The role of cyclin E in the regulation of entry into S phase

Expression of Cyclin E1 in hepatic stellate cells is critical for the induction and progression of liver fibrosis and hepatocellular carcinoma in mice

Hepatocellular carcinoma (HCC) is one of the most severe malignancies with increasing incidence and limited treatment options. Typically, HCC develops during a multistep process involving chronic liver inflammation and liver fibrosis. The latter is characterized by the accumulation of extracellular matrix produced by Hepatic Stellate Cells (HSCs). This process involves cell cycle re-entry and proliferation of normally quiescent HSCs in an ordered sequence that is highly regulated by cyclins and associated cyclin-dependent kinases (CDKs) such as the Cyclin E1 (CCNE1)/CDK2 kinase complex. In the present study, we examined the role of Cyclin E1 (Ccne1) and Cdk2 genes in HSCs for liver fibrogenesis and hepatocarcinogenesis. To this end, we generated conditional knockout mice lacking Ccne1 or Cdk2 specifically in HSCs (Ccne1∆HSC or Cdk2∆HSC). Ccne1∆HSC mice showed significantly reduced liver fibrosis formation and attenuated HSC activation in the carbon tetrachloride (CCl4) model. In a combined model of fibrosis-driven hepatocarcinogenesis, Ccne1∆HSC mice revealed decreased HSC activation even after long-term observation and substantially reduced tumor load in the liver when compared to wild-type controls. Importantly, the deletion of Cdk2 in HSCs also resulted in attenuated liver fibrosis after chronic CCl4 treatment. Single-cell RNA sequencing revealed that only a small fraction of HSCs expressed Ccne1/Cdk2 at a distinct time point after CCl4 treatment. In summary, we provide evidence that Ccne1 expression in a small population of HSCs is sufficient to trigger extensive liver fibrosis and hepatocarcinogenesis in a Cdk2-dependent manner. Thus, HSC-specific targeting of Ccne1 or Cdk2 in patients with liver fibrosis and high risk for HCC development could be therapeutically beneficial.

Anticancer effects of the HDAC inhibitor, 3β,6β‑dihydroxyurs‑12‑en‑27‑oic acid, in MCF‑7 breast cancer cells via the inhibition of Akt/mTOR pathways

Astilbe chinensis (A. chinensis) is a perennial herb that is used to treat chronic bronchitis and pain. The anticancer activity of 3β,6β‑dihydroxyurs‑12‑en‑27‑oic acid (ACT‑3), a major component isolated from A. chinensis, has not yet been investigated in detail. The purpose of the present study was to investigate the histone deacetylase (HDAC) inhibitory and anticancer activities of ACT‑3 compared with suberoylanilide hydroxamic acid (SAHA) in MCF‑7 human breast cancer cells. The purity of ACT‑3 was determined using high‑performance liquid chromatography. In the present study, the effects of ACT‑3 on anticancer effects of MCF‑7 cells were determined by measuring the level of apoptotic cell death and cell cycle regulator using flow cytometry analysis and western blot analysis, respectively. The effects of ACT‑3 on HDAC enzyme activity were measured using assay kits. ACT‑3 and SAHA increased the levels of acetylated histone H3 and reduced the levels of HDAC1 and HDAC3 in MCF‑7 cells. ACT‑3 significantly decreased the cell viability in a concentration‑dependent manner and induced different morphological changes at high concentrations. ACT‑3 and SAHA significantly inhibited the colony formation in MCF‑7 cells. ACT‑3 inhibited total HDAC activity in a dose‑dependent manner. ACT‑3 significantly reduced the expression levels of cyclin D1 and cyclin‑dependent kinase 4, and upregulated the expression levels of p21^WAF1 and p53. A significant increase in the G1 phase cell population was observed in MCF‑7 cells and ACT‑3 induced apoptosis by reducing the ratio of B‑cell lymphoma‑2 (Bcl‑2)/Bcl‑2‑associated X (Bax) and releasing cleaved caspase 9. Additionally, ACT‑3 significantly increased autophagic cell death by inhibiting the serine‑threonine kinase/mammalian target of the rapamycin pathway. Autophagy induction was confirmed via acridine orange staining. ACT‑3 significantly increased the pERK1/2 and p21 in MCF‑7 cells. Thus, the activated ERK pathway played an important role in cell cycle arrest and apoptosis via ERK‑dependent induction of p21 in MCF‑7 cells. These data indicated that ACT‑3 can be used as a promising anticancer agent to overcome the limitations and reduce the side effects of conventional anticancer drugs.

SCUBE3 downregulation modulates hepatocellular carcinoma by inhibiting CCNE1 via TGFβ/PI3K/AKT/GSK3β pathway

OBJECTIVES

We aimed to verify the role of signal peptide-CUB-EGF-like domain-containing protein3 (SCUBE3) in the hepatocellular carcinoma (HCC) progression.

METHODS

The role of SCUBE3 in HCC cell proliferation, apoptosis, and cell cycle in vitro were detected using MTT assay, colony formation assay, 5-ethynyl-2´-deoxyuridine assay (EDU), Celigo cell counting assay, Caspase3/7 activity assay, and flow cytometry. The effect of SCUBE3 on HCC cell proliferation in vivo was inspected by a xenograft tumour model in nude mice. The related mechanisms were further studied.

RESULTS

The level of SCUBE3 was upregulated in HCC tissues and cell lines. Knockdown of SCUBE3 inhibited proliferation, promoted apoptosis, and induced cell cycle arrest in HCC cell lines in vitro and in vivo. Screening of cell cycle-related proteins revealed that CCNL2, CDK6, CCNE1, and CCND1 exhibited a significantly different expression profile. We found that SCUBE3 may promote the proliferation of HCC cells by regulating CCNE1 expression. The pathway enrichment analysis showed that the TGFβ signalling pathway and the PI3K/AKT signalling pathway were significantly altered. Co-immunoprecipitation results showed that SCUBE3 binds to the TGFβRII receptor. SCUBE3 knockdown inhibited the PI3K/AKT signalling pathway and the phosphorylation of GSK3β to inhibit its kinase activity.

CONCLUSIONS

SCUBE3 promotes HCC development by regulating CCNE1 via TGFβ/PI3K/AKT/GSK3β pathway. In addition, SCUBE3 may be a new molecular target for the clinical diagnosis and treatment of HCC.

Anticarcinogenic Effects of Odorant Substances Citral, Citrathal R and Cyclovertal on Breast Cancer in vitro

Purpose

In 2020, breast cancer still represents the most common type of cancer in women worldwide. Depending on the specific molecular subtype, clinical breast cancer management comprises surgery, radiotherapy, chemotherapy and targeted therapy. Furthermore, there are some therapeutic approaches from the field of complementary and alternative medicine. Current research focuses on the elucidation of new therapeutic targets for treatment development. Odorant substances affect apoptosis, proliferation and cell cycle in healthy and cancerous cells. Exact signalling pathways involved are not entirely clear. The present study aims to analyse their therapeutic potential in breast cancer.

Methods

This study focuses on the effect of commonly used odorant substances (citral, citrathal R, cyclovertal, para-cymol, hexylacetat, herbavert, dihydromyrcerol and limonen) on the breast cancer cell lines MDA-MB-231, T47-D and BT474. Methodologically, this study applied cell culturing, MTT assay for detection of IC50 of the odorant substance, RNA purification followed by qRT-PCR, protein isolation and Western Blot, as well as immunocytochemistry. Further, this study investigates the role of transient receptor potential channel V1 (TRPV1), involved in the mechanisms of action for some odorant substances. Therefore, capsazepine, a TRPV1 antagonist, was used.

Results

The odorant substances citral, citrathal R and cyclovertal have significant pro-apoptotic (p < 0.001), anti-proliferative (p < 0.001) and cell cycle-arresting effects measurable in RNA expression as well as in protein levels and immunocytochemical staining. The combination of citral and capsazepine no longer showed significant pro-apoptotic, antiproliferative, and cell cycle inhibitory effects compared to the compounds alone. This indicates that TRPV1 is necessary for the signal transduction of citral.

Conclusion

This present study reveals three odorant substances with effects on cell viability, indicating their potential use in breast cancer therapy.

