PKB/Akt phosphorylates p27, impairs nuclear import of p27 and opposes p27-mediated G1 arrest

Foxm1b transcription factor is essential for development of hepatocellular carcinomas and is negatively regulated by the p19ARF tumor suppressor

Hepatocellular carcinoma (HCC) is a leading cause of cancer-related deaths worldwide. Here, we provide evidence that the Forkhead Box (Fox) m1b (Foxm1b or Foxm1) transcription factor is essential for the development of HCC. Conditionally deleted Foxm1b mouse hepatocytes fail to proliferate and are highly resistant to developing HCC in response to a Diethylnitrosamine (DEN)/Phenobarbital (PB) liver tumor-induction protocol. The mechanism of resistance to HCC development is associated with nuclear accumulation of the cell cycle inhibitor p27(Kip1) protein and reduced expression of the Cdk1-activator Cdc25B phosphatase. We showed that the Foxm1b transcription factor is a novel inhibitory target of the p19(ARF) tumor suppressor. Furthermore, we demonstrated that conditional overexpression of Foxm1b protein in osteosarcoma U2OS cells greatly enhances anchorage-independent growth of cell colonies on soft agar. A p19(ARF) 26-44 peptide containing nine D-Arg to enhance cellular uptake of the peptide was sufficient to significantly reduce both Foxm1b transcriptional activity and Foxm1b-induced growth of U2OS cell colonies on soft agar. These results suggest that this (D-Arg)(9)-p19(ARF) 26-44 peptide is a potential therapeutic inhibitor of Foxm1b function during cellular transformation. Our studies demonstrate that the Foxm1b transcription factor is required for proliferative expansion during tumor progression and constitutes a potential new target for therapy of human HCC tumors.

Lipoxins inhibit Akt/PKB activation and cell cycle progression in human mesangial cells

Lipoxins (LX) are endogenously produced eicosanoids with a spectrum of bioactions that suggest anti-inflammatory, pro-resolution roles for these agents. Mesangial cell (MC) proliferation plays a pivotal role in the pathophysiology of glomerular inflammation and is coupled to sclerosis and tubulointerstitial fibrosis. We have previously reported that LXA4 acts through a specific G-protein-coupled-receptor (GPCR) to modulate MC proliferation in response to the proinflammatory mediators LTD4 and platelet-derived growth factor (PDGF). Further investigations revealed that these effects were mediated by modulation of receptor tyrosine kinase activity. Here we have explored the underlying mechanisms and report inhibition of growth factor (PDGF; epithelial growth factor) activation of Akt/PKB by LXA4. LXA4 (10 nmol/L) modulates PDGF-induced (10 ng/ml, 24 hours) decrements in the levels of cyclin kinase inhibitors p21Cip1 and p27Kip1. PDGF-induced increases in CDK2-cyclin E complex formation are also inhibited by LXA4. The potential of LXA4 as an anti-inflammatory therapeutic is compromised by its degradation; this has been circumvented by synthesis of stable analogs. We report that 15-(R/S)-methyl-LXA4 and 16-phenoxy-LXA4 mimic the native compound with respect to modulation of cell proliferation and PDGF-induced changes in cell cycle proteins. In vivo, MC proliferation in response to PDGF is associated with TGFbeta1 production and the subsequent development of renal fibrosis. Here we demonstrate that prolonged (24 to 48 hours) exposure to PDGF is associated with autocrine TGFbeta1 production, which is significantly reduced by LXA4. In aggregate these data demonstrate that LX inhibit PDGF stimulated proliferation via modulation of the PI-3-kinase pathway preventing mitogen-elicited G1-S phase progression and suggest the therapeutic potential of LX as anti-fibrotic agents.

Acquired resistance to EGFR inhibitors: mechanisms and prevention strategies

Potent and specific, or relatively specific, inhibitors of epidermal growth factor receptor (EGFR) signaling, including monoclonal antibodies and small molecular weight compounds, have been successfully developed. Both types of agent have been found to have significant antitumor activity, especially when used in combination with radio- hormone- and chemotherapy in preclinical studies. Because of the potentiation of the conventional drug activity in these combination settings, inhibitors of EGFR signaling have often been referred to as sensitizers for chemotherapy or radiation, as well as drug resistance reversal agents. Phase II clinical trials in head-and-neck as well as lung cancer suggested this concept of chemosensitization might translate into the clinic, but this remains to be definitively proven in randomized, double-blind Phase III trials. Given the extensive preclinical literature on EGFR blocking drugs and the advanced clinical development of such agents, it is surprising that the possibility of development of acquired resistance to the EGFR inhibitors themselves, a common clinical problem with virtually all other currently used anticancer drugs, remains a largely unexplored subject of investigation. Here we summarize some of the possible mechanisms that can result in acquired resistance to EGFR-targeting drugs. Alternative combination therapies to circumvent and delay this problem are suggested.

Is Akt the Mastermind Behind Age-Related Heart Disease?

Over the past several years, the insulin/insulin-like growth factor (IGF) signaling pathway has become a central figure in the study of organismal aging. Mutations in components of this pathway have led to enhanced longevity in several organisms, but it is still not clear whether and how this pathway contributes to human aging and aging-related diseases. In a new study, Miyauchi and colleagues propose that Akt, a member of the phosphatidylinositol 3-kinase family and a downstream component of the insulin/IGF pathway, plays a central role in the life span of endothelial cells. These findings implicate the insulin/IGF pathway in the development and progression of cardiovascular disease.

The biology of CML blast crisis

Chronic myelogenous leukemia (CML) evolves from a chronic phase characterized by the Philadelphia chromosome as the sole genetic abnormality into blast crisis, which is often associated with additional chromosomal and molecular secondary changes. Although the pathogenic effects of most CML blast crisis secondary changes are still poorly understood, ample evidence suggests that the phenotype of CML blast crisis cells (enhanced proliferation and survival, differentiation arrest) depends on cooperation of BCR/ABL with genes dysregulated during disease progression. Most genetic abnormalities of CML blast crisis have a direct or indirect effect on p53 or Rb (or both) gene activity, which are primarily required for cell proliferation and survival, but not differentiation. Thus, the differentiation arrest of CML blast crisis cells is a secondary consequence of these abnormalities or is caused by dysregulation of differentiation-regulatory genes (ie, C/EBPalpha). Validation of the critical role of certain secondary changes (ie, loss of p53 or C/EBPalpha function) in murine models of CML blast crisis and in in vitro assays of BCR/ABL transformation of human hematopoietic progenitors might lead to the development of novel therapies based on targeting BCR/ABL and inhibiting or restoring the gene activity gained or lost during disease progression (ie, p53 or C/EBPalpha).

Stat5a is tyrosine phosphorylated and nuclear localized in a high proportion of human breast cancers

Signal transducers and activators of transcription (STATs) are latent cytoplasmic transcription factors that are activated and translocated into the nucleus after phosphorylation at a conserved tyrosine residue. Mouse model studies have demonstrated that activated Stat5a acts as a critical survival factor for normal, preneoplastic and malignant mammary epithelial cells. Very limited information is available, however, on the expression, tyrosine phosphorylation status and nuclear localization of Stat5a in human breast cancers. In our study, the pattern of Stat5a cellular localization was analyzed by immunohistochemistry in a series of 83 randomly selected primary human breast adenocarcinomas. Immunoprecipitation/Western blotting and immunohistochemistry assays employing different phospho-specific antibodies verified Stat5a tyrosine phosphorylation status. Stat5a was nuclear localized and tyrosine phosphorylated in 59 of 78 (76%) breast cancers examined; 38 of 78 (49%) demonstrated Stat5a nuclear localization in more than 25% of the breast cancer cells within the adenocarcinomas. Nuclear localized Stat5a was associated positively with increased levels of histologic differentiation (p = 0.03). A statistically significant positive association with p27 nuclear localization also was identified (p = 0.05). No relationship was found between nuclear localized Stat5a and menopausal status, tumor size, ploidy, percentage of cells in S-phase, lymph node metastases, ER, ErbB2, nuclear localized p21 or nuclear localized Stat5b/Stat3. As its role in human breast cancer progression and response to therapy is defined, Stat5a could become a new molecular target for breast cancer therapy.

