p57(Kip2) and cancer: time for a critical appraisal

Lappaol F regulates the cell cycle by activating CDKN1C/p57 in human colorectal cancer cells

CONTEXT

Lappaol F (LAF), a natural lignan from Arctium lappa Linné (Asteraceae), inhibits tumor cell growth in vitro and in vivo. The underlying mechanism involves the suppression of the Yes-associated protein. However, the specific role of LAF in cell cycle regulation remains unknown.

OBJECTIVE

This study determined the molecular mechanism by which LAF regulates cell cycle progression.

MATERIALS AND METHODS

Various colon cancer cell lines (SW480, HCT15, and HCT116) were treated with LAF (25, 50, and 75 μmol/L) for 48 h. The effects of LAF on cell proliferation and cell cycle were determined using sulforhodamine B and flow cytometry assays. Differentially expressed proteins (DEPs) were identified using quantitative proteomics. Bioinformatic analysis of DEPs was conducted via Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses. Expression levels of DEPs in the cell cycle pathway were analyzed using RT-qPCR and western blotting.

RESULTS

LAF suppressed the proliferation of SW480, HCT15, and HCT116 cells (IC₅₀ 47.1, 51.4, and 32.8 μmol/L, respectively) and induced cell cycle arrest at the S phase. A total of 6331 proteins were identified and quantified, of which 127 were differentially expressed between the LAF-treated and untreated groups. GO and KEGG enrichment analyses revealed that DEPs mainly participated in the cell cycle. CDKN1C/p57 showed the most significant differential expression, with the highest fold-change (3.155-fold). Knockdown of CDKN1C/p57 attenuated the S phase cell cycle arrest and proliferation inhibition induced by LAF.

CONCLUSION

LAF exerts antitumor effects via S phase arrest by activating CDKN1C/p57 in colorectal cancer cells.

The significance of CDT1 expression in non-cancerous and cancerous liver in cases with hepatocellular carcinoma

We previously reported that chromatin licensing and DNA replication factor 1 (CDT1) expression was associated with the extent of proliferation of atypical hepatocytes and the time to postoperative recurrence in cases of hepatocellular carcinoma (HCC). This study aimed to clarify the clinical significance or pathogenesis of CDT1 expression in both non-cancerous and cancerous liver in HCC cases, including previously published data. We investigated the association between the expression of CDT1 in non-cancerous or cancerous liver tissues and histologic findings or biochemical examination results in 62 cases. We also examined the dual localization between CDT1 and FbxW7, P57kip2, P53 and c-Myc by confocal laser scanning microscopy. CDT1 mRNA expression was significantly higher in cancerous liver than in non-cancerous liver (p<0.0001). Elevated CDT1 mRNA expression indicates a significantly degree of inflammatory cell infiltration within lobules, along with elevated serum transaminase levels, and hepatic spare decline. CDT1 mRNA was highly expressed in a group of poorly differentiated cancer cells. CDT1 co-localized with P57kip2, Fbwx7, P53 and c-Myc in the nucleus or cytoplasm of hepatocytes and cancer cells. We found that CDT1 mRNA expression could represent the degree of hepatic spare ability and the high carcinogenic state.

Promoter methylation and enhanced SKP2 are associated with the downregulation of CDKN1C in cervical squamous cell carcinoma

PURPOSE

Cervical Squamous Cell Carcinoma (CSCC) is one of the significant causes of cancer deaths among women. Distinct genetic and epigenetic-altered loci, including chromosomal 11p15.5-15.4, have been identified. CDKN1C (Cyclin-Dependent Kinase Inhibitor 1C, p57KIP2), a member of the CIP/KIP family of cyclin-dependent kinase inhibitors (CDKIs), located at 11p15.4, is a putative tumor suppressor. Apart from transcriptional control, S-Phase Kinase Associated Protein 2 (SKP2), an oncogenic E3 ubiquitin ligase, regulates the protein turnover of CDKN1C. But the molecular status of CDKN1C in CSCC and the underlying mechanistic underpinnings have yet to be explored.

METHODS

TCGA and other publicly available datasets were analyzed to evaluate the expression of CDKN1C and SKP2. The expression (transcript/protein) was validated in independent CSCC tumors (n = 155). Copy number alteration and promoter methylation were correlated with the expression. Finally, in vitro functional validation was performed.

RESULTS

CDKN1C was down-regulated, and SKP2 was up-regulated at the transcript and protein levels in CSCC tumors and the SiHa cell line. Notably, promoter methylation (50%) was associated with the downregulation of the CDKN1C transcript. However, high expression of SKP2 was found to be associated with the decreased expression of CDKN1C protein. Independent treatments with 5-aza-dC, MG132, and SKP2i (SKPin C1) in SiHa cells led to an enhanced expression of CDKN1C protein, validating the mechanism of down-regulation in CSCC.

CONCLUSION

Collectively, CDKN1C was down-regulated due to the synergistic effect of promoter hyper-methylation and SKP2 over-expression in CSCC tumors, paving the way for further studies of its role in the pathogenesis of the disease.

p57Kip2 acts as a transcriptional corepressor to regulate intestinal stem cell fate and proliferation

p57Kip2 is a cyclin/CDK inhibitor and a negative regulator of cell proliferation. Here, we report that p57 regulates intestinal stem cell (ISC) fate and proliferation in a CDK-independent manner during intestinal development. In the absence of p57, intestinal crypts exhibit an increased proliferation and an amplification of transit-amplifying cells and of Hopx+ ISCs, which are no longer quiescent, while Lgr5+ ISCs are unaffected. RNA sequencing (RNA-seq) analyses of Hopx+ ISCs show major gene expression changes in the absence of p57. We found that p57 binds to and inhibits the activity of Ascl2, a transcription factor critical for ISC specification and maintenance, by participating in the recruitment of a corepressor complex to Ascl2 target gene promoters. Thus, our data suggest that, during intestinal development, p57 plays a key role in maintaining Hopx+ ISC quiescence and repressing the ISC phenotype outside of the crypt bottom by inhibiting the transcription factor Ascl2 in a CDK-independent manner.

Glucocorticoid mediated inhibition of LKB1 mutant non-small cell lung cancers

The glucocorticoid receptor (GR) is an important anti-cancer target in lymphoid cancers but has been understudied in solid tumors like lung cancer, although glucocorticoids are often given with chemotherapy regimens to mitigate side effects. Here, we identify a dexamethasone-GR mediated anti-cancer response in a subset of aggressive non-small cell lung cancers (NSCLCs) that harbor Serine/Threonine Kinase 11 (STK11/LKB1) mutations. High tumor expression of carbamoyl phosphate synthase 1 (CPS1) was strongly linked to the presence of LKB1 mutations, was the best predictor of NSCLC dexamethasone (DEX) sensitivity (p < 10-16) but was not mechanistically involved in DEX sensitivity. Subcutaneous, orthotopic and metastatic NSCLC xenografts, biomarker-selected, STK11/LKB1 mutant patient derived xenografts, and genetically engineered mouse models with KRAS/LKB1 mutant lung adenocarcinomas all showed marked in vivo anti-tumor responses with the glucocorticoid dexamethasone as a single agent or in combination with cisplatin. Mechanistically, GR activation triggers G1/S cell cycle arrest in LKB1 mutant NSCLCs by inducing the expression of the cyclin-dependent kinase inhibitor, CDKN1C/p57(Kip2). All findings were confirmed with functional genomic experiments including CRISPR knockouts and exogenous expression. Importantly, DEX-GR mediated cell cycle arrest did not interfere with NSCLC radiotherapy, or platinum response in vitro or with platinum response in vivo. While DEX induced LKB1 mutant NSCLCs in vitro exhibit markers of cellular senescence and demonstrate impaired migration, in vivo DEX treatment of a patient derived xenograft (PDX) STK11/LKB1 mutant model resulted in expression of apoptosis markers. These findings identify a previously unknown GR mediated therapeutic vulnerability in STK11/LKB1 mutant NSCLCs caused by induction of p57(Kip2) expression with both STK11 mutation and high expression of CPS1 as precision medicine biomarkers of this vulnerability.

