Recycling the cell cycle: cyclins revisited

Salivary protein histatin 3 regulates cell proliferation by enhancing p27(Kip1) and heat shock cognate protein 70 ubiquitination

Histatins are salivary proteins with antimicrobial activities. We previously reported that histatin 3 binds to heat shock cognate protein 70 (HSC70), which is constitutively expressed, and induces DNA synthesis stimulation and promotes human gingival fibroblast (HGF) survival. However, the underlying mechanisms of histatin 3 remain largely unknown. Here, we found that the KRHH sequence of histatin 3 at the amino acid positions 5-8 was essential for enhancing p27(Kip1) (a cyclin-dependent kinase inhibitor) binding to HSC70 that occurred in a dose-dependent manner; histatin 3 enhanced the binding between p27(Kip1) and HSC70 during the G1/S transition of HGFs as opposed to histatin 3-M(5-8) (substitution of KRHH for EEDD in histatin 3). Histatin 3, but not histatin 3-M(5-8), stimulated DNA synthesis and promoted HGF survival. Histatin 3 dose-dependently enhanced both p27(Kip1) and HSC70 ubiquitination, whereas histatin 3-M(5-8) did not. These findings provide further evidence that histatin 3 may be involved in the regulation of cell proliferation, particularly during G1/S transition, via the ubiquitin-proteasome system of p27(Kip1) and HSC70.

Metabolomic Applications to the Characterization of the Mode-of-Action of CDK Inhibitors

Cyclin-dependent kinases (CDKs) regulate cell cycle progression, and some of them are also involved in the control of cellular transcription. Dysregulation of these critical cellular processes, due to the aberrant expression of some of these proteins, is common in many neoplastic malignancies. Consequently, the development of chemical compounds capable of inhibiting the biological activity of CDKs represents an attractive strategy in the anticancer area. CDK inhibition can trigger apoptosis and could be particularly useful in hematological malignancies, which are more sensitive to inhibition of cell cycle and apoptosis induction. Over the last few years, a number of pharmacological inhibitors of CDKs (CDKIs) belonging to different chemical families have been developed, and some of them have been tested in clinical trials. Given the complexity of the role of CDKs in cell functioning, it would be desirable to develop new tools that could facilitate a better understanding of the new insights into CDK functions and the mode-of-actions of CDKIs. In this context, this chapter describes an experimental approach to evaluate the metabolic consequences of CDKIs at the cellular level based on metabolomics by NMR. More specifically, a description of a strategy to characterize the biochemical effects of CDKIs acting on mammalian cells is provided, including protocols for the extraction of hydrophilic and lipophilic metabolites, the acquisition of 1D and 2D metabolomic Nuclear Magnetic Resonance (NMR) experiments, the identification and quantification of metabolites, and the annotation of the results in the context of biochemical pathways.

Measurement of Cdk1/Cyclin B Kinase Activity by Specific Antibodies and Western Blotting

Quantitative measurement of enzyme activity is a valuable approach to study how cells function. We present a method to measure the activity of the enzyme Cdk1/cyclin B. This enzyme is required by all eukaryotic cells to enter mitosis. Therefore, a biochemical assay to measure Cdk1/cyclin B activity can be used to identify cell populations that are in mitosis or to detect inhibitors of Cdk1/Cyclin B in vitro. A key distinction of the method presented here, compared to others, is that it uses a recombinant protein, a specific antibody, and a western blot apparatus, which makes the technique available to cell and molecular biology laboratories who do not wish to use radioisotopes, which are commonly required for other protein kinase assays.

Comparative analysis of basaloid and conventional squamous cell carcinomas of the esophagus: prognostic relevance of clinicopathological features and protein expression

Basaloid squamous cell carcinoma (BSCC), a variant of squamous cell carcinoma (SCC), is a rare and aggressive epithelial malignancy which has been reported in only 0.1-11 % of primary esophageal carcinomas. In this study, a comparison of clinicopathological features and protein expression between esophageal BSCC (EBSCC) and conventional esophageal SCC (ESCC) cases from Brazil was performed in order to find factors that can be relevant to better characterize EBSCC. The expression of HER2, epidermal growth factor receptor (EGFR), Ki-67, and cyclins (A, B1, and D1) in 111 cases (95 ESCC and 16 EBSCC) was evaluated by immunohistochemistry using tissue microarray. When the clinicopathological data were compared, no significant difference was found between the two histological types. Although the difference is not significant (p = 0.055), the EGFR expression was more frequent in the conventional ESCC than in the EBSCC group. Our results indicate that the clinicopathological profiles of conventional ESCC and EBSCC are similar and provide no indicators for differences in prognosis between these two groups.

Targeting ubiquitination for cancer therapies

Ubiquitination, the structured degradation and turnover of cellular proteins, is regulated by the ubiquitin-proteasome system (UPS). Most proteins that are critical for cellular regulations and functions are targets of the process. Ubiquitination is comprised of a sequence of three enzymatic steps, and aberrations in the pathway can lead to tumor development and progression as observed in many cancer types. Recent evidence indicates that targeting the UPS is effective for certain cancer treatment, but many more potential targets might have been previously overlooked. In this review, we will discuss the current state of small molecules that target various elements of ubiquitination. Special attention will be given to novel inhibitors of E3 ubiquitin ligases, especially those in the SCF family.

Human embryos commonly form abnormal nuclei during development: a mechanism of DNA damage, embryonic aneuploidy, and developmental arrest

STUDY QUESTION

What is the prevalence and developmental significance of morphologic nuclear abnormalities in human preimplantation embryos?

SUMMARY ANSWER

Nuclear abnormalities are commonly found in human IVF embryos and are associated with DNA damage, aneuploidy, and decreased developmental potential.

WHAT IS KNOWN ALREADY

Early human embryonic development is complicated by genomic errors that occur after fertilization. The appearance of extra-nuclear DNA, which has been observed in IVF, may be a result of such errors. However, the mechanism by which abnormal nuclei form and the impact on DNA integrity and embryonic development is not understood.

STUDY DESIGN, SIZE, DURATION

Cryopreserved human cleavage-stage embryos (n = 150) and cryopreserved blastocysts (n = 105) from clinical IVF cycles performed between 1997 and 2008 were donated for research. Fresh embryos (n = 60) of poor quality that were slated for discard were also used. Immunohistochemical, microscopic and cytogenetic analyses at different developmental stages and morphologic grades were performed.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Embryos were fixed and stained for DNA, centromeres, mitotic activity and DNA damage and imaged using confocal microscopy. Rates of abnormal nuclear formation were compared between morphologically normal cleavage-stage embryos, morphologically normal blastocysts, and poor quality embryos. To control for clinical and IVF history of oocytes donors, and quality of frozen embryos within our sample, cleavage-stage embryos (n = 52) were thawed and fixed at different stages of development and then analyzed microscopically. Cleavage-stage embryos (n = 9) were thawed and all blastomeres (n = 62) were disaggregated, imaged and analyzed for karyotype. Correlations were made between microscopic and cytogenetic findings of individual blastomeres and whole embryos.

MAIN RESULTS AND THE ROLE OF CHANCE

The frequency of microscopic nuclear abnormalities was lower in blastocysts (5%; 177/3737 cells) than in cleavage-stage embryos (16%, 103/640 blastomeres, P < 0.05) and highest in arrested embryos (65%; 44/68 blastomeres, P < 0.05). DNA damage was significantly higher in cells with microscopic nuclear abnormalities (γH2AX (phosphorylated (Ser139) histone H2A.X): 87.1%, 74/85; replication protein A: 72.9%, 62/85) relative to cells with normal nuclear morphology (γH2AX: 9.3%, 60/642; RPA: 5.6%, 36/642) (P < 0.05). Blastomeres containing nuclear abnormalities were strongly associated with aneuploidy (Fisher exact test, two-tailed, P < 0.01).

