Cyclin-dependent kinase-associated proteins Cks1 and Cks2 are essential during early embryogenesis and for cell cycle progression in somatic cells

Increased expression of Cks1 protein is associated with lymph node metastasis and poor prognosis in nasopharyngeal carcinoma

Background

The Cks1 protein is an essential factor in regulating cell cycle by mediating the ubiquitination of CDK inhibitor p27^kip1. It has been reported that aberrant expression of Cks1 and p27^kip1 proteins was found in various tumors and related to initiation and progression of carcinomas. However, the potential roles which Cks1 and p27^KIP1 proteins play in NPC remain unclear. This study aims to examine the expression status of Cks1 and p27^kip1 and their possible prognostic significance in NPC.

Methods

Paraffin-embedded specimens with NPC (n = 168) and non-tumor nasopharyngeal tissues (n = 49) were analyzed by IHC.

Results

Expression of Cks1 increased in NPC tissues compared with non-tumor nasopharyngeal tissues (P < 0.05), whereas p27^kip1 protein frequently expressed in non-tumor nasopharyngeal tissues compared with NPC tissues (P < 0.05). There was a significant reverse correlation between Cks1 and p27^kip1 protein expression in NPC (r = −0.189, P < 0.05).In addition, Kaplan-Meier survival curve showed that there was a significant tendency of shorter overall survival (OS) in NPC patients with Cks1 positive expression compared to negative ones, especially in patients with lymph node metastasis (P < 0.001, respectively). But there was no significance between p27^kip1 expression and survival viability of NPC patients. Multivariate Cox regression analysis further identified increased expression of Cks1 was the independent poor prognostic factor for NPC (p = 0.13).

Conclusion

Our research found expression of Cks1 increased and was inverse to the expression of p27^KIP1. High expression of Cks1 was significantly associated with lymph node metastasis and survival status in NPC. In addition, the abnormally high level of Cks1 protein was proved to be an independent poor prognostic factor in NPC. These results may provide novel clue for NPC therapy method.

Electronic supplementary material

The online version of this article (doi:10.1186/s13000-016-0589-9) contains supplementary material, which is available to authorized users.

The Prozone Effect Accounts for the Paradoxical Function of the Cdk-Binding Protein Suc1/Cks

Previous work has shown that Suc1/Cks proteins can promote the hyperphosphorylation of primed Cdk1 substrates through the formation of ternary Cdk1-Cks-phosphosubstrate complexes. This raises the possibility that Cks proteins might be able to both facilitate and interfere with hyperphosphorylation through a mechanism analogous to the prozone effect in antigen-antibody interactions, with substoichiometric Cks promoting the formation of Cdk1-Cks-phosphosubstrate complexes and suprastoichiometric Cks instead promoting the formation of Cdk1-Cks and Cks-phosphosubstrate complexes. We tested this hypothesis through a combination of theory, proof-of-principle experiments with oligonucleotide annealing, and experiments on the interaction of Xenopus cyclin B1-Cdk1-Cks2 with Wee1A in vitro and in Xenopus extracts. Our findings help explain why both Cks under-expression and overexpression interfere with cell-cycle progression and provide insight into the regulation of the Cdk1 system.

Rho-associated kinase (ROCK) function is essential for cell cycle progression, senescence and tumorigenesis

Rho-associated kinases 1 and 2 (ROCK1/2) are Rho-GTPase effectors that control key aspects of the actin cytoskeleton, but their role in proliferation and cancer initiation or progression is not known. Here, we provide evidence that ROCK1 and ROCK2 act redundantly to maintain actomyosin contractility and cell proliferation and that their loss leads to cell-cycle arrest and cellular senescence. This phenotype arises from down-regulation of the essential cell-cycle proteins CyclinA, CKS1 and CDK1. Accordingly, while the loss of either Rock1 or Rock2 had no negative impact on tumorigenesis in mouse models of non-small cell lung cancer and melanoma, loss of both blocked tumor formation, as no tumors arise in which both Rock1 and Rock2 have been genetically deleted. Our results reveal an indispensable role for ROCK, yet redundant role for isoforms 1 and 2, in cell cycle progression and tumorigenesis, possibly through the maintenance of cellular contractility.

Up-regulated CKS2 promotes tumor progression and predicts a poor prognosis in human colorectal cancer

Cyclin-dependent kinases regulatory subunit 2 (CKS2) is a cyclin-dependent kinase-interacting protein, which is essential for cell cycle regulation. Elevated expression of CKS2 has been demonstrated in multiple types of human malignancies. However, the clinical significance, oncogenic functions and related mechanisms of CKS2 in colorectal cancer (CRC) remain largely unexplored. In this study, data from Oncomine database revealed that CKS2 is significantly up-regulated in CRC tissues compared with their normal counterparts. Immunohistochemical analysis of a CRC tissue microarray demonstrated that elevated CKS2 expression is closely associated with enhanced TNM stage, larger tumor size and a poor prognosis in patients with CRC. Multivariate Cox regression analysis revealed that CKS2 and TNM stage are two independent prognostic factors for CRC. Suppression of CKS2 expression resulted in decreased cell viability, increased cell apoptosis, cell cycle arrest and reduced expression of cyclins in Caco-2 and SW620 cells. Furthermore, gain and loss of function studies demonstrated that CKS2 promotes cell invasion in CRC cells through regulating claudin1. Taken together, our study reveal that CKS2 is promising prognostic indicator and contributes to tumor progression in CRC, and support that CKS2-related signaling may represent a novel target for CRC therapy.

A central role for TRPS1 in the control of cell cycle and cancer development

The eukaryotic cell cycle is controlled by a complex regulatory network, which is still poorly understood. Here we demonstrate that TRPS1, an atypical GATA factor, modulates cell proliferation and controls cell cycle progression. Silencing TRPS1 had a differential effect on the expression of nine key cell cycle-related genes. Eight of these genes are known to be involved in the regulation of the G2 phase and the G2/M transition of the cell cycle. Using cell synchronization studies, we confirmed that TRPS1 plays an important role in the control of cells in these phases of the cell cycle. We also show that silencing TRPS1 controls the expression of 53BP1, but not TP53. TRPS1 silencing also decreases the expression of two histone deacetylases, HDAC2 and HDAC4, as well as the overall HDAC activity in the cells, and leads to the subsequent increase in the acetylation of histone4 K16 but not of histone3 K9 or K18. Finally, we demonstrate that TRPS1 expression is elevated in luminal breast cancer cells and luminal breast cancer tissues as compared with other breast cancer subtypes. Overall, our study proposes that TRPS1 acts as a central hub in the control of cell cycle and proliferation during cancer development.