p57Kip2 is an essential regulator of vitamin D receptor-dependent mechanisms

A cyclin-dependent kinase (CDK) inhibitor, p57Kip2, is an important molecule involved in bone development; p57Kip2-deficient (p57-/-) mice display neonatal lethality resulting from abnormal bone formation and cleft palate. The modulator 1α,25-dihydroxyvitamin D3 (l,25-(OH)2VD3) has shown the potential to suppress the proliferation and induce the differentiation of normal and tumor cells. The current study assessed the role of p57Kip2 in the 1,25-(OH)2VD3-regulated differentiation of osteoblasts because p57Kip2 is associated with the vitamin D receptor (VDR). Additionally, 1,25-(OH)2VD3 treatment increased p57KIP2 expression and induced the colocalization of p57KIP2 with VDR in the osteoblast nucleus. Primary p57-/- osteoblasts exhibited higher proliferation rates with Cdk activation than p57+/+ cells. A lower level of nodule mineralization was observed in p57-/- osteoblasts than in p57+/+ cells. In p57+/+ osteoblasts, 1,25-(OH)2VD3 upregulated the p57Kip2 and opn mRNA expression levels, while the opn expression levels were significantly decreased in p57-/- cells. The osteoclastogenesis assay performed using bone marrow cocultured with 1,25-(OH)2VD3-treated osteoblasts revealed a decreased efficiency of 1,25-(OH)2VD3-stimulated osteoclastogenesis in p57-/- cells. Based on these results, p57Kip2 might function as a mediator of 1,25-(OH)2VD3 signaling, thereby enabling sufficient VDR activation for osteoblast maturation.

Fbxo22 promotes cervical cancer progression via targeting p57Kip2 for ubiquitination and degradation

F-box only protein 22 (FBXO22) is a key subunit of the Skp1-Cullin 1-F-box protein (SCF) E3 ubiquitin ligase complex. Little is known regarding its biological function and underlying molecular mechanisms in regulating cervical cancer (CC) progression. In this study, we aim to explore the role and mechanism of FBXO22 in CC progression. The correlation between FBXO22 and clinicopathological characteristics of CC was analyzed by tissue microarray. MTT, colony formation, flow cytometry, Western blotting, qRT-PCR, protein half-life, co-immunoprecipitation, ubiquitination, and xenograft experiments were performed to assess the functions of FBXO22 and potential molecular mechanisms of FBXO22-mediated malignant progression in CC. The expression of FBXO22 protein in CC tissues was higher than that in adjacent non-tumor cervical tissues. Notably, high expression of FBXO22 was significantly associated with high histology grades, positive lymph node metastasis, and poor outcomes in CC patients. Functionally, ectopic expression of FBXO22 promoted cell viability in vitro and induced tumor growth in vivo, while knockdown of FBXO22 exhibited opposite effects. In addition, overexpression of FBXO22 promoted G1/S phase progression and inhibited apoptosis in CC cells. Mechanistically, FBXO22 physically interacted with the cyclin-dependent kinase inhibitor p57Kip2 and subsequently mediated its ubiquitination and proteasomal degradation leading to tumor progression. FBXO22 protein level was found negatively associated with p57Kip2 protein levels in patient CC samples. FBXO22 promotes CC progression partly through regulating the ubiquitination and proteasomal degradation of p57Kip2. Our study indicates that FBXO22 might be a novel prognostic biomarker and therapeutic target for CC.

Cyclin-dependent kinase inhibitors in malignant hematopoiesis

The cell-cycle is a tightly orchestrated process where sequential steps guarantee cellular growth linked to a correct DNA replication. The entire cell division is controlled by cyclin-dependent kinases (CDKs). CDK activation is balanced by the activating cyclins and CDK inhibitors whose correct expression, accumulation and degradation schedule the time-flow through the cell cycle phases. Dysregulation of the cell cycle regulatory proteins causes the loss of a controlled cell division and is inevitably linked to neoplastic transformation. Due to their function as cell-cycle brakes, CDK inhibitors are considered as tumor suppressors. The CDK inhibitors p16^INK4a and p15^INK4b are among the most frequently altered genes in cancer, including hematopoietic malignancies. Aberrant cell cycle regulation in hematopoietic stem cells (HSCs) bears severe consequences on hematopoiesis and provokes hematological disorders with a broad array of symptoms. In this review, we focus on the importance and prevalence of deregulated CDK inhibitors in hematological malignancies.

From cyclins to CDKIs: Cell cycle regulation of skeletal muscle stem cell quiescence and activation

After extensive proliferation during development, the adult skeletal muscle cells remain outside the cell cycle, either as post-mitotic myofibers or as quiescent muscle stem cells (MuSCs). Despite its terminally differentiated state, adult skeletal muscle has a remarkable regeneration potential, driven by MuSCs. Upon injury, MuSC quiescence is reversed to support tissue growth and repair and it is re-established after the completion of muscle regeneration. The distinct cell cycle states and transitions observed in the different myogenic populations are orchestrated by elements of the cell cycle machinery. This consists of i) complexes of cyclins and Cyclin-Dependent Kinases (CDKs) that ensure cell cycle progression and ii) their negative regulators, the Cyclin-Dependent Kinase Inhibitors (CDKIs). In this review we discuss the roles of these factors in developmental and adult myogenesis, with a focus on CDKIs that have emerging roles in stem cell functions.

Anti-cancer function of microRNA-30e is mediated by negative regulation of HELLPAR, a noncoding macroRNA, and genes involved in ubiquitination and cell cycle progression in prostate cancer

Prostate cancer (PCa) progression relies on androgen receptor (AR) function, making AR a top candidate for PCa therapy. However, development of drug resistance is common, which eventually leads to development of castration‐resistant PCa. This warrants a better understanding of the pathophysiology of PCa that facilitates the aberrant activation of key signaling pathways including AR. MicroRNAs (miRNAs) function as regulators of cancer progression as they modulate various cellular processes. Here, we demonstrate a multidimensional function of miR‐30e through the regulation of genes involved in various signaling pathways. We noted loss of miR‐30e expression in prostate tumors, which, when restored, led to cell cycle arrest, induction of apoptosis, improved drug sensitivity of PCa cells and reduced tumor progression in xenograft models. We show that experimental upregulation of miR‐30e reduces expression of mRNAs including AR, FBXO45, SRSF7 and MYBL2 and a novel long noncoding RNA (lncRNA) HELLPAR, which are involved in cell cycle, apoptosis and ubiquitination, and the effects could be rescued by inhibition of miR‐30e expression. RNA immunoprecipitation analysis confirmed direct interactions between miR‐30e and its RNA targets. We noted a newly identified reciprocal relationship between miR‐30e and HELLPAR, as inhibition of HELLPAR improved stabilization of miR‐30e. Transcriptome profiling and quantitative real‐time PCR (qRT‐PCR) validation of miR‐30e‐expressing PCa cells showed differential expression of genes involved in cell cycle progression, apoptosis and ubiquitination, which supports our in vitro study. This study demonstrates an integrated function of miR‐30e on dysregulation of miRNA/lncRNA/mRNA axes that may have diagnostic and therapeutic significance in aggressive PCa.

Molecular Mechanism of Curcumin and Its Analogs as Multifunctional Compounds against Pancreatic Cancer

Pancreatic cancer (PC) is one of the most common malignant tumors with a poor prognosis and high mortality. Surgical resection is the most effective treatment for PC; however, only a minority of patients have resectable tumors. Chemotherapy is the primary treatment for PC. Curcumin is a natural chemical substance obtained from plants with a wide range of pharmacological activities. Research evidence suggests that curcumin can influence PC development through multiple molecular mechanisms. The synthesis of novel curcumin analogs and preparation of curcumin nano-formulations are effective strategies to overcome the low bioavailability of curcumin in the treatment of PC. This review aims to summarize the mechanisms of action of curcumin in preclinical and clinical studies on PC and research progress in enhancing its bioavailability.

