Differential expression of cdc25 cell-cycle-activating phosphatases in human colorectal carcinoma

Upregulation of CDC25B by transcription factor TEAD4 drives invasion and inhibits cisplatin sensitivity through cell adhesion in stomach adenocarcinoma

Cisplatin is crucial in management of advanced stomach adenocarcinoma, whereas development of chemotherapy resistance hinders overall efficacy of cisplatin. This work aims to explore role of CDC25B in cisplatin sensitivity in stomach adenocarcinoma and offer a possible mechanism for explaining its function. By using bioinformatics approaches, CDC25B and TEAD4 expression levels in stomach adenocarcinoma tissues and enriched pathways of CDC25B were analyzed. qRT-PCR of CDC25B and TEAD4 expression in stomach adenocarcinoma cells, CCK-8 detection of cell viability and IC 50 values, and colony formation assay on cell proliferation were performed. Cell adhesion experiment detected cell adhesion ability. Western blot detected expression of proteins related to cell adhesion, specifically Muc-1, ICAM-1, VCAM-1. Dual luciferase assay and ChIP experiment verified binding relationship between TEAD4 and CDC25B. CDC25B was upregulated in stomach adenocarcinoma tissues and cells, enriched in focal adhesion pathway. Treatment with cell adhesion inhibitors revealed that CDC25B overexpression inhibits the sensitivity of stomach adenocarcinoma to cisplatin through the cell adhesion pathway. CDC25B has an upstream transcription factor TEAD4, which targeted and bound to CDC25B and was highly expressed in stomach adenocarcinoma. Rescue experiment revealed that knocking down TEAD4 weakened suppressive impact of CDC25B overexpression on sensitivity of stomach adenocarcinoma cells to cisplatin. Transcription factor TEAD4 could activate the transcription of CDC25B through cell adhesion to drive cell invasion and reduce sensitivity of stomach adenocarcinoma to cisplatin. TEAD4 and CDC25B may become new targets for management of stomach adenocarcinoma.

6-Regioisomeric 5,8-quinolinediones as potent CDC25 inhibitors against colorectal cancers

Precise and accurate control of cell cycle progression is required to maintain cell identity and proliferation. Failing to keep it will lead to genome instability and tumorigenesis. Cell Division Cycle 25 (CDC25) phosphatases are the key to regulating the activity of the master cell cycle controller, cyclin-dependent kinases (CDKs). Dysregulation of CDC25 has been shown to associate with several human malignancies. Here, we reported a series of derivatives of the CDC25 inhibitor, NSC663284, bearing quinones as core scaffolds and morpholin alkylamino side chains. Among these derivatives, the cytotoxic activity of the 6-isomer of 5,8-quinolinedione derivatives (6b, 16b, 17b, and 18b) displayed higher potency against colorectal cancer (CRC) cells. Compound 6b possessed the most antiproliferative activity, with IC₅₀ values of 0.59 μM (DLD1) and 0.44 μM (HCT116). The treatment of compound 6b resulted in a remarkable effect on cell cycle progression, blocking S-phase progression in DLD1 cells straight away while slowing S-phase progression and accumulated cells in the G₂/M phase in HCT116 cells. Furthermore, we showed that compound 6b inhibited CDK1 dephosphorylation and H4K20 methylation in cells. The treatment with compound 6b induced DNA damage and triggered apoptosis. Our study identifies compound 6b as a potent CDC25 inhibitor that induces genome instability and kills cancer cells through an apoptotic pathway, deserving further investigation to fulfill its candidacy as an anti-CRC agent.

Cyclin-dependent kinases as potential targets for colorectal cancer: past, present and future

Colorectal cancer (CRC) is a common cancer in the world and its prevalence is increasing in developing countries. Deregulated cell cycle traverse is a hallmark of malignant transformation and is often observed in CRC as a result of imprecise activity of cell cycle regulatory components, viz. cyclins and cyclin-dependent kinases (CDKs). Apart from cell cycle regulation, some CDKs also regulate processes such as transcription and have also been shown to be involved in colorectal carcinogenesis. This article aims to review cyclin-dependent kinases as potential targets for CRC. Furthermore, therapeutic candidates to target CDKs are also discussed.

METTL3 modulates m6A modification of CDC25B and promotes head and neck squamous cell carcinoma malignant progression

BACKGROUND

N6-methyladenosine (m6A) RNA methylation and its methyltransferase METTL3 have been widely reported to be involved in different cancers by regulating RNA metabolism and function. Here, we aimed to explore the biological function and clinical significance of m6A modification and METTL3 in head and neck squamous cell carcinoma (HNSCC).

METHODS

The prognostic value of METTL3 expression was evaluated using tissue microarray and immunohistochemical staining analyses in a human HNSCC cohort. The biological role and mechanism of METTL3 in HNSCC tumour growth, metastasis and angiogenesis were determined in vitro and in vivo.

RESULTS

M6A levels and METTL3 expressions in HNSCC tissues were significantly increased compared with paired adjacent tissues. Meanwhile, METTL3 was an independent risk factor for the prognosis of HNSCC patients. Moreover, METTL3 overexpression promoted HNSCC cell proliferation, migration, invasion, and angiogenesis, while knockdown of METTL3 had an opposite effect in vivo and in vitro. Mechanistically, METTL3 enhanced the m6A modification of CDC25B mRNA, which maintained its stability and upregulated its expression, thereby activating G2/M phase of cell cycle and leading to HNSCC malignant progression.

CONCLUSIONS

METTL3 may be a potential prognostic biomarker and therapeutic target for HNSCC.

Molecular Alterations in Meningioangiomatosis Causing Epilepsy

Meningioangiomatosis (MA) is a rare process at the intersection of cerebral developmental and neoplastic disorders that often results in epilepsy. We evaluated molecular alterations in MA to characterize its biology and pathogenesis. We searched a comprehensive institutional database for patients with MA treated between 2004 and 2019. Demographic, clinical, surgical, and radiographical data were collected. MA and associated meningioma tissues were evaluated using a next-generation sequencing assay interrogating 1425 cancer-related genes. We studied 5 cases: 3 with MA and 2 with MA associated with a meningioma. Of the MAs associated with a meningioma, 1 had deletions in the NF2 gene in both the MA and the meningioma components, whereas the other had an NF2 deletion in only the MA component. Additional mutations were identified in the MA components, suggesting that MA arises from the meningioma rather than the meningioma resulting from a transformation of the MA. The 3 cases of pure MA showed variants of unknown significance with no alterations in known oncogenic drivers. Our findings provide a starting point to a better understanding of the pathogenesis of this rare lesion. Our study indicates that MA-meningiomas have a neoplastic nature that differs from the hamartomatous/developmental nature of pure MA.

Discovery of Novel Naphthylphenylketone and Naphthylphenylamine Derivatives as Cell Division Cycle 25B (CDC25B) Phosphatase Inhibitors: Design, Synthesis, Inhibition Mechanism, and in Vitro Efficacy against Melanoma Cell Lines

CDC25 phosphatases play a critical role in the regulation of the cell cycle and thus represent attractive cancer therapeutic targets. We previously discovered the 4-(2-carboxybenzoyl)phthalic acid (NSC28620) as a new CDC25 inhibitor endowed with promising anticancer activity in breast, prostate, and leukemia cells. Herein, we report a structure-based optimization of NSC28620, leading to the identification of a series of novel naphthylphenylketone and naphthylphenylamine derivatives as CDC25B inhibitors. Compounds 7j, 7i, 6e, 7f, and 3 showed higher inhibitory activity than the initial lead, with K_i values in the low micromolar range. Kinetic analysis, intrinsic fluorescence studies, and induced fit docking simulations provided a mechanistic understanding of the activity of these derivatives. All compounds were tested in the highly aggressive human melanoma cell lines A2058 and A375. Compound 4a potently inhibited cell proliferation and colony formation, causing an increase of the G2/M phase and a reduction of the G0/G1 phase of the cell cycle in both cell lines.