Cyclin-dependent kinase regulatory subunit 1 promotes cell proliferation by insulin regulation

Cyclin-dependent kinase regulatory subunit 1 (CKS1) helps regulate the cell cycle to increase cell number. However, the hormonal regulation on CKS1 expression is not well understood. We report that CKS1 is involved in the promotion of cell proliferation with insulin regulation in the lepidopteran insect Helicoverpa armigera. CKS1 is expressed in various tissues during the larval feeding stage. CKS1 knockdown results in larval death, body weight decrease, pupation time delay, and small-sized pupa formation. The underlying mechanism involves the blocking of cell proliferation and the repression of gene expression in the insulin pathway after CKS1 knockdown. CKS1 overexpression in the epidermal cell line results in cell proliferation. The N45 amino acid asparagine in the CKS domain is essential for the function of CKS in cell proliferation. CKS1 is upregulated by insulin via an insulin receptor, but is repressed by a high level of steroid hormone 20-hydroxyecdysone (20E). Results suggest that CKS1 promotes cell proliferation and body growth in coordination with the regulatory actions of insulin and steroid hormone 20E.

Comparison of gene expression patterns across 12 tumor types identifies a cancer supercluster characterized by TP53 mutations and cell cycle defects

Transcriptional profile-based subtypes of cancer are often viewed as identifying different diseases from the same tissue origin. Understanding the mechanisms driving the subtypes may be key in development of novel therapeutics but is challenged by lineage-specific expression signals. Using a t-test statistics approach, we compared gene expression subtypes across 12 tumor types, which identified eight transcriptional superclusters characterized by commonly activated disease pathways and similarities in gene expression. One of the largest superclusters was determined by the upregulation of a proliferation signature, significant enrichment in TP53 mutations, genomic loss of CDKN2A (p16(ARF)), evidence of increased numbers of DNA double strand breaks and high expression of cyclin B1 protein. These correlations suggested that abrogation of the P53-mediated apoptosis response to DNA damage results in activation of cell cycle pathways and represents a common theme in cancer. A second consistent pattern, observed in 9 of 11 solid tumor types, was a subtype related to an activated tumor-associated stroma. The similarity in transcriptional footprints across cancers suggested that tumor subtypes are commonly unified by a limited number of molecular themes.

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.

CKS2 in human cancers: Clinical roles and current perspectives (Review)

Cyclin-dependent kinase subunit 2 (CKS2) is indicated in the processes of cell cycle and cell proliferation. Through these processes, CKS2 is identified as a cancer gene, but its role has not been well reviewed. The aim of the present study was to summarize the clinicopathological significance and the molecular mechanisms of CKS2 in human cancers. Its expression was upregulated in the majority of the types of cancer studied. CKS2 was shown to have a function in cancers of the digestive tract, genital tract, thyroid, nerve and certain other types of cancer. CKS2 can promote progression of certain cancers via positive control of proliferation, invasion and migration. Downregulation of CKS2 induces cancer cell apoptosis. CKS2 can change a multitude of cellular mechanisms in cancer pathogenesis by regulating the gene translation of numerous validated targets, such as p53, CDK1, cyclin A, cyclin B1, caspase-3 and Bax. In addition, the molecular mechanism that causes aberrant expression of CKS2 was epigenetic modification of miR-26a and the Y-box-binding protein 1 (YB-1) gene. In conclusion, CKS2 is commonly elevated in cancer, most likely due to its ability to promote cancer cell growth, invasion and migration through regulating certain significant genes. Understanding the mechanisms by which CKS2 is involved with cancer pathogenesis will be useful in the development of tumor therapy for patients with cancer.

Identification and pharmacological inactivation of the MYCN gene network as a therapeutic strategy for neuroblastic tumor cells

The MYC family of transcription factors consists of three well characterized members, c-MYC, L-MYC, and MYCN, deregulated in the majority of human cancers. In neuronal tumors such as neuroblastoma, MYCN is frequently activated by gene amplification, and reducing its expression by RNA interference has been shown to promote growth arrest and apoptosis of tumor cells. From a clinical perspective, RNA interference is not yet a viable option, and small molecule inhibitors of transcription factors are difficult to develop. We therefore planned to identify, at the global level, the genes interacting functionally with MYCN required to promote fitness of tumor cells facing oncogenic stress. To find genes whose inactivation is synthetically lethal to MYCN, we implemented a genome-wide approach in which we carried out a drop-out shRNA screen using a whole genome library that was delivered into isogenic neuroblastoma cell lines expressing or not expressing MYCN. After the screen, we selected for in-depth analysis four shRNAs targeting AHCY, BLM, PKMYT1, and CKS1B. These genes were chosen because they are directly regulated by MYC proteins, associated with poor prognosis of neuroblastoma patients, and inhibited by small molecule compounds. Mechanistically, we found that BLM and PKMYT1 are required to limit oncogenic stress and promote stabilization of the MYCN protein. Cocktails of small molecule inhibitors of CKS1B, AHCY, BLM, and PKMYT1 profoundly affected the growth of all neuroblastoma cell lines but selectively caused death of MYCN-amplified cells. Our findings suggest that drugging the MYCN network is a promising avenue for the treatment of high risk, neuroblastic cancers.

Expression of cyclin kinase subunit 2 in human breast cancer and its prognostic significance

Cyclin kinase subunit 2 (CKS2) protein is a small cyclin-dependent kinase-interacting protein, which is essential for the first metaphase/anaphase transition of mammalian meiosis. CKS2 is up-regulated in various malignancies, suggesting that CKS2 maybe an oncogene. However, data on its expression pattern and clinical relevance in breast cancer are unknown. The aim of this study is to investigate CKS2 expression and its prognostic significance in breast cancer. The CKS2 expression was examined at mRNA and protein levels by real-time quantitative polymerase chain reaction (RT-PCR) and Western blotting analysis in paired breast cancer tissues and the adjacent normal tissues. The expression of CKS2 protein in 126 specimens of breast cancer was determined by immunohistochemistry assay. The relations between CKS2 expression and clinicopathological features were analyzed. The result show the expression of CKS2 mRNA and protein was higher in breast cancer than the adjacent normal tissues. Compared with adjacent normal breast tissues, Overexpression of CKS2 was detected in 56.3% (71/126) patients. Overexpression of CKS2 was significantly associated with large tumor size (P = 0.035), poor cellular differentiation (P = 0.016), lack expression of progesterone receptor (P = 0.006), and decreased overall survival (P = 0.001). In multivariate analysis, CKS2 expression was an independent prognostic factor for overall survival (Hazard ratio [HR] = 3.404, 95% confidence interval [CI] 1.482-7.818; P = 0.004). CKS2 is up-regulated in breast cancer and associated with large tumor size, lack expression of progesterone receptor, poor tumor differentiation and survival. CKS2 may serve as a good prognostic indicator for patients with breast cancer.

