Regulated ectopic expression of cyclin D1 induces transcriptional activation of the cdk inhibitor p21 gene without altering cell cycle progression

Development of a prognostic model based on anoikis-related genes for predicting clinical prognosis and immunotherapy of hepatocellular carcinoma

Hepatocellular Carcinoma (HCC) is the predominant cause of cancer-related mortality worldwide. The majority of HCC patients are diagnosed at advanced stages of the disease, with a high likelihood of metastasis and unfavorable prognosis. Anoikis resistance is a crucial factor contributing to tumor invasion and metastasis, although its specific role in HCC remains unclear. Based on the results of univariate Cox regression and least absolute shrink-age and selection operator (LASSO) analysis, a subset of anoikis-related genes (ARGs) significantly associated with overall survival (OS) was identified. A multivariate Cox regression analysis subsequently identified PDK4, STK11, and TFDP1 as three prognostic ARGs, which were then used to establish a prognostic risk model. Differences in OS caused by risk stratification in HCC patients were demonstrated. The nomogram analysis indicated that the ARGs prognostic signature served as an independent prognostic predictor. In vitro experiments further confirmed the abnormal expression of selected ARGs in HCC. The association between risk scores and OS was further examined through Kaplan-Meier analysis, CIBERSORT analysis, and single-sample gene set enrichment analysis (ssGSEA). This study is a pioneering effort to integrate multiple ARGs and establish a risk-predictive model, providing a unique perspective for the development of personalized and precise therapeutic strategies for HCC.

Regulation of gliomagenesis and stemness through acid sensor ASIC1a

Glioblastoma multiforme (GBM) is the most prevalent and aggressive type of adult gliomas. Despite intensive therapy including surgery, radiation, and chemotherapy, invariable tumor recurrence occurs, which suggests that glioblastoma stem cells (GSCs) render these tumors persistent. Recently, the induction of GSC differentiation has emerged as an alternative method to treat GBM, and most of the current studies aim to convert GSCs to neurons by a combination of transcriptional factors. As the tumor microenvironment is typically acidic due to increased glycolysis and consequently leads to an increased production of lactic acid in tumor cells, in the present study, the role of acid‑sensing ion channel 1a (ASIC1a), an acid sensor, was explored as a tumor suppressor in gliomagenesis and stemness. The bioinformatics data from The Cancer Genome Atlas revealed that ASIC1 expression levels in GBM tumor tissues were lower than those in normal brain, and glioma patients with high ASIC1 expression had longer survival than those with low ASIC1 expression. Our immunohistochemistry data from tissue microarray revealed that ASIC1a expression was negatively associated with glioma grading. Functional studies revealed that the downregulation of ASIC1a promoted glioma cell proliferation and invasion, while upregulation of ASIC1a inhibited their proliferation and invasion. Furthermore, ASIC1a suppressed growth and proliferation of glioma cells through G1/S arrest and apoptosis induction. Mechanistically, ASIC1a negatively modulated glioma stemness via inhibition of the Notch signaling pathway and GSC markers CD133 and aldehyde dehydrogenase 1. ASIC1a is a tumor suppressor in gliomagenesis and stemness and may serve as a promising prognostic biomarker and target for GBM patients.

Bergapten induces G1 arrest of non‑small cell lung cancer cells, associated with the p53‑mediated cascade

The principal subtype of lung cancer, non‑small cell lung cancer (NSCLC) is a life‑threatening malignancy that causes high mortality rates. Bergapten (5‑methoxypsoralen) has been identified to possess anticancer activity against a number of carcinomas. In the present study, the effects of bergapten on NSCLC cells were investigated. The cell viability was determined by MTT assay. Cell cycle distribution was analyzed using flow cytometry. Protein expression and kinase cascade were demonstrated using western blot analysis. The results demonstrated that treatment with bergapten (50 µM for 48 h) inhibited the viability of A549 and NCI‑H460 NSCLC cells to 79.1±2.8% and 74.5±3.1%, respectively, compared with the controls. It was identified that bergapten induced G1 phase accumulation in A549 and NCI‑H460 cells between ~58 and 75% (P<0.01). In addition, bergapten significantly increased the sub‑G1 phase ratio to ~9% (P<0.05) in the two cell types. Further investigation demonstrated that bergapten upregulated the expression of cellular tumor antigen p53 (p53) and its downstream proteins cyclin‑dependent kinase inhibitor 1 and cyclin‑dependent kinase inhibitor 1B, whereas, it downregulated the expression of cyclin D1 and CDK4. Overall, these results suggested that bergapten may inhibit cell viability and trigger G1 arrest and apoptosis in A549 and NCI‑H460 cells, which may be attributed to the activation of p53‑mediated cascades. Therefore, bergapten may be beneficial for NSCLC treatment.

Thyroid Hormone Analogue Stimulates Keratinocyte Proliferation but Inhibits Cell Differentiation in Epidermis

Gross clinical manifestations of thyroid hormone (TH) imbalance are often first seen in the skin where TH plays an integral role in sustaining natural function. Although mounting evidence suggests that TH plays an important role in epidermal proliferation and wound healing, the physiologic role of thyroid hormone in skin is not well understood. In the current study, we investigated the effect of a natural thyroid hormone analogue-3, 3', 5-triiodo-thyroacetic acid (TRIAC) on regulating proliferation and differentiation and its possible molecular mechanism in normal human epidermal keratinocytes and C57BL/6 mice. We determined that TRIAC could stimulate epidermal thickening in mice and promote human keratinocyte proliferation by activating Cyclin D1 expression and promoting entrance into S phase. Moreover, TRIAC might inhibit cell differentiation through repressing the expression of Casein Kinase 1 (CK1), which is a key regulatory protein involved in the control of cell differentiation. Taken together, our data explored the physiologic effect of TRIAC on skin and the possible molecular mechanism of TRIAC, which might be an interesting compound for the treatment of hyperkeratotic skin disorders.

The citrus flavonone hesperetin inhibits growth of aromatase-expressing MCF-7 tumor in ovariectomized athymic mice

Aromatase is responsible for the rate-determining reaction in estrogen synthesis and is a prime target for treating estrogen-receptor-positive breast cancer. Previous in vitro study has demonstrated that apigenin (APG), naringenin (NGN) and hesperetin (HSP) are three of the most potent natural aromatase inhibitors. Because the enzyme inhibition could potentially block breast cancer development, we employed an established postmenopausal breast cancer model to examine the chemopreventive effect of these flavonoids in vivo. Athymic mice were ovariectomized and transplanted with aromatase-overexpressing MCF-7 cells. Dietary administration of HSP at 1000 ppm and 5000 ppm significantly deterred the xenograft growth, while a null effect was observed in mice treated with APG or NGN. Further study illustrated that plasma estrogen in HSP-treated mice was reduced. Messenger RNA expression of the estrogen-responsive gene pS2 was also decreased in the tumors of mice treated with 1000 and 5000 ppm HSP. On the other hand, western analysis indicated that cyclin D1, CDK4 and Bcl-x(L) were reduced in the tumors. This study suggested that HSP could be a potential chemopreventive agent against breast carcinogenesis through aromatase inhibition.

p16( INK4a) positively regulates cyclin D1 and E2F1 through negative control of AUF1

Background

The cyclin-D/CDK4,6/p16^INK4a/pRB/E2F pathway, a key regulator of the critical G1 to S phase transition of the cell cycle, is universally disrupted in human cancer. However, the precise function of the different members of this pathway and their functional interplay are still not well defined.

Methodology/Principal Findings

We have shown here that the tumor suppressor p16^INK4a protein positively controls the expression of cyclin D1 and E2F1 in both human and mouse cells. p16^INK4a stabilizes the mRNAs of the corresponding genes through negative regulation of the mRNA decay-promoting AUF1 protein. Immunoprecipitation of AUF1-associated RNAs followed by RT-PCR indicated that endogenous AUF1 binds to the cyclin D1 and E2F1 mRNAs. Furthermore, AUF1 down-regulation increased the expression levels of these genes, while concurrent silencing of AUF1 and p16^INK4a, using specific siRNAs, restored normal expression of both cyclinD1 and E2F1. Besides, we have shown the presence of functional AU-rich elements in the E2F1 3′UTR, which contributed to p16/AUF1-mediated regulation of E2F1 post-transcriptional events in vivo. Importantly, genome-wide gene expression microarray analysis revealed the presence of a large number of genes differentially expressed in a p16^INK4a -dependent manner, and several of these genes are also members of the AUF1 and E2F1 regulons. We also present evidence that E2F1 mediates p16-dependent regulation of several pro- and anti-apoptotic proteins, and the consequent induction of spontaneous as well as doxorubicin-induced apoptosis.