Effects of tobacco compound 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) on the expression of epigenetically regulated genes in lung carcinogenesis

Cigarette smoking is a major cause of lung cancer. Although tobacco smoking-induced genotoxicity has been well established, there is apparent lack of abundance functional epigenetic effects reported On cigarette smoke-induced lung carcinogenesis. The aim of this study was to determine effects of intratracheal administration of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) utilizing target gene expression DNA methylation patterns in lung tissues of mice following twice weekly for 8 weeks treatment. An unbiased approach where genomic regions was undertaken to assess early methylation changes within mouse pulmonary tissues. A methylated-CpG island recovery assay (MIRA) was performed to map the DNA methylome in lung tissues, with the position of methylated DNA determined using a Genome Analyzer (MIRA-SEQ). Alterations in epigenetic-regulated target genes were confirmed with quantitative reverse transcription-PCR, which revealed 35 differentially hypermethylated genes including Cdkn1C, Hsf4, Hnf1a, Cdx1, and Hoxa5 and 30 differentially hypomethylated genes including Ddx4, Piwi1, Mdm2, and Pce1 in NNK-exposed lung tissue compared with controls. The main pathway of these genes for mediating biological information was analyzed using the Kyoto Encyclopedia of Genes and Genomes database. Among them, Rssf1 and Mdm2 were closely associated with NNK-induced lung carcinogenesis. Taken together, our data provide valuable resources for detecting cigarette smoke-induced lung carcinogenesis.

The FOXM1/RNF26/p57 axis regulates the cell cycle to promote the aggressiveness of bladder cancer

Bladder cancer is one of the most lethal cancers in the world. Despite the continuous development of medical technologies and therapeutic strategies, the overall survival rate of bladder cancer has not changed significantly. Targeted therapy is a new promising method for bladder cancer treatment. Thus, an in-depth study of the molecular mechanism of the occurrence and development of bladder cancer is urgently needed to identify novel therapeutic candidates for bladder cancer. Here, bioinformatics analysis demonstrated that RNF26 was one of the risk factors for bladder cancer. Then, we showed that RNF26 is abnormally upregulated in bladder cancer cells and tissues and that higher RNF26 expression is an unfavorable prognostic factor for bladder cancer. Moreover, we found that RNF26 promotes bladder cancer progression. In addition, we showed that RNF26 expression is promoted by FOXM1 at the transcriptional level through MuvB complex. The upregulated RNF26 in turn degrades p57 (CDKN1C) to regulate the cell cycle process. Collectively, we uncovered a novel FOXM1/RNF26/p57 axis that modulates the cell cycle process and enhances the progression of bladder cancer. Thus, the FOXM1/RNF26/p57 signaling axis could be a candidate target for the treatment of bladder cancer.

CDKN1C as a prognostic biomarker correlated with immune infiltrates and therapeutic responses in breast cancer patients

Breast cancer (BC) prognosis and therapeutic sensitivity could not be predicted efficiently. Previous evidence have shown the vital roles of CDKN1C in BC. Therefore, we aimed to construct a CDKN1C‐based model to accurately predicting overall survival (OS) and treatment responses in BC patients. In this study, 995 BC patients from The Cancer Genome Atlas database were selected. Kaplan‐Meier curve, Gene set enrichment and immune infiltrates analyses were executed. We developed a novel CDKN1C‐based nomogram to predict the OS, verified by the time‐dependent receiver operating characteristic curve, calibration curve and decision curve. Therapeutic response prediction was followed based on the low‐ and high‐nomogram score groups. Our results indicated that low‐CDKN1C expression was associated with shorter OS and lower proportion of naïve B cells, CD8 T cells, activated NK cells. The predictive accuracy of the nomogram for 5‐year OS was superior to the tumour‐node‐metastasis stage (area under the curve: 0.746 vs. 0.634, p < 0.001). The nomogram exhibited excellent predictive performance, calibration ability and clinical utility. Moreover, low‐risk patients were identified with stronger sensitivity to therapeutic agents. This tool can improve BC prognosis and therapeutic responses prediction, thus guiding individualized treatment decisions.

A Beckwith-Wiedemann-Associated CDKN1C Mutation Allows the Identification of a Novel Nuclear Localization Signal in Human p57Kip2

p57^Kip2 protein is a member of the CIP/Kip family, mainly localized in the nucleus where it exerts its Cyclin/CDKs inhibitory function. In addition, the protein plays key roles in embryogenesis, differentiation, and carcinogenesis depending on its cellular localization and interactors. Mutations of CDKN1C, the gene encoding human p57^Kip2, result in the development of different genetic diseases, including Beckwith–Wiedemann, IMAGe and Silver–Russell syndromes. We investigated a specific Beckwith–Wiedemann associated CDKN1C change (c.946 C>T) that results in the substitution of the C-terminal amino acid (arginine 316) with a tryptophan (R316W-p57^Kip2). We found a clear redistribution of R316W-p57^Kip2, in that while the wild-type p57^Kip2 mostly occurs in the nucleus, the mutant form is also distributed in the cytoplasm. Transfection of two expression constructs encoding the p57^Kip2 N- and C-terminal domain, respectively, allows the mapping of the nuclear localization signal(s) (NLSs) between residues 220–316. Moreover, by removing the basic RKRLR sequence at the protein C-terminus (from 312 to 316 residue), p57^Kip2 was confined in the cytosol, implying that this sequence is absolutely required for nuclear entry. In conclusion, we identified an unreported p57^Kip2 NLS and suggest that its absence or mutation might be of relevance in CDKN1C-associated human diseases determining significant changes of p57^Kip2 localization/regulatory roles.

miR-92b-3p Regulates Cell Cycle and Apoptosis by Targeting CDKN1C, Thereby Affecting the Sensitivity of Colorectal Cancer Cells to Chemotherapeutic Drugs

Simple Summary

Multidrug resistance (MDR) limits the effectiveness of colorectal cancer (CRC) treatment and miRNAs play an important role in drug resistance. To search for miRNA targets that may be involved in the CRC MDR phenotype, this study used small RNAomic screens to analyze the expression profiles of miRNAs in CRC HCT8 cell line and its chemoresistant counterpart HCT8/T cell line. It was found that miR-92b-3p was highly expressed in HCT8/T cells and chemotherapeutic drugs could stimulate CRC cells to up-regulate miR-92b-3p expression and conferred cellular resistance to chemotherapeutic drugs. This study revealed a new mechanism of MDR in CRC, elucidating for the first time the direct link between miR-92b-3p/CDKN1C and chemoresistance. In summary, this study suggested that miR-92b-3p could be used as a potential therapeutic target for reversing MDR in chemotherapy and as a candidate biomarker for predicting the efficacy of chemotherapy.

Abstract

Colorectal cancer (CRC) is the third most common malignant tumor in the world and the second leading cause of cancer death. Multidrug resistance (MDR) has become a major obstacle in the clinical treatment of CRC. The clear molecular mechanism of MDR is complex, and miRNAs play an important role in drug resistance. This study used small RNAomic screens to analyze the expression profiles of miRNAs in CRC HCT8 cell line and its chemoresistant counterpart HCT8/T cell line. It was found that miR-92b-3p was highly expressed in HCT8/T cells. Knockdown of miR-92b-3p reversed the resistance of MDR HCT8/T cells to chemotherapeutic drugs in vitro and in vivo. Paclitaxel (PTX, a chemotherapy medication) could stimulate CRC cells to up-regulate miR-92b-3p expression and conferred cellular resistance to chemotherapeutic drugs. In studies on downstream molecules, results suggested that miR-92b-3p directly targeted Cyclin Dependent Kinase Inhibitor 1C (CDKN1C, which encodes a cell cycle inhibitor p57Kip2) to inhibit its expression and regulate the sensitivity of CRC cells to chemotherapeutic drugs. Mechanism study revealed that the miR-92b-3p/CDKN1C axis exerted a regulatory effect on the sensitivity of CRC cells via the regulation of cell cycle and apoptosis. In conclusion, these findings showed that miR-92b-3p/CDKN1C was an important regulator in the development of drug resistance in CRC cells, suggesting its potential application in drug resistance prediction and treatment.

