Browsing by Subject "Liver cancer"
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Item Open Access Acquired expression of transcriptionally active p73 in hepatocellular carcinoma cells(Nature Publishing Group, 2001) Sayan, A. E.; Sayan, B. S.; Findikli, N.; Ozturk, M.p53 and p73 proteins activate similar target genes and induce apoptosis and cell cycle arrest. However, p53, but not p73 is considered a tumour-suppressor gene. Unlike p53, p73 deficiency in mice does not lead to a cancer-prone phenotype, and p73 gene is not mutated in human cancers, including hepatocellular carcinoma. Here we report that normal liver cells express only ΔN-p73 transcript forms giving rise to the synthesis of N-terminally truncated, transcriptionally inactive and dominant negative p73 proteins. In contrast, most hepatocellular carcinoma cells express TA-p73 transcript forms encoding full-length and transcriptionally active p73 proteins, in addition to ΔN-p73. We also show that together with the acquired expression of TA-p73, the 'retinoblastoma pathway' is inactivated, and E2F1-target genes including cyclin E and p14ARF are activated in hepatocellular carcinoma. However, there was no full correlation between 'retinoblastoma pathway' inactivation and TA-p73 expression. Most TA-p73-expressing hepatocellular carcinoma cells have also lost p53 function either by lack of expression or missense mutations. The p73 gene, encoding only ΔN-p73 protein, may function as a tumour promoter rather than a tumour suppressor in liver tissue. This may be one reason why p73 is not a mutation target in hepatocellular carcinoma.Item Open Access Aflatoxin genotoxicity is associated with a defective DNA damage response bypassing p53 activation(John Wiley & Sons, 2011) Gürsoy-Yüzügüllü, Özge; Yüzügüllü, Haluk; Yılmaz, Mustafa; Öztürk, MehmetBackground: Hepatocellular carcinoma (HCC) is a leading cause of cancer deaths. Aflatoxins, which may play a causative role in 5-28% of HCCs worldwide, are activated in liver cells and induce principally G→T mutations, including the TP53 codon 249(G→T) hotspot mutation. The DNA damage checkpoint response acts as an antitumour mechanism against genotoxic agents, but its role in aflatoxin-induced DNA damage is unknown. Aim: We studied the DNA damage checkpoint response of human cells to aflatoxin B1 (AFB1). Methods and results: The treatment of HepG2 hepatoma cells with mutation-inducing doses (3-5μmol/l) of AFB1 induced DNA adducts, 8-hydroxyguanine lesions and DNA strand breaks that lasted several days. Persistent phospho-H2AX and 53BP1 foci were also detected, but cell growth was not affected. AFB1-exposed HepG2 cells formed phospho-H2AX and 53BP1 foci, but failed to phosphorylate both Chk1 and Chk2. Huh7 hepatoma and HCT116 colorectal cancer cell lines also exhibited a similarly incomplete checkpoint response. p53 phosphorylation also failed, and AFB1-exposed cells did not show p53-dependent G1 arrest or a sustained G2/M arrest. These observations contrasted sharply with the fully functional DNA damage response of cells to Adriamycin. Cotreatment of cells with AFB1 did not inhibit p53 and p21Cip1 accumulation induced by Adriamycin. Thus, the deficient checkpoint response to AFB1 was not due to an inhibitory effect, but could be explained by an inefficient activation. Conclusion: Genotoxic doses of AFB1 induce an incomplete and inefficient checkpoint response in human cells. This defective response may contribute to the mutagenic and carcinogenic potencies of aflatoxins.Item Open Access Common telomerase reverse transcriptase promoter mutations in hepatocellular carcinomas from different geographical locations(WJG Press, 2015) Cevik, D.; Yildiz G.; Ozturk, M.AIM: To determine the mutation status of human telomerase reverse transcriptase gene (TERT ) promoter region in hepatocellular carcinoma (HCC) from different geographical regions. METHODS: We analyzed the genomic DNA sequences of 59 HCC samples comprising 15 cell lines and 44 primary tumors, collected from patients living in Asia, Europe and Africa. We amplified a 474 bp DNA fragment of the promoter region of TERT gene including the 1295228 and 1295250 sequence of chromosome 5 by using PCR. Amplicons were then sequenced by Sanger technique and the sequence data were analyzed with by using DNADynamo software in comparison with wild type TERT gene sequence as a reference. RESULTS: The TERT mutations were found highly frequent in HCC. Eight of the fifteen tested cell lines displayed C228T mutation, and one had C250T mutation with a mutation frequency up to 60%. All of the mutations were heterozygous and mutually exclusive. Ten out of forty-four tumors displayed C228T mutation, and additional five tumors had C250T mutation providing evidence for mutation frequency of 34% in primary tumors. Considering the geographic origins of HCC tumors tested, TERT promoter mutation frequencies were higher in African (53%), when compared to non-African (24%) tumors (P = 0.056). There