Heregulin regulation of Akt/protein kinase B in breast cancer cells

Antofine suppresses endotoxin-induced inflammation and metabolic disorder via AMP-activated protein kinase

The inhibition of activated macrophages has been used to develop anti-inflammatory agents for therapeutic intervention to human diseases that cause excessive inflammatory responses. Antofine, a phenanthroindolizidine alkaloid, has a potent anti-inflammatory effect. However, the molecular mechanisms of its anti-inflammatory activity have not yet been fully detailed. In this study, we comprehensively explored the anti-inflammatory effects of antofine on endotoxin-induced inflammation in macrophages using cDNA microarray analysis, thereby elucidating the potential mechanism by which antofine suppresses inflammation. Antofine significantly suppressed the secretion of proinflammatory cytokines such as TNFα and IL-1β and the production of iNOS in LPS-activated Raw264.7 macrophage cells. In addition, antofine can suppress the expressions of several inflammation-related genes (such as ARG-1, IL1F9, IL-10, and IL-33) and extracellular matrix genes (such as TNC and HYAL1), as well as a vasopressor gene (EDN1) in activated macrophage cells, that are induced by LPS stimulation. The gene expression profiles analyzed by GeneMANIA software showed that antofine not only contributed anti-inflammatory activity but also modulated the cellular metabolism via AMPK. Furthermore, antofine also modulated the activation of AMPK and caspase-1, the key regulator in inflammasome-mediated IL-1β maturation, in activated macrophage cells. In conclusion, these data indicated that antofine potentially can not only contribute an anti-inflammatory effect but can also attenuate the metabolic disorders induced by inflammation via AMPK.

The in vitro influences of epidermal growth factor and heregulin-β1 on the efficacy of trastuzumab used in Her-2 positive breast adenocarcinoma

Background

Human epidermal growth factor receptor-2 (Her-2) is over expressed in approximately 25-30% of all primary breast tumors resulting in a distinctive breast cancer subtype associated with a poor prognosis and a decrease in overall survival. Trastuzumab (Herceptin®), an anti-Her-2 monoclonal antibody, has dramatically altered the prognosis of Her-2 positive breast cancer. Trastuzumab is, however, associated with primary and acquired resistance.

Aim and methods

To investigate the in-vitro effects of trastuzumab on cell viability (tetrazolium conversion assay), cell cycling (propidium iodide staining), apoptosis (executioner caspases and annexin-V) and relative surface Her-2 receptor expression (anti-Her-2 affibody molecule) in Her-2-positive (SK-Br-3) and oestrogen receptor positive (MCF-7) breast adenocarcinoma cells and to determine potential augmentation of these effects by two endogenous ligands, epidermal growth factor (EGF) and heregulin-β1 (HRG- β1).

Results

Cell viability was decreased in SK-Br-3 cells by exposure to trastuzumab. This was associated with G1 accumulation and decreased relative surface Her-2 receptor density, supporting the cytostatic nature of trastuzumab in vitro. SK-Br-3 cells exposed to EGF and heregulin-β1 produced differential cell responses alone and in combination with trastuzumab, in some instances augmenting cell viability and cell cycling. Relative surface Her-2 receptor density was reduced substantially by trastuzumab, EGF and heregulin-β1. These reductions were amplified when ligands were used in combination with trastuzumab.

Conclusion

Cell type specific interactions of endogenous ligands appear to be dependent on absolute Her-receptor expression and cross activation of signaling pathways. This supports the notion that receptor density of Her-family members and multiplicity of growth ligands are of mutual importance in breast cancer cell proliferation and therefore also in resistance associated with trastuzumab.

Estrogen receptor β represses Akt signaling in breast cancer cells via downregulation of HER2/HER3 and upregulation of PTEN: implications for tamoxifen sensitivity

Introduction

The inhibition of estrogen receptor (ER) α action with the ER antagonist tamoxifen is an established treatment in the majority of breast cancers. De novo or acquired resistance to this therapy is common. Expression of ERβ in breast tumors has been implicated as an indicator of tamoxifen sensitivity. The mechanisms behind this observation remain largely uncharacterized. In the present study, we investigated whether ERβ can modulate pathways implicated in endocrine resistance development.

Methods

T47-D and MCF-7 ERα-expressing breast cancer cells with tetracycline-regulated expression of ERβ were used as a model system. Expression levels and activity of known regulators of endocrine resistance were analyzed by performing quantitative polymerase chain reaction assays, Western blot analysis and immunostaining, and sensitivity to tamoxifen was investigated by using a cell proliferation kit.

Results

Expression of ERβ in ERα-positive T47-D and MCF-7 human breast cancer cells resulted in a decrease in Akt signaling. The active form of an upstream regulator of Akt, proto-oncogene c-ErbB-2/receptor tyrosine kinase erbB-3 (HER2/HER3) receptor dimer, was also downregulated by ERβ. Furthermore, ERβ increased expression of the important inhibitor of Akt, phosphatase and tensin homologue deleted on chromosome 10 (PTEN). Importantly, ERβ expression increased the sensitivity of these breast cancer cells to tamoxifen.

Conclusions

Our results suggest a link between expression of ERβ and endocrine sensitivity by increasing PTEN levels and decreasing HER2/HER3 signaling, thereby reducing Akt signaling with subsequent effects on proliferation, survival and tamoxifen sensitivity of breast cancer cells. This study supports initiatives to further investigate whether ERβ presence in breast cancer samples is an indicator for endocrine response. Current therapies in ERα-positive breast cancers aim to impair ERα activity with antagonists or by removal of endogenous estrogens with aromatase inhibitors. Data from this study could be taken as indicative for also using ERβ as a target in selected groups of breast cancer.

Following nerve injury neuregulin-1 drives microglial proliferation and neuropathic pain via the MEK/ERK pathway

Following peripheral nerve injury microglia accumulate within the spinal cord and adopt a proinflammatory phenotype a process which contributes to the development of neuropathic pain. We have recently shown that neuregulin-1, a growth factor released following nerve injury, activates erbB 2, 3, and 4 receptors on microglia and stimulates proliferation, survival and chemotaxis of these cells. Here we studied the intracellular signaling pathways downstream of neuregulin-1-erbB activation in microglial cells. We found that neuregulin-1 in vitro induced phosphorylation of ERK1/2 and Akt without activating p38MAPK. Using specific kinase inhibitors we found that the mitogenic effect of neuregulin-1 on microglia was dependant on MEK/ERK1/2 pathway, the chemotactic effect was dependant on PI3K/Akt signaling and survival was dependant on both pathways. Intrathecal treatment with neuregulin-1 was associated with microgliosis and development of mechanical and cold pain related hypersensitivity which was dependant on ERK1/2 phosphorylation in microglia. Spinal nerve ligation results in a robust microgliosis and sustained ERK1/2 phosphorylation within these cells. This pathway is downstream of neuregulin-1/erbB signaling since its blockade resulted in a significant reduction in microglial ERK1/2 phosphorylation. Inhibition of the MEK/ERK1/2 pathway resulted in decreased spinal microgliosis and in reduced mechanical and cold hypersensitivity after peripheral nerve damage. We conclude that neuregulin-1 released after nerve injury activates microglial erbB receptors which consequently stimulates the MEK/ERK1/2 pathway that drives microglial proliferation and contributes to the development of neuropathic pain.

