The phosphatidyl inositol 3-kinase signaling network: implications for human breast cancer

Image-based evaluation of the molecular events underlying HC11 mammary epithelial cell differentiation

We have developed an image-based technique for signal pathway analysis, target validation, and compound screening related to mammary epithelial cell differentiation. This technique used the advantages of optical imaging and the HC11-Lux model system. The HC11-Lux cell line is a subclone of HC11 mammary epithelial cells transfected stably with a luciferase construct of the beta-casein gene promoter (p-344/-1betac-Lux). The promoter activity was imaged optically in real time following lactogenic induction. The imaging signal intensity was closely correlated with that measured using a luminometer following protein extraction (R=0.99, P<0.0001) and consistent with the messenger RNA (mRNA) level of the endogenous beta -casein gene. Using this technique, we examined the roles of JAK2/Stat5A, Raf-1/MEK/MAKP, and PI3K/Akt signal pathways with respect to differentiation. The imaging studies showed that treatment of the cells with epidermal growth factor (EGF), AG490 (JAK2-specific inhibitor), and LY294002 (PI3K-specific inhibitor) blocked lactogenic differentiation in a dose-dependent manner. PD98059 (MEK-specific inhibitor) could reverse EGF-mediated differentiation arrest. These results indicate that these pathways are essential in cell differentiation. This simple, sensitive, and reproducible technique permits visualization and real-time evaluation of the molecular events related to milk protein production. It can be adopted for high-throughput screening of small molecules for their effects on mammary epithelial cell growth, differentiation, and carcinogenesis.

Synergistic effects of Pten loss and WNT/CTNNB1 signaling pathway activation in ovarian granulosa cell tumor development and progression

The mechanisms of granulosa cell tumor (GCT) development may involve the dysregulation of signaling pathways downstream of follicle-stimulating hormone, including the phosphoinosite-3 kinase (PI3K)/AKT pathway. To test this hypothesis, a genetically engineered mouse model was created to derepress the PI3K/AKT pathway in granulosa cells by conditional targeting of the PI3K antagonist gene Pten (Pten(flox/flox);Amhr2(cre/+)). The majority of Pten(flox/flox);Amhr2(cre/+) mice featured no ovarian anomalies, but occasionally ( approximately 7%) developed aggressive, anaplastic GCT with pulmonary metastases. The expression of the PI3K/AKT downstream effector FOXO1 was abrogated in Pten(flox/flox);Amhr2(cre/+) GCT, indicating a mechanism by which GCT cells may increase proliferation and evade apoptosis. To relate these findings to spontaneously occurring GCT, analyses of PTEN and phospho-AKT expression were performed on human and equine tumors. Although PTEN loss was not detected, many GCT (2/5 human, 7/17 equine) featured abnormal nuclear or perinuclear localization of phospho-AKT, suggestive of altered PI3K/AKT activity. As inappropriate activation of WNT/CTNNB1 signaling causes late-onset GCT development and cross talk between the PI3K/AKT and WNT/CTNNB1 pathways has been reported, we tested whether these pathways could synergize in GCT. Activation of both the PI3K/AKT and WNT/CTNNB1 pathways in the granulosa cells of a mouse model (Pten(flox/flox);Ctnnb1(flox(ex3)/+);Amhr2(cre/+)) resulted in the development of GCT similar to those observed in Pten(flox/flox);Amhr2(cre/+) mice, but with 100% penetrance, perinatal onset, extremely rapid growth and the ability to spread by seeding into the abdominal cavity. These data indicate a synergistic effect of dysregulated PI3K/AKT and WNT/CTNNB1 signaling in the development and progression of GCT and provide the first animal models for metastatic GCT.