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Comprehensive analysis of miRNA-mRNA/lncRNA during gonadal development of triploid female rainbow trout (Oncorhynchus mykiss)

Chromosomal ploidy manipulation is one of the means to create excellent germplasm. Triploid fish could provide an ideal sterile model for searching of a underlying mechanism of abnormality in meiosis. The complete understanding of the coding and noncoding RNAs regulating sterility caused by meiosis abnormality is still not well understood. By high-throughput sequencing, we compared the expression profiles of gonadal mRNA, long non-coding RNA (lncRNA), and microRNA (miRNA) at three different developmental stages between the diploid (XX) and triploid (XXX) female rainbow trout. These stages were gonads before differentiation (65 days post fertilisation, dpf), at the beginning of morphological differences (180 dpf) and showing clear difference between diploids and triploids (600 dpf), respectively. A majority of differentially expressed (DE) RNAs were identified, and 22 DE mRNAs related to oocyte meiosis and homologous recombination were characterized. The predicted miRNA-mRNA/lncRNA networks of 3 developmental stages were constructed based on the target pairs of DE lncRNA-miRNA and DE mRNA-miRNA. According to the networks, meiosis-related gene of ccne1 was targeted by dre-miR-15a-5p_R + 1, and 6 targeted DE lncRNAs were identified. Also, qRT-PCR was performed to validate the credibility of the network. Overall, this study explored the potential interplay between coding and noncoding RNAs during the gonadal development of polyploid fish. The mRNA, lncRNA and miRNA screened in this study may be helpful to identify the functional elements regulating fertility of rainbow trout, which may provide reference for character improvement in aquaculture.

Depletion of SNRNP200 inhibits the osteo-/dentinogenic differentiation and cell proliferation potential of stem cells from the apical papilla

BACKGROUND

Tissue regeneration mediated by mesenchymal stem cells (MSCs) is deemed a desirable way to repair teeth and craniomaxillofacial tissue defects. Nevertheless, the molecular mechanisms about cell proliferation and committed differentiation of MSCs remain obscure. Previous researches have proved that lysine demethylase 2A (KDM2A) performed significant function in the regulation of MSC proliferation and differentiation. SNRNP200, as a co-binding factor of KDM2A, its potential effect in regulating MSCs' function is still unclear. Therefore, stem cells from the apical papilla (SCAPs) were used to investigate the function of SNRNP200 in this research.

METHODS

The alkaline phosphatase (ALP) activity assay, Alizarin Red staining, and osteogenesis-related gene expressions were used to examine osteo-/dentinogenic differentiation potential. Carboxyfluorescein diacetate, succinimidyl ester (CFSE) and cell cycle analysis were applied to detect the cell proliferation. Western blot analysis was used to evaluate the expressions of cell cycle-related proteins.

RESULTS

Depletion of SNRNP200 caused an obvious decrease of ALP activity, mineralization formation and the expressions of osteo-/dentinogenic genes including RUNX2, DSPP, DMP1 and BSP. Meanwhile, CFSE and cell cycle assays revealed that knock-down of SNRNP200 inhibited the cell proliferation and blocked cell cycle at the G2/M and S phase in SCAPs. In addition, it was found that depletion of SNRNP200 up-regulated p21 and p53, and down-regulated the CDK1, CyclinB, CyclinE and CDK2.

CONCLUSIONS

Depletion of SNRNP200 repressed osteo-/dentinogenic differentiation potentials and restrained cell proliferation through blocking cell cycle progression at the G2/M and S phase, further revealing that SNRNP200 has crucial effects on preserving the proliferation and differentiation potentials of dental tissue-derived MSCs.

Prognostic Significance of Cyclin E1 Expression in Patients With Chordoma: A Clinicopathological and Immunohistochemical Study

PURPOSE

Chordomas are rare, slow-growing sarcomas without any accepted prognostic biomarkers. Owing to their proximity to critical neurovascular structures, discovering predictive biomarkers in chordoma has been a significant research effort because it may potentially reduce risky therapies in patients with less aggressive tumors. In response, because cyclin E1 overexpression correlates with patient prognosis in several malignancies, we investigated its expression in chordoma and whether it informs patient prognosis.

METHODS

Seventy-five chordoma patient specimens were enrolled in a tissue microarray (TMA) to evaluate cyclin E1 expression via immunohistochemical staining. Western blot was used to assess cyclin E1 expression in chordoma cell lines and fresh tissues. We then correlated cyclin E1 staining intensity in the TMA to clinicopathological features and chordoma patient outcomes.

RESULTS

Sixty-three percent of the chordoma patient specimens in the TMA, fifty-six percent of the fresh chordoma tissues, and all chordoma cell lines showed high cyclin E1 expression. In TMA analysis, cyclin E1 expression positively correlated to chordoma patient disease status. By survival analysis, high cyclin E1 expression was an independent prognostic risk factor for chordoma patients along with advanced disease status and positive surgical margin.

CONCLUSION

Cyclin E1 is a promising biomarker predicting chordoma patient prognosis.

Antitumor Activity of the Cardiac Glycoside αlDiginoside by Modulating Mcl-1 in Human Oral Squamous Cell Carcinoma Cells

We recently isolated a cardiac glycoside (CG), αldiginoside, from an indigenous plant in Taiwan, which exhibits potent tumor-suppressive efficacy in oral squamous cell carcinoma (OSCC) cell lines (SCC2095 and SCC4, IC₅₀ < 0.2 µM; 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays). Here, we report that αldiginoside caused Sphase arrest and apoptosis, through the inhibition of a series of signaling pathways, including those mediated by cyclin E, phospho-CDC25C (p-CDC25C), and janus kinase/signal transducer and activator of transcription (JAK/STAT)3. αldiginoside induced apoptosis, as indicated by caspase activation and poly (ADP-ribose) polymerase (PARP) cleavage. Equally important, αldiginoside reduced Mcl-1 expression through protein degradation, and overexpression of Mcl-1 partially protected SCC2095 cells from αldiginoside’s cytotoxicity. Taken together, these data suggest the translational potential of αldiginoside to foster new therapeutic strategies for OSCC treatment.

Bioinformatic screening for candidate biomarkers and their prognostic values in endometrial cancer

BACKGROUND

Endometrial cancer is a common gynecological cancer with annually increasing incidence worldwide. However, the biomarkers that provide prognosis and progression for this disease remain elusive.

RESULTS

Two eligible human endometrial cancer datasets (GSE17025 and GSE25405) were selected for the study. A total of 520 differentially expressed mRNAs and 30 differentially expressed miRNAs were identified. These mRNAs were mainly enriched in cell cycle, skeletal system development, vasculature development, oocyte maturation, and oocyte meiosis signalling pathways. A total of 160 pairs of differentially expressed miRNAs and mRNAs, including 22 differentially expressed miRNAs and 71 overlapping differentially expressed mRNAs, were validated in endometrial cancer samples using starBase v2.0 project. The prognosis analysis revealed that Cyclin E1 (CCNE1, one of the 82 hub genes, which correlated with hsa-miR-195 and hsa-miR-424) was significantly linked to a worse overall survival in endometrial cancer patients.

CONCLUSIONS

The hub genes and differentially expressed miRNAs identified in this study might be used as prognostic biomarkers for endometrial cancer and molecular targets for its treatment.

Cyclin E1 is a prognostic biomarker and potential therapeutic target in osteosarcoma

While amplified expressed cyclin E1 is a well-known tumorigenic factor and prognostic biomarker in several malignancies, its prognostic predictive potential and function in osteosarcoma is poorly understood. Here we reveal discrete expression pattern, correlation to clinicopathological characteristics and prognosis and overall function of cyclin E1 in osteosarcoma. Sixty-nine osteosarcoma patient tumor specimens were enrolled to construct a tissue microarray to evaluate cyclin E1 expression through immunohistochemical staining. Cyclin E1 expression in osteosarcoma cell lines and fresh tissues was assessed by Western blot. Cyclin E1 gene expression was evaluated using RNA sequencing data acquired from the public database. We correlated staining intensity to clinical characteristics. Cyclin E1 small interfering RNA was used to determine the effect of cyclin E1 silencing on osteosarcoma cell proliferation and chemotherapeutic sensitivity. Sixty-one percent of the osteosarcoma patient specimens in the tissue microarray had high cyclin E1 expression. Cyclin E1 gene was significantly highly expressed in osteosarcoma tissues and cell lines compared to normal tissues. The expression of cyclin E1 positively correlated with disease status, and inversely correlated to prognosis and response to neoadjuvant chemotherapy. The expression of cyclin E1 was an independent prognostic factor for osteosarcoma patients. In addition, silencing cyclin E1 expression in osteosarcoma cells significantly inhibited cell proliferation and increased sensitivity to chemotherapeutics. We conclude that cyclin E1 is overexpressed in osteosarcoma and is a promising biomarker for prognosis and chemotherapeutic response. We confirm aberrant cyclin E1 expression is a potent therapeutic target in osteosarcoma, and its selective inhibition is a rational treatment strategy for osteosarcoma.