Direct binding of the EGF-like domain of neuregulin-1 to integrins ({alpha}v{beta}3 and {alpha}6{beta}4) is involved in neuregulin-1/ErbB signaling

Integrin-growth factor receptor cross-talk plays a role in growth factor signaling, but the specifics are unclear. In a current model, integrins and growth factor receptors independently bind to their ligands (extracellular matrix and growth factors, respectively). We discovered that neuregulin-1 (NRG1), either as an isolated EGF-like domain or as a native multi-domain form, binds to integrins αvβ3 (with a K(D) of 1.36 × 10(-7) m) and α6β4. Docking simulation predicted that three Lys residues at positions 180, 184, and 186 of the EGF-like domain are involved in integrin binding. Mutating these residues to Glu individually or in combination markedly suppressed integrin binding and ErbB3 phosphorylation. Mutating all three Lys residues to Glu (the 3KE mutation) did not affect the ability of NRG1 to bind to ErbB3 but markedly reduced the ability of NRG1 to induce ErbB3 phosphorylation and AKT and Erk1/2 activation in MCF-7 and T47D human breast cancer cells. This suggests that direct integrin binding to NRG1 is critical for NRG1/ErbB signaling. Notably, stimulation of cells with WT NRG1 induced co-precipitation of ErbB3 with α6β4 and with αvβ3 to a much lower extent. This suggests that WT NRG1 induces integrin-NRG1-ErbB3 ternary complex formation. In contrast, the 3KE mutant was much less effective in inducing ternary complex formation than WT NRG1, suggesting that this process depends on the ability of NRG1 to bind to integrins. These results suggest that direct NRG1-integrin interaction mediates integrin-ErbB cross-talk and that α6β4 plays a major role in NRG-ErbB signaling in these cancer cells.

Emerging role of neuregulin as a modulator of muscle metabolism

Neuregulin was described initially as a neurotrophic factor involved in the formation of the neuromuscular junction in skeletal muscle. However, in recent years, neuregulin has been reported to be a myokine that exerts relevant effects on myogenesis and the regulation of muscle metabolism. In this new context, the rapid and chronic metabolic effects of neuregulin appear to be related to muscle contraction. Indeed, the effects of neuregulin resemble those of exercise, which are accompanied by an improvement in insulin sensitivity. In this review, we challenge the classical role assigned to neuregulin in muscle and propound the emerging concept of its involvement in the regulation of energetic metabolism and insulin responsiveness.

Neuregulin β1 enhances peak glutamate-induced intracellular calcium levels through endoplasmic reticulum calcium release in cultured hippocampal neuronsThis article is one of a selection of papers published in a special issue celebrating the 125th anniversary of the Faculty of Medicine at the University of Manitoba

Modulation of intracellular free calcium levels is the primary second messenger system of the neuronal glutamatergic system, playing a role in regulation of all major cellular processes. The protein neuregulin (NRG) β1 acts as an extracellular signaling ligand in neurons, rapidly regulating currents through ionotropic glutamate receptors. The effect NRG may have on glutamate-induced changes in intracellular free calcium concentrations has not been examined, however. In this study, cultured embryonic rat hippocampal neurons were treated with NRGβ1 to determine a possible effect on glutamate-induced intracellular calcium levels. Long-term (24 h), but not short-term (1 h), incubation with NRGβ1 resulted in a significantly greater glutamate-mediated acute peak elevation of intracellular calcium levels than occurred in vehicle-treated neurons. Long-term NRGβ1 incubation significantly enhanced calcium increase induced by specific stimulation of metabotropic glutamate receptors, but did not significantly alter the N-methyl d-aspartate (NMDA)- or KCl-induced calcium increase and paradoxically decreased the effect of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) treatment on intracellular calcium. Metabotropic glutamate receptors cause increased intracellular free calcium via release of calcium from intracellular stores; thus this system was examined in more detail. NRGβ1 treatment significantly (greater than 2-fold) enhanced calcium release from endoplasmic reticulum stores after stimulation of ryanodine receptors with caffeine, but did not significantly increase calcium release from endoplasmic reticulum mediated by inositol trisphosphate (IP3) receptors. In addition, ryanodine receptor inhibition with ruthenium red prevented the glutamate-induced increase in intracellular calcium levels in NRGβ1-treated neurons. These data show that long-term NRGβ1 treatment can enhance glutamate-induced peak intracellular calcium levels through metabotropic glutamate receptor activation by increasing endoplasmic reticulum calcium release through ryanodine receptors.

Phenanthrene-based tylophorine-1 (PBT-1) inhibits lung cancer cell growth through the Akt and NF-kappaB pathways

Tylophorine and related natural compounds exhibit potent antitumor activities. We previously showed that PBT-1, a synthetic C9-substituted phenanthrene-based tylophorine (PBT) derivative, significantly inhibits growth of various cancer cells. In this study, we further explored the mechanisms and potential of PBT-1 as an anticancer agent. PBT-1 dose-dependently suppressed colony formation and induced cell cycle G2/M arrest and apoptosis. DNA microarray and pathway analysis showed that PBT-1 activated the apoptosis pathway and mitogen-activated protein kinase signaling. In contrast, PBT-1 suppressed the nuclear factor kappaB (NF-kappaB) pathway and focal adhesion. We further confirmed that PBT-1 suppressed Akt activation accelerated RelA degradation via IkappaB kinase-alpha and down-regulated NF-kappaB target gene expression. The reciprocal recruitment of RelA and RelB on COX-2 promoter region led to down-regulation of transcriptional activity. We conclude that PBT-1 induces cell cycle G2/M arrest and apoptosis by inactivating Akt and by inhibiting the NF-kappaB signaling pathway. PBT-1 may be a good drug candidate for anticancer chemotherapy.

Akt as a therapeutic target in cancer

BACKGROUND

The phosphatidylinositol 3-kinase (PI3K)/phosphatase and tensin homolog (PTEN)/v-akt murine thymoma viral oncogene homolog (Akt)/mammalian target of rapamycin (mTOR) pathway is central in the transmission of growth regulatory signals originating from cell surface receptors.

OBJECTIVE

This review discusses how mutations occur that result in elevated expression the PI3K/PTEN/Akt/mTOR pathway and lead to malignant transformation, and how effective targeting of this pathway may result in suppression of abnormal growth of cancer cells.

METHODS

We searched the literature for articles which dealt with altered expression of this pathway in various cancers including: hematopoietic, melanoma, non-small cell lung, pancreatic, endometrial and ovarian, breast, prostate and hepatocellular.

RESULTS/CONCLUSIONS

The PI3K/PTEN/Akt/mTOR pathway is frequently aberrantly regulated in various cancers and targeting this pathway with small molecule inhibitors and may result in novel, more effective anticancer therapies.

Scrib regulates PAK activity during the cell migration process

Genetic studies have highlighted the key role of Scrib in the development of Metazoans. Deficiency in Scrib impairs many aspects of cell polarity and cell movement although the mechanisms involved remain unclear. In mammals, Scrib belongs to a protein complex containing betaPIX, an exchange factor for Rac/Cdc42, and GIT1, a GTPase activating protein for ARF6 implicated in receptor recycling and exocytosis. Here we show that the Scrib complex associates with PAK, a serine-threonine kinase family crucial for cell migration. PAK colocalizes with members of the Scrib complex at the leading edge of heregulin-treated T47D breast cancer cells. We demonstrate that the Scrib complex is required for epithelial cells and primary mouse embryonic fibroblasts to efficiently respond to chemoattractant cues. In Scrib-deficient cells, the pool of cortical PAK is decreased, thereby precluding its proper activation by Rac. Loss of Scrib also impairs the polarized distribution of active Rac at the leading edge and compromises the regulated activation of the GTPase in T47D cells and mouse embryonic fibroblasts. These data underscore the role of Scrib in cell migration and show the strong impact of Scrib in the function of PAK and Rac, two key molecules implicated in this process.

