Cdkn3 Knockout Mice Develop Hematopoietic Malignancies

Blood ◽  
2016 ◽  
Vol 128 (22) ◽  
pp. 1537-1537 ◽  
Author(s):  
Zejin Sun ◽  
Donna Cerabona ◽  
Ying He ◽  
Grzegorz Nalepa

Abstract Cyclin dependent kinase inhibitor 3 (CDKN3) is a dual-specificity cell cycle regulatory phosphatase. In interphase, CDKN3 prevents premature G1/S transition by dephosphorylating interphase cyclin-dependent kinases (CDKs) to prevent premature inactivation of the RB pathway. During cell division, CDKN3 dephosphorylates the key mitotic kinase CDK1 at threonine-161 to extinguish CDK1 activity at the exit from mitosis. CDKN3 knockdown in cultured cells impairs the spindle assembly checkpoint (SAC), accelerates cell cycle progression and causes chromosomal instability, suggesting that it may function as a tumor suppressor. However, since CDKN3 has been reported as overexpressed in some malignancies and mutated or silenced in others, it is unclear whether it functions as an oncogene or a tumor suppressor. To understand the in vivo role of CDKN3 in carcinogenesis, we generated the first Cdkn3 conditional knockout mouse model. We found that Cdkn3-/- mice were viable, non-dysmorphic and born at expected Mendelian ratios, indicating that this gene is dispensable for normal embryonic development. In agreement with the postulated role of this phosphatase in cell cycle progression and regulation of CDKs, we found that Cdkn3-/- cells had increased CDK1, CDK2 and CDK4 activity; increased inhibitory phosphorylation of Rb; increased DNA replication and proliferation; and impaired SAC. Increased CDK activity and accelerated cell cycle progression caused genomic instability reflected by increased frequency of in vivo micronucleation during hematopoiesis as well as higher frequency of aneuploidy and multinucleation and accumulation of supernumerary centrosomes in Cdkn3-/- cells cultured ex vivo. Cdkn3-/- mice had increased myeloid colony-forming units in progenitor assays. Long-term observation of Cdkn3-/- mice revealed an increased risk of death from a variety of hematopoietic (leukemia and lymphoma) and non-hematopoietic (lung, prostate and ovarian) malignancies. Our findings establish Cdkn3 as an in vivo tumor suppressor in bone marrow and a variety of other tissues. In the long term, Cdkn3-/- mice will serve as a tool to dissect the function of this phosphatase in cell cycle control in more detail, and may prove useful in preclinical studies of chemotherapy of CDK-hyperactive, genomically unstable leukemia and lymphoma. Disclosures No relevant conflicts of interest to declare.

2012 ◽  
pp. 235-243 ◽  
Author(s):  
Norman Balcazar Morales ◽  
Cecilia Aguilar de Plata

Growth factors, insulin signaling and nutrients are important regulators of β-cell mass and function. The events linking these signals to regulation of β-cell mass are not completely understood. Recent findings indicate that mTOR pathway integrates signals from growth factors and nutrients with transcription, translation, cell size, cytoskeleton remodeling and mitochondrial metabolism. mTOR is a part of two distinct complexes; mTORC1 and mTORC2. The mammalian TORC1 is sensitive to rapamycin and contains Raptor, deptor, PRAS40 and the G protein β-subunit-like protein (GβL). mTORC1 activates key regulators of protein translation; ribosomal S6 kinase (S6K) and eukaryote initiation factor 4E-binding protein 1. This review summarizes current findings about the role of AKT/mTORC1 signaling in regulation of pancreatic β cell mass and proliferation. mTORC1 is a major regulator of β-cell cycle progression by modulation of cyclins D2, D3 and cdk4/cyclin D activity. These studies uncovered key novel pathways controlling cell cycle progression in β-cells in vivo. This information can be used to develop alternative approaches to expand β-cell mass in vivo and in vitro without the risk of oncogenic transformation. The acquisition of such knowledge is critical for the design of improved therapeutic strategies for the treatment and cure of diabetes as well as to understand the effects of mTOR inhibitors in β-cell function.


2019 ◽  
Vol 10 (1) ◽  
pp. 130-134 ◽  
Author(s):  
Saeed Noorolyai ◽  
Elham Baghbani ◽  
Leili Aghebati Maleki ◽  
Amir Baghbanzadeh Kojabad ◽  
Dariush Shanehbansdi ◽  
...  