LIMITATIONS, REASONS FOR CAUTION

The embryos used were de-identified, and the clinical and IVF history was unknown.

WIDER IMPLICATIONS OF THE FINDINGS

This study explores a mechanism of abnormal embryonic development post-fertilization. While most of the current data have explored abnormal meiotic chromosome segregation in oocytes as a primary mechanism of reproductive failure, abnormal nuclear formation during early mitotic cell division in IVF embryos also plays a significant role. The detection of abnormal nuclear formation may have clinical application in noninvasive embryo selection during IVF.

STUDY FUNDING/COMPETING INTERESTS

The study was supported by Columbia University and the New York Stem Cell Foundation. Authors declare no competing interest.

Isoflavone lupiwighteone induces cytotoxic, apoptotic, and antiangiogenic activities in DU-145 prostate cancer cells

Isoflavones constitute a large series of compounds found in many plants. They make up an important part of the diet and have a broad spectrum of biological activities such as cytotoxic and antitumor effects. Lupiwighteone (Lup) is an isoflavone-type compound. It is distributed widely in wild-growing plants such as Glycyrrhiza glabra, Lupinus, and Lotus pedunculatus. On the basis of existing research, Lup shows antioxidant and antimicrobial effects, but its antitumor activity has not been reported as yet. This study aimed to examine the antitumor activity of Lup, explore its antitumor mechanism in a human prostate carcinoma cell line (DU-145), and evaluate its antiangiogenetic activity in the human umbilical vein endothelial cell line (HUVEC). The results showed that Lup could inhibit the growth of DU-145 and HUVEC cells in a concentration-dependent and time-dependent manner by a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay. Flow cytometry analysis indicated that Lup could induce cell cycle arrest, cells apoptosis, mitochondrial membrane potential loss, and an increase in intracellular reactive oxygen species of DU-145 cells. Upregulation of Bax, cytochrome c, caspase-3, and PARP-1 protein expressions and downregulation of Bcl-2, procaspase-9, and p-Akt protein expressions were observed by western blot after the treatment of Lup. Furthermore, the effects of Lup on the cellular behavior of HUVECs were also investigated. Altogether, our data proved the anticancer and antiangiogenesis potential of Lup.

Mitogen-activated protein kinase kinase 3 induces cell cycle arrest via p38 activation mediated Bmi-1 downregulation in hepatocellular carcinoma

The underlying molecular pathogenesis of hepatocellular carcinoma (HCC) remains poorly understood. Mitogen-activated protein kinase kinase 3 (MKK3), has been reported as a novel tumor suppressor in breast cancer. However, its potential suppressive role in HCC has not been evaluated. In the current study, the biologic functions of MKK3 in HCC were investigated and a previously unreported cell cycle regulation mechanism was observed. MKK3 overexpression suppressed HepG2 and PLC‑PRF‑5 cell proliferation and induced cell cycle arrest in the two cell lines. In addition, MKK3 overexpression upregulated the cyclin-dependent kinase inhibitors, p16 INK4A and p15 INK4B in HCC cells. Their negative regulator, Bim‑1, was downregulated following MKK3 overexpression. Moreover, MKK3 activated p38 in HCC cells and SB203580, a p38 inhibitor, reversed the tumor suppressive effect of MKK3. In conclusion, the results identify MKK3 as a tumor suppressor and highlighted the significance of p38 pathway aberration in HCC.

Plasmodium P-Type Cyclin CYC3 Modulates Endomitotic Growth during Oocyst Development in Mosquitoes

Cell-cycle progression and cell division in eukaryotes are governed in part by the cyclin family and their regulation of cyclin-dependent kinases (CDKs). Cyclins are very well characterised in model systems such as yeast and human cells, but surprisingly little is known about their number and role in Plasmodium, the unicellular protozoan parasite that causes malaria. Malaria parasite cell division and proliferation differs from that of many eukaryotes. During its life cycle it undergoes two types of mitosis: endomitosis in asexual stages and an extremely rapid mitotic process during male gametogenesis. Both schizogony (producing merozoites) in host liver and red blood cells, and sporogony (producing sporozoites) in the mosquito vector, are endomitotic with repeated nuclear replication, without chromosome condensation, before cell division. The role of specific cyclins during Plasmodium cell proliferation was unknown. We show here that the Plasmodium genome contains only three cyclin genes, representing an unusual repertoire of cyclin classes. Expression and reverse genetic analyses of the single Plant (P)-type cyclin, CYC3, in the rodent malaria parasite, Plasmodium berghei, revealed a cytoplasmic and nuclear location of the GFP-tagged protein throughout the lifecycle. Deletion of cyc3 resulted in defects in size, number and growth of oocysts, with abnormalities in budding and sporozoite formation. Furthermore, global transcript analysis of the cyc3-deleted and wild type parasites at gametocyte and ookinete stages identified differentially expressed genes required for signalling, invasion and oocyst development. Collectively these data suggest that cyc3 modulates oocyst endomitotic development in Plasmodium berghei.

The malaria parasite is a single-celled organism that multiplies asexually in a non-canonical way in both vertebrate host and mosquito vector. In the mosquito midgut, atypical cell division occurs in oocysts, where repeated nuclear division (endomitosis) precedes cell division, which then gives rise to many sporozoites in a process known as sporogony. The molecular mechanisms controlling this process are poorly understood. In many model organisms including mouse and yeast cells the cell cycle is regulated by members of the cyclin protein family, but the role of this family in the malaria parasite is unknown. Here, we show that there are only three cyclin genes and investigate the function of the single P-type cyclin (CYC3) in the rodent malaria parasite, Plasmodium berghei. We show that CYC3 has a cytoplasmic and nuclear localisation throughout most of the parasite lifecycle and by gene deletion we demonstrate that CYC3 is important for normal oocyst development, maturation and sporozoite formation. Moreover, we show that deletion of cyc3 affects the transcription of genes required for cell signalling and oocyst development. The data suggest that CYC3 modulates asexual multiplication in oocysts and plays a vital role in parasite development in the mosquito.

Adapalene inhibits the activity of cyclin-dependent kinase 2 in colorectal carcinoma

Cyclin-dependent kinase 2 (CDK2) has been reported to be overexpressed in human colorectal cancer; it is responsible for the G1‑to‑S‑phase transition in the cell cycle and its deregulation is a hallmark of cancer. The present study was the first to use idock, a free and open‑source protein‑ligand docking software developed by our group, to identify potential CDK2 inhibitors from 4,311 US Food and Drug Administration‑approved small molecular drugs with a re‑purposing strategy. Among the top compounds identified by idock score, nine were selected for further study. Among them, adapalene (ADA; CD271,6‑[3‑(1‑adamantyl)‑4‑methoxyphenyl]‑2‑naphtoic acid) exhibited the highest anti‑proliferative effects in LOVO and DLD1 human colon cancer cell lines. Consistent with the expected properties of CDK2 inhibitors, the present study demonstrated that ADA significantly increased the G1‑phase population and decreased the expression of CDK2, cyclin E and retinoblastoma protein (Rb), as well as the phosphorylation of CDK2 (on Thr‑160) and Rb (on Ser‑795). Furthermore, the anti‑cancer effects of ADA were examined in vivo on xenograft tumors derived from DLD1 human colorectal cancer cells subcutaneously inoculated in BALB/C nude mice. ADA (20 mg/kg orally) exhibited marked anti‑tumor activity, comparable to that of oxaliplatin (40 mg/kg), and dose‑dependently inhibited tumor growth (P<0.05), while combined administration of ADA and oxaliplatin produced the highest therapeutic effect. To the best of our knowledge, the present study was the first to indicate that ADA inhibits CDK2 and is a potential candidate drug for the treatment of human colorectal cancer.