Bioinformatics-based discovery and characterization of an AKT-selective inhibitor 9-chloro-2-methylellipticinium acetate (CMEP) in breast cancer cells

AKT is a promising target for anticancer drug development. In this work, a bioinformatics approach was applied to search for AKT inhibitors based on the correlation analysis between phospho-Ser473 AKT expression level and the antiproliferative data of NCI small molecule compounds against NCI 60 cancer cell lines, the candidate compounds were then subject to AKT kinase assay. The possible effects of potent compound on PI3K/AKT, PDK1, and MAPK, its antiproliferative and apoptosis-inducing effects on breast cancer cells which have high-levels of AKT activation were assessed by Western blot analysis, cell viability assay, and apoptosis assay. One compound, CMEP (NSC632855, 9-chloro-2-methylellipticinium acetate) was identified with all three correlation algorithm, Pearson's, Sperman's, and Kendall's, showing a high-ranked correlation coefficient. CMEP inhibits only AKT, but does not inhibit PI3K, PDK1, or MAPK. CMEP also inhibits heregulin-induced AKT activation, does not inhibit heregulin-induced MAPK activation in MCF-7 breast cancer cells. Increased concentrations of ATP reverse the AKT inhibitory effect of CMEP. CMEP inhibits growth and induces apoptosis in breast cancer cells which have high-levels of AKT activation and lack functional PTEN; however, CMEP only shows a minimal activity in NIH3T3 cells which do not have AKT activation. In conclusion, a lead compound CMEP, as an AKT selective inhibitor has been identified started with a bioinformatics-based approach. CMEP inhibits growth and induces apoptosis in cancer cells which have high-levels of AKT activation and lack PTEN or harbor PTEN mutation.

Upstream signaling inhibition enhances rapamycin effect on growth of kidney cancer cells

OBJECTIVES

To test the hypothesis that blockage of epidermal growth factor receptor (EGFR) or methylethylketone (MEK)1/2 kinase activities impairs the growth of kidney cancer cells and magnifies the growth inhibitory effect of the mammalian target of rapamycin (mTOR) inhibitor rapamycin.

METHODS

The kidney cancer cells from eight cell lines (including a pair in which the VHL gene or an empty vector was transfected in a VHL(mut) cell line) were tested for the effect of treatment with an EGFR inhibitor or an MEK1/2 inhibitor on the phosphorylation status of the phosphatidyl inositol 3-OH kinase (PI3K) and mitogen-activated protein kinase (MAPK) pathways after stimulation with EGF. In vitro growth assays were performed with EGFR inhibitors (gefitinib or erlotinib) or with MEK1/2 inhibitors (UO126 or PD184352) alone or in combination with rapamycin. The effects of PD184352, rapamycin, and their combination in the cell cycle were evaluated by flow cytometry.

RESULTS

The growth suppressive effect of combined gefitinib (or erlotinib) and rapamycin was greater than the effect of each drug alone and was not dependent on VHL status. By affecting downstream signaling, the MEK1/2 inhibitors U0126 and PD184352 blocked growth more effectively than did the EGFR inhibitors in selected renal cell carcinoma lines; this effect was enhanced by the addition of rapamycin. At the cell cycle level, the combination resulted in enhanced G1 arrest. Although eIF4E overexpression has been suggested to make cells resistant to rapamycin, we observed marked growth inhibition with rapamycin as a single agent in SKRC39, which has marked overexpression of eIF4E.

CONCLUSIONS

The results of our study have shown that combined mTOR and other upstream inhibitors have strong potential in the treatment of renal cell carcinoma.

The effect of estradiol on in vivo tumorigenesis is modulated by the human epidermal growth factor receptor 2/phosphatidylinositol 3-kinase/Akt1 pathway

To determine whether the epidermal growth factor receptor 2 (ErbB2) and Akt1 can alter the in vivo growth of MCF-7 cells, parental cells or cells stably transfected with constitutively active Akt1 (myr-Akt1) or dominant-negative Akt1 mutants (K179M-Akt1 and R25C-Akt1) were implanted into athymic nude mice. Tumor growth was monitored in the presence or absence of the antiestrogen tamoxifen and the selective ErbB2 inhibitor, AG825. MCF-7 [parental or empty vector transfected, cytomegalovirus (CMV)] and myr-Akt1 cells formed tumors upon estradiol supplementation after 20-30 d (59-, 29-, and 17-fold increase in tumor volume, respectively). Tamoxifen and AG825 blocked the estradiol effect by 93 and 96% in MCF-7 xenografts, 88 and 81% in CMV xenografts, and 91% in myr-Akt1 xenografts. Furthermore, AG825 suppressed the growth of established tumors in CMV and myr-Akt1 inoculated animals by 68 and 75%, respectively, as compared with continued estrogen supplementation, suggesting a role for ErbB2. When K179M-Akt1 or R25C-Akt1 cells were injected into ovariectomized animals, tumor growth was reduced upon estradiol treatment by 95% and 98%, respectively, supporting a role for Akt1. In contrast to ovariectomized animals, in intact animals, myr-Akt1 cells could establish tumors without estradiol priming after 40-50 d (20-fold increase in tumor volume). Loss of Akt1 phosphorylation was associated with tumor growth inhibition. Immunohistochemical assays showed that in tumors from parental and CMV xenografts, estradiol decreased estrogen receptor-alpha expression and induced progesterone receptor expression and Akt phosphorylation, effects that were inhibited by tamoxifen, AG825, and R25C-Akt1 by 89, 82, and 77% for progesterone receptor expression and 48, 66, and 73% for pAkt expression, respectively. Cumulatively, our results suggest that Akt1 and ErbB2 are involved in in vivo tumorigenesis and modulation of estrogen receptor-alpha expression and activity.

Oncological implications of hypoxia inducible factor-1alpha (HIF-1alpha) expression

Solid tumours contain regions of hypoxia, which may be a prognostic indicator and determinant of malignant progression, metastatic development and chemoradio-resistance. The degree of intra-tumoural hypoxia has been shown to be positively correlated with the expression of the transcription factor hypoxia-inducible factor 1. HIF-1 is composed of 2 sub-units, namely HIF-1alpha and HIF-1beta. The production of hypoxia inducible factor 1-alpha has been identified as a key element in allowing cells to adapt and survive in a hostile hypoxic environment via a variety of pathways. HIF-1alpha is stabilised by hypoxia at the protein level, and also by the oncogenes HER2neu, v-src and ras. There are over 60 target genes for HIF-1, many of which are activated in cancers in comparison to equivalent normal tissues. Chemotherapeutic modulation of HIF-1 pathways has shown promise for patients with chemo-radio resistant or recurrent tumours in Phase II clinical trials. We herein review the existing literature on hypoxia inducible factor-1alpha, particularly its role in carcinogenesis and clinical implications of its over-expression.