Purpose: Colorectal cancer (CRC) remains a universal and lethal cancer owing to metastatic and relapsing disease. Currently, the role of microRNAs has been checked in tumorigeneses. Numerous studies have revealed that between the tumor suppressor miRNAs, the reduced expression of miR-146a-5p and -193a-5p in several cancers including CRC tissues are related with tumor progression and poor prognosis of patients. The purpose of this study is to examine the role of miR-146 a-5p and -193 a-5p in CRC cell cycle progression. Methods: The miR-193a-5p and -146 a-5p mimics were transfected into HT-29 CRC cells via jetPEI transfection reagent and their impact was assessed on p53, cyclin B, and NF-kB gene expression. The inhibitory effect of these miRNAs on cell cycle was assessed by flow cytometry. The consequence of miR-193a-5p and miR-146 a-5p on the protein expression level of Murine double minute 2 (MDM2) was assessed by western blotting. Results: miR193a-5p and -146a-5p regulated the expression of MDM2 protein and p53, cyclin B, and NF-kB gene expression in CRC cells. Treatment of HT-29 cells with miRNA-146a-5p and -193a-5p induced G1 cell cycle arrest. Conclusion: The findings of our study suggest that miR146a-5p and -193a-5p may act as a potential tumor suppressor by their influence on cell cycle progression in CRC cells. Thus, miRNA-146a-5p and -193a-5p restoration may be recommended as a potential therapeutic goal in the treatment of CRC patients.


2019 ◽  
Vol 218 (12) ◽  
pp. 4042-4062 ◽  
Author(s):  
Reito Watanabe ◽  
Masatoshi Hara ◽  
Ei-ichi Okumura ◽  
Solène Hervé ◽  
Daniele Fachinetti ◽  
...  

The kinetochore is essential for faithful chromosome segregation during mitosis. To form a functional kinetochore, constitutive centromere-associated network (CCAN) proteins are assembled on the centromere chromatin that contains the centromere-specific histone CENP-A. CENP-C, a CCAN protein, directly interacts with the CENP-A nucleosome to nucleate the kinetochore structure. As CENP-C is a hub protein for kinetochore assembly, it is critical to address how the CENP-A–CENP-C interaction is regulated during cell cycle progression. To address this question, we investigated the CENP-C C-terminal region, including a conserved CENP-A–binding motif, in both chicken and human cells and found that CDK1-mediated phosphorylation of CENP-C facilitates its binding to CENP-A in vitro and in vivo. We observed that CENP-A binding is involved in CENP-C kinetochore localization during mitosis. We also demonstrate that the CENP-A–CENP-C interaction is critical for long-term viability in human RPE-1 cells. These results provide deeper insights into protein-interaction network plasticity in centromere proteins during cell cycle progression.


2013 ◽  
Vol 24 (11) ◽  
pp. 1676-1687 ◽  
Author(s):  
Wen Dui ◽  
Bin Wei ◽  
Feng He ◽  
Wei Lu ◽  
Changqing Li ◽  
...  

Cell cycle progression is controlled by a complex regulatory network consisting of interacting positive and negative factors. In humans, the positive regulator Skp2, an F-box protein, has been a subject of intense investigation in part because of its oncogenic activity. By contrast, the molecular and developmental functions of its Drosophila homologue, dSkp2, are poorly understood. Here we investigate the role of dSkp2 by focusing on its functional relationship with Dacapo (Dap), the Drosophila homologue of the cyclin-dependent kinase inhibitors p21cip1/p27kip1/p57kip2. We show that dSkp2 interacts physically with Dap and has a role in targeting Dap for ubiquitination and proteasome-mediated degradation. We present evidence that dSkp2 regulates cell cycle progression by antagonizing Dap in vivo. dSkp2 knockdown reduces cell density in the wing by prolonging the cell doubling time. In addition, the wing phenotype caused by dSkp2 knockdown resembles that caused by dap overexpression and can be partially suppressed by reducing the gene dose of dap. Our study thus documents a conserved functional relationship between dSkp2 and Dap in their control of cell cycle progression, suggesting the possibility of using Drosophila as a model system to study Skp2-mediated tumorigenesis.


