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ZBTB33 (Kaiso) Differentially Regulates Cell Cycle Through cyclin D1 and cyclin E1 in a Cell Specific Manner [RNA-seq]

ABSTRACT: The emerging correlation between aberrant DNA methylation patterns leading to transcriptional responses that promote and progress many cancers has prompted an interest in discerning the associated regulatory mechanisms. ZBTB33 (also known as Kaiso) is a specialized transcription factor that selectively recognizes mCpG-containing sites as well as a sequence-specific DNA target (termed the KBS) utilizing three Cys2His2 zinc fingers. Increasing reports link ZBTB33 overexpression and transcriptional activities with metastatic potential and poor prognosis, though the specific cellular consequences appear to be dependent on disease phenotype. There is currently little mechanistic insight into how various cellular phenotypes are then able to harness the transcriptional capabilities of ZBTB33 to differentially promote and progress the disease state. Here we have mechanistically interrogated the cell cycle responses mediated by the transcriptional activities of ZBTB33 in two different cell lines. Utilizing a series of ZBTB33 depletion and overexpression studies, we have determined that in HeLa cells ZBTB33 directly occupies the promoter regions of cyclin D1 and cyclin E1 in a KBS and methyl-specific manner, respectively, inducing increased proliferation by promoting RB1 hyper-phosphorylation, allowing for E2F transcriptional activity that coordinates an accelerated G1- to S-phase transition. Conversely, in HEK293 cells ZBTB33 indirectly regulates Cyclin E abundance resulting in reduced RB1 phosphorylation, decreased E2F activity and a decelerated transition through G1-phase. Thus, we have identified a novel mechanism by which ZBTB33 directly mediates the highly coordinated cyclin D1/cyclin E1/RB1/E2F signaling pathway controlling the passage through the G1-phase restriction point and accelerating cellular proliferation in a cancer cell line.

ORGANISM(S): Homo sapiens

PROVIDER: GSE81781 | GEO | 2017/01/30

SECONDARY ACCESSION(S): PRJNA322534

REPOSITORIES: GEO

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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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ZBTB33 (Kaiso) Differentially Regulates Cell Cycle Through cyclin D1 and cyclin E1 in a Cell Specific Manner [RNA-seq]

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