Conclusion/Significance

These findings show that the cyclin-dependent kinase inhibitor p16 ^INK4a is also a modulator of transcription and apoptosis through controlling the expression of two major transcription regulators, AUF1 and E2F1.

Dysregulation of the cell cycle and chromosomal imbalances in juxtaglomerular cell tumors - a comparative study with endocrine tumors of the pancreas

Two juxtaglomerular cell tumors (JGCTs) were investigated in comparison with 14 endocrine tumors of the pancreas (ETPs), focusing on the cell cycle, apoptosis, and cytogenetic changes. JGCTs revealed nuclear accumulation of Cyclin D(1), together with the cyclin-dependent kinase inhibitors p21(Cip1/Waf1) and p27(Kip1). In contrast, no accumulation of Cyclin D(3), p53, p16(INK4a), or Mdm-2 was seen. Bcl-2 protein was intensively, but Rb only moderately, expressed. This immunoreactive profile was not found in the ETPs, which were negative for Bcl-2, p27(Kip1), p21(Cip1/Waf1), and - with one exception - for Cyclin D(1) (1/14) but expressed Cyclin D(3) in 7/14 cases. JGCTs displayed characteristic genetic alterations with combined losses of chromosomes 9, 11, 15, and 21 and gains of chromosome 18. In contrast, no characteristic pattern of genetic alterations was found in ETPs. In both, the amount of chromosomal aberrations correlated with tumor size. In small ETPs and JGCTs, genetic losses dominated over gains of chromosomes, whereas in large/malignant ETPs, gains and losses were equally affected. Thus, JGCTs represent a special type of renal endocrine neoplasm characterized by deregulation of cell cycle components and a typical profile of chromosomal aberrations. Since only two JCTs were investigated, further studies for validation of these results are, however, necessary.

p21/Wafl/Cipl cellular expression in chronic long-lasting hepatitis C: correlation with HCV proteins (C, NS3, NS5A), other cell-cycle related proteins and selected clinical data

Studies indicate that proteins of hepatitis C virus (HCV) disturb expression of cell-cycle-related proteins. A disturbed cell-cycle control is a hepatocellular carcinoma (HCC) risk factor in patients with HCV-related liver damage. The present study aimed to analyse the cellular expression of p21/Wafl/Cipl (p21) in long-lasting chronic hepatitis C (CH-C), its correlation with the key oncogenic HCV proteins (C, NS3, NS5A), other cell-cycle-related proteins (PCNA, Ki-67, cyclin D1, p53) and selected clinical data. Archival liver biopsies, obtained from patients with CH-C, normal livers, and hepatocellular carcinoma (HCC) specimens were analysed by immunocytochemistry and ImmunoMax technique. In CH-C overexpression of p21 protein was demonstrated. Positive correlations of p21 protein expression in CH-C involved age of the patients, grading, and liver steatosis. Moreover, expression of p21 correlated significantly with expression of p53 protein, of D1 cyclin and Ki-67. Although Ki-67 antigen was related to p21 expression, only Ki-67 expression proved to be directly related to liver staging. Expression of the NS3 protein, which prevailed in CH-C patients, manifested correlation with p21 expression, and that of cyclin D1. In presence of preserved potential for regeneration, overexpression of p21 indicates inhibition of cell cycle in hepatocytes, which probably plays a protective role for the chronically damaged cells. Out of the three HCV proteins only NS3 seems to affect control of p21 protein expression in in vivo infection. Nevertheless, the studies indicate that neither expression of p21 protein nor that of viral NS3 protein can serve as a marker of progression of CH-C to HCC in vivo.

Isoquercitrin isolated from Hyptis fasciculata reduces glioblastoma cell proliferation and changes beta-catenin cellular localization

Isoquercitrin isolated from the aerial parts of Hyptis fasciculata was evaluated according to its capacity to interfere with glioblastoma (Gbm) cell growth. Gbm cells were incubated with isoquercitrin, quercetin, or rutin at concentrations of 25, 50, and 100 mumol/l for 24, 48, and 72 h. Quercetin and rutin affected Gbm cell proliferation after treatment times of longer than 24 h. However, increasing concentrations of isoquercitrin inhibited 50% of Gbm cell proliferation at 24 h and further reached nearly 90% inhibition at 72 h. This effect did not affect cell morphology, cell viability, or cleaved capase-3 levels, indicating that isoquercitrin did not induce Gbm cell death. A marked reduction in cyclin D1 levels and an increase in p27 levels were observed when 100 micromol/l of isoquercitrin was added to Gbm cells. Interestingly, nuclear beta-catenin staining observed in a subpopulation of untreated Gbm cells was found in the cytoplasm after 100-micromol/l isoquercitrin treatment. Collectively, these data show that isoquercitrin reduces Gbm cell growth without inducing apoptosis, possibly by modulating the control of the cell cycle. Our data also suggest that beta-catenin-mediated signaling may be involved on the antiproliferative activity of isoquercitrin.

Changes in transcriptome after in vivo exposure to ionising radiation reveal a highly specialised liver response

PURPOSE

To identify transcriptional gene-networks involved in the early in vivo response of liver cells to radiation exposure and improve our understanding of the molecular processes responsible for tissue radiosensitivity.

MATERIALS AND METHODS

Transcriptome variations of liver RNA samples were measured 3 hours post-irradiation using microarray technology. The results were confirmed and extended using real-time polymerase-chain-reaction (RT-PCR).

RESULTS

We identified quantitative changes in the expression of 126 genes, most of which were observed for the first time. We show that some modifications, such as the upregulation of the cyclin-dependent kinase inhibitor 1A (Cdkn1A) gene, persisted for at least two months after the initial exposure. Other genes regulated by the transformation-related protein 53 (Trp53/p53) such as Bcl2-associated X protein (Bax) or etoposide-induced-2.4 (Ei24/PIG8) were not upregulated. Grouping differentially expressed genes into functional categories revealed that the primary response of liver cells to radiation exposure was the enhancement of oxidoreductase activity and inhibition of cell proliferation, involving cell cycle progression and apoptosis-related genes.

CONCLUSIONS

The data provides evidence of gene expression modifications associated with the hepatic response to radiation exposure. One of the main differences observed with radiation-sensitive tissues such as the spleen was cell proliferation. The comparison of our data with transcriptome modifications in different biological models enabled the identification of networks of genes that might be co-regulated. Overall, our expression data revealed genes and cellular pathways that might help to improve our understanding of the molecular basis underlying tissue radiosensitivity and to identify possible targets for novel therapeutic strategies.

The molecular programme of tumour reversion: the steps beyond malignant transformation

How cells become malignant has preoccupied scientists for over a century. However, the converse question is also valid: are tumour cells capable of reverting from their malignant state? Askanazy's studies in 1907 indicated that teratoma cells could differentiate into normal somatic tissues and current evidence indicates that some tumour cells have acquired the molecular circuitry that results in the negation of chromosomal instability, translocations, oncogene activation and loss of tumour suppressor genes. Studying these extremely rare events of tumour reversion and deciphering these pathways, which involve SIAH1, presenilin 1, TSAP6 and translationally controlled tumour protein (TCTP), could lead to new avenues in cancer treatment.