Inhibition of CDC25B With WG-391D Impedes the Tumorigenesis of Ovarian Cancer

Novel inhibitors are urgently needed for use as targeted therapies to improve the overall survival (OS) of patients with ovarian cancer. Here, we show that cell division cycle 25B (CDC25B) is over-expressed in ovarian tumors and associated with poor patient prognosis. All previously reported CDC25B inhibitors have been identified by their ability to reversibly inhibit the catalytic dephosphorylation activity of CDC25B in vitro; however, none of these compounds have entered clinical trials for ovarian cancer therapy. In this study, we synthesized a novel small molecule compound, WG-391D, that potently down-regulates CDC25B expression without affecting its catalytic dephosphorylation activity. The inhibition of CDC25B by WG-391D is irreversible, and WG-391D should therefore exhibit potent antitumor activity against ovarian cancer. WG-391D induces cell cycle progression arrest at the G2/M phase. Half maximal inhibitory concentration (IC₅₀) values of WG-391D for inhibition of the proliferation and migration of eight representative ovarian cancer cell lines (SKOV3, ES2, OVCAR8, OVTOKO, A2780, IGROV1, HO8910PM, and MCAS) and five primary ovarian tumor cell lines (GFY004, GFY005, CZ001, CZ006, and CZ008) were lower than 10 and 1 μM, respectively. WG-391D inhibited tumor growth in nude mice inoculated with SKOV3 cells or a patient-derived xenograft (PDX). The underlying mechanisms were associated with the down-regulation of CDC25B and subsequent inactivation of cell division cycle 2 (CDC2) and the serine/threonine kinase, AKT. In conclusion, this study demonstrates that WG-391D exhibits strong antitumor activity against ovarian cancer and indicates that the down-regulation of CDC25B by inhibitors could provide a rationale for ovarian cancer therapy.

Ligand-based chemoinformatic discovery of a novel small molecule inhibitor targeting CDC25 dual specificity phosphatases and displaying in vitro efficacy against melanoma cells

CDC25 phosphatases are important regulators of the cell cycle and represent promising targets for anticancer drug discovery. We recently identified NSC 119915 as a new quinonoid CDC25 inhibitor with potent anticancer activity. In order to discover more active analogs of NSC 119915, we performed a range of ligand-based chemoinformatic methods against the full ZINC drug-like subset and the NCI lead-like set. Nine compounds (3, 5-9, 21, 24, and 25) were identified with Ki values for CDC25A, -B and -C ranging from 0.01 to 4.4 μM. One of these analogs, 7, showed a high antiproliferative effect on human melanoma cell lines, A2058 and SAN. Compound 7 arrested melanoma cells in G2/M, causing a reduction of the protein levels of CDC25A and, more consistently, of CDC25C. Furthermore, an intrinsic apoptotic pathway was induced, which was mediated by ROS, because it was reverted in the presence of antioxidant N-acetyl-cysteine (NAC). Finally, 7 decreased the protein levels of phosphorylated Akt and increased those of p53, thus contributing to the regulation of chemosensitivity through the control of downstream Akt pathways in melanoma cells. Taken together, our data emphasize that CDC25 could be considered as a possible oncotarget in melanoma cells and that compound 7 is a small molecule CDC25 inhibitor that merits to be further evaluated as a chemotherapeutic agent for melanoma, likely in combination with other therapeutic compounds.

Indirect p53-dependent transcriptional repression of Survivin, CDC25C, and PLK1 genes requires the cyclin-dependent kinase inhibitor p21/CDKN1A and CDE/CHR promoter sites binding the DREAM complex

The transcription factor p53 is central to cell cycle control by downregulation of cell cycle-promoting genes upon cell stress such as DNA damage. Survivin (BIRC5), CDC25C, and PLK1 encode important cell cycle regulators that are repressed following p53 activation. Here, we provide evidence that p53-dependent repression of these genes requires activation of p21 (CDKN1A, WAF1, CIP1). Chromatin immunoprecipitation (ChIP) data indicate that promoter binding of B-MYB switches to binding of E2F4 and p130 resulting in a replacement of the MMB (Myb-MuvB) by the DREAM complex. We demonstrate that this replacement depends on p21. Furthermore, transcriptional repression by p53 requires intact DREAM binding sites in the target promoters. The CDE and CHR cell cycle promoter elements are the sites for DREAM binding. These elements as well as the p53 response of Survivin, CDC25C, and PLK1 are evolutionarily conserved. No binding of p53 to these genes is detected by ChIP and mutation of proposed p53 binding sites does not alter the p53 response. Thus, a mechanism for direct p53-dependent transcriptional repression is not supported by the data. In contrast, repression by DREAM is consistent with most previous findings and unifies models based on p21-, E2F4-, p130-, and CDE/CHR-dependent repression by p53. In conclusion, the presented data suggest that the p53-p21-DREAM-CDE/CHR pathway regulates p53-dependent repression of Survivin, CDC25C, and PLK1.

Crosstalk between kinases, phosphatases and miRNAs in cancer

Reversible phosphorylation of proteins, performed by kinases and phosphatases, is the major post translational protein modification in eukaryotic cells. This intracellular event represents a critical regulatory mechanism of several signaling pathways and can be related to a vast array of diseases, including cancer. Cancer research has produced increasing evidence that kinase and phosphatase activity can be compromised by mutations and also by miRNA silencing, performed by small non-coding and endogenously produced RNA molecules that lead to translational repression. miRNAs are believed to target about one-third of human mRNAs while a single miRNA may target about 200 transcripts simultaneously. Regulation of the phosphorylation balance by miRNAs has been a topic of intense research over the last years, spanning topics going as far as cancer aggressiveness and chemotherapy resistance. By addressing recent studies that have shown miRNA expression patterns as phenotypic signatures of cancers and how miRNA influence cellular processes such as apoptosis, cell cycle control, angiogenesis, inflammation and DNA repair, we discuss how kinases, phosphatases and miRNAs cooperatively act in cancer biology.

Cloning and prokaryotic expression of human Cdc25C

AIM: To clone the human Cdc25C gene and construct a recombinant prokaryotic system to express this protein.

METHODS: Total RNA were isolated from human hepatocellular carcinoma Bel-7404 cells and reverse transcribed, and the resulting cDNA was used as a template to amplify the human Cdc25C gene by RT-PCR. The amplified PCR product was cloned into pMD18-T and pET-32a (+) vectors and sequenced. Next, pET-32a(+)-Cdc25C was transformed into chemically competent E. coli strains, including BL21 (DE3), BL21 (DE3) pLysS and Transetta (DE3), to express the protein after induction with 0.25 mmol/L IPTG and ArtMediaTM protein expression, respectively. The fusion protein was identified by Coomassie staining and mass spectrometry analysis.

RESULTS: The Cdc25C gene and pMD18-T-Cdc25C and pET-32a(+)-Cdc25C vectors were obtained successfully. Three strains of E. coli which harbored the recombinant plasmid could express the TRx-His-Cdc25C fusion protein. The expressed protein was identical to the Cdc25C protein as revealed by Coomassie staining and mass spectrometry.

CONCLUSION: The recombinant protein of tumor-associated antigen Cdc25C has been successfully obtained.

