Akt/protein kinase B isoforms are differentially regulated by epidermal growth factor stimulation

AKT induces senescence in primary esophageal epithelial cells but is permissive for differentiation as revealed in organotypic culture

Epidermal growth factor receptor (EGFR) overexpression and activation is critical in the initiation and progression of cancers, especially those of epithelial origin. EGFR activation is associated with the induction of divergent signal transduction pathways and a gamut of cellular processes; however, the cell-type and tissue-type specificity conferred by certain pathways remains to be elucidated. In the context of the esophageal epithelium, a prototype stratified squamous epithelium, EGFR overexpression is relevant in the earliest events of carcinogenesis as modeled in a three-dimensional organotypic culture system. We demonstrate that the phosphatidylinositol 3-kinase (PI3K)/AKT signaling pathway, and not the MEK/MAPK (mitogen-activated protein kinase) pathway, is preferentially activated in EGFR-mediated esophageal epithelial hyperplasia, a premalignant lesion. The hyperplasia was abolished with direct inhibition of PI3K and of AKT but not with inhibition of the MAPK pathway. With the introduction of an inducible AKT vector in both primary and immortalized esophageal epithelial cells, we find that AKT overexpression and activation is permissive for complete epithelial formation in organotypic culture, but imposes a growth constraint in cells grown in monolayer. In organotypic culture, AKT mediates changes related to cell shape and size with an expansion of the differentiated compartment.

Cardiac myxoma cells exhibit embryonic endocardial stem cell features

The origin of myxoma, the most frequent tumour of the heart, remains uncertain. Previous phenotypic characterizations have shown heterogeneous results and the most recent hypothesis suggests that cardiac myxoma originates from a primitive pluripotential cardiogenic cell. We investigated the expression of actin isoforms in 30 left atrial myxomas by immunohistochemistry and in eight consecutive tumours by RT-PCR. alpha-Smooth muscle actin (alpha-SMA) protein and/or transcripts were detected in all cases, whereas alpha-cardiac actin was observed in few cases and alpha-skeletal actin was always absent. Besides classical features, vessel-like structures were characterized by cells expressing CD34 and, less frequently, alpha-SMA. Confocal microscopy showed focal co-expression of CD34 and alpha-SMA in myxoma cells, suggesting a gradual loss of stem endothelial markers and the acquisition of myocytic antigens. In order to confirm this hypothesis, early cardiac differentiation markers were also investigated. RT-PCR documented the presence of transcripts for Sox9 (100%), Notch1 (87.5%), NFATc1 (37.5%), Smad6, metalloproteinases 1 and 2 alone or in variable combinations and the absence of ErbB3 and WT1. Myxoma cells maintained phenotypic heterogeneity in vitro, including the expression of alpha-SMA and the presence of stress fibres. These findings document in cardiac myxoma cells phenotypic markers of the embryonic endothelial-to-mesenchymal transformation that precedes terminal differentiation of endocardial cushions, supporting the hypothesis that cardiac myxoma cells may derive from adult developmental remnants.

Imaging and Oncologic Drug Development

For decades anatomic imaging with computed tomography or magnetic resonance imaging has facilitated drug development in medical oncology by providing quantifiable and objective evidence of response to cancer therapy. In recent years metabolic imaging with [18F]fluorodeoxyglucose–positron emission tomography has added an important component to the oncologist's armamentarium for earlier detection of response that is now widely used and appreciated. These modalities along with ultrasound and optical imaging (bioluminescence, fluorescence, near-infrared imaging, multispectral imaging) have become used increasingly in preclinical studies in animal models to document the effects of genetic alterations on cancer progression or metastases, the detection of minimal residual disease, and response to various therapeutics including radiation, chemotherapy, or biologic agents. The field of molecular imaging offers potential to deliver a variety of probes that can image noninvasively drug targets, drug distribution, cancer gene expression, cell surface receptor or oncoprotein levels, and biomarker predictors of prognosis, therapeutic response, or failure. Some applications are best suited to accelerate preclinical anticancer drug development, whereas other technologies may be directly transferable to the clinic. Efforts are underway to apply noninvasive in vivo imaging to specific preclinical or clinical problems to accelerate progress in the field. Because resources are limited, and patient suffering from failed or ineffective therapy continues, a concerted effort is being made to address these issues. Many simultaneous activities involving academia; the pharmaceutical, device, and biotechnology industries; US Food and Drug Administration; National Cancer Institute; Centers for Medicare and Medicaid Services; and specialized networks sponsored by the National Institutes of Health are beginning to address these issues to develop consensus recommendations and progress in this important area.

Activation of Akt and ERK signalling pathways induced by etoposide confer chemoresistance in gastric cancer cells

AIMS

To identify whether phosphatidylinositol 3-kinase/Akt and mitogen-activated protein kinase/extracellular-regulated protein kinases signalling pathways are implicated in the chemoresistance of gastric cancer and to explore the possible mechanisms.

METHODS

Gastric cancer cell lines SGC7901 and BGC823 were exposed to etoposide, Wortmannin+etoposide or PD98059+etoposide. Cell cycle distribution and cell apoptosis were detected using flow cytometry and Hoechst 33258 staining. Cells viability was determined by a colourimetric assay utilising 3-(4,5-dimethyl thiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT). Akt activity was detected using non-radioactive immunoprecipitation-kinase assay. Western blotting was exploited to evaluate the level of phosphorylated ERK1/2 and expressions of c-Myc and p53 protein.

RESULTS

Etoposide suppressed the viability of SGC7901 and BGC823 cells in a time- and dose-dependent manner; PD98059 and Wortmannin were able to enhance the cytotoxicity of etoposide. The apoptotic levels of cells treated with Wortmannin+etoposide or PD98059+etoposide were significantly higher than those of cells treated with etoposide only. Phospho-ERK1/2, Akt activity and expression of c-Myc were significantly induced by etoposide in a time-dependent manner; moreover, there was a weak effect on the expression of p53 protein. Both Wortmannin and PD98059 elevated the level of p53 expression strikingly, however, only PD98059 suppressed the up-regulation trend of c-Myc expression induced by etoposide.

CONCLUSION

Chemotherapy reagent activated phosphatidylinositol 3-kinase/Akt and mitogen-activated protein kinase/extracellular-regulated protein kinases signalling pathways, which decreased the chemotherapy sensitivity of gastric cancer cell lines SGC7901 and BGC823 via suppressing the expression of p53 and enhancing the expression of c-Myc. This may be one of the molecular mechanisms of gastric cancer chemoresistance.

Expression of Akt (protein kinase B) and its isoforms in malignant lymphomas

Akt (protein kinase B) is a serine/threonine kinase involved in the regulation of cell survival signals. Akt is expressed in T- and B-lymphocytes and is activated in response to cytokine and antigen-receptor stimulation. Three isoforms of Akt have been identified, Akt-1, -2 and -3, but the expression pattern and specific functions of each have not yet been determined for many cell types. To determine whether Akt signaling is enhanced in human malignant lymphomas and to analyse the expression pattern of Akt isoforms in these neoplasms, Akt-1, -2 and -3 expression was studied in 38 cell lines derived from hematopoietic neoplasms, by RT-PCR and western blot analysis. The level of phosphorylated (active) Akt was also analysed in cell lines as well as in 72 human malignant non-Hodgkin's lymphoma tissues. The results suggest that there is constitutive activation of Akt in the majority of primary human lymphomas and hematopoietic cell lines and support its proposed key role in lymphoma cell survival.

Gefitinib and the modulation of the signaling pathways downstream of epidermal growth factor receptor in human liver cancer cells

BACKGROUND

The transforming growth factor-alpha (TGF-alpha)/epidermal growth factor receptor (EGFR) signaling pathway has been demonstrated to have a pivotal role in hepatocarcinogenesis. We examined whether abrogation of the TGF-alpha/EGFR signaling pathway with a selective EGFR tyrosine kinase inhibitor, gefitinib, could inhibit the proliferation of human hepatocellular carcinoma (HCC) cells.

METHODS

Cellular growth was monitored by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays. Cell-cycle distribution was analyzed by flow cytometric analysis. Activities of signaling molecules were evaluated by Western blot analysis.

RESULTS

HCC cells expressed EGFR at variable levels; however, extracellular signal-regulated kinase (ERK)1/2 and AKT, key signaling molecules downstream of EGFR, were not constitutively active in the cells. When HCC cells were treated with TGF-alpha, cellular growth was accelerated in a manner dependent on activation of ERK1/2 and AKT. When the cells were co-treated with gefitinib and TGF-alpha, enhanced proliferation and activation of ERK1/2 and AKT were canceled, and the cell-cycle promotion by TGF-alpha was inhibited by co-treatment with gefitinib and TGF-alpha, independently of expression levels of EGFR. In contrast, gefitinib did not show an antiproliferative effect on HCC cells cultivated under the 10% serum condition.

CONCLUSIONS

The present data demonstrated that gefitinib exerted an antiproliferative action on HCC cells under a limited condition when signaling pathways downstream of EGFR were activated by TGF-alpha.