Oligonucleotide microarray analysis of ameloblastoma compared with dentigerous cyst

BACKGROUND

Ameloblastoma is a benign, but locally invasive tumor known for its high rate of recurrence. However, few comprehensive genetic studies have been conducted about its tumorigenesis. Our aim was to identify possible genes involved in the development and progression of ameloblastoma, using microarray analysis with dentigerous cyst as a control.

METHODS

Total RNA was extracted from two fresh dentigerous cysts and ameloblastoma specimens. Following microarray analysis, semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry were performed on selected genes.

RESULTS

Seventy-three genes were overexpressed and 49 were underexpressed. These genes were divided into categories according to function. The microarray results for 13 selected genes were verified with semiquantitative RT-PCR.

CONCLUSIONS

We identified important genes related to the development and progression of ameloblastoma through a large-scale gene expression analysis. This study will stimulate further investigations on genes significant for early diagnosis and prognosis of ameloblastoma.

HER2 signaling downregulation by trastuzumab and suppression of the PI3K/Akt pathway: an unexpected effect on TRAIL-induced apoptosis

We investigated whether HER2 downregulation by trastuzumab modulates the responsiveness of breast cancer cells to TNF-related apoptosis-inducing ligand (TRAIL). Interestingly, in contrast to increased response to TRAIL in SKBr3 cells, trastuzumab decreased the susceptibility of BT474 cells to TRAIL. This decrease was also observed after exogenous inhibition of PI3-K/Akt kinase, but not MAPK/ERK kinase (MEK)/mitogen-activated protein kinase (MAPK). In BT474 cells, but not SKBr3 cells, inhibition of the HER2/phosphatidylinositol 3' kinase (PI3K)/Akt pathway resulted in downregulation of the pro-apoptotic receptors TRAIL-receptor 1 (TRAIL-R1) and TRAIL-R2. TRAIL-induced caspase-8 activation, Bid processing, drop of DeltaPsi(m), and poly ADP-ribose polymerase (PARP) cleavage but not in caspase-9 activation, and these events were inhibited in HER2/PI3K/Akt-suppressed BT474 cells, which on the other hand exhibited downregulation of Bcl-xL and increased response to mitomycin C. We show that HER2/PI3K/Akt pathway may play a specific pro-apoptotic role in certain cell type by inducing TRAIL-R1 and -R2 expression and thereby enhancing responsiveness to TRAIL.

EGFR gene amplification in breast cancer: correlation with epidermal growth factor receptor mRNA and protein expression and HER-2 status and absence of EGFR-activating mutations

The human epidermal growth factor receptor (HER) family of receptor tyrosine kinase has been extensively studied in breast cancer; however, systematic studies of EGFR gene amplification and protein overexpression in breast carcinoma are lacking. We studied EGFR gene amplification by chromogenic in situ hybridization (CISH) and protein expression by immunohistochemistry in 175 breast carcinomas, using tissue microarrays. Tumors with >5 EGFR gene copies per nucleus were interpreted as positive for gene amplification. Protein overexpression was scored according to standardized criteria originally developed for HER-2. EGFR mRNA levels, as measured by Affymetrix U133 Gene Chip microarray hybridization, were available in 63 of these tumors. HER-2 gene amplification by fluorescence in situ hybridization (FISH) and protein overexpression by immunohistochemistry were also studied. EGFR gene amplification (copy number range: 7-18; median: 12) was detected in 11/175 (6%) tumors, and protein overexpression was found in 13/175 (7%) tumors. Of the 11 tumors, 10 (91%) with gene amplification also showed EGFR protein overexpression (2+ or 3+ by immunohistochemistry). The EGFR mRNA level, based on Affymetrix U133 chip hybridization data, was increased relative to other breast cancer samples in three of the five tumors showing gene amplification. Exons 19 and 21 of EGFR, the sites of hotspot mutations in lung adenocarcinomas, were screened in the 11 EGFR-amplified tumors but no mutations were found. Three of these 11 tumors also showed HER-2 overexpression and gene amplification. Approximately 6% of breast carcinomas show EGFR amplification with EGFR protein overexpression and may be candidates for trials of EGFR-targeted antibodies or small inhibitory molecules.

Herceptin-induced inhibition of ErbB2 signaling involves reduced phosphorylation of Akt but not endocytic down-regulation of ErbB2

The anti-proliferative effect of the ErbB2 specific antibody Herceptin in cells overexpressing ErbB2 has previously been explained by endocytic downregulation of ErbB2. However, in the following, we demonstrate that Herceptin inhibited proliferation of ErbB2 overexpressing cells without downregulating ErbB2. Herceptin did also not induce endocytosis of ErbB2. Herceptin was found to blunt proliferation of SKBr3 cells overexpressing EGFR, ErbB2, and ErbB3 and expressing functional PTEN, probably by recruiting PTEN to the plasma membrane. Akt was found to be constitutively phosphorylated both in SKBr3 cells overexpressing EGFR, ErbB2 and ErbB3, and in SKOv3 cells, overexpressing EGFR and ErbB2. However, phosphorylation of Akt was inhibited by Herceptin only in SKBr3 cells. SKOv3 cells, which lack the tumour suppressor protein Ras homolog member I, was found to have constitutively phosphorylated mitogen activated protein kinase and functionally increased Ras activity. SKOv3 cells further had low expression levels of PTEN. We thus confirm that the anti-proliferative effect of Herceptin in SKBr3 cells is due to recruitment of PTEN to the plasma membrane and conclude that Herceptin does not blunt phosphatidyl inositol 3 kinase-induced growth in cells with constitutive Ras activity. We further conclude that endocytic downregulation of ErbB2 does not contribute to Herceptin's antiproliferative effect.

The efficacy of Herceptin therapies is influenced by the expression of other erbB receptors, their ligands and the activation of downstream signalling proteins

ErbB2 and EGFR are attractive oncology therapeutic targets as their overexpression in tumors predicts a poorer clinical outcome in a variety of epithelial malignancies. However, clinical results with therapeutic compounds targeting these receptors have been mixed. Therefore, there is a need for improved predictive biomarkers for these targeted therapeutics. In this study we analysed tissue microarrays of patients treated with combination chemotherapy and Herceptin for expression or phosphorylation of signalling proteins associated with erbB receptors to identify protein biomarkers that are predictive of breast cancer patient response. A comparison of expression or phosphorylation of these markers with patient outcome revealed that response to Herceptin depended not only on expression levels of erbB2 but also on expression of EGFR, expression of erbB ligands, expression of other receptors and phosphorylation of downstream proteins. Elucidating the biological effects of EGFR/erbB2 targeted therapeutics will enable patient tumor profiling to identify likely responders and the determination of biologically effective doses that allows chronic administration of these agents in order to maximise efficacy.

Involvement of the Akt/PKB signaling pathway with disease processes

Akt/PKB is a serine/threonine kinase, which controls vital cellular functions such as cell survival/apoptosis, cell cycle progression and glucose metabolism. Akt/PKB acts down-stream from growth factors and hormones and is a key mediator of their pro-survival, proliferative and metabolic effects. Akt/PKB carries out these diverse tasks through phosphorylation of a number of cellular substrates. The substrates of Akt/PKB, which promote the inhibition of apoptosis after being phosphorylated by Akt, include the Forkhead transcription factors and the Bcl-2 family member Bad. The cyclin dependent kinase inhibitors are substrates of Akt which when phosphorylated relinquish their inhibitory influence on cell cycle progression. Akt mediates many of the stimulatory effects of insulin on glucose metabolism through deactivation of glycogen synthase kinase, activation of phosphofructokinase, and modulation of glucose transporter activity. Consequently, Akt can be implicated in the pathological processes, which are associated with defects in regulation of apoptosis/survival and energy metabolism.