2013 ◽  
Vol 200 (6) ◽  
pp. 743-756 ◽  
Author(s):  
Yongxin Zou ◽  
Jun Mi ◽  
Wenxing Wang ◽  
Juanjuan Lu ◽  
Wei Zhao ◽  
...  

Cullin-RING ubiquitin ligases (CRLs) participate in the regulation of diverse cellular processes including cell cycle progression. Mutations in the X-linked CUL4B, a member of the cullin family, cause mental retardation and other developmental abnormalities in humans. Cells that are deficient in CUL4B are severely selected against in vivo in heterozygotes. Here we report a role of CUL4B in the regulation of replication licensing. Strikingly, CDC6, the licensing factor in replication, was positively regulated by CUL4B and contributed to the loading of MCM2 to chromatin. The positive regulation of CDC6 by CUL4B depends on CDK2, which phosphorylates CDC6, protecting it from APCCDH1-mediated degradation. Thus, aside being required for cell cycle reentry from quiescence, CDK2 also contributes to pre-replication complex assembly in G1 phase of cycling cells. Interestingly, the up-regulation of CDK2 by CUL4B is achieved via the repression of miR-372 and miR-373, which target CDK2. Our findings thus establish a CUL4B–CDK2–CDC6 cascade in the regulation of DNA replication licensing.


1994 ◽  
Vol 14 (5) ◽  
pp. 3022-3029 ◽  
Author(s):  
M G Goebl ◽  
L Goetsch ◽  
B Byers

The transition from G1 to S phase of the cell cycle in Saccharomyces cerevisiae requires the activity of the Ubc3 (Cdc34) ubiquitin-conjugating enzyme. S. cerevisiae cells lacking a functional UBC3 (CDC34) gene are able to execute the Start function that initiates the cell cycle but fail to form a mitotic spindle or enter S phase. The Ubc3 (Cdc34) enzyme has previously been shown to catalyze the attachment of multiple ubiquitin molecules to model substrates, suggesting that the role of this enzyme in cell cycle progression depends on its targeting an endogenous protein(s) for degradation. In this report, we demonstrate that the Ubc3 (Cdc34) protein is itself a substrate for both ubiquitination and phosphorylation. Immunochemical localization of the gene product to the nucleus renders it likely that the relevant substrates similarly reside within the nucleus.


Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 1556-1556
Author(s):  
Alisha A Mohamed-Hadley ◽  
Dan Liebermann

Abstract Abstract 1556 c-MYC, which can promote cell cycle progression, genomic instability, and block differentiation, is among the most frequently affected genes in human cancers, making this oncoprotein and its down-stream effectors attractive targets for drug discovery. MYC triggered apoptosis provides a built in failsafe program to limit unchecked cell growth when expressed in inappropriate conditions, ensuring that it is restricted to the correct environment. Tumors from cells over-expressing c-MYC often have mutations that disable the apoptotic program. The ramifications with regard to tumor etiology and progression, as well as the response of malignancies to different therapies has been tremendously enhanced by many studies involving the identification of targets involved in the MYC-triggered apoptotic response and on the flip side, identifying which apoptotic regulators are disabled in tumor cells. Many questions still remain to be answered. The biological and genetic setting appears to determine how a cell responds to altered MYC expression. The gadd45 gene family plays pivotal roles as stress sensors that modulate signaling in response to physiological and environmental stressors, also modulating susceptibility of cells for transformation in vitro and tumor development in vivo. Gadd45 behaves as either tumor suppressor or oncogene depending upon the transforming oncogene and the cell type (Tront et al., Cancer Research 66:8448-54, 2006; Tront et al., Cancer Research, in press). To elucidate the role Gadd45a plays in response to the proto-oncogene c-MYC in myeloid cells, bone marrow (BM) cells from wild type (WT) and Gadd45a null mice were retrovirally infected to constitutively express c-MYC. We observed that the response of myeloid cells to deregulated MYC expression depends on the status of the Gadd45 family of stress response genes. We showed that Gadd45a null BM expressing constitutive c-MYC exhibited less apoptosis than its WT counterpart in expansion media (IL-3, IL-6, SCF), demonstrating that Gadd45a is required for optimal MYC mediated apoptosis. We have clarified that there is no apparent enhancement of cell cycle progression; therefore, loss of gadd45a in conjunction with constitutive MYC expression results in decreased apoptosis with no effect on cell proliferation. Next we determined that the stress response Gadd45a gene functions as a tumor suppressor when MYC is deregulated in myeloid cells, via decreased expression of phospho-p38 MAPK, and the concomitant reduction of both activated phospho-PU.1 and the anti-apoptotic protein, MCL-1. MYC infected cells proliferating in GM-CSF differentiating media displayed a similar block/delay in differentiation regardless of gadd45a status. Interestingly, the percent of apoptosis was higher in the Gadd45a null cells expressing constitutive MYC as compared to the WT counterpart, which appears after cells are maintained in culture. Data is consistent with loss of Gadd45a being associated with diminished GM-CSF receptors, which can account for the increased apoptosis. Experiments will be presented to explain how Gadd45a regulates the apoptotic response, depending upon the specific cytokine. Finally, experiments are underway to assess how loss of Gadd45a in vivo can impact on MYC-mediated leukemia using in vivo mouse models and primary human AML BM. Disclosures: No relevant conflicts of interest to declare.