Creating oral squamous cancer cells: a cellular model of oral-esophageal carcinogenesis

Immortalization and malignant transformation are important steps in tumor development. The ability to induce these processes from normal human epithelial cells with genetic alterations frequently found in the corresponding human cancer would significantly enhance our understanding of tumor development. Alterations in several key intracellular regulatory pathways (the pRB, p53, and mitogenic signaling pathways and the telomere maintenance system) appear to be sufficient for the neoplastic transformation of normal human cells. Nevertheless, in vitro transformation models to date depend on viral oncogenes, most prominently the simian virus 40 early region, to induce immortalization and malignant transformation of normal human epithelial cells. Here, we demonstrate a transformation model creating oral-esophageal cancer cells by using a limited set of genetic alterations frequently observed in the corresponding human cancer. In a stepwise model, cyclin D1 overexpression and p53 inactivation led to immortalization of oral keratinocytes. Additional ectopic epithelial growth factor receptor overexpression followed by c-myc overexpression as well as consecutive reactivation of telomerase induced by epithelial growth factor receptor sufficed to transform oral epithelial cells, truly recapitulating the development of the corresponding human disease.

Requirement for NF-(kappa)B in interleukin-4-induced androgen receptor activation in prostate cancer cells

BACKGROUND

Accumulating evidence suggest a critical role of activation of androgen receptor (AR) by nonandrogen in the development of androgen independent prostate cancer. Previous study identified that interleukin-4 (IL-4) enhances AR activation in the absence of androgen or in the very low levels of androgen in prostate cancer cells. In this study, the mechanism of IL-4-induced AR activation was investigated.

METHODS & RESULTS

The induction of AR activation by IL-4 can be suppressed by expression of the I(kappa)B(alpha), an inhibitor of NF-(kappa)B. The enhanced expression of AR-mediated prostate-specific antigen (PSA) by IL-4 was blocked by the expression of I(kappa)B(alpha). IL-4 increases NF-(kappa)B transcriptional activity in prostate cancer cells which can be blocked by the addition of IL-4 antibody. IL-4 can also rapidly activate NF-kappaB. Furthermore, the IL-4-induced NF-kappaB activation and nuclear translocation can be blocked by LY294002, a PI3K/Akt specific inhibitor, suggesting that IL-4-induced NF-(kappa)B activation is mediated by activation of PI3K/Akt pathway.

CONCLUSION

In combination with previous study that IL-4 activates PI3K/Akt pathway, activation of PI3K/Akt > NF-(kappa)B pathways may be responsible for IL-4-induced AR activation in prostate cancer cells. Taken together, these studies suggest that IL-4 > PI3K/Akt > NF-(kappa)B signaling pathways, which activate AR signaling, may play an important role during the progression of androgen independent prostate cancer cells.

Novel therapies in lung cancer

This article reviews novel therapies that are under development for non-small cell lung cancer and small cell lung cancer.

Hydrogen peroxide and epidermal growth factor activate phosphatidylinositol 3-kinase and increase sodium transport in A6 cell monolayers

Activation of phosphatidylinositol 3-kinase (PI 3-kinase) is required for insulin stimulation of sodium transport in A6 cell monolayers. In this study, we investigate whether stimulation of the PI 3-kinase by other agents also provoked an increase in sodium transport. Both epidermal growth factor (EGF) and H2O2provoked a rise in sodium transport that was inhibited by LY-294002, an inhibitor of PI 3-kinase activity. PI 3-kinase activity was estimated in extracts from A6 cell monolayers directly by performance of a PI 3-kinase assay. We also estimated the relative importance of the PI 3-kinase pathway by two different methods: 1) coprecipitation of the p85 regulatory subunit with anti-phosphotyrosine antibodies and 2) phosphorylation of PKB on both Ser 473 and Thr 308 residues observed by Western blotting. Since the mitogen-activated protein kinase (MAPK) pathway has also been implicated in the regulation of sodium transport, we also investigated whether this pathway is turned on by insulin, H2O2, or EGF. Phosphorylation of ERK1/2 was increased only transiently by insulin and H2O2but quite sustainedly by EGF. Inhibitors of this pathway (U-0126 and PD-98059) failed to affect the insulin and H2O2stimulation of sodium transport but increased substantially the stimulation induced by EGF. The latter effect was associated with an increase in PKB phosphorylation, thus suggesting that the stimulation of the MAPK pathway prevents, in part, the stimulation of the PI 3-kinase pathway in the transport of sodium stimulated by EGF.

Tumor necrosis factor-{alpha} decreases Akt protein levels in 3T3-L1 adipocytes via the caspase-dependent ubiquitination of Akt

TNF-alpha is a mediator of insulin resistance in sepsis, obesity, and type 2 diabetes and is known to impair insulin signaling in adipocytes. Akt (protein kinase B) is a crucial signaling mediator for insulin. In the present study we examined the posttranslational mechanisms by which short-term (<6-h) exposure of 3T3-L1 adipocytes to TNF-alpha decreases Akt levels. TNF-alpha treatment both increased the ubiquitination of Akt and decreased its protein level. The decrease in protein was associated with the presence of an (immunoreactive) Akt fragment after TNF-alpha treatment, indicative of Akt cleavage. The broad-spectrum caspase inhibitor t-butoxycarbonyl-Asp(O-Me)-fluoromethyl ketone markedly suppressed these effects of TNF-alpha. The caspase-6 inhibitor Z-Val-Glu(OMe)-Ile-Asp(OMe)-CH(2)F potently suppressed Akt ubiquitination, degradation, and fragment formation, whereas the proteasome inhibitor Z-Leu-Leu-Leu-CHO modestly attenuated the decline in Akt levels. Exposure to TNF-alpha also enhanced the association of Akt with an E3 ligase activity. Adipocytes preexposed to TNF-alpha for 5 h and then stimulated with insulin for 30 min exhibited decreased levels of Akt, phosphorylated Akt, as well as phosphorylated Mdm2, which is a known direct substrate of Akt, and glucose uptake. Caspase inhibition attenuated these inhibitory effects of TNF-alpha. Collectively, our results suggest that TNF-alpha induces the caspase-dependent degradation of Akt via the cleavage and ubiquitination of Akt, which results in its degradation through the 26S proteasome. Furthermore, the caspase- and proteasome-mediated degradation of Akt due to TNF-alpha exposure leads to impaired Akt-dependent insulin signaling in adipocytes. These findings expand the mechanism by which TNF-alpha impairs insulin signaling.

Scalaradial Inhibition of Epidermal Growth Factor Receptor-Mediated Akt Phosphorylation Is Independent of Secretory Phospholipase A2

The marine natural product 12-epi-scalaradial (SLD) is a specific secretory phospholipase A(2) (sPLA(2)) inhibitor. However, little is known about whether this compound has other pharmacological effects. Here, we revealed a novel effect of SLD on epidermal growth factor receptor (EGFR)-mediated Akt phosphorylation. SLD dose- and time-dependently inhibited epidermal growth factor (EGF)-stimulated Akt phosphorylation, which is required for Akt activation. SLD also blocked the EGF-stimulated membrane translocation of 3-phosphoinositide-dependent protein kinase 1 and inhibited phosphatidylinositol 3-kinase activity. This inhibition is specific for SLD because other phospholipase inhibitors, including sPLA(2) inhibitor thioetheramide-phosphatidylcholine, cytosolic PLA(2) inhibitor arachidonyl trifluoromethyl ketone, cytosolic PLA(2) and Ca(2+)-independent PLA(2) inhibitor methyl arachidonyl fluorophosphonate, phospholipase C inhibitor U73122, and cyclooxygenases inhibitor indomethacin, failed to inhibit EGF-stimulated Akt phosphorylation. Furthermore, arachidonic acid, the main sPLA(2)-catalyzed metabolite, was not able to rescue SLD inhibition of EGF-stimulated Akt phosphorylation. Overexpression of group IIA or group X sPLA(2) did not reverse the inhibitory effect of SLD on Akt phosphorylation, either. Our results demonstrate that SLD inhibits EGFR-mediated Akt phosphorylation, and this novel effect of SLD is independent of sPLA(2).

[Immunohistochemistry study of EGFR expression in head and neck squamous cell carcinoma]

EGFR is an important transmembrane receptor member of the family of tyrosine kinases, that translates signals from both outside and inside the cell and plays a key role in numerous proceses that affect tumour development, growth, progresion, differentiation, inhibition of apoptosis and metastasis. Immunohistochemistry studies have shown that 40-80% of head and neck squamous cell carcinomas express EGFR and it has been suggested as a potential independent prognostic parameter. The objective of this study is to evaluate by immunohistochemistry the expresi6n of EGFR in a series of Head and Neck Squamous Cell Carcinoma and correlate it to clinico-pathological features and prognostic significance. We investigated expression of EGFR in 44 samples. There was a high expression in 41% of the cases. Even if we have not found that the expression of EGFR correlated with the prognosis of these patients the presence of EGFR is very important because there are chemical agents or drugs that can inhibit its activity.