Phosphoinositide 3-kinase/AKT signaling can promote AIB1 stability independently of GSK3 phosphorylation

The transcriptional coactivator AIB1 is an oncogene overexpressed in different types of tumors, including breast cancer. Although the subcellular compartimentalization of AIB1 seems to be intimately linked to abnormal proliferation, the molecular mechanisms that regulate its subcellular distribution are not well defined. Here, we report that the nuclear accumulation and half-life of AIB1 vary between cancer cell lines. Using these differences as an experimental model, our results reveal that alterations to the Akt signaling pathway and nuclear export determine the stability of AIB1 and nuclear content of this coactivator. Moreover, our results show that AIB1 is degraded in the nucleus by the proteasome in an ubiquitin-dependent manner. However, this process does not require phosphorylation by GSK3, thereby revealing an alternative mechanism for regulating the turnover of AIB1. We define a new region at the carboxy terminus of AIB1 that is required for proteasome-dependent transcriptional activation and is preceded by a PEST domain that is required for adequate protein turnover. Based on differences in Akt signaling and the subcellular distribution of AIB1 between different cell lines, our results suggest that dysregulation of nuclear shuttling and proteasomal degradation may modulate the oncogenic potential of AIB1.

Redox regulation of cell survival

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) play important roles in regulation of cell survival. In general, moderate levels of ROS/RNS may function as signals to promote cell proliferation and survival, whereas severe increase of ROS/RNS can induce cell death. Under physiologic conditions, the balance between generation and elimination of ROS/RNS maintains the proper function of redox-sensitive signaling proteins. Normally, the redox homeostasis ensures that the cells respond properly to endogenous and exogenous stimuli. However, when the redox homeostasis is disturbed, oxidative stress may lead to aberrant cell death and contribute to disease development. This review focuses on the roles of key transcription factors, signal-transduction pathways, and cell-death regulators in affecting cell survival, and how the redox systems regulate the functions of these molecules. The current understanding of how disturbance in redox homeostasis may affect cell death and contribute to the development of diseases such as cancer and degenerative disorders is reviewed. We also discuss how the basic knowledge on redox regulation of cell survival can be used to develop strategies for the treatment or prevention of those diseases.

Breast cancer metastasis suppressor-1 differentially modulates growth factor signaling

That metastatic tumor cells grow in selective non-native environments suggests an ability to differentially respond to local microenvironments. BRMS1, like other metastasis suppressors, halts ectopic growth (metastasis) without blocking orthotopic tumor formation. BRMS1-expressing tumor cells reach secondary sites but do not colonize distant tissues, compelling the hypothesis that BRMS1 selectively restricts the ability of tumor cells to respond to exogenous regulators in different tissues. Here we report that BRMS1 expression in metastatic human breast cancer cells leads to a selective reduction in epidermal growth factor receptor expression and downstream (AKT) signaling. Signaling through another receptor tyrosine kinase, hepatocyte growth factor receptor (c-Met), remains unaltered despite reduced levels of the signaling intermediate phosphatidylinositol (4,5)-bisphosphate. Interestingly, reduced downstream calcium signaling is observed following treatment with platelet-derived growth factor, consistent with decreased phosphatidylinositol (4,5)-bisphosphate. However, platelet-derived growth factor receptor expression is unaltered. Thus, BRMS1 differentially attenuates cellular responses to mitogenic signals, not only dependent upon the specific signal received, but at varying steps within the same signaling cascade. Specific modulation of signaling responses received from the microenvironment may ultimately dictate which environments are permissive/restrictive for tumor cell growth and provide insights into the biology underlying metastasis.

PRL PTPs: mediators and markers of cancer progression

Aberrant protein tyrosine phosphorylation resulting from the altered activity of protein tyrosine phosphatases (PTPs) is increasingly being implicated in the genesis and progression of human cancer. Accumulating evidence indicates that the dysregulated expression of members of the phosphatase of regenerating liver (PRL) subgroup of PTPs is linked to these processes. Enhanced expression of the PRLs, notably PRL-1 and PRL-3, promotes the acquisition of cellular properties that confer tumorigenic and metastatic abilities. Up-regulation of PRL-3 is associated with the progression and eventual metastasis of several types of human cancer. Indeed, PRL-3 shows promise as a biomarker and prognostic indicator in colorectal, breast, and gastric cancers. However, the substrates and molecular mechanisms of action of the PRLs have remained elusive. Recent findings indicate that PRLs may function in regulating cell adhesion structures to effect epithelial-mesenchymal transition. The identification of PRL substrates is key to understanding their roles in cancer progression and exploiting their potential as exciting new therapeutic targets for cancer treatment.