Anastatica hierochuntica (L.) methanolic and aqueous extracts exert antiproliferative effects through the induction of apoptosis in MCF-7 breast cancer cells

Breast cancer therapy using anticancer bioactive compounds derived from natural products as adjuvant treatment has gained recognition due to expensive and toxic conventional chemotherapeutic drugs. The whole plant of Anastatica hierochuntica (L.) (A. hierochuntica) has been investigated for its pharmacologically important anticancer properties but without categorizing the biological activities of the plant parts. We assessed the anticancer potential of different parts of A. hierochuntica (seeds, stems and leaves) and explored their mechanisms of action using the human breast cancer cell line, MCF-7. Currently, we investigated the antiproliferative effects of methanolic (MSD, MST, ML) and aqueous (ASD, AST, AL) extracts of A. hierochuntica plant parts on the MCF-7 cells using cell viability assays. Flow cytometry, Western Blot, DNA fragmentation, and gene expression assays were performed to evaluate apoptosis and cell cycle regulatory proteins. The results indicate that the methanolic and aqueous extracts decreased MCF-7 cell viability in a dose-dependent manner. The induction of apoptosis was observed in all the methanolic and aqueous-treated MCF-7 cells. The cell death process was confirmed by the visualization of DNA fragmentation and cleavage of the intrinsic apoptotic pathways, caspase-9 and caspase-3, the key enzyme causing apoptosis hallmarks. In addition, the most pro-apoptotic extracts, ASD and ML, up-regulated the expression of pro-apoptotic Bax, tumor suppressor TP53 genes and the cyclin inhibitor CDKN1A gene. In conclusion, of the aqueous and methanolic extracts of A. hierochuntica plant parts exerting antiproliferative effects through the induction of apoptosis in breast cancer MCF-7 cells, ASD and ML extracts were the most promising natural-based drugs for the treatment of breast cancer.

Besnoitia besnoiti-driven endothelial host cell cycle alteration

Besnoitia besnoiti is an important obligate intracellular parasite of cattle which primarily infects host endothelial cells of blood vessels during the acute phase of infection. Similar to the closely related parasite Toxoplasma gondii, B. besnoiti has fast proliferating properties leading to rapid host cell lysis within 24–30 h p.i. in vitro. Some apicomplexan parasites were demonstrated to modulate the host cellular cell cycle to successfully perform their intracellular development. As such, we recently demonstrated that T. gondii tachyzoites induce G2/M arrest accompanied by chromosome missegregation, cell spindle alteration, formation of supernumerary centrosomes, and cytokinesis impairment when infecting primary bovine umbilical vein endothelial cells (BUVEC). Here, we follow a comparative approach by using the same host endothelial cell system for B. besnoiti infections. The current data showed that—in terms of host cell cycle modulation—infections of BUVEC by B. besnoiti tachyzoites indeed differ significantly from those by T. gondii. As such, cyclin expression patterns demonstrated a significant upregulation of cyclin E1 in B. besnoiti–infected BUVEC, thereby indicating parasite-driven host cell stasis at G1-to-S phase transition. In line, the mitotic phase of host cell cycle was not influenced since alterations of chromosome segregation, mitotic spindle formation, and cytokinesis were not observed. In contrast to respective T. gondii–related data, we furthermore found a significant upregulation of histone H3 (S10) phosphorylation in B. besnoiti–infected BUVEC, thereby indicating enhanced chromosome condensation to occur in these cells. In line to altered G1/S-transition, we here additionally showed that subcellular abundance of proliferating cell nuclear antigen (PCNA), a marker for G1 and S phase sub-stages, was affected by B. besnoiti since infected cells showed increased nuclear PCNA levels when compared with that of control cells.

Pharmacological Stimulation of Nurr1 Promotes Cell Cycle Progression in Adult Hippocampal Neural Stem Cells

Nuclear receptor related-1 (Nurr1) protein performs a crucial role in hippocampal neural stem cell (hNSC) development as well as cognitive functions. We previously demonstrated that the pharmacological stimulation of Nurr1 by amodiaquine (AQ) promotes spatial memory by enhancing adult hippocampal neurogenesis. However, the role of Nurr1 in the cell cycle regulation of the adult hippocampus has not been investigated. This study aimed to examine changes in the cell cycle-related molecules involved in adult hippocampal neurogenesis induced by Nurr1 pharmacological stimulation. Fluorescence-activated cell sorting (FACS) analysis showed that AQ improved the progression of cell cycle from G0/G1 to S phase in a dose-dependent manner, and MEK1 or PI3K inhibitors attenuated this progression. In addition, AQ treatment increased the expression of cell proliferation markers MCM5 and PCNA, and transcription factor E2F1. Furthermore, pharmacological stimulation of Nurr1 by AQ increased the expression levels of positive cell cycle regulators such as cyclin A and cyclin-dependent kinases (CDK) 2. In contrast, levels of CDK inhibitors p27KIP1 and p57KIP2 were reduced upon treatment with AQ. Similar to the in vitro results, RT-qPCR analysis of AQ-administered mice brains revealed an increase in the levels of markers of cell cycle progression, PCNA, MCM5, and Cdc25a. Finally, AQ administration resulted in decreased p27KIP1 and increased CDK2 levels in the dentate gyrus of the mouse hippocampus, as quantified immunohistochemically. Our results demonstrate that the pharmacological stimulation of Nurr1 in adult hNSCs by AQ promotes the cell cycle by modulating cell cycle-related molecules.

MicroRNA-195: a review of its role in cancers

MicroRNAs (miRNAs) are small and highly conserved noncoding RNAs that regulate gene expression at the posttranscriptional level by binding to the 3′-UTR of target mRNAs. Recently, increasing evidence has highlighted their profound roles in various pathological processes, including human cancers. Deregulated miRNAs function as either oncogenes or tumor suppressor genes in multiple cancer types. Among them, miR-195 has been reported to significantly impact oncogenicity in various neoplasms by binding to critical genes and signaling pathways, enhancing or inhibiting the progression of cancers. In this review, we focus on the expression of miR-195 in regulatory mechanisms and tumor biological processes and discuss the future potential therapeutic implications of diverse types of human malignancies.

Natural Compounds as Modulators of Cell Cycle Arrest: Application for Anticancer Chemotherapies

Natural compounds from various plants, microorganisms and marine species play an important role in the discovery novel components that can be successfully used in numerous biomedical applications, including anticancer therapeutics. Since uncontrolled and rapid cell division is a hallmark of cancer, unraveling the molecular mechanisms underlying mitosis is key to understanding how various natural compounds might function as inhibitors of cell cycle progression. A number of natural compounds that inhibit the cell cycle arrest have proven effective for killing cancer cells in vitro, in vivo and in clinical settings. Significant advances that have been recently made in the understanding of molecular mechanisms underlying the cell cycle regulation using the chemotherapeutic agents is of great importance for improving the efficacy of targeted therapeutics and overcoming resistance to anticancer drugs, especially of natural origin, which inhibit the activities of cyclins and cyclin-dependent kinases, as well as other proteins and enzymes involved in proper regulation of cell cycle leading to controlled cell proliferation.

Dihydroartemisinin alleviates bile duct ligation-induced liver fibrosis and hepatic stellate cell activation by interfering with the PDGF-βR/ERK signaling pathway

Liver fibrosis represents a frequent event following chronic insult to trigger wound healing responses in the liver. Activation of hepatic stellate cells (HSCs), which is a pivotal event during liver fibrogenesis, is accompanied by enhanced expressions of a series of marker proteins and pro-fibrogenic signaling molecules. Artemisinin, a powerful antimalarial medicine, is extracted from the Chinese herb Artemisia annua L., and can inhibit the proliferation of cancer cells. Dihydroartemisinin (DHA), the major active metabolite of artemisinin, is able to attenuate lung injury and fibrosis. However, the effect of DHA on liver fibrosis remains unclear. The aim of this study was to investigate the effect of DHA on bile duct ligation-induced injury and fibrosis in rats. DHA improved the liver histological architecture and attenuated collagen deposition in the fibrotic rat liver. Experiments in vitro showed that DHA inhibited the proliferation of HSCs and arrested the cell cycle at the S checkpoint by altering several cell-cycle regulatory proteins. Moreover, DHA reduced the protein expressions of a-SMA, α1 (I) collagen and fibronectin, being associated with interference of the platelet-derived growth factor β receptor (PDGF-βR)-mediated ERK pathway. These data collectively revealed that DHA relieved liver fibrosis possibly by targeting HSCs via the PDGF-βR/ERK pathway. DHA may be a therapeutic antifibrotic agent for the treatment of hepatic fibrosis.