was also a weak inverse correlation between TERT promoter mutations and murine double minute 2 single nucleotide polymorphism 309 TG polymorphism (P = 0.058). Mutation frequency was nearly two times higher in established HCC cell lines (60%) compared to the primary tumors (34%). CONCLUSION: TERT promoter is one of most frequent mutational targets in liver cancer, and hepatocellular carcinogenesis is highly associated with the loss of telomere-dependent cellular senescence control. © The Author(s) 2015.Item Open Access Evaluation of ATAD2 as a potential target in hepatocellular carcinoma(Springer, 2021-11-05) Gürsoy Yüzügüllü, Özge; Ekin, U.; Özen, C.; Korhan, P.; Bağırsakcı, E.; Yılmaz, F.; Uzuner, H.; Alotaibi, H.; Kırmızıbayrak, P. B.; Atabey, N.; Karakülah, G.; Öztürk, M.; Yüzügüllü, HalukPurpose Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related death worldwide with lack of effec-tive systemic chemotherapy. In this study, we aimed to evaluate the value of ATPase family AAA domain-containing protein 2 (ATAD2) as a biomarker and potential therapeutic target for HCC.Methods The expression of ATAD2 was tested in different HCC patient cohorts by immunohistochemistry and comparative transcriptional analysis. The co-expression of ATAD2 and proliferation markers was compared during liver regeneration and malignancy with different bioinformatics tools. The cellular effects of ATAD2 inactivation in liver malignancy was tested on cell cycle, apoptosis, and colony formation ability as well as tumor formation using RNA interference. The genes affected by ATAD2 inactivation in three different HCC cell lines were identified by global gene expression profiling and bioinformatics tools.Results ATAD2 overexpression is closely correlated with HCC tumor stage. There was gradual increase from dysplasia, well-differentiated and poorly-differentiated HCC, respectively. We also observed transient upregulation of ATAD2 expres-sion during rat liver regeneration in parallel to changes in Ki-67 expression. ATAD2 knockdown resulted in apoptosis and decreased cell survival in vitro and decreased tumor formation in some HCC cell lines. However, three other HCC cell lines tested were not affected. Similarly, gene expression response to ATAD2 inactivation in different HCC cell lines was highly heterogeneous.Conclusions ATAD2 is a potential proliferation marker for liver regeneration and HCC. It may also serve as a therapeutic target despite heterogeneous response of malignant cells.Item Open Access Reprogramming of replicative senescence in hepatocellular carcinoma-derived cells(National Academy of Sciences, 2006) Ozturk, N.; Erdal, E.; Mumcuoglu, M.; Akcali, K. C.; Yalcin, O.; Senturk, S.; Arslan-Ergul, A.; Gur, B.; Yulug, I.; Cetin Atalay, R.; Yakicier, C.; Yagci, T.; Tez, M.; Ozturk, M.Tumor cells have the capacity to proliferate indefinitely that is qualified as replicative immortality. This ability contrasts with the intrinsic control of the number of cell divisions in human somatic tissues by a mechanism called replicative senescence. Replicative immortality is acquired by inactivation of p53 and p16INK4a genes and reactivation of hTERT gene expression. It is unknown whether the cancer cell replicative immortality is reversible. Here, we show the spontaneous induction of replicative senescence in p53-and p16 INK4a-deficient hepatocellular carcinoma cells. This phenomenon is characterized with hTERT repression, telomere shortening, senescence arrest, and tumor suppression. SIP1 gene (ZFHX1B) is partly responsible for replicative senescence, because short hairpin RNA-mediated SIP1 inactivation released hTERT repression and rescued clonal hepatocellular carcinoma cells from senescence arrest. © 2006 by The National Academy of Sciences of the USA.Item Open Access Role of FLT3 in the proliferation and aggressiveness of hepatocellular carcinoma(TÜBİTAK, 2016) Aydın, Muammer Merve; Bayın, Nermin Sumru; Acun, T.; Yakıcıer, M. C.; Akçalı, K. C.Background/aim: Previously we showed that Fms-like tyrosine kinase (FLT3) changes its cellular localization upon partial hepatectomy, suggesting a role in liver regeneration. FLT3 was also shown to play an important function in cellular proliferation and activation of PI3K and Ras. Thus, we aimed to investigate the role of FLT3 in hepatocellular tumorigenesis utilizing in vitro and in vivo models. Materials and methods: We used Snu398 cells that express FLT3. We investigated these cells in vitro proliferation and invasion abilities by treatment with the FLT3 inhibitor K-252a or by knocking-down with FLT3 shRNA,. Furthermore, the effect of blocking FLT3 activity and expression during in vivo tumorigenesis was assessed with xenograft models. Results: After K-252a treatment or stable knock-down, these cells proliferation and migration abilities were highly diminished in vitro. In addition, significant diminution in tumorigenicity of Snu398 cells was also obtained in vivo. When FLT3 knocked-down Snu398 