Cdk inhibitor p27Kip1 and hormone dependence in breast cancer

p27Kip1 is an important regulator of the G1 to S transition. While a potent inhibitor of cyclin-dependent-kinase (Cdk)2, p27 is also involved in assembly of cyclin D/Cdk4 complexes. Although rarely mutated, p27 is functionally downregulated in many human cancers by mechanisms involving enhanced degradation, cytoplasmic mislocalization, and/or sequestration by cyclin D/Cdk complexes in response to oncogenic signals. Therefore, low levels and/or cytoplasmic localized p27 have been associated with enhanced malignancy and poor patient prognosis in many neoplasias including breast cancer. Recent data discussed below suggest that a threshold of p27 is required for response to antiestrogens and, conversely, that low levels predict for antiestrogen resistance. These results imply that hormone receptor-positive tumors with low and/or cytosolic p27 respond poorly to antiestrogens and should be considered for alternative therapeutic strategies.

Mechanism of action of anti-HER2 monoclonal antibodies: scientific update on trastuzumab and 2C4

The HER family of transmembrane tyrosine kinase receptors is composed of four members, BER1 to HER4. HER2 is a ligand-orphan receptor expressed in many human tumors and overexpressed in 25-30% of breast cancers. HER2 amplifies the signal provided by other receptors of the HER family by forming heterodimers. The essential role of HER2 in the HER signaling network led to the development of anti-HER2 monoclonal antibodies (MAbs) for cancer therapy. In particular, the humanized MAb trastuzumab (Herceptin) has antitumor activity against HER2-overexpressing human breast tumor cells and is widely used for the treatment of women with HER2 overexpressing breast cancers. Trastuzumab induces HER2 receptor downmodulation and, as a result, inhibits critical signalling pathways (i.e. ras-Raf-MAPK and PI3K/Akt) and blocks cell cycle progression by inducing the formation of p27/Cdk2 complexes. Trastuzumab also inhibits HER2 cleavage, preceding antibody-induced receptor downmodulation, and this effect might contribute to its antitumor activity in some cancers. In vivo, trastuzumab inhibits angiogenesis and induces antibody-dependent cellular cytotoxicity. A limitation of trastuzumab is that its activity is largely restricted to breast cancers with the highest level of HER2 overexpression or HER2 gene amplification. However, there is a large population of breast cancers and of many other tumors that have low or moderate HER2 expression. In such tumors, HER2 functions as a preferred coreceptor to form heterodimers with HER1 (EGFR), HER3 or HER4. For this reason, a humanized monoclonal antibody, called 2C4, that targets the role of HER2 as a coreceptor is under active development. 2C4 binds to a different epitope of HER2 ectodomain than trastuzumab and sterically hinders HER2 recruitment in heterodimers with other HER receptors. This results in the inhibition of signalling by HER2-based heterodimers both in cells with low and high HER2 expression. In vitro and in vivo antitumor activity has been reported in a range of breast and prostate tumor models. Therefore, 2C4 may have potential against a wide variety of solid tumors. Phase I trials are underway.

Transforming growth factor-beta induces Cdk2 relocalization to the cytoplasm coincident with dephosphorylation of retinoblastoma tumor suppressor protein

Background

The transforming growth factor-β (TGF-β) signaling pathway functions to prevent tumorigenesis, and loss of sensitivity to TGF-β-mediated cell cycle arrest is nearly ubiquitous among human cancers. Our previous studies demonstrated that rapamycin potentiates TGF-β-induced cell cycle arrest in nontransformed epithelial cells and partially restores TGF-β-induced growth arrest of some human cancer cell lines. Growth arrest correlated with increased binding of p21 and p27 to cyclin-dependent kinase-2 (Cdk2), and inhibition of Cdk2 kinase activity. However, it was unclear how TGF-β caused increased binding of p21 and p27 to Cdk2.

Methods

Cell fractionation and immunofluorescence microscopy experiments were performed to examine the effect of TGF-β on the intracellular localization of Cdk2, p21, and p27. Kinase assays were performed on cytoplasmic and nuclear extracts to determine how TGF-β altered Cdk2 activity in both subcellular compartments.

Results

In breast epithelial cells treatment with TGF-β induced a decrease in nuclear Cdk2 concentrations and relocalization of Cdk2 to the cytoplasm. Cdk2 relocalization to the cytoplasm correlated with dephosphorylation of nuclear retinoblastoma tumor suppressor protein and decreased nuclear Cdk2 activity. In these epithelial cell lines, p21 and p27 were localized primarily in the cytoplasm. Decreases in nuclear Cdk2 concentrations correlated with increased binding of Cdk2 to cytoplasmic p21 and p27.

Conclusion

Cooperative growth arrest induced by treatment with TGF-β + rapamycin causes inhibition of nuclear Cdk2 activity through multiple mechanisms, including Cdk2 relocalization to the cytoplasm, increased p27 and p21 binding to Cdk2, and increased phosphorylation of nuclear Cdk2 on its inhibitory site, Tyr¹⁵.

Cyclin-Dependent Kinase 6 Inhibits Proliferation of Human Mammary Epithelial Cells

Many defects in cancer cells are in molecules regulating G1-phase cyclin-dependent kinases (cdks), which are responsible for modulating the activities of Rb family growth-suppressing proteins. Models for understanding how such defects affect proliferation assume that cdks are responsible for sequentially phosphorylating, and hence inactivating, the growth-suppressing functions of Rb family proteins, thus promoting cell cycle progression. However, cdks also play a role in formation of growth-suppressing forms of pRb family molecules, including the “hypophosphorylated” species of pRb itself. Here, it is shown that normal human mammary epithelial cells have a high amount of cdk6 protein and activity, but all breast tumor-derived cell lines analyzed had reduced levels, with several having little or no cdk6. Immunohistochemical studies showed reduced levels of cdk6 in breast tumor cells as compared with normal breast tissue in vivo. Cdk6 levels in two breast tumor cell lines were restored to those characteristic of normal human mammary epithelial cells by DNA transfection. The cells had a reduced growth rate compared with parental tumor cells; cells that lost ectopic expression of cdk6 reverted to the faster growth rate of parental cells. Cell lines with restored cdk6 levels accumulated higher amounts of the Rb family protein p130 as well as E2F4, a suppressing member of the E2F family of transcription factors, in their nuclei. The results suggest that cdk6 restrains rather than stimulates breast epithelial cell proliferation and that its loss or down-regulation could play a role in breast tumor development.

Inhibition of Breast and Ovarian Tumor Growth through Multiple Signaling Pathways by Using Retrovirus-mediated Small Interfering RNA against Her-2/neu Gene Expression

The Her-2/neu oncogene is overexpressed in approximately 30% of breast and ovarian cancer cases and often indicates a poor prognosis. Therapeutic agents against Her-2/neu have been intensively sought over the past decade. Here we show that small interfering RNA (siRNA) can silence the expression of Her-2/neu in models of human breast or ovarian cancer through retrovirus-mediated transfer of an siRNA against Her-2/neu. Cells infected with retrovirus expressing anti-Her-2/neu siRNA exhibit slower proliferation, increased apoptosis, increased G0/G1 arrest, and decreased tumor growth. Changes in cell cycle-associated factors included decreased levels of phosphatidylinositol 3-kinase, pAkt, and cyclin D1 and increased levels of p27 and phosphorylated retinoblastoma protein. Knockdown of Her-2/neu expression by siRNA is also associated with increased expression of the anti-angiogenic factor thrombospondin-1 and decreased expression of the pro-angiogenic vascular endothelial growth factor, suggesting that Her-2/neu stimulates tumor growth at least in part by regulating angiogenesis. siRNA-mediated gene silencing of Her-2/neu and increasing the expression of thrombospondin-1 may be a useful therapeutic strategy for Her-2/neu-over-expressing breast or ovarian cancer.