TGF-β-Smad2 dependent activation of CDC 25A plays an important role in cell proliferation through NFAT activation in metastatic breast cancer cells

In late stages of cancer, TGF-β promotes the metastasis process by enhancing the invasiveness of cancer cells and inducing the epithelial-to-mesenchymal transition (EMT), a process that is concomitantly associated with breast cancer metastasis. Metastasis comprises of multiple steps with the regulation of complex network of signaling. Metastasis is associated with both the EMT and cell proliferation, but yet it has not been clearly distinguished how the balance between the cell proliferation and EMT is maintained together. Recently, it has been accounted that a transcription factor, NFAT has an important role for switching tumor suppressive to progressive effect of TGF-β and NFAT has a role in TGF-β mediated EMT by regulating N-cadherin. CDC 25A phosphatase, an important cell cycle regulator is overexpressed in breast cancer. Our results demonstrate that TGF-β regulating the CDC 25A in a Smad2 dependent way, translocates NFAT to nucleus and NFAT in co-operation with Smad2 promotes the tumor progression by upregulating the CDK2, CDK4, and cyclin E. This result signifies that TGF-β by regulating NFAT in different ways maintains the balance between EMT and cell proliferation mechanism concurrently during the late stage of breast cancer.

Androgens upregulate Cdc25C protein by inhibiting its proteasomal and lysosomal degradation pathways

Cdc25C is a cell cycle protein of the dual specificity phosphatase family essential for activating the cdk1/Cyclin B1 complex in cells entering into mitosis. Since altered cell cycle is a hallmark of human cancers, we investigated androgen regulation of Cdc25C protein in human prostate cancer (PCa) cells, including androgen-sensitive (AS) LNCaP C-33 cells and androgen-independent (AI) LNCaP C-81 as well as PC-3 cells. In the regular culture condition containing fetal bovine serum (FBS), Cdc25C protein levels were similar in these PCa cells. In a steroid-reduced condition, Cdc25C protein was greatly decreased in AS C-33 cells but not AI C-81 or PC-3 cells. In androgen-treated C-33 cells, the Cdc25C protein level was greatly elevated, following a dose- and a time-dependent manner, correlating with increased cell proliferation. This androgen effect was blocked by Casodex, an androgen receptor blocker. Nevertheless, epidermal growth factor (EGF), a growth stimulator of PCa cells, could only increase Cdc25C protein level by about 1.5-fold. Altered expression of Cdc25C in C-33 cells and PC-3 cells by cDNA and/or shRNA transfection is associated with the corresponding changes of cell growth and Cyclin B1 protein level. Actinomycin D and cycloheximide could only partially block androgen-induced Cdc25C protein level. Treatments with both proteasomal and lysosomal inhibitors resulted in elevated Cdc25C protein levels. Immunoprecipitation revealed that androgens reduced the ubiquitination of Cdc25C proteins. These results show for the first time that Cdc25C protein plays a role in regulating PCa cell growth, and androgen treatments, but not EGF, greatly increase Cdc25C protein levels in AS PCa cells, which is in part by decreasing its degradation. These results can lead to advanced PCa therapy via up-regulating the degradation pathways of Cdc25C protein.

CDC25A(Q110del): a novel cell division cycle 25A isoform aberrantly expressed in non-small cell lung cancer

OBJECTIVE

Lung cancer remains number one cause of cancer related deaths worldwide. Cell cycle deregulation plays a major role in the pathogenesis of Non-Small Cell Lung Cancer (NSCLC). CDC25A represents a critical cell cycle regulator that enhances cell cycle progression. In this study we aimed to investigate the role of a novel CDC25A transcriptional variant, CDC25A(Q110del), on the regulation of the CDC25A protein, and its impact on prognosis of NSCLC patients.

METHODOLOGY/PRINCIPAL FINDINGS

Here we report a novel CDC25A transcript variant with codon 110 (Glutamine) deletion, that we termed CDC25A(Q110del) in NSCLC cells. In 9 (75%) of the 12 NSCLC cell lines, CDC25A(Q110del) expression accounted for more than 20% of the CDC25A transcripts. Biological effects of CDC25A(Q110del) were investigated in H1299 and HEK-293F cells using UV radiation, flowcytometry, cyclohexamide treatment, and confocal microscopy. Compared to CDC25A(wt), CDC25A(Q110del) protein had longer half-life; cells expressing CDC25A(Q110del) were more resistant to UV irradiation and showed more mitotic activity. Taqman-PCR was used to quantify CDC25A(Q110del) expression levels in 88 primary NSCLC tumor/normal tissue pairs. In patients with NSCLC, Kaplan Meier curves showed tumors expressing higher levels of CDC25A(Q110del) relative to the adjacent lung tissues to have significantly inferior overall survival (P = .0018).

SIGNIFICANCE

Here we identified CDC25A(Q110del) as a novel transcriptional variant of CDC25A in NSCLC. The sequence-specific nature of the abnormality could be a prognostic indicator in NSCLC patients as well as a candidate target for future therapeutic strategies.

Genotoxic stress modulates CDC25C phosphatase alternative splicing in human breast cancer cell lines

CDC25 (cell division cycle 25) phosphatases are essential for cell cycle control under normal conditions and in response to DNA damage. They are represented by three isoforms, CDC25A, B and C, each of them being submitted to an alternative splicing mechanism. Alternative splicing of many genes is affected in response to genotoxic stress, but the impact of such a stress on CDC25 splicing has never been investigated. In this study, we demonstrate that genotoxic agents (doxorubicin, camptothecin, etoposide and cisplatin), alter the balance between CDC25C splice variants in human breast cancer cell lines both at the mRNA and protein levels. This modulation occurs during the response to moderate, sub-lethal DNA damage. Our results also suggest that the CDC25C splice variants expression shift induced by a genotoxic stress is dependent on the ATM/ATR signaling but not on p53. This study highlights the modulation of CDC25C alternative splicing as an additional regulatory event involved in cellular response to DNA damage in breast cancer cells.

Discovery of new inhibitors of Cdc25B dual specificity phosphatases by structure-based virtual screening

Cell division cycle 25 (Cdc25) proteins are highly conserved dual specificity phosphatases that regulate cyclin-dependent kinases and represent attractive drug targets for anticancer therapies. To discover more potent and diverse inhibitors of Cdc25 biological activity, virtual screening was performed by docking 2.1 million compounds into the Cdc25B active site. An initial subset of top-ranked compounds was selected and assayed, and 15 were found to have enzyme inhibition activity at micromolar concentration. Among these, four structurally diverse inhibitors with a different inhibition profile were found to inhibit human MCF-7, PC-3, and K562 cancer cell proliferation and significantly affect the cell cycle progression. A subsequent hierarchical similarity search with the most active reversible Cdc25B inhibitor found led to the identification of an additional set of 19 ligands, three of which were confirmed as Cdc25B inhibitors with IC(50) values of 7.9, 4.2, and 9.9 μM, respectively.

The role of protein tyrosine phosphatases in colorectal cancer

Colorectal cancer is one of the most common oncogenic diseases in the Western world. Several cancer associated cellular pathways have been identified, in which protein phosphorylation and dephosphorylation, especially on tyrosine residues, are one of most abundant regulatory mechanisms. The balance between these processes is under tight control by protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs). Aberrant activity of oncogenic PTKs is present in a large portion of human cancers. Because of the counteracting role of PTPs on phosphorylation-based activation of signal pathways, it has long been thought that PTPs must act as tumor suppressors. This dogma is now being challenged, with recent evidence showing that dephosphorylation events induced by some PTPs may actually stimulate tumor formation. As such, PTPs might form a novel attractive target for anticancer therapy. In this review, we summarize the action of different PTPs, the consequences of their altered expression in colorectal cancer, and their potential as target for the treatment of this deadly disease.

