FOXM1
Forkhead box protein M1 (Forkhead-related protein FKHL16) (Hepatocyte nuclear factor 3 forkhead homolog 11) (HFH-11) (HNF-3/fork-head homolog 11) (M-phase phosphoprotein 2) (MPM-2 reactive phosphoprotein 2) (Transcription factor Trident) (Winged-helix factor from INS-1 cells) [FKHL16] [HFH11] [MPP2] [WIN]
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Cellular senescence of endothelial cells causes vascular dysfunction, promotes atherosclerosis, and contributes to the development of age-related vascular diseases. Sirtuin 6 (SIRT6), a conserved NAD -dependent protein deacetylase, has beneficial effects against aging, despite the fact that its functional mechanisms are largely uncharacterized. Here, we show that SIRT6 protects endothelial cells from senescence. SIRT6 expression is progressively decreased during both oxidative stress-induced senescence and replicative senescence. SIRT6 deficiency leads to endothelial dysfunction, growth arrest, and premature senescence. Using genetically engineered endothelial cell-specific SIRT6 knockout mice, we also show that down-regulation of SIRT6 expression in endothelial cells exacerbates vascular aging. Expression microarray analysis demonstrated that SIRT6 modulates the expression of multiple genes involved in cell cycle regulation. Specifically, SIRT6 appears to regulate the expression of forkhead box M1 (FOXM1), a critical transcription factor for cell cycle progression and senescence. Overexpression of FOXM1 ameliorates SIRT6 deficiency-induced endothelial cell senescence. In this work, we demonstrate the role of SIRT6 as an anti-aging factor in the vasculature. These data may provide the basis for future novel therapeutic approaches against age-related vascular disorders.
Keywords
- FOXM1
- SIRT6
- cell cycle
- endothelial cell
- senescence
Following up on previous work demonstrating the involvement of the transcription factor forkhead box M1 (FOXM1) in the biology and outcome of a high-risk subset of newly diagnosed multiple myeloma (nMM), this study evaluated whether FOXM1 gene expression may be further upregulated upon tumor recurrence in patients with relapsed multiple myeloma (rMM). Also assessed was the hypothesis that increased levels of FOXM1 diminish the sensitivity of myeloma cells to commonly used myeloma drugs, such as the proteasome inhibitor bortezomib (Bz) and the DNA intercalator doxorubicin (Dox). FOXM1 message was evaluated in 88 paired myeloma samples from patients with nMM and rMM, using gene expression microarrays as measurement tool. Sources of differential gene expression were identified and outlier analyses were performed using statistical methods. Two independent human myeloma cell lines (HMCLs) containing normal levels of FOXM1 (FOXM1 ) or elevated levels of lentivirus-encoded FOXM1 (FOXM1 ) were employed to determine FOXM1-dependent changes in cell proliferation, survival, efflux-pump activity, and drug sensitivity. Levels of retinoblastoma (Rb) protein were determined with the assistance of Western blotting. Upregulation of FOXM1 occurred in 61 of 88 (69%) patients with rMM, including 4 patients that exhibited > 20-fold elevated expression peaks. Increased FOXM1 levels in FOXM1 myeloma cells caused partial resistance to Bz (1.9-5.6 fold) and Dox (1.5-2.9 fold) in vitro, using FOXM1 myeloma as control. Reduced sensitivity of FOXM1 cells to Bz was confirmed in vivo using myeloma-in-mouse xenografts. FOXM1-dependent regulation of total and phosphorylated Rb agreed with a working model of myeloma suggesting that FOXM1 governs both chromosomal instability (CIN) and E2F-dependent proliferation, using a mechanism that involves interaction with NIMA related kinase 2 (NEK2) and cyclin dependent kinase 6 (CDK6), respectively. These findings enhanced our understanding of the emerging FOXM1 genetic network in myeloma and provided preclinical support for the therapeutic targeting of the FOXM1-NEK2 and CDK4/6-Rb-E2F pathways using small-drug CDK and NEK2 inhibitors. Clinical research is warranted to assess whether this approach may overcome drug resistance in FOXM1 myeloma and, thereby, improve the outcome of patients in which the transcription factor is expressed at high levels.