Eupatilin exhibits a novel anti-tumor activity through the induction of cell cycle arrest and differentiation of gastric carcinoma AGS cells

In many cases, the process of cancer cell differentiation is associated with the programmed cell death. In the present study, interestingly, we found that eupatilin, one of the pharmacologically active ingredients of Artemisia asiatica that has been reported to induce apoptosis in human gastric cancer AGS cells, also triggers differentiation of these cells. Treatment of AGS cells with eupatilin induced cell cycle arrest at the G(1) phase with the concomitant induction of p21(cip1), a cell cycle inhibitor. This led us to test whether eupatilin may trigger AGS cells to differentiate into the matured phenotypes of epithelial cells and this phenomenon may be coupled to the apoptosis. Eupatilin induced changes of AGS cells to a more flattened morphology with increased cell size, granularity, and mitochondrial mass. It also markedly induced trefoil factor 1 (TFF1), a gene responsible for the gastrointestinal cell differentiation. Eupatilin dramatically induced redistribution of tight junction proteins such as occludin and ZO-1, and F-actin at the junctional region between cells. It also induced phosphorylation of extracellular signal-regulated kinase 2 and p38 kinase. Blockade of ERK signaling by PD098059 or the dominant-negative ERK2 significantly reduced eupatilin-induced TFF1 and p21 expression as well as ZO-1 redistribution, indicating that ERK cascades may mediate eupatilin-induced AGS cell differentiation. Collectively, our results suggest that eupatilin acts as a novel anti-tumor agent by inducing differentiation of gastrointestinal cancer cells rather than its direct role in inducing apoptotic cell death.

Effects of granulosa cell-specific deletion of Rb in Inha-alpha null female mice

Our laboratory is interested in the gonadal growth regulatory properties of inhibins, members of the TGFbeta superfamily. We have previously shown that female mice lacking inhibins (Inha(-/-)) develop granulosa cell tumors and that concurrent loss of p27 accelerates tumor development. It has also been shown that the retinoblastoma protein RB regulates the G(1) to S phase transition of the cell cycle by controlling the activity of transcription factors and stabilizing the levels of the cell cycle inhibitor P27. Based on these data, we hypothesized that concurrent loss of Rb and inhibins in the ovary will exacerbate tumor formation. To test this hypothesis, we generated an ovarian granulosa cell conditional knockout (cKO) of Rb using the Cre/lox recombination system in the background of Inha(-/-) mice. Inha(-/-)/Rb cKO females show a modest increase in mortality rates compared with Inha(-/-) females. Although histologically similar to Inha(-/-) ovarian tumors, tumors from Inha(-/-)/Rb cKO females show increased number of mitotic figures and apoptotic rates. Interestingly, P27 levels are decreased in Inha(-/-)/Rb cKO ovarian tumors, likely due to the combined effect of Rb loss and increased Skp2 expression, which targets P27 to the proteosome. We propose that Rb loss may cause cell cycle delay or arrest, followed by apoptosis and that increases in p107 and p130 levels may compensate for Rb loss. These findings confirm the importance of P27 as a cell cycle regulator in granulosa cells and suggest functional compensation between RB-like proteins in ovarian tumorigenesis.

Cell cycle checkpoint and apoptosis induction in glioblastoma cells and fibroblasts irradiated with carbon beam

This study was conducted in order to evaluate the cytotoxicity of high linear-energy-transfer (LET) ionizing radiation (IR) on glioblastoma cells and fibroblasts using different modes of cell inactivation assays. Two human glioblastoma cell lines with or without p53-mutation, and fibroblasts were used as materials. Gamma rays and 290 MeV/u carbon beams with LET values of 20, 40, 80 keV/mum were used. To evaluate cell inactivation, we used colony formation assay, morphological detection of apoptosis, and flow-cytometry. Serial expressions of p53 and p21 were analyzed by immunoblotting. High-LET IR reduced the reproductive potency of these cells to identical levels in spite of differences in gamma-sensitivity, and yield of cell death correlated to LET values. A p53-wild-type glioblastoma cell line demonstrated a higher yield of apoptosis than other cell lines, whereas fibroblasts hardly displayed any cell death indicating senescence-like growth arrest even after high LET IR. A p53-mutant tumor cell line demonstrated very low yield of cell death with prominent G2/M arrest. Results of radiosensitivity differ according to what mode of cell inactivation is selected. While fibroblasts depend on G1 block after IR, G2/M blocks may play crucial roles in the radioresistance of p53-mutant glioblastoma cells.

Cell cycle and apoptosis regulators in Spitz nevi: comparison with melanomas and common nevi

BACKGROUND

Deregulated cell cycle control is one of the hallmarks of tumor development. The expression of different cell cycle regulators has been used in various neoplasms as an adjunct to diagnosis.

OBJECTIVE

We sough to determine the expression of cell cycle and apoptosis regulators in Spitz nevi and to appraise its value as a diagnostic adjunct in the differential diagnosis from melanomas and common nevi.

METHODS

Ki-67, p-27, p-16, p-53, p-21, Rb, cyclin D1, cyclin A, cyclin B1, bcl-2, and bax expression was assessed by immunohistochemistry in 10 Spitz nevi and was compared with 16 melanomas and 20 common nevi immunohistochemical expression.

RESULTS

P-27 (60% +/- 20.13), p-16 (62.00% +/- 10.85), and bcl-2 (46.00% +/- 42.47) were highly expressed in Spitz nevi, whereas Ki-67 (2.80% +/- 2.55), Rb (3.75% +/- 4.55), p-53 (2.30% +/- 0.10), cyclin A (0.70% +/- 1.56), B1 (0.20% +/- 0.34), and bax (2.65% +/- 6.37) demonstrated a limited expression. Cyclin D1 (8.60% +/- 7.30) and p-21 (6.40% +/- 5.37) showed a moderate expression. The expression of bax (P = .001), Ki-67 (P < .0001), Rb (P < .0001), p-16 (P < .0001), cyclin A (P < .0001), and cyclin B1 (P < .0001) was significantly higher in melanomas in comparison with Spitz nevi, whereas p-27 expression was significantly higher in Spitz nevi (P < .0001). A trend for significant difference in favor of melanomas was also observed for p-53 (P = .002). On the other hand, no difference was detected for bcl-2 (P = .275), p-21 (P = .055), or cyclin D1 (P = .077). Spitz nevi demonstrated a trend for a higher expression for p-21 (P = .008) and cyclin D1 (P = .006), whereas they exhibited lower p-16 (P = .004) in comparison with common nevi.

LIMITATIONS

The number of Spitz nevi was relatively small.

CONCLUSION

Spitz nevi differ from melanomas in their immunohistochemical pattern of expression of cell cycle and apoptosis regulators and more closely resemble common benign nevi.

Transcriptional upregulation of p57 (Kip2) by the cyclin-dependent kinase inhibitor BMS-387032 is E2F dependent and serves as a negative feedback loop limiting cytotoxicity

In spite of the fact that cyclin-dependent kinase (cdk) inhibiting drugs are potent transcriptional repressors, we discover that p57 (Kip2, CDKN1C) transcription is significantly upregulated by three small molecule cdk inhibitors, including BMS-387032. Treatment of MDA-MB-231 breast cancer cells with BMS-387032 led to a stabilization of the E2F1 protein that was accompanied by significant increases in the p57 mRNA and protein. This increase did not occur in an E2F1-deficient cell line. An E2F1-estrogen receptor fusion protein activated the endogenous p57 promoter in response to hydroxytamoxifen treatment in the presence of cycloheximide. Luciferase constructs driven by the p57 promoter verified that upregulation of p57 mRNA by BMS-387032 is transcriptional and dependent on E2F-binding sites in the promoter. Expression of exogenous p57 significantly decreased the fraction of cells in S phase. Furthermore, p57-deficient MDA-MB-231 cell lines were significantly more sensitive to BMS-387032-induced apoptosis than controls. The results presented in this manuscript demonstrate that small molecule cdk inhibitors transcriptionally activate p57 dependent upon E2F1 and that this activation in turn serves to limit E2F1's death-inducing activity.

Lycopene inhibition of IGF-induced cancer cell growth depends on the level of cyclin D1

BACKGROUND

Insulin-like growth factors (IGFs) play an important role in normal and cancerous cell proliferation. Moreover, in recent studies IGF-I has been implicated as a major cancer risk factor. The tomato carotenoid lycopene and all-trans retinoic acid (atRA) have been shown to inhibit growth factor-induced proliferation of different types of cancer cells. This action is associated with inhibition of cell cycle progression in G0/G1 phase. Cyclin D1 acts as a growth factor sensor in G1 phase and is overexpressed in many breast cancer tumors. We have previously demonstrated that slowdown of serum-stimulated cell cycle progression from G1 to S phase by lycopene correlates with reduction in cyclin D1 levels, suggesting that the expression of this protein is a main target for lycopene's action.