Small interfering RNAs targeted to interleukin-4 and respiratory syncytial virus reduce airway inflammation in a mouse model of virus-induced asthma exacerbation

Asthma exacerbations are caused primarily by viral infections. Antisense and small interfering RNA (siRNA) technologies have gained attention as potential antiasthma and antiviral approaches. In this study we analyzed whether gene silencing of interleukin (IL)-4 expression and respiratory syncytial virus (RSV) replication by RNA interference is able to suppress allergen- and virus-induced responses in a mouse model of virus-induced asthma exacerbation. Knockdown efficacy of IL-4 siRNA molecules was analyzed in the human HEK293T cell line by cotransfection of six different siRNAs with a plasmid carrying mouse IL-4. The most potent siRNA was then used in a mouse model of RSV-induced asthma exacerbation. BALB/c mice were sensitized intraperitoneally with ovalbumin (OVA) and then infected 12 days later intranasally with RSV Long strain (1×10(6) TCID50/mouse), followed 1 day later by intranasal challenge with OVA for 3 days. Mice were pretreated intranasally three times with either siRNA to IL-4 or GFP control, 2 days before, and on the first two OVA challenge days. siRNAs to RSV or rhinovirus control were inoculated intranasally once, 3 hr before RSV infection. Combined anti-IL-4 and anti-RSV siRNAs were able to significantly reduce total cell counts and eosinophilia in bronchoalveolar lavage fluid, development of airway hyperresponsiveness, and airway inflammation and to downregulate IL-4 mRNA expression and RSV viral RNA, but to upregulate IFN-γ levels in lung tissues. We conclude that anti-helper T cells type 2 and antiviral siRNAs may constitute a new therapeutic approach for treatment of virus induced asthma exacerbations.

Changes in granulosa cells gene expression associated with growth, plateau and atretic phases in medium bovine follicles

Background

The objective of this study was to build the transcriptomic profile of granulosa cells originating from follicles 6 to 9 mm in diameter in dairy cattle using microarrays.

Methods

Granulosa cells originating from three different phases of antral follicle growth were compared: growing (G), plateau (P) and atresia (A), as categorized by flow cytometry profiles of DNA. The growing and atretic conditions were each hybridized against the plateau condition as a reference in order to understand the specific biological mechanisms modulated in this class of follicles.

Results

2,942 genes were differentially expressed (P < 0.05) in P vs. G and 1,974 in A vs. P. A clear segregation of the 3 phases was confirmed by between group analysis (BGA). The first characteristic of the plateau phase is the activation of the upstream regulators TP53 and PTEN which participate in the reduction of cell growth through MYC, FOS and E2F1-2-3. We also observed the down-regulation of steroidogenesis genes: CYP11A1 and CYP19A1, in the granulosa cells of the plateau phase relative to the growth phase. On the other hand, the A vs. P contrast showed up-regulation of multiple transcripts associated to apoptosis: CCT2, DAB2, DSG2 and TGM2.

Conclusions

This study offers multiple candidate genes to be further studied in order to elucidate their role in the modulation of follicular development and, ultimately, of oocyte quality.

A novel synthetic 1,3-phenyl bis-thiourea compound targets microtubule polymerization to cause cancer cell death

Microtubules are essential cytoskeletal components with a central role in mitosis and have been particularly useful as a cancer chemotherapy target. We synthesized a small molecule derivative of a symmetrical 1,3-phenyl bis-thiourea, (1,1'-[1,3-phenylene]bis[3-(3,5-dimethylphenyl)thiourea], named "41J"), and identified a potent effect of the compound on cancer cell survival. 41J is cytotoxic to multiple cancer cell lines at nanomolar concentrations. Cell death occurred by apoptosis and was preceded by mitotic arrest in prometaphase. Prometaphase arrest induced by 41J treatment was accompanied by dissociation of cyclin B1 levels from the apparent mitotic stage and by major spindle abnormalities. Polymerization of purified tubulin in vitro was directly inhibited by 41J, suggesting that the compound works by directly interfering with microtubule function. Compound 41J arrested the growth of glioblastoma multiforme xenografts in nude mice at doses that were well-tolerated, demonstrating a relatively specific antitumor effect. Importantly, 41J overcame drug resistance due to β-tubulin mutation and P-glycoprotein overexpression. Compound 41J may serve as a useful new lead compound for anticancer therapy development.

Cks confers specificity to phosphorylation-dependent CDK signaling pathways

Cks is an evolutionarily conserved protein that regulates cyclin-dependent kinase (CDK) activity. Clarifying the underlying mechanisms and cellular contexts of Cks function is critical because Cks is essential for proper cell growth, and its overexpression has been linked to cancer. We observe that budding-yeast Cks associates with select phosphorylated sequences in cell cycle-regulatory proteins. We characterize the molecular interactions responsible for this specificity and demonstrate that Cks enhances CDK activity in response to specific priming phosphosites. Identification of the binding consensus sequence allows us to identify putative Cks-directed CDK substrates and binding partners. We characterize new Cks-binding sites in the mitotic regulator Wee1 and discover a new role for Cks in regulating CDK activity at mitotic entry. Together, our results portray Cks as a multifunctional phosphoadaptor that serves as a specificity factor for CDK activity.

Overexpression of CDC28 protein kinase regulatory subunit 1B confers an independent prognostic factor in nasopharyngeal carcinoma

Data mining on public domain identified that CDC28 protein kinase regulatory subunit 1B (CKS1B) transcript was highly expressed in nasopharyngeal carcinoma (NPC). The expression of CKS1B protein and its clinicopathological associations in patients with NPC were further evaluated. Immunoexpression of CKS1B was retrospectively assessed in biopsies of 124 consecutive NPC patients without initial distant metastasis and treated with consistent guidelines. The correlations between CKS1B immunoexpression levels and clinicopathological features, as well as patient survivals, were analyzed. High CKS1B expression (49.2%) was correlated with the 7th American Joint Committee on Cancer (AJCC) stage (p = 0.014). In multivariate analyses, high CKS1B expression emerged as an independent prognostic factor for worse disease-specific survival (p < 0.001), metastasis-free survival (p < 0.001), and local recurrence-free survival (p = 0.001). High expression of CKS1B is common and associated with adverse prognostic factors and might confer tumor aggressiveness through dysregulation of the cyclin-dependent protein kinase (intrinsic regulatory activity) during cell cycle progression.

