of adequate glucose. Yeast phenomic experiments were conducted to assess potential influences of Warburg metabolism on gene-drug interaction underlying the cellular response to doxorubicin. Homologous genes from yeast phenomic and cancer pharmacogenomics data were analyzed to infer evolutionary conservation of gene-drug interaction and predict therapeutic relevance.

METHODS

Cell proliferation phenotypes (CPPs) of the yeast gene knockout/knockdown library were measured by quantitative high-throughput cell array phenotyping (Q-HTCP), treating with escalating doxorubicin concentrations under conditions of respiratory or glycolytic metabolism. Doxorubicin-gene interaction was quantified by departure of CPPs observed for the doxorubicin-treated mutant strain from that expected based on an interaction model. Recursive expectation-maximization clustering (REMc) and Gene Ontology (GO)-based analyses of interactions identified functional biological modules that differentially buffer or promote doxorubicin cytotoxicity with respect to Warburg metabolism. Yeast phenomic and cancer pharmacogenomics data were integrated to predict differential gene expression causally influencing doxorubicin anti-tumor efficacy.

RESULTS

Yeast compromised for genes functioning in chromatin organization, and several other cellular processes are more resistant to doxorubicin under glycolytic conditions. Thus, the Warburg transition appears to alleviate requirements for cellular functions that buffer doxorubicin cytotoxicity in a respiratory context. We analyzed human homologs of yeast genes exhibiting gene-doxorubicin interaction in cancer pharmacogenomics data to predict causality for differential gene expression associated with doxorubicin cytotoxicity in cancer cells. This analysis suggested conserved cellular responses to doxorubicin due to influences of homologous recombination, sphingolipid homeostasis, telomere tethering at nuclear periphery, actin cortical patch localization, and other gene functions.

CONCLUSIONS

Warburg status alters the genetic network required for yeast to buffer doxorubicin toxicity. Integration of yeast phenomic and cancer pharmacogenomics data suggests evolutionary conservation of gene-drug interaction networks and provides a new experimental approach to model their influence on chemotherapy response. Thus, yeast phenomic models could aid the development of precision oncology algorithms to predict efficacious cytotoxic drugs for cancer, based on genetic and metabolic profiles of individual tumors.

Rapid and accurate structure-based therapeutic peptide design using GPU accelerated thermodynamic integration

Peptide-based therapeutics are an alternative to small molecule drugs as they offer superior specificity, lower toxicity, and easy synthesis. Here we present an approach that leverages the dramatic performance increase afforded by the recent arrival of GPU accelerated thermodynamic integration (TI). GPU TI facilitates very fast, highly accurate binding affinity optimization of peptides against therapeutic targets. We benchmarked TI predictions using published peptide binding optimization studies. Prediction of mutations involving charged side-chains was found to be less accurate than for non-charged, and use of a more complex 3-step TI protocol was found to boost accuracy in these cases. Using the 3-step protocol for non-charged side-chains either had no effect or was detrimental. We use the benchmarked pipeline to optimize a peptide binding to our recently discovered cancer target: EME1. TI calculations predict beneficial mutations using both canonical and non-canonical amino acids. We validate these predictions using fluorescence polarization and confirm that binding affinity is increased. We further demonstrate that this increase translates to a significant reduction in pancreatic cancer cell viability.

Mus81 knockdown sensitizes colon cancer cells to chemotherapeutic drugs by activating CHK1 pathway

PURPOSE

The inhibition of Mus81, a critical DNA repair gene, is recently related to the chemosensitivity of several human cancer cells such as hepatocellular carcinoma (HCC) cells. However, the role of Mus81 knockdown in chemotherapy response of colon cancer cells remains largely unknown.