MLL1 promotes cervical carcinoma cell tumorigenesis and metastasis through interaction with β-catenin

MLL protein genes encode a family of crucial transcription factors that play a key role in multiple cancer development. The functions of different MLL proteins have not been definitively studied. MLL1 is a histone methyltransferase that mediates histone H3 lysine 4, and it has been found to have aberrant expression in several tumors. However, the function of MLL1 in cervical carcinoma is little known. We used tissue analysis, cell culture experiments, and molecular profiling to investigate the mechanism of MLL1 in cervical carcinoma development. We report here that MLL1 is overexpressed in cervical carcinoma tissues and cell lines, and its overexpression is correlated with the tumor grade. Through FACScan flow cytometry assay, we found that MLL1 promotes cell proliferation by promoting the G₁/S transition through transcriptional activation of CCND1 in cervical carcinoma cells. Furthermore, we utilized co-immunoprecipitation and glutathione S-transferase pull-down assays to identify β-catenin as the transcription partner for MLL1 and demonstrated that MLL1 and β-catenin act in synergy in the transcriptional activation of CCND1 in cervical carcinoma cells. In addition, transwell assay and anchorage-independent cell growth assay also revealed that MLL1 promotes metastasis of cervical carcinoma cells through interaction with β-catenin. Our study not only demonstrated a role for MLL1 in the proliferation and metastasis of cervical carcinoma cells but also revealed the interaction of MLL1 with β-catenin to play a different role.

Different cell cycle modifications repress apoptosis at different steps independent of developmental signaling in Drosophila

Genetic manipulations of the cell cycle repress apoptosis independent of developmental signaling. The findings have broader relevance to understanding the coordination of cell proliferation and apoptosis in development and disease.

Apoptotic cell death is important for the normal development of a variety of organisms. Apoptosis is also a response to DNA damage and an important barrier to oncogenesis. The apoptotic response to DNA damage is dampened in specific cell types during development. Developmental signaling pathways can repress apoptosis, and reduced cell proliferation also correlates with a lower apoptotic response. However, because developmental signaling regulates both cell proliferation and apoptosis, the relative contribution of cell division to the apoptotic response has been hard to discern in vivo. Here we use Drosophila oogenesis as an in vivo model system to determine the extent to which cell proliferation influences the apoptotic response to DNA damage. We find that different types of cell cycle modifications are sufficient to repress the apoptotic response to ionizing radiation independent of developmental signaling. The step(s) at which the apoptosis pathway was repressed depended on the type of cell cycle modification—either upstream or downstream of expression of the p53-regulated proapoptotic genes. Our findings have important implications for understanding the coordination of cell proliferation with the apoptotic response in development and disease, including cancer and the tissue-specific responses to radiation therapy.

Anastrozole and everolimus in advanced gynecologic and breast malignancies: activity and molecular alterations in the PI3K/AKT/mTOR pathway

BACKGROUND

Since PI3K/AKT/mTOR pathway activation diminishes the effects of hormone therapy, combining aromatase inhibitors (anatrozole) with mTOR inhibitors (everolimus) was investigated.

PATIENTS AND METHODS

We evaluated anastrozole and everolimus in 55 patients with metastatic estrogen (ER) and/or progesterone receptor (PR)-positive breast and gynecologic tumors. Endpoints were safety, antitumor activity and molecular correlates.

RESULTS

Full doses of anastrozole (1 mg PO daily) and everolimus (10 mg PO daily) were well tolerated. Twelve of 50 evaluable patients (24%) (median = 3 prior therapies) achieved stable disease (SD) ≥ 6 months/partial response (PR)/complete response (CR) (n = 5 (10%) with PR/CR): 9 of 32 (28%) with breast cancer (n=5 (16%) with PR/CR); 2 of 10 (20%), ovarian cancer; and 1 of 6 (17%), endometrial cancer. Six of 22 patients (27%) with molecular alterations in the PI3K/AKT/mTOR pathway achieved SD ≥ 6 months/PR/CR. Six of 8 patients (75%) with SD ≥ 6 months/PR/CR with molecular testing demonstrated at least one alteration in the PI3K/AKT/mTOR pathway: mutations in PIK3CA (n=3) and AKT1 (n=1) or PTEN loss (n=3). All three responders (CR (n = 1); PR (n=2)) who had next generation sequencing demonstrated additional alterations: amplifications in CCNE1, IRS2, MCL1, CCND1, FGFR1 and MYC and a rearrangement in PRKDC.

CONCLUSIONS

Combination anastrozole and everolimus is well tolerated at full approved doses, and is active in heavily-pretreated patients with ER and/or PR-positive breast, ovarian and endometrial cancers. Responses were observed in patients with multiple molecular aberrations. CLINICAL TRAILS INCLUDED: NCT01197170.

Human papillomavirus 16 oncoprotein E7 stimulates UBF1-mediated rDNA gene transcription, inhibiting a p53-independent activity of p14ARF

High-risk human papillomavirus oncoproteins E6 and E7 play a major role in HPV-related cancers. One of the main functions of E7 is the degradation of pRb, while E6 promotes the degradation of p53, inactivating the p14^ARF-p53 pathway. pRb and p14^ARF can repress ribosomal DNA (rDNA) transcription in part by targeting the Upstream Binding Factor 1 (UBF1), a key factor in the activation of RNA polymerase I machinery. We showed, through ectopic expression and siRNA silencing of p14^ARF and/or E7, that E7 stimulates UBF1-mediated rDNA gene transcription, partly because of increased levels of phosphorylated UBF1, preventing the inhibitory function of p14^ARF. Unexpectedly, activation of rDNA gene transcription was higher in cells co-expressing p14^ARF and E7, compared to cells expressing E7 alone. We did not find a difference in P-UBF1 levels that could explain this data. However, p14^ARF expression induced E7 to accumulate into the nucleolus, where rDNA transcription takes place, providing an opportunity for E7 to interact with nucleolar proteins involved in this process. GST-pull down and co-immunoprecipitation assays showed interactions between p14^ARF, UBF1 and E7, although p14^ARF and E7 are not able to directly interact. Co-expression of a pRb-binding-deficient mutant (E7C24G) and p14^ARF resulted in EC24G nucleolar accumulation, but not in a significant higher activation of rDNA transcription, suggesting that the inactivation of pRb is involved in this phenomenon. Thus, p14^ARF fails to prevent E7-mediated UBF1 phosphorylation, but could facilitate nucleolar pRb inactivation by targeting E7 to the nucleolus. While others have reported that p19^ARF, the mouse homologue of p14^ARF, inhibits some functions of E7, we showed that E7 inhibits a p53-independent function of p14^ARF. These results point to a mutually functional interaction between p14^ARF and E7 that might partly explain why the sustained p14^ARF expression observed in most cervical pre-malignant lesions and malignancies may be ineffective.

MicroRNA-195-5p is a potential diagnostic and therapeutic target for breast cancer

MicroRNAs (miRNAs) are a class of highly conserved, small endogenous single-strand non-coding RNAs. They are aberrantly expressed in the circulation and tissue of patients with cancer. Therefore, it has been suggested that they may act as key regulators of carcinogenesis. The aim of the present study was to examine the expression level of miR-195-5p in human breast cancer and its potential role in carcinogenesis. The expression level of miR-195-5p was measured in 40 breast cancer specimens and adjacent normal breast tissues by quantitative polymerase chain reaction (qPCR). Next, to explore the potential function of miR-195-5p, we used MDA-MB-231 human breast cancer cells and carried out MTT, colony formation, Transwell chamber migration and cell cycle assays. The dual-luciferase reporter assay was also performed to determine putative targets of miR-195-5p, which were validated using qPCR and western blot assays. We found that miR-195-5p expression was significantly decreased in the 40 breast cancer specimens when compared with that in the adjacent normal breast tissues (P<0.05). Overexpression of miR-195-5p inhibited cell proliferation, reduced cell colony formation, suppressed cell migration and caused an accumulation of cells in the G1 phase of the cell cycle. In the 3'-untranslated region (3'-UTR) of cyclin E1 (CCNE1), we found two putative target sites which may bind miR-195-5p, suggesting that CCNE1 is a direct target of miR-195-5p. Furthermore, through qPCR and western blot assays we showed that overexpression of miR-195-5p reduced CCNE1 mRNA and protein levels, respectively. Our study suggests that miR-195-5p may act as a tumor suppressor in breast cancer. Therefore, targeting of this miRNA may provide a novel strategy for the diagnosis and treatment of patients with this lethal disease.