Expression and clinical significance of cyclin kinase subunit 2 in colorectal cancer

The overexpression of cyclin kinase subunit 2 (CKS2) is tightly correlated with tumor aggressiveness and prognosis in various malignancies, including gastric, breast, liver and prostate cancer. However, whether CKS2 is upregulated in colorectal cancer (CRC) remains unknown. The aim of the present study was to analyze CKS2 expression levels in CRC, and to determine the clinical diagnostic and prognostic values of CKS2 overexpression in CRC patients. CKS2 expression was analyzed at the mRNA and protein levels by quantitative (q)PCR and western blot analysis. CKS2 expression was significantly upregulated in CRC compared with the adjacent non-cancer and normal colorectal tissues. The overexpression of CKS2 was correlated with poor differentiation and the pathological stage. In addition, CKS2 overexpression was correlated with aggressive tumor progression in CRC, which indicated that CKS2 may serve as a good CRC biomarker.

miR-26a and its target CKS2 modulate cell growth and tumorigenesis of papillary thyroid carcinoma

Background

While many studies have shown that levels of miR-26a are lower in papillary thyroid carcinoma (PTC), the role and mechanism of miR-26a in PTC are unclear.

Method

We used database searches to select potential mRNA targets of miR-26a. Anti-miR-26a, miR-26a mimic, siRNA for CKS2 and their effects on cell growth, cell-cycle distribution and colony formation were evaluated. We also evaluate the over-expressed miR-26a in TPC-1 cells in severe combined immune-deficient mice. We used luciferase reporter assays, real-time PCR and western blot analysis to measure the expression and activity of miR-26a, CKS2, and related factors such as cyclin B1, cyclin A, cdk1, bcl-xl and Akt. Finally, we measured the relationship between the levels of miR-26a and CKS2 in PTC and normal thyroid tissues.

Results

Relative to normal thyroid tissues, miR-26a is consistently down-regulated in TPC specimens, and CKS2 was identified as a potential target. Up-regulated miR-26a expression or down-regulated CKS2 expression in TPC-1 and CGTH W3 cells lines caused G2 phase-arrest. Decreased miR-26a expression or increased CKS2 expression could have inverse function on PTC cell lines. CyclinB1, cyclinA, bcl-xl and AKt are indirectly regulated by miR-26a in a CKS2-dependent manner. Finally, CKS2 is overexpressed in PTC specimens relative to normal thyroid tissue, and a significant inverse correlation exists between miR-26a and CKS2 expression in clinical PTC specimens.

Conclusion

Our data indicate that miR-26a functions as a growth-suppressive miRNA in PTC, and that its suppressive effects are mediated mainly by repressing CKS2 expression.

Cks1 enhances transcription efficiency at the GAL1 locus by linking the Paf1 complex to the 19S proteasome

Cks1 was originally identified based on genetic interactions with CDC28, the gene that encodes Cdk1 in the budding yeast Saccharomyces cerevisiae. Subsequent work has shown that Cks1 binds Cdc28 and modulates its activity against certain substrates. However, the Cks1/Cdc28 complex also has a role in transcriptional chromatin remodeling not related to kinase activity. In order to elucidate protein networks associated with Cks1 transcriptional functions, proteomic analysis was performed on immunoaffinity-purified Cks1, identifying a physical interaction with the Paf1 complex. Specifically, we found that the Paf1 complex component Rtf1 interacts directly with Cks1 and that this interaction is essential for efficient recruitment of Cks1 to chromatin in the context of GAL1 gene induction. We further found that Cks1 in this capacity serves as an adaptor allowing Rtf1 to recruit 19S proteasome particles, shown to be required for efficient RNA production from some rapidly inducible genes such as GAL1.

Telmisartan exerts pleiotropic effects in endothelial cells and promotes endothelial cell quiescence and survival

OBJECTIVE

Telmisartan, an angiotensin II type 1 receptor blocker, and amlodipine, a calcium channel blocker, are antihypertensive agents clinically used as monotherapy or in combination. They exert beneficial cardiovascular effects independently of blood pressure lowering and classic mechanisms of action. In this study, we investigate molecular mechanisms responsible for the off-target effects of telmisartan and telmisartan-amlodipine in endothelial cells (ECs), using an unbiased genomic approach.

APPROACH AND RESULTS

In human umbilical vein ECs, microarray analysis of gene expression followed by pathway enrichment analysis and quantitative polymerase chain reaction validation revealed that telmisartan modulates the expression of key genes responsible for cell cycle progression and apoptosis. Amlodipine's effect was similar to control. ECs exposed to telmisartan, but not amlodipine, losartan, or valsartan, exhibited a dose-dependent impairment of cell growth and failed to enter the S-phase of the cell cycle. Similarly, telmisartan inhibited proliferation in COS-7 cells lacking the angiotensin II type 1 receptor. In telmisartan-treated ECs, phosphorylation and activation of Akt, as well as MDM2, were reduced, leading to accumulation of p53 in the nucleus, where it represses the transcription of cell cycle-promoting genes. Phosphorylation of glycogen synthase kinase-3β was also reduced, resulting in rapid proteolytic turnover of CyclinD1. Telmisartan induced downregulation of proapoptotic genes and protected ECs from serum starvation-induced and 7-ketocholesterol-induced apoptosis.

CONCLUSIONS

Telmisartan exerts antiproliferative and antiapoptotic effects in ECs. This may account for the improved endothelial dysfunction observed in the clinical setting.

Flipping the switch from g1 to s phase with e3 ubiquitin ligases

The cell cycle ensures genome maintenance by coordinating the processes of DNA replication and chromosome segregation. Of particular importance is the irreversible transition from the G1 phase of the cell cycle to S phase. This transition marks the switch from preparing chromosomes for replication ("origin licensing") to active DNA synthesis ("origin firing"). Ubiquitin-mediated proteolysis is essential for restricting DNA replication to only once per cell cycle and is the major mechanism regulating the G1 to S phase transition. Although some changes in protein levels are attributable to regulated mRNA abundance, protein degradation elicits very rapid changes in protein abundance and is critical for the sharp and irreversible transition from one cell cycle stage to the next. Not surprisingly, regulation of the G1-to-S phase transition is perturbed in most cancer cells, and deregulation of key molecular events in G1 and S phase drives not only cell proliferation but also genome instability. In this review we focus on the mechanisms by which E3 ubiquitin ligases control the irreversible transition from G1 to S phase in mammalian cells.