Estrogen-induced apoptosis in a breast cancer model resistant to long-term estrogen withdrawal

Estrogen suppression through the use of an aromatase inhibitor is an effective endocrine treatment option for postmenopausal breast cancer patients with estrogen receptor (ER)-positive disease, however, there are concerns that long-term estrogen deprivation will inevitably lead to resistance. To address the issue of acquired resistance to long-term estrogen deprivation our laboratory has developed an ER+/PR- hormone-independent breast cancer cell line, MCF-7:5C which is a variant clone of wild-type MCF-7 cells. Originally, these cells were cultured in estrogen-free MEM containing 5% charcoal-stripped calf serum and were found to be resistant to both estradiol (E(2)) and antiestrogens. Interestingly, a completely different phenomenon was observed when MCF-7:5C cells were cultured in phenol red-free RPMI 1640 medium containing 10% charcoal-stripped fetal bovine serum (SFS). Using DNA quantitation assays, we examined the effect of E(2) on the growth of MCF-7:5C cells under different media conditions. Our results showed that 10(-9)M E(2) caused a dramatic 90% reduction in the growth of MCF-7:5C cells cultured in RPMI medium containing 10% SFS but did not have any significant inhibitory effects on cells cultured in MEM media. Additional experiments were performed to determine whether the medium or the serum facilitated the inhibitory effects of E(2) and the results indicated that it was the serum. Annexin V and DAPI staining confirmed that the E(2)-induced growth inhibition of MCF-7:5C cells was due to apoptosis. We also examined the tumorigenic potential of MCF-7:5C cells by injecting 1x10(7)cells/site into ovariectomized athymic mice and found that these cells, previously cultured in RPMI media, spontaneously grew into tumors in the absence of E(2). Overall, these results show that low concentrations (>10(-11)M) of E(2) are capable of inducing apoptosis in an aromatase resistant breast cancer cell model and that this effect is highly influenced by the medium in which the cells are grown.

EGF receptor transactivation mediates ANG II-stimulated mitogenesis in intestinal epithelial cells through the PI3-kinase/Akt/mTOR/p70S6K1 signaling pathway

The role of epidermal growth factor receptor (EGFR) tyrosine kinase and its downstream targets in the regulation of the transition from the G0/G1 phase into DNA synthesis in response to ANG II has not been previously investigated in intestinal epithelial IEC-18 cells. ANG II induced a rapid and striking EGFR tyrosine phosphorylation, which was prevented by selective inhibitors of EGFR tyrosine kinase activity (e.g., AG-1478) or by broad-spectrum matrix metalloproteinase (MMP) inhibitor GM-6001. Pretreatment of these cells with either AG-1478 or GM-6001 reduced ANG II-stimulated DNA synthesis by approximately 50%. To elucidate the downstream targets of EGFR, we demonstrated that ANG II stimulated phosphorylation of Akt at Ser473, mTOR at Ser2448, p70S6K1 at Thr389, and S6 ribosomal protein at Ser(235/236). Pretreatment with AG-1478 inhibited Akt, p70S6K1, and S6 ribosomal protein phosphorylation. Inhibition of phosphatidylinositol (PI)3-kinase with LY-294002 or mTOR/p70S6K1 with rapamycin reduced [3H]thymidine incorporation by 50%, i.e., to levels comparable to those achieved by addition of either AG-1478 or GM-6001. Utilizing Akt small-interfering RNA targeted to Akt1 and Akt2, Akt protein knockdown dramatically inhibited p70S6K1 and S6 ribosomal protein phosphorylation. In contrast, AG-1478 or Akt gene silencing exerted no detectable inhibitory effect on ANG II-induced extracellular signal-regulated kinase 1/2 phosphorylation in IEC-18 cells. Taken together, our results demonstrate that EGFR transactivation mediates ANG II-stimulated mitogenesis through the PI3-kinase/Akt/mTOR/p70S6K1 signaling pathway in IEC-18 cells.

Mechanical Stretch Stimulates Protein Kinase B/Akt Phosphorylation in Epidermal Cells via Angiotensin II Type 1 Receptor and Epidermal Growth Factor Receptor

Mechanical stress is known to modulate fundamental events such as cell life and death. Mechanical stretch in particular has been identified as a positive regulator of proliferation in skin keratinocytes and other cell systems. In the present study it was investigated whether antiapoptotic signaling is also stimulated by mechanical stretch. It was demonstrated that mechanical stretch rapidly induced the phosphorylation of the proto-oncogene protein kinase B (PKB)/Akt at both phosphorylation sites (serine 473/threonine 308) in different epithelial cells (HaCaT, A-431, and human embryonic kidney-293). Blocking of phosphoinositide 3-OH kinase by selective inhibitors (LY-294002 and wortmannin) abrogated the stretch-induced PKB/Akt phosphorylation. Furthermore mechanical stretch stimulated phosphorylation of epidermal growth factor receptor (EGFR) and the formation of EGFR membrane clusters. Functional blocking of EGFR phosphorylation by either selective inhibitors (AG1478 and PD168393) or dominant-negative expression suppressed stretch-induced PKB/Akt phosphorylation. Finally, the angiotensin II type 1 receptor (AT1-R) was shown to induce positive transactivation of EGFR in response to cell stretch. These findings define a novel signaling pathway of mechanical stretch, namely the activation of PKB/Akt by transactivation of EGFR via angiotensin II type 1 receptor. Evidence is provided that stretch-induced activation of PKB/Akt protects cells against induced apoptosis.

Inactivation of akt and NF-kappaB play important roles during indole-3-carbinol-induced apoptosis in breast cancer cells

Despite significant advances in treatment, breast cancer is still the second leading cause of cancer-related deaths in women in the United States. Therefore, significant efforts are being given to develop novel strategies for the prevention of breast cancer in recent years. Our laboratory and others have been studying the effects of a potential chemopreventive agent, indole-3-carbinol (I3C), in breast cancer cells. We have previously shown that I3C induces apoptosis in breast cancer cells and found that the induction of apoptotic processes was partly mediated by dysregulation of anti- and pro-apoptotic molecules. However, the precise molecular mechanism(s) by which I3C induces apoptosis in breast cancer cells has not been fully elucidated. For the present study, we focused our investigation on important cell signaling molecules such as Akt and NF-kappaB during I3C-induced apoptosis in breast cancer cells. We found that I3C induces apoptotic processes in MCF10A-derived cell lines with premalignant (DCIS.com) and malignant (MCF10CA1a) phenotypes but not in nontumorigenic parental MCF10A cells. Immunoprecipitation, kinase assays, and Western blot analysis showed that I3C specifically inhibits Akt kinase activity and abrogates the EGF-induced activation of Akt in breast cancer cells. NF-kappaB DNA-binding analysis and transfection studies with Akt cDNA and NF-kappaB-Luc reporter constructs revealed that Akt gene transfection directly activates NF-kappaB, and this activation was completely abrogated by I3C treatment. In addition, I3C also abrogated the EGF-induced activation of NF-kappaB, which was mediated via the Akt signaling pathway. From these results, we conclude that there is a direct cross-talk between Akt and NF-kappaB pathways and that the inactivation of Akt and NF-kappaB activity plays important roles in mediating I3C-induced apoptosis in breast cancer cells. These results also suggest that I3C may be a potential chemopreventive agent by virtue of its selective apoptosis-inducing ability in premalignant and malignant breast epithelial cells.

Epidermal growth factor receptor regulates aberrant expression of insulin-like growth factor-binding protein 3

Epidermal growth factor receptor (EGFR) is frequently overexpressed in esophageal carcinoma and its precursor lesions. To gain insights into how EGFR overexpression affects cellular functions in primary human esophageal cells, we performed gene expression profiling and identified insulin-like growth factor-binding protein (IGFBP)-3 as the most up-regulated gene. IGFBP-3 regulates cell proliferation through both insulin-like growth factor-dependent and independent mechanisms. We found that IGFBP-3 mRNA and protein expression was increased in EGFR-overexpressing primary and immortalized human esophageal cells. IGFBP-3 was also up-regulated in EGFR-overexpressing cells in organotypic culture and in EGFR transgenic mice. Furthermore, IGFBP-3 mRNA was overexpressed in 80% of primary esophageal squamous cell carcinomas and 60% of primary esophageal adenocarcinomas. Concomitant up-regulation of EGFR and IGFBP-3 was observed in 60% of primary esophageal squamous cell carcinomas. Immunohistochemistry revealed cytoplasmic localization of IGFBP-3 in the preponderance of preneoplastic and neoplastic esophageal lesions. IGFBP-3 was also overexpressed in esophageal cancer cell lines at both mRNA (60%) and protein (40%) levels. IGFBP-3 secreted by cancer cells was capable of binding to insulin-like growth factor I. Functionally, epidermal growth factor appeared to regulate IGFBP-3 expression in esophageal cancer cell lines. Finally, suppression of IGFBP-3 by small interfering RNA augmented cell proliferation, suggesting that IGFBP-3 may inhibit tumor cell proliferation as a negative feedback mechanism. In aggregate, we have identified for the first time that IGFBP-3 is an aberrantly regulated gene through the EGFR signaling pathway and it may modulate EGFR effects during carcinogenesis.