MeSH Terms
- Animals
- Antineoplastic Agents
- Bortezomib
- Cell Line, Tumor
- Cell Proliferation
- Cell Survival
- Doxorubicin
- Drug Resistance
- Drug Tolerance
- Forkhead Box Protein M1
- Gene Expression Profiling
- Gene Expression Regulation, Neoplastic
- Humans
- Mice, Inbred NOD
- Mice, Knockout
- Mice, SCID
- Multiple Myeloma
- Up-Regulation
- Xenograft Model Antitumor Assays
Keywords
- Cellular senescence
- Plasma-cell neoplasm
- Small-drug inhibitor
- Targeted cancer therapy
Abemaciclib is an ATP-competitive, reversible kinase inhibitor selective for CDK4 and CDK6 that has shown antitumor activity as a single agent in hormone receptor positive (HR ) metastatic breast cancer in clinical trials. Here, we examined the mechanistic effects of abemaciclib treatment using [i]in vitro[/i] and [i]in vivo[/i] breast cancer models. Treatment of estrogen receptor positive (ER ) breast cancer cells with abemaciclib alone led to a decrease in phosphorylation of Rb, arrest at G1, and a decrease in cell proliferation. Moreover, abemaciclib exposure led to durable inhibition of pRb, TopoIIα expression and DNA synthesis, which were maintained after drug removal. Treatment of ER breast cancer cells also led to a senescence response as indicated by accumulation of β-galactosidase, formation of senescence-associated heterochromatin foci, and a decrease in FOXM1 positive cells. Continuous exposure to abemaciclib altered breast cancer cell metabolism and induced apoptosis. In a xenograft model of ER breast cancer, abemaciclib monotherapy caused regression of tumor growth. Overall these data indicate that abemaciclib is a CDK4 and CDK6 inhibitor that, as a single agent, blocks breast cancer cell progression, and upon longer treatment can lead to sustained antitumor effects through the induction of senescence, apoptosis, and alteration of cellular metabolism.
Keywords
- abemaciclib
- apoptosis
- cell cycle
- hormone receptor positive breast cancer
- senescence
Inadequate pancreatic β cell function underlies type 1 and type 2 diabetes mellitus. Strategies to expand functional cells have focused on discovering and controlling mechanisms that limit the proliferation of human β cells. Here, we developed an engraftment strategy to examine age-associated human islet cell replication competence and reveal mechanisms underlying age-dependent decline of β cell proliferation in human islets. We found that exendin-4 (Ex-4), an agonist of the glucagon-like peptide 1 receptor (GLP-1R), stimulates human β cell proliferation in juvenile but not adult islets. This age-dependent responsiveness does not reflect loss of GLP-1R signaling in adult islets, since Ex-4 treatment stimulated insulin secretion by both juvenile and adult human β cells. We show that the mitogenic effect of Ex-4 requires calcineurin/nuclear factor of activated T cells (NFAT) signaling. In juvenile islets, Ex-4 induced expression of calcineurin/NFAT signaling components as well as target genes for proliferation-promoting factors, including NFATC1, FOXM1, and CCNA1. By contrast, expression of these factors in adult islet β cells was not affected by Ex-4 exposure. These studies reveal age-dependent signaling mechanisms regulating human β cell proliferation, and identify elements that could be adapted for therapeutic expansion of human β cells.
MeSH Terms
- Adult
- Aging
- Animals
- Calcineurin
- Cyclin A1
- Exenatide
- Female
- Forkhead Box Protein M1
- Glucagon-Like Peptide 1
- Glucagon-Like Peptide-1 Receptor
- Humans
- Insulin
- Insulin Secretion
- Insulin-Secreting Cells
- Male
- Mice, Inbred NOD
- Middle Aged
- NFATC Transcription Factors
- Peptides
- Signal Transduction
- Venoms
Several transcription factors, including the master regulator of the epidermis, p63, are involved in controlling human keratinocyte proliferation and differentiation. Here, we report that in normal keratinocytes, the expression of FOXM1, a member of the Forkhead superfamily of transcription factors, is controlled by p63. We observe that, together with p63, FOXM1 strongly contributes to the maintenance of high proliferative potential in keratinocytes, whereas its expression decreases during differentiation, as well as during replicative-induced senescence. Depletion of FOXM1 is sufficient to induce keratinocyte senescence, paralleled by an increased ROS production and an inhibition of ROS-scavenger genes (SOD2, CAT, GPX2, PRDX). Interestingly, FOXM1 expression is strongly reduced in keratinocytes isolated from old human subjects compared with young subjects. FOXM1 depletion sensitizes both normal keratinocytes and squamous carcinoma cells to apoptosis and ROS-induced apoptosis. Together, these data identify FOXM1 as a key regulator of ROS in normal dividing epithelial cells and suggest that squamous carcinoma cells may also use FOXM1 to control oxidative stress to escape premature senescence and apoptosis.
