Cyclin F drives proliferation through SCF-dependent degradation of the retinoblastoma-like tumor suppressor p130/RBL2

Cell cycle gene expression programs fuel proliferation and are universally dysregulated in cancer. The retinoblastoma (RB)-family of proteins, RB1, RBL1/p107 and RBL2/p130, coordinately repress cell cycle gene expression, inhibiting proliferation and suppressing tumorigenesis. Phosphorylation of RB-family proteins by cyclin dependent kinases is firmly established. Like phosphorylation, ubiquitination is essential to cell cycle control, and numerous proliferative regulators, tumor suppressors, and oncoproteins are ubiquitinated. However, little is known about the role of ubiquitin signaling in controlling RB-family proteins. A systems genetics analysis of CRISPR/Cas9 screens suggested the potential regulation of the RB-network by cyclin F, a substrate recognition receptor for the SCF family of E3 ligases. We demonstrate that RBL2/p130 is a direct substrate of SCFcyclin F. We map a cyclin F regulatory site to a flexible linker in the p130 pocket domain, and show that this site mediates binding, stability, and ubiquitination. Expression of a mutant version of p130, which cannot be ubiquitinated, severely impaired proliferative capacity and cell cycle progression. Consistently, we observed reduced expression of cell cycle gene transcripts, as well a reduced abundance of cell cycle proteins, analyzed by quantitative, iterative immunofluorescent imaging. These data suggest a key role for SCFcyclin F in the CDK-RB network and raise the possibility that aberrant p130 degradation could dysregulate the cell cycle in human cancers.

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Cyclin F drives proliferation through SCF-dependent degradation of the retinoblastoma-like tumor suppressor p130/RBL2

10.1101/2021.04.23.441013 ◽

2021 ◽

Author(s):

Taylor P. Enrico ◽

Wayne Stallaert ◽

Elizaveta T. Wick ◽

Peter Ngoi ◽

Seth M. Rubin ◽

...

Keyword(s):

Gene Expression ◽

Cell Cycle ◽

Cell Cycle Control ◽

Cell Cycle Gene ◽

Loss Of Function ◽

E3 Ligases ◽

Dependent Protein ◽

Cyclin F ◽

Cell Cycle Gene Expression

AbstractCell cycle gene expression programs fuel proliferation and are dysregulated in many cancers. The retinoblastoma-family proteins, RB, p130/RBL2 and p107/RBL1, coordinately repress cell cycle gene expression, inhibiting proliferation and suppressing tumorigenesis. Ubiquitin-dependent protein degradation is essential to cell cycle control, and numerous proliferative regulators, tumor suppressors, and oncoproteins are ubiquitinated. However, little is known about the role of ubiquitin signaling in controlling RB-family proteins. A systems genetics analysis of several hundred CRISPR/Cas9 loss-of-function screens suggested the potential regulation of the RB-network by cyclin F, a substrate recognition receptor for the SCF family of E3 ligases. We demonstrate that RBL2/p130 is a direct substrate of SCFcyclin F. We map a cyclin F regulatory site to a flexible linker in the p130 pocket domain, and show that this site mediates binding, stability, and ubiquitination. Expression of a non-degradable p130 represses cell cycle gene expression and strongly reduces proliferation. These data suggest that SCFcyclin Fplays a key role in the CDK-RB network and raises the possibility that aberrant p130 degradation could dysregulate the cell cycle in human cancers.

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A toxin-antitoxin system associated transcription factor of Caulobacter crescentus can influence cell cycle-regulated gene expression during the SOS response

10.1101/2020.07.22.216945 ◽

2020 ◽

Author(s):

Koyel Ghosh ◽

Kamilla Ankær Brejndal ◽

Clare L. Kirkpatrick

Keyword(s):