Calmodulin modulates Akt activity in human breast cancer cell lines

Growth factor-induced activation of Akt occurs in the majority of human breast cancer cell lines resulting in a variety of cellular outcomes, including suppression of apoptosis and enhanced survival. We demonstrate that epidermal growth factor (EGF)-initiated activation of Akt is mediated by the ubiquitous calcium sensing molecule, calmodulin, in the majority of human breast cancer cell lines. Specifically, in estrogen receptor (ER)-negative, but not ER-positive, breast cancer cells, Akt activation is abolished by treatment with the calmodulin antagonist, W-7. Suppression of calmodulin expression by siRNAs against all three calmodulin genes in c-Myc-overexpressing mouse mammary carcinoma cells results in significant inhibition of EGF-induced Akt activation. Additionally, transient expression of constitutively active Akt (Myr-Akt) can overcome W-7-mediated suppression of Akt activation. These results confirm the involvement of calmodulin in the Akt pathway. The calmodulin independence of EGF-initiated Akt signaling in some cells was not explained by calmodulin expression level. Additionally, it was not explained by ER status or activation, since removal of estrogen and ablation of the ER did not convert the ER-positive, W-7 insensitive, MCF-7 cell line to calmodulin dependent signaling. However, forced overexpression of either epidermal growth factor receptor (EGFR) or ErbB2 did partially restore calmodulin dependent EGF-stimulated Akt activation. This is consistent with observation that W-7 sensitive cells tend to be estrogen independent and express high levels of EGFR family members. In an attempt to address how calmodulin is regulating Akt activity, we looked at localization of fluorescently tagged Akt and calmodulin in MCF-7 and SK-BR-3 cells. We found that both Akt and calmodulin translocate to the membrane after EGF-stimulation, and this translocation to the same sub-cellular compartment is inhibited by the calmodulin inhibitor W-7. Thus, calmodulin may be regulating Akt activity by modulating its sub-cellular location and is a novel target in the poor prognosis, ER-negative subset of breast cancers.

Alpha-lipoic acid induces apoptosis in hepatoma cells via the PTEN/Akt pathway

We report here that alpha-lipoic acid (alpha-LA), a naturally-occurring antioxidant, scavenges reactive oxygen species (ROS) followed by an increase in apoptosis of human hepatoma cells. Apoptosis induced by alpha-LA was dependent upon the activation of the caspase cascade and the mitochondrial death pathway. alpha-LA induced increases in caspase-9 and caspase-3 but had no significant effect on caspase-8 activity. Apoptosis induced by alpha-LA was found to be mediated through the tensin homologue deleted on chromosome 10 (PTEN)/Akt pathway. Prior to cell apoptosis, PTEN was activated and its downstream target Akt was inhibited. Our findings indicate that increasing ROS scavenging could be a therapeutic strategy to treat cancer.

Phellinus linteus suppresses growth, angiogenesis and invasive behaviour of breast cancer cells through the inhibition of AKT signalling

The antitumour activity of a medicinal mushroom Phellinus linteus (PL), through the stimulation of immune system or the induction of apoptosis, has been recently described. However, the molecular mechanisms responsible for the inhibition of invasive behaviour of cancer cells remain to be addressed. In the present study, we demonstrate that PL inhibits proliferation (anchorage-dependent growth) as well as colony formation (anchorage-independent growth) of highly invasive human breast cancer cells. The growth inhibition of MDA-MB-231 cells is mediated by the cell cycle arrest at S phase through the upregulation of p27^Kip1 expression. Phellinus linteus also suppressed invasive behaviour of MDA-MB-231 cells by the inhibition of cell adhesion, cell migration and cell invasion through the suppression of secretion of urokinase-plasminogen activator from breast cancer cells. In addition, PL markedly inhibited the early event in angiogenesis, capillary morphogenesis of the human aortic endothelial cells, through the downregulation of secretion of vascular endothelial growth factor from MDA-MB-231 cells. These effects are mediated by the inhibition of serine-threonine kinase AKT signalling, because PL suppressed phosphorylation of AKT at Thr³⁰⁸ and Ser⁴⁷³ in breast cancer cells. Taken together, our study suggests potential therapeutic effect of PL against invasive breast cancer.