Cancer specificity of promoters of the genes involved in cell proliferation control

Core promoters with adjacent regions of the human genes CDC6, POLD1, CKS1B, MCM2, and PLK1 were cloned into a pGL3 vector in front of the Photinus pyrails gene Luc in order to study the tumor specificity of the promoters. The cloned promoters were compared in their ability to direct luciferase expression in different human cancer cells and in normal fibroblasts. The cancer-specific promoter BIRC5 and non-specific CMV immediately early gene promoter were used for comparison. All cloned promoters were shown to be substantially more active in cancer cells than in fibroblasts, while the PLK1 promoter was the most cancer-specific and promising one. The specificity of the promoters to cancer cells descended in the series PLK1, CKS1B, POLD1, MCM2, and CDC6. The bidirectional activity of the cloned CKS1B promoter was demonstrated. It apparently directs the expression of the SHC1 gene, which is located in a "head-to-head" position to the CKS1B gene in the human genome. This feature should be taken into account in future use of the CKS1B promoter. The cloned promoters may be used in artificial genetic constructions for cancer gene therapy.

Cks1: Structure, Emerging Roles and Implications in Multiple Cancers

Deregulation of the cell cycle results in loss of normal control mechanisms that prevent aberrant cell proliferation and cancer progression. Regulation of the cell cycle is a highly complex process with many layers of control. One of these mechanisms involves timely degradation of CDK inhibitors (CKIs) like p27^Kip1 by the ubiquitin proteasomal system (UPS). Cks1 is a 9 kDa protein which is frequently overexpressed in different tumor subtypes, and has pleiotropic roles in cell cycle progression, many of which remain to be fully characterized. One well characterized molecular role of Cks1 is that of an essential adaptor that regulates p27^Kip1 abundance by facilitating its interaction with the SCF-Skp2 E3 ligase which appends ubiquitin to p27^Kip1 and targets it for degradation through the UPS. In addition, emerging research has uncovered p27^Kip1-independent roles of Cks1 which have provided crucial insights into how it may be involved in cancer progression. We review here the structural features of Cks1 and their functional implications, and also some recently identified Cks1 roles and their involvement in breast and other cancers.

Oncogenic potential of cyclin kinase subunit-2 in cholangiocarcinoma

BACKGROUND

Cyclin kinase subunit-2 (Cks2), a member of the human Cks family, plays an important role in the regulation of meiosis and mitosis; and its abnormal expression is usually associated with carcinogenesis. However, its exact functions and molecular mechanisms remain unclear.

AIMS

To observe Cks2 expression in cholangiocarcinoma and explore its role in the carcinogenesis of cholangiocarcinoma and possible mechanism.

METHODS

Cks2 expression in cholangiocarcinoma was detected with immunostaining and RT-PCR. MTT, colony formation, immunofluorescence, flow cytometry and Western blotting were performed to explore the role of Cks2 in cholangiocarcinoma and possible mechanism.

RESULTS

Cks2 was significantly elevated in cholangiocarcinoma tissues and its over-expression was associated with poor differentiation, CA19-9 and poor prognosis. Furthermore, Cks2 down-regulation inhibited cholangiocarcinoma cell proliferation and colony formation in vitro, and the growth of cholangiocarcinoma xenografts in animals; especially, enhanced the sensitivity of cholangiocarcinoma cells to chemotherapy. We further found that Cks2 knockdown induced cholangiocarcinoma cell cycle arrest in G2/M phase through down-regulation of Cyclin A and Cyclin B1 and Bax up-regulation and activation, mitochondrial membrane permeabilization and caspase-3 activation, which resulted in facilitating cholangiocarcinoma apoptosis.

CONCLUSIONS

These findings suggest that Cks2 may serve as an independent prognostic factor in patients with cholangiocarcinoma, and play an important role in the carcinogenesis of cholangiocarcinoma by facilitating cell cycle progression and Bax-mediated mitochondrial caspase-dependent apoptosis.

The CDK subunit CKS2 counteracts CKS1 to control cyclin A/CDK2 activity in maintaining replicative fidelity and neurodevelopment

CKS proteins are evolutionarily conserved cyclin-dependent kinase (CDK) subunits whose functions are incompletely understood. Mammals have two CKS proteins. CKS1 acts as a cofactor to the ubiquitin ligase complex SCF^SKP2 to promote degradation of CDK inhibitors, such as p27. Little is known about the role of the closely related CKS2. Using a Cks2^−/− knockout mouse model, we show that CKS2 counteracts CKS1 and stabilizes p27. Unopposed CKS1 activity in Cks2^−/− cells leads to loss of p27. The resulting unrestricted cyclin A/CDK2 activity is accompanied by shortening of the cell cycle, increased replication fork velocity, and DNA damage. In vivo, Cks2^−/− cortical progenitor cells are limited in their capacity to differentiate into mature neurons, a phenotype akin to animals lacking p27. We propose that the balance between CKS2 and CKS1 modulates p27 degradation, and with it cyclin A/CDK2 activity, to safeguard replicative fidelity and control neuronal differentiation.

Cks1 promotion of S phase entry and proliferation is independent of p27Kip1 suppression

Cks1 is an activator of the SCF(Skp2) ubiquitin ligase complex that targets the cell cycle inhibitor p27(Kip1) for degradation. The loss of Cks1 results in p27(Kip1) accumulation and decreased proliferation and inhibits tumorigenesis. We identify here a function of Cks1 in mammalian cell cycle regulation that is independent of p27(Kip1). Specifically, Cks1(-/-); p27(Kip1-/-) mouse embryonic fibroblasts retain defects in the G(1)-S phase transition that are coupled with decreased Cdk2-associated kinase activity and defects in proliferation that are associated with Cks1 loss. Furthermore, concomitant loss of Cks1 does not rescue the tumor suppressor function of p27(Kip1) that is manifest in various organs of p27(Kip1-/-) mice. In contrast, defects in mitotic entry and premature senescence manifest in Cks1(-/-) cells are p27(Kip1) dependent. Collectively, these findings establish p27(Kip1)-independent functions of Cks1 in regulating the G(1)-S transition.