2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Deping Yang ◽  
Bo Yang ◽  
Yanjun Zhu ◽  
Qianlin Xia ◽  
Yan Zhang ◽  
...  

Abstract Background Recently, more and more studies have highlighted the critical regulatory roles of circular RNAs (circRNAs), a class of non-coding RNAs, in the progression of many human cancers, including prostate cancer (PCa). circRNA microarray analysis was performed to identify circRNAs that are differentially expressed in PCa tissues. Methods 104 pairs of PCa tissues and matched adjacent normal prostate tissues (at least 2 cm distal to the tumor margin) were obtained. circRNA microarray analysis was performed on four pairs of PCa tissues and matched adjacent normal prostate tissues to investigate the potential involvement of circRNAs in PCa. Flow cytometric analysis was performed to investigate whether the effect of circDPP4 on PCa cell proliferation was associated with the alteration in cell cycle progression. The role of circDPP4 in PCa tumor growth was further explored in vivo. Results We found that circDPP4 was overexpressed in PCa tissues and cell lines, and its expression was closely associated with Gleason score and clinical stage of PCa patients. In vitro loss- and gain-of-function experiments demonstrated that circDPP4 knockdown inhibited, whereas circDPP4 overexpression promoted the proliferation, migration, invasion and cell cycle progression of PCa cells. Knockdown of circDPP4 also suppressed PCa tumor growth in vivo. We further found that circDPP4 functioned as a competing endogenous RNA (ceRNA) for miR-195 in PCa cells, and miR-195 negatively regulated the expression of oncogenic cyclin D1. Rescue experiments suggested that restoration of miR-195 blocked the oncogenic role of circDPP4 in PCa cells. Conclusions Taken together, our findings revealed a novel regulatory mechanism between circDPP4 and miR-195/cyclin D1 axis, and offered novel strategies for the treatment of PCa.


Blood ◽  
2015 ◽  
Vol 126 (23) ◽  
pp. 4800-4800
Author(s):  
Chandrika S. Gowda ◽  
Chunhua Song ◽  
Yali Ding ◽  
Sunil Muthusami ◽  
Kimberly Payne ◽  
...  