A Permissive Role for Phosphatidylinositol 3-Kinase in the Stat5- mediated Expression of Cyclin D2 by the Interleukin-2 Receptor

The interleukin-2 (IL-2) receptor promotes T cell proliferation in part by inducing the expression of D-type cyclins, which enable cells to progress from the G1 to S phase of the cell cycle. We previously showed that the IL-2 receptor induces expression of cyclin D2 by activating the transcription factor Stat5, which binds directly and immediately to a site upstream of the cyclin D2 promoter. We show here that subsequent transcription of the cyclin D2 gene occurs by a delayed, cycloheximide-sensitive mechanism, which implies the involvement of additional regulatory mechanisms. The transcription factor c-Myc is induced by Stat5 and is reported to bind to two E box motifs in the cyclin D2 promoter. However, in IL-2-stimulated T cells, c-Myc does not appear to be involved in cyclin D2 induction, since we found that these two E boxes are preferentially bound by USF-1 and USF-2 and, moreover, are dispensable for cyclin D2 promoter activity. Instead, we found that Stat5 activates the phosphatidylinositol 3-kinase (PI3 kinase) pathway by a delayed, cycloheximide-sensitive mechanism and that PI3 kinase activity is essential for the induction of cyclin D2 by Stat5. Chromatin immunoprecipitation experiments revealed that PI3 kinase is required for the optimal binding of RNA polymerase II to the promoters of cyclin D2 as well as other genes. Our results reveal a novel link between PI3 kinase and RNA polymerase II promoter binding activity and demonstrate discrete, coordinated roles for the PI3 kinase and Stat5 pathways in cyclin D2 transcription.

Insulin and cancer

Obesity has recently been linked to mortality from the majority of cancers. The insulin/insulin-like growth factor (IGF) system may partly explain this effect. The metabolic syndrome, associated with hyperinsulinemia, may modulate this effect. Recent evidence supports the role of insulin and IGF-1 as important growth factors, acting through the tyrosine kinase growth factor cascade in enhancing tumor cell proliferation. In addition, the metabolic syndrome associated with a chronic inflammatory state and accompanying cytokine abnormalities may also contribute to tumor progression. Growing links between insulin and the etiology as well as prognosis in colon, prostate, pancreatic, and, particularly, breast cancer are reviewed. Of particular concern is the evidence that elevated IGF-1 may interfere with cancer therapy, adversely affecting prognosis. The role of insulin is of concern because of the increasing levels of obesity and the associated metabolic syndrome. Weight gain, through typical Western diet; limited levels of activity; and, more recently, stress-related changes in neuroendocrine function may lead to insulin resistance and hyperinsulinemia. The opportunity for a multidisciplinary approach involving nutrition, exercise, and stress reduction in an integrative setting may be crucial to limiting the insulin-resistant state and improving cancer outcomes.

Molecular mechanisms underlying IGF-I-induced attenuation of the growth-inhibitory activity of trastuzumab (Herceptin) on SKBR3 breast cancer cells

The clinical usefulness of trastuzumab (Herceptin; Genentech, San Francisco, CA) in breast cancer treatment is limited by the rapid development of resistance. We previously reported that IGF-I signaling confers resistance to the growth-inhibitory actions of trastuzumab in a model system, but the underlying molecular mechanism remains unknown. We used SKBR3/neo cells (expressing few IGF-I receptors) and SKBR3/IGF-IR cells (overexpressing IGF-I receptor) as our experimental model. IGF-I antagonized the trastuzumab-induced increase in the level of the Cdk inhibitor p27(Kip1). This resulted in decreased association of p27(Kip1) with Cdk2, restoration of Cdk2 activity and attenuation of cell-cycle arrest in G(1) phase, all of which had been induced by trastuzumab treatment in SKBR3/IGF-IR cells. We also found that the decrease in p27(Kip1) induced by IGF-I was accompanied by an increase in expression of Skp2, which is a ubiquitin ligase for p27(Kip1), and by increased Skp2 association with p27(Kip1). A specific proteasome inhibitor (LLnL) completely blocked the ability of IGF-I to reduce the p27(Kip1) protein level, while IGF-I increased p27(Kip1) ubiquitination. This suggests that the action of IGF-I in conferring resistance to trastuzumab involves targeting of p27(Kip1) to the ubiquitin/proteasome degradation machinery. Finally, specific inhibitors of MAPK and PI3K suggest that the IGF-I-mediated reduction in p27(Kip1) protein level by increased degradation predominantly involves the PI3K pathway. Our results provide an example of resistance to an antineoplastic therapy that targets one tyrosine kinase receptor by increased signal transduction through an alternative pathway in a complex regulatory network.

Cell-cycle targeted therapies

Eukaryotic organisms depend on an intricate and evolutionary conserved cell cycle to control cell division. The cell cycle is regulated by a number of important protein families which are common targets for mutational inactivation or overexpression in human tumours. The cyclin D and E families and their cyclin-dependent kinase partners initiate the phosphorylation of the retinoblastoma tumour suppressor protein and subsequent transition through the cell cycle. Cyclin/cdk activity and therefore control of cell division is restrained by two families of cyclin dependent kinase inhibitors. A greater understanding of the cell cycle has led to the development of a number of compounds with the potential to restore control of cell division in human cancers. This review will introduce the protein families that regulate the cell cycle, their aberrations in malignant progression and pharmacological strategies targeting this important process.

PI3K/Akt and apoptosis: size matters

Recent research has examined Akt and Akt-related serine-threonine kinases in signaling cascades that regulate cell survival and are important in the pathogenesis of degenerative diseases and in cancer. We seek to recapitulate the research that has helped to define the current understanding of the role of the Akt pathway under normal and pathologic conditions, also in view of genetic models of Akt function. In particular, we will evaluate the mechanisms of Akt regulation and the role of Akt substrates in Akt-dependent biologic responses in the decisions of cell death and cell survival. Here, we hope to establish the mechanisms of apoptosis suppression by Akt kinase as a framework for a more general understanding of growth factor-dependent regulation of cell survival.

The V109G Polymorphism of the p27 Gene CDKN1B Indicates a Worse Outcome in Node-Negative Breast Cancer Patients

Although p27 plays a central role in cell cycle regulation, its role in breast cancer prognosis is controversial. Furthermore, the p27 gene CDKN1B carries a polymorphism with unknown functional relevance. This study was designed to evaluate p27 expression and p27 genotyping with respect to early breast cancer prognosis. 279 patients with infiltrating metastasis-free breast cancer were included in this study. p27 expression was determined in tumor tissue specimens from 261 patients by immunohistochemistry. From 108 patients, the CDKN1B genotype was examined by PCR and subsequent direct sequencing. 55.2% of the tumors were considered p27 positive. p27 expression did not correlate with any of the established parameters except for nodal involvement but significantly correlated to prolonged disease-free survival. In 35% of the tumors analyzed, the CDKN1B gene showed a polymorphism at codon 109 (V109G). The V109G polymorphism correlated with greater nodal involvement. In the node-negative subgroup, V109G correlated significantly with a shortened disease-free survival. In conclusion, the determination of the CDKN1B genotype might be a powerful tool for the prognosis of patients with early breast cancer.

Cell cycle genes in a mouse mammary hyperplasia model

Human mammary epithelial cells emerge spontaneously from senescence, exhibiting eroding telomeric sequences, and ultimately enter crisis to generate the type of chromosomal abnormalities seen in early stages of breast cancer. In a mouse mammary tumor model, the spontaneous escape of senescence can be observed as an increase in DNA synthesis that is reflected by alterations in the cell cycle profile and increases in the expression levels and activities of cell cycle molecular components. This review provides an overview of gene alterations in the cell cycle components in mouse mammary hyperplasia.

p27 deregulation in breast cancer: prognostic significance and implications for therapy

p27 is a key regulator of G1-to-S phase progression. It prevents premature activation of cyclin E-cdk2 in G1 and promotes the assembly and activation of D-type cyclin-cdks. While the p27 gene is rarely mutated in human cancers, the action of p27 is impaired in breast and other human cancers through accelerated p27 proteolysis, sequestration by cyclin D-cdks, and by p27 mislocalization in tumor cell cytoplasm. Reduced p27 protein is strongly associated with high histopathologic tumor grade, reflecting a lack of tumor differentiation. Loss of p27 is also an indicator of poor patient outcome in a majority of breast cancer studies, including node negative disease. The broad application of p27 in the clinical evaluation of breast cancer prognosis will require a consensus on methods of tumor fixation, staining, and scoring. This review will focus on mechanisms of p27 regulation in normal cells and how deregulation of p27 may arise in breast and other human cancers. The prognostic significance of p27 in human breast cancer and the possible therapeutic implications of these findings will also be reviewed.