Increased Constitutive Activity of PKB/Akt in Tamoxifen Resistant Breast Cancer MCF-7 Cells

The tamoxifen-resistant (TAM-R) MCF-7 breast cancer cell line has been used as a model to identify the signalling pathways that enable resistant cancer cells to grow independently of steroid hormones. In TAM-R cells, peptide growth factor signalling pathways appear to be important in modified cell behaviour, growth and survival. The PI3 kinase signalling components Akt1 and Akt2 are expressed at similar levels by both parental wild-type MCF-7 and TAM-R cells, but Akt1 phosphorylation is significantly increased in TAM-R cells grown under basal conditions. High levels of basal Akt, GSK3 alpha / beta and p70S6 kinase phosphorylation are all inhibited by the PI3 kinase inhibitor, LY 294002. The ligands for the EGFR/erbB1 receptor, EGF (epidermal growth factor) and TGF alpha (transforming growth factor- alpha ) demonstrate an increased ability to activate Akt in TAM-R compared with parental MCF-7 cells and it is proposed that the preferred autocrine or paracrine activation of Akt occurs via the erbB heterodimer EGFR/erbB2 in TAM-R cells. Akt phosphorylation is reduced by gefitinib ("Iressa"/ZD1839). The results suggest that the PI3 kinase pathway plays a role in proliferation of TAM-R cells and is important in the increased EGF induced membrane ruffling detected in the resistant cells. Increased Akt1 activation may contribute to the aggressive phenotype of tamoxifen resistant ER (oestrogen receptor) positive breast cancers.

Review of epidermal growth factor receptor biology

The epidermal growth factor receptor (EGFR) is a transmembrane glycoprotein that constitutes one of four members of the erbB family of tyrosine kinase receptors. Binding of EGFR to its cognate ligands leads to autophosphorylation of receptor tyrosine kinase and subsequent activation of signal transduction pathways that are involved in regulating cellular proliferation, differentiation, and survival. Although present in normal cells, EGFR is overexpressed in a variety of tumor cell lines and has been associated with poor prognosis and decreased survival. EGFR activation also plays a role in resistance to chemotherapy and radiation treatment in tumor cells. Over the past two decades, much effort has been directed at developing anticancer agents that can interfere with EGFR activity. The most common pharmacologic approaches to inhibiting EGFR have been to develop monoclonal antibodies and small-molecule inhibitors. Monoclonal antibodies block ligand binding to the extracellular domain, whereas the small-molecule inhibitors exert their effects at the intracellular portion of the receptor to prevent tyrosine kinase phosphorylation and subsequent activation of signal transduction pathways. A number of EGFR inhibitors have been developed that can arrest tumor growth and, in some cases, cause tumor regression. When used in combination with cytotoxic treatments, chemotherapy, and radiation, EGFR inhibitors have been able to potentiate their anticancer activity.

Autocrine signalling through erbB receptors promotes constitutive activation of protein kinase B/Akt in breast cancer cell lines

The protein kinase PKB/Akt plays a pivotal role in promoting cell survival and proliferation. This study investigated the regulation of PKB/Akt activity in breast cancer cells. In primary invasive breast cancers PKB/Akt exhibited elevated phosphorylation at regulatory site Ser473 in 80% of cases, using immunohistochemistry. The degree of phospho-PKB/Akt immunoreactivity was positively correlated with the extent of its nuclear accumulation. Moderate/strong staining was seen in 31% of the samples but was absent in tumour-associated normal breast epithelia. To examine the mechanisms of PKB/Akt activation, we studied its phosphorylation in a panel of breast cancer cell lines. PKB/Akt was constitutively phosphorylated on both regulatory sites (Thr308 and Ser473) in the absence of serum growth factors in 7 of 8 lines but not in two cell lines derived from normal breast epithelia. Further analysis revealed that constitutive PKB/Akt phosphorylation was associated with loss of PTEN phosphatase expression (CAL51, MDA-MB-468, BT549 cells) and constitutive activation of erbB2 (SKBR3, BT474 cells). In two further breast cancer lines (T47D and HS578T) PKB/Akt phosphorylation was dependent upon autocrine factors acting primary through the epidermal growth factor receptor (EGFR) and erbB2. Conditioned medium from HS578T cells stimulated EGFR-dependent PKB/Akt phosphorylation in normal breast cells. These results demonstrate that PKB/Akt is frequently activated in breast cancer through diverse mechanisms, including autocrine signalling via erbB receptors.

Prognostic relevance of activated Akt kinase in node-negative breast cancer: a clinicopathological study of 99 cases

Patients with lymphnode-negative breast cancer show a 10-year tumor recurrence rate of approximately 30%. Therefore, it is important to identify high-risk patients who would benefit from further adjuvant therapy. For this purpose, we examined the activation state of two kinases important in the regulation of cell proliferation and apoptosis in a series of 99 node-negative breast cancer cases with a mean follow-up of 10 years: Akt and extracellular regulated kinase (ERK1/2). The activation of Akt and ERK1/2 was investigated by immunohistochemistry using phospho-specific antibodies. The results were correlated with HER-2/neu expression, histological grading, receptor status, overall survival (OS) as well as with cell proliferation (Ki67 immunoreactivity, mitotic count) and tumor apoptosis assessed by TUNEL staining. Activation of Akt (pAkt) but not activation of ERK1/2 (pERK1/2) correlated with HER-2/neu overexpression (P<0.05) and was related to reduced tumor apoptosis (P<0.05). No association was found between pAkt or pERK1/2 with cell proliferation assessed by Ki67 and mitotic count (MC). Survival analysis of receptor status, HER2/neu expression, histological grading, MC and pAkt immunoexpression showed a significant correlation with decreased OS, but only pAkt reached statistical significance in the multivariate Cox regression analysis (P=0.015). Activation of Akt in node-negative breast cancer may indicate aggressive tumor behavior and may constitute an independent prognostic factor of OS. The determination of pAkt status may be of value in identifying high-risk patients, who would benefit from adjuvant therapy, and gives a rationale to investigate new therapy strategies by specific inhibition of the Akt signaling pathway in breast cancer.

Enhancement of the p27Kip1-mediated antiproliferative effect of trastuzumab (Herceptin) on HER2-overexpressing tumor cells

The oncogenic activity of the overexpressed HER2 tyrosine kinase receptor requires its localization in the plasma membrane. The antitumor effect of anti-HER2 antibodies (Abs) is mainly dependent on receptor downregulation and comprises p27Kip1-mediated G1 cell cycle arrest. However, one major limitation of anti-HER2 therapy is the reversibility of tumor growth inhibition after discontinuation of treatment caused by the mitogenic signaling associated with cell surface receptor re-expression. We found that the level of p27Kip1 upregulation, inhibition of Cdk2 activity and magnitude of G1 arrest induced by the humanized Ab trastuzumab (Herceptin, HCT) on BT474 and SKBr3 HER2-overexpressing breast cancer cells correlates with the level of cell surface receptor. Thus, continuous exposure of cells to HCT for 72 hr results in downregulation of the cell surface receptor and a concurrent increase in the level of p27Kip1 protein. Discontinuation of Ab exposure after the first 8 hr results in failure to upregulate p27Kip1 and arrest of cell cycle progression. We show that the lysosomotropic amine chloroquine (CQ) augments receptor internalization in HER2-overexpressing cells either pretreated or continuously treated with HCT and leads to an increased and sustained inhibitory effect. The enhanced CQ-dependent loss of functional HER2 from the cell surface resulted in sustained inactivation of the serine/threonine kinase Akt, upregulation of p27Kip1 protein and inhibition of cyclin E/Cdk2 activity. Potentiation of the inhibitory effect of HCT by CQ was directly related to loss of HER2 from the plasma membrane since prevention of Ab-mediated receptor endocytosis by engagement of the receptor with immobilized HCT abrogated the effect of CQ.