Role of dual specificity tyrosine-phosphorylation-regulated kinase 1B (Dyrk1B) in S-phase entry of HPV E7 expressing cells from quiescence

The high-risk human papillomavirus (HPV) is the causative agent for cervical cancer. The HPV E7 oncogene promotes S-phase entry from quiescent state in the presence of elevated cell cycle inhibitor p27Kip1, a function that may contribute to carcinogenesis. However, the mechanism by which HPV E7 induces quiescent cells to entry into S-phase is not fully understood. Interestingly, we found that Dyrk1B, a dual-specificity kinase and negative regulator of cell proliferation in quiescent cells, was upregulated in E7 expressing cells. Surprisingly and in contrast to what was previously reported, Dyrk1B played a positive role in S-phase entry of quiescent HPV E7 expressing cells. Mechanistically, Dyrk1B contributed to p27 phosphorylation (at serine 10 and threonine 198), which was important for the proliferation of HPV E7 expressing cells. Moreover, Dyrk1B up-regulated HPV E7. Taken together, our studies uncovered a novel function of Dyrk1B in high-risk HPV E7-mediated cell proliferation. Dyrk1B may serve as a target for therapy in HPV-associated cancers.

CHARACTERIZATION AND CELULAR PROLIFERATION OF OVARIAN STRUCTURES OF EWES BY THE TECHNIQUE OF AGNOR: OVARIAN MORFOMETRY AND CORRELATIONS

The AgNOR staining technique for nucleolar organizer regions (NORs) is characterized by marking proteins related to ribossomal ribonucleic acid evaluating celular proliferation. The objective was to study the ovarian morphometry and the value of AgNOR thecnique application to evaluate the proliferation of healthy cels from ovarian structures in crossbred ewe. 102 pairs of ovaries were collected and from the largest follicle of each ovary was measured its diameter. From the largest corpus luteum (CL) was measured the diameter and width, classifying the CL in: included, protruberant, massive and cavity, followed by AgNOR staining. The significance level was 5%. It had difference (p<0.05) for the diameter of the largest follicle between right (RO): 4.2±2,3mm and left (LO): 3.6±2,2mm sides. There was a correlation (p<0.01) between the NORs of internal theca (IT) and external theca (ET): RO (0.46) and LO (0.61); NORs of granulosa and IT: RO (0.54) and LO (0.59); and NORs of granulosa and ET: RO (0.34) and LO (0.38). Was conclude that the NORs quantification was appropriate to study the determination of the potential for ovarian structures proliferation, which was similar for right and left sides.

A novel DAG-dependent mechanism links PKCɑ and Cyclin B1 regulating cell cycle progression

Through the years, different studies showed the involvement of Protein Kinase C (PKC) in cell cycle control, in particular during G1/S transition. Little is known about their role at G2/M checkpoint. In this study, using K562 human erythroleukemia cell line, we found a novel and specific mechanism through which the conventional isoform PKC⍺ positively affects Cyclin B1 modulating G2/M progression of cell cycle. Since the kinase activity of this PKC isoform was not necessary in this process, we demonstrated that PKC⍺, physically interacting with Cyclin B1, avoided its degradation and stimulated its nuclear import at mitosis. Moreover, the process resulted to be strictly connected with the increase in nuclear diacylglycerol levels (DAG) at G2/M checkpoint, due to the activity of nuclear Phospholipase C β1 (PLCβ1), the only PLC isoform mainly localized in the nucleus of K562 cells. Taken together, our findings indicated a novel DAG dependent mechanism able to regulate the G2/M progression of the cell cycle.

Role of Cdk1 in DNA damage-induced G1 checkpoint abrogation by the human papillomavirus E7 oncogene

The high-risk human papillomavirus (HPV) E7 oncogene abrogates DNA damage-induced G1 checkpoint but the mechanism is not fully understood. The G1 kinase Cdk2 is activated in E7-expressing cells. However, whether Cdk2 is required for E7 to abrogate the G1 checkpoint is not known. Accumulating evidence implicates a role for the mitotic Cdk1 in G1/S phase transition in the absence of Cdk2. We therefore examined the expression and requirement of Cdk1 and Cdk2 in the G1 checkpoint abrogation in E7-expressing cells. Although both Cdk1 and Cdk2 were up-regulated in E7-expressing cells upon DNA damage, down-regulation of Cdk1 but not Cdk2 impairs the ability of E7 to abrogate the G1 checkpoint. Our study thus demonstrated an important role for Cdk1 in bypassing the G1 checkpoint in E7-expressing cells. To understand the mechanism by which E7 activates Cdk1, we examined the transcription factor B-Myb. Our studies demonstrated that downregulation of B-Myb reduced the steady-state level of Cdk1 and induced G1 arrest in E7-expressing cells upon DNA damage. In addition, it remains a mystery how E7 promotes cell cycle progression in the presence of Cdk inhibitor p21. As p21 binds Cdk1 with lower affinity than Cdk2, our results suggest a mechanism by which E7 bypasses the inhibitory effect of p21. Nonetheless, our studies demonstrated that p21 still possessed partial ability to arrest cells at G1 phase in E7-expressing cells. These studies shed light on mechanisms by which HPV E7 modulates cell cycle checkpoint.

The Non-Canonical Role of Aurora-A in DNA Replication

Aurora-A is a well-known mitotic kinase that regulates mitotic entry, spindle formation, and chromosome maturation as a canonical role. During mitosis, Aurora-A protein is stabilized by its phosphorylation at Ser51 via blocking anaphase-promoting complex/cyclosome-mediated proteolysis. Importantly, overexpression and/or hyperactivation of Aurora-A is involved in tumorigenesis via aneuploidy and genomic instability. Recently, the novel function of Aurora-A for DNA replication has been revealed. In mammalian cells, DNA replication is strictly regulated for preventing over-replication. Pre-replication complex (pre-RC) formation is required for DNA replication as an initiation step occurring at the origin of replication. The timing of pre-RC formation depends on the protein level of geminin, which is controlled by the ubiquitin–proteasome pathway. Aurora-A phosphorylates geminin to prevent its ubiquitin-mediated proteolysis at the mitotic phase to ensure proper pre-RC formation and ensuing DNA replication. In this review, we introduce the novel non-canonical role of Aurora-A in DNA replication.