MeSH Terms
- Carcinoma, Squamous Cell
- Cell Death
- Cell Differentiation
- Cell Line, Tumor
- Cell Proliferation
- Cellular Senescence
- Forkhead Box Protein M1
- Humans
- Keratinocytes
- Oxidative Stress
- Reactive Oxygen Species
- Skin Aging
Keywords
- FOXM1
- head and neck cancer
- oxidative stress
- p63
- senescence
- skin
Maternal embryonic leucine zipper kinase (MELK), a serine/threonine protein kinase, has oncogenic properties and is overexpressed in many cancer cells. The oncogenic function of MELK is attributed to its capacity to disable critical cell-cycle checkpoints and reduce replication stress. Most functional studies have relied on the use of siRNA/shRNA-mediated gene silencing. In the present study, we have explored the biological function of MELK using MELK-T1, a novel and selective small-molecule inhibitor. Strikingly, MELK-T1 triggered a rapid and proteasome-dependent degradation of the MELK protein. Treatment of MCF-7 (Michigan Cancer Foundation-7) breast adenocarcinoma cells with MELK-T1 induced the accumulation of stalled replication forks and double-strand breaks that culminated in a replicative senescence phenotype. This phenotype correlated with a rapid and long-lasting ataxia telangiectasia-mutated (ATM) activation and phosphorylation of checkpoint kinase 2 (CHK2). Furthermore, MELK-T1 induced a strong phosphorylation of p53 (cellular tumour antigen p53), a prolonged up-regulation of p21 (cyclin-dependent kinase inhibitor 1) and a down-regulation of FOXM1 (Forkhead Box M1) target genes. Our data indicate that MELK is a key stimulator of proliferation by its ability to increase the threshold for DNA-damage tolerance (DDT). Thus, targeting MELK by the inhibition of both its catalytic activity and its protein stability might sensitize tumours to DNA-damaging agents or radiation therapy by lowering the DNA-damage threshold.
MeSH Terms
- Apoptosis
- Ataxia Telangiectasia Mutated Proteins
- Azepines
- Benzamides
- Breast Neoplasms
- Cell Line, Tumor
- Cell Proliferation
- DNA Damage
- Enzyme Inhibitors
- Female
- Forkhead Box Protein M1
- Forkhead Transcription Factors
- Gene Expression Regulation, Neoplastic
- Humans
- MCF-7 Cells
- Protein-Serine-Threonine Kinases
Keywords
- chemical biology
- deoxyribonucleic acid (DNA) damage response
- maternal embryonic leucine zipper kinase (MELK) kinase
- senescence
- small molecule inhibitors
FOXM1 is a transcription factor that has been shown to promote cell proliferation in many tissues during early development and high cell turnover tissues in adults. In a number of tumour cell lines, enrichment of FOXM1 has been shown to reduce the DNA damage response (DDR) and induction of senescence by a range of DNA-damaging agents, suggesting a role for the protein in DNA repair. Endogenous FOXM1 is expressed at detectable levels in hepatocytes of mice up to 2 weeks of age, but not in older mice. The aim of this investigation has been to better understand the role of the protein in DDR in normal cells in vivo. Mice with artificially prolonged elevated FOXM1 expression in hepatocytes, were exposed to alkylating diethylnitrosamine. FOXM1-enriched mice had dampened DDR after treatment with this alkylating agent, which was consistent with observed increase in expression of genes involved in DNA repair. Paradoxically, mice with FOXM1 expression, within weeks after exposure to the DNA-damaging agent, had increased levels of potentially senescent hepatocytes with large nuclear foci, containing 53BP1. Similarly, spontaneous accumulation of these cells seen with normal ageing in mice was increased with FOXM1 enrichment. Despite its known abilities to promote proliferation and DNA repair, and to reduce ROS, enrichment of FOXM1, as with other oncoproteins, may cause increased persistent DNA lesions and/or senescence in normal murine hepatocytes.