Gene Expression ◽

Cell Cycle ◽

Dna Damage ◽

Transcription Factor ◽

Caulobacter Crescentus ◽

Sos Response ◽

Cell Cycle Gene ◽

Regulated Gene Expression ◽

Cell Cycle Gene Expression

AbstractToxin-antitoxin (TA) systems are widespread in bacterial chromosomes but their functions remain enigmatic. Although many are transcriptionally upregulated by stress conditions, it is unclear what role they play in cellular responses to stress and to what extent the role of a given TA system homologue varies between different bacterial species. In this work we investigate the role of the DNA damage-inducible TA system HigBA of Caulobacter crescentus in the SOS response and discover that in addition to the toxin HigB affecting cell cycle gene expression through inhibition of the master regulator CtrA, HigBA possesses a transcription factor third component, HigC, which both auto-regulates the TA system and acts independently of it. Through HigC, the system exerts downstream effects on antibiotic (ciprofloxacin) resistance and cell cycle gene expression. HigB and HigC had inverse effects on cell cycle gene regulation, with HigB reducing and HigC increasing the expression of CtrA-dependent promoters. Neither HigBA nor HigC had any effect on formation of persister cells in response to ciprofloxacin. Rather, their role in the SOS response appears to be as transcriptional and post-transcriptional regulators of cell cycle-dependent gene expression, transmitting the status of the SOS response as a regulatory input into the cell cycle control network via CtrA.ImportanceAlmost all bacteria respond to DNA damage by upregulating a set of genes that helps them to repair and recover from the damage, known as the SOS response. The set of genes induced during the SOS response varies between species, but frequently includes toxin-antitoxin systems. However, it is unknown what the consequence of inducing these systems is, and whether they provide any benefit to the cells. We show here that the DNA damage-induced TA system HigBA of the asymmetrically dividing bacterium Caulobacter crescentus affects the cell cycle regulation of this bacterium. HigBA also has a transcription factor encoded immediately downstream of it, named here HigC, which controls expression of the TA system and potentially other genes as well. Therefore, this work identifies a new role for TA systems in the DNA damage response, distinct from non-specific stress tolerance mechanisms which had been proposed previously.

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Bimodal Degradation of MLL Protein by the Cell Cycle SCFSkp2 and APCCdc20 E3 Lilgases Assures Cell Cycle Execution: A Critical Regulatory Circuit Lost in Leukemogenic MLL-Fusions.

Blood ◽

10.1182/blood.v110.11.828.828 ◽

2007 ◽

Vol 110 (11) ◽

pp. 828-828 ◽

Cited By ~ 1

Author(s):

Han Liu ◽

David Chen ◽

Todd Westergard ◽

Shugaku Takeda ◽

Satoru Sasagawa ◽

...

Keyword(s):

Gene Expression ◽

Cell Cycle ◽

Cell Cycle Progression ◽

Hox Genes ◽

S Phase ◽

Polycomb Group ◽

Cell Cycle Gene ◽

E3 Ligases ◽

M Phase ◽

Phase Progression

Abstract The MLL (mixed lineage leukemia) gene encodes a highly conserved 3,969 aa histone H3 K4 methyl transferase, of which chromosome translocations result in poor prognostic infant and therapy-related leukemias. Mysteriously, the pathognomonic MLL leukemia fusions consist of a common amino(N)-terminal ∼1400 aa of MLL fused in frame with more than 60 different partners with no shared characteristics. The most well known genetic function of MLL is to antagonize polycomb group of proteins for proper Hox gene expression. Consequently deregulated Hox genes caused by MLL translocations contribute to the MLL leukemogenesis. Besides Hox genes, it remains largely undetermined whether MLL participates in other biological processes. The 500kD MLL precursor undergoes evolutionarily conserved proteolytic maturation mediated by Taspase1 (Hsieh et al. 2003, MCB, 23, 186–194; Hsieh et al. 2003, Cell, 115, 293–303). Our recent studies on Taspase1 knockout cells established an MLL-E2F axis in orchestrating core cell cycle gene expression including Cyclins and possibly Cdk inhibitors (Takeda et al. 2006, Genes & Development, 20, 2397–2409). As MLL actively participates in the cell cycle regulation, we investigated the regulation of MLL through cell cycle transition. We uncovered a unique biphasic expression of MLL conferred by defined windows of degradation mediated by specialized cell cycle E3 ligases. Specifically, SCFSkp2 and APCCdc20 mark MLL for degradation at S phase and late M phase, respectively. Abolished peak expression of MLL incurs corresponding defects in G1/S transition and M phase progression. Conversely, over-expression of MLL blocks S phase progression. Remarkably, MLL degradation initiates at its N-terminal ∼1400 aa that is retained in all MLL leukemia fusions. We examined prevalent MLL-fusions, including MLL-AF4, MLL-AF9, MLL-ELL and MLL-ELL, and observed their increased resistance to degradation. Furthermore, the same resistance was observed with the leukemogenic MLL-lacZ but not the non-leukemogenic MLL-Myc tag fusion. Thus, non-oscillating expression of MLL-fusions through the cell cycle, resulted from impaired degradation, likely constitutes the universal mechanism underlying all MLL leukemias. Our data conclude an essential post-translational regulation of MLL by the cell cycle ubiquitin/proteasome system (UPS) to assure the temporal necessity of MLL in coordinating cell cycle progression. Future studies aim at providing a comprehensive analysis on the cell cycle consequences associated with MLL-fusions using genetically modified cells derived from mice carrying various MLL-fusion knockin alleles, including MLL-AF4, MLL-AF9, and MLL-CBP.

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