Establishment and Characterization of a Cell Line (S-RMS1) Derived from an Infantile Spindle Cell Rhabdomyosarcoma with SRF-NCOA2 Fusion Transcript

Background: Spindle cell rhabdomyosarcoma (S-RMS) is a rare tumor that was previously considered as an uncommon variant of embryonal RMS (ERMS) and recently reclassified as a distinct RMS subtype with NCOA2, NCOA1, and VGLL2 fusion genes. In this study, we established a cell line (S-RMS1) derived from a four-month-old boy with infantile spindle cell RMS harboring SRF-NCOA2 gene fusion. Methods: Morphological and molecular characteristics of S-RMS1 were analyzed and compared with two RMS cell lines, RH30 and RD18. Whole genome sequencing of S-RMS1 and clinical exome sequencing of genomic DNA were performed. Results: S-RMS1 showed cells small in size, with a fibroblast-like morphology and positivity for MyoD-1, myogenin, desmin, and smooth muscle actin. The population doubling time was 3.7 days. Whole genome sequencing demonstrated that S-RMS1 retained the same genetic profile of the tumor at diagnosis. A Western blot analysis showed downregulation of AKT-p and YAP-p while RT-qPCR showed upregulation of endoglin and GATA6 as well as downregulation of TGFßR1 and Mef2C transcripts. Conclusion: This is the first report of the establishment of a cell line from an infantile spindle cell RMS with SRF-NCOA2 gene fusion. S-RMS1 should represent a useful tool for the molecular characterization of this rare and almost unknown tumor.

Cyclin-dependent kinase inhibitors (CDKIs) and the DNA damage response: The link between signaling pathways and cancer

At the cellular level, DNA repair mechanisms are crucial in maintaining both genomic integrity and stability. DNA damage appears to be a central culprit in tumor onset and progression. Cyclin-dependent kinases (CDKs) and their regulatory partners coordinate the cell cycle progression. Aberrant CDK activity has been linked to a variety of cancers through deregulation of cell-cycle control. Besides DNA damaging agents and chromosome instability (CIN), disruptions in the levels of cell cycle regulators including cyclin-dependent kinase inhibitors (CDKIs) would result in unscheduled proliferation and cell division. The INK4 and Cip/Kip (CDK interacting protein/kinase inhibitor protein) family of CDKI proteins are involved in cell cycle regulation, transcription regulation, apoptosis, and cell migration. A thorough understanding of how these CDKIs regulate the DNA damage response through multiple signaling pathways may provide an opportunity to design efficient treatment strategies to inhibit carcinogenesis.

Functional Versatility of the CDK Inhibitor p57Kip2

The cyclin/CDK inhibitor p57^Kip2 belongs to the Cip/Kip family, with p21^Cip1 and p27^Kip1, and is the least studied member of the family. Unlike the other family members, p57^Kip2 has a unique role during embryogenesis and is the only CDK inhibitor required for embryonic development. p57^Kip2 is encoded by the imprinted gene CDKN1C, which is the gene most frequently silenced or mutated in the genetic disorder Beckwith-Wiedemann syndrome (BWS), characterized by multiple developmental anomalies. Although initially identified as a cell cycle inhibitor based on its homology to other Cip/Kip family proteins, multiple novel functions have been ascribed to p57^Kip2 in recent years that participate in the control of various cellular processes, including apoptosis, migration and transcription. Here, we will review our current knowledge on p57^Kip2 structure, regulation, and its diverse functions during development and homeostasis, as well as its potential implication in the development of various pathologies, including cancer.

Regulation of p27Kip1 and p57Kip2 Functions by Natural Polyphenols

In numerous instances, the fate of a single cell not only represents its peculiar outcome but also contributes to the overall status of an organism. In turn, the cell division cycle and its control strongly influence cell destiny, playing a critical role in targeting it towards a specific phenotype. Several factors participate in the control of growth, and among them, p27^Kip1 and p57^Kip2, two proteins modulating various transitions of the cell cycle, appear to play key functions. In this review, the major features of p27 and p57 will be described, focusing, in particular, on their recently identified roles not directly correlated with cell cycle modulation. Then, their possible roles as molecular effectors of polyphenols’ activities will be discussed. Polyphenols represent a large family of natural bioactive molecules that have been demonstrated to exhibit promising protective activities against several human diseases. Their use has also been proposed in association with classical therapies for improving their clinical effects and for diminishing their negative side activities. The importance of p27^Kip1 and p57^Kip2 in polyphenols’ cellular effects will be discussed with the aim of identifying novel therapeutic strategies for the treatment of important human diseases, such as cancers, characterized by an altered control of growth.

High Dosage Lithium Treatment Induces DNA Damage and p57Kip2 Decrease

Lithium salt is the first-line therapeutic option for bipolar disorder and has been proposed as a potential antitumoral drug. The effects of LiCl treatment were investigated in SH-SY5Y, a human neuroblastoma cell line and an in vitro model of dopaminergic neuronal differentiation. LiCl, at the dosage used in psychiatric treatment, does not affect cell proliferation, while at higher doses it delays the SH-SY5Y cell division cycle and for prolonged usage reduces cell viability. Moreover, the ion treatment affects DNA integrity as demonstrated by accumulation of p53 and γH2AX (the phosphorylated form of H2AX histone), two important markers of genome damage. p57^Kip2, a CIP/Kip protein, is required for proper neuronal maturation and represents a main factor of response to stress including genotoxicity. We evaluated the effect of lithium on p57^Kip2 levels. Unexpectedly, we found that lithium downregulates the level of p57^Kip2 in a dose-dependent manner, mainly acting at the transcriptional level. A number of different approaches, mostly based on p57^Kip2 content handling, confirmed that the CKI/Kip reduction plays a key role in the DNA damage activated by lithium and suggests the unanticipated view that p57^Kip2 might be involved in DNA double-strand break responses. In conclusion, our study identified novel roles for p57^Kip2 in the molecular mechanism of lithium at high concentration and, more in general, in the process of DNA repair.

Aberrant DNA methylation of Cyclind-CDK4-p21 is associated with chronic fluoride poisoning

Endemic fluorosis is a serious problem in public health, affecting thousands of people. Abnormal proliferation and activation of osteoblasts in skeletal fluorosis lesions play a leading role and osteoblast proliferation is finely regulated by the cell cycle. There are a few reports on fluoride-induced DNA methylation. However, the role of DNA methylation of the cyclin/cyclin-dependent kinase (CDK)/cyclin-dependent kinase inhibitor (CKI) regulatory network in skeletal fluorosis has not been investigated. We used a population study and in vitro experiment to explore the relationship between the pathogenesis of skeletal fluorosis and methylation of Cyclin d1/CDK4/p21. The results showed a positive relationship between fluoride exposure and expression of Cyclin d1/CDK4, and a negative relationship between fluoride exposure and expression of P21. Hypermethylation of p21 was found in the fluoride-exposed population, and low expression of p21 attributed to promoter hypermethylation was confirmed in vitro. However, no changes in methylation levels of Cyclin d1 and CDK4 genes were observed in the population exposed to fluoride and NaF-treated osteoblasts. These results show that methylation of p21 gene has a significant impact on the proliferation of osteoblasts during the development of skeletal fluorosis. The present study was a first attempt to link the methylation of the Cyclin d1/CDK4/p21 regulatory network with osteoblast proliferation in skeletal fluorosis.

Roles of p53 Family Structure and Function in Non-Canonical Response Element Binding and Activation

The p53 canonical consensus sequence is a 10-bp repeat of PuPuPuC(A/T)(A/T)GPyPyPy, separated by a spacer with up to 13 bases. C(A/T)(A/T)G is the core sequence and purine (Pu) and pyrimidine (Py) bases comprise the flanking sequence. However, in the p53 noncanonical sequences, there are many variations, such as length of consensus sequence, variance of core sequence or flanking sequence, and variance in number of bases making up the spacer or AT gap composition. In comparison to p53, the p53 family members p63 and p73 have been found to have more tolerance to bind and activate several of these noncanonical sequences. The p53 protein forms monomers, dimers, and tetramers, and its nonspecific binding domain is well-defined; however, those for p63 or p73 are still not fully understood. Study of p63 and p73 structure to determine the monomers, dimers or tetramers to bind and regulate noncanonical sequence is a new challenge which is crucial to obtaining a complete picture of structure and function in order to understand how p63 and p73 regulate genes differently from p53. In this review, we will summarize the rules of p53 family non-canonical sequences, especially focusing on the structure of p53 family members in the regulation of specific target genes. In addition, we will compare different software programs for prediction of p53 family responsive elements containing parameters with canonical or non-canonical sequences.

CDYL promotes the chemoresistance of small cell lung cancer by regulating H3K27 trimethylation at the CDKN1C promoter

Rationale: Chemoresistance frequently occurs in patients with small cell lung cancer (SCLC) and leads to a dismal prognosis. However, the mechanisms underlying this process remain largely unclear.