MeSH Terms
- Aging
- Animals
- Cell Nucleus
- DNA Repair
- Forkhead Box Protein M1
- Forkhead Transcription Factors
- Hepatocytes
- Mice
- Mice, Inbred C57BL
Cellular senescence is a stable cell cycle arrest, caused by insults, such as: telomere erosion, oncogene activation, irradiation, DNA damage, oxidative stress, and viral infection. Extrinsic stimuli such as cell culture stress can also trigger this growth arrest. Senescence is thought to have evolved as an example of antagonistic pleiotropy, as it acts as a tumor suppressor mechanism during the reproductive age, but can promote organismal aging by disrupting tissue renewal, repair, and regeneration later in life. The mechanisms underlying the senescence growth arrest are broadly considered to involve p16(INK4A) -pRB and p53-p21(CIP1/WAF1/SDI1) tumor suppressor pathways; but it is not known what makes the senescence arrest stable and what the critical downstream targets are, as they are likely to be key to the establishment and maintenance of the senescent state. MYB-related protein B (B-MYB/MYBL2), a member of the myeloblastosis family of transcription factors, has recently emerged as a potential candidate for regulating entry into senescence. Here, we review the evidence which indicates that loss of B-MYB expression has an important role in causing senescence growth arrest. We discuss how B-MYB acts, as the gatekeeper, to coordinate transit through the cell cycle, in conjunction with the multivulval class B (MuvB) complex and FOXM1 transcription factors. We also evaluate the evidence connecting B-MYB to the mTOR nutrient signaling pathway and suggest that inhibition of this pathway leading to an extension of healthspan may involve activation of B-MYB.
MeSH Terms
- Aging
- Animals
- Cell Cycle Checkpoints
- Cell Proliferation
- Cellular Senescence
- Humans
- Proto-Oncogene Proteins c-myb
- Signal Transduction
Keywords
- B-MYB
- MuvB
- aging
- cellular senescence
- growth arrest
Ovarian carcinoma is the most lethal gynaecological malignancy. Better understanding of the molecular pathogenesis of this disease and effective targeted therapies are needed to improve patient outcomes. MicroRNAs play important roles in cancer progression and have the potential for use as either therapeutic agents or targets. Studies in other cancers have suggested that miR-506 has anti-tumour activity, but its function has yet to be elucidated. We found that deregulation of miR-506 in ovarian carcinoma promotes an aggressive phenotype. Ectopic over-expression of miR-506 in ovarian cancer cells was sufficient to inhibit proliferation and to promote senescence. We also demonstrated that CDK4 and CDK6 are direct targets of miR-506, and that miR-506 can inhibit CDK4/6-FOXM1 signalling, which is activated in the majority of serous ovarian carcinomas. This newly recognized miR-506-CDK4/6-FOXM1 axis provides further insight into the pathogenesis of ovarian carcinoma and identifies a potential novel therapeutic agent.
MeSH Terms
- 3' Untranslated Regions
- Binding Sites
- Cell Line, Tumor
- Cell Proliferation
- Cell Survival
- Cellular Senescence
- Cyclin-Dependent Kinase 4
- Cyclin-Dependent Kinase 6
- Female
- Forkhead Box Protein M1
- Forkhead Transcription Factors
- Gene Expression Regulation, Neoplastic
- Genotype
- Humans
- MicroRNAs
- Neoplasms, Cystic, Mucinous, and Serous
- Ovarian Neoplasms
- Phenotype
- Signal Transduction
- Time Factors
- Transfection
Keywords
- FOXM1
- miR-506
- ovarian carcinoma
- proliferation
- senescence