The proinvasive activity of Wnt‐2 is mediated through a noncanonical Wnt pathway coupled to GSK‐3β and c‐ Jun/AP‐1 signaling

Inappropriate activation of the Wnt/APC/beta-catenin signaling pathways plays a critical role at early stages in a variety of human cancers. However, their respective implication in tumor cell invasion is still hypothetical. Here, we show that two activators of the canonical Wnt/beta-catenin transcription pathway, namely Dvl-2, the Axin 501-560 fragment binding glycogen synthase kinase -3beta (GSK-3beta), and the negative Wnt regulator wt-Axin did not alter cell invasion into type I collagen. In addition, both Dvl-2 and Axin 501-560 exerted a permissive action on the proinvasive activity of HGF and intestinal trefoil factor. Upstream activation of Wnt signaling by the Wnt-2 and Wnt-3a ligands, stable overexpression of Wnt-2, as well as GSK-3beta inhibition by lithium, SB216763, and GSK-3beta dominant negative forms (K85R and R96E) conferred the invasive phenotype through several proinvasive pathways. Induction of the matrix metalloprotease MMP-7 (matrilysin) gene and protein by Wnt-2 was abolished by inactivation of the AP-1 binding site in the promoter. Accordingly, invasion induced by Wnt-2 was prevented by soluble FRP-3 and FRP-1, sequestration of Gbetagamma subunits, depletion of the GSK-3beta protein by RNA interference, the c-Jun dominant negative mutant TAM67 and was not reversed by wt-Axin. Thus, the proinvasive activity of Wnt-2 is mediated by a noncanonical Wnt pathway using GSK-3beta and the AP-1 oncogene. Our data provide a potential clue for our understanding of the action and crosstalk between Wnt activators and other proinvasive pathways, in relation with matrix substrates and proteases in human cancers.

AKT involvement in cisplatin chemoresistance of human uterine cancer cells

OBJECTIVE

The aim of this study was to investigate the possible involvement of Akt activity and specific isoforms (Akt1, Akt2, and Akt3) in the resistance of human uterine cancer cells to cisplatin.

METHODS

Two different endometrial (HEC-1-A and KLE) and one cervical (HeLa) cancer cell lines all known as wild-type PTEN (tumor suppressor phosphatase tensin homologue, a lipid phosphatase involved in the negative regulation of Akt activity) were used for these studies.

RESULTS

Basal levels of Akt1, Akt2, and Akt3 mRNAs were determined by real-time quantitative RT-PCR studies and Western blot analyses were carried out to determine protein abundance of each isoforms. Akt1 mRNA and protein were present in all cell lines studied. Akt2 and Akt3 mRNAs and proteins were strongly expressed in KLE cells. Surprisingly, Akt phosphorylation was found in KLE expressing high levels of wild-type PTEN protein. KLE cells remained resistant to PI 3-K inhibitor, indicating that Akt phosphorylation might be, in part, independent of PI 3-K in this cell line. Cisplatin induced apoptosis in HeLa and HEC-1-A cells, but KLE cells expressing Akt2 and Akt3 remained more resistant to cisplatin. Knockout of Akt isoforms using specific siRNA technology increased the sensitivity of KLE cells toward cisplatin and caused a significant induction of cell death.

CONCLUSION

Taken together, these results suggest that specific Akt isoforms such as Akt2 and Akt3 might be involved in chemoresistance to cisplatin and that these isoforms could be putative targets for gene therapy in uterine cancers.

Acetylcholine and bradykinin trigger preconditioning in the heart through a pathway that includes Akt and NOS

In the rabbit heart, bradykinin and ACh trigger preconditioning by a mechanism involving ATP-sensitive potassium channel-dependent production of reactive oxygen species (ROS). Recent evidence indicates that the pathway by which bradykinin causes ROS generation includes nitric oxide synthase (NOS) and protein kinase G (PKG). On the other hand, Akt was shown to be essential for ACh to generate ROS. This study determines whether these two G-coupled receptor agonists indeed have similar signaling targets, i.e., whether Akt is involved in bradykinin's pathway and whether NOS is involved in ACh's pathway. Isolated adult rabbit cardiomyocytes were incubated for 15 min in reduced MitoTracker red, which becomes fluorescent only after exposure to ROS. Bradykinin (400 nM) and ACh (250 microM) caused a 51.4 +/- 14.8% and 39.8 +/- 11.7% increase, respectively, in ROS production (P <0.005). Coincubation of either agonist with Akt inhibitor (20 microM) or infection of cells with an adenovirus containing dominant negative Akt abolished this increase. The NO donor S-nitroso-N-acetyl penicillamine (SNAP, 1 microM) also increased the ROS signal by 40.8 +/- 15.7%, but this increase was unaffected by Akt inhibitor (39.0 +/- 6.4%), implying that Akt is upstream of NOS. ACh-induced ROS production could be abolished by either of the NOS inhibitors Nomega-monomethyl-L-arginine monoacetate (100 microM) and L-N5-(1-iminoethyl)ornithine hydrochloride (L-NIO, 5 microM). L-NIO also blocked the anti-infarct effect of ACh (550 microM) in isolated rabbit hearts exposed to 30 min of regional ischemia. We conclude that both bradykinin and ACh trigger ROS generation by sequentially activating Akt and NOS.

Bile salt exposure causes phosphatidyl-inositol-3-kinase-mediated proliferation in a Barrett's adenocarcinoma cell line

BACKGROUND

The mechanisms by which gastroesophageal reflux promotes malignant progression in Barrett's esophagus are poorly understood. The phosphatidylinositol-3-kinase (PI3 kinase)/Akt pathway regulates proliferation and apoptosis. We hypothesized that the PI3 kinase/Akt pathway mediates the pro-proliferative and antiapoptotic effects of bile.

METHODS

The Barrett's adenocarcinoma cell line, SEG-1, was exposed to the conjugated bile salt, glycochenodeoxycholic acid (GCDA). Cell number was measured by the MTT incorporation assay and by Coulter counter. PI3 kinase/Akt activity was inferred from Western blots of phosphorylated and total Akt. Proliferation and apoptosis were determined by BrdU incorporation and cell death ELISA.

RESULTS

A dose-dependent cell number increase was seen with a 20-minute exposure to GCDA. On Western blot, 200 micromol/L GCDA caused a 3-fold increase in Akt phosphorylation within 20 minutes, which was inhibited by 90% with the addition of PI3 kinase inhibitor, LY294002. LY294002 produced dose-dependent inhibition of GCDA-induced cell number increases. 200 micromol/L GCDA decreased apoptosis by 25%. Addition of LY294002 did not completely inhibit the antiapoptotic effect of bile.

CONCLUSIONS

Bile salts activate the PI3 kinase/Akt signaling pathway and stimulate cell growth in SEG-1. The majority of this PI3 kinase-mediated effect is secondary to increases in proliferation rather than to decreases in apoptosis.

Human intestinal epithelial cell survival and anoikis. Differentiation state-distinct regulation and roles of protein kinase B/Akt isoforms

We have shown previously that human intestinal epithelial cell survival and anoikis are distinctively regulated according to the state of differentiation. Here we analyzed the roles of protein kinase B/Akt isoforms in such differentiation state distinctions. Anoikis was induced in undifferentiated and differentiated enterocytes by inhibition of focal adhesion kinase (Fak; pharmacologic inhibition or overexpression of dominant-negative mutants) or beta1 integrins (antibody blocking) or by maintaining cells in suspension. Expression/activation parameters of Akt isoforms (Akt-1, Akt-2, and Akt-3) and Fak were analyzed. Activity of Akt isoforms was also blocked by inhibition of phosphatidylinositol 3-kinase or by overexpression of dominant-negative mutants. Here we report the following. 1) The expression/activation levels of Akt-1 increase overall during enterocytic differentiation, and those of Akt-2 decrease, whereas Akt-3 is not expressed. 2) Akt-1 activation is dependent on beta1 integrins/Fak signaling, regardless of the differentiation state. 3) Akt-2 activation is dependent on beta1 integrins/Fak signaling in undifferentiated cells only. 4) Activation of Akt-1 is phosphatidylinositol 3-kinase-dependent, whereas that of Akt-2 is not. 5) Akt-2 does not promote survival or apoptosis/anoikis. 6) Akt-1 is essential for survival. 7) Akt-2 cannot substitute for Akt-1 in the suppression of anoikis. Hence, the expression and regulation of Akt isoforms show differentiation state-specific distinctions that ultimately reflect upon their selective implication in the mediation of human intestinal epithelial cell survival. These data provide new insights into the synchronized regulation of cell survival/death that is required in the dynamic renewal process of tissues such as the intestinal epithelium.