Methods: The effects of chromodomain Y-like (CDYL) on chemoresistance in SCLC were determined using Western blotting, immunohistochemistry, cell counting kit-8 assays, flow cytometry, and tumorigenicity experiments, and the underlying mechanisms were investigated using mRNA sequencing, chromatin immunoprecipitation-qPCR, electrophoretic mobility shift assays, co-immunoprecipitation, GST pull down assays, bisulfite sequencing PCR, ELISA, and bioinformatics analyses.

Results: CDYL is expressed at high levels in chemoresistant SCLC tissues from patients, and elevated CDYL levels correlate with an advanced clinical stage and a poor prognosis. Furthermore, CDYL expression is significantly upregulated in chemoresistant SCLC cells. Using gain- and loss-of-function methods, we show that CDYL promotes chemoresistance in SCLC in vitro and in vivo. Mechanistically, CDYL promotes SCLC chemoresistance by silencing its downstream mediator cyclin-dependent kinase inhibitor 1C (CDKN1C). Further mechanistic investigations showed that CDYL recruits the enhancer of zeste homolog 2 (EZH2) to regulate trimethylation of lysine 27 in histone 3 (H3K27me3) at the CDKN1C promoter region and promotes transcriptional silencing. Accordingly, the EZH2 inhibitor GSK126 de-represses CDKN1C and decreases CDYL-induced chemoresistance in SCLC.

Principal conclusions: Based on these results, the CDYL/EZH2/CDKN1C axis promotes chemoresistance in SCLC, and these markers represent promising therapeutic targets for overcoming chemoresistance in patients with SCLC.

Effects of Intestinal Microbial⁻Elaborated Butyrate on Oncogenic Signaling Pathways

The intestinal microbiota is well known to have multiple benefits on human health, including cancer prevention and treatment. The effects are partially mediated by microbiota-produced short chain fatty acids (SCFAs) such as butyrate, propionate and acetate. The anti-cancer effect of butyrate has been demonstrated in cancer cell cultures and animal models of cancer. Butyrate, as a signaling molecule, has effects on multiple signaling pathways. The most studied effect is its inhibition on histone deacetylase (HDAC), which leads to alterations of several important oncogenic signaling pathways such as JAK2/STAT3, VEGF. Butyrate can interfere with both mitochondrial apoptotic and extrinsic apoptotic pathways. In addition, butyrate also reduces gut inflammation by promoting T-regulatory cell differentiation with decreased activities of the NF-κB and STAT3 pathways. Through PKC and Wnt pathways, butyrate increases cancer cell differentiation. Furthermore, butyrate regulates oncogenic signaling molecules through microRNAs and methylation. Therefore, butyrate has the potential to be incorporated into cancer prevention and treatment regimens. In this review we summarize recent progress in butyrate research and discuss the future development of butyrate as an anti-cancer agent with emphasis on its effects on oncogenic signaling pathways. The low bioavailability of butyrate is a problem, which precludes clinical application. The disadvantage of butyrate for medicinal applications may be overcome by several approaches including nano-delivery, analogue development and combination use with other anti-cancer agents or phytochemicals.

The long non-coding RNA Kcnq1ot1 controls maternal p57 expression in muscle cells by promoting H3K27me3 accumulation to an intragenic MyoD-binding region

BACKGROUND

The cell-cycle inhibitor p57^kip2 plays a critical role in mammalian development by coordinating cell proliferation and differentiation in many cell types. p57^kip2 expression is finely regulated by several epigenetic mechanisms, including paternal imprinting. Kcnq1ot1, a long non-coding RNA (LncRNA), whose gene maps to the p57^Kip2 imprinting domain, is expressed exclusively from the paternal allele and participates in the cis-silencing of the neighboring imprinted genes through chromatin-level regulation. In light of our previous evidence of a functional interaction between myogenic factors and imprinting control elements in the regulation of the maternal p57^Kip2 allele during muscle differentiation, we examined the possibility that also Kcnq1ot1 could play an imprinting-independent role in the control of p57^Kip2 expression in muscle cells.

RESULTS

We found that Kcnq1ot1 depletion by siRNA causes the upregulation of the maternal and functional p57^Kip2 allele during differentiation, suggesting a previously undisclosed role for this LncRNA. Consistently, Chromatin Oligo-affinity Precipitation assays showed that Kcnq1ot1 physically interacts not only with the paternal imprinting control region of the locus, as already known, but also with both maternal and paternal alleles of a novel p57^Kip2 regulatory region, located intragenically and containing two binding sites for the muscle-specific factor MyoD. Moreover, chromatin immunoprecipitation assays after Kcnq1ot1 depletion demonstrated that the LncRNA is required for the accumulation of H3K27me3, a chromatin modification catalyzed by the histone-methyl-transferase EZH2, at the maternal p57^kip2 intragenic region. Finally, upon differentiation, the binding of MyoD to this region and its physical interaction with Kcnq1ot1, analyzed by ChIP and RNA immunoprecipitation assays, correlate with the loss of EZH2 and H3K27me3 from chromatin and with p57^Kip2 de-repression.

CONCLUSIONS

These findings highlight the existence of an imprinting-independent role of Kcnq1ot1, adding new insights into the biology of a still mysterious LncRNA. Moreover, they expand our knowledge about the molecular mechanisms underlying the tight and fine regulation of p57^Kip2 during differentiation and, possibly, its aberrant silencing observed in several pathologic conditions.

Long noncoding RNA TALNEC2 plays an oncogenic role in breast cancer by binding to EZH2 to target p57KIP2 and involving in p-p38 MAPK and NF-κB pathways

We aimed to investigate the potential role and regulatory mechanism of long noncoding RNA tumor-associated lncRNA expressed in chromosome 2 (TALNEC2) in breast cancer. The expression of TALNEC2 in breast cancer tissues and cells were investigated. MCF-7 and MDA-MB-231 cells were transfected with small interfering RNA (siRNA) duplexes for targeting TALNEC2 (si-TALNEC2), enhancer of zeste homolog 2 (EZH2; si-EZH2) and p57^KIP2 (si-p57 ^KIP2 ), and their corresponding controls (si-NC). The viability, colony forming ability, cell cycle, apoptosis, and autophagy of transfected cells were assessed. The expressions of p-p38 mitogen-activated protein kinase (MAPK) and nuclear factor κB (NF-κB) pathway-related proteins were investigated. The results showed that TALNEC2 was highly expressed in breast cancer tissues and cells. Knockdown of TALNEC2 significantly inhibited the malignant behaviors of MCF-7 and MDA-MB-231 cells, including inhibiting cell viability and colony forming, arresting cell cycle at G0/G1 phase, inducing cell apoptosis, and promoting cell autophagy. EZH2 was a TALNEC2 binding protein, which was upregulated in breast cancer tissues and cells and could negatively regulate p57 ^KIP2 . Effects of TALNEC2 knockdown on malignant behaviors of MCF-7 cells were reversed by p57 ^KIP2 knockdown. The expressions of p-p38, RelA, and RelB in MCF-7 cells were decreased after knockdown of TALNEC2 or EZH2, which were reversed by knockdown of p57 ^KIP2 concurrently. In conclusion, TALNEC2 may play an oncogenic role in breast cancer by binding to EZH2 to target p57 ^KIP2 . Activation of p-p38 MAPK and NF-κB pathways may be key mechanisms mediating the oncogenic role of TALNEC2 in breast cancer. TALNEC2 may serve as a promising target in the therapy of breast cancer.

Cellular localization of the cell cycle inhibitor Cdkn1c controls growth arrest of adult skeletal muscle stem cells

Adult skeletal muscle maintenance and regeneration depend on efficient muscle stem cell (MuSC) functions. The mechanisms coordinating cell cycle with activation, renewal, and differentiation of MuSCs remain poorly understood. Here, we investigated how adult MuSCs are regulated by CDKN1c (p57^kip2), a cyclin-dependent kinase inhibitor, using mouse molecular genetics. In the absence of CDKN1c, skeletal muscle repair is severely impaired after injury. We show that CDKN1c is not expressed in quiescent MuSCs, while being induced in activated and proliferating myoblasts and maintained in differentiating myogenic cells. In agreement, isolated Cdkn1c-deficient primary myoblasts display differentiation defects and increased proliferation. We further show that the subcellular localization of CDKN1c is dynamic; while CDKN1c is initially localized to the cytoplasm of activated/proliferating myoblasts, progressive nuclear translocation leads to growth arrest during differentiation. We propose that CDKN1c activity is restricted to differentiating myoblasts by regulated cyto-nuclear relocalization, coordinating the balance between proliferation and growth arrest.