AIM OF THE STUDY

To determine whether the reported reduction in cyclin D1 level is the key mechanism for lycopene and atRA inhibitory action on IGF-I-induced cell cycle progression.

RESULTS

Human breast (MCF-7) and endometrial (ECC-1) cancer cells were synchronized in G0/G1 phase by serum deprivation followed by stimulation with IGF-I. Cell treatment with lycopene and atRA inhibited IGF-I-stimulated cell cycle progression from G1 to S phase and decreased retinoblastoma protein (pRb) phosphorylation. These events were associated with a reduction in cyclin D1 and p21(CIP1/WAF1) level, but not that of p27(KIP1). To test the hypothesis that the decrease in cyclin D1 has a major role in the inhibitory effects of lycopene and atRA, we examined the ability of these two agents to suppress cell cycle progression in MCF-7.7D1.13 cells which are capable of expressing cyclin D1 under the control of the Zn-inducible metallothionein promoter. Our results showed that ectopic expression of cyclin D1 can overcome cell cycle inhibition caused by lycopene and atRA.

CONCLUSIONS

Our findings suggest that attenuation of cyclin Dl levels by lycopene and atRA is an important mechanism for the reduction of the mitogenic action of IGF-I.

Gain of 11q/cyclin D1 overexpression is an essential early step in skin cancer development and causes abnormal tissue organization and differentiation

Non-melanoma skin cancers, in particular keratoacanthomas (KAs) and squamous cell carcinomas (SCCs), have become highly frequent tumor types especially in immune-suppressed transplant patients. Nevertheless, little is known about essential genetic changes. As a paradigm of 'early' changes, that is, changes still compatible with tumor regression, we studied KAs by comparative genomic hybridization and show that gain of chromosome 11q is not only one of the most frequent aberration (8/18), but in four tumors also the only aberration. Furthermore, 11q gain correlated with amplification of the cyclin D1 locus (10/14), as determined by fluorescence in situ hybridization, and overexpression of cyclin D1 protein (25/31), as detected by immunohistochemistry. For unraveling the functional consequence, we overexpressed cyclin D1 in HaCaT skin keratinocytes. These cells only gained little growth advantage in conventional and in organotypic co-cultures. However, although the control vector-transfected cells formed a well-stratified and orderly differentiated epidermis-like epithelium, they showed deregulation of tissue architecture with an altered localization of proliferation and impaired differentiation. The most severe phenotype was seen in a clone that additionally upregulated cdk4 and p21. These cells lacked terminal differentiation, exhibited a more autonomous growth in vitro and in vivo and even formed tumors in two injection sites with a growth pattern resembling that of human KAs. Thus, our results identify 11q13 gain/cyclin D1 overexpression as an important step in KA formation and point to a function that exceeds its known role in proliferation by disrupting tissue organization and thereby allowing abnormal growth.

Cyclin D1 and p21 is elevated in the giant cells of giant cell tumors

Alterations of cell cycle regulatory proteins, especially those that regulate G1 to S transition, have been implicated in the pathogenesis of a wide variety of human tumors. In previous studies we showed that that there is overexpression of cyclin D1 protein predominately in the giant cell component of giant cell tumors of bone. The purpose of this study was to investigate the mechanisms that may be responsible for cyclin D1 accumulation in giant cell tumors. Giant cell tumors have high levels of cyclin D1 mRNA and the giant cell-enriched population of these tumors have significantly more mRNA and protein expression of cyclin D1 than the mononuclear cell population. The giant cells also expressed higher levels of p21 protein and more p21 bound to cyclin D1 than the mononuclear cells. It is possible that p21 may be contributing to the cyclin D1 accumulation that occurs in the giant cells and perhaps even giant cell formation in these tumors. Additional studies are required to confirm the role of p21 in the pathogenesis of these tumors.

Differential transcriptional regulation of human telomerase in a cellular model representing important genetic alterations in esophageal squamous carcinogenesis

Telomerase activity is observed in approximately 90% of human cancer including esophageal squamous cell cancer. Normal somatic cells do not display telomerase activity on a regular basis. The major mechanism to regulate telomerase activity in human cells is the transcriptional control of the catalytic subunit, the human reverse transcriptase gene hTERT. However, the manner in which telomerase activity is regulated during malignant transformation and whether this regulation is influenced by single genetic alterations important in this process are not well understood. In this study we investigated the transcriptional regulation and activity of human telomerase in a cellular model representing important known genetic alterations observed in esophageal cancer. We characterized the respective cells with regard to their telomere biology and telomerase expression, transcriptional regulation using promoter--as well as electrophoretic mobility shift assay--analyses and their promoter methylation status. We could demonstrate that telomerase expression and subsequent activity are differentially regulated in the progression from normal esophageal epithelial cells to genetically defined esophageal cells harboring a specific genetic alteration frequently found in esophageal cancer and compared those changes with esophageal cancer cells. Whereas primary esophageal cells are mainly regulated by Sp1, in cells harboring a genetic alteration as cyclin D1 overexpression other transcription factors like E2F and c-myc as well as promoter methylation influence hTERT transcription. This model demonstrates that the transcriptional regulation of telomerase is influenced by a given genetic alteration important in esophageal cancer, and therefore provides new insight in telomerase regulation during carcinogenesis.

p21WAF1 modulates NF-kappaB signaling and induces anti-apoptotic protein Bcl-2 in Tax-expressing rat fibroblast

Of the cell cycle-associated genes regulated by human T-cell leukemia virus type-1 (HTLV-1) Tax, cyclin-dependent kinase (CDK) inhibitor p21WAF1 is upregulated in HTLV-1-infected cells. Previously, we reported that p21WAF1 stimulated Tax-dependent NF-kappaB activation which influences a variety of cellular processes, including proliferation, differentiation, and apoptosis. In HTLV-1-infected cells, Tax is primarily involved in the constitutive activation of NF-kappaB signaling. Here, we demonstrate that p21WAF1 affects Tax-dependent NF-kappaB signaling by inducing p100/52, an NF-kappaB-related protein. W4, a Tax-transformed rat fibroblast cell line, exhibits the constitutive activation of NF-kappaB signaling, potentially mediated by overexpression of RelB. Ectopic expression of p21WAF1 in W4 cells, which lack endogenous expression due to methylation of the p21WAF1 promoter, induces the expression of p100/52. Bcl-2 expression was also upregulated by ectopic p21WAF1 in this cell line, suggesting that p21WAF1 plays an important role in the regulation of apoptosis by modulating NF-kappaB signaling in Tax-expressing rat fibroblasts. We also address the expression of NF-kappaB-related proteins in HTLV-1-infected cells.

The role of cyclin D2 and p21/waf1 in human T-cell leukemia virus type 1 infected cells

Background

The human T-cell leukemia virus type 1 (HTLV-1) Tax protein indirectly influences transcriptional activation, signal transduction, cell cycle control, and apoptosis. The function of Tax primarily relies on protein-protein interactions. We have previously shown that Tax upregulates the cell cycle checkpoint proteins p21/waf1 and cyclin D2. Here we describe the consequences of upregulating these G₁/S checkpoint regulators in HTLV-1 infected cells.

Results

To further decipher any physical and functional interactions between cyclin D2 and p21/waf1, we used a series of biochemical assays from HTLV-1 infected and uninfected cells. Immunoprecipitations from HTLV-1 infected cells showed p21/waf1 in a stable complex with cyclin D2/cdk4. This complex is active as it phosphorylates the Rb protein in kinase assays. Confocal fluorescent microscopy indicated that p21/waf1 and cyclin D2 colocalize in HTLV-1 infected, but not in uninfected cells. Furthermore, in vitro kinase assays using purified proteins demonstrated that the addition of p21/waf1 to cyclin D2/cdk4 increased the kinase activity of cdk4.

Conclusion

These data suggest that the p21/cyclin D2/cdk4 complex is not an inhibitory complex and that p21/waf1 could potentially function as an assembly factor for the cyclin D2/cdk4 complex in HTLV-1 infected cells. A by-product of this assembly with cyclin D2/cdk4 is the sequestration of p21/waf1 away from the cyclin E/cdk2 complex, allowing this active cyclin-cdk complex to phosphorylate Rb pocket proteins efficiently and push cells through the G₁/S checkpoint. These two distinct functional and physical activities of p21/waf1 suggest that RNA tumor viruses manipulate the G₁/S checkpoint by deregulating cyclin and cdk complexes.