Amantadine inhibits cellular proliferation and induces the apoptosis of hepatocellular cancer cells in vitro

Hepatocellular carcinoma (HCC) is one of the most aggressive malignancies worldwide, and its incidence associated with viral infection has increased in recent years. Amantadine is a tricyclic symmetric amine that can effectively protect against the hepatitis C virus. However, its antitumor properties remain unclear. In the present study, the effects of amantadine on tumor cell viability, cell cycle regulation and apoptosis were investigated. The growth of HepG2 and SMMC‑7721 cells (HCC cell lines) was detected by an MTT assay. Flow cytometry was used to investigate cell cycle regulation and apoptosis. Reverse transcription‑quantitative polymerase chain reaction and western blot analysis were also performed to examine the expression of cell cycle‑ and apoptosis‑related genes and proteins, including cyclin E, cyclin D1, cyclin‑dependent kinase 2 (CDK2), B‑cell lymphoma 2 (Bcl‑2) and Bax. Our results demonstrated that amantadine markedly inhibited the proliferation of HepG2 and SMMC‑7721 cells in a dose‑ and time‑dependent manner and arrested the cell cycle at the G0/G1 phase. The levels of the cell cycle‑related genes and proteins (cyclin D1, cyclin E and CDK2) were reduced by amantadine, and apoptosis was significantly induced. Amantadine treatment also reduced Bcl‑2 and increased the Bax protein and mRNA levels. Additionally, Bcl‑2/Bax ratios were lower in the two HCC cell lines following amantadine treatment. Collectively, these results emphasize the role of amantadine in suppressing proliferation and inducing apoptosis in HCC cells, advocating its use as a novel tumor-suppressive therapeutic candidate.

DNAJs: more than substrate delivery to HSPA

Proteins are essential components of cellular life, as building blocks, but also to guide and execute all cellular processes. Proteins require a three-dimensional folding, which is constantly being challenged by their environment. Challenges including elevated temperatures or redox changes can alter this fold and result in misfolding of proteins or even aggregation. Cells are equipped with several pathways that can deal with protein stress. Together, these pathways are referred to as the protein quality control network. The network comprises degradation and (re)folding pathways that are intertwined due to the sharing of components and by the overlap in affinity for substrates. Here, we will give examples of this sharing and intertwinement of protein degradation and protein folding and discuss how the fate of a substrate is determined. We will focus on the ubiquitylation of substrates and the role of Hsp70 co-chaperones of the DNAJ class in this process.

Effects of Antidepressants on DSP4/CPT-Induced DNA Damage Response in Neuroblastoma SH-SY5Y Cells

DNA damage is a form of cell stress and injury. Increased systemic DNA damage is related to the pathogenic development of neurodegenerative diseases. Depression occurs in a relatively high percentage of patients suffering from degenerative diseases, for whom antidepressants are often used to relieve depressive symptoms. However, few studies have attempted to elucidate why different groups of antidepressants have similar effects on relieving symptoms of depression. Previously, we demonstrated that neurotoxins N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4)- and camptothecin (CPT) induced the DNA damage response in SH-SY5Y cells, and DSP4 caused cell cycle arrest which was predominately in the S-phase. The present study shows that CPT treatment also resulted in similar cell cycle arrest. Some classic antidepressants could reduce the DNA damage response induced by DSP4 or CPT in SH-SY5Y cells. Cell viability examination demonstrated that both DSP4 and CPT caused cell death, which was prevented by spontaneous administration of some tested antidepressants. Flow cytometric analysis demonstrated that a majority of the tested antidepressants protect cells from being arrested in S-phase. These results suggest that blocking the DNA damage response may be an important pharmacologic characteristic of antidepressants. Exploring the underlying mechanisms may allow for advances in the effort to improve therapeutic strategies for depression appearing in degenerative and psychiatric diseases.

Pituitary tumor transforming gene: a novel therapeutic target for glioma treatment

Glioma which has strong proliferation and angiogenesis ability is the most common and malignant primary tumor in central nervous system. Pituitary tumor transforming gene (PTTG) is found in pituitary tumor, and plays important role in cell proliferation, cell cycle, cell apoptosis, and angiogenesis. However, the role of PTTG in glioma is still incompletely investigated. Here, we explored the correlation between PTTG and glioma grade, as well as micro-vessel density (MVD). In addition, siRNA was used to silence PTTG expression in glioma cell lines including U87MG, U251, and SHG44. Cell proliferation, apoptosis, invasion, and angiogenesis were studied both in vitro and in vivo. Our results demonstrated that PTTG expression was significantly up-regulated in glioma, and had positive correlation with glioma grade and MVD. Silencing of PTTG inhibited glioma cell proliferation, migration/invasion, and angiogenesis, induced cell apoptosis, suppressed cell invasion, and arrested cell cycle at G0/G1 stage. Silencing of PTTG could also inhibit tumor growth, invasion, and angiogenesis in vivo. Our data indicated that PTTG might be a potential target for glioma treatment.

NOAD, a novel nitric oxide donor, induces G2/M phase arrest and apoptosis in human hepatocellular carcinoma Bel-7402 cells

O(2)-(2,4-dinitro-5-{[2-(12-en-28-b-d-galactopyranosyl-oleanolate-3-yl)-oxy-2-oxoethyl]amino}phenyl)1-(N-hydroxyethylmethylamino)diazen-1-ium-1,2-diolate (NOAD), a novel NO-releasing derivative of oleanolic acid (OA), is an active cytotoxic component. In this study, NOAD induced a rise in intracellular NO levels and showed cytotoxic effects which were prevented by hemoglobin (NO scavenger). Meanwhile, NOAD induced G2/M phase cell cycle arrest in a concentration-dependent manner. Analysis of the cell cycle regulatory proteins demonstrated that NOAD did not change the steady-state levels of cyclin A, cyclin B, cyclin E, Cdk2 and Cdk4, but decreased the protein levels of Cdk1 and Cdc25C. Meanwhile, the levels of phosphorylation of Cdc25C and Cdk1 were significantly increased by NOAD in a concentration-dependent manner. Moreover, NOAD modulated the phosphorylation of protein kinases Chk2. During the G2/M arrest, cyclin-dependent kinase inhibitors (CDKIs), p21(WAF1/CIP1) and p27(kip1) were increased in a concentration-dependent manner. In addition, NOAD also caused a marked increase in the apoptotic cells, as characterized by fragmented nuclei, sub G1 formation, the level of 8-OHDG increase and poly (ADP-ribose) polymerase (PARP) cleavage, which was associated with activation of caspase-3, caspase-8 and caspase-9. Up-regulation of Bax and down-regulation of Bcl-2 were also observed in Bel-7402 cells treated with NOAD. These data suggest that NOAD produces anti-tumor effect via induction of G2/M cell cycle arrest and apoptosis.

Downregulation of Sp1 is involved in β-lapachone-induced cell cycle arrest and apoptosis in oral squamous cell carcinoma

β-lapachone (β-lap) is a naturally occurring quinone obtained from the bark of lapacho tree (Tabebuia avellanedae) with anti-proliferative properties against various cancers. The present study investigated the cell proliferation and apoptosis effect of β-lap on two oral squamous cell carcinoma lines (OSCCs). We carried out a series of 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl-2H-tetrazolium (MTS) assays, 4',6-diamidino-2-phenylindole (DAPI) staining, cell cycle analysis, and western blot analysis to characterize β-lap and its underlying signaling pathway. We demonstrated that β-lap-treated cells significantly reduced cell proliferation but increased DNA condensation and increased sub-G1 population in OSCCs. Particularly, β-lap suppresses activation of transcription factor specificity protein 1 (Sp1) followed by apoptosis in a concentration-dependent manner in OSCCs. Furthermore, β-lap modulated protein expression levels of cell cycle regulatory proteins and apoptosis-related proteins that are known as Sp1 target genes, resulting in apoptosis. Our results collectively indicated that β-lap was able to modulate Sp1 transactivation and induce apoptosis through the regulation of cell cycle and apoptosis-related proteins. Therefore, β-lap may be used in cancer prevention and therapies to improve clinical outcome as an anticancer drug candidate.