MECHANISMS OF ENDOCRINOLOGY: Cell cycle regulation in adrenocortical carcinoma

Adrenocortical carcinomas (ACCs) are rather rare endocrine tumors that often have a poor prognosis. The reduced survival rate associated with these tumors is due to their aggressive biological behavior, combined with the scarcity of effective treatment options that are currently available. The recent identification of the genomic alterations present in ACC have provided further molecular mechanisms to develop consistent strategies for the diagnosis, prevention of progression and treatment of advanced ACCs. Taken together, molecular and genomic advances could be leading the way to develop personalized medicine in ACCs similarly to similar developments in lung or breast cancers. In this review, we focused our attention to systematically compile and summarize the alterations in the cell cycle regulation that were described so far in ACC as they are known to play a crucial role in cell differentiation and growth. We have divided the analysis according to the major transition phases of the cell cycle, G1 to S and G2 to M. We have analyzed the most extensively studied checkpoints: the p53/Rb1 pathway, CDC2/cyclin B and topoisomerases (TOPs). We reached the conclusion that the most important alterations having a potential application in clinical practice are the ones related to p53/Rb1 and TOP 2. We also present a brief description of on-going clinical trials based on molecular alterations in ACC. The drugs have targeted the insulin-like growth factor receptor 1, TOP 2, polo-like kinase1, cyclin-dependent kinase inhibitors, p53 reactivation and CDC25.

PSMD2 regulates breast cancer cell proliferation and cell cycle progression by modulating p21 and p27 proteasomal degradation

Alterations in the ubiquitin-proteasome system (UPS) and UPS-associated proteins have been implicated in the development of many human malignancies. In this study, we investigated the expression profiles of 797 UPS-related genes using HiSeq data from The Cancer Genome Atlas and identified that PSMD2 was markedly upregulated in breast cancer. High PSMD2 expression was significantly correlated with poor prognosis. Gene set enrichment analysis revealed that transcriptome signatures involving proliferation, cell cycle, and apoptosis were critically enriched in specimens with elevated PSMD2. Consistently, PSMD2 knockdown inhibited cell proliferation and arrested cell cycle at G0/G1 phase in vitro, as well as suppressed tumor growth in vivo. Rescue assays demonstrated that the cell cycle arrest caused by silencing PSMD2 partially resulted from increased p21 and/or p27. Mechanically, PSMD2 physically interacted with p21 and p27 and mediated their ubiquitin-proteasome degradation with the cooperation of USP14. Notably, intratumor injection of therapeutic PSMD2 small interfering RNA effectively delayed xenograft tumor growth accompanied by p21 and p27 upregulation. These data provide novel insight into the role of PSMD2 in breast cancer and suggest that PSMD2 may be a potential therapeutic target.

Genetic and Epigenetic Control of CDKN1C Expression: Importance in Cell Commitment and Differentiation, Tissue Homeostasis and Human Diseases

The CDKN1C gene encodes the p57^Kip2 protein which has been identified as the third member of the CIP/Kip family, also including p27^Kip1 and p21^Cip1. In analogy with these proteins, p57^Kip2 is able to bind tightly and inhibit cyclin/cyclin-dependent kinase complexes and, in turn, modulate cell division cycle progression. For a long time, the main function of p57^Kip2 has been associated only to correct embryogenesis, since CDKN1C-ablated mice are not vital. Accordingly, it has been demonstrated that CDKN1C alterations cause three human hereditary syndromes, characterized by altered growth rate. Subsequently, the p57^Kip2 role in several cell phenotypes has been clearly assessed as well as its down-regulation in human cancers. CDKN1C lies in a genetic locus, 11p15.5, characterized by a remarkable regional imprinting that results in the transcription of only the maternal allele. The control of CDKN1C transcription is also linked to additional mechanisms, including DNA methylation and specific histone methylation/acetylation. Finally, long non-coding RNAs and miRNAs appear to play important roles in controlling p57^Kip2 levels. This review mostly represents an appraisal of the available data regarding the control of CDKN1C gene expression. In addition, the structure and function of p57^Kip2 protein are briefly described and correlated to human physiology and diseases.

Downregulated CDKN1C/p57kip2 drives tumorigenesis and associates with poor overall survival in breast cancer

CDKN1C, also known as p57^kip2, is considered to be a potential tumor suppressor implicated in several kinds of human cancers. However, the current knowledge of CDKN1C in breast cancer remains obscure. In the present study, we demonstrated that CDKN1C was dramatically downregulated in breast cancer compared with normal tissues by using real-time quantitative polymerase chain reaction, western blot and two public data portals: The Cancer Genome Atlas (TCGA) and Oncomine datasets. Moreover, the expression of CDKN1C was correlated with age and tumor size in the TCGA cohort containing 708 cases of breast cancer. Low expression of CDKN1C was significantly associated with poor overall survival (OS) in the TCGA cohort and validated cohort composed of 1402 patients. Multivariate Cox regression analysis indicated that CDKN1C was an independent prognostic factor for worse OS (HR = 1.78, 95% CI: 1.09-2.89, p = 0.020). Furthermore, gene set enrichment analysis (GSEA) revealed that CDKN1C was significantly correlated with gene signatures involving DNA repair, cell cycle, glycolysis, adipogenesis, and two critical signaling pathways mTORC1 and PI3K/Akt/mTOR. In conclusion, our data suggested an essential role of CDKN1C in the tumorgenesis of breast cancer. Targeting CDKN1C may be a promising strategy for anticancer therapeutics.

MicroRNA-103 Promotes Proliferation and Inhibits Apoptosis in Spinal Osteosarcoma Cells by Targeting p57

Osteosarcoma is one of the most aggressive malignancies with poor prognosis rates. Many studies have demonstrated that miRNAs were involved in osteosarcoma, but the role of miR-103a in osteosarcoma remains elusive. In this study, we detected the expression levels of miR-103 in osteosarcoma and non-osteosarcoma tissues and cell lines. The binding effect of miR-103 on p57 was detected by luciferase reporter assay. After altering expressions of miR-103 or p57, viability, migration, invasion, and apoptosis of MG63 cells and expressions of proteins related with the JNK/STAT and mTOR pathways were all detected. We found the higher expression of miR-103 in osteosarcoma tissues and cell lines compared with non-osteosarcoma tissues and cell lines. miR-103 overexpression promoted survival, migration, and invasion of MG63 cells. Knockdown of miR-103a inhibited cell survival, migration, and invasion by upregulating the expression of p57, which was a target of miR-103. Moreover, miR-103a overexpression activated the JNK/STAT and mTOR pathways probably through inhibiting p57 expression. In conclusion, miR-103a acted as an oncogene in osteosarcoma, probably through activating the JNK/STAT and mTOR pathways by inhibiting p57 expression.

The E2A splice variant E47 regulates the differentiation of projection neurons via p57(KIP2) during cortical development

During corticogenesis, distinct classes of neurons are born from progenitor cells located in the ventricular and subventricular zones, from where they migrate towards the pial surface to assemble into highly organized layer-specific circuits. However, the precise and coordinated transcriptional network activity defining neuronal identity is still not understood. Here, we show that genetic depletion of the basic helix-loop-helix (bHLH) transcription factor E2A splice variant E47 increased the number of Tbr1-positive deep layer and Satb2-positive upper layer neurons at E14.5, while depletion of the alternatively spliced E12 variant did not affect layer-specific neurogenesis. While ChIP-Seq identified a big overlap for E12- and E47-specific binding sites in embryonic NSCs, including sites at the cyclin-dependent kinase inhibitor (CDKI) Cdkn1c gene locus, RNA-Seq revealed a unique transcriptional regulation by each splice variant. E47 activated the expression of the CDKI Cdkn1c through binding to a distal enhancer. Finally, overexpression of E47 in embryonic NSCs in vitro impaired neurite outgrowth, and overexpression of E47 in vivo by in utero electroporation disturbed proper layer-specific neurogenesis and upregulated p57(KIP2) expression. Overall, this study identifies E2A target genes in embryonic NSCs and demonstrates that E47 regulates neuronal differentiation via p57(KIP2).