Cyclin-dependent kinase-associated protein Cks2 is associated with bladder cancer progression

In this observational retrospective study, expression of possible cancer-related genes was measured in patients with a pathological diagnosis of superficial bladder cancer. Further measurements were made in those who subsequently developed muscle-invasive cancer. Seven of the 45 patients with superficial bladder cancer progressed to muscle-invasive cancer. Expression of fatty acid binding protein 5 (FABP5), poly(A) binding protein cytoplasmic 1 (PABPC1), DEAD box polypeptide 5 (DDX5), splicing factor 3b subunit 1 (SF3B1), murine mammary tumour integration site 6 (EIF3S6), tropomyosin 2β (TPM2), transgelin (TAGLN) and cyclin-dependent kinase-associated protein (Cks2) genes was measured in bladder samples using real-time reverse transcription-polymerase chain reaction. FABP5, PABPC1, DDX5, SF3B1, EIF3S6 and Cks2 expression levels were significantly increased, and TPM2 and TAGLN were significantly decreased, in superficial bladder cancer compared with normal bladder tissue. In patients who developed muscle-invasive cancer, the Cks2 gene showed significantly increased expression after, compared with before, invasion. The Cks2 gene may have potential as a biomarker for predicting superficial bladder cancer progression to muscle-invasive cancer.

Cks85A and Skp2 interact to maintain diploidy and promote growth in Drosophila

The Cks or Suc1 proteins are highly conserved small proteins that play remarkably diverse roles in the cell cycle. All Cks homologues have the ability to associate with Cyclin dependent kinases (Cdks) and in many cases this interaction has been shown to be important for function. Here we characterize the null and RNAi knockdown phenotype of the Drosophila Cks1 (Cks85A) gene. Cks85A is essential for viability in Drosophila. Cks85A null animals have reduced overall growth and this correlates with reduced ploidy and impaired DNA replication in endoreplicating cells. Interestingly, Cks85A is also required for the maintenance of diploidy in mitotically cycling cells. The requirement for Cks85A in growth is similar to that of the mammalian Cks1, which was found to interact with the SCF(Skp2) ubiquitin ligase. We identified the Drosophila Skp2 gene and generated null alleles. Comparison of these mutants to null mutants for Cks85A reveals a remarkably similar dual requirement in growth and in maintenance of diploidy. We find that Cks85A interacts directly with the SCF(Skp2) ubiquitin ligase and genetic evidence indicates that this is its major molecular function. The closely related Cks30A cannot interact with the SCF(Skp2) and cannot functionally compensate for loss of Cks85A. We also find that the critical growth promoting and diploidy maintaining functions of Cks85A and Skp2 are independent of known SCF(Skp2) substrates, p27 and Cdt1, indicating that other critical substrates remain to be identified.

Cyclin-dependent kinase subunit (Cks) 1 or Cks2 overexpression overrides the DNA damage response barrier triggered by activated oncoproteins

Cyclin-dependent kinase subunit (Cks) proteins are small cyclin-dependent kinase-interacting proteins that are frequently overexpressed in breast cancer, as well as in a broad spectrum of other human malignancies. However, the mechanistic link between Cks protein overexpression and oncogenesis is still unknown. In this work, we show that overexpression of Cks1 or Cks2 in human mammary epithelial and breast cancer-derived cells, as well as in other cell types, leads to override of the intra-S-phase checkpoint that blocks DNA replication in response to replication stress. Specifically, binding of Cks1 or Cks2 to cyclin-dependent kinase 2 confers partial resistance to the effects of inhibitory tyrosine phosphorylation mediated by the intra-S-phase checkpoint, allowing cells to continue replicating DNA even under conditions of replicative stress. Because many activated oncoproteins trigger a DNA damage checkpoint response, which serves as a barrier to proliferation and clonal expansion, Cks protein overexpression likely constitutes one mechanism whereby premalignant cells can circumvent this DNA damage response barrier, conferring a proliferative advantage under stress conditions, and therefore contributing to tumor development.

Preliminary evidence for leukocyte transcriptional signatures for pediatric ventilator-associated pneumonia

OBJECTIVE

Ventilator-associated pneumonia (VAP) is a significant contributor to intensive care unit (ICU) morbidity and mortality and presents a significant diagnostic challenge. Our hypothesis was that blood RNA expression profiles can be used to track the response to VAP in children, using the same methods that proved informational in adults.

DESIGN

A pilot, nonrandomized, repeated measures case-control study of changes in the abundance of total RNA in buffy coat and clinical scores for VAP.

SETTING

A large, multispecialty university-based pediatric ICU and cardiac ICU.

PATIENTS

Seven children requiring intubation and mechanical ventilation.

INTERVENTIONS

Blood samples were drawn at time of enrollment and every 48 hours for a maximum of 11 samples (21 days). Patients ranged in age from 1 to 18 months (mean 8 months). All patients survived to the end of the study. Of the 7 patients studied, 4 developed VAP.

MEASUREMENTS AND MAIN RESULTS

Statistical analysis of the Affymetrix Human Genome Focus GeneChip signal was conducted on normalized expression values of 8793 probe sets using analysis of variance (ANOVA) with a false discovery rate of 0.10. The expression patterns of 48 genes appeared to discriminate between the 2 classes of ventilated children: those with and those without pneumonia. Gene expression network analysis revealed several gene ontologies of interest, including cell proliferation, differentiation, growth, and apoptosis, as well as genes not previously implicated in sepsis.

CONCLUSIONS

These preliminary data are the first in critically ill children supporting the hypothesis that there is a detectable VAP signal in gene expression profiles. Larger studies are needed to validate these preliminary findings and test the diagnostic value of longitudinal changes in leukocyte RNA signatures.

Over-expression of CKS1B activates both MEK/ERK and JAK/STAT3 signaling pathways and promotes myeloma cell drug-resistance

Here we demonstrate the crucial role of CKS1B in multiple myeloma (MM) progression and define CKS1B-mediated SKP2/p27^Kip1-independent down-stream signaling pathways. Forced-expression of CKS1B in MM cells increased cell multidrug-resistance. CKS1B activates STAT3 and MEK/ERK pathways. In contrast, SKP2 knockdown or p27^Kip1 over-expression resulted in activation of the STAT3 and MEK/ERK pathways. Further investigations showed that BCL2 is a downstream target of MEK/ERK signaling. Stimulation of STAT3 and MEK/ERK signaling pathways partially abrogated CKS1B knockdown induced MM cell death and growth inhibition. Targeting STAT3 and MEK/ ERK signaling pathways by specific inhibitors induced significant MM cell death and growth inhibition in CKS1B-overexpressing MM cells and their combinations resulted in synergy. Thus, our findings provide a rationale for targeting STAT3 and MEK/ERK/ BCL2 signaling in aggressive CKS1B-overexpressing MM.

