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Rocaglamide selectively inhibits the G1-S-phase transition in cancer cells by activation of the ATM/ATR-mediated Chk1/2 cell cycle checkpoints

ABSTRACT: The cell division cycle is tightly controlled in normal cells. Cancer cells are characterized by deregulation in cell division cycle, which is associated with increased DNA replication and elevated cellular proliferation. Recently, genetic studies indicate that cyclin dependent kinases CDK2, CDK4 and CDK6 are not essential for the mammalian cell cycle, instead, they are only required for the proliferation of specific cell types.Thus, targeting the activities of CDK2, CDK4 and CDK6 may be a promising approach for cancer treatment. Rocaglamides (Roc) (= Flavaglines), derived from the traditional Chinese medicinal plant Aglaia, are a group of naturally occurring herbal chemicals characterized by a cyclopenta[b]benzofurans skeleton. A number of Roc derivatives have been found to have potent inhibitory effects on tumor growth with IC50 concentrations at the nM rages. Roc-mediated inhibition of proliferation was first found to be associated with inhibition of protein synthesis in 1998. In this study, using the representative Roc-A compound we revealed a novel mechanistic function of Roc. We show that Roc-A induces rapid activation of ATM (ataxiatelangiectasia mutated) and ATR (ataxia-telangiectasia and Rad3-related) kinases. Activated ATM and ATR in turn activate the downstream checkpoint kinases CHK1 and CHK2. The latter then phosphorylate Cdc25A that leads to a phosphorylation-mediated degradation of Cdc25A. Usually, ATR and ATM are activated in response to DNA damage. However, in this study we show that Roc-A does not directly induce DNA breaks. To elucidate the molecular mechanism by which Roc-A activates ATM and ATR we performed a time-resolved microarray analysis to compare Roc-A-inducible genes in malignant vs. normal T lymphocytes. Based on the dynamic gene responses we found that Roc-A stimulates in Jurkat, but not in normal T lymphocytes, a set of genes responsive to DNA damage and nucleotide excision repair. This finding provides a hint of the molecular bases for Roc-induced activation of ATM and ATR. This finding also revealed a new scope for cancer treatment using Roc-A.

ORGANISM(S): Homo sapiens

PROVIDER: GSE41072 | GEO | 2013/10/12

SECONDARY ACCESSION(S): PRJNA175681

REPOSITORIES: GEO

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Project description:The cell division cycle is tightly controlled in normal cells. Cancer cells are characterized by deregulation in cell division cycle, which is associated with increased DNA replication and elevated cellular proliferation. Recently, genetic studies indicate that cyclin dependent kinases CDK2, CDK4 and CDK6 are not essential for the mammalian cell cycle, instead, they are only required for the proliferation of specific cell types.Thus, targeting the activities of CDK2, CDK4 and CDK6 may be a promising approach for cancer treatment. Rocaglamides (Roc) (= Flavaglines), derived from the traditional Chinese medicinal plant Aglaia, are a group of naturally occurring herbal chemicals characterized by a cyclopenta[b]benzofurans skeleton. A number of Roc derivatives have been found to have potent inhibitory effects on tumor growth with IC50 concentrations at the nM rages. Roc-mediated inhibition of proliferation was first found to be associated with inhibition of protein synthesis in 1998. In this study, using the representative Roc-A compound we revealed a novel mechanistic function of Roc. We show that Roc-A induces rapid activation of ATM (ataxiatelangiectasia mutated) and ATR (ataxia-telangiectasia and Rad3-related) kinases. Activated ATM and ATR in turn activate the downstream checkpoint kinases CHK1 and CHK2. The latter then phosphorylate Cdc25A that leads to a phosphorylation-mediated degradation of Cdc25A. Usually, ATR and ATM are activated in response to DNA damage. However, in this study we show that Roc-A does not directly induce DNA breaks. To elucidate the molecular mechanism by which Roc-A activates ATM and ATR we performed a time-resolved microarray analysis to compare Roc-A-inducible genes in malignant vs. normal T lymphocytes. Based on the dynamic gene responses we found that Roc-A stimulates in Jurkat, but not in normal T lymphocytes, a set of genes responsive to DNA damage and nucleotide excision repair. This finding provides a hint of the molecular bases for Roc-induced activation of ATM and ATR. This finding also revealed a new scope for cancer treatment using Roc-A. The isolation time points for Roc A treated D6 T-cells were recorded at t=[1,2,3,4,6,8,10,14,20,28,36] hours after stimulation. Post-stimulation time points for Jurkat cells are t=[0.5,1,2,3,4,5,6,7,8,10,12,14,16,20,24,28,32,36]. Unstimulated control time points were taken at t=[0,4,10,16,24,36] hours for Jurkat cells at t=[0,6,14,24,36] hours.

Project description:Cdk4 and Cdk6 are two related kinases that bind D-type cyclins and regulate cell cycle progression. Due to their relevance in cancer, Cdk4/6 inhibitors are currently in advanced clinical trials in multiple tumor types. Cdk4/6 are inhibited by INK4 proteins that exert tumor suppressing functions. To test the significance of this inhibitory mechanism we have generated knock-in mice that express a Cdk6 mutant (Cdk6 R31C) insensitive to INK4-mediated inhibition. Cdk6R/R mice display altered development of the hematopoietic system without resulting in enhanced tumor susceptibility, either in the presence or absence of p53. The presence of the Cdk6 R31C allele results in defective potential of hematopoietic progenitors in adoptive transfer assays or after induced damage. These defects are rescued after complete insensitivity to INK4 inhibitors in Cdk4R/R; Cdk6R/R double mutant mice, and INK4-resistant mice display increased susceptibility to hematopoietic and endocrine tumors. In BCR-ABL-transformed hematopoietic cells, the presence of the Cdk6 R31C allele results in increased binding of p16INK4a to wild-type Cdk4, whereas the double mutant is fully insensitive to INK4 inhibitors resulting in accelerated disease onset. Our observations reveal that Cdk4 and Cdk6 cooperate in tumor development and suggest a role for Cdk6 in buffering INK4 protein levels thus contributing to the development of hematopoietic tumors. The presence of the Cdk4 R24C and Cdk6 R31C alleles results in relevant changes in the expression profiles of cancer cells including deregulation of apoptosis and other processes. p185BCR-ABL1 was used to transform wild-type or double knock-in Cdk4 R24C; Cdk6 R31C fetal livers. Cell lines were isolated as spontaneous immortal and transformed clones after transduction of fetal liver with a p185 BCR-ABL1-transgene. RNA was isolated from asynchronous cultures. Two-condition experiment, Cdk4R-Cdk6R cells versus wild-type cells. Biological replicates: 3 control replicates, 3 transfected replicates.

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Rocaglamide selectively inhibits the G1-S-phase transition in cancer cells by activation of the ATM/ATR-mediated Chk1/2 cell cycle checkpoints

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