Deciphering 5-fluorouracil mediated molecular mechanisms required for cell death

Thesis (Master)--Izmir Institute of Technology, Molecular Biology and Genetics, Izmir, 2011Includes bibliographical references (leaves: 26-31)Text in English; Abstract: Turkish and Englishix, 31 leavesThe chemotherapy agent 5-Fluorouracil (5-FU) is an antimetabolite that has been in use to treat several cancers for decades. In cells, it is converted into three distinct fluoro-based nucleotide analogues which interfere with DNA-synthesis and repair leading to impairment of the genome and, eventually apoptotic cell death. Current knowledge also state that 5-FU induced damage is signaling through a p53-dependent induction of death inducing complex (DISC) formation and further caspase-8 activation in certain cell types and members of the TNF-receptor family has been proposes to be required for the process. Here, we introduce calcium (Ca2+) as a messenger for p53 activation in the cellular response triggered by 5-FU. Using a combination of pharmacological and genetic approaches, we show that treatment of cultured colon carcinoma cells stimulates entry of extracellular Ca2+ through L-type plasma membrane channels and that this event direct posttranslational phosphorylation of at least two specific p53 serine residues (ser15 and ser33) by means of Calmodulin (CaM) activity. Obstructing this pathway by the Ca2+-chelator BAPTA or by two different inhibitors of CaM efficiently blocks 5-FU-induced cell death. The fact that a widely used therapeutic drug, such as 5-FU, is signaling by these means could provide new therapeutic intervention points, or specify new combinatorial treatment regimes

Nilotinib significantly induces apoptosis in imatinib resistant K562 cells with wild-type BCR-ABL, as effectively as in parental sensitive counterparts

Chronic myeloid leukemia (CML) is a hematological malignancy characterized by high levels of immature white blood cells. CML is caused by the translocation between chromosomes 9 and 22 (which results in the formation of the Philadelphia chromosome) creating BCR-ABL fusion protein. Imatinib and nilotinib are chemotherapeutic drugs which specifically bind to the BCR-ABL and inhibit cancer cells. Nilotinib is more effective in this respect than imatinib. We have shown that nilotinib induces apoptosis in imatinib-resistant K562 CML cells which have the wild-type BCR-ABL fusion gene almost to the same extent as it does in the parental sensitive cells by the increase in caspase-3 enzyme activity and the decrease in mitochondrial membrane potential. This effect of nilotinib, even in low concentrations, may indicate the efficacy of the usage of nilotinib in imatinib-resistant CML with less risk of undesired cytotoxic effects in the remaining cells of the body. © 2010 W. S. Maney & Son Ltd

Apoptotic effects of resveratrol, a grape polyphenol, on imatinib-sensitive and resistant K562 chronic myeloid leukemia cells

To examine the antiproliferative and apoptotic effects of resveratrol on imatinib-sensitive and imatinib-resistant K562 chronic myeloid leukemia cells. Antiproliferative effects of resveratrol were determined by the 3-Bis[2-methoxy-4-nitro-5-sulphophenyl]-2H-tetrazolium-5-carboxanilide inner salt (XTT) cell proliferation assay. Apoptotic effects of resveratrol on sensitive K562 and resistant K562/IMA-3 cells were determined through changes in caspase-3 activity, loss of mitochondrial membrane potential (MMP), and apoptosis by annexin V-(FITC). The concentrations of resveratrol that inhibited cell growth by 50% (IC(50)) were calculated as 85 and 122 μM for K562 and K562/IMA-3 cells, respectively. There were 1.91-, 7.42- and 14.73-fold increases in loss of MMP in K562 cells treated with 10, 50, and 100 μM resveratrol, respectively. The same concentrations of resveratrol resulted in 2.21-, 3.30- and 7.65-fold increases in loss of MMP in K562/IMA-3 cells. Caspase-3 activity increased 1.04-, 2.77- and 4.8-fold in K562 and 1.02-, 1.41- and 3.46-fold in K562/IMA-3 cells in response to the same concentrations of resveratrol, respectively. Apoptosis was induced in 58.7%- and 43.3% of K562 and K562/IMA-3 cells, respectively, in response to 100 μM resveratrol. Taken together these results may suggest potential use of resveratrol in CML, as well as in patients with primary and/or acquired resistance to imatinib

Checkpoint inhibition of origin firing prevents inappropriate replication outside of S-phase

Checkpoints maintain the order of cell cycle events during DNA damage or incomplete replication. How the checkpoint response is tailored to different phases of the cell cycle remains poorly understood. The S-phase checkpoint for example results in the slowing of replication, which in budding yeast occurs by Rad53-dependent inhibition of the initiation factors Sld3 and Dbf4. Despite this, we show here that Rad53 phosphorylates both of these substrates throughout the cell cycle at the same sites as in S-phase, suggesting roles for this pathway beyond S-phase. Indeed, we show that Rad53-dependent inhibition of Sld3 and Dbf4 limits re-replication in G2/M, preventing gene amplification. In addition, we show that inhibition of Sld3 and Dbf4 in G1 prevents premature initiation at all origins at the G1/S transition. This study redefines the scope of the ‘S-phase checkpoint’ with implications for understanding checkpoint function in cancers that lack cell cycle controls

Checkpoint inhibition of origin firing prevents inappropriate replication outside of S-phase