Epigallocatechin-3-gallate inhibits epidermal growth factor receptor signaling pathway. Evidence for direct inhibition of ERK1/2 and AKT kinases

Epidermal growth factor receptor (EGFR) activation is absolutely required for cervical cell proliferation. This suggests that EGFR-inhibitory agents may be of therapeutic value. In the present study, we investigated the effects of epigallocatechin-3-gallate (EGCG), a bioactive green tea polyphenol, on EGFR signaling in cervical cells. EGCG inhibits epidermal growth factor-dependent activation of EGFR, and EGFR-dependent activation of the mitogen-activated protein kinases ERK1/2. EGCG also inhibits EGFR-dependent AKT activity. The EGCG-dependent reduction in ERK and AKT activity is associated with reduced phosphorylation of downstream substrates, including p90RSK, FKHR, and BAD. These changes are associated with increased p53, p21(WAF-1), and p27(KIP-1) levels, reduced cyclin E level, and reduced CDK2 kinase activity. Consistent with these findings, flow cytometry and TUNEL (terminal deoxynucleotidyl-transferase-mediated dUTP nick end labeling) staining revealed EGCG-dependent G(1) arrest. Moreover, sustained EGCG treatment caused apoptotic cell death. In addition to inhibiting EGFR, cell-free studies demonstrated that EGCG directly inhibits ERK1/2 and AKT, suggesting that EGCG acts simultaneously at multiple levels to inhibit EGF-dependent signaling. Importantly, the EGCG inhibition is selective, as EGCG does not effect the EGFR-dependent activation of JNK. These results suggest that EGCG acts to selectively inhibit multiple EGF-dependent kinases to inhibit cell proliferation.

Targeted expression of HGF/SF in mouse mammary epithelium leads to metastatic adenosquamous carcinomas through the activation of multiple signal transduction pathways

Overexpression of hepatocyte growth factor (HGF), also called scatter factor (SF), and its receptor c-Met are associated with poor prognosis for cancer patients. In particular, breast cancer cells can produce HGF that acts in a paracrine as well as in an autocrine manner. Therefore, HGF and c-Met are putative targets for cancer therapy. To explore HGF/c-Met signaling in breast cancer, we have generated transgenic mice expressing HGF specifically in mammary epithelium under the transcriptional control of the whey acidic protein (WAP) gene promoter. WAP-HGF transgenic females developed hyperplastic ductal trees and multifocal invasive tumors after several pregnancies, some of which progressed to lung metastases. Tumors produced HGF and displayed phosphorylated c-Met, which correlated with increased Akt as well as c-myc activation. A high growth rate, as demonstrated by Ki67 nuclear antigen staining, and a lack of progesterone receptor were characteristic of the tumors. Immunohistochemical analysis revealed areas of osteopontin (Opn) expression in WAP-HGF tumors and lung metastases in agreement with a previously reported role for Opn in invasive growth. We suggest that these mice may serve as a new breast cancer model for the evaluation of the effects of unscheduled HGF expression in breast cancer.

Kinase-dead PKB gene therapy combined with hyperthermia for human breast cancer

We have previously demonstrated that protein kinase B (PKB) is a mediator of heat-induced apoptosis for human breast cancer cells. To investigate the therapeutic potential of abrogating the function of this important survival protein, a novel replication-deficient adenovirus was constructed, wherein a mutant, kinase-inactive PKB gene (AAA) was inserted downstream of the CMV promoter. Two human breast cancer cell lines, MCF-7 and MDA-468, were treated, along with the MCF-10 serving as a "normal" mammary epithelial comparator. Apoptosis was increased with adv.AAA (25 PFU/cell) infection alone, but was significantly enhanced with the addition of heat exposure. Differential survival was observed with the MDA-468 cancer cells being more sensitive than the MCF-7 cells. The MCF-10 cells, in contrast, were most resistant to these treatments. Results from the clonogenic assay reflected the apoptosis data, with an apparent additive interaction between adv.AAA and hyperthermia treatments, again with greater differential sensitivity of the malignant, compared to the "normal" mammary epithelial cells. Heat or adv.beta-gal treatments led to phosphorylation of PKB and Forkhead, but this phosphorylation was reduced with adv.AAA therapy. In parallel, the combination of adv.AAA and heat treatment reduced PKB kinase activity more so than with either heat or adv.beta-gal alone. In conclusion, our results demonstrate that inhibition of the PKB-dependent survival pathway will promote apoptosis and thermosensitization in malignant breast cancer cells, with relative sparing of their normal counterpart, suggesting that a therapeutic gain could be achievable using this therapeutic strategy.

Negative regulation of SCFSkp2 ubiquitin ligase by TGF-β signaling

TGF-beta is a multifunctional growth factor whose best-known function is to inhibit cell growth and suppress tumor formation. TGF-beta causes cells to accumulate in mid-to-late G1 phase by blocking the transition from G1 to S. It has been shown that TGF-beta inhibits Cdk2-cyclin E kinase activity by promoting the binding of cell cycle inhibitor p27Kip1 to the kinase complexes. Here, we show that TGF-beta treatment leads to stabilization of p27Kip1 during G1 to S transition. We found that TGF-beta negatively regulates components of the SCF complex, which degrades the p27Kip1 during the G1 to S transition, through two distinct mechanisms. Using a pulse-chase analysis, we demonstrated that the stability of Skp2 decreases in the presence of TGF-beta. Destabilization of Skp2 by ubiquitin-mediated proteolysis was also demonstrated that in an in vitro degradation system, using cell extracts prepared from TGF-beta-treated cultured cells. In addition, TGF-beta treatment decreases the levels of Cks1 mRNA. The deficiency of Cks1 in TGF-beta-treated cells likely contributes to the stabilization of p27Kip1 and destabilization of Skp2, because in the absence of Cks1, SCFSkp2 cannot ubiquitinate p27Kip1; instead, self-ubiquitination of Skp2 occurs. Thus, stabilization of the cell cycle inhibitor p27Kip1 and cell growth inhibition in response to TGF-beta occur in part through limiting the threshold of the SCFSkp2 ubiquitin ligase by transcriptional and post-transcriptional mechanisms.

The cyclin D3-CDK4-p27kip1 holoenzyme in thyroid epithelial cells: activation by TSH, inhibition by TGFbeta, and phosphorylations of its subunits demonstrated by two-dimensional gel electrophoresis

The cAMP-dependent mitogenic stimulation elicited by thyroid-stimulating hormone (TSH) in primary cultures of canine thyroid epithelial cells is unique as it upregulates the cyclin-dependent kinase (CDK) inhibitor p27kip1 but not D-type cyclins. TSH and cAMP promote the assembly of required cyclin D3-CDK4 complexes and their nuclear import. Here, the nuclear translocation of these complexes strictly correlated in individual cells with the enhanced presence of nuclear p27. p27, like cyclin D3, supported the TSH-stimulated pRb-kinase activity of the CDK4 complex and, as demonstrated using the high-resolution power of the two-dimensional (2D) gel electrophoresis, the phosphorylation of CDK4, presumably by the nuclear CDK-activating kinase. In the presence of TSH, transforming growth factor beta (TGFbeta) did not affect the assembly of cyclin D3-CDK4, but it strongly inhibited the pRb-kinase activity associated with both cyclin D3 and p27, not only by preventing the nuclear import of cyclin D3-CDK4 and its binding to p27, but also by inhibiting CDK4 phosphorylation within residual p27-bound cyclin D3-CDK4 complexes. No alterations of the relative abundance of multiple (un)phosphorylated forms of cyclin D3 and p27 demonstrated by 2D-gel electrophoresis were associated with these processes. This study suggests a crucial positive role of p27 in the TSH-stimulated nuclear import, phosphorylation, and catalytic activity of cyclin D3-bound CDK4. Moreover, it demonstrates a technique to directly assess the in vivo phosphorylation of endogenous CDK4, which might appear as a last regulated step targeted by the antagonistic cell cycle effects of TSH and TGFbeta.