METHODS AND MATERIALS

The effects of Mus81 knockdown by lentivirus-mediated short hairpin RNA in sensitivity of HCT116 and LS180 colon cancer cell lines to four therapeutic drugs, including cisplatin (CDDP), were evaluated by MTT assay as well as a mouse model. Apoptosis and cell cycle distribution of HCT116 cell line was detected by flow cytometric analysis. Western blot was also employed to determine the expression of CHK1 pathway and apoptosis-related proteins in HCT116 cells and the xenograft mouse tumors.

RESULTS

Mus81 knockdown could significantly improve the chemosensitivity of colon cancer cells in vitro and in vivo, especially to CDDP. Mus81 knockdown also induced S phase arrest and elevated apoptosis in CDDP treated HCT116 cells through activating CHK1/CDC25A/CDK2 and CHK1/p53/Bax pathways, while these effects could be counteracted by CHK1 inhibition.

CONCLUSION

Mus81 knockdown improves the chemosensitivity of colon cancer cells by inducing S phase arrest and promoting apoptosis through activating CHK1 pathway.

Synaptotagmin-7 is overexpressed in hepatocellular carcinoma and regulates hepatocellular carcinoma cell proliferation via Chk1-p53 signaling

Background

Synaptotagmin-7 (Syt-7) is a member of the synaptotagmin (Syt) family, which plays an important role in many physiological and pathological processes. However, to the best of our knowledge, there is no study describing its function in tumors, particularly in hepatocellular carcinoma (HCC). Therefore, in this study, we examined the role of Syt-7 in HCC and attempted to elucidate its underlying mechanism.

Materials and methods

We examined the expression levels of Syt-7 in HCC cell lines and normal hepatocytes by real-time quantitative polymerase chain reaction analysis. The effects of Syt-7 knockdown on in vitro cell growth were assessed by Celigo image cytometry, MTT assay, colony formation assay, and cell cycle analysis. In vivo tumorigenesis was evaluated using a nude mouse model. The underlying molecular mechanism was evaluated using a PathScan Stress Signaling Antibody Array.

Results

Syt-7 mRNA levels were highly expressed in Huh-7 and Hep3B cells; moderately expressed in SMMC-7721, HepG2, and BEL-7402 cells; and lowly expressed in normal hepatocytes L-O2. Functional experiments demonstrated that Syt-7 knockdown significantly suppressed cell proliferation and induced cell cycle arrest by increasing phosphorylation of Chk1 and p53. Furthermore, Syt-7 knockdown remarkably reduced the growth of xenograft tumors in mice.

Conclusion

The results of this study suggest that Syt-7 plays a vital role in tumorigenesis and in the development of HCC. Syt-7 can be used as a new diagnostic and therapeutic target in HCC.

Feedback regulation of methyl methanesulfonate and ultraviolet-sensitive gene clone 81 via ATM/Chk2 pathway contributes to the resistance of MCF-7 breast cancer cells to cisplatin

The methyl methanesulfonate and ultraviolet-sensitive gene clone 81 protein is a structure-specific nuclease that plays important roles in DNA replication and repair. Knockdown of methyl methanesulfonate and ultraviolet-sensitive gene clone 81 has been found to sensitize cancer cells to chemotherapy. However, the underlying molecular mechanism is not well understood. We found that methyl methanesulfonate and ultraviolet-sensitive gene clone 81 was upregulated and the ATM/Chk2 pathway was activated at the same time when MCF-7 cells were treated with cisplatin. By using lentivirus targeting methyl methanesulfonate and ultraviolet-sensitive gene clone 81 gene, we showed that knockdown of methyl methanesulfonate and ultraviolet-sensitive gene clone 81 enhanced cell apoptosis and inhibited cell proliferation in MCF-7 cells under cisplatin treatment. Abrogation of ATM/Chk2 pathway inhibited cell viability in MCF-7 cells in response to cisplatin. Importantly, we revealed that ATM/Chk2 was required for the upregulation of methyl methanesulfonate and ultraviolet-sensitive gene clone 81, and knockdown of methyl methanesulfonate and ultraviolet-sensitive gene clone 81 resulted in inactivation of ATM/Chk2 pathway in response to cisplatin. Meanwhile, knockdown of methyl methanesulfonate and ultraviolet-sensitive gene clone 81 activated the p53/Bcl-2 pathway in response to cisplatin. These data suggest that the ATM/Chk2 may promote the repair of DNA damage caused by cisplatin by sustaining methyl methanesulfonate and ultraviolet-sensitive gene clone 81, and the double-strand breaks generated by methyl methanesulfonate and ultraviolet-sensitive gene clone 81 may activate the ATM/Chk2 pathway in turn, which provide a novel mechanism of how methyl methanesulfonate and ultraviolet-sensitive gene clone 81 modulates DNA damage response and repair.