Bcr-Abl upregulates cytosolic p21WAF-1/CIP-1 by a phosphoinositide-3-kinase (PI3K)-independent pathway

Chronic myeloid leukaemia invariably progresses from a drug-sensitive to a drug-resistant, aggressive acute leukaemia. The mechanisms responsible for this are unknown, although loss of p53 has been reported in approximately 25% of cases. Elevated expression of Bcr-Abl is also associated with disease progression. We have shown that cells expressing high levels of Bcr-Abl also express elevated levels of p53 and the cell cycle inhibitor, p21WAF-1. Despite this, cells continue to cycle and are drug resistant. As p21WAF-1 inhibitory activity is associated with nuclear localization, we investigated its localization in Bcr-Abl-expressing cells, and found that it is predominantly cytoplasmic. We have also shown that it associates physically with the serine/threonine kinase AKT, but this association and the cytosolic location of p21WAF-1 are phosphinositide-3-kinase (PI3K) independent. Cytosolic p21WAF-1 has been reported to have a prosurvival role in other transformed cells. In Bcr-Abl-expressing cells, p21WAF-1 rapidly diminishes as the cells are sensitized to apoptosis, using the inhibitor STI571. It is possible therefore that p21WAF-1 could also have a positive, prosurvival role in these cells. This study suggests that, by retaining p21WAF-1 in a cytosolic location, Bcr-Abl can evade the cell cycle arrest normally induced by nuclear p21WAF-1 and therefore also enable the cells to negate an important feature of a tumour suppressor response.

p21WAF1 expression in invasive breast cancer and its association with p53, AP-2, cell proliferation, and prognosis

AIMS

To evaluate the expression and prognostic relevance of p21(WAF1) in breast cancer and to investigate its association with p53, activator protein 2 (AP-2), and cell proliferation (as assessed by Ki-67 expression).

METHODS

p21(WAF1) expression was analysed immunohistochemically in a large prospective, consecutive series of 420 patients with breast cancer diagnosed and treated between 1990 and 1995 at Kuopio University Hospital, Kuopio, Finland. Inter-relations between p21(WAF1) expression and p53, AP-2, and Ki-67 were evaluated. The expression of p21(WAF1) was also compared with clinicopathological parameters and the patients' survival.

RESULTS

In general, nuclear p21(WAF1) expression was low in carcinomas (median, 2.5%; range, 0-70%). Expression was lowest in lobular carcinomas (chi(2) = 7.4; p = 0.025). p21(WAF1) positive tumours were more often p53 positive (chi(2) = 4.2; p = 0.041) but expression of p21(WAF1) did not correlate with AP-2 expression or Ki-67 in the whole patient group. In addition, the combined expression of p21 and p53 was not associated with AP-2 expression. High nuclear p21(WAF1) positivity (n = 160; 38%) was associated with poor differentiation (chi(2) = 8.1; p = 0.017). In the univariate analyses, p21(WAF1) expression had no prognostic value for predicting breast cancer related survival (BCRS) or recurrence free survival (RFS) in the whole patient group or in the subgroups investigated. However, in postmenopausal patients with lymph node metastases, and oestrogen receptor (ER) and/or progesterone receptor (PR) positive tumours, high p21(WAF1) expression predicted response to adjuvant hormonal treatment with antioestrogens. In the univariate analysis, the significant factors for predicting BCRS were Ki-67 expression, stage, lymph node status, histological grade, ER and PR status, and those for RFS were Ki-67 expression, stage, and lymph node status. In the multivariate analysis, the independent predictors of shorter BCRS were high cell proliferation activity measured by Ki-67 expression (p < 0.001), advanced stage (p < 0.001), and poor differentiation (p = 0.048). Shorter RFS was independently predicted by high cell proliferative activity (p < 0.001) and advanced stage (p < 0.001).

CONCLUSIONS

The regulation of p21(WAF1) seems to occur independently of p53 or AP-2 and analysing p21(WAF1) expression provided no prognostic information for patients with breast cancer.

Involvement of G1/S cyclins in estrogen-independent proliferation of estrogen receptor-positive breast cancer cells

Estrogen receptor-mediated transcription is enhanced by overexpression of G1/S cyclins D1, E or A in the presence as well in the absence of estradiol. Excess of G1/S cyclins also prevents the inhibition of transactivation of estrogen receptor (ER) by the pure antiestrogen ICI 182780. Cyclin D1 mediates this transactivation independent of complex formation to its CDK4/6 partner. This raises the possibility that overexpression of G1/S cyclins renders growth of ER-positive breast cancer hormone-independent and resistant to treatment with antiestrogens. Transient transfection of ER-positive breast cancer cell lines T47D and MCF7 with G1/S cyclins could overcome the growth arrest induced by ICI 182780 treatment. The ability of various cyclin D1 mutants to overcome the ICI 182780 mediated growth arrest corresponded with their ability to stimulate cyclin A- and E2F- promoter based reporter activities in the presence of ICI 182780. Transfection of a mutant cyclin D1 (cyclin D1-KE) that was unable to bind CDK4 and was reported to transactivate ER in the presence of ICI 182780, could not stimulate proliferation in ICI 182780 treated cells. On the other hand, cyclin D1-LALA, which is unable to stimulate ERE transactivation, could overcome the ICI 182780 cell cycle arrest. Furthermore, transient transfection of T47D cells using cyclin D1 together with a catalytic inactive mutant of CDK4 (CDK4-DN) indicated that the observed effect is due to binding to CDK inhibitors. However, a moderate, sixfold overexpression of cyclin D1 in stably transfected MCF7 cells did not overcome the ICI 182780 mediated growth arrest. These results indicate that CDK-independent transactivation of the estrogen receptor by cyclin D1 is by itself, not sufficient to result in estradiol-independent growth of breast cancer cells, whereas a vast overexpression of G1/S cyclins is able to do so, most likely by capturing of CDK inhibitors.

Overexpression of cyclin D1 enhances taxol induced mitotic death in MCF7 cells

Treatment of MCF7 human breast cancer cells with taxol induces G2/M arrest followed by mitotic death. A moderate overexpression of ectopic cyclin D1 accelerated these G2/M associated events and resulted in a reduced clonogenic survival upon taxol treatment. Taxol treatment resulted in elevated expression of p53 and of p21, which was more pronounced and persistent in cyclin D1 overexpressing cells. Overexpression of cyclin D1 altered sensitivity to taxol by modulating exit from mitosis, which is controlled by p21. These results indicate that overexpression of cyclin D1 sensitizes MCF7 cells to treatment with taxol.

Activation of AKT/PKB in breast cancer predicts a worse outcome among endocrine treated patients

Akt/PKB is a serine/threonine protein kinase that regulates cell cycle progression, apoptosis and growth factor mediated cell survival in association with tyrosine kinase receptors. The protein is a downstream effector of erbB-2 with implications in breast cancer progression and drug resistance in vitro. We aimed to examine the role of Akt-1 in breast cancer patients, by determining whether the expression (Akt-1) and/or activation (pAkt) were related to prognostic markers and survival. The expression of erbB-2, heregulin beta 1 and Bcl-2 was also assessed by flow cytometry or immunohistochemistry. This study comprised 93 patients, aged <50 who were treated with tamoxifen and/or goserelin. We found that pAkt was associated with lower S-phase fraction (P=0.001) and the presence of heregulin beta 1-expressing stromal cells (P=0.017). Neither Akt-1 nor pAkt was related with other factors. Tumour cells-derived heregulin beta 1 was found mainly in oestrogen receptor negative (P=0.026) and node negative (P=0.005) cases. Survival analysis revealed that pAkt positive patients were more prone to relapse with distant metastasis, independently of S-phase fraction and nodal status (multivariate analysis; P=0.004). The results suggest that activation of Akt may have prognostic relevance in breast cancer.