Farnesyltransferase inhibitors in hematologic malignancies: new horizons in therapy

Farnesyltransferase inhibitors (FTIs) are small-molecule inhibitors that selectively inhibit farnesylation of a number of intracellular substrate proteins such as Ras. Preclinical work has revealed their ability to effectively inhibit tumor growth across a wide range of malignant phenotypes. Many hematologic malignancies appear to be reasonable disease targets, in that they express relevant biologic targets, such as Ras, mitogen-activated protein kinase (MAPK), AKT, and others that may depend on farnesyl protein transferase (FTase) activity to promote proliferation and survival. A host of phase 1 trials have been recently launched to assess the applicability of FTIs in hematologic malignancies, many of which demonstrate effective enzyme target inhibition, low toxicity, and some clinical responses. As a result, phase 2 trials have been initiated in a variety of hematologic malignancies and disease settings to further validate clinical activity and to identify downstream signal transduction targets that may be modified by these agents. It is anticipated that these studies will serve to define the optimal roles of FTIs in patients with hematologic malignancies and provide insight into effective methods by which to combine FTIs with other agents.

Expression of minichromosome maintenance proteins in vascular smooth muscle cells is ERK/MAPK dependent

Proliferation of vascular smooth muscle cells (VSMC) represents a key event for the pathogenesis of postangioplasty restenosis. Minichromosome maintenance proteins (MCM) form essential components of the prereplicative complex at DNA replication origins and are regulated by E2F. The present studies were designed to investigate the signal transduction pathways controlling the expression of MCM6 and MCM7 in VSMC in response to mitogenic stimuli. MCM6 and MCM7 expression was substantially increased after stimulation with platelet-derived growth factor-BB and insulin. Pretreatment with PD98059, a specific inhibitor of the extracellular signal-regulated kinases (ERK)-mitogen-activated protein kinase (MAPK), competely inhibited the mitogen-induced MCM6 and MCM7 mRNA and protein expression, demonstrating a critical role for this pathway in transmitting transmembrane signals required for the initiation of DNA replication. The p38MAPK inhibitor SB203580, the phosphatidylinositol 3 kinase (PI3-kinase) pathway inhibitor wortmannin, and the protein kinase C pathway (PKC) inhibitor Gö 6976 did not significantly affect mitogen-induced MCM6 and MCM7 expression. Transient transfection experiments revealed that PD98059 inhibited mitogen-induced MCM6 and MCM7 transcriptional activation. In addition, blockade of ERK/MAPK signaling with PD98059 strongly inhibited phosphorylation of the retinoblastoma protein (Rb) and activity of a luciferase reporter plasmid driven by multiple E2F elements. Inhibition of mitogen-induced MCM6 and MCM7 expression by PD98059 was reversed by ectopic overexpression of E2F, indicating that ERK/MAPK signaling is required for events that occur upstream of E2F release from phosphorylated Rb. In combination, these data demonstrate that the ERK/MAPK signal transduction pathway plays a central role in regulating E2F-dependent MCM expression and DNA replication in VSMC.

The phosphoinositide 3-kinase/Akt pathway regulates cell cycle progression of HL60 human leukemia cells through cytoplasmic relocalization of the cyclin-dependent kinase inhibitor p27(Kip1) and control of cyclin D1 expression

The serine/threonine protein kinase Akt, a downstream effector of phosphoinositide 3-kinase (PI3K), plays a pivotal role in tumorigenesis because it affects the growth and survival of cancer cells. Several laboratories have demonstrated that Akt inhibits transcriptional activation of a number of related forkhead transcription factors now referred to as FoxO1, FoxO3, and FoxO4. Akt-regulated forkhead transcription factors are involved in the control of the expression of both the cyclin-dependent kinase (cdk) inhibitor p27(Kip1) and proapoptotic Bim protein. Very little information is available concerning the importance of the PI3K/Akt pathway in HL60 human leukemia cells. Here, we present our findings showing that the PI3K/Akt axis regulates cell cycle progression of HL60 cells through multiple mechanisms also involving the control of FoxO1 and FoxO3. To this end, we took advantage of a HL60 cell clone (HL60AR cells) with a constitutively activated PI3K/Akt axis. When compared with parental (PT) HL60 cells, HL60AR cells displayed higher levels of phosphorylated FoxO1 and FoxO3. In AR cells forkhead factors localized predominantly in the cytoplasm, whereas in PT cells they were mostly nuclear. AR cells proliferated faster than PT cells and showed a lower amount of the cdk inhibitor p27(Kip1), which was mainly found in the cytoplasm and was hyperphosphorylated on threonine residues. AR cells also displayed higher levels of cyclin D1 and phosphorylated p110 Retinoblastoma protein. The protein levels of cdk2, cdk4, and cdk6 were not altered in HL60AR cells, whereas the activities of both ckd2 and cdk6 were higher in AR than in PT cells. These results show that in HL60 cells the PI3K/Akt signaling pathway may be involved in the control of the cell cycle progression most likely through mechanisms involving the activation of forkhead transcription factors.

Receptor synergy of interleukin-6 (IL-6) and insulin-like growth factor-I in myeloma cells that highly express IL-6 receptor alpha [corrected]

Interleukin-6 (IL-6) is a growth and antiapoptotic factor for human myeloma cells. The autocrine loop and increased expression of the growth factor receptors have been postulated as the mechanisms of tumorigenesis. Here we show that IL-6 stimulation induced the phosphorylation of insulin-like growth factor-I (IGF-I) receptors in a human myeloma cell line, NOP2, highly expressing IL-6 receptor alpha (IL-6R alpha) and in the IL-6R alpha-transfected U266 cell line. IL-6-dependent complex formation of IL-6R alpha with IGF-I receptor beta was found in NOP2 where IL-6R alpha colocalized with IGF-I receptors at lipid rafts. Moreover, the IL-6-induced phosphorylation of IGF-I receptor beta was not blocked by a Janus kinase 2 (Jak2) inhibitor. In addition to the activation of the signal transducer and activator of transcription 3 and extracellular signal-regulated kinase 1/2, IL-6 stimulation led to the activation of Akt, presumably following the phosphorylation of IGF-I receptors. Thus, our results suggest that in NOP2, IL-6R alpha and IGF-I receptors exist on the plasma membrane in close proximity, facilitating the efficient assembly of 2 receptors in response to IL-6. The synergistic effects of highly expressed IL-6R alpha on IGF-I receptor-mediated signals provide a novel insight into the Jak-independent IL-6 signaling mechanism of receptor cross-talk in human myeloma cells.

Pten dose dictates cancer progression in the prostate

Complete inactivation of the PTEN tumor suppressor gene is extremely common in advanced cancer, including prostate cancer (CaP). However, one PTEN allele is already lost in the vast majority of CaPs at presentation. To determine the consequence of PTEN dose variations on cancer progression, we have generated by homologous recombination a hypomorphic Pten mouse mutant series with decreasing Pten activity: Pten(hy/+) > Pten(+/-) > Pten(hy/-) (mutants in which we have rescued the embryonic lethality due to complete Pten inactivation) > Pten prostate conditional knockout (Pten(pc)) mutants. In addition, we have generated and comparatively analyzed two distinct Pten(pc) mutants in which Pten is inactivated focally or throughout the entire prostatic epithelium. We find that the extent of Pten inactivation dictate in an exquisite dose-dependent fashion CaP progression, its incidence, latency, and biology. The dose of Pten affects key downstream targets such as Akt, p27(Kip1), mTOR, and FOXO3. Our results provide conclusive genetic support for the notion that PTEN is haploinsufficient in tumor suppression and that its dose is a key determinant in cancer progression.