Effect of estradiol on estrogen receptor-alpha gene expression and activity can be modulated by the ErbB2/PI 3-K/Akt pathway

Epidermal growth factor (EGF), insulin-like growth factor-I (IGF-I), and heregulin-beta1 (HRG-beta1), can modulate the expression and activity of the estrogen receptor-alpha (ER-alpha) via the phosphatidylinositol 3-kinase (PI 3-K)/Akt pathway in the ER-alpha-positive breast cancer cell line, MCF-7. Estradiol can also rapidly activate PI 3-K/Akt in these cells (nongenomic effect). The recent study examines whether Akt is involved in the ER-alpha regulation by estradiol (genomic effect). Stable transfection of parental MCF-7 cells with a dominant-negative Akt mutant, as well as the PI 3-K inhibitors wortmannin and LY 294,002, blocked the effect of estradiol on ER-alpha expression and activity by 70-80 and 55-63%, respectively. Stable transfection of MCF-7 cells with a constitutively active Akt mimicked the effect of estradiol. The changes in ER-alpha expression and activity were abrogated in response to estradiol by an arginine to cysteine mutation in the pleckstrin homology (PH) domain of Akt (R25C), suggesting the involvement of this amino acid in the interaction between Akt and ER-alpha. Experiments employing selective ErbB inhibitors demonstrate that the effect of estradiol on ER-alpha expression and activity is mediated by ErbB2 and not by EGFR. Moreover, anchorage-dependent and -independent growth assays, cell cycle and membrane ruffling analyses showed that Akt exerts estrogen-like activity on cell growth and membrane ruffling and that a selective ErbB2 inhibitor, but not anti-ErbB2 antibodies directed to the extracellular domain, can block these effects. In the presence of constitutively active Akt, tamoxifen only partially inhibits cell growth. In contrast, in cells stably transfected with either a dominant-negative Akt or with R25C-Akt, as well as in parental cells in the presence of a selective ErbB2 inhibitor, the effect of estradiol on anchorage-dependent and -independent cell growth was inhibited by 50-75 and 100%, respectively. Dominant-negative Akt inhibited membrane ruffling by 54%; however, R25C-Akt did not have any effect, suggesting that kinase activity plays an important role in this process. Scatchard analysis demonstrated a 67% reduction in estrogen-binding capacity in cells transfected with constitutively active Akt. No change in binding affinity of estradiol to the receptor was observed upon transfection with either Akt mutant. Taken together, our results suggest that estradiol treatment results in binding to membrane ER-alpha and interaction with a heterodimer containing ErbB2, leading to tyrosine phosphorylation. This results in the activation of PI 3-K and Akt. Akt, in turn, may interact with nuclear ER-alpha, altering its expression and activity.

Novel approaches with targeted therapies in bladder cancer. Therapy of bladder cancer by blockade of the epidermal growth factor receptor family

The improved understanding of the molecular biology of urothelial malignancies is helping to define the role of new targets and prognostic indices that can direct the most appropriate choice of treatment for advanced disease. Many human tumors express high levels of growth factors and their receptors that can be used as potential therapeutical targets. Tyrosine-kinase receptors, including many growth factor receptors such the receptors for epidermal growth factor (EGF), vascular endothelial growth factor (VEGF), and Her2/neu, have been found overexpressed in urothelial tumors. For many of these growth factor receptors, the degree of expression has been associated with the progression of cancer and a poor prognosis. Among the best studied growth factor receptors are the two members of EGF receptor familiy EGFr (ErbB-1), and Her2/neu (ErbB-2). Several preclinical studies in bladder cancer models, have confirmed that systemic administration of growth factor inhibitors inhibits the growth and metastasis of human transitional cell carcinoma established in the bladder wall of athymic nude mice. Additional studies indicate that therapy with EGFR inhibitors enhances the activity of conventional cytoreductive chemotherapeutic agents, in part by inhibiting tumor cell proliferation, angiogenesis, and inducing apoptosis. Novel targeted therapy hold promise to improve the current results of bladder cancer treatment. Based on the success seen with anti-HER2 monoclonal antibodies (Herceptin) and the promising results with EGFR targeted agents (IMC-C225 Cetuximab, ZD1389 Iressa, OSI-774 Tarceva, GW 57016) in other tumor types, and based on the results obtained in preclinical models, there is a great interest in assessing these agents in patients with bladder cancer. Several trials are now ongoing testing these new agents alone or in combination with chemotherapy in bladder cancer patients. The integration of these newer biologic agents, probably to supplement rather than to supplant chemotherapeutic drugs, should be a primary direction of research with the objective to interfere with multiple aspects of bladder cancer progression. However, the value of integration of biologically targeted agents into combined modality treatment for patients with bladder cancer has still to be proven.

A deletion mutant of heregulin increases the sensitivity of breast cancer cells to chemotherapy without promoting tumorigenicity

Heregulin (HRG) is an activator of the erbB2-, erbB3- and erbB4-(erbB-2/3/4) signaling pathway. Transfection of full-length HRG cDNA into the estrogen (E2)-dependent cell line MCF-7 promoted an invasive E2-independent phenotype, as well as persistent activation of the erbB-2/3/4 receptors. Moreover, HRG expression in MCF-7 cells renders the cells sensitive to the topoisomerase II inhibitor doxorubicin (Doxo). In an attempt to dissociate the tumorigenic effect of HRG from the sensitizing effect to chemotherapy, we constructed a structural deletion mutant of HRG. Transfection of the deletion mutant of HRG described in this study (HRG/M) into MCF-7 cells resulted in the dissociation of the tumor-promoting activity of HRG from the sensitization to Doxo, that is, although the cells did not become more aggressive or E2-independent they became more sensitive to Doxo. HRG/M was unable to autophosphorylate the erbB receptors and did not affect the level of MAPK phosphorylation. Furthermore, the intracellular localization of the protein was different from that of the full-length protein. Our data show that the HRG/M sequences are sufficient to sensitize MCF-7 cells to Doxo, and provide evidence that this sensitization is independent of erbB2 activation.