Protolimonoids and norlimonoids from the stem bark of Toona ciliata var. pubescens

Six new tirucallane protolimonoids, toonapubesins A-F (1-6), one new rearranged tirucallane protolimonoid, toonapubesin G (7), and two new 21,22,23-trinorapotirucallane limonoids, toonapubesic acids A (8) and B (9), possessing an unprecedented carbon skeleton, along with five known tirucallane protolimonoids (10-14) and one known apotirucallane limonoid (15), were isolated from the stem bark of Toona ciliata var. pubescens. Their structures and relative configurations were determined by detailed spectroscopic analysis and by chemical methods. The proposed structures of 8 and 11 were confirmed by X-ray diffraction analysis of their respective derivatives (8a and 11a). The absolute configuration of 8 was determined by a novel solid-state TDDFT ECD approach on its derivative 8a while the absolute configuration of 10 was determined by the modified Mosher's method. In addition, the structures of dyvariabilin H (10c) proposed by Sticher et al. and cneorin-NP(36) (11b) by Mondon et al. were corrected as 10 and 11, respectively. Toonapubesin G (7) showed promising inhibitory activity against CDC25B with an IC(50) value of 2.1 μM, while compound 8a showed significant cell protecting activity against H(2)O(2)-induced SH-SY5Y cell damage with 11.5% increase in cell viability.

MicroRNA-148a is down-regulated in human pancreatic ductal adenocarcinomas and regulates cell survival by targeting CDC25B

MicroRNAs (miRNAs: short non-coding RNAs) are emerging as a class of potential novel tumor markers, as their dysregulation is being increasingly reported in various types of cancers. In the present study, we investigated the transcription status of miRNA-148a (miR-148a) in human pancreatic ductal adenocarcinoma (PDAC) and its role in the regulation of the dual specificity protein phosphatase CDC25B. We observed that miR-148a exhibited a significant 4-fold down-regulation in PDAC as opposed to normal pancreatic ductal cells. In addition, we observed that stable lentiviral-mediated overexpression of miR-148a in the pancreatic cancer cell line IMIM-PC2, inhibited tumor cell growth and colony formation. Furthermore, CDC25B was identified as a potential target of miR-148a by in silico analysis using PicTar, Targetscan and miRanda in conjunction with gene ontology analysis. The proposed interaction between miR-148a and the 3' untranslated region (UTR) of CDC25B was verified by in-vitro luciferase assays. We demonstrate that the activity of a luciferase reporter containing the 3'UTR of CDC25B was repressed in the presence of miR-148a mimics, confirming that miR-148a targets the 3'UTR of CDC25B. Finally, CDC25B was down-regulated at the protein level in miR-148a overexpressing IMIM-PC2-cells, and in transiently transfected pancreatic cell lines (as detected by Western blot analysis), as well as in patient tumor samples (as detected by immunohistochemistry). In summary, we identified CDC25B as a novel miR-148a target which may confer a proliferative advantage in PDAC.

Differential expression of CDC25 phosphatases splice variants in human breast cancer cells

BACKGROUND

CDC25 phosphatases control cell cycle progression by activating cyclin dependent kinases. The three CDC25 isoforms encoding genes are submitted to alternative splicing events which generate at least two variants for CDC25A and five for both CDC25B and CDC25C. An over-expression of CDC25 was reported in several types of cancer, including breast cancer, and is often associated with a poor prognosis. Nevertheless, most of the previous studies did not address the expression of CDC25 splice variants. Here, we evaluated CDC25 spliced transcripts expression in anti-cancerous drug-sensitive and resistant breast cancer cell lines in order to identify potential breast cancer biomarkers.

METHODS

CDC25 splice variants mRNA levels were evaluated by semi-quantitative RT-PCR and by an original real-time RT-PCR assay.

RESULTS

CDC25 spliced transcripts are differentially expressed in the breast cancer cell lines studied. An up-regulation of CDC25A2 variant and an increase of the CDC25C5/C1 ratio are associated to the multidrug-resistance in VCREMS and DOXOR breast cancer cells, compared to their sensitive counterpart cell line MCF-7. Additionally, CDC25B2 transcript is exclusively over-expressed in VCREMS resistant cells and could therefore be involved in the development of certain type of drug resistance.

CONCLUSIONS

CDC25 splice variants could represent interesting potential breast cancer prognostic biomarkers.

Overexpression of CDC25B, CDC25C and phospho-CDC25C (Ser216) in vulvar squamous cell carcinomas are associated with malignant features and aggressive cancer phenotypes

BACKGROUND

CDC25 phosphatases are important regulators of the cell cycle. Their abnormal expression detected in a number of tumors implies that their dysregulation is involved in malignant transformation. However, the role of CDC25s in vulvar cancer is still unknown. To shed light on their roles in the pathogenesis and to clarify their prognostic values, expression of CDC25A, CDC25B and CDC25C in a large series of vulvar squamous cell carcinomas were examined.

METHODS

Expression of CDC25A, CDC25B, CDC25C and phosphorylated (phospho)-CDC25C (Ser216) were examined in 300 vulvar carcinomas using immunohistochemistry. Western blot analysis was utilized to demonstrate CDC25s expression in vulvar cancer cell lines. Kinase and phosphatase assays were performed to exclude cross reactivity among CDC25s isoform antibodies.

RESULTS

High nuclear CDC25A and CDC25B expression were observed in 51% and 16% of the vulvar carcinomas, respectively, whereas high cytoplasmic CDC25C expression was seen in 63% of the cases. In cytoplasm, nucleus and cytoplasm/nucleus high phospho-CDC25C (Ser216) expression was identified in 50%, 70% and 77% of the carcinomas, respectively. High expression of CDC25s correlated significantly with malignant features, including poor differentiation and infiltration of vessel for CDC25B, high FIGO stage, presence of lymph node metastases, large tumor diameter, poor differentiation for CDC25C and high FIGO stage, large tumor diameter, deep invasion and poor differentiation for phospho-CDC25C (Ser216). In univariate analysis, high expression of phospho-CDC25C (Ser216) was correlated with poor disease-specific survival (p = 0.04). However, such an association was annulled in multivariate analysis.

CONCLUSIONS

Our results suggest that CDC25C and phospho-CDC25C (Ser216) play a crucial role and CDC25B a minor role in the pathogenesis and/or progression of vulvar carcinomas. CDC25B, CDC25C and phospho-CDC25C (Ser216) were associated with malignant features and aggressive cancer phenotypes. However, the CDC25s isoforms were not independently correlated to prognosis.

Overexpression of CDC25B, CDC25C and phospho-CDC25C (Ser216) in vulvar squamous cell carcinomas are associated with malignant features and aggressive cancer phenotypes

BACKGROUND

CDC25 phosphatases are important regulators of the cell cycle. Their abnormal expression detected in a number of tumors implies that their dysregulation is involved in malignant transformation. However, the role of CDC25s in vulvar cancer is still unknown. To shed light on their roles in the pathogenesis and to clarify their prognostic values, expression of CDC25A, CDC25B and CDC25C in a large series of vulvar squamous cell carcinomas were examined.

METHODS

Expression of CDC25A, CDC25B, CDC25C and phosphorylated (phospho)-CDC25C (Ser216) were examined in 300 vulvar carcinomas using immunohistochemistry. Western blot analysis was utilized to demonstrate CDC25s expression in vulvar cancer cell lines. Kinase and phosphatase assays were performed to exclude cross reactivity among CDC25s isoform antibodies.