Cyclin D1 overexpression and p53 inactivation immortalize primary oral keratinocytes by a telomerase-independent mechanism

The immortalization of human cells is a critical step in multistep carcinogenesis. Oral-esophageal carcinomas, a model system to investigate molecular mechanisms underlying squamous carcinogenesis, frequently involve cyclin D1 overexpression and inactivation of the p53 tumor suppressor. Therefore, our goal was to establish the functional role of cyclin D1 overexpression and p53 inactivation in the immortalization of primary human oral squamous epithelial cells (keratinocytes) as an important step toward malignant transformation. Cyclin D1 overexpression alone was found to induce extension of the replicative life span of normal oral keratinocytes, whereas the combination of cyclin D1 overexpression and p53 inactivation led to their immortalization. This study also demonstrates that immortalization of oral keratinocytes can be independent of telomerase activation, involving an alternative pathway of telomere maintenance (ALT).

Reconstitution of cyclin D1-associated kinase activity drives terminally differentiated cells into the cell cycle

Terminal cell differentiation entails definitive withdrawal from the cell cycle. Although most of the cells of an adult mammal are terminally differentiated, the molecular mechanisms preserving the postmitotic state are insufficiently understood. Terminally differentiated skeletal muscle cells, or myotubes, are a prototypic terminally differentiated system. We previously identified a mid-G(1) block preventing myotubes from progressing beyond this point in the cell cycle. In this work, we set out to define the molecular basis of such a block. It is shown here that overexpression of highly active cyclin E and cdk2 in myotubes induces phosphorylation of pRb but cannot reactivate DNA synthesis, underscoring the tightness of cell cycle control in postmitotic cells. In contrast, forced expression of cyclin D1 and wild-type or dominant-negative cdk4 in myotubes restores physiological levels of cdk4 kinase activity, allowing progression through the cell cycle. Such reactivation occurs in myotubes derived from primary, as well as established, C2C12 myoblasts and is accompanied by impairment of muscle-specific gene expression. Other terminally differentiated systems as diverse as adipocytes and nerve cells are similarly reactivated. Thus, the present results indicate that the suppression of cyclin D1-associated kinase activity is of crucial importance for the maintenance of the postmitotic state in widely divergent terminally differentiated cell types.

Distinct mechanisms of cell cycle arrest control the decision between differentiation and senescence in human neuroblastoma cells

Retinoic acid (RA) induces cell cycle arrest and differentiation of human neuroblastoma (NB) cells. Typically, NB cells differentiate along the neuronal lineage, but quiescent, "flat" cell types frequently have been described after treatment with differentiating agents. Two indistinguishable subclones of the cell line SK-N-SH, SK-N-SH-N (SH-N) and SK-N-SH-F (SH-F), display dramatically different responses to RA. In SH-N, RA induces neuronal differentiation, but in SH-F it transforms the small neuroblastic cells into large, flattened, epithelium-like cells. Here we analyze the mechanistic basis for the different effects of RA in the two NB subclones. First, we show that the flattened RA-treated SH-F expresses markers of cells undergoing replicative senescence. Inhibition of DNA synthesis by RA is significantly more rapid in SH-F than in SH-N. SH-F, which expresses basal amounts of p16(INK4A), responds to RA with elevation of p18(INK4C), marked down-regulation of cyclin D1, and swift inhibition of cyclin D-dependent kinases (cdks). Conversely, after addition of RA, SH-N retains cell cycling due to high expression of cyclin D1, the absence of Ink4 inhibitors, and accumulation of p21(Cip1). These changes result in sustained cdk activity. Accordingly, overexpression of p21(Cip1) but not p16(INK4A) induces neuronal differentiation of untreated NB cells. We propose that rapid inhibition of cdks by RA in NB leads to early cell cycle arrest, prevents neuronal differentiation, and results in a senescence-like state.

Cyclin D1 overexpression associates with radiosensitivity in oral squamous cell carcinoma

Overexpression of cyclin D1, a G1 cell cycle regulator, is often found in many different tumor types, including oral squamous cell carcinomas (SCC). Recent laboratory experiments have demonstrated that cyclin D1 levels can influence radiosensitivity in various cell lines. This study evaluated the relationship between cyclin D1 expression levels and radiosensitivity in nine oral SCC cell lines (HSC2, HSC3, HSC4, SCC15, SCC25, SCC66, SCC111, Ca9-22, and NAN2) and 41 clinical patients with oral SCC who underwent preoperative radiation therapy. Radiosensitivity of the nine oral SCC cell lines differed greatly in their response to radiation, assessed by a standard colony formation assay. Likewise, the expression of cyclin D1 varied, and the magnitude of the cyclin D1 expression correlated with increased tumor radiosensitivity. The similar significant association between the response to preoperative radiation therapy and cyclin D1 overexpression was observed in the oral SCC patients who were treated with preoperative radiation therapy. These results suggest that cyclin D1 expression levels correlate to radiosensitivity and could be used to predict the effectiveness of radiation therapy on oral SCC.

Accumulation of high levels of the p53 and p130 growth-suppressing proteins in cell lines stably over-expressing cyclin-dependent kinase 6 (cdk6)

Cyclin-dependent kinase 6(cdk6) is present in randomly proliferating cultures of 3T3 cells but has little detectable enzymatic activity. Significant activity is detected only during a short period in early G1 phase. To examine the possible functions of cdk6 in 3T3 cells, lines stably over-expressing cdk6 were constructed and compared to normal 3T3 cells or cell lines with reduced cdk6 levels due to expression of a dominant-negative form of the protein. Over-expression of cdk6 in cells, which led to high levels of activity even in proliferating cultures, had dramatic effects. Cell lines stably over-expressing wild-type cdk6 had a markedly reduced growth rate compared to parental 3T3 cells or lines expressing a dominant-negative form of cdk6. They also over-produced the p53 and p130 proteins and had increased sensitivity to UV-irradiation. Irradiation resulted in accumulation of the Bax protein and rapid cell death. Levels of p53 and p130 proteins were down-regulated and the growth rate of the cells was increased by introduction of the dominant-negative form of cdk6 into cells over-expressing cdk6, indicating that cdk6 is involved in the overproduction of p53 and p130. The results suggest that cdk6, through regulation of growth-suppressing molecules, may play a role in halting cellular growth when proliferation is inappropriate.

p53-independent upregulation of p21WAF1 in NIH 3T3 cells malignantly transformed by mot-2

Mot-2 protein is shown to interact with p53 and inhibit its transcriptional activation function. Mot-2 overexpressing stable clones of NIH 3T3 cells were malignantly transformed, however, they had a high level of expression of a p53 downstream gene, p21WAF1. The present study was undertaken to elucidate possible molecular mechanism(s) of such upregulation. An increased level of p21WAF1 expression was detected in stable transfectants although an exogenous reporter gene driven by p21WAF1 promoter exhibited lower activity in these cells suggesting that some post-transcriptional mechanism contributes to upregulation. Western analyses of transient and stable clones revealed that upregulation of p21WAF1 in stable NIH 3T3/mot-2 cells may be mediated by cyclin D1 and cdk-2.

Cyclin D3 and megakaryocyte development: exploration of a transgenic phenotype

The roles of cell cycle regulatory proteins in megakaryocyte development are poorly understood. We have previously demonstrated that cyclin D3 is expressed in megakaryocytes and is induced upon treatment with Mpl ligand. Transgenic mice in which cyclin D3 is overexpressed in the megakaryocytic lineage show features similar to in vivo Mpl ligand treatment, including increased megakaryocyte number and ploidy. Terminal maturation and platelet production are not enhanced, however, and transgenic megakaryocytes show a defect in demarcation membrane development. We have examined expression of the transcription factor nuclear factor (NF)-E2, known to be involved in cytoplasmic maturation and platelet fragmentation, in these transgenic mice and controls treated with Mpl ligand. Our findings demonstrate marked induction of NF-E2 mRNA in control megakaryocytes in response to Mpl ligand, but no NF-E2 increase in transgenic cells, potentially explaining the lack of platelet increase in these transgenic mice. Transgenic megakaryocytes treated with Mpl ligand display a limited increase in NF-E2. In response to literature reports of Mpl ligand-induced transient increases in p21Cip1/WAF1 mRNA in polyploidizing megakaryocytic cell lines, we have examined p21 transcript levels in both normal and transgenic megakaryocytes. In normal mouse spleen, only a small percentage of megakaryocytes express detectable levels of p21 mRNA, with the majority of these cells expressing at high intensity. p21 levels are not affected by treatment with Mpl ligand, while the frequency of expressing cells increases transiently. Transgenic megakaryocytes exposed to Mpl ligand also show an increased frequency of p21-positive cells, and stimulation with Mpl ligand resulted in a further increase in this frequency. The nature of this effect will require further investigation.