MicroRNA-7 arrests cell cycle in G1 phase by directly targeting CCNE1 in human hepatocellular carcinoma cells

Growing evidence has demonstrated that the aberrant expression of miRNA is a hallmark of malignancies, indicating the important roles of miRNA in the development and progression of cancer. MiR-7 is considered as a tumor suppressor miRNA in multiple types of cancer. However, the role of miR-7 in human hepatocellular carcinoma (HCC) and its underlying mechanism remain elusive. In this study, we found that overexpression of miR-7 arrested cell cycle at G1 to S transition in HCC. By combinational use of bioinformatic prediction, reporter assay, quantitative real-time PCR (qRT-PCR) and Western blot, we confirmed that CCNE1, an important mediator in G1/S transition is one of new direct target genes of miR-7. Further studies revealed that silencing of CCNE1 recapitulated the effects of miR-7 overexpression, whereas enforced expression of CCNE1 reversed the suppressive effects of miR-7 in cell cycle regulation. Finally, analysis of qRT-PCR showed a reciprocal relationship between miR-7 and CCNE1 in clinical cancer tissues and multiple types of tumor cell lines. These findings indicate that miR-7 exerts tumor-suppressive effects in hepatocarcinogenesis through the suppression of oncogene CCNE1 expression and suggest a therapeutic application of miR-7 in HCC.

Cell Culture Models and Pharmacological Perspective for the Study of Breast Cancer Markers

Among the most prevalent neoplasias, breast cancer shows an astonishing tendency. Unfortunately this cancer has a high mortality worldwide, requiring sustained management of all actors involved in public health in order to get an early diagnosis and treatment. The methods associated with conventional cytogenetics and molecular cell culture, besides early detection of gene expression patterns associated with cancer susceptibility, have contributed to identify inherited genes and metabolic disorders related to obesity, which are also involved in breast cancer. In any case, a broad study of the above mentioned factors can give a predictive value to support the design of public health models to determine cancer risk in order to decrease the mortality from this disease. (1) Cell cultures offers a wide range of scientific approach for the study of breast cancer, including the analysis of biological function of several compounds in search of increasingly effective treatments with fewer side effects against this malignancy. (2).

Prognostic value of cyclin E expression in breast cancer: a meta-analysis

Cyclin E is an important regulator of cell cycle progression. Various studies examined the relationship between cyclin E overexpression with the clinical outcome in patients with breast cancer but yielded conflicting results. Electronic databases updated to May 2013 were searched to find relevant studies. A meta-analysis was conducted with eligible studies which quantitatively evaluated the relationship between cyclin E overexpression and survival of patients with breast cancer. Survival data were aggregated and quantitatively analyzed. We conducted a final analysis of 7,759 patients from 23 eligible studies and evaluated the correlation between cyclin E overexpression and survival in patients with breast cancer. Combined hazard ratios suggested that cyclin E overexpression had an unfavorable impact on overall survival (OS) (hazard ratio (HR) = 1.30, 95% confidence interval (CI), 1.12-1.49) and breast cancer-specific survival (BCSS) (HR = 1.48, 95% CI, 1.03-1.93), but not disease-free survival (HR = 1.11; 95% CI, 0.96-1.27) in patients with breast cancer. Significantly, risks were found among stage I-II breast cancer for (HR = 1.75; 95% CI, 1.30-2.19). Cyclin E overexpression is associated with poor OS and BCSS in breast cancer.

Complementary and dose-dependent action of AtCCS52A isoforms in endoreduplication and plant size control

· The dimension of organs depends on the number and the size of their component cells. Formation of polyploid cells by endoreduplication cycles is predominantly associated with increases in the cell size and implicated in organ growth. In plants, the CCS52A proteins play a major role in the switch from mitotic to endoreduplication cycles controlling thus the number of mitotic cells and the endoreduplication events in the differentiating cells. · Arabidopsis has two CCS52A isoforms; AtCCS52A1 and AtCCS52A2. Here we focused on their roles in endoreduplication and cell size control during plant development. We demonstrate their complementary and dose-dependent actions that are dependent on their expression patterns. Moreover, the impact of CCS52A overexpression on organ size in transgenic plants was dependent on the expression level; while enhanced expression of the CCS52A genes positively correlated with the ploidy levels, organ sizes were negatively affected by strong overexpression whereas milder overexpression resulted in a significant increase in the organ sizes. · Taken together, these finding support both complementary and dose-dependent actions for the Arabidopsis CCS52A isoforms in plant development and demonstrate that elevated ectopic CCS52A expression positively correlates with organ size, opening a route to higher biomass production.

Targeting low molecular weight cyclin E (LMW-E) in breast cancer

Low molecular weight cyclin E (LMW-E) plays an important oncogenic role in breast cancer. LMW-E, which is not found in normal tissue, can promote the formation of aggressive tumors and can lead to increased genomic instability and tumorigenesis. Additionally, breast cancer patients whose tumors express LMW-E have a very poor prognosis. Therefore, we investigated LMW-E as a potential specific target for treatment either alone or in combination therapy. We hypothesized that because LMW-E binds to CDK2 more efficiently than full length cyclin E, resulting in increased activity, CDK inhibitors could be used to target tumors with LMW-E bound to CDK2. To test the hypothesis, an inducible full length and LMW-E MCF7-Tet-On system was established. Cyclin E (full length (EL) or LMW-E) is only expressed upon induction of the transgene. The doubling times of cells were unchanged when the transgenes were induced. However, upon induction, the kinase activity associated with LMW-E was much higher than that in the EL induced cells or any of the uninduced cells. Additionally only the LMW-E induced cells underwent chromosome aberrations and increased polyploidy. By examining changes in proliferation and survival in cells with induced full length and LMW-E, CDK inhibitors alone were determined to be insufficient to specifically inhibit LMW-E expressing cells. However, in combination with doxorubicin, the CDK inhibitor, roscovitine (seliciclib, CYC202), synergistically led to increased cell death in LMW-E expressing cells. Clinically, the combination of CDK inhibitors and chemotherapy such as doxorubicin provides a viable personalized treatment strategy for those breast cancer patients whose tumors express the LMW-E.

Down-regulation of the cyclin E1 oncogene expression by microRNA-16-1 induces cell cycle arrest in human cancer cells

Cyclin E1 (CCNE1), a positive regulator of the cell cycle, controls the transition of cells from G1 to S phase. In numerous human tumors, however, CCNE1 expression is frequently dysregulated, while the mechanism leading to its dysregulation remains incompletely defined. Herein, we showed that CCNE1 expression was subject to post-transcriptional regulation by a microRNA miR-16-1. This was evident at protein level of CCNE1 as well as its mRNA level. Further evident by dual luciferase reporter assay revealed that two evolutionary conserved binding sites on 3' UTR of CCNE1 were the direct functional target sites. Moreover, we showed that miR-16-1 induced G0/G1 cell cycle arrest by targeting CCNE1 and siRNA against CCNE1 partially phenocopied miR-16-1-induced cell cycle phenotype whereas substantially rescued anti-miR-16-1- induced phenotype. Together, all these results demonstrate that miR-16-1 plays a vital role in modulating cellular process in human cancers and indicate the therapeutic potential of miR-16-1 in cancer therapy.

The chromatin-remodeling protein Osa interacts with CyclinE in Drosophila eye imaginal discs

Coordinating cell proliferation and differentiation is essential during organogenesis. In Drosophila, the photoreceptor, pigment, and support cells of the eye are specified in an orchestrated wave as the morphogenetic furrow passes across the eye imaginal disc. Cells anterior of the furrow are not yet differentiated and remain mitotically active, while most cells in the furrow arrest at G(1) and adopt specific ommatidial fates. We used microarray expression analysis to monitor changes in transcription at the furrow and identified genes whose expression correlates with either proliferation or fate specification. Some of these are members of the Polycomb and Trithorax families that encode epigenetic regulators. Osa is one; it associates with components of the Drosophila SWI/SNF chromatin-remodeling complex. Our studies of this Trithorax factor in eye development implicate Osa as a regulator of the cell cycle: Osa overexpression caused a small-eye phenotype, a reduced number of M- and S-phase cells in eye imaginal discs, and a delay in morphogenetic furrow progression. In addition, we present evidence that Osa interacts genetically and biochemically with CyclinE. Our results suggest a dual mechanism of Osa function in transcriptional regulation and cell cycle control.