Signaling pathways required for matrix metalloproteinase-9 induction by betacellulin in head-and-neck squamous carcinoma cells

The mechanisms by which c-erbB-dependent signaling contribute to the invasive potential of HNSCC remain to be fully elucidated. We have previously shown that c-erbB autocrine and/or paracrine stimulation upregulates MMP-9 but has no effect on the related gelatinase, MMP-2. BTC, a major c-erbB ligand, has the ability to efficiently activate all c-erbB receptors and to bind directly to EGFR and c-erbB-4. BTC is commonly expressed in HNSCC cells and exerts the most potent effects in terms of MMP induction relative to other c-erbB ligands so far tested. In the present study, we explored the contribution of major downstream events triggered by BTC/c-erbB receptor signaling to the regulation of MMP-9 and in vitro invasiveness of HNSCC cells. In human HNSCC cell lines, SIHN-006 and Detroit-562, BTC treatment resulted in rapid tyrosine phosphorylation of all c-erbB receptors whereas both endogenous MMP-9 and BTC-stimulated MMP-9 were predominantly mediated via EGFR. BTC induced ERK1/2, JNK/SAPK and Akt phosphorylation with differing kinetics but not p38 kinase. The BTC-dependent activation of JNK and PI3K/Akt pathways occurred predominantly via EGFR, whereas activation of the MEK-1/ERK pathway occurred via all 4 c-erbB receptors, although again predominantly via EGFR. Selective inhibition of ERK/MAPK (by PD98059 or U0126) and PI3K (by LY294002 or wortmannin) led to marked reduction of both basal and BTC-induced MMP-9 activity and invasive ability of HNSCC cells. In contrast, inhibition of p38 kinase with SB203580 produced no such effects. A specific inhibitor of NF-kappa B, BAY 11-7085, also blocked the stimulatory effect of BTC. No remarkable inhibition of MMP-9 and invasion was observed on targeting other cellular activities, such as PKA, PKC and PLC-gamma. Taken together, our data show that BTC induces MMP-9 production and invasion primarily through activation of EGFR, MAPK and PI3K/Akt in HNSCC cells.

Epidermal growth factor and trefoil factor family 2 synergistically trigger chemotaxis on BEAS-2B cells via different signaling cascades

Injured areas of the respiratory epithelium are subject to rapid repair by the migration of adjacent epithelial cells, a process termed "restitution". Rapid re-epithelialization is promoted by interactions between migrating cells and the extracellular matrix proteins. Furthermore, epidermal growth factor (EGF) as well as trefoil factor family (TFF) peptides are well known regulators of epithelial restitution due to their motogenic effects. Migration of the human bronchial epithelial cell line BEAS-2B in modified Boyden chambers was used as a model system for airway restitution. EGF or recombinant human TFF2 or TFF3 showed mainly chemotactic activity. The motogenic response was strictly dependent upon a haptotactic substrate, but to different degrees. EGF induced phosphorylation of extracellular signal-regulated kinases (ERK) 1/2, c-Jun-N-terminal kinase, p38, Akt, and p70S6K in BEAS-2B cells. Using specific inhibitors, the signaling cascades responsible for the motogenic response were shown to differ drastically when EGF was compared with TFF2. The motogenic effect of TFF2 was previously demonstrated to depend on ERK1/2 and protein kinase C activation; whereas the EGF-triggered motogenic response was completely independent of ERK1/2 activation but sensitive to the inhibition of phosphoinositide 3-kinase, p38, protein kinase C, or nuclear factor kappaB. However, the motogenic effects of EGF and TFF2 are additive. These data suggest that luminal EGF and TFF peptides can act synergistically in the human respiratory epithelium to enhance rapid repair processes in the course of diseases such as asthma.

Dual Kinase Inhibition in the Treatment of Breast Cancer: Initial Experience with the EGFR/ErbB‐2 Inhibitor Lapatinib

Dual inhibition of ErbB-1 (EGFR) and ErbB-2 (HER-2) tyrosine kinases has been found to exert greater biologic effects in the inhibition of signaling pathways promoting cancer cell proliferation and survival than inhibition of either receptor alone. The novel dual EGFR/ErbB-2 tyrosine kinase inhibitor lapatinib (GlaxoSmithKline; Research Triangle Park, NC) has been shown to inhibit tumor cell growth in vitro and in xenograft models for a variety of human tumors. Preliminary findings in a phase I study of lapatinib in patients with solid tumors indicate doses up to 1,800 mg per day are well tolerated. No grade 4 toxicities were observed and only two of 43 patients had grade 3 toxicity (diarrhea). Clinical activity of lapatinib was observed in these patients; nine patients with a variety of tumors remained on study for > or =4 months, one with a complete response (head and neck cancer). In a phase IB study in pretreated metastatic cancer patients with disease that could be biopsied, grade 1 or 2 diarrhea and rash were the most common adverse events. Three patients with breast cancer refractory to trastuzumab (Herceptin; Genentech, Inc.; South San Francisco, CA) had partial responses and 12 patients with a variety of tumors had stable disease. Assessment of biologic correlates in these patients indicates that increased tumor cell apoptosis on the terminal deoxynucleotide transferase-mediated dUTP nick-end labeling assay correlates with clinical response. Lapatinib currently is being evaluated in phase II and phase III trials in patients with metastatic breast cancer.

Folic acid reduces nuclear translocation of beta-catenin in rectal mucosal crypts of patients with colorectal adenomas

We have demonstrated that folic acid inhibits cell proliferation and epidermal growth factor receptor (EGFR) activation in colon cancer cell lines. We examined the effect of one year supplemental folic acid (5 mg/day) on the rectal mucosal expression of beta-catenin and pGSK3beta, known to be affected by EGF-R, in patients with colorectal adenomas. Folic acid treatment significantly reduced nuclear expression of beta-catenin (P < 0.05) and cellular expression of pGSK3beta (P < 0.01) when compared to placebo. Folic acid may exert its chemopreventive effect, at least in part, through inhibition of nuclear translocation of beta-catenin.

Androgen receptor in prostate cancer

The normal development and maintenance of the prostate is dependent on androgen acting through the androgen receptor (AR). AR remains important in the development and progression of prostate cancer. AR expression is maintained throughout prostate cancer progression, and the majority of androgen-independent or hormone refractory prostate cancers express AR. Mutation of AR, especially mutations that result in a relaxation of AR ligand specificity, may contribute to the progression of prostate cancer and the failure of endocrine therapy by allowing AR transcriptional activation in response to antiandrogens or other endogenous hormones. Similarly, alterations in the relative expression of AR coregulators have been found to occur with prostate cancer progression and may contribute to differences in AR ligand specificity or transcriptional activity. Prostate cancer progression is also associated with increased growth factor production and an altered response to growth factors by prostate cancer cells. The kinase signal transduction cascades initiated by mitogenic growth factors modulate the transcriptional activity of AR and the interaction between AR and AR coactivators. The inhibition of AR activity through mechanisms in addition to androgen ablation, such as modulation of signal transduction pathways, may delay prostate cancer progression.

Membrane-associated HB-EGF modulates HGF-induced cellular responses in MDCK cells

In MDCK cells, hepatocyte growth factor/scatter factor (HGF/SF) induces epithelial cell dissociation, scattering, migration, growth and formation of branched tubular structures. By contrast, these cells neither scatter nor form tubular structures in response to the epidermal growth factor (EGF) family of growth factors. Heparin-binding EGF-like growth factor (HB-EGF) is a member of the EGF family of growth factors and is synthesized as a membrane-associated precursor molecule (proHB-EGF). ProHB-EGF is proteolytically cleaved to release a soluble ligand (sHB-EGF) that activates the EGF receptor. Although recent studies suggest possible physiological functions, the role of proHB-EGF remains largely undefined. Using MDCK cells stably expressing proHB-EGF, a noncleavable deletion mutant of proHB-EGF or soluble HB-EGF, we show that epithelial cell functions differ depending on the form of HB-EGF being expressed. Expression of noncleavable membrane-anchored HB-EGF promoted cell-matrix and cell-cell interactions and decreased cell migration, HGF/SF-induced cell scattering and formation of tubular structures. By contrast, expression of soluble HB-EGF induced increased cell migration, decreased cell-matrix and cell-cell interactions and promoted the development of long unbranched tubular structures in response to HGF/SF. These findings suggest that HB-EGF can not only modulate HGF/SF-induced cellular responses in MDCK cells but also that membrane-bound HB-EGF and soluble HB-EGF give rise to distinctly different effects on cell-cell and cell-extracellular matrix interactions.