RESULTS

High nuclear CDC25A and CDC25B expression were observed in 51% and 16% of the vulvar carcinomas, respectively, whereas high cytoplasmic CDC25C expression was seen in 63% of the cases. In cytoplasm, nucleus and cytoplasm/nucleus high phospho-CDC25C (Ser216) expression was identified in 50%, 70% and 77% of the carcinomas, respectively. High expression of CDC25s correlated significantly with malignant features, including poor differentiation and infiltration of vessel for CDC25B, high FIGO stage, presence of lymph node metastases, large tumor diameter, poor differentiation for CDC25C and high FIGO stage, large tumor diameter, deep invasion and poor differentiation for phospho-CDC25C (Ser216). In univariate analysis, high expression of phospho-CDC25C (Ser216) was correlated with poor disease-specific survival (p = 0.04). However, such an association was annulled in multivariate analysis.

CONCLUSIONS

Our results suggest that CDC25C and phospho-CDC25C (Ser216) play a crucial role and CDC25B a minor role in the pathogenesis and/or progression of vulvar carcinomas. CDC25B, CDC25C and phospho-CDC25C (Ser216) were associated with malignant features and aggressive cancer phenotypes. However, the CDC25s isoforms were not independently correlated to prognosis.

Overexpression of CDC25B and LAMC2 mRNA and protein in esophageal squamous cell carcinomas and premalignant lesions in subjects from a high-risk population in China

Molecular events associated with the initiation and progression of esophageal squamous cell carcinoma (ESCC) remain poorly understood but likely hold the key to effective early detection approaches for this almost invariably fatal cancer. CDC25B and LAMC2 are two promising early detection candidates emerging from new molecular studies of ESCC. To further elucidate the role of these two genes in esophageal carcinogenesis, we did a series of studies to (a) confirm RNA overexpression, (b) establish the prevalence of protein overexpression, (c) relate protein overexpression to survival, and (d) explore their potential as early detection biomarkers. Results of these studies indicated that CDC25B mRNA was overexpressed (>/=2-fold overexpression in tumor compared with normal) in 64% of the 73 ESCC cases evaluated, whereas LAMC2 mRNA was overexpressed in 89% of cases. CDC25B protein expression was categorized as positive in 59% (144 of 243) of ESCC cases on a tumor tissue microarray, and nonnegative LAMC2 patterns of protein expression were observed in 82% (225 of 275) of cases. Multivariate-adjusted proportional hazard regression models showed no association between CDC25B protein expression score and risk of death [hazard ratio (HR) for each unit increase in expression score, 1.00; P = 0.90]; however, several of the LAMC2 protein expression patterns strongly predicted survival. Using the cytoplasmic pattern as the reference (the pattern with the lowest mortality), cases with a diffuse pattern had a 254% increased risk of death (HR, 3.52; P = 0.007), cases with no LAMC2 expression had a 169% increased risk of death (HR, 2.69; P = 0.009), and cases with a peripheral pattern had a 130% greater risk of death (HR, 2.30; P = 0.02). CDC25B protein expression scores in subjects with esophageal biopsies diagnosed as normal (n = 35), dysplastic (n = 23), or ESCC (n = 32) increased significantly with morphologic progression. For LAMC2, all normal and dysplastic patients had a continuous pattern of protein expression, whereas all ESCCs showed alternative, noncontinuous patterns. This series of studies showed that both CDC25B and LAMC2 overexpress RNA and protein in a significant majority of ESCC cases. The strong relation of LAMC2 pattern of protein expression to survival suggests a role in prognosis, whereas the association of CDC25B with morphologic progression indicates a potential role as an early detection marker.

Discovery of novel Cdc25 phosphatase inhibitors with micromolar activity based on the structure-based virtual screening

Cdc25 phosphatases have been considered as attractive drug targets for anticancer therapy because of the correlation of their overexpression with a wide variety of cancers. We have been able to identify five novel Cdc25 phosphatase inhibitors with micromolar activity by means of a computer-aided drug design protocol involving the homology modeling of Cdc25A and the virtual screening with the automated AutoDock program implementing the effects of ligand solvation in the scoring function. Because the newly discovered inhibitors are structurally diverse and reveal a significant potency with IC 50 values lower than 10 microM, they can be considered for further development by structure-activity relationship studies or de novo design methods. The differences in binding modes of the identified inhibitors in the active sites of Cdc25A and B are discussed in detail.

Toward the virtual screening of Cdc25A phosphatase inhibitors with the homology modeled protein structure

Cdc25 phosphatases have been considered as attractive drug targets for anticancer therapy due to the correlation of their overexpression with a wide variety of cancers. As a method for the discovery of novel inhibitors of Cdc25 phosphatases, we have evaluated the computer-aided drug design protocol involving the homology modeling of Cdc25A and virtual screening with the two docking tools: FlexX and the modified AutoDock program implementing the effects of ligand solvation in the scoring function. The homology modeling with the X-ray crystal structure of Cdc25B as a template provides a high-quality structure of Cdc25A that enables the structure-based inhibitor design. Of the two docking programs under consideration, AutoDock is found to be more accurate than FlexX in terms of scoring putative ligands. A detailed binding mode analysis of the known inhibitors shows that they can be stabilized in the active site of Cdc25A through the simultaneous establishment of the multiple hydrogen bonds and the hydrophobic interactions. The present study demonstrates the usefulness of the modified AutoDock program as a docking tool for virtual screening of new Cdc25 phosphatase inhibitors as well as for binding mode analysis to elucidate the activities of known inhibitors.

Differential phosphorylation of Cdc25C phosphatase in mitosis

Cdc25 dual-specificity phosphatases coordinate entry into mitosis through activating dephosphorylation of the Mitosis-Promoting Factor, Cdk1-cyclin B1. Activation of Cdc25C at the G2/M transition, involves its dissociation from 14-3-3, together with its hyperphosphorylation on several sites within its regulatory N-terminal domain, mediated by cyclin-dependent kinases and Plk1. Growing evidence suggests that phosphorylation intermediates are likely to precede complete hyperphosphorylation of Cdc25C. To address whether such variants occur in mitotic cells, we raised antibodies directed against different mitotic phosphorylation sites of human Cdc25C, and characterized the phosphorylated species detectable in HeLa cells. In the present study, we provide first-time evidence for the existence of multiple species of Cdc25C in mitotic cell extracts, including full-length and splice variants with different phosphorylation patterns, thereby revealing an intricate network of Cdc25C phosphatases, likely to have distinct biological functions.

Small interfering RNA targeting CDC25B inhibits liver tumor growth in vitro and in vivo

Background

Using gene expression profiling, we previously identified CDC25B to be significantly highly expressed in hepatocellular carcinoma (HCC) compared to non-tumor liver. CDC25B is a cell cycle-activating phosphatase that positively regulates the activity of cyclin-dependent kinases, and is over-expressed in a variety of human malignancies. In this study, we validated the over-expression of CDC25B in HCC, and further investigated its potential as a therapeutic target for the management of HCC.

Results

Quantitative real-time polymerase chain reaction and immunohistochemical staining of patient samples confirmed the significant over-expression of CDC25B in HCC compared to non-tumor liver samples (P < 0.001). Thus, intefering with the expression and activity of CDC25B may be a potential way to intervene with HCC progression. We used RNA interference to study the biological effects of silencing CDC25B expression in HCC cell lines (Hep3B and Hep40), in order to validate its potential as a therapeutic target. Using small oligo siRNAs targeting the coding region of CDC25B, we effectively suppressed CDC25B expression by up to 90%. This was associatetd with significant reductions in cell growth rate, cell migration and invasion through the matrigel membrane, and caused significant cell cycle delay at the G2 phase. Finally, suppression of CDC25B significantly slowed the growth of Hep40 xenografts in nude mice.

