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Results for “Anaphase-promoting complex/cyclosome (APC/C)”

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The Use of APC/C Antagonists to Promote Mitotic Catastrophe in Cancer Cells.

The multiprotein subunit E3 ubiquitin ligase Anaphase-Promoting Complex/Cyclosome (APC/C) plays a key role in the control of mitosis progression. APC/C is the ultimate effector of the Spindle Assembly Checkpoint (SAC), the signaling system of higher organisms including the human that monitors the proper attachment of chromosomes to microtubules during cell division. Defects in this process result in genome instability, aneuploidy, premature aging, and cancer. APC/C roles in the SAC require its activation by the protein Cdc20. Interfering with APC/C activation by Cdc20 impairs APC/C substrate recognition, resulting in a delayed mitotic exit and eventually inducing cell death. This may be advantageous for the treatment of cancer and malignancies associated with SAC dysregulation. Here we describe a protocol to interfere with mitotic exit through the use of commercially available (Apcin, proTAME) as well as innovative small molecules we have developed that function as antagonists of APC/C activation by Cdc20. We show that the use of these molecules alone and in combination is effective to promote mitotic catastrophe and suppress cell expansion in 2D and 3D (spheroids) cancer cells of different tissue origin, including breast, cervical, and ovarian cancer.

Humans

Cdk1 and PP2A constitute a molecular switch controlling orderly degradation of atypical E2Fs.

Dynamic oscillations in the phosphorylation and ubiquitination of key proliferative regulators are defining features of the eukaryotic cell cycle. Resetting the cell cycle at the mitosis-to-G1 transition requires activation of the E3 ubiquitin ligase Anaphase-Promoting Complex/Cyclosome (APC/C), which ensures cell cycle irreversibility by targeting dozens of substrates for degradation, safeguarding genome integrity. However, the overall coupling of substrate phosphorylation with target recognition and degradation by the APC/C remains relatively unexplored. As a paradigm for further defining these rules, we focused on E2F7 and E2F8-atypical E2F-family proteins that coordinate cell cycle gene expression by restraining the pro-proliferative transcriptional activity of E2F1. Leveraging complementary cell and cell-free systems, we demonstrate that flexible domains at the amino-termini of E2F7 and E2F8 contain APC/C recognition motifs adjacent to critical Thr residues, whose phosphorylation by Cdk1 is rate-limiting for degradation. The removal of this phosphorylation by PP2A serves as a molecular switch, coupling the degradation of E2F7 and E2F8 to the G1 phase, coinciding with the rise of E2F1. Collectively, these findings highlight a critical role for Cdk1-PP2A signaling in controlling the orderly degradation of APC/C substrates, ensuring precisely timed assembly of the transcriptional infrastructure that coordinates cell cycle commitment and progression.

Protein Phosphatase 2

Cdk1 and PP2A constitute a molecular switch controlling orderly degradation of atypical E2Fs.

Dynamic oscillations in the phosphorylation and ubiquitination of key proliferative regulators are defining features of the eukaryotic cell cycle. Resetting the cell cycle at the mitosis-to-G1 transition requires activation of the E3 ubiquitin ligase Anaphase-Promoting Complex/Cyclosome (APC/C), which ensures cell cycle irreversibility by targeting dozens of substrates for degradation, safeguarding genome integrity. However, the overall coupling of substrate phosphorylation with target recognition and degradation by the APC/C remains relatively unexplored. As a paradigm for further defining these rules, we focused on E2F7 and E2F8 - atypical E2F-family proteins that coordinate cell cycle gene expression by restraining the pro-proliferative transcriptional activity of E2F1. Leveraging complementary cell and cell-free systems, we demonstrate that flexible domains in the amino-termini of E2F7 and E2F8 contain APC/C recognition motifs adjacent to critical Thr residues, whose phosphorylation by Cdk1 is rate limiting for degradation. The removal of this phosphorylation by PP2A phosphatase serves as a molecular switch, coupling the degradation of E2F7 and E2F8 to the G1 phase, coinciding with the rise of E2F1. Collectively, these findings highlight a critical role for Cdk1-PP2A signaling in controlling the orderly degradation of APC/C substrates, ensuring precisely timed assembly of the transcriptional infrastructure that coordinates cell cycle commitment and progression.

APC/C substrate

Targeting Mitotic Exit in Malignant Cells.

In order to sustain genomic stability by correct DNA replication and mitosis and thus avoid malignant transformation of cells, the cell cycle is a strictly regulated process. Aberrant cell cycle regulation and defects in mitosis in malignant cells are targets of various cancer therapies. Cancer cells may survive antimitotic treatment due to mitotic slippage with a residual activity of the ubiquitin ligase anaphase-promoting complex (APC/C) and a continuous slow ubiquitin-proteasome-dependent cyclin B-degradation leading to mitotic exit. The combination of antimitotic chemotherapeutics with proteasome inhibitors to block cyclin B-proteolysis or with targeted inhibitors of the APC/C and the antiapoptotic protein Mcl-1 seems a promising approach to improve treatment response in different malignancies by enhancing mitotic arrest and apoptosis.The influence of conventional spindle poisons and new targeted substances and of their combinations on mitosis and apoptosis has not yet been conclusively clarified. Most models have been verified on cell lines whose biology may differ from that of tumors growing in vivo. To study the impact of various antimitotic substances on cell proliferation, especially detect onset of apoptosis depending on different cell cycle phases and thus to identify a possibly entity-dependent mechanism of those agents and their combinations, a combined approach with live-cell imaging and soft-agar colony assays in cultured patient-derived xenografts (PDX) was established.

Humans

Viral inhibition of the anaphase promoting complex enhances replication by elevating nucleotide pools.

The anaphase promoting complex/cyclosome (APC/C) is a large, ubiquitin ligase and a central regulator of cell cycle progression. By targeting key substrates for degradation during mitosis and G1 phase, the APC/C coordinates metabolic fluctuations that occur during the cell cycle. A diverse range of viruses have convergently evolved mechanisms to bind and inhibit the APC/C; however, a molecular understanding for these interactions has never been demonstrated. Here, we use chicken anemia virus (CAV), a small single-stranded DNA virus encoding only three proteins, to demonstrate the importance of viral APC/C inhibition during replication. We show that the Vp3 protein of CAV inhibits the APC/C, causing a dramatic mitotic arrest during infection. The mutant virus lacking Vp3 is defective for replication and can be rescued by APC/C inhibition. Metabolomic profiling during CAV infection revealed that Vp3 expression mediates a broad increase in nucleotide pools. Moreover, viral inhibition of the APC/C resulted in stabilization of enzymes required for nucleotide biosynthesis. These findings suggest that the APC/C is a general target of many viruses to elevate nucleotide levels and facilitate viral genome replication.

Anaphase-Promoting Complex-Cyclosome