The transcription factor FOXO3a is a crucial cellular target of gefitinib (Iressa) in breast cancer cells

Gefitinib is a specific inhibitor of the epidermal growth factor receptor (EGFR) that causes growth delay in cancer cell lines and human tumor xenografts expressing high levels of EGFR. An understanding of the downstream cellular targets of gefitinib will allow the discovery of biomarkers for predicting outcomes and monitoring anti-EGFR therapies and provide information for key targets for therapeutic intervention. In this study, we investigated the role of FOXO3a in gefitinib action and resistance. Using two gefitinib-sensitive (i.e., BT474 and SKBR3) as well as three other resistant breast carcinoma cell lines (i.e., MCF-7, MDA-MB-231, and MDA-MB-453), we showed that gefitinib targets the transcription factor FOXO3a to mediate cell cycle arrest and cell death in sensitive breast cancer cells. In the sensitive cells, gefitinib treatment causes cell cycle arrest predominantly at the G(0)-G(1) phase and apoptosis, which is associated with FOXO3a dephosphorylation at Akt sites and nuclear translocation, whereas in the resistant cells, FOXO3a stays phosphorylated and remains in the cytoplasm. The nuclear accumulation of FOXO3a in response to gefitinib was confirmed in tumor tissue sections from breast cancer patients presurgically treated with gefitinib as monotherapy. We also showed that knockdown of FOXO3a expression using small interfering RNA (siRNA) can rescue sensitive BT474 cells from gefitinib-induced cell-proliferative arrest, whereas reintroduction of active FOXO3a in resistant MDA-MB-231 cells can at least partially restore cell-proliferative arrest and sensitivity to gefitinib. These results suggest that the FOXO3a dephosphorylation and nuclear localization have a direct role in mediating the gefitinib-induced proliferative arrest and in determining sensitivity to gefitinib.

Activation of KLF8 transcription by focal adhesion kinase in human ovarian epithelial and cancer cells

KLF8 (Krüppel-like factor 8) is a transcription factor downstream of focal adhesion kinase (FAK) important in the regulation of the cell cycle and also plays a critical role in oncogenic transformation and epithelial to mesenchymal transition. Here we report the mechanisms by which FAK regulates KLF8 expression in human ovarian epithelial and cancer cells. We show that the overexpression of both KLF8 and FAK in the human ovarian cancer cells as compared with the normal human ovarian surface epithelial cells is critical for cell growth. Using promoter luciferase reporter assays, we demonstrate that exogenous FAK strongly promotes the activity of the KLF8 promoter, and knockdown of FAK inhibits it. KLF8 promoter activity and mRNA levels are induced by expression of constitutively active (CA) phosphatidylinositol 3-kinase (PI3K) or CA-Akt but are repressed by dominant negative Akt or the PI3K inhibitor LY294002. Disruption of an Sp1 binding site in the KLF8 promoter abolishes the FAK- or Sp1-mediated promoter activation. Sp1 knockdown prevents the KLF8 promoter from being activated by Sp1 or CA-Akt, and expression of CA-Akt enhances Sp1 expression in SKOV3ip1 cells. Chromatin immunoprecipitation and oligonucleotide precipitation results show that Sp1 binds to the KLF8 promoter. Taken together, our data suggest that FAK induces KLF8 expression in human ovarian cancer cells by activating the PI3K-Akt signaling pathway, leading to the activation of KLF8 promoter by Sp1.