Deregulation of p27 by oncogenic signaling and its prognostic significance in breast cancer

p27 is a key regulator of progression from G1 to S phase. Although the gene encoding p27 is rarely mutated in human cancers, p27 is functionally inactivated in a majority of human cancers through accelerated p27 proteolysis, through sequestration by cyclin D-cyclin-dependent kinase complexes and by cytoplasmic mislocalization. Here we review mechanisms whereby oncogenic activation of receptor tyrosine kinase and Ras pathways lead to accelerated p27 proteolysis and p27 mislocalization in cancer cells. The prognostic significance of p27 in human breast cancer is also reviewed.

Akt activation disrupts mammary acinar architecture and enhances proliferation in an mTOR-dependent manner

Activation of the serine/threonine kinase Akt/PKB positively impacts on three cellular processes relevant to tumor progression: proliferation, survival, and cell size/growth. Using a three-dimensional culture model of MCF-10A mammary cells, we have examined how Akt influences the morphogenesis of polarized epithelial structures. Activation of a conditionally active variant of Akt elicits large, misshapen structures, which primarily arise from the combined effects of Akt on proliferation and cell size. Importantly, Akt activation amplifies proliferation during the early stages of morphogenesis, but cannot overcome signals suppressing proliferation in late-stage cultures. Akt also cooperates with oncoproteins such as cyclin D1 or HPV E7 to promote proliferation and morphogenesis in the absence of growth factors. Pharmacological inhibition of the Akt effector, mammalian target of rapamycin (mTOR), with rapamycin prevents the morphological disruption elicited by Akt activation, including its effect on cell size and number, and the cooperative effect of Akt on oncogene-driven proliferation, indicating that mTOR function is required for the multiple biological effects of Akt activation during morphogenesis.

Cytoplasmic p21Cip1 is involved in Ras-induced inhibition of the ROCK/LIMK/cofilin pathway

Accumulating evidence suggests that p21(Cip1) located in the cytoplasm might play a role in promoting transformation and tumor progression. Here we show that oncogenic H-RasV12 contributes to the loss of actin stress fibers by inducing cytoplasmic localization of p21(Cip1), which uncouples Rho-GTP from stress fiber formation by inhibiting Rho kinase (ROCK). Concomitant with the loss of stress fibers in Ras-transformed cells, there is a decrease in the phosphorylation level of cofilin, which is indicative of a compromised ROCK/LIMK/cofilin pathway. Inhibition of MEK in Ras-transformed NIH3T3 results in restoration of actin stress fibers accompanied by a loss of cytoplasmic p21(Cip1), and increased phosphorylation of cofilin. Ectopic expression of cytoplasmic but not nuclear p21(Cip1) in Ras-transformed cells was effective in preventing stress fibers from being restored upon MEK inhibition and inhibited phosphorylation of cofilin. p21(Cip1) was also found to form a complex with ROCK in Ras-transformed cells in vivo. Furthermore, inhibition of the PI 3-kinase pathway resulted in loss of p21(Cip1) expression accompanied by restoration of phosphocofilin, which was not accompanied by stress fiber formation. These results suggest that restoration of cofilin phosphorylation in Ras-transformed cells is necessary but not sufficient for stress fiber formation. Our findings define a novel mechanism for coupling cytoplasmic p21(Cip1) to the control of actin polymerization by compromising the Rho/ROCK/LIMK/cofilin pathway by oncogenic Ras. These studies suggest that localization of p21(Cip1) to the cytoplasm in transformed cells contributes to pathways that favor not only cell proliferation, but also cell motility thereby contributing to invasion and metastasis.

Phosphorylation of p27Kip1 at threonine 198 by p90 ribosomal protein S6 kinases promotes its binding to 14-3-3 and cytoplasmic localization

The cyclin-dependent kinase inhibitor p27Kip1 plays an important role in cell cycle regulation. The cyclin-dependent kinase-inhibitory activity of p27Kip1 is regulated by changes in its concentration and its subcellular localization. Several reports suggest that phosphorylation of p27Kip1 at serine 10, threonine 157, and threonine 187 regulate its localization. We have previously identified that carboxyl-terminal threonine 198 (Thr198) in p27Kip1 is a novel phosphorylation site and that Akt is associated with the phosphorylation at the site (Fujita, N., Sato, S., Katayama, K., and Tsuruo, T. (2002) J. Biol. Chem. 277, 28706-28713). We show herein that activation of the Ras/Raf/mitogen-activated protein kinase kinase (MAPK kinase/MEK) pathway also regulates phosphorylation of p27Kip1 at Thr198. MAPKs were not directly associated with p27Kip1 phosphorylation at Thr198, but the p90 ribosomal protein S6 kinases (RSKs) could bind to and directly phosphorylate p27Kip1 at Thr198 in a Ras/Raf/MEK-dependent manner. RSK-dependent phosphorylation promoted the p27Kip1 binding to 14-3-3 and its cytoplasmic localization. To prove the direct relationship between 14-3-3 binding and cytoplasmic localization, we constructed a p27Kip1-R18 fusion protein in which the R18 peptide was fused to the carboxyl-terminal region of p27Kip1. The R18 peptide is known to interact with 14-3-3 independent of phosphorylation. The p27Kip1-R18 distributed mainly in the cytosol, whereas mutant p27Kip1-R18 (p27Kip1-R18-K2) that had no 14-3-3 binding capability existed mainly in the nucleus. These results indicate that RSKs play a crucial role in cell cycle progression through translocation of p27Kip1, in addition to Akt, to the cytoplasm in a phosphorylation and 14-3-3 binding-dependent manner.

Additive effects of tamoxifen and the farnesyl transferase inhibitor FTI-277 on inhibition of MCF-7 breast cancer cell-cycle progression

The efficacy of tamoxifen in the hormonal therapy of breast cancer is well established, but therapeutic resistance is inevitable. FTIs are a new class of anticancer drugs that are in phase III clinical evaluation. Since the mechanisms of action of these 2 classes of drugs are different, we tested the combination of tamoxifen and FTI-277 on inhibiting proliferation of hormone-dependent MCF-7 human breast cancer cells. An additive effect on cell proliferation was demonstrated, accompanied by an additive G(0)/G(1) arrest. The major effect of the combination of the 2 drugs was to maintain p21(waf/cip1) at an intermediate level, higher than that observed in the presence of tamoxifen alone. This was associated with an additive effect on inactivation of cyclin E-Cdk2 complexes and decreased phosphorylation of pRb and p130 pocket proteins. These effects were accompanied by increased association of 2 CDIs, p27(kip1) and p21(waf/cip1), with cyclin E-Cdk2 complexes. These data demonstrate that the additive effect is likely predominantly due to the recruitment of p27(kip1) and, to a lesser extent, p21(waf/cip1) into the cyclin E-Cdk2 complexes. Together, these results suggest that the combination of FTI and tamoxifen may increase the antitumor effect of either drug alone in breast cancer.

Novel therapeutic strategies targeting the epidermal growth factor receptor (EGFR) family and its downstream effectors in breast cancer

From the early experience with tamoxifen to the current use of Herceptin, targeted therapy has been proven to be an important part of breast cancer (BC) treatment. In the last decade, advances in molecular biology have allowed scientists to design highly individualized, 'smart' pharmaceuticals, capable of manipulating the growth factor pathways and the genes that are involved in the development and maintenance of the malignant phenotype. The epidermal growth factor receptor (EGFR) family, as one of the best studied growth factor pathways in cancer, resembles a 'treasure island' by providing a wide range of biologically relevant targets involved in breast carcinogenesis. While a large number of new agents targeting this pathway are continuingly being tested in preclinical experiments, clinicians are witnessing the migration of some of these agents to daily practice. The aim of this review is to provide clinicians with an updated synopsis of the most advanced anti-erbB therapeutic strategies with activity against BC.