cells were injected into nude mice, we did not detect αSMA expression in these tumors, suggesting a role for FLT3 in in vivo invasiveness. Conclusion: Our data provided evidence that FLT3 has a crucial role both in hepatocarcinogenesis and its invasiveness. Therefore, targeting FLT3 and/or its activity may be a promising tool for combating hepatocellular carcinomas.Item Open Access Targeting PI3K/AKT/mTOR pathway identifies differential expression and functional role of IL8 in liver cancer stem cell enrichment(American Association for Cancer Research, 2019) Kahraman, D. C.; Kahraman, Tamer; Çetin-Atalay, R.Activation of the PI3K/Akt/mTOR pathway is an important signaling mechanism involved in the development and the progression of liver cancer stem cell (LCSC) population during acquired Sorafenib resistance in advanced hepatocellular carcinoma (HCC). Therefore, identification of novel therapeutic targets involving this pathway and acting on LCSCs is highly essential. Here, we analyzed the bioactivities and the molecular pathways involved in the action of small-molecule PI3K/Akt/mTOR pathway inhibitors in comparison with Sorafenib, DNA intercalators, and DAPT (CSC inhibitor) on CD133/EpCAM-positive LCSCs. Sorafenib and DNA intercalators lead to the enrichment of LCSCs, whereas Rapamycin and DAPT significantly reduced CD133/EpCAM positivity. Sequential treatment with Rapamycin followed by Sorafenib decreased the ratio of LCSCs as well as their sphere formation capacity, as opposed to Sorafenib alone. Under the stress of the inhibitors, differential expression analysis of 770 cancer pathway genes using network-based systems biology approach singled out IL8 expression association with LCSCs. Furthermore, IL8 secretion and LCSC enrichment ratio was also positively correlated. Following IL8 inhibition with its receptor inhibitor Reparixin or siRNA knockdown, LCSC features of HCC cells were repressed, and sensitivity of cells to Sorafenib increased significantly. Furthermore, inflammatory cytokines (IL8, IL1β, and IL11) were also upregulated upon treatment with HCC-approved kinase inhibitors Sorafenib and Regorafenib. Hence, chemotherapeutic stress alters inflammatory cytokine gene expression in favor of hepatic CSC population survival. Autocrine IL8 signaling is identified as a critical event, and its inhibition provides a promising complimentary therapeutic approach for the prevention of LCSC population enrichment.Item Open Access Therapeutic approaches to the prevention of liver fibrosis and cancer progression(Bilkent University, 2015-08) Aydın, Muammer MerveIn our previous studies on liver regeneration, we demonstrated that following partial hepatectomy (PH) FLT3 contributes cellular proliferation that provides a basis for liver regeneration. Moreover, we were able to suggest a potential role for FLT3 in hepatocarcinogenesis for the first time. Therefore, we further investigated the effect of FLT3 inhibition on the invasiveness and aggressiveness of hepatocarcinogenesis. Our findings were parallel to our previous results supporting the contribution of FLT3 in hepatocarcinogenesis. Thus, we are presenting FLT3 as a novel candidate for the diagnosis and treatment of HCC. We also focused on liver fibrosis since it is the initial wound healing response generated by the liver against damaging insults. Liver fibrosis is a reversible process, but if its progression is not prevented it might turn into cirrhosis and end up with HCC. Toll-like receptors (TLRs) have been reported to contribute to this fibrotic response generated in the liver resulting from the activating effects of various danger ligands. We show that using suppressive oligodeoxynucleotide (ODN) A151 might control TLR dependent immune activation that takes place after the induction of liver fibrosis. Our results show that suppressive ODN A151 administration has a negative effect on αSMA expression and collagen accumulation, which are the major events taking place during liver fibrogenesis. Additionally, this suppressive effect of suppressive ODN A151 was revealed to be systemic. Splenocytes of suppressive ODN A151 administered mice showed different cytokine secretion patterns and antigen presenting cell (APC) function after being stimulated with various TLR ligands. These findings suggested us that using suppressive ODN might be a rational and novel approach to control the liver fibrogenesis and even prevent its progression into cirrhosis reducing the number of liver transplantations needed by the patients. Finally, we focused on HSPs, some of which are also known to activate TLR signaling. Additionally, HSP27 has a role in actin cytoskeleton organization and controlling cellular motility, which are among the events that take place in liver fibrogenesis. Therefore, for the first time we present preliminary data on the potential role of HSP27 in liver fibrosis and quercetin treatment as a therapeutic approach due to its HSP27 and αSMA expression changing effects.