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Manohar S, Neurohr GE. Too big not to fail: emerging evidence for size-induced senescence. FEBS J 2024; 291:2291-2305. [PMID: 37986656 DOI: 10.1111/febs.16983] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2023] [Revised: 10/02/2023] [Accepted: 10/17/2023] [Indexed: 11/22/2023]
Abstract
Cellular senescence refers to a permanent and stable state of cell cycle exit. This process plays an important role in many cellular functions, including tumor suppression. It was first noted that senescence is associated with increased cell size in the early 1960s; however, how this contributes to permanent cell cycle exit was poorly understood until recently. In this review, we discuss new findings that identify increased cell size as not only a consequence but also a cause of permanent cell cycle exit. We highlight recent insights into how increased cell size alters normal cellular physiology and creates homeostatic imbalances that contribute to senescence induction. Finally, we focus on the potential clinical implications of these findings in the context of cell cycle arrest-causing cancer therapeutics and speculate on how tumor cell size changes may impact outcomes in patients treated with these drugs.
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Affiliation(s)
- Sandhya Manohar
- Department of Biology, Institute for Biochemistry, ETH Zürich, Switzerland
| | - Gabriel E Neurohr
- Department of Biology, Institute for Biochemistry, ETH Zürich, Switzerland
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2
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Foy R, Lew KX, Saurin AT. The search for CDK4/6 inhibitor biomarkers has been hampered by inappropriate proliferation assays. NPJ Breast Cancer 2024; 10:19. [PMID: 38438376 PMCID: PMC10912267 DOI: 10.1038/s41523-024-00624-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2023] [Accepted: 02/16/2024] [Indexed: 03/06/2024] Open
Abstract
CDK4/6 inhibitors are effective at treating advanced HR+ /HER2- breast cancer, however biomarkers that can predict response are urgently needed. We demonstrate here that previous large-scale screens designed to identify which tumour types or genotypes are most sensitive to CDK4/6 inhibitors have misrepresented the responsive cell lines because of a reliance on metabolic proliferation assays. CDK4/6-inhibited cells arrest in G1 but continue to grow in size, thereby producing more mitochondria. We show that this growth obscures the arrest using ATP-based proliferation assays but not if DNA-based assays are used instead. Furthermore, lymphoma lines, previously identified as the most sensitive, simply appear to respond the best using ATP-based assays because they fail to overgrow during the G1 arrest. Similarly, the CDK4/6 inhibitor abemaciclib appears to inhibit proliferation better than palbociclib because it also restricts cellular overgrowth through off-target effects. DepMap analysis of screening data using reliable assay types, demonstrates that palbociclib-sensitive cell types are also sensitive to Cyclin D1, CDK4 and CDK6 knockout/knockdown, whereas the palbociclib-resistant lines are sensitive to Cyclin E1, CDK2 and SKP2 knockout/knockdown. Potential biomarkers of palbociclib-sensitive cells are increased expression of CCND1 and RB1, and reduced expression of CCNE1 and CDKN2A. Probing DepMap with similar data from metabolic assays fails to reveal these associations. Together, this demonstrates why CDK4/6 inhibitors, and any other anti-cancer drugs that arrest the cell cycle but permit continued cell growth, must now be re-screened against a wide-range of cell types using an appropriate proliferation assay. This would help to better inform clinical trials and to identify much needed biomarkers of response.
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Affiliation(s)
- Reece Foy
- Cellular and Systems Medicine, Jacqui Wood Cancer Centre, School of Medicine, University of Dundee, Dundee, DD1 9SY, UK.
| | - Kah Xin Lew
- Cellular and Systems Medicine, Jacqui Wood Cancer Centre, School of Medicine, University of Dundee, Dundee, DD1 9SY, UK
| | - Adrian T Saurin
- Cellular and Systems Medicine, Jacqui Wood Cancer Centre, School of Medicine, University of Dundee, Dundee, DD1 9SY, UK.