ING5 is phosphorylated by CDK2 and controls cell proliferation independently of p53

Inhibitor of growth (ING) proteins have multiple functions in the control of cell proliferation, mainly by regulating processes associated with chromatin regulation and gene expression. ING5 has been described to regulate aspects of gene transcription and replication. Moreover deregulation of ING5 is observed in different tumors, potentially functioning as a tumor suppressor. Gene transcription in late G1 and in S phase and replication is regulated by cyclin-dependent kinase 2 (CDK2) in complex with cyclin E or cyclin A. CDK2 complexes phosphorylate and regulate several substrate proteins relevant for overcoming the restriction point and promoting S phase. We have identified ING5 as a novel CDK2 substrate. ING5 is phosphorylated at a single site, threonine 152, by cyclin E/CDK2 and cyclin A/CDK2 in vitro. This site is also phosphorylated in cells in a cell cycle dependent manner, consistent with it being a CDK2 substrate. Furthermore overexpression of cyclin E/CDK2 stimulates while the CDK2 inhibitor p27^KIP1 represses phosphorylation at threonine 152. This site is located in a bipartite nuclear localization sequence but its phosphorylation was not sufficient to deregulate the subcellular localization of ING5. Although ING5 interacts with the tumor suppressor p53, we could not establish p53-dependent regulation of cell proliferation by ING5 and by phospho-site mutants. Instead we observed that the knockdown of ING5 resulted in a strong reduction of proliferation in different tumor cell lines, irrespective of the p53 status. This inhibition of proliferation was at least in part due to the induction of apoptosis. In summary we identified a phosphorylation site at threonine 152 of ING5 that is cell cycle regulated and we observed that ING5 is necessary for tumor cell proliferation, without any apparent dependency on the tumor suppressor p53.

Cks overexpression enhances chemotherapeutic efficacy by overriding DNA damage checkpoints

Cdc kinase subunit (Cks) proteins Cks1 and Cks2 are adaptor-like proteins that bind many cyclin-dependent kinases. A wealth of clinical data has shown that Cks proteins are overexpressed in many types of human cancers and this often correlates with increased tumor aggressiveness. Previously, we showed that Cks overexpression abrogates the intra-S-phase checkpoint, a major barrier to oncogene-mediated transformation. Interestingly, the intra-S-phase checkpoint is crucial for the cellular response to replication stress, a major pathway of apoptosis induction by many chemotherapeutic agents. Here, we demonstrate cancer cells that overexpress Cks1 or Cks2 override the intra-S-phase checkpoint in the presence of replication stress-inducing chemotherapies such as 5-Fluorouracil (5-FU) and methotrexate (MTX) leading to enhanced sensitivity in vitro and in vivo. Furthermore, enforced expression of Cks1 in an MTX-resistant breast cancer cell line was found to restore drug sensitivity. Our results suggest that Cks proteins are important determinants of apoptosis induction of replication stress-inducing chemotherapies such as 5-FU.

Validation of signalling pathways: Case study of the p16-mediated pathway

p16 is recognized as a tumor suppressor gene due to the prevalence of its genetic inactivation in all types of human cancers. Additionally, p16 gene plays a critical role in controlling aging, regulating cellular senescence, detection and maintenance of DNA damage. The molecular mechanism behind these events involves p16-mediated signaling pathway (or p16- Rb pathway), the focus of our study. Understanding functional dependence between dynamic behavior of biological components involved in the p16-mediated pathway and aforesaid molecular-level events might suggest possible implications in the diagnosis, prognosis and treatment of human cancer. In the present work, we employ reverse-engineering approach to construct the most detailed computational model of p16-mediated pathway in higher eukaryotes. We implement experimental data from the literature to validate the model, and under various assumptions predict the dynamic behavior of p16 and other biological components by interpreting the simulation results. The quantitative model of p16-mediated pathway is created in a systematic manner in terms of Petri net technologies.

Indole diketopiperazines from endophytic Chaetomium sp 88194 induce breast cancer cell apoptotic death

Diketopiperazines are important secondary metabolites of the fungi with variety bioactivities. Several species belonging to genus Chaetomium produce compounds of this class, such as chetomin. To identify new antitumor agents, secondary metabolites of fungus Chaetomium sp 88194 were investigated and three new indole diketopiperazines, Chaetocochins G (1), Oidioperazines E (2) and Chetoseminudin E (3), along with two known compounds Chetoseminudins C (4) and N-acetyl-β-oxotryptamine (5), were obtained. Chaetocochins G and Chetoseminudin E were recrystallized in CHCl₃ containing a small amount of MeOH, and their structures with absolute configuration were established by spectroscopic data interpretation and single-crystal X-ray diffraction analysis. The absolute configuration of Oidioperazines E was defined by comparing of experimental and calculated electronic circular dichroism spectra. These isolates were also evaluated the anticancer activity, and Chaetocochins G displayed more potent cytotoxicity in MCF-7 cells than the common chemotherapeutic agent (5-fluorouracil) associated with G2/M cell cycle arrest. More importantly, Chaetocochins G induced cell apoptotic death via caspase-3 induction and proteolytic cleavage of poly (ADP-ribose) polymerase, concomitantly with increased Bax and decreased Bcl-2 expression. Our findings suggested that indole diketopiperazines from endophytic Chaetomium sp 88194 may be potential resource for developing anti-cancer reagents.

Human cytomegalovirus riding the cell cycle

Human cytomegalovirus (HCMV) infection modulates the host cell cycle to create an environment that is optimal for viral gene expression, DNA replication, and production of infectious virus. The virus mostly infects quiescent cells and thus must push the cell into G1 phase of the cell cycle to co-opt the cellular mechanisms that could be used for DNA synthesis. However, at the same time, cellular functions must be subverted such that synthesis of viral DNA is favored over that of the host. The molecular mechanisms by which this is accomplished include altered RNA transcription, changes in the levels and activity of cyclin-dependent kinases, and other proteins involved in cell cycle control, posttranslational modifications of proteins, modulation of protein stability through targeted effects on the ubiquitin-proteasome degradation pathway, and movement of proteins to different cellular locations. When the cell is in the optimal G0/G1 phase, multiple signaling pathways are altered to allow rapid induction of viral gene expression once negative factors have been eliminated. For the most part, the cell cycle will stop prior to initiation of host cell DNA synthesis (S phase), although many cell cycle proteins characteristic of the S/G2/M phase accumulate. The environment of a cell progressing through the cell cycle and dividing is not favorable for viral replication, and HCMV has evolved ways to sense whether cells are in S/G2 phase, and if so, to prevent initiation of viral gene expression until the cells cycle back to G1. A major target of HCMV is the anaphase-promoting complex E3 ubiquitin ligase, which is responsible for the ubiquitination and subsequent degradation of cyclins A and B and other cell cycle proteins at specific phases in the cell cycle. This review will discuss the effects of HCMV infection on cell cycle regulatory pathways, with the focus on selected viral proteins that are responsible for these effects.

Functional characterization of the diatom cyclin-dependent kinase A2 as a mitotic regulator reveals plant-like properties in a non-green lineage

BACKGROUND

Cyclin-dependent kinases (CDKs) are crucial regulators of cell cycle progression in eukaryotes. The diatom CDKA2 was originally assigned to the classical A-type CDKs, but its cell cycle phase-specific transcription at the G2-to-M phase transition is typical for plant-specific B-type CDKs.