Estradiol rapidly activates Akt via the ErbB2 signaling pathway

Previously, we have demonstrated that the two mitogenic growth factors epidermal growth factor and IGF-I can activate Akt and estrogen receptor-alpha (ERalpha) in the hormone-dependent breast cancer cell line, MCF-7. In this report we now show that estradiol can also rapidly activate phosphatidylinositol 3-kinase (PI 3-K)/Akt and that this effect is mediated by the ErbB2 signaling pathway. Treatment of cells with estradiol resulted in phosphorylation of Akt and a 9-fold increase in Akt activity in 10 min. Akt activation was blocked by wortmannin and LY 294,002, two inhibitors of PI 3-K; by genistein, a protein tyrosine kinase inhibitor and an ER agonist; by AG825, a selective ErbB2 inhibitor; and by the antiestrogens ICI 182,780 and 4-hydroxy-tamoxifen; but not by rapamycin, an inhibitor of the ribosomal protein kinase p70S6K; nor by AG30, a selective epidermal growth factor receptor inhibitor. Akt activation by estradiol was abrogated by an arginine-to-cysteine mutation in the pleckstrin homology domain of Akt (R25C). Growth factors also activated Akt in the ER-negative variant of MCF-7, MCF-7/ADR, but estradiol did not induce Akt activity in these cells. Transient transfection of ERalpha into these cells restored Akt activation by estradiol, suggesting that estradiol activation of Akt requires the ERalpha. Estradiol did not activate Akt in MCF-7 cells stably transfected with an anti-ErbB2-targeted ribozyme, further confirming a role for ErbB2. In vitro kinase assays using immunoprecipitation and anti-Akt1, -Akt2, and -Akt3-specific antibodies demonstrated that Akt1 is activated by estradiol in MCF-7 cells whereas Akt3 is the activated isoform in ER-negative MDA-MB231 cells, implying that selective activation of Akt subtypes plays a role in the actions of estradiol. Taken together, our data suggest that estradiol, bound to membrane ERalpha, interacts with and activates an ErbB dimer containing ErbB2, inducing activation of PI 3-K/Akt.

Heregulin-beta1 regulates the estrogen receptor-alpha gene expression and activity via the ErbB2/PI 3-K/Akt pathway

This study examines whether the serine/threonine protein kinase, Akt, is involved in the crosstalk between the ErbB2 and estrogen receptor-alpha (ER-alpha) pathways. Treatment of MCF-7 cells with 10(-9) M heregulin-beta1 (HRG-beta1) resulted in a rapid phosphorylation of Akt and a 15-fold increase in Akt activity. Akt phosphorylation was blocked by inhibitors of phosphatidylinositol 3-kinase (PI 3-K), by antiestrogens, the protein tyrosine kinase inhibitor, genistein, and by AG825, a selective ErbB2 inhibitor; but not by AG30, a selective EGFR inhibitor. Akt phosphorylation by HRG-beta1 was abrogated by an arginine to cysteine mutation (R25C) in the pleckstrin homology (PH) domain of Akt, and HRG-beta1 did not induce Akt phosphorylation in the ER-negative variant of MCF-7, MCF-7/ADR. Transient transfection of ER-alpha into these cells restored Akt phosphorylation by HRG-beta1, suggesting the requirement of ER-alpha. HRG-beta1 did not activate Akt in MCF-7 cells stably transfected with an anti-ErbB2-targeted ribozyme, further confirming a role for ErbB2. Stable transfection of the cells with a dominant negative Akt or with the R25C-Akt mutant, as well as PI 3-K inhibitors, blocked the effect of HRG-beta1 on ER-alpha expression and activity and on the growth of MCF-7 cells. Stable transfection of MCF-7 cells with a constitutively active Akt mimicked the effect of HRG-beta1. Experiments employing selective ErbB inhibitors demonstrate that the effect of HRG-beta1 on ER-alpha expression and activity is also mediated by ErbB2 and not by EGFR, demonstrating that ErbB2 is the primary mediator of the effects of HRG-beta1 on ER-alpha regulation. Taken together, our data suggest that HRG-beta1, bound to the ErbB2 ErbB3 heterodimer, in the presence of membrane ER-alpha, interacts with and activates PI 3-K/Akt. Akt leads to nuclear ER-alpha phosphorylation, thereby altering its expression and transcriptional activity.

AKT2 is frequently upregulated in HER-2/neu-positive breast cancers and may contribute to tumor aggressiveness by enhancing cell survival

Amplification or overexpression of the HER-2/neu gene in breast cancers is associated with aggressive behavior and resistance to therapeutic regimens. The molecular mechanisms that contribute to therapeutic resistance/survival of HER-2/neu-overexpressing tumor cells have not been well defined. To determine if phosphatidylinositol 3-kinase/AKT signaling contributes to cell survival in HER-2/neu-positive breast cancers, we performed immunohistochemical analyses to evaluate expression of HER-2/neu and AKT in a series of 52 breast carcinomas. Elevated expression of HER-2/neu was found to correlate with overexpression of AKT2 protein and activation of AKT kinase. HER-2/neu-overexpressing breast cancer cell lines were resistant to apoptosis induced by UV treatment and hypoxia, which was suppressed in the presence of the phosphatidylinositol 3-kinase inhibitors LY294002 and wortmannin, indicating a link between AKT activation and stress resistance in HER-2/neu-overexpressing cells. These observations suggest that AKT signaling augments resistance to stress-induced apoptosis in breast cancer cells overexpressing HER-2/neu.

Normal breast epithelial cells induce apoptosis of breast cancer cells via Fas signaling

Fas/Fas ligand (Fas L) death pathway is an important mediator of apoptosis. Deregulation of Fas pathway is reported to be involved in the immune escape of breast cancer and the resistance to anti-cancer drugs. In this study, we demonstrated that conditioned medium by normal breast epithelial cells (NBEC-CM) induced apoptosis of MCF-7 and T-47D Fas-sensitive cells but had no effect on MDA-MB-231 Fas-resistant cells. Inhibition of PI3 kinase or NF-kappaB by specific inhibitors or transient transfections restored the sensitivity of MDA-MB-231 cells to NBEC-induced apoptosis. Moreover, the constitutive activation of NF-kappaB was controlled by PI3 kinase because inhibition of PI3 kinase reduced NF-kappaB activity. Inducible activation of NF-kappaB rendered MCF-7 cells resistant to NBEC-CM- and Fas agonist antibody-triggered apoptosis. Therefore, constitutive or inducible activation of PI3 kinase and/or NF-kappaB in breast cancer cells rendered them resistant to NBEC-triggered apoptosis. In addition, Fas neutralizing antibody and dominant negative Fas abolished NBEC-triggered apoptosis. Western blot and confocal microscopy analysis showed an increase of membrane Fas/Fas L when cells were induced into apoptotis by NBEC-CM. Taken together, these data show that NBEC induced apoptosis in breast cancer cells via Fas signaling.

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.

HER-2/neu overexpression is rare in hepatocellular carcinoma and not predictive of anti-HER-2/neu regulation of cell growth and chemosensitivity

BACKGROUND

The overexpression of HER-2/neu oncogene has been implicated in the development and modulation of many types of cancer. However, whether HER-2/neu overexpression plays a similar role in hepatocellular carcinoma (HCC) has not been determined.

METHODS

Tissue specimens from 36 HCC patients who had been enrolled in 3 separate prospective clinical trials of systemic chemotherapy were studied by immunohistochemical staining. A polyclonal antibody (A0485; DAKO, Copenhagen, Denmark) against HER-2/neu and a horseradish peroxidase-based visualization system (Envision+, DAKO) was used. Scoring criteria was in accordance with the manufacturer's guidelines. Twelve HCC cell lines were examined for HER-2/neu overexpression by Western blotting. Single-agent growth regulatory activity of the anti-HER-2/neu antibody, trastuzumab (Herceptin; Genentech, South San Francisco, CA), and its combinative cytotoxicity with chemotherapeutic agents (doxorubicin, gemcitabine, cisplatin, irinotecan) were determined by a tetrazolium-based colorimetric assay (MTT test).