Indirect participation of Hsp90 in the regulation of the cyclin E turnover

Cyclin E is the Cdk2-regulatory subunit required for the initiation of DNA replication at the G1/S transition. It accumulates in late G1 phase and gets rapidly degraded by the ubiquitin/proteasome pathway during S phase. The degradation of cyclin E is a consequence of its phosphorylation and subsequent isomerization by the peptidyl-prolyl isomerase Pin1. We show that in the colon cancer cells HT-29 the inhibition of the chaperone function of Hsp90 by geldanamycin (GA) enhances the ubiquitinylation of cyclin E and triggers active degradation via the proteasome pathway. As Hsp90 forms multiprotein complexes with and regulates the function and cell contents of numerous signaling proteins, this observation suggests a direct interaction between Hsp90 and cyclin E. However, experiments using cell lysate fractionation did not reveal the presence of complexes containing both Hsp90 and cyclin E. Coupled transcription/translation experiments also failed to detect the formation of complexes between newly synthesized cyclin E and Hsp90. We conclude that Hsp90 can regulate the degradation of cellular proteins without binding to them, by an indirect mechanism. This conclusion postulates a new category of proteins that are affected by the inactivation of Hsp90. Our observations do not support the possible involvement of a PPIase in this indirect mechanism. Besides, we did not observe active geldanamycin-dependent degradation of cyclin E in the prostate cancer-derived cell line DU-145, indicating that the Hsp90-dependent stabilization of cyclin E requires specific regulatory mechanism which may be lost in certain types of cancer cells.

sSgo1, a major splice variant of Sgo1, functions in centriole cohesion where it is regulated by Plk1

Shugoshin 1 (Sgo1) functions as a protector of centromeric cohesion of sister chromatids in higher eukaryotes. Here, we provide evidence for a previously unrecognized role for Sgo1 in centriole cohesion. Sgo1 depletion via RNA interference induces the formation of multiple centrosome-like structures in mitotic cells that result from the separation of paired centrioles. Sgo1+/- mitotic murine embryonic fibroblasts display split centrosomes. Localization study of two major endogenous splice variants of Sgo1 indicates that the smaller variant, sSgo1, is found at the centrosome in interphase and at spindle poles in mitosis. sSgo1 interacts with Plk1 and its spindle pole localization is Plk1 dependent. Centriole splitting induced by Sgo1 depletion or expression of a dominant negative mutant is suppressed by ectopic expression of sSgo1 or by Plk1 knockdown. Our studies strongly suggest that sSgo1 plays an essential role in protecting centriole cohesion, which is partly regulated by Plk1.

Cyclin E overexpression impairs progression through mitosis by inhibiting APC(Cdh1)

Overexpression of cyclin E, an activator of cyclin-dependent kinase 2, has been linked to human cancer. In cell culture models, the forced expression of cyclin E leads to aneuploidy and polyploidy, which is consistent with a direct role of cyclin E overexpression in tumorigenesis. In this study, we show that the overexpression of cyclin E has a direct effect on progression through the latter stages of mitotic prometaphase before the complete alignment of chromosomes at the metaphase plate. In some cases, such cells fail to divide chromosomes, resulting in polyploidy. In others, cells proceed to anaphase without the complete alignment of chromosomes. These phenotypes can be explained by an ability of overexpressed cyclin E to inhibit residual anaphase-promoting complex (APC^Cdh1) activity that persists as cells progress up to and through the early stages of mitosis, resulting in the abnormal accumulation of APC^Cdh1 substrates as cells enter mitosis. We further show that the accumulation of securin and cyclin B1 can account for the cyclin E–mediated mitotic phenotype.

HuR contributes to cyclin E1 deregulation in MCF-7 breast cancer cells

Many cancers overexpress cyclin E1 and its tumor-specific low molecular weight (LMW) isoforms. However, the mechanism of cyclin E1 deregulation in cancers is still not well understood. We show here that the mRNA-binding protein HuR increases cyclin E1 mRNA stability in MCF-7 breast carcinoma cells. Thus, mRNA stabilization may be a key event in the deregulation of cyclin E1 in MCF-7 cells. Compared with MCF10A immortalized breast epithelial cells, MCF-7 cells overexpress full-length cyclin E1 and its LMW isoforms and exhibit increased cyclin E1 mRNA stability. Increased mRNA stability is associated with a stable adenylation state and an increased ratio of cytoplasmic versus nuclear HuR. UV cross-link competition and UV cross-link immunoprecipitation assays verified that HuR specifically bound to the cyclin E1 3'-untranslated region. Knockdown of HuR with small interfering RNA (siRNA) in MCF-7 cells decreased cyclin E1 mRNA half-life (t(1/2)) and its protein level: a 22% decrease for the full-length isoforms and 80% decrease for the LMW isoforms. HuR siRNA also delayed G(1)-S phase transition and inhibited MCF-7 cell proliferation, which was partially recovered by overexpression of a LMW isoform of cyclin E1. Overexpression of HuR in MCF10A cells increased cyclin E1 mRNA t(1/2) and its protein level. Taken together, our data show that HuR critically contributes to cyclin E1 overexpression and its growth-promoting function, at least in part by increasing cyclin E1 mRNA stability, which provides a new mechanism of cyclin E1 deregulation in breast cancer.

Expression of thymidylate synthase in human cells is an early G(1) event regulated by CDK4 and p16INK4A but not E2F

Thymidylate synthase (TS) is the enzyme that catalyses the last step in de novo thymidylate synthesis. It is of interest clinically because it is an effective target for drugs such as 5-fluorouracil, often used in combination therapy. Despite a number of earlier reports indicating that TS is a cell cycle-dependent enzyme, this remains equivocal. Here, we show that in HCT116 cells synchronised by serum starvation, there is a clear dissociation between the expression of cyclin E (a well-characterised cell-cycle protein) and TS. Although both cyclin E and TS mRNA and protein increased during G₁, TS upregulation was delayed. Moreover, TS levels did not decrease following S-phase completion while cyclin E decreased sharply. Similarly, clear differences were seen between cyclin E and TS as asynchronously growing HCT116 cells were growth-inhibited by low-serum treatment. In contrast to previous reports using rodent cells, adenovirus-mediated over-expression of E2F1 and cyclin E in three human cell lines had no effect on TS. Cell-cycle progression was blocked by treatment of cells with pharmacological inhibitors of CDK2 and CDK4 and by ectopic expression of p16INK4A. Whereas CDK2 inhibition had no effect on TS levels, inhibition of CDK4 was associated with decreased TS protein levels. These results provide the first evidence that drugs targeting CDK4 may be useful with anti-TS drugs as combination therapy for cancer.

Cyclin-dependent kinase 2/cyclin E complex is involved in p120 catenin (p120ctn)-dependent cell growth control: a new role for p120ctn in cancer

Depending on its cellular localization, p120 catenin (p120ctn) can participate in various processes, such as cadherin-dependent cell-cell adhesion, actin cytoskeleton remodeling, and intracellular trafficking. Recent studies also indicate that p120ctn could regulate cell proliferation and contact inhibition. This report describes a new function of p120ctn in the regulation of cell cycle progression. Overexpression of the p120ctn isoform 3A in human colon adenocarcinoma cells (HT-29) results in cytoplasmic accumulation of the protein, as observed in many tumors. This cytoplasmic increase is correlated with a reduction in proliferation and inhibition of DNA synthesis. Under these conditions, experiments on synchronized cells revealed a prolonged S phase associated with cyclin E stabilization. Both confocal microscopy and biochemical analysis showed that cyclin E and cyclin-dependent kinase 2 colocalized with p120ctn in centrosomes during mitosis. These proteins are associated in a functional complex evidenced by coimmunoprecipitation experiments and the emergence of Thr199-phosphorylated nucleophosmin/B23. Such post-translational modification of this centrosomal target has been shown to trigger the initiation of centrosome duplication. Therefore, p120ctn-mediated accumulation of cyclin E in centrosomes may participate in abnormal amplification of centrosomes and the inhibition of DNA replication, thus leading to aberrant mitosis and polyploidy. Because these modifications are often observed in cancer, p120ctn may represent a new therapeutic target for future therapy.

Cytokine and integrin stimulation synergize to promote higher levels of GATA-2, c-myb, and CD34 protein in primary human hematopoietic progenitors from bone marrow

We have previously shown that engagement of the integrins VLA-4 and VLA-5 to the fibronectin fragment CH-296 in combination with cytokines sustained the capacity of cultured human CD34(+) cells to undergo hematopoiesis in immunodeficient mice for 7 to 12 months, whereas this capacity was rapidly lost in cells cultured in suspension with the same cytokines. In the current study, we assessed the molecular pathways that might explain the loss of long-term engraftment capacity in cells cultured in suspension. Although the cell cycle profile was similar between cells cultured in suspension versus on fibronectin, levels of cell death were higher in the suspended cultures. While the CDK inhibitors p27Kip1 and p57Kip2 were present at equal levels in cells from both cultures, low levels of p21Cip1 were detectable only in the cytoplasmic compartment of cells cultured in suspension. Cytoplasmic location of p21Cip1 has been linked to monocytic differentiation. The levels of c-myb and GATA-2, transcription factors associated with stem cell maintenance, were higher in cells cultured on fibronectin as compared with suspension. In contrast, the levels of PU.1, which is induced during myeloid differentiation, were higher in cells cultured in suspension. There were no significant differences in surface expression of CD34 on the cells after culture, but total CD34 protein, assessed by immunoblotting, was significantly higher in cells cultured on fibronectin. Our data suggest that, in the presence of cytokines, the engagement of VLA-4 and VLA-5 integrins to the fibronectin fragment CH-296 preserves the expression of specific transcription factors associated with primitive stem cell maintenance. In contrast, a lack of integrin engagement leads to the induction of cellular markers associated with myeloid differentiation.