RESULTS

Here, we report the functional characterization of CDKA2 from the diatom Phaeodactylum tricornutum. Through a yeast two-hybrid library screen, CDKA2 was found to interact with the G2/M-specific CDK scaffolding factor CKS1. Localization of CDKA2 was found to be nuclear in interphase cells, while in cells undergoing cytokinesis, the signal extended to the cell division plane. In addition, overexpression of CDKA2 induced an overall reduction in the cell growth rate. Expression analysis of cell cycle marker genes in the overexpression lines indicates that this growth reduction is primarily due to a prolongation of the mitotic phase.

CONCLUSIONS

Our study indicates a role for CDKA2 during cell division in diatoms. The functional characterization of a CDK with clear CDKB properties in a non-green organism questions whether the current definition of B-type CDKs being plant-specific might need revision.

Cyclin-dependent kinase inhibitors and the treatment of gastrointestinal cancers

The cell cycle is a highly conserved and tightly regulated biological system that controls cellular proliferation and differentiation. The cell cycle regulatory proteins, which include the cyclins, the cyclin-dependent kinases (CDKs), and the CDK inhibitors, are critical for the proper temporal and spatial regulation of cellular proliferation. Conversely, alterations in cell cycle regulatory proteins, leading to the loss of normal cell-cycle control, are a hallmark of many cancers, including gastrointestinal cancers. Accordingly, overexpression of CDKs and cyclins and by contrast loss of CDK inhibitors, are all linked to gastrointestinal cancers and are often associated with less favorable prognoses and outcomes. Because of the importance that the cell cycle regulatory proteins play in tumorigenesis, currently there is a broad spectrum of cell-cycle inhibitors under development that, as a group, hold promise as effective cancer treatments. In support of this approach to cancer treatment, the growing availability of molecular diagnostics techniques may help in identifying patients who have driving abnormalities in the cell-cycle machinery and are thus more likely to respond to cell-cycle inhibitors. In this review, we discuss the prevalence of cell-cycle abnormalities in patients with gastrointestinal cancers and provide a preclinical and clinical overview of new agents that target cell-cycle abnormalities with a special emphasis on gastrointestinal cancers.

Memory CD8(+) T cells colocalize with IL-7(+) stromal cells in bone marrow and rest in terms of proliferation and transcription

It is believed that memory CD8⁺ T cells are maintained in secondary lymphoid tissues, peripheral tissues, and BM by homeostatic proliferation. Their survival has been shown to be dependent on IL-7, but it is unclear where they acquire it. Here we show that in murine BM, memory CD8⁺ T cells individually colocalize with IL-7⁺ reticular stromal cells. The T cells are resting in terms of global transcription and do not express markers of activation, for example, 4-1BB (CD137), IL-2, or IFN-γ, despite the expression of CD69 on about 30% of the cells. Ninety-five percent of the memory CD8⁺ T cells in BM are in G₀ phase of cell cycle and do not express Ki-67. Less than 1% is in S/M/G₂ of cell cycle, according to propidium iodide staining. While previous publications have estimated the extent of proliferation of CD8⁺ memory T cells on the basis of BrdU incorporation, we show here that BrdU itself induces proliferation of CD8⁺ memory T cells. Taken together, the present results suggest that CD8⁺ memory T cells are maintained as resting cells in the BM in dedicated niches with their survival conditional on IL-7 receptor signaling.

Adiponectin mediates antiproliferative and apoptotic responses in endometrial carcinoma by the AdipoRs/AMPK pathway

OBJECTIVE

Determine the serum adiponectin levels in endometrial carcinoma (EC) cases and controls and explore the correlation between them. We assessed the functions of AdipoR1 and AdipoR2 in endometrial cancer cells to determine whether the AMPK/ERK and Akt pathways mediate the effects of adiponectin-induced apoptosis and anti-proliferation.

MATERIAL AND METHODS

The serum adiponectin levels were measured via enzyme-linked immunosorbent assay (ELISA). The proliferation and apoptosis rates were determined with MTT and annexin V/PI assays. To evaluate the activation of AMPK, ERK, and Akt and the expression of Bcl-2 and Cyclin D1, western blot analysis was performed in Ishikawa 3-H-12 cells. We down-regulated AdipoRs by si-RNA to assess their functions.

RESULTS

The serum adiponectin levels were significantly decreased in patients with EC compared to controls. The adiponectin-induced apoptosis and anti-proliferation effects in EC cells were blocked by Compound C. Ishikawa 3-H-12 cells exhibited time- and dose-dependent increases in the p-AMPK levels after treatment with adiponectin. Adiponectin treatment reduced the levels of ERK and Akt phosphorylations and cyclin D1 and Bcl-2 mRNA and protein expression. Compound C blocked the effects on ERK, Akt, cyclin D1, and Bcl-2. AdipoR1 and AdipoR2 were involved in adiponectin-induced growth inhibition and ERK activation inhibition. We speculated that AdipoR1 has a greater role than adipoR2 in apoptosis and Akt activation inhibition after adiponectin treatment.

CONCLUSION

Adiponectin was an apoptotic and anti-proliferation agent for EC cells, and these effects were dependent on the AMPK/ERK and Akt pathways. AdipoR1 and AdipoR2 may play different roles in this process.

Cyclin C mediates stress-induced mitochondrial fission and apoptosis

Mitochondria are dynamic organelles that undergo constant fission and fusion cycles. In response to cellular damage, this balance is shifted dramatically toward fission. Cyclin C-Cdk8 kinase regulates transcription of diverse gene sets. Using knockout mouse embryonic fibroblasts (MEFs), we demonstrate that cyclin C directs the extensive mitochondrial scission induced by the anticancer drug cisplatin or oxidative stress. This activity is independent of transcriptional regulation, as Cdk8 is not required for this activity. Furthermore, adding purified cyclin C to unstressed permeabilized MEF cultures induced complete mitochondrial fragmentation that was dependent on the fission factors Drp1 and Mff. To regulate fission, a portion of cyclin C translocates from the nucleus to the cytoplasm, where it associates with Drp1 and is required for its enhanced mitochondrial activity in oxidatively stressed cells. In addition, although HeLa cells regulate cyclin C in a manner similar to MEF cells, U2OS osteosarcoma cultures display constitutively cytoplasmic cyclin C and semifragmented mitochondria. Finally, cyclin C, but not Cdk8, is required for loss of mitochondrial outer membrane permeability and apoptosis in cells treated with cisplatin. In conclusion, this study suggests that cyclin C connects stress-induced mitochondrial hyperfission and programmed cell death in mammalian cells.