Prognostic implication of cyclin E expression and its relationship with cyclin D1 and p27Kip1 expression on tissue microarrays of node negative breast cancer

BACKGROUND AND OBJECTIVES

Altered expression of cell-cycle regulators is prevalent in clinical breast cancer. This study was performed to analyze the impact of cyclin E expression to the outcome of breast cancer together with cyclin D1 and p27Kip1.

METHODS

The correlation between cyclin D1/E and p27Kip1 expression was analyzed in tissue arrays of 175 node-negative breast cancers treated by the same chemotherapy composed of fluorouracil, cyclophosphamide, and methotrexate. Data from the immunohistochemical assays of three molecules were correlated and were analyzed with clinical outcome of the patients.

RESULTS

Cyclin E expression was observed in 48 (27.4%) of 175 breast carcinomas. Cyclin E expression was significantly increased in young age patients and poorly differentiate tumors. Expression of cyclin E was significantly increased in cyclin D1 expressing tumors (P = 0.034). p27Kip1 expression was preserved above the 50% level in 87 tumors (49.7%) and was inversely correlated with cyclin E expression (P = 0.042). Ki67 labeling index was significantly increased in cyclin E-expressing tumors (P = 0.033) and was inversely related with p27Kip1 expression. In multivariate survival analysis, cyclin E expression was significant for the prediction of poor survival of the patients.

CONCLUSIONS

Cyclin E expression was associated with poor prognosis and intimately correlated with the expression of cyclin D1 and p27Kip1. Integration of TMA technology allowed a high-throughput analysis for correlating molecular in situ findings with clinico-pathologic information.

Prognostic significance of the F-box protein Skp2 expression in diffuse large B-cell lymphoma

The F-box protein Skp2 positively regulates the G1-S transition by promoting degradation of the cyclin-dependent kinase inhibitor p27(kip1) (p27). Recent evidence has suggested an oncogenic role of Skp2 in not only carcinogenesis but also lymphomagenesis. In this study, we performed immunohistochemical analysis on the cell-cycle-associated proteins, Skp2, p27, and Ki-67, in 27 patients with de novo diffuse large B-cell lymphoma (DLBCL), evaluating the correlation between the clinical characteristics and expression levels of these proteins. The patients were classified into two groups according to the positivity for Skp2 expression: a high Skp2 expression group (>60% positive for Skp2 in lymphoma cells) and a low Skp2 expression group (< or = 60%). A high level of Skp2 expression significantly correlated with advanced clinical stage (P = 0.029), although the increase did not correlate with age, gender, LDH levels, presence of extranodal disease, or performance status and resulted in no correlation with the International Prognostic Index-based risk grading. However, it was noteworthy that the high Skp2 expression group demonstrated a significantly worse prognosis than the low Skp2 expression group (P = 0.0007). The expression level of Skp2 correlated with that of Ki-67 but not necessarily with that of p27. The p27 expression level did not correlate patients' prognosis. Taken together, it was suggested that Skp2 was a valuable and independent marker predicting the outcome in DLBCL.

Inactivation of NF-kappaB by genistein is mediated via Akt signaling pathway in breast cancer cells

Genistein, a natural isoflavonoid found in soybean products, has been proposed to be associated with a lower rate of breast cancer in Asian women. Studies from our laboratory and others have shown that genistein can induce apoptosis by regulating the expression of apoptosis-related genes in breast cancer cells. However, the precise molecular mechanism(s) by which genistein induces apoptotic cell death is not clear. In order to investigate such mechanism, we tested the role of Akt and NF-kappaB in genistein-treated MDA-MB-231 breast cancer cells. We found that inhibition of cell growth and induction of apoptosis by genistein are partly mediated through the downregulation of Akt and NF-kappaB pathways. Gel shift assay showed that NF-kappaB DNA-binding activity in MDA-MB-231 cells transfected with Akt cDNA was induced, suggesting that there is a cross-talk between NF-kappaB and Akt signaling pathway. Moreover, we found that genistein could abrogate EGF and Akt induced NF-kappaB activation. From these results, we conclude that the inactivation of NF-kappaB by genistein in MDA-MB-231 breast cancer cells is partly mediated via Akt pathway, which could be useful for rational design of strategies for the prevention and/or treatment of breast cancer.

The role of cyclin-dependent kinase inhibitor p27Kip1 in anti-HER2 antibody-induced G1 cell cycle arrest and tumor growth inhibition

Cyclin-dependent kinase (CDK) inhibitor p27Kip1 binds to the cyclin E.CDK2 complex and plays a major role in controlling cell cycle and cell growth. Our group and others have reported that anti-HER2 monoclonal antibodies exert inhibitory effects on HER2-overexpressing breast cancers through G1 cell cycle arrest associated with induction of p27Kip1 and reduction of CDK2. The role of p27Kip1 in anti-HER2 antibody-induced cell cycle arrest and growth inhibition is, however, still uncertain. Here we have provided several lines of evidence supporting a critical role for p27Kip1 in the anti-HER2 antibody-induced G1 cell cycle arrest and tumor growth inhibition. Induction of p27Kip1 and G1 growth arrest by anti-HER2 antibody, murine 4D5, or humanized trastuzumab (Herceptin) are concentration-dependent, time-dependent, irreversible, and long-lasting. The magnitude of G1 cell cycle arrest induced by trastuzumab or 4D5 is well correlated with the level of p27Kip1 protein induced. Up-regulation of p27Kip1 and G1 growth arrest could no longer be removed with as little as 14 h of treatment with trastuzumab. Anti-HER2 antibody-induced p27Kip1 protein, G1 arrest, and growth inhibition persist at least 5 days after a single treatment. The magnitude of growth inhibition of breast cancer cells induced by anti-HER2 antibody closely parallels the level of p27Kip1 induced. Induced expression of exogenous p27Kip1 results in a p27Kip1 level-dependent G1 cell cycle arrest and growth inhibition similar to that obtained with anti-HER2 antibodies. Reducing p27Kip1 expression using p27Kip1 small interfering RNA blocks anti-HER2 antibody-induced p27Kip1 up-regulation and G1 arrest. Treatment with anti-HER2 antibody significantly increases the half-life of p27Kip1 protein. Inhibition of ubiquitin-proteasome pathway, but not inhibition of calpain and caspase activities, up-regulates p27Kip1 protein to a degree comparable with that obtained with anti-HER2 antibodies. We have further demonstrated that anti-HER2 antibody significantly decreases threonine phosphorylation of p27Kip1 protein at position 187 (Thr-187) and increases serine phosphorylation of p27Kip1 protein at position 10 (Ser-10). Expression of S10A and T187A mutant p27Kip1 protein increases the fraction of cells in G1 and reduces a further antibody-induced G1 arrest. Consequently, p27Kip1 plays an important role in the anti-HER2 antibody-induced G1 cell cycle arrest and tumor growth inhibition through post-translational regulation. Regulation of the phosphorylation of p27Kip1 protein is one of the post-translational mechanisms by which anti-HER2 antibody upregulates the protein.

Searching for the gatekeeper oncogene of prostate cancer

Prostate cancer is a common malignancy that has a heterogeneous etiology and a variable outcome. Nearly all prostatic adenocarcinoma results from androgen-dependent tumor promotion. However, the cause of prostate cancer initiation is not well understood and only a few of the target oncogenes activated during prostate cancer initiation have been identified. Prostate cancer risk is strongly influenced by family history. Several genetic loci have been found to cosegregate with prostate cancer occurrence in high-risk families. Some candidate oncogenes that map to these loci have been implicated by the identification of mutations in high-risk kindreds. However, the roles of the putative oncogene products in the biochemical pathways that mediate carcinogenesis remain obscure and their influence on cancer etiology has yet to be supported by gene targeting experiments in mice. Moreover, the genes that have been implicated in hereditary prostate cancers do not appear to be mutated in sporadic cancers. Karyotypic and loss of heterozygosity analysis of sporadic prostate cancers have identified 8p, 10q, and 17p as the loci most often disrupted. Candidate oncogenes have been identified at each of these regions. Additional genes with pathogenic significance in prostate cancer have been identified by analysis of cDNA microarrays comparing benign and malignant prostate tissue, by differential genetic analysis of benign and malignant prostatic epithelium, and by induction of experimental prostate cancer in genetically engineered mice.