Upregulation of miR-21 by Ras in vivo and its role in tumor growth

miR-21 is a microRNA (miRNA) frequently overexpressed in human cancers. Here we show that miR-21 is upregulated both in vitro and in vivo by oncogenic Ras, thus linking this miRNA to one of the most frequently activated oncogenes in human cancers. Ras regulation of miR-21 occurs with a delayed kinetic and requires at least two Ras downstream pathways. A screen of human thyroid cancers and non-small-cell lung cancers for the expression of miR-21 reveals that it is overexpressed mainly in anaplastic thyroid carcinomas, the most aggressive form of thyroid cancer, whereas in lung its overexpression appears to be inversely correlated with tumor progression. We also show that a LNA directed against miR-21 slows down tumor growth in mice. Consistently, a search for mRNAs downregulated by miR-21 shows an enrichment for mRNAs encoding cell cycle checkpoints regulators, suggesting an important role for miR-21 in oncogenic Ras-induced cell proliferation.

Expression and biological-clinical significance of hTR, hTERT and CKS2 in washing fluids of patients with bladder cancer

BACKGROUND

at present, pathogenesis of bladder cancer (BC) has not been fully elucidated. Aim of this study is to investigate the role of human telomerase RNA (hTR), human telomerase reverse transcriptase (hTERT) and CDC28 protein kinase regulatory subunit 2 (CKS2) in bladder carcinogenesis and their possible clinical significance;

METHODS

the transcript levels of hTR, hTERT and CKS2 were quantified by Real time reverse transcriptase chain reaction in exfoliated cells from bladder washings of 36 patients with BC and 58 controls. The statistical significance of differences between BC bearing patients and control groups, in the general as well as in the stratified analysis (superficial or invasive BC), was assessed by Student's t test. Non parametric Receiver Operating Characteristics analysis (ROC) was performed to ascertain the accuracy of study variables to discriminate between BC and controls. The clinical value of concomitant examination of hTR, hTERT and CKS2 was evaluated by logistic regression analysis;

RESULTS

a significant decrease in hTR and a significant increase in hTERT or CKS2 gene expression were found between BC bearing patients and controls, as well as in the subgroups analysis. The area under the curve (AUC) indicated an average discrimination power for the three genes, both in the general and subgroups analysis, when singularly considered. The ability to significantly discriminate between superficial and invasive BC was observed only for hTR transcript levels. A combined model including hTR and CKS2 was the best one in BC diagnosis;

CONCLUSIONS

our results, obtained from a sample set particularly rich of exfoliated cells, provide further molecular evidence on the involvement of hTR, hTERT and CKS2 gene expression in BC carcinogenesis. In particular, while hTERT and CKS2 gene expression seems to have a major involvement in the early stages of the disease, hTR gene expression, seems to be more involved in progression. In addition, our findings suggest that the studied genes have a clinical role in discriminating between BC and controls in the general as well as in the stratified analysis, when singularly considered. A combined model improved over the single marker BC diagnosis.

The APC/C recruits cyclin B1-Cdk1-Cks in prometaphase before D box recognition to control mitotic exit

Prior associations with the APC/C complex during prometaphase makes cyclin B1 a better substrate for the cell cycle–regulating ubiquitin ligase in metaphase (see also a related paper by Di Fiore et al. in this issue).

The ubiquitin ligase anaphase-promoting complex/cyclosome (APC/C) is activated at prometaphase by mitotic phosphorylation and binding of its activator, Cdc20. This initiates cyclin A degradation, whereas cyclin B1 is stabilized by the spindle checkpoint. Upon checkpoint release, the RXXL destruction box (D box) was proposed to direct cyclin B1 to core APC/C or Cdc20. In this study, we report that endogenous cyclin B1–Cdk1 is recruited to checkpoint-inhibited, phosphorylated APC/C in prometaphase independently of Cdc20 or the cyclin B1 D box. Like cyclin A, cyclin B1 binds the APC/C by the Cdk cofactor Cks and the APC3 subunit. Prior binding to APC/C^Cdc20 makes cyclin B1 a better APC/C substrate in metaphase, driving mitotic exit and cytokinesis. We conclude that in prometaphase, the phosphorylated APC/C can recruit both cyclin A and cyclin B1 in a Cks-dependent manner. This suggests that the spindle checkpoint blocks D box recognition of APC/C-bound cyclin B1, whereas distinctive complexes between the N terminus of cyclin A and Cdc20 evade checkpoint control.

FoxM1 is up-regulated by obesity and stimulates beta-cell proliferation

beta-Cell mass expansion is one mechanism by which obese animals compensate for insulin resistance and prevent diabetes. FoxM1 is a transcription factor that can regulate the expression of multiple cell cycle genes and is necessary for the maintenance of adult beta-cell mass, beta-cell proliferation, and glucose homeostasis. We hypothesized that FoxM1 is up-regulated by nondiabetic obesity and initiates a transcriptional program leading to beta-cell proliferation. We performed gene expression analysis on islets from the nondiabetic C57BL/6 Leptin(ob/ob) mouse, the diabetic BTBR Leptin(ob/ob) mouse, and an F2 Leptin(ob/ob) population derived from these strains. We identified obesity-driven coordinated up-regulation of islet Foxm1 and its target genes in the nondiabetic strain, correlating with beta-cell mass expansion and proliferation. This up-regulation was absent in the diabetic strain. In the F2 Leptin(ob/ob) population, increased expression of Foxm1 and its target genes segregated with higher insulin and lower glucose levels. We next studied the effects of FOXM1b overexpression on isolated mouse and human islets. We found that FoxM1 stimulated mouse and human beta-cell proliferation by activating many cell cycle phases. We asked whether FOXM1 expression is also responsive to obesity in human islets by collecting RNA from human islet donors (body mass index range: 24-51). We found that the expression of FOXM1 and its target genes is positively correlated with body mass index. Our data suggest that beta-cell proliferation occurs in adult obese humans in an attempt to expand beta-cell mass to compensate for insulin resistance, and that the FoxM1 transcriptional program plays a key role in this process.