Ubiquitylation of cyclin E requires the sequential function of SCF complexes containing distinct hCdc4 isoforms

Cyclin E, an activator of cyclin-dependent kinase 2 (Cdk2), is targeted for proteasomal degradation by phosphorylation-dependent multiubiquitylation via the ubiquitin ligase SCF(hCdc4). SCF ubiquitin ligases are composed of a core of conserved subunits and one variable subunit (an F box protein) involved in substrate recognition. We show here that multiubiquitylation of cyclin E requires the sequential function of two distinct splice variant isoforms of the F box protein hCdc4 known as alpha and gamma. SCF(hCdc4alpha) binds a complex containing cyclin E, Cdk2, and the prolyl cis/trans isomerase Pin1 and promotes the activity of Pin1 without directly ubiquitylating cyclin E. However, due to the action of this SCF(hCdc4alpha)-Pin1 complex, cyclin E becomes an efficient ubiquitylation substrate of SCF(hCdc4gamma). Furthermore, in the context of Cdc4alpha and cyclin E, mutational data suggest that Pin1 isomerizes a noncanonical proline-proline bond, with the possibility that Cdc4alpha may serve as a cofactor for altering the specificity of Pin1.

Detection of Low Molecular Weight Derivatives of Cyclin E1 Is a Function of Cyclin E1 Protein Levels in Breast Cancer

Cyclin E1 regulates the initiation of the S phase program in the mammalian cell division cycle. In normal cells, cyclin E1 protein expression is tightly controlled through a combination of transcriptional and proteolytic regulatory processes. However, in many types of human tumor, cyclin E1 expression is frequently dysregulated, including overexpression, nonperiodic expression relative to cell division, and generation of low molecular weight (LMW) derivatives. LMW derivatives of cyclin E1 have been proposed to be generated by the in vivo proteolytic cleavage of the full-length cyclin E1 protein by a yet to be identified tumor-specific protease. Recently, it was suggested that overexpression of full-length or LMW derivatives of cyclin E1 are independent variables associated with poor outcome in patients with breast cancer. However, we have extensively analyzed cyclin E1 protein expression in primary breast tumors and breast tumor-derived cell lines and found that the ability to detect LMW derivatives of cyclin E1 correlates only with the level of cyclin E1 protein. When cyclin E1 levels on Western blots are normalized, LMW derivatives of cyclin E1 were observed at roughly equal levels in all primary breast tumors, breast tumor-derived cell lines, immortalized nontransformed human mammary epithelial cells, and normal breast tissue. Therefore, the detection of LMW derivatives of cyclin E1 is likely a function of cyclin E1 protein levels, and the activity of the proteolytic machinery responsible for their generation is not a tumor-specific property.

The transcription factor B-Myb is essential for S-phase progression and genomic stability in diploid and polyploid megakaryocytes

The cell-cycle-regulated Myb-family transcription factor B-Myb is crucial during S phase in many diploid cell types. We have examined the expression and function of B-Myb in megakaryocytic differentiation, during which cells progress from a diploid to a polyploid state. In contrast to terminal differentiation of most haematopoietic cells, during which B-myb is rapidly downregulated, differentiation of megakaryocytes is accompanied by continued B-myb RNA and protein expression. Overexpression of B-Myb in a megakaryoblastic cell line resulted in an increase in the number of cells entering S phase and, upon induction of differentiation, the fraction of cells actively endoreplicating increased. By contrast, reduction of B-Myb levels using short interfering (si)RNA resulted in a decline in S-phase progression during both normal and endoreplicative DNA synthesis. This effect correlated with aberrant localisation of initiation of DNA replication within the nucleus and an increased fraction of cells in mitosis. Chromosomal fragmentation and other aberrations, including shorter, thicker chromatids, end-to-end fusion, and loss of a chromatid, suggest that reduced B-Myb activity is also associated with structural chromosomal instability.

Deregulation of cyclin E in human cells interferes with prereplication complex assembly

Deregulation of cyclin E expression has been associated with a broad spectrum of human malignancies. Analysis of DNA replication in cells constitutively expressing cyclin E at levels similar to those observed in a subset of tumor-derived cell lines indicates that initiation of replication and possibly fork movement are severely impaired. Such cells show a specific defect in loading of initiator proteins Mcm4, Mcm7, and to a lesser degree, Mcm2 onto chromatin during telophase and early G1 when Mcm2-7 are normally recruited to license origins of replication. Because minichromosome maintenance complex proteins are thought to function as a heterohexamer, loading of Mcm2-, Mcm4-, and Mcm7-depleted complexes is likely to underlie the S phase defects observed in cyclin E-deregulated cells, consistent with a role for minichromosome maintenance complex proteins in initiation of replication and fork movement. Cyclin E-mediated impairment of DNA replication provides a potential mechanism for chromosome instability observed as a consequence of cyclin E deregulation.

Cell cycle progression without cyclin E/CDK2: breaking down the walls of dogma

G1 is the phase of the cell cycle wherein the cell is responsive to growth factor-dependent signals. As such, G1 regulation is frequently disrupted in cancer through deregulation of cyclin/CDK activity; deregulation of G1 phase provides tumorigenic cells with a growth advantage. Cyclin E, the regulatory cyclin for CDK2, is considered a requisite regulator of G1 progression. Cyclin E is overexpressed in cancer, suggesting that cyclin E/CDK2 deregulation contributes to tumorigenesis. Two papers now challenge both the concept that cyclin E/CDK2 is a requisite component of the cell cycle machine and efforts to develop cyclin E/CDK2 inhibitors as antiproliferative therapeutics.

Immunohistochemical expression of cyclin E in endometrial adenocarcinoma (endometrioid type) and its clinicopathological significance

PURPOSE

Cyclin E is known as a G1-S phase regulatory protein and its abnormal expression has been implicated in cellular proliferation. This study aimed to investigate the correlation of cyclin E expression with tumorigenesis of the endometrium, proliferative activity, and clinicopathological features of endometrial adenocarcinoma.

METHODS

Immunohistochemical staining for cyclin E in addition to cyclin-dependent kinase 2 (cdk2), Ki67, p27, and p53 was performed by the labeled streptavidin-biotin method on formalin-fixed, paraffin-embedded tissues of normal endometria (20 cases), endometrial hyperplasias (20 cases), and endometrial adenocarcinomas (endometrioid type) (127 cases). Positive staining was expressed as a labeling index (LI) based on percentages of positive nuclei in tumor cells.

RESULTS

Immunohistochemistry showed that the nuclei of the cells were positive for cyclin E. Both proliferative and secretory endometria, and endometrial hyperplasia regardless of type were negligible for cyclin E expression. The expression in normal endometrium and hyperplasia was significantly less than that in endometrial adenocarcinomas (P<0.0001). LIs of cyclin E in well-differentiated, moderately differentiated, and poorly differentiated endometrial adenocarcinomas were 31.5+/-33.3%, 37.8+/-31.9%, and 51.1+/-30.8%, respectively. Cyclin E expression increased significantly more in histological grades. The LI of cyclin E in carcinoma was positively correlated with that of cdk2, Ki67, and p53 but not with p27. The cyclin E expression was correlated with myometrial invasion and lymph-vascular space involvement, but not with FIGO stage, lymph node metastasis, coexisting endometrial hyperplasia, estrogen receptor, progesterone receptor, and menopause.

CONCLUSION

Cyclin E as a complex with cdk2 is associated with carcinogenesis and disease progression in endometrial adenocarcinoma, and might be a prognostic indicator of endometrial adenocarcinoma.

High-throughput tissue microarray analysis of G1-cyclin alterations in classical Hodgkin's lymphoma indicates overexpression of cyclin E1

Deregulation of G1-cyclins (CCN) plays a key role in the pathogenesis of many human malignancies, including non-Hodgkin's lymphomas (NHLs). In contrast to NHL, little is known about phenotypic and genotypic changes in the regulation of the cell cycle in classical Hodgkin's lymphoma (cHL). To facilitate analysis of aberrant gene expression in cHL, a lymphoma tissue microarray (TMA) containing 752 cores of 330 different cHL samples was constructed. Direct comparison of Epstein-Barr virus (EBV) latent membrane protein 1 (LMP-1) expression in Hodgkin's and Reed-Sternberg (HRS) cells on conventional full sections with the corresponding duplicate/triplicate tumour cores on the TMA showed a concordance of 100%, indicating that cHL-TMA is a reliable and representative method for evaluating gene expression profiles in situ. Using TMA technology, protein expression and gene amplification of different G1-CCNs in cHL were analysed. Among the G1-CCNs analysed, cyclin E (CCNE) was expressed in 212/253 cases (84%). In most of the individual tumours, over 75% of the HRS cells stained positive for CCNE, suggesting that CCNE is overexpressed in cHL. This overexpression was not due to CCNE gene amplification, as judged by fluorescence in situ hybridization, and did not correlate with EBV infection, as assessed by the expression of LMP-1. Thus, the overexpression of CCNE could be caused by profound changes in HRS cell-cycle regulation that could contribute to the malignant phenotype.