Deregulated expression of cell cycle-associated proteins in solid pseudopapillary tumor of the pancreas

Solid pseudopapillary tumor of the pancreas was studied in a 20-year-old woman and a 54-year-old woman. In the younger patient, the tumor had metastasized to the liver 8 years after distal pancreatectomy. In both neoplasms, the distinct histologic pattern of solid, pseudopapillary, and degenerative cystic areas was present. Analysis by means of immunohistochemistry revealed a diffuse expression for vimentin, neuron-specific enolase, and a focal positivity for al-antitrypsin, whereas epithelial markers were negative in the tumor of the older patient and only focally expressed in the tumor of the younger patient. Immunohistochemical analysis of cell cycle-associated proteins provided an overexpression of cyclin D1 and cyclin D3 in both tumors, although to varying degrees. In addition, the cyclin-dependent kinase inhibitors p21, and to a lesser extent p27, were up-regulated just as mdm2. There was no accumulation of p53 protein, and Ki67-positive cells were extremely scarce. Analysis of the liver metastases showed an immunoreactive profile similar to that of the primary tumor. The results show a deregulation of the cell cycle with overexpression of cell cycle-activating proteins D1 and D3 and a probably counterbalancing upregulation of the cyclin-dependent kinase inhibitors p21 and p27. The findings may explain the low pool of Ki67-reactive tumor cells and the generally good clinical outcome of these tumors. Whether a more profound dysbalance of the cell cycle regulation is responsible for the development of metastatic disease remains to be clarified.

Ectopic expression of cyclin D1 impairs the proliferation and enhances the apoptosis of a murine lymphoid cell line

Cyclin D1, a key regulator of the cell cycle, acts as an oncogene when over-expressed in several types of cancer. In some B-chronic lymphoproliferative disorders, the over-expression of cyclin D1 protein is thought to confer a proliferative phenotype. We have generated BaF3 pro-B cell derivatives in which cyclin D1 can be induced rapidly and reversibly in a dose-dependent manner by the hormone muristerone A. When non-expressing clones displayed the same proliferative capacity as the parental cell line, in the sub-clones, a moderate induction of cyclin D1 lengthened the proliferation rate. The over-expression of cyclin D1 had the same effects on cell proliferation but also led ultimately to cell death by apoptosis. The induction of cyclin D1 in growth factor-deprived cells as well as in anticancer drug-treated cells also reinforced the magnitude of apoptosis. Thus, the expression of cyclin D1 in lymphoid cells does not confer a proliferative advantage but rather alters the response of cells towards apoptotic stimuli in a p53-independent manner.

Cyclin D1 expression in transitional cell carcinoma of the bladder: correlation with p53, waf1, pRb and Ki67

Normal cell proliferation is closely regulated by proteins called cyclins. One of these, cyclin D1, in combination with its corresponding cyclin-dependent kinase (cdk), is essential for G(1)/S phase transition. Cyclin/cdk complexes are generally inhibited by cyclin-dependent kinase inhibitors(ckis), some of which are induced by wild-type p53. The aims of this study were: to investigate levels of cyclin D1 expression in transitional cell carcinoma (TCC) of the bladder; to correlate these results with data concerning the expression of p53, waf1, pRb and Ki67; and to determine whether cyclin D1 expression could predict clinical outcome. Paraffin-sections from 150 newly diagnosed bladder tumours (Ta/T1 = 97; T2-T4 = 53) were stained for cyclin D1 using immunohistochemistry and a cyclin D1 index assigned. These results were correlated with data relating to the expression of p53 and waf1 by the same tumours. A representative subset of 54 tumours (Ta/T1 = 28; T2-T4 = 26) was also stained for Ki67 and 55 were stained for pRb. The clinical course of each patient was recorded and multivariate analyses of risk factors for tumour recurrence, stage progression and overall survival were performed. Positive staining for cyclin D1 was found in 83% of tumours. The staining pattern varied between tumours with nuclear, cytoplasmic or a combination of the two evident in different tumours. 89% of Ta/T1 and 74% of T2-T4 tumours showed nuclear staining with or without cytoplasmic staining. The median value for cyclin D1 staining was significantly higher in Ta/T1 tumours (41%) compared with T2-T4 tumours (8%, P< 0.005) with 26% of muscle-invasive tumours demonstrating absent staining. In addition, the median value for cyclin D1 staining was significantly higher in G1/G2 tumours (43%) compared with G3 tumours (14%, P< 0.005). There was a significant positive correlation between expression of cyclin D1 and waf1 expression (P< 0.0001) as well as pRb expression but not between cyclin D1 expression and expression of p53. Ki67 expression was significantly associated with increasing tumour stage (P< 0.005) and histological grade (P< 0.05) but did not correlate with cyclin D1 expression. A cyclin D1 index > or = 8% was associated with significantly better survival in those patients with muscle-invasive disease (T2-T4). In addition, there was a significantly higher progression rate for those patients with Ta/T1 disease whose tumours demonstrated cytoplasmic cyclin D1 staining. These results indicate that cyclin D1 expression is significantly higher in low-stage, well differentiated bladder tumours and strongly correlates with waf1 expression. In a multivariate analysis, cyclin D1 expression is an independent prognostic indicator of survival in those patients with muscle-invasive disease.

TNF-alpha induced p21(WAF1) but not Bax in colon cancer cells WiDr with mutated p53: important role of protein stabilization

The p21(WAF1)induces cell cycle arrest at G(1)and its expression is regulated by the functional p53. TNF-alpha induced expression of p21(WAF1)at protein and mRNA levels in a dose-dependent fashion with an association with G(1)-arrest in human colon cancer cells WiDr that carry mutated p53 at codon 273 (His(273)). However, TNF-alpha did not affect the levels of the Bax protein, which also has p53-binding sites on its promoter and causes apoptosis. Further experiments suggested that cycloheximide (CHX), a protein synthesis inhibitor, increased the levels of p21(WAF1)mRNA and the induction of p21(WAF1)mRNA by TNF-alpha did not require new protein synthesis. Co-transfection of the p53 His(273)expression construct with a luciferase gene controlled by the p21(WAF1)promoter showed that the p53 His(273)was inactive, although TNF-alpha increased the transcriptional rate of p21(WAF1)in these cells. Further study found that TNF-alpha markedly stabilized the p21(WAF1)protein. These findings suggest that TNF-alpha induces expression of p21(WAF1)through a distinct pathway from Bax and that protein stabilization is an important mechanism in the expression of p21(WAF1)independent of p53.

Induction of p21WAF1/CIP1 and cyclin D1 expression by the Src oncoprotein in mouse fibroblasts: role of activated STAT3 signaling

While the activated viral Src oncoprotein, v-Src, induces uncontrolled cell growth, the mechanisms underlying cell cycle deregulation by v-Src have not been fully defined. Previous studies demonstrated that v-Src induces constitutively active STAT3 signaling that is required for cell transformation and recent data have implicated STAT3 in the transcriptional control of critical cell cycle regulators. Here we show in mouse fibroblasts stably transformed by v-Src that mRNA and protein levels of p21 (WAF1/CIP1), cyclin D1, and cyclin E are elevated. Using reporter constructs in transient-transfection assays, the cyclin D1 and p21 promoters were both found to be transcriptionaly induced by v-Src in a STAT3-dependent manner. The kinase activities of cyclin D/CDK4, 6 and cyclin E/CDK2 complexes were only slightly elevated, consistent with the findings that coordinate increases in p21, cyclin D1 and cyclin E resulted in an increase in cyclin/CDK/p21 complexes. Similar results were obtained in NIH3T3 and BALB/c 3T3 cells stably transformed by v-Src, indicating that these regulatory events associated with STAT3 signaling represent common mechanisms independent of cell line or clonal variation. These findings suggest that STAT3 has an essential role in the regulation of critical cell cycle components in v-Src transformed mouse fibroblasts.