Tamoxifen and tamoxifen ethyl bromide induce apoptosis in acutely damaged mammary epithelial cells through modulation of AKT activity

Normal human mammary epithelial cells (HMECs), unlike estrogen receptor-positive (ER+) breast cancers, typically express low nuclear levels of ER (ER-'poor'). We previously demonstrated that 1.0 microM tamoxifen (Tam) induced apoptosis in ER-'poor' HMECs acutely transduced with human papillomavirus-16 E6 (HMEC-E6) through a rapid mitochondrial signaling pathway. Here, we show that plasma membrane-associated E2-binding sites initiate the rapid apoptotic effects of Tam in HMEC-E6 cells through modulation of AKT activity. At equimolar concentrations, Tam and tamoxifen ethyl bromide (QTam), a membrane impermeant analog of Tam, rapidly induced apoptosis in HMEC-E6 cells associated with an even more rapid decrease in phosphorylation of AKT at serine-473. Treatment of HMEC-E6 cells with 1.0 microM QTam resulted in a 50% decrease in mitochondrial transmembrane potential, sequential activation of caspase-9 and -3, and a 90% decrease in AKT Ser-473 phosphorylation. The effects of both Tam and QTam were blocked by expression of constitutively active AKT (myristoylated AKT or AKT-Thr308Asp/Ser473Asp). These data indicate that Tam and QTam induce apoptosis in HMEC-E6 cells through a plasma membrane-activated AKT-signaling pathway that results in (1) decreased AKT phosphorylation at Ser-473, (2) mitochondrial membrane depolarization, and (3) activated caspase-9 and -3.

Akt2, phosphatidylinositol 3-kinase, and PTEN are in lipid rafts of intestinal cells: role in absorption and differentiation

BACKGROUND AND AIMS

In intestinal Na absorptive cells, phosphatidylinositol 3-kinase (PI 3-K) is involved in rapid epidermal growth factor (EGF) stimulation of Na absorption by the brush border membrane (BBM) Na(+)/H(+) exchanger NHE3. However, how NHE3 is regulated by the PI 3-K pathway and the role of Akt2 are poorly defined.

METHODS

The localization of Akt, PI 3-K, and NHE3 was determined by either immunocytochemistry and/or membrane fractionation using OptiPrep density gradient centrifugation.

RESULTS

In ileum, active total Akt was present most in the villi and basal layer of the crypts, and Akt2 was mostly in villi. In villus cells, PI 3-K and Akt2 were mostly at the apical surface at which they were present partially in lipid rafts (LR). EGF increased PI 3-K and active Akt2 in ileal BBM at the same time that it increased PI 3-K-dependent trafficking of NHE3 to BBM and stimulation of Na absorption. However, Akt2 was only active in the detergent soluble (DS) pool and not LR of ileal BBM, which correlated with the presence of PTEN in LR. In Caco-2 cells, while EGF stimulated BB NHE3, Akt2 was active in both LR and DS pools. This correlated with the lack of PTEN in the LR of Caco-2 membranes. Akt2 also correlated with epithelial cell differentiation. Akt2 amount and activity were greater in differentiated than undifferentiated Caco-2 cells.

CONCLUSIONS

These results suggest that LR may play an important role in determining the function of PI 3-K/Akt2 signaling, including stimulation of intestinal Na absorption. These results also suggest that LR-associated Akt2 may be involved in enterocyte differentiation.

Epidermal growth factor receptor-dependent, NF-kappaB-independent activation of the phosphatidylinositol 3-kinase/Akt pathway inhibits ultraviolet irradiation-induced caspases-3, -8, and -9 in human keratinocytes

Both phosphatidylinositol 3-kinase (PI3K)/Akt and NF-kappaB pathways function to promote cellular survival following stress. Recent evidence indicates that the anti-apoptotic activity of these two pathways may be functionally dependent. Ultraviolet (UV) irradiation causes oxidative stress, which can lead to apoptotic cell death. Human skin cells (keratinocytes) are commonly exposed to UV irradiation from the sun. We have investigated activation of the PI3K/Akt and NF-kappaB pathways and their roles in protecting human keratinocytes (KCs) from UV irradiation-induced apoptosis. This activation of PI3K preceded increased levels (3-fold) of active/phosphorylated Akt. UV (50 mJ/cm2 from UVB source) irradiation caused rapid recruitment of PI3K to the epidermal growth factor receptor (EGFR). Pretreatment of KCs with EGFR inhibitor PD169540 abolished UV-induced Akt activation/phosphorylation, as did the PI3K inhibitors LY294002 or wortmannin. This inhibition of Akt activation was associated with a 3-4-fold increase of UV-induced apoptosis, as measured by flow cytometry and DNA fragmentation ELISA. In contrast to Akt, UV irradiation did not detectably increase nuclear localization of NF-kappaB, indicating that it was not strongly activated. Consistent with this observation, interference with NF-kappaB activation by adenovirus-mediated overexpression of dominant negative IKK-beta or IkappaB-alpha did not increase UV-induced apoptosis. However, adenovirus-mediated overexpression of constitutively active Akt completely blocked UV-induced apoptosis observed with PI3K inhibition by LY294002, whereas adenovirus mediated overexpression of dominant negative Akt increased UV-induced apoptosis by 2-fold. Inhibition of UV-induced activation of Akt increased release of mitochondrial cytochrome c 3.5-fold, and caused appearance of active forms of caspase-9, caspase-8, and caspase-3. Constitutively active Akt abolished UV-induced cytochrome c release and activation of caspases-9, -8, and -3. These data demonstrate that PI3K/Akt is essential for protecting human KCs against UV-induced apoptosis, whereas NF-kappaB pathway provides little, if any, protective role.

Hepatocyte growth factor exerts a proliferative effect on oval cells through the PI3K/AKT signaling pathway

Hepatocyte growth factor (HGF) is a potent mitogen for a variety of cells including hepatocytes. While rat oval cells are supposed to be one of hepatic stem cells, biological effects of HGF on oval cells and their relevant signal transduction pathways remain to be determined. We sought to investigate them on OC/CDE22 rat oval cells, which are established from the liver of rats fed a choline-deficient/DL-ethionine-supplemented diet. The oval cells were cultured on fibronectin-coated dishes and stimulated with recombinant HGF, transforming growth factor-alpha (TGF-alpha), and thrombopoietin (TPO) under the serum-free medium condition. HGF treatment enhanced [3H]thymidine incorporation into oval cells in a dose-dependent manner. On the contrary, treatment with TGF-alpha or TPO had no significant effects on [3H]thymidine incorporation into the oval cells. c-Met protein was phosphorylated at the tyrosine residues after the HGF treatment. AKT, extracellular signal-regulated kinase 1/2 (ERK1/2), and p70(s6k) were simultaneously activated after the HGF stimulation, peaking at 30min after the treatment. The activation of AKT, p70(s6k), and ERK1/2 induced by HGF was abolished by pre-treatment with LY294002, a phosphoinositide 3-OH kinase (PI3K) inhibitor, and U0126, a mitogen-activated protein kinase/ERK kinase (MEK) inhibitor, respectively. When the cells were pre-treated with LY294002 prior to the HGF stimulation, the proliferative action of HGF was completely abrogated, implying that the PI3K/AKT signaling pathway is responsible for the biological effect of HGF. These in vitro data indicate that HGF exerts a proliferative action on hepatic oval cells via activation of the PI3K/AKT signaling pathway.

Mesenchymal stem cells modified with Akt prevent remodeling and restore performance of infarcted hearts

Transplantation of adult bone marrow-derived mesenchymal stem cells has been proposed as a strategy for cardiac repair following myocardial damage. However, poor cell viability associated with transplantation has limited the reparative capacity of these cells in vivo. In this study, we genetically engineered rat mesenchymal stem cells using ex vivo retroviral transduction to overexpress the prosurvival gene Akt1 (encoding the Akt protein). Transplantation of 5 x 10(6) cells overexpressing Akt into the ischemic rat myocardium inhibited the process of cardiac remodeling by reducing intramyocardial inflammation, collagen deposition and cardiac myocyte hypertrophy, regenerated 80-90% of lost myocardial volume, and completely normalized systolic and diastolic cardiac function. These observed effects were dose (cell number) dependent. Mesenchymal stem cells transduced with Akt1 restored fourfold greater myocardial volume than equal numbers of cells transduced with the reporter gene lacZ. Thus, mesenchymal stem cells genetically enhanced with Akt1 can repair infarcted myocardium, prevent remodeling and nearly normalize cardiac performance.

Role of PI 3-kinase and PIP3 in submandibular gland branching morphogenesis

The mouse submandibular gland (SMG) epithelium undergoes extensive morphogenetic branching during embryonic development as the first step in the establishment of its glandular structure. However, the specific signaling pathways required for SMG branching morphogenesis are not well understood. Using E13 mouse SMG organ cultures, we showed that inhibitors of phosphatidylinositol 3-kinase (PI 3-kinase), wortmannin and LY294002, substantially inhibited branching morphogenesis in SMG. Branching morphogenesis of epithelial rudiments denuded of mesenchyme was inhibited similarly, indicating that PI 3-kinase inhibitors act directly on the epithelium. Immunostaining and Western analysis demonstrated that the p85 isoform of PI 3-kinase is expressed in epithelium at levels higher than in the mesenchyme. A target of PI 3-kinase, Akt/protein kinase B (PKB), showed decreased phosphorylation at Ser(473) by Western analysis in the presence of PI 3-kinase inhibitors. The major lipid product of PI 3-kinase, phosphatidylinositol 3,4,5-trisphosphate (PIP(3)), was added exogenously to SMG via a membrane-transporting carrier in the presence of PI 3-kinase inhibitors and was found to stimulate cleft formation, the first step of branching morphogenesis. Together, these data indicate that PI 3-kinase plays a role in the regulation of epithelial branching morphogenesis in mouse SMG acting through a PIP(3) pathway.