Checkpoints maintain the order of cell cycle events during DNA damage or incomplete replication. How the checkpoint response is tailored to different phases of the cell cycle remains poorly understood. The S-phase checkpoint for example results in the slowing of replication, which in budding yeast occurs by Rad53-dependent inhibition of the initiation factors Sld3 and Dbf4. Despite this, we show here that Rad53 phosphorylates both of these substrates throughout the cell cycle at the same sites as in S-phase, suggesting roles for this pathway beyond S-phase. Indeed, we show that Rad53-dependent inhibition of Sld3 and Dbf4 limits re-replication in G2/M, preventing gene amplification. In addition, we show that inhibition of Sld3 and Dbf4 in G1 prevents premature initiation at all origins at the G1/S transition. This study redefines the scope of the ‘S-phase checkpoint’ with implications for understanding checkpoint function in cancers that lack cell cycle controls

Deciphering 5-fluorouracil mediated molecular mechanisms required for cell death

Thesis (Master)--Izmir Institute of Technology, Molecular Biology and Genetics, Izmir, 2011Includes bibliographical references (leaves: 26-31)Text in English; Abstract: Turkish and Englishix, 31 leavesThe chemotherapy agent 5-Fluorouracil (5-FU) is an antimetabolite that has been in use to treat several cancers for decades. In cells, it is converted into three distinct fluoro-based nucleotide analogues which interfere with DNA-synthesis and repair leading to impairment of the genome and, eventually apoptotic cell death. Current knowledge also state that 5-FU induced damage is signaling through a p53-dependent induction of death inducing complex (DISC) formation and further caspase-8 activation in certain cell types and members of the TNF-receptor family has been proposes to be required for the process. Here, we introduce calcium (Ca2+) as a messenger for p53 activation in the cellular response triggered by 5-FU. Using a combination of pharmacological and genetic approaches, we show that treatment of cultured colon carcinoma cells stimulates entry of extracellular Ca2+ through L-type plasma membrane channels and that this event direct posttranslational phosphorylation of at least two specific p53 serine residues (ser15 and ser33) by means of Calmodulin (CaM) activity. Obstructing this pathway by the Ca2+-chelator BAPTA or by two different inhibitors of CaM efficiently blocks 5-FU-induced cell death. The fact that a widely used therapeutic drug, such as 5-FU, is signaling by these means could provide new therapeutic intervention points, or specify new combinatorial treatment regimes

Role of autophagy in the progression and suppression of leukemias

Autophagy is a physiological process in which cellular components are degraded by the lysosomal machinery. Thereby, organelles are recycled and monomers are produced in order to maintain energy production. Current studies indicate autophagy might suppress or augment survival of cancer cells. Therefore, by elucidating the role of autophagy in cancer pathogenesis, novel therapeutic intervention points may be revealed. Leukemia therapy has advanced in recent years; but a definitive cure is still lacking. Since autophagy often is deregulated in this particular type of cancer, it is clear that future findings will have clinical implications. This review will discuss the current knowledge of autophagy in blood cancers. © 2011 Elsevier Ireland Ltd

Imatinib induces autophagy through BECLIN-1 and ATG5 genes in chronic myeloid leukemia cells

Locate full-text(opens in a new window)|Full Text(opens in a new window)|View at Publisher| Export | Download | Add to List | More... Hematology Volume 16, Issue 2, March 2011, Pages 95-99 Imatinib induces autophagy through BECLIN-1 and ATG5 genes in chronic myeloid leukemia cells (Article) Can, G., Ekiz, H.A., Baran, Y. Department of Molecular Biology and Genetics, Faculty of Science, Izmir Institute of Technology, 35430 Urla, Izmir, Turkey View references (35) Abstract Imatinib is a chemotherapeutic drug used for the treatment of chronic myeloid leukemia (CML). Recent data showed imatinib-induced cell death in various types of cancers. Autophagy is the physiological process in which cellular components are broken down by the lysosomal activation. In this study, we aimed to examine the effects of imatinib on autophagy in addition to apoptosis in CML cells. Results suggested that imatinib induces autophagy in CML cells through inducing over-expression of BECLIN-1 and ATG5 genes with the statistical significance. Our results demonstrated that autophagy might be involved in imatinib-induced cell death.Turkish Academy of Science

Helicase Subunit Cdc45 Targets the Checkpoint Kinase Rad53 to Both Replication Initiation and Elongation Complexes after Fork Stalling.

Across eukaryotes, disruption of DNA replication causes an S phase checkpoint response, which regulates multiple processes, including inhibition of replication initiation and fork stabilization. How these events are coordinated remains poorly understood. Here, we show that the replicative helicase component Cdc45 targets the checkpoint kinase Rad53 to distinct replication complexes in the budding yeast Saccharomyces cerevisiae. Rad53 binds to forkhead-associated (FHA) interaction motifs in an unstructured loop region of Cdc45, which is phosphorylated by Rad53 itself, and this interaction is necessary for the inhibition of origin firing through Sld3. Cdc45 also recruits Rad53 to stalled replication forks, which we demonstrate is important for the response to replication stress. Finally, we show that a Cdc45 mutation found in patients with Meier-Gorlin syndrome disrupts the functional interaction with Rad53 in yeast. Together, we present a single mechanism by which a checkpoint kinase targets replication initiation and elongation complexes, which may be relevant to human disease