Conditional knock-out of integrin-linked kinase demonstrates an essential role in protein kinase B/Akt activation

Protein kinase B (PKB/Akt) plays a pivotal role in signaling pathways downstream of phosphatidylinositol 3-kinase, regulating fundamental processes such as cell survival, cell proliferation, differentiation, and metabolism. PKB/Akt activation is regulated by phosphoinositide phospholipid-mediated plasma membrane anchoring and by phosphorylation on Thr-308 and Ser-473. Whereas the Thr-308 site is phosphorylated by PDK-1, the identity of the Ser-473 kinase has remained unclear and controversial. The integrin-linked kinase (ILK) is a potential regulator of phosphorylation of PKB/Akt on Ser-473. Utilizing double-stranded RNA interference (siRNA) as well as conditional knock-out of ILK using the Cre-Lox system, we now demonstrate that ILK is essential for the regulation of PKB/Akt activity. ILK knock-out had no effect on phosphorylation of PKB/Akt on Thr-308 but resulted in almost complete inhibition of phosphorylation on Ser-473 and significant inhibition of PKB/Akt activity, accompanied by significant stimulation of apoptosis. The inhibition of PKB/Akt Ser-473 phosphorylation was rescued by kinase-active ILK but not by a kinase-deficient mutant of ILK, suggesting a role for the kinase activity of ILK in the stimulation of PKB/Akt phosphorylation. ILK knock-out also resulted in the suppression of phosphorylation of GSK-3beta on Ser-9 and cyclin D1 expression. These data establish ILK as an essential upstream regulator of PKB/Akt activation.

Decisions on life and death: FOXO Forkhead transcription factors are in command when PKB/Akt is off duty

Forkhead transcription factors of the FOXO family are important downstream targets of protein kinase B (PKB)/Akt, a kinase shown to play a decisive role in cell proliferation and cell survival. Direct phosphorylation by PKB/Akt inhibits transcriptional activation by FOXO factors, causing their displacement from the nucleus into the cytoplasm. Work from recent years has shown that this family of transcription factors regulates the expression of a number of genes that are crucial for the proliferative status of a cell, as well as a number of genes involved in programmed cell death. As such, these transcription factors appear to play an essential role in many of the effects of PKB/Akt on cell proliferation and survival. Indeed, in cells of the hematopoietic system, mere activation of a FOXO factor is sufficient to activate a variety of proapoptotic genes and to trigger apoptosis. In contrast, in most other cell types, activation of FOXO blocks cellular proliferation and drives cells into a quiescent state. In such cell types, FOXO factors also provide the protective mechanisms that are required to adapt to the altered metabolic state of quiescent cells. Thus, as PKB/Akt signaling is switched off, FOXO factors take over to determine the fate of a cell, long-term survival in a quiescent state, or programmed cell death. This review summarizes our current understanding of the mechanisms by which PKB/Akt and FOXO factors regulate these decisions.

Inhibitory effect of p27kip1 mediated by adenovirus on model of esophageal carcinoma in nude mice

AIM

To investigate the inhibitory effect of p27kip1 mediated by adenovirus vector on esophageal carcinoma in vivo.

METHODS

Eca109 cells were injected into the subcutaneous tissue of nude mice to establish tumors. The transplanted tumors were reproduced among the nude mice contionually after original grafts grew well. The model of esophageal carcinoma in nude mice was established by transplanting the tumor tissue mass into the subcutaneous tissue of nude mice .The successful constructed recombinant adenoviral vector carrying p27kip1 gene and LacZ recombinant adenovirus were directly injected into the esophageal tumors in nude mice respectively. Compared with control group, the growth curves of tumor were drawed and the growth inhibition rates of tumor were calculated.

RESULTS

The growth of tumors in gene therapy group with p27kip1 was obviously suppressed, which had a significant difference compared with control group (P < 0.001). The growth inhibition rate of tumor reached 64.1%.

CONCLUSION

p27kip1 gene therapy mediated by adenovirus vector has significant inhibitory effect on esophageal carcinoma in vivo.

Increased p27, an essential component of cell cycle control, in Alzheimer's disease

A number of recent findings have demonstrated re-expression of cell cycle-related proteins in vulnerable neurones in Alzheimer's disease. We hypothesize that this attempt by neurones to re-enter mitosis is a response to external growth stimuli that leads to an abortive re-entry into the cell cycle and, ultimately, neuronal degeneration. In this study, to further delineate the role of mitotic processes in the pathogenesis of Alzheimer's disease, we investigated p27, a cyclin-dependent kinase inhibitor that plays a negatively regulatory role in cell cycle progression that, once phosphorylated at Thr187, is degraded via an ubiquitin-proteasome pathway. Here we report that both p27 and phosphorylated p27 (Thr187) show increases in the cytoplasm of vulnerable neuronal populations in Alzheimer's disease vs. age-matched control subjects. Importantly, phosphorylated p27 (Thr187) shows considerable overlap with tau-positive neurofibrillary pathology, including neurofibrillary tangles, dystrophic neurites and neuropil threads. The findings presented here suggest that dysregulation of the cell cycle plays a crucial role in the pathogenesis of Alzheimer's disease that may provide a novel mechanistic basis for therapeutic intervention.

Therapeutic potential of phosphoinositide 3-kinase inhibitors

At least one Holy Grail for many academic researchers and pharmaceutical research divisions alike has been to identify therapeutically useful selective PI3K inhibitors. There are several different but closely related PI3Ks which are thought to have distinct biological roles. Until now, however, researchers have been frustrated by poor selectivity of the available pharmacological inhibitors, which are unable to distinguish the different isoforms of PI3K adequately. Fortunately, recently published work gives cause for optimism; there are now several patent specifications published that describe new PI3K inhibitors, including some that are more selective for the delta isoform of PI3K. Given the involvement of PI3Ks in a plethora of biological settings, such isoform-selective inhibitors may have immense potential use for the treatment of patients with inflammatory and autoimmune disorders as well as cancer and cardiovascular diseases.

Involvement of PI3K/Akt pathway in cell cycle progression, apoptosis, and neoplastic transformation: a target for cancer chemotherapy

The PI3K/Akt signal transduction cascade has been investigated extensively for its roles in oncogenic transformation. Initial studies implicated both PI3K and Akt in prevention of apoptosis. However, more recent evidence has also associated this pathway with regulation of cell cycle progression. Uncovering the signaling network spanning from extracellular environment to the nucleus should illuminate biochemical events contributing to malignant transformation. Here, we discuss PI3K/Akt-mediated signal transduction including its mechanisms of activation, signal transducing molecules, and effects on gene expression that contribute to tumorigenesis. Effects of PI3K/Akt signaling on important proteins controlling cellular proliferation are emphasized. These targets include cyclins, cyclin-dependent kinases, and cyclin-dependent kinase inhibitors. Furthermore, strategies used to inhibit the PI3K/Akt pathway are presented. The potential for cancer treatment with agents inhibiting this pathway is also addressed.

Cell-cycle dysregulation and anticancer therapy

Cell-cycle dysregulation is a hallmark of tumor cells. The ability of normal cells to undergo cell-cycle arrest after damage to DNA is crucial for the maintenance of genomic integrity. The biochemical pathways that stop the cell cycle in response to cellular stressors are called checkpoints. Defective checkpoint function results in genetic modifications that contribute to tumorigenesis. The regulation of checkpoint signaling also has important clinical implications because the abrogation of checkpoint function can alter the sensitivity of tumor cells to chemotherapeutics. Here, we provide an overview of the mechanisms that regulate the cell cycle, current anticancer therapies that target checkpoint signaling pathways, and strategies for the development of novel chemotherapeutic agents.