t10,c12-Conjugated linoleic acid stimulates mammary tumor progression in Her2/ErbB2 mice through activation of both proliferative and survival pathways

The t10,c12 isomer of conjugated linoleic acid (CLA) inhibits rat mammary carcinogenesis, metastasis from a transplantable mouse mammary tumor and angiogenesis; however, it stimulates mammary tumorigenesis in transgenic mice overexpressing ErbB2 in the mammary epithelium (ErbB2 transgenic mice). In the current study, we report that a 4-week supplementation of the diet with 0.5% trans-10, cis-12 conjugated linoleic acid (t10,c12-CLA) stimulated the growth of established ErbB2-overexpressing mammary tumors by 30% and increased the number of new tumors from 11% to 82%. Additionally, when t10,c12-CLA supplementation of ErbB2 transgenic mice was initiated at 21 weeks of age, a time just prior to tumor appearance, overall survival was decreased from 46.4 weeks in the control to 39.0 weeks in the CLA group, and survival after detection of a palpable tumor from 7.5 to 4.6 weeks. Short-term supplementation from 10 to 14 weeks or 21 to 25 weeks of age temporarily accelerated tumor development, but over the long term, there was no significant effect on mammary tumorigenesis. Long term as well as a short 4-week supplementation increased mammary epithelial hyperplasia and lobular development, and altered the mammary stroma; this was reversible in mice returned to the control diet. t10,c12-CLA altered proliferation and apoptosis of the mammary epithelium, although this differed depending on the length of administration and/or the age of the mice. The increased tumor development with t10,c12-CLA was associated with increased phosphorylation of the IGF-I/insulin receptor, as well as increased signaling through the mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase and phosphatidylinositol 3-kinase/Akt pathways; however, neither phospho-ErbB2 nor ErbB2 was altered.

Up regulation in gene expression of chromatin remodelling factors in cervical intraepithelial neoplasia

BACKGROUND

The highest rates of cervical cancer are found in developing countries. Frontline monitoring has reduced these rates in developed countries and present day screening programs primarily identify precancerous lesions termed cervical intraepithelial neoplasias (CIN). CIN lesions described as mild dysplasia (CIN I) are likely to spontaneously regress while CIN III lesions (severe dysplasia) are likely to progress if untreated. Thoughtful consideration of gene expression changes paralleling the progressive pre invasive neoplastic development will yield insight into the key casual events involved in cervical cancer development.

RESULTS

In this study, we have identified gene expression changes across 16 cervical cases (CIN I, CIN II, CIN III and normal cervical epithelium) using the unbiased long serial analysis of gene expression (L-SAGE) method. The 16 L-SAGE libraries were sequenced to the level of 2,481,387 tags, creating the largest SAGE data collection for cervical tissue worldwide. We have identified 222 genes differentially expressed between normal cervical tissue and CIN III. Many of these genes influence biological functions characteristic of cancer, such as cell death, cell growth/proliferation and cellular movement. Evaluation of these genes through network interactions identified multiple candidates that influence regulation of cellular transcription through chromatin remodelling (SMARCC1, NCOR1, MRFAP1 and MORF4L2). Further, these expression events are focused at the critical junction in disease development of moderate dysplasia (CIN II) indicating a role for chromatin remodelling as part of cervical cancer development.

CONCLUSION

We have created a valuable publically available resource for the study of gene expression in precancerous cervical lesions. Our results indicate deregulation of the chromatin remodelling complex components and its influencing factors occur in the development of CIN lesions. The increase in SWI/SNF stabilizing molecule SMARCC1 and other novel genes has not been previously illustrated as events in the early stages of dysplasia development and thus not only provides novel candidate markers for screening but a biological function for targeting treatment.