ZGDHu-1 induces G₂/M phase arrest and apoptosis in Kasumi-1 cells

The present study examined the effects of N,N′-di-(m-methylphenyi)-3, 6-dimethyl-1, 4-dihydro-1,2,4,5-tetrazine-1,4-dicarboamide (ZGDHu-1), a novel oxazine derivative, in Kasumi-1 cells. Following incubation with various concentrations of ZGDHu-1, fluorescence-activated cell sorting (FACS) was used in order to detect changes in mitochondrial membrane permeability in Kasumi-1 cells. Western blot analysis was performed in order to analyze the expression of nuclear factor-κB, inhibitor of κB and AML1/ETO. In addition FACS was used to analyze leukemia cell cycles and the expression levels of cyclin, cyclin-dependent kinases and cyclin-dependent kinase inhibitors in G₂/M phase were determined using FACS and western blot analysis. The upregulation of reactive oxygen species production and mitochondrial membrane permeability was ascribed to apoptosis. The growth of Kasumi-1 cells was inhibited through the downregulation of nuclear factor-κB, degradation of AML1/ETO fusion protein and cell cycle arrest at the G₂/M phase. This study documented that G₂/M regulatory molecules, including cyclin B1, cell division control (cdc)2 and cdc25c were downregulated and checkpoint kinase 1 (CHK1), p53, p27, phospho-cdc25c, phospho-CHK1 and phospho-p53 were upregulated following treatment with ZGDHu-1. In the present study, pretreatment with CHIR-124, a selective CHK1 inhibitor, abrogated G₂/M arrest via ZGDHu-1. These results demonstrated the anti-tumor activity of ZGDHu-1, which may therefore a potential target for further investigation and may be useful for the treatment of patients with t(8;21) acute myeloid leukemia.

GCNF-dependent activation of cyclin D1 expression via repression of Mir302a during ESC differentiation

Cyclin D1 plays an important role in the regulation of cellular proliferation and its expression is activated during gastrulation in the mouse; however, it remains unknown how cyclin D1 expression is regulated during early embryonic development. Here, we define the role of germ cell nuclear factor (GCNF) in the activation of cyclin D1 expression during embryonic stem cell (ESC) differentiation as a model of early development. During our study of GCNF knockout (GCNF(-) (/) (-) ) ESC, we discovered that loss of GCNF leads to the repression of cyclin D1 activation during ESC differentiation. This was determined to be an indirect effect of deregulation Mir302a, which is a cyclin D1 suppressor via binding to the 3'UTR of cyclin D1 mRNA. Moreover, we showed that Mir302 is a target gene of GCNF that inhibits Mir302 expression by binding to a DR0 element within its promoter. Inhibition of Mir302a using Mir302 inhibitor during differentiation of GCNF(-) (/) (-) ESCs restored cyclin D1 expression. Similarly over-expression of GCNF during differentiation of GCNF(-) (/) (-) ESCs rescued the inhibition of Mir302a expression and the activation of cyclin D1. These results reveal that GCNF plays a key role in regulating activation of cyclin D1 expression via inhibition of Mir302a.

New Compound Classes: Protein-Protein Interactions

"Protein-protein interactions (PPIs) are one of the most promising new targets in drug discovery. With estimates between 300,000 and 650,000 in human physiology, targeted modulation of PPIs would tremendously extend the "druggable" genome. In fact, in every disease a wealth of potentially addressable PPIs can be found making pharmacological intervention based on PPI modulators in principle a generally applicable technology. An impressing number of success stories in small-molecule PPI inhibition and natural-product PPI stabilization increasingly encourage academia and industry to invest in PPI modulation. In this chapter examples of both inhibition as well as stabilization of PPIs are reviewed including some of the technologies which has been used for their identification."

Ser or Leu: structural snapshots of mistranslation in Candida albicans

Candida albicans is a polymorphic opportunistic fungal pathogen normally residing as commensal on mucosal surfaces, skin and gastrointestinal and genitourinary tracts. However, in immunocompromised patients C. albicans can cause superficial mucosal infections or life-threatening disseminated candidemia. A change in physiological conditions triggers a cascade of molecular events leading to morphogenetic alterations and increased resistance to damage induced by host defenses. The complex biology of this human pathogen is reflected in its morphological plasticity and reinforced by the ability to ambiguously translate the universal leucine CUG codon predominantly as serine, but also as leucine. Mistranslation affects more than half of C. albicans proteome and it is widespread across many biological processes. A previous analysis of CTG-codon containing gene products in C. albicans suggested that codon ambiguity subtly shapes protein function and might have a pivotal role in signaling cascades associated with morphological changes and pathogenesis. In this review we further explore this hypothesis by highlighting the role of ambiguous decoding in macromolecular recognition of key effector proteins associated with the regulation of signal transduction cascades and the cell cycle, which are critical processes for C. albicans morphogenic plasticity under a variety of environmental conditions.

High nuclear/cytoplasmic ratio of Cdk1 expression predicts poor prognosis in colorectal cancer patients

Background

Cdk1 (cyclin-dependent kinase 1) is critical regulator of the G2-M checkpoint. Cyclin-dependent kinase pathways are considered possible targets for cancer treatment; however, the prognostic role of Cdk1 in colorectal cancer is still controversial. Therefore, we attempted to determine the impact of Cdk1 on the clinical outcome of colorectal cancer patients to further identify its role in colorectal cancer.

Methods

Cdk1 immunoreactivity was analyzed by immunohistochemistry (IHC) in 164 cancer specimens from primary colorectal cancer patients. The medium follow-up time after surgery was 3.7 years (range: 0.01 to 13.10 years). The prognostic value of Cdk1 on overall survival was determined by Kaplan-Meier analysis and Cox proportional hazard models.

Results

All samples displayed detectable Cdk1 expression with predominant location in the cytoplasm and nucleus. A high Cdk1 nuclear/cytoplasmic (N/C) expression ratio was correlated with poor overall survival (5-year survival rate: 26.3% vs 46.9%, N/C ratio ≥1.5 vs N/C ratio <1.5, log-rank p = 0.027). Accordingly, a Cdk1 N/C expression ratio ≥1.5 was identified as an independent risk factor by multivariate analysis (hazard ratio = 1.712, P = 0.039).

Conclusions

We suggest that Cdk1 N/C expression ratio determined by IHC staining could be an independent prognostic marker for colorectal cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2407-14-951) contains supplementary material, which is available to authorized users.

Anti-proliferative properties of kahweol in oral squamous cancer through the regulation specificity protein 1

Kahweol, the coffee-specific deterpene, has been shown to have potential anti-cancer effects against several cancers. However, the molecular mechanisms underlying the anti-cancer activity of kahweol have not yet established. In this study, we investigated whether kahweol could show anti-cancer effects on oral squamous cell lines (OSCCs), HN22 and HSC4. We conducted an 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxy-phenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay, 4'-6-diamidino2-phenylindole (DAPI) staining, propidium iodide staining, immunocytochemistry, and Western blot analysis for the characterization of kahweol and the underlying signaling pathway. We determined that kahweol-treated cells showed significantly decreased cell viability and increased nuclear condensation and an increased sub-G1 population in OSCCs. Interestingly, suppression of the transcription factor specificity protein 1 (Sp1) was followed by induced apoptosis by kahweol in a dose-dependent manner. In addition, kahweol modulated the protein expression level of the Sp1 regulatory genes including cell cycle regulatory proteins and anti-apoptotic proteins, resulting in apoptosis. Taken together, results from these findings suggest that kahweol may be a potential anti-cancer drug candidate to induce apoptotic cell death through downregulation of Sp1 in OSCCs.

p53 protein-mediated up-regulation of MAP kinase phosphatase 3 (MKP-3) contributes to the establishment of the cellular senescent phenotype through dephosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2)

Growth arrest is one of the essential features of cellular senescence. At present, the precise mechanisms responsible for the establishment of the senescence-associated arrested phenotype are still incompletely understood. Given that ERK1/2 is one of the major kinases controlling cell growth and proliferation, we examined the possible implication of ERK1/2. Exposure of normal rat epithelial cells to etoposide caused cellular senescence, as manifested by enlarged cell size, a flattened cell body, reduced cell proliferation, enhanced β-galactosidase activity, and elevated p53 and p21. Senescent cells displayed a blunted response to growth factor-induced cell proliferation, which was preceded by impaired ERK1/2 activation. Further analysis revealed that senescent cells expressed a significantly higher level of mitogen-activated protein phosphatase 3 (MKP-3, a cytosolic ERK1/2-targeted phosphatase), which was suppressed by blocking the transcriptional activity of the tumor suppressor p53 with pifithrin-α. Inhibition of MKP-3 activity with a specific inhibitor or siRNA enhanced basal ERK1/2 phosphorylation and promoted cell proliferation. Apart from its role in growth arrest, impairment of ERK1/2 also contributed to the resistance of senescent cells to oxidant-elicited cell injury. These results therefore indicate that p53-mediated up-regulation of MKP-3 contributes to the establishment of the senescent cellular phenotype through dephosphorylating ERK1/2. Impairment of ERK1/2 activation could be an important mechanism by which p53 controls cellular senescence.