Epidermal growth factor receptor mediates increased cell proliferation, migration, and aggregation in esophageal keratinocytes in vitro and in vivo

Epidermal growth factor receptor (EGFR) overexpression is observed in a number of malignancies, especially those of esophageal squamous cell origin. However, little is known about the biological functions of EGFR in primary esophageal squamous epithelial cells. Using newly established primary human esophageal squamous epithelial cells as a platform, we overexpressed EGFR through retroviral transduction and established novel three-dimensional organotypic cultures. Additionally, EGFR was targeted in a cell type- and tissue-specific fashion to the esophageal epithelium in transgenic mice. EGFR overexpression in primary esophageal keratinocytes resulted in the biochemical activation of Akt and STAT pathways and induced enhanced cell migration and cell aggregation. When established in organotypic culture, EGFR-overexpressing cells had evidence of epithelial cell hyperproliferation and hyperplasia. These effects were also observed in EGFR-overexpressing transgenic mice and the esophageal cell lines established thereof. In particular, EGFR-induced effects upon aggregation appear to be mediated through the relocalization of p120 from the cytoplasm to the membrane and increased interaction with E-cadherin. EGFR modulates cell migration through the up-regulation of matrix metalloproteinase 1. Taken together, the functional effects of EGFR overexpression help to explain its role in the initiating steps of esophageal squamous carcinogenesis.

ACh and adenosine activate PI3-kinase in rabbit hearts through transactivation of receptor tyrosine kinases

Adenosine and acetylcholine (ACh) trigger preconditioning through different signaling pathways. We tested whether either could activate myocardial phosphatidylinositol 3-kinase (PI3-kinase), a putative signaling protein in ischemic preconditioning. We used phosphorylation of Akt, a downstream target of PI3-kinase, as a reporter. Exposure of isolated rabbit hearts to ACh increased Akt phosphorylation 2.62 +/- 0.33 fold (P = 0.001), whereas adenosine caused a significantly smaller increase (1.52 +/- 0.08 fold). ACh-induced activation of Akt was abolished by the tyrosine kinase blocker genistein indicating at least one tyrosine kinase between the muscarinic receptor and Akt. ACh-induced Akt activation was blocked by the Src tyrosine kinase inhibitor 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2) and by 4-(3-chloroanilino)-6,7-dimethoxyquinazoline (AG-1478), an epidermal growth factor receptor (EGFR) inhibitor, suggesting phosphorylation of a receptor tyrosine kinase in an Src tyrosine kinase-dependent manner. ACh caused tyrosine phosphorylation of the EGFR, which could be blocked by PP2, thus supporting this receptor hypothesis. AG-1478 failed to block the cardioprotection of ACh, however, suggesting that other receptor tyrosine kinases might be involved. Therefore, G(i) protein-coupled receptors can activate PI3-kinase/Akt through transactivation of receptor tyrosine kinases in an Src tyrosine kinase-dependent manner.

Activation of ERK and Akt signaling in focal cerebral ischemia: modulation by TGF-alpha and involvement of NMDA receptor

Cerebral ischemia activates ERK and Akt pathways. We studied whether these activations were affected by treatment with the protective growth factor transforming growth factor-alpha (TGF-alpha), and whether they were mediated through N-methyl D-aspartate (NMDA) receptors. The middle cerebral artery was occluded in rats and signaling was studied 1 h later. Noncompetitive NMDA receptor antagonist MK-801 was injected i.p. before the occlusion, whereas in other rats TGF-alpha was given intraventricularly before and after occlusion. Ischemia caused ERK phosphorylation in the nucleus, localized in the endothelium and neurons. Phosphorylation of ERK was prevented by TGF-alpha, but it was enhanced in the nucleus and cytoplasm by MK-801. Also, MK-801 but not TGF-alpha increased p-Akt. Results suggest that preventing ERK activation is related to the protective effect of TGF-alpha, whereas the protective effect of MK-801 is associated with activation of pro-survival Akt. While results support that NMDA receptor signaling precludes Akt activation, we did not find evidence to support that it underlies ischemia-induced ERK phosphorylation. This study illustrates that neuroprotection results from a fine balance between death and survival signaling pathways.

Epidermal growth factor and transforming growth factor alpha mimic the effects of insulin in human fat cells and augment downstream signaling in insulin resistance

The ability of the growth factors epidermal growth factor (EGF), transforming growth factor alpha, and platelet-derived growth factor to exert insulin-like effects on glucose transport and lipolysis were examined in human and rat fat cells. No effects were found in rat fat cells, whereas EGF (EC(50) for glucose transport approximately 0.02 nm) and transforming growth factor alpha (EC(50) approximately 0.2 nm), but not platelet-derived growth factor, mimicked the effects of insulin (EC(50) approximately 0.2 nm) on both pathways. EGF receptors, but not EGF, were abundantly expressed in human fat cells as well as in human skeletal muscle. EGF increased the tyrosine phosphorylation of several proteins (the EGF receptor, insulin receptor substrate (IRS)-1, IRS-2, and Grb2-associated binder 1), whereas Shc and Gab2 were only weakly and inconsistently phosphorylated. p85, the regulatory subunit of phosphatidylinositol 3-kinase (PI 3-kinase), was also found to associate with all of these docking molecules, showing that EGF activated PI 3-kinase pools that were additional to those of insulin. EGF and/or insulin increased protein kinase B/Akt serine phosphorylation to a similar extent, whereas mitogen-activated protein kinase phosphorylation was more pronounced for EGF than for insulin. The impaired insulin-stimulated downstream signaling, measured as protein kinase B/Akt serine phosphorylation, in insulin-resistant cells (Type 2 diabetes) was improved by the addition of EGF. Thus, EGF receptors, but not EGF, are abundantly expressed in human fat cells and skeletal muscle. EGF mimics the effects of insulin on both the metabolic and mitogenic pathways but utilize in part different signaling pathways. Both insulin and EGF increase the tyrosine phosphorylation and activation of IRS-1 and IRS-2, whereas EGF is also capable of activating additional PI 3-kinase pools and, thus, can augment the downstream signaling of insulin in insulin-resistant states like Type 2 diabetes.

Elevated Akt phosphorylation as an indicator of renal tubular epithelial cell stress

Characterization of the phosphoinositide 3-kinase-signaling pathway in a human renal tubular epithelial cell (TEC) line HKC-8 revealed high levels of Akt phosphorylation in serum-starved cultures. In contrast to Erk1/2, little additional phosphorylation of Akt was observed after cytokine or serum stimulation. Replacement of the conditioned medium attenuated Akt phosphorylation such that 90 min after the addition of warmed serum-free media, Akt phosphorylation had fallen sufficiently to allow an epidermal growth factor-stimulated increase to be detected readily. Although the mechanism by which the phosphoinositide 3-kinase/Akt pathway is activated in serum-starved TEC is unknown, the mediator responsible is secreted from these cells. Thus, conditioned media removed from a dish of quiescent TECs stimulated Akt phosphorylation in washed TEC cultures within 10 min. Biochemical characterization of the bioactive agent identified a heat labile factor of small apparent molecular mass. The basal level of Akt phosphorylation observed in serum-starved cultures was inhibited by wortmannin at concentrations that demonstrated its dependence on 3-phosphoinositide synthesis (IC(50) = 8 nm). Regular removal of conditioned media from TEC cultures and its replacement with serum free media resulted in a sustained attenuation of Akt phosphorylation. Interestingly, after 5 days of this treatment, washed TEC cultures contained a greater number of viable cells than cultures maintained in conditioned media throughout. This observation was not explained by a difference in the rate of DNA synthesis. Instead, the number of cells undergoing apoptosis increased markedly in the unwashed cultures. Consequently, we propose that in HKC-8 cells Akt phosphorylation is up-regulated in an effort to minimize cell death. This stress-activated response is initiated by a factor secreted into the conditioned medium that stimulates the phosphoinositide 3-kinase signaling pathway.

Essential role of AKT-1/protein kinase B alpha in PTEN-controlled tumorigenesis

PTEN is mutated at high frequency in many primary human cancers and several familial cancer predisposition disorders. Activation of AKT is a common event in tumors in which the PTEN gene has been inactivated. We previously showed that deletion of the murine Pten gene in embryonic stem (ES) cells led to increased phosphatidylinositol triphosphate (PIP(3)) accumulation, enhanced entry into S phase, and better cell survival. Since PIP(3) controls multiple signaling molecules, it was not clear to what degree the observed phenotypes were due to deregulated AKT activity. In this study, we mutated Akt-1 in Pten(-/-) ES cells to directly assess the role of AKT-1 in PTEN-controlled cellular processes, such as cell proliferation, cell survival, and tumorigenesis in nude mice. We showed that AKT-1 is one of the major downstream effectors of PTEN in ES cells and that activation of AKT-1 is required for both the cell survival and cell proliferation phenotypes observed in Pten(-/-) ES cells. Deletion of Akt-1 partially reverses the aggressive growth of Pten(-/-) ES cells in vivo, suggesting that AKT-1 plays an essential role in PTEN-controlled tumorigenesis.