Defining ETS transcription regulatory networks and their contribution to breast cancer progression

ETS factors are members of one of the largest families of evolutionarily conserved transcription factors, regulating critical functions in normal cell homeostasis, that when perturbed contribute to tumor progression. The well documented alterations in ETS factor expression and function during breast cancer progression result in pleiotropic effects manifested by the downstream effect on their target genes. Multiple ETS factors bind to the same regulatory sites present on target genes, suggesting redundant or competitive functions. Furthermore, additional events contribute to, or may be necessary for, target gene regulation. In order to advance our understanding of the ETS-dependent regulation of breast cancer progression and metastasis, this prospect article puts forward a model for examining the effects of simultaneous expression of multiple transcription factors on the transcriptome of non-metastatic and metastatic breast cancer. Compared to existing RNA profiles defined following expression of individual transcription factors, the anti- and pro-metastatic signatures obtained by examining specific ETS regulatory networks will significantly improve our ability to accurately predict tumor progression and advance our understanding of gene regulation in cancer. Coordination of multiple ETS gene functions also mediates interactions between tumor and stromal cells and thus contributes to the cancer phenotype. As such, these new insights may provide a novel view of the ETS gene family as well as a focal point for studying the complex biological control involved in tumor progression.

mTOR signalling in human cancer

Inhibitors of mTOR, the mammalian target of rapamycin, have been extensively studied in clinical trials for cancer treatment. Results have been promising, mostly in certain lymphomas, but in solid tumours the results have been generally less encouraging. However, recent results, particularly in renal cell carcinoma, have provided renewed interest in the role of mTOR inhibitors in solid tumours. A rational, and potentially more successful, development of these agents (i.e., RAD001, temsirolimus and AP23573) likely relies in a deeper knowledge of mTOR signalling in cancer, both at the preclinical and clinical levels. These would allow a better selection of patients more likely to respond to the use of biologically active doses of the agents and the development of mechanistically based combinations with other agents. The goal of this review is to provide an update on the complex signalling of mTOR in cancer and on the biological effects of mTOR inhibitors in cancer cells.

p204 protein is a novel modulator of ras activity

The murine p200 family protein, p204, modulates cell proliferation and tissue differentiation. Many of its activities are exerted in the nucleus. However, in cardiac myocytes, p204 accumulated in the cytoplasm. A yeast two-hybrid assay revealed a p204-cytoplasmic Ras protein interaction. This was confirmed (i) by coimmunoprecipitation of p204 with Ras in mouse heart extract and with endogenous or ectopic H-Ras and K-Ras in cell lysates as well as (ii) by binding of purified H-Ras-GTP to purified p204 in vitro. p204 inhibited (i) the cleavage of RasGTP to RasGDP by RasGAP; (ii) the binding to RasGTP of Raf-1, phosphatidylinositol 3-kinase, and Ral-GDS, effectors of Ras signaling; and (iii) activation by the Ras pathway of the phosphorylation and thus activation of downstream targets (e.g. MEK, Akt, and p38 MAPK). Oncogenic Ras expression triggered the phosphorylation and translocation of p204 from the nucleus to the cytoplasm. This is expected to increase the interaction between the two proteins. Translocation triggered by Ras oncoprotein was blocked by the LY294002 inhibitor of phosphatidylinositol 3-kinase. Ras did not promote phosphorylation or translocation to the cytoplasm of mutated p204 in which serine 179 was replaced by alanine. p204 overexpression inhibited the anchorage-independent proliferation of cells expressing Ras(Q61L) oncoprotein. Ras oncoprotein triggered in MEF3T3 cells the rearrangement of the actin cytoskeleton and the enhancement of cell migration through a membrane. Overexpression of p204 inhibited both. Ras oncoprotein or activated, wild-type Ras was described to increase Egr-1 transcription factor expression. We report that a sequence in the gene encoding p204 bound Egr-1, and Egr-1 activated p204 expression. Ras oncoprotein or activated wild-type Ras increased the expression in 3T3 cells of p204 together with that of Egr-1. Furthermore, the activation of expression of a single copy of K-ras oncogene in cultured murine embryonic cells induced the expression of a high level of p204 as well as its distribution between the nuclei and the cytoplasm. Thus, p204 may serve as a negative feedback inhibitor of Ras activity.