Human cytomegalovirus immediate-early protein 2 (IE2)-mediated activation of cyclin E is cell-cycle-independent and forces S-phase entry in IE2-arrested cells

In human cytomegalovirus (HCMV) infection, the isolated expression of the viral immediate-early protein 2 (IE2) 86 kDa regulatory protein coincides with an up-regulation of cyclin E gene expression, both in fibroblasts and U373 cells. Since IE2 also interferes with cell-cycle progression, it is unclear whether IE2 is a genuine activator of cyclin E or whether IE2-arrested cells contain elevated levels of cyclin E primarily as a consequence of them being arrested at the beginning of S phase. It is important to distinguish between these possibilities in order to define and analyse at a mechanistic level the proliferative and anti-proliferative capacities of IE2. Here we have shown that IE2 can activate cyclin E independent of the cell-cycle state and can therefore function as a genuine activator of cyclin E gene expression. A mutant of IE2 that failed to activate cyclin E also failed to promote G1/S transition. Instead, cells became arrested in G1. S-phase entry could be rescued in these cells by co-expression of cyclin E, but these cells still arrested in early S phase, as is the case with wild-type IE2. Our data demonstrate that IE2 can promote two independent cell-cycle functions at the same time: (i) the induction of G1/S transition via up-regulation of cyclin E, and (ii) a block in cell-cycle progression in early S phase. In G1, the proliferative activity of IE2 appears to be dominant over the anti-proliferative force, whereas after G1/S transition, this situation is reversed.

Aberrant ubiquitin-mediated proteolysis of cell cycle regulatory proteins and oncogenesis

The ubiquitin pathway plays a central role in the regulation of cell growth and cell proliferation by controlling the abundance of key cell cycle proteins. Increasing evidence indicates that unscheduled proteolysis of many cell cycle regulators contributes significantly to tumorigenesis and is indeed found in many types of human cancers. Aberrant proteolysis with oncogenic potential is elicited by two major mechanisms: defective degradation of positive cell cycle regulators (i.e., proto-oncoproteins) and enhanced degradation of negative cell cycle regulators (i.e., tumor suppressor proteins). In many cases, increased protein stability is a result of mutations in the substrate that prevent the recognition of the protein by the ubiquitin-mediated degradation machinery. Alternatively, the specific recognition proteins mediating ubiquitination (ubiquitin ligases) are not expressed or harbor mutations rendering them inactive. In contrast, the overexpression of a ubiquitin ligase may result in the enhanced degradation of a negative cell cycle regulator. This chapter aims to review the involvement of the ubiquitin pathway in the scheduled destruction of some important cell cycle regulators and to discuss the implications of their aberrant degradation for the development of cancer.

E7070: a novel synthetic sulfonamide targeting the cell cycle progression for the treatment of cancer

Cell cycle regulation and cell growth are interesting targets in the search for new antitumor agents as these processes are highly disturbed in malignant cells. E7070 is a novel synthetic sulfon-amide that targets the G1 phase of the cell cycle and is currently in clinical development for the treatment of solid tumors. The potential antitumor activity of the compound was discovered through optimization of the structure-activity relationships of a series of sulfonamide structures. E7070 causes a blockade in the G1/S transition through inhibition of the activation of both cyclin-dependent kinase 2 and cyclin E. Preclinical studies with E7070 showed activity in multiple tumor types, most prominently in colon and lung cancer. A phase I clinical program was conducted with E7070 evaluating different treatment regimens. Dose-limiting toxicities were hematological, including neutropenia and thrombocytopenia. Preliminary results of phase II studies demonstrated limited antitumor activity following treatment with E7070 as single agent in heavily pretreated patients with non-small cell lung and colon cancer. Studies evaluating the activity of E7070 in combination with other chemotherapeutic agents are being conducted.

Protease inhibitor-induced stabilization of p21(waf1/cip1) and cell-cycle arrest in chemical carcinogen-exposed mammary and lung cells

In previous studies, we have shown that human breast and lung carcinoma cells and mouse nontransformed type II lung cells fail to undergo cell-cycle arrest in G(1) phase in response to treatment with hydrocarbon carcinogens but rather accumulate in the S phase with damaged DNA. This situation may lead to replication of DNA on a damaged template and enhance frequency of mutations. The mechanism of this G(1) arrest failure was examined. Western immunoblot analyses of MCF7 human mammary cancer cells exposed to actinomycin D (used as a positive control for G(1) cell-cycle arrest) or hydrocarbon carcinogens revealed that while all of these chemicals caused an increase in p53, only trace levels of p21(waf1/cip1) protein were observed in the hydrocarbon carcinogen-treated samples. Similarly, in murine lung E10 type II cells, p53 but not p21(waf1/cip1) protein increased in response to benzo[a]pyrene dihydrodiol epoxide. Treatment of either MCF7 mammary or E10 lung cells with the protease inhibitor calpain I resulted in increased levels of p21(waf1/cip1) protein and enhancement of arrest of the cells in early phases of the cell cycle (G(1) and early S phase). The results suggest that failure of cell-cycle arrest in carcinogen-treated mammary and lung cells is related to increased protease-mediated degradation of p21(waf1/cip1) and/or related regulatory proteins.

Human F-box protein hCdc4 targets cyclin E for proteolysis and is mutated in a breast cancer cell line

Cyclin E, one of the activators of the cyclin-dependent kinase Cdk2, is expressed near the G1-S phase transition and is thought to be critical for the initiation of DNA replication and other S-phase functions. Accumulation of cyclin E at the G1-S boundary is achieved by periodic transcription coupled with regulated proteolysis linked to autophosphorylation of cyclin E. The proper timing and amplitude of cyclin E expression seem to be important, because elevated levels of cyclin E have been associated with a variety of malignancies and constitutive expression of cyclin E leads to genomic instability. Here we show that turnover of phosphorylated cyclin E depends on an SCF-type protein-ubiquitin ligase that contains the human homologue of yeast Cdc4, which is an F-box protein containing repeated sequences of WD40 (a unit containing about 40 residues with tryptophan (W) and aspartic acid (D) at defined positions). The gene encoding hCdc4 was found to be mutated in a cell line derived from breast cancer that expressed extremely high levels of cyclin E.

Polyamine depletion stabilizes p53 resulting in inhibition of normal intestinal epithelial cell proliferation

The p53 nuclear phosphoprotein plays a critical role in transcriptional regulation of target genes involved in growth arrest and apoptosis. The natural polyamines, including spermidine, spermine, and their precursor putrescine, are required for cell proliferation, and decreasing cellular polyamines inhibits growth of the small intestinal mucosa. In the current study, we investigated the mechanisms of regulation of p53 gene expression by cellular polyamines and further determined the role of the gene product in the process of growth inhibition after polyamine depletion. Studies were conducted both in vivo and in vitro using rats and the IEC-6 cell line, derived from rat small intestinal crypt cells. Levels for p53 mRNA and protein, transcription and posttranscription of the p53 gene, and cell growth were examined. Depletion of cellular polyamines by treatment with alpha-difluoromethylornithine (DFMO) increased p53 gene expression and caused growth inhibition in the intact small intestinal mucosa and the cultured cells. Polyamine depletion dramatically increased the stability of p53 mRNA as measured by the mRNA half-life but had no effect on p53 gene transcription in IEC-6 cells. Induction of p53 mRNA levels in DFMO-treated cells was paralleled by an increase in the rate of newly synthesized p53 protein. The stability of p53 protein was also increased after polyamine depletion, which was associated with a decrease in Mdm2 expression. When polyamine-deficient cells were exposed to exogenous spermidine, a decrease in p53 gene expression preceded an increase in cellular DNA synthesis. Inhibition of the p53 gene expression by using p53 antisense oligodeoxyribonucleotides significantly promoted cell growth in the presence of DFMO. These findings indicate that polyamines downregulate p53 gene expression posttranscriptionally and that growth inhibition of small intestinal mucosa after polyamine depletion is mediated, at least partially, through the activation of p53 gene.