The expression of keratin k10 in the basal layer of the epidermis inhibits cell proliferation and prevents skin tumorigenesis

Forced expression of K10, a keratin normally expressed in postmitotic, terminally differentiating epidermal keratinocytes, inhibits the progression of the cell cycle in cultured cells (Paramio, J. M., Casanova, M. Ll., Segrelles, C., Mittnacht, S., Lane, E. B., and Jorcano, J. L. (1999) Mol. Cell. Biol. 19, 3086-3094). This process requires a functional retinoblastoma (pRb) gene product and is mediated by K10-induced inhibition of Akt and PKCzeta, two signaling intermediates belonging to the phosphoinositide (PI) 3-kinase signal transduction pathway (Paramio, J. M., Segrelles, C., Ruiz, S., and Jorcano, J. L. (2001) Mol. Cell. Biol. 21, 7449-7459). Extending earlier in vitro studies to the in vivo situation, this work analyzes the alterations found in transgenic mice that ectopically express K10 in the proliferative basal cells of the epidermis. Increased expression of K10 led to a hypoplastic and hyperkeratotic epidermis due to a dramatic decrease in skin keratinocyte proliferation in association with the inhibition of Akt and PKCzeta activities. The inhibition of cell proliferation and Akt and PKCzeta activities was also observed although to a minor extent in low hK10-expressing mice. These animals displayed no overt epidermal phenotype nor overexpression of K10. In these non-phenotypic mice, ectopic K10 expression also resulted in decreased skin tumorigenesis. Collectively, these data demonstrate that keratin K10 in vivo functions include the control of epithelial proliferation in skin epidermis.

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

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

Role for the adaptor protein Grb10 in the activation of Akt

Grb10 is a member of the Grb7 family of adapter proteins lacking intrinsic enzymatic function and encodes functional domains including a pleckstrin homology (PH) domain and an SH2 domain. The role of different Grb10 splice variants in signal transduction of growth factors like insulin or insulin-like growth factor has been described as inhibitory or stimulatory depending on the presence of a functional PH and/or SH2 domain. Performing a yeast two-hybrid screen with the c-kit cytoplasmic tail fused to LexA as a bait and a mouse embryo cDNA library as prey, we found that the Grb10 SH2 domain interacted with the c-kit receptor tyrosine kinase. In the course of SCF-mediated activation of c-kit, Grb10 is recruited to the c-kit receptor in an SH2 domain- and phosphotyrosine-dependent but PH domain-independent manner. We found that Akt and Grb10 form a constitutive complex, suggesting a role for Grb10 in the translocation of Akt to the cell membrane. Indeed, coexpression studies revealed that Grb10 and c-kit activate Akt in a synergistic manner. This dose-dependent effect of Grb10 is wortmannin sensitive and was also seen at a lower level in cells in which c-kit was not expressed. Expression of a Grb10 mutant lacking the SH2 domain as well as a mutant lacking the PH domain did not influence Akt activity. Grb10-induced Akt activation was observed without increased phosphatidylinositol 3-kinase (PI3-kinase) activity, suggesting that Grb10 is a positive regulator of Akt downstream of PI3-kinase. Significantly, deficient activation of Akt by a constitutively activated c-kit mutant lacking the binding site for PI3-kinase (c-kitD814V/Y719F) could be fully compensated by overexpression of Grb10. In Ba/F3 cells, the incapacity of c-kitD814V/Y719F to induce interleukin-3 (IL-3)-independent growth could be rescued by overexpression of Grb10. In contrast, expression of the SH2 deletion mutant of Grb10 together with c-kitD814V/Y719F did not render Ba/F3 cells independent of IL-3. In summary, we provide evidence that Grb10 is part of the c-kit signaling pathway and that the expression level of Grb10 critically influences Akt activity. We propose a model in which Grb10 acts as a coactivator for Akt by virtue of its ability to form a complex with Akt and its SH2 domain-dependent translocation to the cell membrane.

Ceramide-induced inhibition of Akt is mediated through protein kinase Czeta: implications for growth arrest

We recently demonstrated that ceramide-coated balloon catheters limit vascular smooth muscle cell (VSMC) growth after stretch injury in vivo. In that study, inhibition of VSMC growth was correlated with a decrease in phosphorylation of the cell survival kinase Akt (protein kinase B). Utilizing cultured A7r5 VSMCs, we have now examined the mechanism by which ceramide inhibits Akt phosphorylation/activation. Our initial studies showed that ceramide-induced inhibition of Akt phosphorylation was not mediated through diminution in phosphoinositide 3-kinase activity. As we have previously demonstrated that protein kinase Czeta (PKCzeta) is a target of ceramide, we proposed an alternative signaling mechanism by which ceramide induces inhibition of Akt through activation of PKCzeta. We demonstrate that C(6)-ceramide (but not the inactive analog dihydro-C(6)-ceramide) induced PKCzeta activity and also caused a selective increase in the association between Akt and PKCzeta, without affecting PKCepsilon, in A7r5 cells. In addition, the ability of ceramide to significantly decrease platelet-derived growth factor-induced Akt phosphorylation or cell proliferation was abrogated in A7r5 cells overexpressing a dominant-negative mutant of PKCzeta. Taken together, these data suggest that ceramide-mediated activation of PKCzeta leads to diminished Akt activation and consequent growth arrest in VSMCs. The therapeutic potential for ceramide to limit dysregulated VSMC growth has direct applicability to vascular diseases such as restenosis and atherosclerosis.

Differential regulation of Akt kinase isoforms by the members of the TCL1 oncogene family

The members of the TCL1 proto-oncogene family (TCL1, MTCP1, and TCL1b) bind to Akt1, increasing its phosphorylation status and kinase activity. This is thought to be secondary to the formation of TCL1-Akt oligomers within which Akt is preferentially phosphorylated. Here we show that, in contrast to Akt1 and Akt2, which bind to all members of the TCL1 family, Akt3 specifically interacts with TCL1 but not with MTCP1 or TCL1b. This association is functional, as the presence of TCL1 but not MTCP1 or TCL1b increased Akt3 kinase activity in in vitro kinase assays. Functional specificity is determined by the Akt pleckstrin homology domain as chimeric Akt1, where Akt1 PH domain was replaced by that of Akt3 was no longer able to interact with MTCP1 or TCL1b and its kinase activity was solely enhanced by TCL1. Moreover, we show that, in TCL1-overexpressing SUPT-11 T-cell leukemia and P3HR-1 Burkitt's lymphoma cell lines, TCL1 interacts with endogenous Akt1, Akt2, and Akt3. TCL1 enhanced hetero-oligomerization of Akt1 with Akt3 and as a consequence facilitated transphosphorylation of Akt molecules, which may contribute to Akt activation and TCL1-induced leukemogenesis in vivo.

Signaling mechanisms of heparin-binding epidermal growth factor-like growth factor in vascular smooth muscle cells

A host of growth factors have been implicated in vascular pathologies; one such factor is heparin-binding epidermal growth factor-like growth factor (HB-EGF). Although HB-EGF has been shown to stimulate mitogenesis and chemotaxis of vascular smooth muscle cells (VSMC), its signaling mechanism remains undefined. In this study, we examined possible signal transduction pathways by which HB-EGF leads to mitogenesis in cultured rat VSMC. HB-EGF induced phosphorylation of the EGF receptor (EGFR) with maximum phosphorylation at 0.5 to 1 minute, whereas erbB4, the other receptor to which HB-EGF binds, was not activated on HB-EGF stimulation. HB-EGF induced a time- and concentration-dependent phosphorylation of mitogen-activated protein kinase (MAPK; p42/44 MAPK, extracellular signal-regulating kinase [ERK] 1/2). It also activated Akt and p70S6 kinase (p70S6K) but not p38 MAPK. HB-EGF-induced phosphorylation of these kinases was blocked by the EGFR kinase inhibitor AG1478. To investigate signaling molecules involved in HB-EGF-induced DNA synthesis, we pretreated VSMC with the specific ERK kinase mitogen-activated kinase (MEK) inhibitor PD98059 and the phosphatidylinositol 3-kinase inhibitor LY294002. These inhibitors significantly blocked HB-EGF-induced DNA synthesis. PD98059 inhibited HB-EGF-induced ERK activation, whereas it had no effect on Akt activation by HB-EGF. By contrast, LY294002 inhibited HB-EGF-induced Akt and p70S6K activation without effecting ERK activation by HB-EGF. These results demonstrate that HB-EGF-induced mitogenesis requires both ERK and phosphatidylinositol 3-kinase (Akt and p70S6K) pathways activated through EGFR, thereby providing a new mechanistic insight by which HB-EGF contributes to vascular remodeling.