Hypercortisolism due to a Pituitary Adenoma Associated with Beckwith-Wiedemann Syndrome

BACKGROUND

Beckwith-Wiedemann syndrome (BWS) is an overgrowth syndrome with an increased risk of cancer. Most BWS patients show a molecular defect in the 11p15 region that contains imprinted genes. BWS has been associated with malignant neoplasms during infancy. Descriptions of benign tumors, especially in adult patients, are rarer.

METHODS/RESULTS

We report the case of a BWS patient with pituitary adenoma caused by loss of methylation (LOM) at ICR2 (locus CDKN1C/KCNQ1OT1). The patient was referred to an endocrinology unit for suspicion of Cushing's disease due to a history of macroglossia and hemihyperplasia. Biological tests led to the diagnosis of ACTH-dependent hypercortisolism. MRI showed a microadenoma of the pituitary gland, confirming the diagnosis of Cushing's disease. DNA methylation analysis revealed LOM at ICR2 that was in a mosaic state in the patient's leukocytes, but was present in nearly all cells of the pituitary adenoma. The epigenetic defect was associated with a somatic USP8 mutation in the adenoma.

CONCLUSION

Pituitary adenoma rarely occurs in patients with BWS. However, BWS should be considered in cases of pituitary adenoma with minor and/or major signs of BWS. The association between ICR2 LOM and USP8 mutation in the adenoma is questionable. © 2016 S. Karger AG, Basel.

A p57 conditional mutant allele that allows tracking of p57-expressing cells

p57^Kip2 (p57) is a maternally expressed imprinted gene regulating growth arrest which belongs to the CIP/KIP family of cyclin-dependent kinase inhibitors. While initially identified as a cell cycle arrest protein through inhibition of cyclin and cyclin-dependent kinase complexes, p57 activity has also been linked to differentiation, apoptosis, and senescence. In addition, p57 has recently been shown to be involved in tumorigenesis and cell fate decisions in stem cells. Yet, p57 function in adult tissues remains poorly characterized due to the perinatal lethality of p57 knock-out mice. To analyze p57 tissue-specific activity, we generated a conditional mouse line (p57^FL-ILZ/+ ) by flanking the coding exons 2-3 by LoxP sites. To track p57-expressing or mutant cells, the p57^FL-ILZ allele also contains an IRES-linked β-galactosidase reporter inserted in the 3' UTR of the gene. Here, we show that the β-galactosidase reporter expression pattern recapitulates p57 tissue specificity during development and in postnatal mice. Furthermore, we crossed the p57^FL-ILZ/+ mice with PGK-Cre mice to generate p57^cKO-ILZ/+ animals with ubiquitous loss of p57. p57^cKO-ILZ/+ mice display developmental phenotypes analogous to previously described p57 knock-outs. Thus, p57^FL-ILZ/+ is a new genetic tool allowing expression and functional conditional analyses of p57.

A Systematic Analysis of Negative Growth Control Implicates the DREAM Complex in Cancer Cell Dormancy

Epithelial ovarian cancer (EOC) generates multicellular aggregates called spheroids that detach from the primary tumor and disseminate through ascites. Spheroids possess a number of characteristics of tumor dormancy including withdrawal from the cell cycle and resistance to chemotherapeutics. This report systematically analyzes the effects of RNAi depletion of 21 genes that are known to contribute to negative regulation of the cell cycle in 10 ovarian cancer cell lines. Interestingly, spheroid cell viability was compromised by loss of some cyclin-dependent kinase inhibitors such as p57Kip2, as well as Dyrk1A, Lin52, and E2F5 in most cell lines tested. Many genes essential for EOC spheroid viability are pertinent to the mammalian DREAM repressor complex. Mechanistically, the data demonstrate that DREAM is assembled upon the induction of spheroid formation, which is dependent upon Dyrk1A. Loss of Dyrk1A results in retention of the b-Myb-MuvB complex, elevated expression of DREAM target genes, and increased DNA synthesis that is coincident with cell death. Inhibition of Dyrk1A activity using pharmacologic agents Harmine and INDY compromises viability of spheroids and blocks DREAM assembly. In addition, INDY treatment improves the response to carboplatin, suggesting this is a therapeutic target for EOC treatment.Implications: Loss of negative growth control mechanisms in cancer dormancy lead to cell death and not proliferation, suggesting they are an attractive therapeutic approach. Mol Cancer Res; 15(4); 371-81. ©2016 AACR.

CDK inhibitors for muscle stem cell differentiation and self-renewal

Regeneration of muscle is undertaken by muscle stem cell populations named satellite cells which are normally quiescent or at the G0 phase of the cell cycle. However, upon signals from damaged muscle, satellite cells lose their quiescence, and enter the G1 cell cycle phase to expand the population of satellite cell progenies termed myogenic precursor cells (MPCs). Eventually, MPCs stop their cell cycle and undergo terminal differentiation to form skeletal muscle fibers. Some MPCs retract to quiescent satellite cells as a self-renewal process. Therefore, cell cycle regulation, consisting of satellite cell activation, proliferation, differentiation and self-renewal, is the key event of muscle regeneration. In this review, we summarize up-to-date progress on research about cell cycle regulation of myogenic progenitor cells and muscle stem cells during embryonic myogenesis and adult muscle regeneration, aging, exercise and muscle diseases including muscular dystrophy and muscle fiber atrophy, especially focusing on cyclin-dependent kinase inhibitors (CDKIs).

Transcriptome sequencing reveals a profile that corresponds to genomic variants in Waldenström macroglobulinemia

Whole-genome sequencing has identified highly prevalent somatic mutations including MYD88, CXCR4, and ARID1A in Waldenström macroglobulinemia (WM). The impact of these and other somatic mutations on transcriptional regulation in WM remains to be clarified. We performed next-generation transcriptional profiling in 57 WM patients and compared findings to healthy donor B cells. Compared with healthy donors, WM patient samples showed greatly enhanced expression of the VDJ recombination genes DNTT, RAG1, and RAG2, but not AICDA Genes related to CXCR4 signaling were also upregulated and included CXCR4, CXCL12, and VCAM1 regardless of CXCR4 mutation status, indicating a potential role for CXCR4 signaling in all WM patients. The WM transcriptional profile was equally dissimilar to healthy memory B cells and circulating B cells likely due increased differentiation rather than cellular origin. The profile for CXCR4 mutations corresponded to diminished B-cell differentiation and suppression of tumor suppressors upregulated by MYD88 mutations in a manner associated with the suppression of TLR4 signaling relative to those mutated for MYD88 alone. Promoter methylation studies of top findings failed to explain this suppressive effect but identified aberrant methylation patterns in MYD88 wild-type patients. CXCR4 and MYD88 transcription were negatively correlated, demonstrated allele-specific transcription bias, and, along with CXCL13, were associated with bone marrow disease involvement. Distinct gene expression profiles for patients with wild-type MYD88, mutated ARID1A, familial predisposition to WM, chr6q deletions, chr3q amplifications, and trisomy 4 are also described. The findings provide novel insights into the molecular pathogenesis and opportunities for targeted therapeutic strategies for WM.

p57(Kip2) knock-in mouse reveals CDK-independent contribution in the development of Beckwith-Wiedemann syndrome