Functional modules in the Arabidopsis core cell cycle binary protein-protein interaction network

As in other eukaryotes, cell division in plants is highly conserved and regulated by cyclin-dependent kinases (CDKs) that are themselves predominantly regulated at the posttranscriptional level by their association with proteins such as cyclins. Although over the last years the knowledge of the plant cell cycle has considerably increased, little is known on the assembly and regulation of the different CDK complexes. To map protein-protein interactions between core cell cycle proteins of Arabidopsis thaliana, a binary protein-protein interactome network was generated using two complementary high-throughput interaction assays, yeast two-hybrid and bimolecular fluorescence complementation. Pairwise interactions among 58 core cell cycle proteins were tested, resulting in 357 interactions, of which 293 have not been reported before. Integration of the binary interaction results with cell cycle phase-dependent expression information and localization data allowed the construction of a dynamic interaction network. The obtained interaction map constitutes a framework for further in-depth analysis of the cell cycle machinery.

Transcritpional effects of S100B on neuroblastoma cells: perturbation of cholesterol homeostasis and interference on the cell cycle

S100B is a Ca2+ binding protein mainly secreted by astrocytes in the vertebrate brain that is considered a multifunctional cytokine and/or a damage-associated molecular pattern (DAMP) protein and a marker of brain injury and neurodegeneration when measured in different body fluids. It has been widely shown that this protein can exert diverse effects in neural cultures depending on its concentration, having detrimental effects at micromolar concentrations. The molecular mechanisms underlying this effect are still largely unknown. This study attempts to delineate the genome-wide gene expression analysis of the events associated with exposure to micromolar concentration of S100B in a human neuroblastoma cell line. In this experimental condition cells undergo a severe perturbation of lipid homeostasis along with cell cycle arrest. These mechanisms might reasonably mediate some aspects of the S100B-related detrimental effects of S100B, although obvious differences between mature neurons and neuroblastoma cells have to be considered.

Changes in expression of cell-cycle-related genes in PC-3 prostate cancer cells caused by ovine uterine serpin

The hormonal-regulated serpin, ovine uterine serpin (OvUS), also called uterine milk protein (UTMP), inhibits proliferation of lymphocytes and prostate cancer (PC-3) cells by blocking cell-cycle progression. The present aim was to identify cell-cycle-related genes regulated by OvUS in PC-3 cells using the quantitative human cell-cycle RT(2) Profiler PCR array. Cells were cultured +/-200 microg/ml recombinant OvUS (rOvUS) for 12 and 24 h. At 12 h, rOvUS increased expression of three genes related to cell-cycle checkpoints and arrest (CDKN1A, CDKN2B, and CCNG2). Also, 14 genes were down-regulated including genes involved in progression through S (MCM3, MCM5, PCNA), M (CDC2, CKS2, CCNH, BIRC5, MAD2L1, MAD2L2), G(1) (CDK4, CUL1, CDKN3) and DNA damage checkpoint and repair genes RAD1 and RBPP8. At 24 h, rOvUS decreased expression of 16 genes related to regulation and progression through M (BIRC5, CCNB1, CKS2, CDK5RAP1, CDC20, E2F4, MAD2L2) and G(1) (CDK4, CDKN3, TFDP2), DNA damage checkpoints and repair (RAD17, BRCA1, BCCIP, KPNA2, RAD1). Also, rOvUS down-regulated the cell proliferation marker gene MKI67, which is absent in cells at G(0). Results showed that OvUS blocks cell-cycle progression through upregulation of cell-cycle checkpoint and arrest genes and down-regulation of genes involved in cell-cycle progression.

CKS proteins protect mitochondrial genome integrity by interacting with mitochondrial single-stranded DNA-binding protein

Cyclin-dependent kinase subunit (CKS) proteins interact with cyclin-dependent kinases (CDKs) with high affinity. Mammalian CKS1 and CKS2 bind CDK1 and CDK2 and partake in the control of cell cycle progression. We identified CKS-interacting proteins by affinity purification followed by mass spectrometry in the human lymphocytic cell line Ramos. Apart from known interactors, such as CDKs, we identified a novel CDK-dependent interaction between CKS proteins and the mitochondrial single-stranded DNA-binding protein (mtSSB). mtSSB bound both CKS1 and CKS2 and underwent CDK-dependent phosphorylation. mtSSB is known to participate in replication of mitochondrial DNA. We demonstrated that mitochondrial morphology and DNA integrity were compromised in cells depleted of both CKS proteins or that had inhibited CDK activity. These features are consistent with the hypothesis of CKS-dependent regulation of mtSSB function and support a direct role of cell cycle proteins in controlling mitochondrial DNA replication.

Loss of cks1 homeostasis deregulates cell division cycle

Genetic and biochemical studies have provided considerable insight into the multiple functions of cyclin-dependent kinase subunit (cks)1 in cell division cycle. In addition to enhanced substrate targeting by specific ubiquitin ligases SCF(skp2) and APC/C, its direct interaction with proteasome components normalizes multiple cell cycle regulators. Importantly, it also acts as a transcriptional regulator. cks1 overexpression reflects poor prognosis in malignancy thus indicating its possible role in tumour diagnosis and management. The present review compiles the multiple functional roles of cks1 in cell division with specific emphasis on its molecular mechanisms. Its docking functions and the possible downstream proteolytic and transcriptional targets are described. The spatial configuration of cks1-cdk2 complex and the structural organization of cks1-p27-skp2 assembly required for p27 ubiquitination are discussed in detail. In addition to enhanced p27 degradation, the possible other mechanisms which underlie its pathological functions in human cancer progression are also discussed. Though there are apparent gaps in information, the turnover mechanism of cks1 is well addressed and presents opportunity to exploit the target for disease management.

Upregulation of the cycline kinase subunit CKS2 increases cell proliferation rate in gastric cancer

PURPOSE

CKS2 was identified as an upregulated gene in gastric cancer via our DNA microarray. This study was to verify the upregulation of CKS2 in many gastric cancer patients and to examine the CKS2-mediated cellular response.

METHODS

CKS2 upregulation was analyzed using reverse transcriptase PCR, real-time PCR, and immunohistochemical and clinicopathological analyses. GFP-CKS2 or CKS2-siRNA was used to analyze the cellular localization and proliferation.

RESULTS

The strong upregulation of mRNA and protein levels of CKS2 was identified. In CKS2-overexpressing cells, tumor suppressor p53 and p21(cip1) were downregulated and cell growth was increased. In contrast, CKS2-siRNA-transfected cells showed an increased tumor suppressor expression and decreased cell growth.

CONCLUSIONS

We showed that CKS2 was significantly upregulated in gastric cancers and a high level of CKS2 was highly correlated with histologic tumor differentiation and pathological grade of the tumor size, lymph node, and metastasis stage. We suggest that the cell cycle regulator CKS2 might be deeply involved in gastric cancer progression.