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CtIP activates its own and cyclin D1 promoters via the E2F/RB pathway during G1/S progression.

ABSTRACT: Cell cycle progression from G(1) to S phase is mainly controlled by E2F transcription factors and RB family proteins. Previously we showed that the presence of CtIP is essential for G(1)/S transition in primary mouse blastocysts, as well as in NIH 3T3 cells. However, how CtIP executes this function remains to be elucidated. Here we show that in NIH 3T3 cells the expression of CtIP is regulated by the E2F/RB pathway during late G(1) and S phases. The presence of wild-type CtIP, but not the E157K mutant form, which failed to interact with RB, enhanced its own promoter activity. Chromatin immunoprecipitation analysis indicated that the recruitment of CtIP to its promoter occurs concomitantly with TFIIB, a component of the RNA polymerase II complex, and with dissociation of RB from the promoter during late G(1) and G(1)/S transition. Similar positive regulation of cyclin D1 expression by CtIP was also observed. Consistently, cells expressing the CtIP(E157K) protein alone exhibited growth retardation, an increase in the G(1) population, and a decrease in the S-phase population. Taken together, these results suggest that, contrary to the postulated universal corepressor role, CtIP activates a subset of E2F-responsive promoters by releasing RB-imposed repression and therefore promotes G(1)/S progression.

SUBMITTER: Liu F

PROVIDER: S-EPMC1446954 | biostudies-literature | 2006 Apr

REPOSITORIES: biostudies-literature

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CtIP activates its own and cyclin D1 promoters via the E2F/RB pathway during G1/S progression.

Liu Feng F Lee Wen-Hwa WH

Molecular and cellular biology 20060401 8

Cell cycle progression from G(1) to S phase is mainly controlled by E2F transcription factors and RB family proteins. Previously we showed that the presence of CtIP is essential for G(1)/S transition in primary mouse blastocysts, as well as in NIH 3T3 cells. However, how CtIP executes this function remains to be elucidated. Here we show that in NIH 3T3 cells the expression of CtIP is regulated by the E2F/RB pathway during late G(1) and S phases. The presence of wild-type CtIP, but not the E157K ...[more]

PMID: 16581787

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Project description:BackgroundBreast cancer (BC) is one of the most frequently observed malignancies globally, yet drug development for BC has been encountering escalating challenges. Commiphora myrrha is derived from the dried resin of C. myrrha (T. Nees) Engl., and is widely adopted in China for treating BC. However, the anti-BC effect and underlying mechanism of C. myrrha remain largely unclear.MethodsMTT assay, EdU assay, and colony formation were used to determine the effect of C. myrrha n-hexane extract (CMHE) on the proliferation of human BC cells. Cell cycle distribution and apoptosis were assessed via flow cytometry analysis. Moreover, metastatic potential was evaluated using wound-scratch assay and matrigel invasion assay. The 4T1 breast cancer-bearing mouse model was established to evaluate the anti-BC efficacy of CMHE in vivo. RNA-sequencing analysis, quantitative real-time PCR, immunoblotting, immunohistochemical analysis, RNA interference assay, and database analysis were conducted to uncover the underlying mechanism of the anti-BC effect of CMHE.ResultsWe demonstrated the significant inhibition in the proliferative capability of BC cell lines MDA-MB-231 and MCF-7 by CMHE. Moreover, CMHE-induced G0/G1 phase arrest and apoptosis of the above two BC cell lines were also observed. CMHE dramatically repressed the metastatic potential of these two cells in vitro. Additionally, the administration of CMHE remarkably suppressed tumor growth in 4T1 tumor-bearing mice. No obvious toxic or side effects of CMHE administration in mice were noted. Furthermore, immunohistochemical (IHC) analysis demonstrated that CMHE treatment inhibited the proliferative and metastatic abilities of cancer cells, while also promoting apoptosis in the tumor tissues of mice. Based on RNA sequencing analysis, quantitative real-time PCR, immunoblotting, and IHC assay, the administration of CMHE downregulated Cyclin D1/CDK4-Rb signaling pathway in BC. Furthermore, RNA interference assay and database analysis showed that downregulated Cyclin D1/CDK4 signaling cascade participated in the anti-BC activity of CMHE.ConclusionCMHE treatment resulted in the suppression of BC cell growth through the stimulation of cell cycle arrest at the G0/G1 phase and the induction of apoptotic cell death via the inhibition of the Cyclin D1/CDK4-Rb pathway, thereby enhancing the anti-BC effect of CMHE. CMHE has potential anti-BC effects, particularly in those harboring aberrant activation of Cyclin D1/CDK4-Rb signaling.

Project description:The retinoblastoma tumor suppressor protein (Rb) regulates early G1 phase checkpoints, including the DNA damage response, as well as cell cycle exit and differentiation. The widely accepted model of G1 cell cycle progression proposes that cyclin D:Cdk4/6 partially inactivates the Rb tumor suppressor during early G1 phase by progressive multi-phosphorylation, termed hypo-phosphorylation, resulting in release of E2F transcription factors. However, this model remains largely unproven biochemically and the biologically active form(s) of Rb remains unknown. Here we find that Rb is un-phosphorylated in G0 cells and becomes exclusively mono-phosphorylated throughout all of early G1 phase by cyclin D:Cdk4/6. Early G1 phase mono-phosphorylated Rb is composed of 14 independent isoforms that are all targeted by the E1a oncoprotein, but each shows a preferential binding pattern to specific E2F1-4 transcription factors. At the late G1 Restriction Point, cyclin E:Cdk2 inactivates Rb by a quantum hyper-phosphorylation (>12 phosphates/Rb). Cells undergoing a DNA damage response activate cyclin D:Cdk4/6 to generate mono-phosphorylated Rb that regulates global transcription. In contrast, a non-phosphorylatable ?Cdk-Rb allele was non-functional for regulating a DNA damage response, but functional for driving cell cycle exit and differentiation during myogenesis. These observations fundamentally change our understanding of G1 cell cycle progression and show that there is no progressive multi-phosphorylation or hypo-phosphorylation inactivation of Rb during early G1 phase by cyclin D:Cdk4/6. Instead, cyclin D:Cdk4/6 generates functionally active, mono-phosphorylated Rb that is the only Rb isoform present in cells during early G1 phase. Global transcriptional analysis of murine embryonic fibroblasts (MEFs) with conditional deletion of the endogenous RB gene by treatment with cell permeable TAT-Cre. Comparison to unaltered MEFs and MEFs with physiological level of exogenous wildtype or phospho-mutant RB expressed at time of RB gene deletion.

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CtIP activates its own and cyclin D1 promoters via the E2F/RB pathway during G1/S progression.

Publications

CtIP activates its own and cyclin D1 promoters via the E2F/RB pathway during G1/S progression.

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