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Düster R, Anand K, Binder SC, Schmitz M, Gatterdam K, Fisher RP, Geyer M. Structural basis of Cdk7 activation by dual T-loop phosphorylation. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.02.14.580246. [PMID: 38405971 PMCID: PMC10888979 DOI: 10.1101/2024.02.14.580246] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 02/27/2024]
Abstract
Cyclin-dependent kinase 7 (Cdk7) occupies a central position in cell-cycle and transcriptional regulation owing to its function as both a CDK-activating kinase (CAK) and part of the general transcription factor TFIIH. Cdk7 forms an active complex upon association with Cyclin H and Mat1, and its catalytic activity is regulated by two phosphorylations in the activation segment (T loop): the canonical activating modification at T170 and another at S164. Here we report the crystal structure of the fully activated human Cdk7/Cyclin H/Mat1 complex containing both T-loop phosphorylations. Whereas pT170 coordinates a set of basic residues conserved in other CDKs, pS164 nucleates an arginine network involving all three subunits that is unique to the ternary Cdk7 complex. We identify differential dependencies of kinase activity and substrate recognition on individual phosphorylations within the Cdk7 T loop. The CAK function of Cdk7 is not affected by T-loop phosphorylation, whereas activity towards non-CDK substrates is increased several-fold by phosphorylation at T170. Moreover, dual T-loop phosphorylation at both T170 and S164 stimulates multi-site phosphorylation of transcriptional substrates-the RNA polymerase II (RNAPII) carboxy-terminal domain (CTD) and the SPT5 carboxy-terminal repeat (CTR) region. In human cells, Cdk7-regulatory phosphorylation is a two-step process in which phosphorylation of S164 precedes, and may prime, T170 phosphorylation. Thus, dual T-loop phosphorylation can regulate Cdk7 through multiple mechanisms, with pS164 supporting tripartite complex formation and possibly influencing Cdk7 processivity, while the canonical pT170 enhances kinase activity towards critical substrates involved in transcription.
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Affiliation(s)
- Robert Düster
- Institute of Structural Biology, University of Bonn, Venusberg-Campus 1, 53127 Bonn, Germany
- Department of Oncological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Kanchan Anand
- Institute of Structural Biology, University of Bonn, Venusberg-Campus 1, 53127 Bonn, Germany
| | - Sophie C. Binder
- Institute of Structural Biology, University of Bonn, Venusberg-Campus 1, 53127 Bonn, Germany
| | - Maximilian Schmitz
- Institute of Structural Biology, University of Bonn, Venusberg-Campus 1, 53127 Bonn, Germany
| | - Karl Gatterdam
- Institute of Structural Biology, University of Bonn, Venusberg-Campus 1, 53127 Bonn, Germany
| | - Robert P. Fisher
- Department of Oncological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Matthias Geyer
- Institute of Structural Biology, University of Bonn, Venusberg-Campus 1, 53127 Bonn, Germany
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Manohar S, Estrada ME, Uliana F, Vuina K, Alvarez PM, de Bruin RAM, Neurohr GE. Genome homeostasis defects drive enlarged cells into senescence. Mol Cell 2023; 83:4032-4046.e6. [PMID: 37977116 PMCID: PMC10659931 DOI: 10.1016/j.molcel.2023.10.018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2022] [Revised: 06/30/2023] [Accepted: 10/16/2023] [Indexed: 11/19/2023]
Abstract
Cellular senescence refers to an irreversible state of cell-cycle arrest and plays important roles in aging and cancer biology. Because senescence is associated with increased cell size, we used reversible cell-cycle arrests combined with growth rate modulation to study how excessive growth affects proliferation. We find that enlarged cells upregulate p21, which limits cell-cycle progression. Cells that re-enter the cell cycle encounter replication stress that is well tolerated in physiologically sized cells but causes severe DNA damage in enlarged cells, ultimately resulting in mitotic failure and permanent cell-cycle withdrawal. We demonstrate that enlarged cells fail to recruit 53BP1 and other non-homologous end joining (NHEJ) machinery to DNA damage sites and fail to robustly initiate DNA damage-dependent p53 signaling, rendering them highly sensitive to genotoxic stress. We propose that an impaired DNA damage response primes enlarged cells for persistent replication-acquired damage, ultimately leading to cell division failure and permanent cell-cycle exit.