STC2 as a novel mediator for Mus81-dependent proliferation and survival in hepatocellular carcinoma

Methyl methansulfonate and UV sensitive gene clone 81 (Mus81) is a critical DNA repair gene that has been implicated in development of several cancers including hepatocellular carcinoma (HCC). However, whether Mus81 can affect proliferation and survival of HCC remains unknown. In the present study, we demonstrated that the knockdown of Mus81 was associated with suppressed proliferation and elevated apoptosis of HCC cells in vitro and in vivo. Multilayered screenings, including DNA microarray, high content screen, and real-time PCR validation, identified STC2 as a proliferation-facilitating gene significantly down-regulated in HCC cells upon Mus81 knockdown. STC2 expression was also closely correlated to Mus81 expression in HCC tissues. More importantly, the restoration of STC2 expression recovered the compromised cell proliferation and survival in Mus81 depleted HCC cells. Furthermore, Mus81 knockdown was associated with the activation of APAF1, APC, and PTEN pathways and concurrent inhibition of MAPK pathway through decreasing STC2 expression. In conclusion, Mus81 knockdown suppresses proliferation and survival of HCC cells likely by downregulating STC2 expression, implicating Mus81 as a therapeutic target for HCC.

Mus81 knockdown improves chemosensitivity of hepatocellular carcinoma cells by inducing S-phase arrest and promoting apoptosis through CHK1 pathway

As a critical endonuclease in DNA repair, Mus81 is traditionally regarded as a tumor suppressor, but recently correlated with the sensitivity of mitomycin C and 5-fluorouracil in colon cancer and breast cancer cells. However, its role in chemosensitivity of other human malignancies still remains unknown. This study therefore aims to investigate the effects of Mus81 knockdown on the chemosensitivity of hepatocellular carcinoma (HCC), a usually chemorefractory tumor, and explore the underlying mechanisms. Mus81 expression in HepG2 and Bel-7402 HCC cell lines was depleted by lentivirus-mediated short hairpin RNA and the elevated sensitivity of these Mus81-inhibited HCC cells to therapeutic agents, especially to epirubicin (EPI), was evidenced by MTT assay and an HCC chemotherapy mouse model. Flow cytometric analysis also showed that Mus81 knockdown lead to an obvious S-phase arrest and an elevated apoptosis in EPI-treated HepG2 and Bel-7402 cells, which could be rescued by CHK1 inhibition. The activation of CHK1/CDC25A/CDK2 pathway was also demonstrated in Mus81-inhibited HepG2 cells and xenograft mouse tumors under EPI treatment. Meanwhile, the apoptosis of HepG2 cells in response to EPI was remarkably promoted by Mus81 knockdown through activating p53/Bax/Caspase-3 pathway under the controlling of CHK1. In addition, CHK2 inhibition slightly raised CHK1 activity, thereby enhancing the S-phase arrest and apoptosis induced by EPI in Mus81-suppressed HCC cells. In conclusion, Mus81 knockdown improves the chemosensitivity of HCC cells by inducing S-phase arrest and promoting apoptosis through CHK1 pathway, suggesting Mus81 as a novel therapeutic target for HCC.