The microfilament system and malignancy

Increased motile activity, increased rate of cell proliferation and removal of growth inhibiting cell-cell contacts are hallmarks of tumorigenesis. Activation of cell motility and migration is caused by activation of receptors, turning on the growth cycle. Increased expression of metalloproteinases, breaking cell:cell contacts and organ confines, allows the spread of malignant cancer cells to other sites in the organism. It has become increasingly clear that most transmembrane proteins (growth factor receptors, adhesion proteins and ion channels) are either permanently or transiently associated with the sub-membraneous system of actin microfilaments (MF), whose force generating capacity they control. Although there has been great progress in our understanding of the physiological importance of the MF-system, as will be exemplified in this issue of SCB, many aspects of actin microfilament formation and its regulation are still unclear. Redox control of the actin (MF)-system in cell motility and migration and its perturbations in pathophysiology, including cancer, is an emerging field of research.

Modelling breast cancer: one size does not fit all

Breast cancer is not a single disease, but is instead a collection of diseases that have distinct histopathological features, genetic and genomic variability, and diverse prognostic outcomes. Thus, no individual model would be expected to completely recapitulate this complex disease. Here, the models commonly used to investigate breast cancer including cell lines, xenografts and genetically engineered mice, are discussed to help address the question: what is the most powerful way to investigate this heterogeneous disease?

Forkhead proteins are critical for bone morphogenetic protein-2 regulation and anti-tumor activity of resveratrol

Osteoporosis is a major public health problem and the most obvious preventive strategy, hormone replacement therapy, has lost favor due to recent findings of the Women's Health Initiative regarding increased risks of breast cancer and cardiovascular disease. Resveratrol, a naturally occurring compound possessing estrogenic activity, is thought to have considerable potential for therapy of osteoporosis. In the present study, resveratrol was found to exhibit bone-protective effects equivalent to those exerted by hormone replacement therapy and decrease the risk of breast cancer in the in vivo and in vitro models. Forkhead proteins were found to be essential for both effects of resveratrol. The bone-protective effect was attributable to induction of bone morphogenetic protein-2 through Src kinase-dependent estrogen receptor activation and FOXA1 is required for resveratrol-induced estrogen receptor-dependent bone morphogenetic protein-2 expression. The tumor-suppressive effects of resveratrol were the consequence of Akt inactivation-mediated FOXO3a nuclear accumulation and activation. Resveratrol is therefore anticipated to be highly effective in management of postmenopausal osteoporosis without an increased risk of breast cancer.

Effect of Genistein on the expression of Akt and phosphorylated Akts in human gastric carcinoma cell line

AIM: To investigate the effects of Genestein on the expression of Akt and its phosphorylated proteins (p-Akts) in human gastric carcinoma cell line SGC-7901.

METHODS: SGC-7901 cells were exposed to 0、5、10、20、40 and 80 μmol/L Genistein for 24 h. The effect of Genistein on cell proliferation was measured by methyl thiazolyl tetrazolium (MTT) assay, and the apoptosis of SGC-7901 cells was evaluated by Hoechst 33342 staining. The expression of Akt and p-Akts (Ser473 and Thr308) were measured by Western blot.

RESULTS: The inhibitory rate was 6.85% ± 3.71%, 13.19% ± 1.90%, 20.94% ± 1.83%, 29.58% ± 1.19% and 41.75% ± 1.92%, respectively, as SGC-7901 cells were exposed to 5, 10, 20, 40 and 80 μmol/L Genistein for 24 h. Typical morphological changes of apoptosis were induced by Genistein at the concentrations (20-80 μmol/L). Genistein had no marked influences on Akt expression. Both Ser473 and Thr308 were expressed in SGC-7901 cells 24 h after Genistein treatment, and they were decreased with the increasing of Genistein concentrations. The weakest expression appeared as 80 μmol/L Genistein was used.

CONCLUSION: The anti-cancer action of Genistein may be associated with the decreased expression of p-Akt (Ser473) and p-Akt (Thr308).