Conclusion

Our data provide evidence that the inhibition of CDC25B expression and activity lead to suppression of tumor cell growth and motility, and may therefore be a feasible approach in the clinical management of HCC.

2-Methoxyestradiol inhibits hepatocellular carcinoma cell growth by inhibiting Cdc25 and inducing cell cycle arrest and apoptosis

PURPOSE

2-Methoxyestradiol (2-ME) is a physiological metabolite of estrogen, which can inhibit growth of many types of tumor cells, including hepatocellular carcinoma, both in vitro and in vivo. The exact mechanisms of its action are still unclear. We have studied the mechanisms of growth inhibition of several of human and rat hepatoma and normal liver cells by 2-ME.

METHODS

Human (Hep3B, HepG2, PLC/PRF5) and rat (McA-RH7777, JM-1) hepatoma and normal rat (CRL-1439) and human (CRL-11233) liver cell lines were cultured in vitro, in presence of 2-ME, and its IC50s were determined. Cell cycle arrest, Cdc25 phosphatase inhibition and apoptosis induction were studied. Finally, the effect of 2-ME on the growth of JM-1 rat hepatoma cells in rat liver was determined in vivo.

RESULTS

The IC50 range for growth inhibition of hepatoma cells was found to be between 0.5 and 3 microM. In contrast, normal rat hepatocytes and liver cell lines were resistant to 2-ME up to 20 microM. JM-1 cells were arrested in the G2/M phase of the cell cycle. Cdc25A and Cdc25B, cell cycle controlling phosphatases, activities were inhibited in vitro and 2-ME was found to likely bind to their catalytic site cysteines. As a consequence, their cellular substrates Cdk1 and Cdk2 were tyrosine phosphorylated. Caspase-3 was cleaved suggesting apoptotic cell death. Moreover, growth of JM-1 tumors, which were transplanted into rat liver, was also inhibited by treatment with 2-ME in vivo.

CONCLUSIONS

2-Methoxyestradiol is a selective, potent and relatively non-toxic hepatoma growth inhibitor both in vitro and in vivo. Cell cycle arrest of hepatoma cells was likely mediated by binding and inactivation of the Cdc25 phosphatases and induction of apoptosis.

Variations in intracellular levels of TATA binding protein can affect specific genes by different mechanisms

We previously showed that reduced intracellular levels of the TATA binding protein (TBP), brought about by tbp heterozygosity in DT40 cells, resulted in a mitotic delay reflecting reduced expression of the mitotic regulator cdc25B but did not significantly affect overall transcription. Here we extend these findings in several ways. We first provide evidence that the decrease in cdc25B expression reflects reduced activity of the cdc25B core promoter in the heterozygous (TBP-het) cells. Strikingly, mutations in a previously described repressor element that overlaps the TATA box restored promoter activity in TBP-het cells, supporting the idea that the sensitivity of this promoter to TBP levels reflects a competition between TBP and the repressor for DNA binding. To determine whether cells might have mechanisms to compensate for fluctuations in TBP levels, we next examined expression of the two known vertebrate TBP homologues, TLP and TBP2. Significantly, mRNAs encoding both were significantly overexpressed relative to levels observed in wild-type cells. In the case of TLP, this was shown to reflect regulation of the core promoter by both TBP and TLP. Together, our results indicate that variations in TBP levels can affect the transcription of specific promoters in distinct ways, but overall transcription may be buffered by corresponding alterations in the expression of TBP homologues.

CDC25B: relationship with angiogenesis and prognosis in non–small cell lung carcinoma

The CDC25 phosphatases are cell cycle regulators known to play an important role in cancer cell growth. Increased expression of CDC25B has been reported in tumors of different tissue origins, including non-small cell lung carcinoma (NSCLC). We analyzed primary tumors and corresponding healthy lung tissues from 177 patients with NSCLC for relative expression levels of CDC25B by reverse transcription-polymerase chain reaction, with the dual aims of investigating the relationships between CDC25B expression and angiogenesis as well as prognosis. Eighty-one (45.76%) of the 177 patients with NSCLC overexpressed the CDC25B gene; there was no significant difference in CDC25B expression among sex, age, T or N status, or clinical stages of NSCLC. Concerning the possible involvement of CDC25B in angiogenesis, high expression of CDC25B correlated with positive expression of endothelin-1 (chi(2) test; P = .0002), one of the major angiogenic factors in NSCLC. A significant association was also found with the number of intratumoral microvessels (chi(2) test; P = .03). Statistical analysis of survival data revealed that elevated CDC25B expression was significantly associated with shorter survival in terms of both overall survival and disease-free interval (P = .04 for both), maintaining its independent prognostic role in a Cox proportional hazards model (P = .009). A rich and varied engagement of many cellular pathways could cause or maintain a cancer; our study may offer insights into these mechanisms in lung cancer, suggesting that CDC25B might play an important role in the angiogenic process and in determining the prognosis of patients with NSCLC.

CDC25 phosphatases in cancer cells: key players? Good targets?

Cell division cycle 25 (CDC25) phosphatases regulate key transitions between cell cycle phases during normal cell division, and in the event of DNA damage they are key targets of the checkpoint machinery that ensures genetic stability. Taking only this into consideration, it is not surprising that CDC25 overexpression has been reported in a significant number of human cancers. However, in light of the significant body of evidence detailing the stringent complexity with which CDC25 activities are regulated, the significance of CDC25 overexpression in a subset of cancers and its association with poor prognosis are proving difficult to assess. We will focus on the roles of CDC25 phosphatases in both normal and abnormal cell proliferation, provide a critical assessment of the current data on CDC25 overexpression in cancer, and discuss both current and future therapeutic strategies for targeting CDC25 activity in cancer treatment.

Differential mitotic degradation of the CDC25B phosphatase variants

CDC25 phosphatases control cell-cycle progression by dephosphorylating and activating cyclin-dependent kinases. CDC25B, one of the three members of this family in human cells, is thought to regulate initial mitotic events. CDC25B is an unstable protein whose proteasomal degradation is proposed to be controlled by beta-TrCP. Here, we have investigated the regulation of CDC25B during mitosis, using time-lapse video microscopy. We found that CDC25B expression is high during early mitosis, and that its degradation occurs after the metaphase-anaphase transition and cyclin B1 destruction. We also show that CDC25B degradation after metaphase is dependent on the integrity of the KEN-box and RRKSE motifs that are located within the alternatively spliced B domain, and that the CDC25B2 splice variant, that lacks this domain, is stable during mitosis. Furthermore, we show that the N-terminal region of CDC25B, encompassing the B domain, undergoes major conformational changes during mitosis that can be monitored by intramolecular fluorescence resonance energy transfer variation of specific CDC25B biosensors. This study demonstrates that CDC25B splice variants have differential mitotic stabilities, a feature that is likely to have major consequences on the local control of cyclin-dependent kinase-cyclin activities during mitotic progression.

Androgen receptor coregulators and their involvement in the development and progression of prostate cancer

The androgen receptor signaling axis plays an essential role in the development, function and homeostasis of male urogenital structures including the prostate gland although the mechanism by which the AR axis contributes to the initiation, progression and metastatic spread of prostate cancer remains somewhat enigmatic. A number of molecular events have been proposed to act at the level of the AR and associated coregulators to influence the natural history of prostate cancer including deregulated expression, somatic mutation, and post-translational modification. The purpose of this article is to review the evidence for deregulated expression and function of the AR and associated coactivators and corepressors and how such events might contribute to the progression of prostate cancer by controlling the selection and expression of AR targets.