Inactivation of p53 in Human Keratinocytes Leads to Squamous Differentiation and Shedding via Replication Stress and Mitotic Slippage

Tumor suppressor p53 is a major cellular guardian of genome integrity, and its inactivation is the most frequent genetic alteration in cancer, rising up to 80% in squamous cell carcinoma (SCC). By adapting the small hairpin RNA (shRNA) technology, we inactivated endogenous p53 in primary epithelial cells from the epidermis of human skin. We show that either loss of endogenous p53 or overexpression of a temperature-sensitive dominant-negative conformation triggers a self-protective differentiation response, resulting in cell stratification and expulsion. These effects follow DNA damage and exit from mitosis without cell division. p53 preserves the proliferative potential of the stem cell compartment and limits the power of proto-oncogene MYC to drive cell cycle stress and differentiation. The results provide insight into the role of p53 in self-renewal homeostasis and help explain why p53 mutations do not initiate skin cancer but increase the likelihood that cancer cells will appear.

Fluorescein hydrazones as novel nonintercalative topoisomerase catalytic inhibitors with low DNA toxicity

Fluorescein hydrazones (3a-3l) were synthesized in three steps with 86-91% overall yields. Topo I- and IIα-mediated relaxation and cell viability assay were evaluated. 3d inhibited 47% Topo I (camptothecin, 34%) and 20% Topo II (etoposide 24%) at 20 μM. 3l inhibited 61% Topo II (etoposide 24%) at 20 μM. 3d and 3l were further evaluated to determine their mode of action with diverse methods of kDNA decatenation, DNA-Topo cleavage complex, comet, DNA intercalating/unwinding, and Topo IIα-mediated ATP hydrolysis assays. 3d functioned as a nonintercalative dual inhibitor against the catalytic activities of Topo I and Topo IIα. 3l acted as a Topo IIα specific nonintercalative catalytic inhibitor. 3d activated apoptotic proteins as it increased the level of cleaved capase-3 and cleaved PARP in a dose- and time-dependent manner. The dose- and time-dependent increase of G1 phase population was observed by treatment of 3d along with the increase of p27(kip1) and the decrease of cyclin D1 expression.

Desacetyluvaricin induces S phase arrest in SW480 colorectal cancer cells through superoxide overproduction

Annonaceous acetogenins (ACGs) are a group of fatty acid-derivatives with potent anticancer effects. In the present study, we found desacetyluvaricin (Dau) exhibited notable in vitro antiproliferative effect on SW480 human colorectal carcinoma cells with IC50 value of 14 nM. The studies on the underlying mechanisms revealed that Dau inhibited the cancer cell growth through induction of S phase cell cycle arrest from 11.3% (control) to 33.2% (160 nM Dau), which was evidenced by the decreased protein expression of cyclin A Overproduction of superoxide, intracellular DNA damage, and inhibition of MEK/ERK signaling pathway, were also found involved in cells exposed to Dau. Moreover, pre-treatment of the cells with ascorbic acid significantly prevented the Dau-induced overproduction of superoxide, DNA damage and cell cycle arrest. Taken together, our results suggest that Dau induces S phase arrest in cancer cells by firstly superoxide overproduction and subsequently the involvement of various signaling pathways.

MicroRNA-188 suppresses G1/S transition by targeting multiple cyclin/CDK complexes

BACKGROUND

Accelerated cell cycle progression is the common feature of most cancers. MiRNAs can act as oncogenes or tumor suppressors by directly modulating cell cycle machinery. It has been shown that miR-188 is upregulated in UVB-irradiated mouse skin and human nasopharyngeal carcinoma CNE cells under hypoxic stress. However, little is known about the function of miR-188 in cell proliferation and growth control.

RESULTS

Overexpression of miR-188 inhibits cell proliferation, tumor colony formation and G1/S cell cycle transition in human nasopharyngeal carcinoma CNE cells. Using bioinformatics approach, we identify a series of genes regulating G1/S transition as putative miR-188 targets. MiR-188 inhibits both mRNA and protein expression of CCND1, CCND3, CCNE1, CCNA2, CDK4 and CDK2, suppresses Rb phosphorylation and downregulates E2F transcriptional activity. The expression level of miR-188 also inversely correlates with the expression of miR-188 targets in human nasopharyngeal carcinoma (NPC) tissues. Moreover, studies in xenograft mouse model reveal that miR-188 is capable of inhibiting tumor initiation and progression by suppressing target genes expression and Rb phosphorylation.

CONCLUSIONS

This study demonstrates that miR-188 exerts anticancer effects, via downregulation of multiple G1/S related cyclin/CDKs and Rb/E2F signaling pathway.

Taspase1 cleaves MLL1 to activate cyclin E for HER2/neu breast tumorigenesis

Taspase1, a highly conserved threonine protease, cleaves nuclear transcriptional regulators mixed-lineage leukemia (MLL, MLL1), MLL2, TFIIA, and ALF to orchestrate a wide variety of biological processes. In vitro studies thus far demonstrated that Taspase1 plays important roles in the proliferation of various cancer cell lines, including HER2-positive breast cancer cells. To investigate the role of Taspase1 in breast tumorigenesis in vivo, we deleted Taspase1 from mouse mammary glands by generating MMTV-neu;MMTV-cre;Tasp1(F/-) mice. We demonstrate that initiation of MMTV-neu- but not MMTV-wnt-driven breast cancer is blocked in the absence of Taspase1. Importantly, Taspase1 loss alone neither impacts normal development nor pregnancy physiology of the mammary gland. In mammary glands Taspase1 deficiency abrogates MMTV-neu-induced cyclins E and A expression, thereby preventing tumorigenesis. The mechanisms were explored in HER2-positive breast cancer cell line BT474 and HER2-transformed MCF10A cells and validated using knockdown-resistant Taspase1. As Taspase1 was shown to cleave MLL which forms complexes with E2F transcription factors to regulate Cyclins E, A, and B expression in mouse embryonic fibroblasts (MEFs), we investigated whether the cleavage of MLL by Taspase1 constitutes an essential in vivo axis for HER2/neu-induced mammary tumorigenesis. To this end, we generated MMTV-neu;MLL(nc/nc) transgenic mice that carry homozygous non-cleavable MLL alleles. Remarkably, these mice are also protected from HER2/neu-driven breast tumorigenesis. Hence, MLL is the primary Taspase1 substrate whose cleavage is required for MMTV-neu-induced tumor formation. As Taspase1 plays critical roles in breast cancer pathology, it may serve as a therapeutic target for HER2-positive human breast cancer.