RESUMO
The cyclin-dependent kinase 1 (Cdk1) drives cell division. To uncover additional functions of Cdk1, we generated knockin mice expressing an analog-sensitive version of Cdk1 in place of wild-type Cdk1. In our study, we focused on embryonic stem cells (ESCs), because this cell type displays particularly high Cdk1 activity. We found that in ESCs, a large fraction of Cdk1 substrates is localized on chromatin. Cdk1 phosphorylates many proteins involved in epigenetic regulation, including writers and erasers of all major histone marks. Consistent with these findings, inhibition of Cdk1 altered histone-modification status of ESCs. High levels of Cdk1 in ESCs phosphorylate and partially inactivate Dot1l, the H3K79 methyltransferase responsible for placing activating marks on gene bodies. Decrease of Cdk1 activity during ESC differentiation de-represses Dot1l, thereby allowing coordinated expression of differentiation genes. These analyses indicate that Cdk1 functions to maintain the epigenetic identity of ESCs.
Assuntos
Proteína Quinase CDC2/metabolismo , Células-Tronco Embrionárias/fisiologia , Epigênese Genética , Trifosfato de Adenosina/análogos & derivados , Trifosfato de Adenosina/metabolismo , Animais , Proteína Quinase CDC2/genética , Diferenciação Celular , Células Cultivadas , Imunoprecipitação da Cromatina/métodos , Feminino , Histona-Lisina N-Metiltransferase/genética , Histona-Lisina N-Metiltransferase/metabolismo , Humanos , Células MCF-7 , Masculino , Camundongos , Camundongos Knockout , Fosforilação , Proteínas de Saccharomyces cerevisiae/metabolismoRESUMO
E-type cyclins (cyclins E1 and E2) are components of the core cell cycle machinery and are overexpressed in many human tumor types. E cyclins are thought to drive tumor cell proliferation by activating the cyclin-dependent kinase 2 (CDK2). The cyclin E1 gene represents the site of recurrent integration of the hepatitis B virus in the pathogenesis of hepatocellular carcinoma, and this event is associated with strong up-regulation of cyclin E1 expression. Regardless of the underlying mechanism of tumorigenesis, the majority of liver cancers overexpress E-type cyclins. Here we used conditional cyclin E knockout mice and a liver cancer model to test the requirement for the function of E cyclins in liver tumorigenesis. We show that a ubiquitous, global shutdown of E cyclins did not visibly affect postnatal development or physiology of adult mice. However, an acute ablation of E cyclins halted liver cancer progression. We demonstrated that also human liver cancer cells critically depend on E cyclins for proliferation. In contrast, we found that the function of the cyclin E catalytic partner, CDK2, is dispensable in liver cancer cells. We observed that E cyclins drive proliferation of tumor cells in a CDK2- and kinase-independent mechanism. Our study suggests that compounds which degrade or inhibit cyclin E might represent a highly selective therapeutic strategy for patients with liver cancer, as these compounds would selectively cripple proliferation of tumor cells, while sparing normal tissues.
Assuntos
Ciclina E/metabolismo , Neoplasias Hepáticas/metabolismo , Animais , Carcinogênese/genética , Carcinogênese/metabolismo , Linhagem Celular Tumoral , Proliferação de Células , Ciclina E/deficiência , Ciclina E/genética , Quinase 2 Dependente de Ciclina/metabolismo , Ciclinas/deficiência , Ciclinas/genética , Ciclinas/metabolismo , Progressão da Doença , Feminino , Humanos , Neoplasias Hepáticas/genética , Neoplasias Hepáticas Experimentais/genética , Neoplasias Hepáticas Experimentais/metabolismo , Neoplasias Hepáticas Experimentais/patologia , Masculino , Camundongos , Camundongos Knockout , Proteínas Oncogênicas/deficiência , Proteínas Oncogênicas/genética , Proteínas Oncogênicas/metabolismoRESUMO
Cyclins and cyclin-dependent kinases (CDKs) are hyperactivated in numerous human tumors. To identify means of interfering with cyclins/CDKs, we performed nine genome-wide screens for human microRNAs (miRNAs) directly regulating cell-cycle proteins. We uncovered a distinct class of miRNAs that target nearly all cyclins/CDKs, which are very effective in inhibiting cancer cell proliferation. By profiling the response of over 120 human cancer cell lines, we derived an expression-based algorithm that can predict the response of tumors to cell-cycle-targeting miRNAs. Using systemic administration of nanoparticle-formulated miRNAs, we inhibited tumor progression in seven mouse xenograft models, including three treatment-refractory patient-derived tumors, without affecting normal tissues. Our results highlight the utility of using cell-cycle-targeting miRNAs for treatment of refractory cancer types.