Inhibiting transient protein-protein interactions: lessons from the Cdc25 protein tyrosine phosphatases

Transient protein-protein interactions have key regulatory functions in many of the cellular processes that are implicated in cancerous growth, particularly the cell cycle. Targeting these transient interactions as therapeutic targets for anticancer drug development seems like a good idea, but it is not a trivial task. This Review discusses the issues and difficulties that are encountered when considering these transient interactions as drug targets, using the example of the cell division cycle 25 (Cdc25) phosphatases and their cyclin-dependent kinase (CDK)-cyclin protein substrates.

Fluorinated Cpd 5, a pure arylating K-vitamin derivative, inhibits human hepatoma cell growth by inhibiting Cdc25 and activating MAPK

We previously synthesized several K-vitamin derivatives, which are potent growth inhibitors of human tumor cells, including Hep3B human hepatoma cells. Among these, Cpd 5 was the most potent. However, being a quinone derivative, Cpd 5 has the potential for generating toxic reactive oxygen species (ROS). We therefore synthesized a fluorinated derivative of Cpd 5, F-Cpd 5. The calculated reduction potential of F-Cpd 5 was much higher than that for Cpd 5 and it was not predicted to generate ROS. This was supported by our observation that F-Cpd 5 generated significantly lower ROS than Cpd 5. F-Cpd 5 was three times more potent than Cpd 5 in inhibiting Hep3B cell growth. Interestingly, under identical culture conditions, F-Cpd 5 inhibited mitogen-induced DNA synthesis in normal rat hepatocytes 12-fold less potently than Hep3B cells. F-Cpd 5 was found to induce caspase-3 cleavage and nuclear DNA laddering, evidences for apoptosis. It preferentially inhibited the activities of the cell cycle controlling phosphatases Cdc25A and Cdc25B, by binding to their catalytic cysteines. Consequently, inhibitory tyrosine phosphorylation of the Cdc25 substrate kinases Cdk2 and Cdk4 were induced. F-Cpd 5 also induced phosphorylation of the MAPK proteins ERK1/2, JNK1/2 and p38 in Hep3B cells and the MAPK inhibitors (U0126, JNKI-II, and SB 203580) antagonized its growth inhibition. F-Cpd 5 inhibited the action of cytosolic ERK phosphatase activity, which likely caused the ERK phosphorylation. F-Cpd 5 thus differentially inhibited growth of normal and tumor cells by preferentially inhibiting the actions of Cdc25A and Cdc25B phosphatases and inducing MAPK phosphorylation.

PM-20, a novel inhibitor of Cdc25A, induces extracellular signal-regulated kinase 1/2 phosphorylation and inhibits hepatocellular carcinoma growth in vitro and in vivo

We have synthesized several new phenyl maleimide compounds, which are potent growth inhibitors of several human tumor cell lines. Among these, PM-20 was the most potent with an IC50 of 700 nmol/L for Hep3B human hepatoma cell growth. Two other derivatives, PM-26 and PM-38, did not inhibit Hep3B cell growth even at 100 micromol/L. Interestingly, under identical experimental conditions, PM-20 inhibited DNA synthesis of primary cultures of normal hepatocytes at a 10-fold higher concentration than that needed to inhibit the DNA synthesis of the Hep3B hepatoma cells. PM-20 affected two cellular signaling pathways in Hep3B cells: Cdc25 phosphatase and extracellular signal-regulated kinase (ERK) 1/2. It competitively inhibited the activity of Cdc25 (preferentially Cdc25A) by binding to the active site, likely through the catalytic cysteine, but did not inhibit PTP1B, CD45, or MKP-1 phosphatases. As a result of its action, tyrosine phosphorylation of the cellular Cdc25A substrates Cdk2 and Cdk4 was induced. It also induced strong and persistent phosphorylation of the Cdc25A substrate ERK1/2. Hep3B cell lysates were found to contain ERK2 phosphatase(s) activity, which was inhibited by the actions of PM-20. However, activity of exogenous dual-specificity ERK2 phosphatase MKP1 was not inhibited. Induction of ERK1/2 phosphorylation correlated with the potency of growth inhibition in tumor cell lines and inhibition of ERK1/2 phosphorylation by the mitogen-activated protein kinase (MAPK)/ERK kinase 1/2 inhibitor U0126 or overexpression of the cdc25A gene in Hep3B cells antagonized the growth inhibitory actions of PM-20. Growth of transplantable rat hepatoma cells in vivo was also inhibited by PM-20 action with a concomitant induction of pERK in the tumors. The mechanism(s) of growth inhibition of Hep3B hepatoma cells by the phenyl maleimide PM-20 involves prolonged ERK1/2 phosphorylation, likely resulting from inhibition of the ERK phosphatase Cdc25A. PM-20 thus represents a novel class of tumor growth inhibitor that inhibits mainly Cdc25A, is dependent on ERK activation, and has a considerable margin of selectivity for tumor cells compared with normal cells.

RNA interference knockdown of hU2AF35 impairs cell cycle progression and modulates alternative splicing of Cdc25 transcripts

U2AF is a heterodimeric splicing factor composed of a large (U2AF65) and a small (U2AF35) subunit. In humans, alternative splicing generates two U2AF35 variants, U2AF35a and U2AF35b. Here, we used RNA interference to specifically ablate the expression of each isoform in HeLa cells. Our results show that knockdown of the major U2AF35a isoform reduced cell viability and impaired mitotic progression, leading to accumulation of cells in prometaphase. Microarray analysis revealed that knockdown of U2AF35a affected the expression level of approximately 500 mRNAs, from which >90% were underrepresented relative to the control. Among mRNAs underrepresented in U2AF35a-depleted cells we identified an essential cell cycle gene, Cdc27, for which there was an increase in the ratio between unspliced and spliced RNA and a significant reduction in protein level. Furthermore, we show that depletion of either U2AF35a or U2AF35b altered the ratios of alternatively spliced isoforms of Cdc25B and Cdc25C transcripts. Taken together our results demonstrate that U2AF35a is essential for HeLa cell division and suggest a novel role for both U2AF35 protein isoforms as regulators of alternative splicing of a specific subset of genes.

Induction of the adenoma-carcinoma progression and Cdc25A-B phosphatases by the trefoil factor TFF1 in human colon epithelial cells

TFF1 is overexpressed in inflammatory diseases and human cancers of the digestive and urogenital systems. To examine the transforming potential of TFF1 in human colon epithelial cells, premalignant PC/AA/C1 adenoma cells (PC) derived from a patient with familial adenomatous polyposis (FAP) were transformed by the TFF1 cDNA and used as a model of the adenoma-carcinoma transition. Constitutive expression of TFF1 increased anchorage-independent cell growth in soft agar, and induced or potentiated the growth of colon PC-TFF1 and kidney MDCKts.src-TFF1 tumor xenografts in athymic mice. This resulted in reduction of thapsigargin-induced apoptosis and promotion of collagen type I invasion through several oncogenic pathways. Using the differential display approach to identify TFF1 target genes, we found that the dual specific phosphatases Cdc25A and B implicated in cell cycle transitions are strongly upregulated under active forms in both PC-TFF1 and HCT8/S11-TFF1 colon cancer cells. Accordingly, TFF1 expression is absent in normal human colon crypts but is induced in correlation with Cdc25a and b transcript levels and tumor grade in familial and sporadic colon adenomas and carcinomas. We propose that TFF1 and Cdc25A-B cooperate with other dominant oncogenic pathways to induce the adenoma and adenocarcinoma transitions. Agents that target TFF1/Cdc25 signaling pathways may be useful for treating patients with TFF1-positive solid tumors.