A clinicopathological study of p53, p21 (WAF1/CIP1) and cyclin D1 expression in human prostate cancers

A series of 66 prostate cancer samples were studied immunohistochemically for expression of p53, p21, a cyclin-dependent kinase inhibitor regulated by p53, and cyclin D1, a cell cycle regulatory protein. Twenty samples (30%) showed positive staining for p53, 14 (21%) for p21, and 20 (30%) for cyclin D1. p53 expression was correlated with a high Gleason score while p21 and cyclin D1 did not demonstrate any clear clinicopathological factors. A positive correlation between p53 and p21 expression was observed, however these samples with both positive immunoreactivity had no p53 mutation, suggesting the possibility that p53 may be wild-type and induce p21 expression, and/or p21 is likely to be induced by a p53-independent pathway.

Requirement of cyclin D1 in mesangial cell mitogenesis

Abstract. Hyperplasia of mesangial cells (MC) is a frequent finding in glomerulonephritis. The control and function of cyclin D1, a regulator of cell cycle progression, in MC proliferation in vivo and in vitro were investigated. In a rat model of mesangioproliferative glomerulonephritis, increases in the number of cyclin D1-positive MC nuclei were prominent on day 5 of the disease, preceding the peak of MC hyperplasia. In growth-arrested rat MC in culture, mitogenic stimulation with serum or platelet-derived growth factor (PDGF) led to rapid increases in cyclin D1 protein expression. Transforming growth factor-beta1 inhibited PDGF induction of cyclin D1 protein at 12 h. In an examination of the subcellular distribution of cyclin D1, it was observed that stimulation of MC with PDGF for 6 h caused translocation of cyclin D1 from the cytoplasm into the nucleus. Coincubation with PDGF and transforming growth factor-beta1 completely inhibited this effect, without altering the cellular cyclin D1 protein abundance at that time point. To test whether reduction of cyclin D1 protein levels was sufficient to inhibit mitogenesis, MC were transfected with antisense oligonucleotides (ODN) complementary to rat cyclin D1 mRNA. Antisense ODN against cyclin D1 reduced the serum- or PDGF-induced protein expression of cyclin D1 to 27 or 10% of control levels, respectively. These inhibitory effects were correlated with diminished cyclin-dependent kinase 4 activity. Antisense ODN against cyclin D1 also decreased the PDGF-induced increase in p21(Waf-1) protein levels. The MC proliferation caused by serum or PDGF was markedly inhibited by antisense ODN against cyclin D1, as measured by [(3)H]thymidine uptake and cell counts. It is concluded that increased cyclin D1 protein expression of MC is required for MC proliferation. Targeting cyclin D1 expression may represent an effective means to inhibit MC proliferation in vitro and in vivo.

The central region of Gadd45 is required for its interaction with p21/WAF1

Cell cycle arrest represents an important response to genotoxic stress and the tumor suppressor p53 has been described to act as a critical effector in this biological event. Upon stress, p53 becomes transcriptionally active and up-regulates the transcription of downstream effector genes, which contain p53 recognition sites in their regulatory regions. Among the genes activated are p21 and GADD45, each of which independently exhibits growth-suppressive activity. The Gadd45 protein has been described to form a complex with p21, and thus, work was undertaken to map the regions of Gadd45 involved in this interaction and to examine the roles of those two proteins in growth suppression. In this report, a Gadd45 overlapping peptide library and a series of Gadd45 deletion mutants were used to define the domains of Gadd45 involved in the association with p21. Results using both in vitro and in vivo methods have shown that the interaction of Gadd45 with p21 involves a central region of Gadd45. Interestingly, the p21-binding domain of Gadd45 also encodes the Cdc2-binding activity, indicating that the central region of Gadd45 may serve as an important "core," through which Gadd45 protein is able to present cross-talk with other cell cycle regulators. In addition, GADD45 inhibition of Cdc2 kinase activity was compared with Myd118 and CR6, two other members of the GADD45 family. GADD45 was shown to generate the strongest inhibitory effect on Cdc2 activity. Finally, results from short-term survival assays further demonstrated that p21 and GADD45 act upon different cellular pathways to exert their growth-suppressive function.

Regulation of the G1 phase of the mammalian cell cycle

In any multi-cellular organism, the balance between cell division and cell death maintains a constant cell number. Both cell division cycle and cell death are highly regulated events. Whether the cell will proceed through the cycle or not, depends upon whether the conditions required at the checkpoints during the cycle are fulfilled. In higher eucaryotic cells, such as mammalian cells, signals that arrest the cycle usually act at a G1 checkpoint. Cells that pass this restriction point are committed to complete the cycle. Regulation of the G1 phase of the cell cycle is extremely complex and involves many different families of proteins such as retinoblastoma family, cyclin dependent kinases, cyclins, and cyclin kinase inhibitors.

Growth inhibition of human glioma cells by transfection-induced P21 and its effects on telomerase activity

The aim of this study is to investigate the effect of the p21 gene transfection on the growth of cultured human glioma cell lines, and analyze the telomerase activity, and detection of telomerase components in p21 transfectant. The p21 gene was transfected into human glioma cell lines, U251MG and T98G with our novel liposome. The cell growth was assessed by counting the number of trypan blue-excluding cells in a hemocytometer and flow cytometry analysis. The expression of P21 protein and its mRNA were examined by Western and Northern blot analysis. The telomerase activity was assayed by TRAP (telomerase repeat amplification protocol)/TRAP-HPA (hybridization protection assay) method qualitatively and quantitatively. The length of telomere was measured by Southern blot analysis. The expression of telomerase components (hTERT, hTERC and TEP1) were examined by RT-PCR (reverse transcriptase-polymerase chain reaction). The p21 transfectant demonstrated the expression of P21 protein and its mRNA. The p21 transfection of human glioma cells results in growth inhibition and G0/G1 arrest. The p21 transfectant revealed a decrease of telomerase activity and hTERT expression as compared with control cells. These results suggest that p21 transfection induces G0/G1 arrest in human glioma cells which associates with the reduction in the telomerase activity and hTERT expression.

A role for E2F1 in Ras activation of p21(WAF1/CIP1) transcription

We recently reported that E2F1 could transactivate the p21 promoter via cis-acting elements between -119 to +16 bp of the p21 gene. Here we show that activated V12-H-Ras can induce the p21 promoter through the same region of the p21 promoter by a p53-independent mechanism in NIH3T3 cells. In contrast, activated Ras was not able to induce the p21 promoter in E2F1-/- fibroblasts, suggesting that E2F1 is required for induction of the p21 promoter by activated Ras. Cotransfection of increasing concentrations of dominant negative E2F1 alone, or with dominant negative DP1 into NIH3T3 cells suppressed induction of the p21 promoter by activated Ras. These data suggest that p53-independent induction of the p21 promoter by activated Ras is mediated at least in part by E2F1. Oncogene (2000) 19, 961 - 964.

Signal transduction pathways controlling the switch between keratinocyte growth and differentiation

Self-renewing epithelia are characterized by a high turnover rate and a fine balance between growth and differentiation. Such a balance is influenced by many exogenous factors, including gradients of diffusible molecules, cell/substrate adhesion contacts, and direct cell-cell communication. The inter-connection between these various extracellular signals and underlying intracellular pathways is clearly of great interest. Primary keratinocytes of either human or murine origin provide an ideal experimental system to elucidate early signaling events involved in the control of epithelial differentiation. Relative to established cell lines, use of a primary system eliminates the possibility of alterations in critical regulatory events which may occur during prolonged propagation in culture. Primary keratinocytes are easily grown in large numbers, and their differentiation can be induced under well-defined culture conditions. The ensuing rapid and homogeneous response is amenable to careful biochemical analysis. Gene transfer technology (transient transfections, adenoviral and retroviral vectors), together with the use of keratinocytes derived from gene knockout and transgenic mice, makes it possible to assess the specific contribution of individual genes to the control of the differentiation process. This review focuses on the significant progress that has been made over the last few years in our understanding of the specific signals that trigger keratinocyte differentiation, the underlying signaling pathways, and how they impinge on specific transcription and cell-cycle control mechanisms associated with the onset of keratinocyte differentiation. Recent developments and future directions in this important area of research will be highlighted.