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Affiliation(s)
- Sandhya Manohar
- Institute for Biochemistry, Department of Biology, ETH Zürich 8093, Zürich, Zürich, Switzerland
| | - Marianna E Estrada
- Institute for Biochemistry, Department of Biology, ETH Zürich 8093, Zürich, Zürich, Switzerland
| | - Federico Uliana
- Institute for Biochemistry, Department of Biology, ETH Zürich 8093, Zürich, Zürich, Switzerland
| | - Karla Vuina
- Laboratory for Molecular Cell Biology, University College London, London WC1E 6BT, UK
| | - Patricia Moyano Alvarez
- Institute for Biochemistry, Department of Biology, ETH Zürich 8093, Zürich, Zürich, Switzerland
| | - Robertus A M de Bruin
- Laboratory for Molecular Cell Biology, University College London, London WC1E 6BT, UK; UCL Cancer Institute, University College London, London WC1E 6BT, UK
| | - Gabriel E Neurohr
- Institute for Biochemistry, Department of Biology, ETH Zürich 8093, Zürich, Zürich, Switzerland.
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Khurana A, Chadha Y, Schmoller KM. Too big not to fail: Different paths lead to senescence of enlarged cells. Mol Cell 2023; 83:3946-3947. [PMID: 37977113 DOI: 10.1016/j.molcel.2023.10.024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2023] [Revised: 10/18/2023] [Accepted: 10/18/2023] [Indexed: 11/19/2023]
Abstract
In this issue of Molecular Cell, Crozier et al.,1 Foy et al.,2 Manohar et al.,3 and Wilson et al.4 show how excessive cell growth caused by a temporary G1 arrest leads to permanent cell cycle exit at different stages of the cell cycle.
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Affiliation(s)
- Arohi Khurana
- Institute of Functional Epigenetics, Molecular Targets and Therapeutics Center, Helmholtz Zentrum München, Neuherberg, Germany
| | - Yagya Chadha
- Institute of Functional Epigenetics, Molecular Targets and Therapeutics Center, Helmholtz Zentrum München, Neuherberg, Germany
| | - Kurt M Schmoller
- Institute of Functional Epigenetics, Molecular Targets and Therapeutics Center, Helmholtz Zentrum München, Neuherberg, Germany.
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Foy R, Crozier L, Pareri AU, Valverde JM, Park BH, Ly T, Saurin AT. Oncogenic signals prime cancer cells for toxic cell overgrowth during a G1 cell cycle arrest. Mol Cell 2023; 83:4047-4061.e6. [PMID: 37977117 DOI: 10.1016/j.molcel.2023.10.020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2022] [Revised: 07/10/2023] [Accepted: 10/17/2023] [Indexed: 11/19/2023]
Abstract
CDK4/6 inhibitors are remarkable anti-cancer drugs that can arrest tumor cells in G1 and induce their senescence while causing only relatively mild toxicities in healthy tissues. How they achieve this mechanistically is unclear. We show here that tumor cells are specifically vulnerable to CDK4/6 inhibition because during the G1 arrest, oncogenic signals drive toxic cell overgrowth. This overgrowth causes permanent cell cycle withdrawal by either preventing progression from G1 or inducing genotoxic damage during the subsequent S-phase and mitosis. Inhibiting or reverting oncogenic signals that converge onto mTOR can rescue this excessive growth, DNA damage, and cell cycle exit in cancer cells. Conversely, inducing oncogenic signals in non-transformed cells can drive these toxic phenotypes and sensitize the cells to CDK4/6 inhibition. Together, this demonstrates that cell cycle arrest and oncogenic cell growth is a synthetic lethal combination that is exploited by CDK4/6 inhibitors to induce tumor-specific toxicity.
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Affiliation(s)
- Reece Foy
- Cellular and Systems Medicine, Jacqui Wood Cancer Centre, School of Medicine, University of Dundee, Dundee DD1 9SY, UK
| | - Lisa Crozier
- Cellular and Systems Medicine, Jacqui Wood Cancer Centre, School of Medicine, University of Dundee, Dundee DD1 9SY, UK
| | - Aanchal U Pareri
- Cellular and Systems Medicine, Jacqui Wood Cancer Centre, School of Medicine, University of Dundee, Dundee DD1 9SY, UK
| | - Juan Manuel Valverde
- Cellular and Systems Medicine, Jacqui Wood Cancer Centre, School of Medicine, University of Dundee, Dundee DD1 9SY, UK
| | - Ben Ho Park
- Vanderbilt-Ingram Cancer Center, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - Tony Ly
- Molecular Cell and Developmental Biology, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
| | - Adrian T Saurin
- Cellular and Systems Medicine, Jacqui Wood Cancer Centre, School of Medicine, University of Dundee, Dundee DD1 9SY, UK.
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