Breast cancer that is accompanied by a high level of cyclin
September 25, 2017
Breast cancer that is accompanied by a high level of cyclin E expression usually exhibits poor prognosis and clinical outcome. level by interacting with cyclin E. Overexpression of DEC1 repressed the interaction between cyclin E and its E3 ligase Fbw7cell death through MIC-1 in response to DNA damage stress.11 Thus, DEC1 has multifaceted roles in cancer progression. However, whether it also affects cancer progression through regulating the cell cycle factors has not yet been clearly established. buy CIQ Cyclin E, a member of the cyclin family, binds to and activates the Cdk2.12 The level of cyclin E protein oscillates throughout the cell cycle and peaks at around the beginning of the S phase, but subsequent degradation of the cyclin E protein is needed for the orderly cell progression buy CIQ to occur, which is regulated by E2Fs-dependent cyclin E transcription and ubiquitin-mediated cyclin E proteolysis.13 Two types of ubiquitin ligases are known to trigger the ubiquitin-mediated degradation of cyclin E, and these are the Cul1-(SCF) or Cul3-(BCR) dependent ubiquitin ligases.14, 15, 16, 17 Cyclin E that is bound to Cdk2 is targeted for ubiquitination by Cul1-dependent ubiquitin ligase, and this ubiquitination requires the phosphorylation of cyclin E at specific residues (Thr62, Ser372, Thr380 and Ser384).12, 17, 18 During the G1S phase transition of the cell cycle progression, the formation of cyclin E/Cdk2 complex occurs in the nuclei and it needs to reach certain threshold in order to trigger the initiation of DNA replication.7, 19 However, abnormal stabilization of cyclin E inhibits transcription by increasing the initiation of replication and subsequently induces delay in the S phase.20, 21 Dysregulated activity of cyclin E is known to cause cell lineage-specific abnormalities such as impaired maturation as a result of increased genetic instability, buy CIQ cell proliferation and apoptosis or senescence via several different mechanisms.16, 22 In this study, we showed that DEC1 stabilized cyclin E without affecting its mRNA level. We also demonstrated that DEC1 stabilized cyclin E by blocking the proteasome pathway and hence, repressed the ubiquitination of cyclin E through reducing the interaction between cyclin E and Fbw7on cyclin E was compromised by DEC1, since cells that overexpressed Fbw7and cyclin E whether or not the cells were under serum starvation (Figures 3gCj). In addition, we also investigated the ubiquitination of endogenous cyclin E in the cells in which either DEC1 or Fbw7 had been knocked down as well as in the cells in which both DEC1 and Fbw7 had been knocked down (Figure 3k). This demonstrated that the inhibition of cyclin E ubiquitination by DEC1 was dependent on the presence of Fbw7. Taken together these results indicated that DEC1 stabilized cyclin E protein through blocking the ubiquitin-mediated proteasomal degradation of cyclin E, which probably occurred through a reduction of interaction between cyclin E and Fbw7and experiments indicated that DEC1 functioned as a tumor suppressor and inhibited cell growth. Discussion As an important transcription factor, DEC1 plays an important role in cell differentiation, proliferation and apoptosis.31, 32, 33, 34, 35 In this study, we found in this study that DEC1 could affect the level of cyclin E in a cell, not through its transcriptional activity (Figures 2b and c; Supplementary Figures S2A and D), but through protein-protein interaction, and this effectively allowed DEC1 to regulate the cell cycle progression, consequently resulting in the regulation of cell proliferation. As shown in Figures 2 and ?and3,3, DEC1 upregulated the level of cyclin E protein in a dose-dependent pathway and prolonged the half-life of cyclin E, and the underlying mechanism by which it achieved this was through interfering with the interaction between cyclin E and Fbw7, thereby reducing the Fbw7-mediated ubiquitination of cyclin E (Figures 3gCj). In addition to increasing the protein level of cyclin E through inhibiting the Fbw7-mediated ubiquitination and degradation pathway, DEC1 also decreased the level of p21 (Supplementary Figure S5) and enhanced the binding of cyclin E to Cdk2 as well as the kinase activity of the cyclin E/Cdk2 complex (Figures 5a and d), suggesting that multiple mechanisms could be at work.36 More and more evidences have shown that Rabbit polyclonal to IWS1 cyclin E may function as a switch’ or a double-edged sword: however, high expression of cyclin E promotes a faster transition from G1 to S phase,37, 38 which is why cyclin E is always expressed at a high level in various types of cancers and its expression correlates with tumorigenesis;39, 40 however, excessive cyclin E would interfere with the assembly of the pre-replication complex and lead to replication stress, DNA damage and genomic instability, which will block buy CIQ the S-phase progression and cause cell cycle arrest.21, 41, 42 In this study, we have verified the following: (i) DEC1 could promote the nuclear accumulation of cyclin E/Cdk2 and inhibit the formation.