CDKN1C encodes the cyclin-CDK inhibitor p57(Kip2) (p57), a negative regulator of the cell cycle and putative tumour suppressor. Genetic and epigenetic alterations causing loss of p57 function are the most frequent cause of Beckwith-Wiedemann syndrome (BWS), a genetic disorder characterized by multiple developmental anomalies and increased susceptibility to tumour development during childhood. So far, BWS development has been attributed entirely to the deregulation of proliferation caused by loss of p57-mediated CDK inhibition. However, a fraction of BWS patients have point mutations in CDKN1C located outside of the CDK inhibitory region, suggesting the involvement of other parts of the protein in the disease. To test this possibility, we generated knock-in mice deficient for p57-mediated cyclin-CDK inhibition (p57(CK) (-) ), the only clearly defined function of p57. Comparative analysis of p57(CK) (-) and p57(KO) mice provided clear evidence for CDK-independent roles of p57 and revealed that BWS is not caused entirely by CDK deregulation, as several features of BWS are caused by the loss of CDK-independent roles of p57. Thus, while the genetic origin of BWS is well understood, our results underscore that the underlying molecular mechanisms remain largely unclear. To probe these mechanisms further, we determined the p57 interactome. Several partners identified are involved in genetic disorders with features resembling those caused by CDKN1C mutation, suggesting that they could be involved in BWS pathogenesis and revealing a possible connection between seemingly distinct syndromes. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Maternal-fetal conflict, genomic imprinting and mammalian vulnerabilities to cancer

Antagonistic coevolution between maternal and fetal genes, and between maternally and paternally derived genes may have increased mammalian vulnerability to cancer. Placental trophoblast has evolved to invade maternal tissues and evade structural and immunological constraints on its invasion. These adaptations can be co-opted by cancer in intrasomatic selection. Imprinted genes of maternal and paternal origin favour different degrees of proliferation of particular cell types in which they reside. As a result, the set of genes favouring greater proliferation will be selected to evade controls on cell-cycle progression imposed by the set of genes favouring lesser proliferation. The dynamics of stem cell populations will be a particular focus of this intragenomic conflict. Gene networks that are battlegrounds of intragenomic conflict are expected to be less robust than networks that evolve in the absence of conflict. By these processes, maternal-fetal and intragenomic conflicts may undermine evolved defences against cancer.

The developmental expression of the CDK inhibitor p57(kip2) (Cdkn1c) in the early mouse placenta

p57(kip2) (encoded by the Cdkn1c gene) is a member of the cip/kip family of cyclin-dependent kinase inhibitors that mediates cell cycle arrest in G1, allowing cells to differentiate. In the placenta, p57(kip2) is involved in endoreduplication, formation of trophoblast giant cells, trophoblast invasion, and expansion of placental cell layers. Here, we quantitatively and qualitatively define the cell- and region-specific expression of mouse placental p57(kip2) using laser-capture microdissection, in situ hybridization, and immunohistochemistry. Cdkn1c RNA was quantified by real-time quantitative PCR. Co-expression of Pl1 was used to identify trophoblast giant cells while Tbpba was used to identify spongiotrophoblast cells. Timed sacrifices were also carried out at embryonic days E7.5, E8.5, E9.5, and E12.5 to profile the expression in embryos and their placentas. At E8.5, intense expression of Cdkn1c was seen in invasive TGCs and the ectoplacental cone. Cdkn1c expression was more diffuse and more abundant in the labyrinth that in the junctional zone at both E9.5 and E12.5. Immunohistochemistry revealed robust p57(kip2) staining in trophoblast giant cells and in the ectoplacental cone at E8.5. p57(kip2) protein was seen in giant cells and throughout the labyrinth, although its abundance was reduced in the junctional zone at E9.5, and became more diffuse by E12.5. The early and intense expression in trophoblast giant cells is consistent with a role for p57(kip2) in the invasive phenotype of these cells. Mol. Reprod. Dev. 83: 405-412, 2016. © 2016 Wiley Periodicals, Inc.

Down-regulation of the cyclin-dependent kinase inhibitor p57 is mediated by Jab1/Csn5 in hepatocarcinogenesis

Down-regulation of p57 (KIP2) cyclin-dependent kinase inhibitors accelerates the growth and invasion of hepatocellular carcinoma (HCC), suggesting that p57 may play an important role in liver carcinogenesis. However, the mechanism or oncogenic signal leading to p57 down-regulation in HCC remains to be determined. Herein, we demonstrated that Jab1/Csn5 expression is negatively correlated with p57 levels in HCC tissues. Kaplan-Meier analysis of tumor samples revealed that high Jab1/Csn5 expression with concurrent low p57 expression is associated with poor overall survival. The inverse pattern of Jab1 and p57 expression was also observed during carcinogenesis in a chemically induced rat HCC model. We also found that mechanistically, Jab1-mediated p57 proteolysis in HCC cells is dependent on 26S-proteasome inhibitors. We further demonstrated that direct physical interaction between Jab1 and p57 triggers p57 down-regulation, independently of Skp2 and Akt pathways, in HCC cells. These data suggest that Jab1 is an important upstream negative regulator of p57 and that aberrant expression of Jab1 in HCC could lead to a significant decrease in p57 levels and contribute to tumor cell growth. Furthermore, restoration of p57 levels induced by loss of Jab1 inhibited tumor cell growth and further increased cell apoptosis in HCC cells. Moreover, silencing Jab1 expression further enhanced the antitumor effects of cisplatin-induced apoptosis in HCC cells.

CONCLUSION

Jab1-p57 pathway confers resistance to chemotherapy and may represent a potential target for investigational therapy in HCC.

Cancer cell-selective killing polymer/copper combination

Chemotherapy has been adopted for cancer treatment for decades. However, its efficacy and safety are frequently compromised by the multidrug-resistance of cancer cells and the poor cancer cell selectivity of anticancer drugs. Hereby, we report a combination of a pyridine-2-thiol containing polymer and copper which can effectively kill a wide spectrum of cancer cells, including drug resistant cancer cells, while sparing normal cells. The polymer nanoparticle enters cells via an exofacial thiol facilitated route, and releases active pyridine-2-thiol with the help of intracellularly elevated glutathione (GSH). Due to their high GSH level, cancer cells are more vulnerable to the polymer/copper combination. In addition, RNA microarray analysis revealed that the treatment can reverse cancer cells' upregulated oncogenes (CIRBP and STMN1) and downregulated tumor suppressor genes (CDKN1C and GADD45B) to further enhance the selectivity for cancer cells.

Histone Deacetylase Inhibitors Increase p27(Kip1) by Affecting Its Ubiquitin-Dependent Degradation through Skp2 Downregulation

Histone deacetylase inhibitors (HDACIs) represent an intriguing class of pharmacologically active compounds. Currently, some HDACIs are FDA approved for cancer therapy and many others are in clinical trials, showing important clinical activities at well tolerated doses. HDACIs also interfere with the aging process and are involved in the control of inflammation and oxidative stress. In vitro, HDACIs induce different cellular responses including growth arrest, differentiation, and apoptosis. Here, we evaluated the effects of HDACIs on p27^Kip1, a key cyclin-dependent kinase inhibitor (CKI). We observed that HDACI-dependent antiproliferative activity is associated with p27^Kip1 accumulation due to a reduced protein degradation. p27^Kip1 removal requires a preliminary ubiquitination step due to the Skp2-SCF E3 ligase complex. We demonstrated that HDACIs increase p27^Kip1 stability through downregulation of Skp2 protein levels. Skp2 decline is only partially due to a reduced Skp2 gene expression. Conversely, the protein decrease is more profound and enduring compared to the changes of Skp2 transcript. This argues for HDACIs effects on Skp2 protein posttranslational modifications and/or on its removal. In summary, we demonstrate that HDACIs increase p27^Kip1 by hampering its nuclear ubiquitination/degradation. The findings might be of relevance in the phenotypic effects of these compounds, including their anticancer and aging-modulating activities.

Cellular Response upon Stress: p57 Contribution to the Final Outcome

Progression through the cell cycle is one of the most important decisions during the life of a cell and several kinds of stress are able to influence this choice. p57 is a cyclin-dependent kinase inhibitor belonging to the CIP/KIP family and is a well-known regulator of the cell cycle during embryogenesis and tissue differentiation. p57 loss has been reported in a variety of cancers and great effort has been spent during the past years studying the mechanisms of p57 regulation and the effects of p57 reexpression on tumor growth. Recently, growing amount of evidence points out that p57 has a specific function in cell cycle regulation upon cellular stress that is only partially shared by the other CIP/KIP inhibitors p21 and p27. Furthermore, it is nowadays emerging that p57 plays a role in the induction of apoptosis and senescence after cellular stress independently of its cell cycle related functions. This review focuses on the contribution that p57 holds in regulating cell cycle arrest, apoptosis, and senescence after cellular stress with particular attention to the response of cancer cells.