Abstract IKZF1 (Ikaros) encodes a DNA-binding protein that acts as a tumor suppressor in acute lymphoblastic leukemia. Deletion of one Ikaros allele results in the development of high-risk B-cell acute lymphoblastic leukemia (B-ALL) with a high incidence of relapse and poor prognosis. The mechanisms through which Ikaros suppresses leukemogenesis and that regulate Ikaros tumor suppressor activity in leukemia are unknown. Using a systems biology approach, we determined that Ikaros regulates transcription of genes that control two pathways that are crucial in leukemia cell proliferation: 1) cell cycle progression and 2) the phosphatidylinositol 3-kinase (PI3K) pathway. Gain- and loss-of-function experiments demonstrate that Ikaros represses the transcription of genes that promote cell cycle progression and the PI3K pathway and activates transcription of a gene that suppresses the PI3K pathway. We show that in high-risk B-ALL with deletion of one Ikaros allele, the function of Ikaros as a transcriptional regulator is impaired due to reduced DNA-binding affinity for promoters of its target genes. It has been shown that Ikaros DNA-binding affinity is regulated via direct phosphorylation by pro-oncogenic Casein Kinase II (CK2). CK2 is overexpressed in high-risk B-ALL as compared to normal B-cell precursors, which further reduces Ikaros function in high-risk B-ALL. Treatment of primary high-risk B-ALL (with deletion of one Ikaros allele) using the CK2 specific inhibitor, CX-4945, restored Ikaros function as a transcriptional regulator of the genes that regulate cell cycle progression and the PI3K pathway, and was associated with cell cycle arrest and loss of phosphorylation of the AKT kinase - a downstream target of the PI3K pathway. The use of serial quantitative chromatin immunoprecipitation (qChIP) analyses spanning the promoters of Ikaros target genes demonstrated that Ikaros can repress transcription of its target genes by two different mechanisms: 1) via recruitment of histone deacetylase 1 (HDAC1), which is associated with the formation of repressive chromatin characterized by H3K27me3 and loss of H3K9ac; and 2) via an HDAC1-independent mechanism which is associated with the formation of repressive chromatin characterized by H3K9me3, along with the loss of H3K9ac. The therapeutic effect of CK2 inhibition by CX-4945 on high-risk B-ALL was demonstrated in vivo using 4 different xenografts: 3 different high-risk primary pre-B-ALL xenografts and Nalm6 xenografts. Treatment with CX-4945 showed a strong therapeutic effect in all 4 xenografts, as evidence by reduced leukemia cell number in bone marrow and in spleen, along with prolonged survival of all xenografts. Expression analysis of Ikaros target genes that regulate cell cycle progression and the PI3K pathway in leukemia cells treated in vivo with CX-4945 revealed an expression pattern that was highly similar to that observed with Ikaros overexpression. This suggests that CK2 inhibition in vivo exerts its therapeutic effect on high-risk B-ALL via restoration of Ikaros function as transcriptional regulator of genes that promote cell cycle progression and the PI3K pathway. In summary, our results reveal that: 1) Ikaros functions as a tumor suppressor by suppressing cell cycle progression and the PI3K pathway; 2) Ikaros regulates transcription by inducing two distinct epigenetic alterations at promoters of its target genes and 3) CK2 inhibition with CX-4945 restores Ikaros function as a transcriptional regulator in vivo, and has a strong therapeutic effect in primary xenografts of high-risk B-ALL. These results provide support for the use of CK2 inhibitors in clinical trials for high-risk B-ALL. Supported by the National Institutes of Health R01 HL095120, and the Four Diamonds Fund Endowment. Disclosures No relevant conflicts of interest to declare.


2020 ◽  
Vol 40 (9) ◽  
Author(s):  
Ritu Chaudhary ◽  
Bruna R. Muys ◽  
Ioannis Grammatikakis ◽  
Supriyo De ◽  
Kotb Abdelmohsen ◽  
...  

ABSTRACT Circular RNAs (circRNAs) are a class of noncoding RNAs produced by a noncanonical form of alternative splicing called back-splicing. To investigate a potential role of circRNAs in the p53 pathway, we analyzed RNA sequencing (RNA-seq) data from colorectal cancer cell lines (HCT116, RKO, and SW48) that were untreated or treated with a DNA-damaging agent. Surprisingly, unlike the strong p53-dependent induction of hundreds of p53-induced mRNAs upon DNA damage, only a few circRNAs were upregulated from p53-induced genes. circ-MDM2, an annotated circRNA from the MDM2 locus, was one of the handful of circRNAs that originated from a p53-induced gene. Given the central role of MDM2 in suppressing p53 protein levels and p53 activity, we investigated the function of circ-MDM2. Knocking down circ-MDM2 with small interfering RNAs (siRNAs) that targeted circ-MDM2 did not alter MDM2 mRNA or MDM2 protein levels but resulted in increased basal p53 levels and growth defects in vitro and in vivo. Consistent with these results, transcriptome profiling showed increased expression of several direct p53 targets, reduced retinoblastoma protein (Rb) phosphorylation, and defects in G1-S progression upon silencing circ-MDM2. Our results on the initial characterization of circ-MDM2 identify a new player from the MDM2 locus that suppresses p53 levels and cell cycle progression.


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