Achaete-scute like 2 (ascl2) is a target of Wnt signalling and is upregulated in intestinal neoplasia

Achaete-scute like (ASCL)2 is a basic helix-loop-helix transcription factor essential for the maintenance of proliferating trophoblasts during placental development. Using oligonucleotide microarrays we identified ascl2 as a gene significantly upregulated in colorectal adenocarcinomas (n=36 cancers, n=16 normals; 15-fold, P<0.0001). This finding was confirmed by quantitative reverse transcriptase (RT)-PCR on large intestinal cancers (n=29 cancers, n=16 normals; 10-fold, P<0.0001). In situ hybridization for ascl2 demonstrated expression at the base of small and large intestinal crypts (n=304), but in no other normal tissues excepting placenta. By in situ hybridization, 52-71% of colorectal adenomas (n=187), 50-73% of large (n=327) and 33-64% of small intestinal adenocarcinomas (n=124) were positive for ascl2 expression. Upregulation of murine ascl2 was also observed using oligonucleotide microarrays, quantitative RT-PCR and in situ hybridization on apcmin/+ and apc1638N/+ smad4-/+ tumours. Tumour cell lines stably transfected with LEF1(DN) or APC2, or transiently transfected with short-interfering RNA (siRNA) against beta-catenin showed a significant downregulation of ascl2. Colocalization of ascl2 with nuclear beta-catenin was observed in 73 small intestinal adenocarcinomas (P=0.0008) and apcmin/+ tumours. Preliminary in vitro data suggest ascl2 may promote progression through the G2/M cell cycle checkpoint. In summary, ascl2 is a putative regulator of proliferation that is overexpressed in intestinal neoplasia.

Synthesis of miltirone analogues as inhibitors of Cdc25 phosphatases

Miltirone analogues were synthesized and evaluated for inhibitory activity against Cdc25 and PTP1B. Most of the compounds demonstrated potent Cdc25 inhibitory activity, and several exhibited higher selectivity for Cdc25 than for PTP1B. In a cytotoxic assay, most of the compounds displayed cytotoxicity against the tumor cell lines A549 and HCT-116, producing IC(50) values in the micromolar range.

Increased expression and activity of CDC25C phosphatase and an alternatively spliced variant in prostate cancer

Alterations in the control of cell cycle progression have been implicated in a wide variety of malignant neoplasms, including prostate cancer. CDC25 phosphatases belong to the tyrosine phosphatase family and play a critical role in regulating cell cycle progression by dephosphorylating cyclin-dependent kinases at inhibitory residues. CDC25C plays an important role in the G2-M transition by activating Cdc2/Cyclin B1 complexes. To determine whether CDC25C activity is altered in prostate cancer, we have examined the expression of CDC25C and an alternatively spliced variant in human prostate cancer samples and cell lines. CDC25C protein is up-regulated in prostate cancer in comparison with normal prostate tissue and is present almost exclusively in its active dephosphorylated form. Expression of a biologically active alternatively spliced CDC25C isoform is also increased in prostate cancer and expression of alternatively spliced CDC25C is correlated to occurrence of biochemical (prostate-specific antigen) recurrence. We have also developed a quantitative reverse transcriptase-PCR analysis of Ki-67 expression as a method of measuring proliferative activity in prostate cancer from RNA samples. Based on this analysis of Ki67 expression, some but not all of this increase in CDC25C and its alternatively spliced variants is correlated with increased proliferation in prostate cancer. This data suggests that CDC25C might play an important role in prostate cancer progression and could be used to monitor and predict the aggressiveness of this disease.

Screening the active constituents of Chinese medicinal herbs as potent inhibitors of Cdc25 tyrosine phosphatase, an activator of the mitosis-inducing p34cdc2 kinase

OBJECTIVE

To screen and evaluate the active constituents of Chinese medicinal herbs as potent inhibitors of Cdc25 phosphatase.

METHODS

The affinity chromatography purified glutashione-S-transferase/Cdc25A phosphatase fusion protein and Cdc2/cyclin B from the extracts of starfish M phase oocytes are used as the cell cycle-specific targets for screening the antimitotic constituents. We tested 9 extracts isolated from the Chinese medicinal herbs and vegetables including the agents currently used in cancer treatment by measuring the inhibition of Cdc25A phosphatase and Cdc2 kinase activity. The antitumor activity of the extracts was also evaluated by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay and flow cytometry.

RESULTS

Cdc25A inhibitory activity and antitumor activity are detected in the extracts isolated from three Chinese medicinal herbs Agrimona pilosa; Herba solani lyrati; Galla chinesis.

CONCLUSION

We found three extracts isolated from Chinese medicinal herbs have potential inhibitory activity of Cdc25 phosphatase using a highly specific mechanism-based screen assay for antimitotic drug discovery.

Redox regulation of the Cdc25 phosphatases

The Cdc25 phosphatases are essential for cell-cycle control in eukaryotes under normal conditions and in response to DNA damage via checkpoint controls. Recent evidence indicates direct control of the Cdc25s, and therefore the cell cycle, in response to changes in cellular redox status. These redox changes may originate intracellularly from mitochondrial leakage or in response to specific external triggers leading to production of reactive oxygen species (ROS). This review shows that the known chemistry and biology of the Cdc25s favor a direct role for these phosphatases in temporarily blocking cell-cycle progression until favorable reducing conditions are restored. First, the Cdc25s contain a highly reactive cysteine at the active site that can react directly with ROS, leading to enzyme inactivation. Second, the ROS-inactivated form of Cdc25 is expected to prevent cell-cycle progression based on precedent from cellular responses to DNA damage. Third, ROS-mediated oxidation of the Cdc25s leads to an intramolecular disulfide that is readily reversible by the cellular reductant thioredoxin. Finally, in vivo data supporting a direct role for the Cdc25s in redox regulation are considered.

CDK4 and MDM2 gene alterations mainly occur in highly proliferative and aggressive mantle cell lymphomas with wild-type INK4a/ARF locus

Amplification of 12q13 locus occurs in some mantle cell lymphomas (MCL), potentially involving CDK4 and MDM2 genes. To determine the role of these genes in MCL, we have examined their gene status and expression and their relationship to INK4a/ARF and p53 gene aberrations in 69 tumors. Increased CDK4 gene copy number was detected in 4 of 19 (21%) highly proliferative blastoid variants and was associated with mRNA and protein overexpression. Three additional cases showed mRNA overexpression with no structural alterations of the gene. MDM2 gene overexpression was detected in three blastoid tumors (16%) with no relationship to gene copy gains. INK4a/ARF and p53 aberrations were observed in 13 and 12 tumors, respectively. Four of the seven lymphomas with CDK4 aberrations had concurrent inactivation of p53 gene, whereas only one case had a concomitant homozygous deletion of INK4a/ARF. No other gene alterations were found in the three cases with MDM2 overexpression. Patients with INK4a/ARF deletions or simultaneous aberrations of p53 and CDK4 had a significantly shorter median survival (17 months) than patients with isolated alterations of p53, MDM2, or CDK4 (32 months) and patients with no alterations in any of these genes (77 months). The prognostic impact of the concomitant oncogenic alterations of the p14ARF/p53 and p16INK4a/CDK4 pathways was independent of the proliferation of the tumors. These findings indicate that CDK4 and MDM2 gene alterations mainly occur in MCL with a wild-type INK4a/ARF locus and may contribute to the higher proliferation and more aggressive behavior of the tumors.