RESULTS

All but one of the HCC tumor tissues were negative for HER-2/neu expression. The only patient with positive HER-2/neu expression was a 57-year-old male patient who achieved stabilization of disease for 2 months after chemotherapy. Eight of the 35 patients with negative HER-2/neu expression had had partial remission after chemotherapy (P = 0.78). Only one (Tong cells) of the 12 HCC cell lines had a significant level of HER-2/neu expression. However, trastuzumab up to 10 microg/mL had no discernible growth inhibitory or chemosensitizing effect on Tong cells or any other cell lines.

CONCLUSIONS

HER-2/neu overexpression is rare in human HCC tissues, and anti-HER-2/neu regulation appears to play little role in the treatment of this tumor.

Expression of erbB/HER receptors, heregulin and P38 in primary breast cancer using quantitative immunohistochemistry

The purpose of this study was to investigate the frequency of expression of the erbB/HER family of growth factor receptors, their ligand heregulin, and the two different signaling pathways p38 and mitogen-activated protein kinase (MAPK), as well as the status of HER-2 phosphorylation in tumor specimens from patients with primary breast cancer. The level of expression of these proteins was measured by quantitative immunohistochemistry combined with microscope-based image analysis in paraffin-embedded breast cancer tissue from 35 patients. The frequency of expression was: EGFR (51%), HER-2 (54%), P-HER-2 (48%), HER-3 (48%), HER-4 (57%), heregulin (48%), p38 (17%), MAPK (48%). There was evidence of associations among the coexpression of heregulin, EGFR, HER-2, and HER-3. Also, there was evidence of a positive association between P-MAPK and HER-4. HER-3 was expressed at high levels in patients younger than 50 years of age. There was a trend for expression of higher levels of HER-4 in tumors larger than 2 cm. The expression of EGFR, HER-2, heregulin, p38 and MAPK was independent of age, tumor size, number of lymph nodes involved or hormone receptor status. The HER family of growth factor receptors appear to be regulated independently in invasive breast cancer. Assessing the expression of multiple tumor markers by quantitative immuno-histochemistry is feasible. Further research is needed to determine the prognostic and predictive roles of the various associations between HER receptors, their ligands and signal transduction molecules in patients with early-stage breast cancer.

Delayed mammary gland involution in MMTV-AKT1 transgenic mice

AKT1/protein kinase Balpha is a protein-serine/threonine kinase that regulates multiple targets involved in cell survival and cell cycle progression in a variety of cell types including breast cancer cells. To explore the role of Akt1 in mammary gland function and tumorigenesis, transgenic mice were generated that express human AKT1 under the control of the MMTV promoter. Virgin transgenic mice did not exhibit a dominant phenotype, but upon cessation of lactation, a notable delay in involution occurred compared to age-matched non-transgenic mice. The delay in involution coincided with increased hyperplasia as evidenced by an increased number of binucleated epithelial cells and a marked elevation in cyclin D1 expression in mammary epithelium. The delayed involution phenotype corresponded to increased phosphorylation of Thr308 in AKT1 and Ser136 in BAD, but not phosphorylation of Ser21 in GSK-3alpha. There was no evidence of mammary dysplasia or neoplasia during the lifespan of multiparous transgenic mice. These data suggest that AKT1 is involved in cell survival in the lactating and involuting mammary gland, but that overexpression of AKT1 alone is insufficient to induce transformation.

Heregulin-dependent activation of phosphoinositide 3-kinase and Akt via the ErbB2/ErbB3 co-receptor

The ErbB2/ErbB3 heregulin co-receptor has been shown to couple to phosphoinositide (PI) 3-kinase in a heregulin-dependent manner. The recruitment and activation of PI 3-kinase by this co-receptor is presumed to occur via its interaction with phosphorylated Tyr-Xaa-Xaa-Met (YXXM) motifs occurring in the ErbB3 C terminus. In this study, mutant ErbB3 receptor proteins expressed in COS7 cells were used to investigate PI 3-kinase-dependent signaling pathways activated by the ErbB2/ErbB3 co-receptor. We observed that a mutant ErbB3 protein with each of its six YXXM motifs containing a Tyr --> Phe substitution was unable to bind either the p85 regulatory or p110 catalytic subunit of PI 3-kinase. However, restoration of a single YXXM motif was sufficient to mediate association with the PI 3-kinase holoenzyme, although at a lower level than wild-type ErbB3. When ErbB3 YXXM motifs were restored in pairs, evidence for cooperativity between two, those incorporating Tyr-1273 and Tyr-1286, was observed. Interestingly, we have shown that an apparent association of PI 3-kinase activity with ErbB2/Neu was due to the residual presence of ErbB3 in ErbB2 immunoprecipitates. The necessity of ErbB3 association with PI 3-kinase for downstream signaling to the effector kinase Akt was also investigated. Here, the heregulin-dependent translocation of Akt to the plasma membrane and its subsequent activation was observed in intact NIH-3T3 fibroblasts. Recruitment of PI 3-kinase to ErbB3 was required for both activities, and it appeared that ErbB2 activation alone was not sufficient to activate PI 3-kinase signaling in these cells.

Growth retardation and increased apoptosis in mice with homozygous disruption of the Akt1 gene

The serine/threonine kinase Akt has been implicated in the control of cell survival and metabolism. Here we report the disruption of the most ubiquitously expressed member of the akt family of genes, akt1, in the mouse. Akt1(-/-) mice are viable but smaller when compared to wild-type littermates. In addition, the life span of Akt1(-/-) mice, upon exposure to genotoxic stress, is shorter. However, Akt1(-/-) mice do not display a diabetic phenotype. Increased spontaneous apoptosis in testes, and attenuation of spermatogenesis is observed in Akt1(-/-) male mice. Increased spontaneous apoptosis is also observed in the thymi of Akt1(-/-) mice, and Akt1(-/-) thymocytes are more sensitive to apoptosis induced by gamma-irradiation and dexamethasone. Finally, Akt1(-/-) mouse embryo fibroblasts (MEFs) are more susceptible to apoptosis induced by TNF, anti-Fas, UV irradiation, and serum withdrawal.

Tiam1 overexpression potentiates heregulin-induced lymphoid enhancer factor-1/beta -catenin nuclear signaling in breast cancer cells by modulating the intercellular stability

Heregulin-beta1 (HRG) promotes motility, scattering, and invasiveness of breast cancer cells. Tiam1, a newly identified guanine nucleotide exchange factor, has been shown to inhibit or promote cell migration in a cell type-dependent manner. In this study, we identified Tiam1 as a target of HRG signaling. HRG stimulation of breast cancer epithelial cells induced the phosphorylation and redistribution of Tiam1 to the membrane ruffles and the loosening of intercellular junctions. In addition, HRG-mediated scattering of breast epithelial cells was accompanied by stimulation of tyrosine phosphorylation and redistribution of beta-catenin from the cell junctions to the cytosol and, finally, entry into the nucleus. Decompaction of breast cancer epithelial cells by HRG was accompanied by a transient physical association of the tyrosine-phosphorylated beta-catenin with the activated human epidermal growth factor receptor 2 and subsequent nuclear translocation of beta-catenin, as well as beta-catenin-dependent transactivation of T-cell factor.lymphoid enhancer factor-1. All of these HRG-induced phenotypic changes were regulated in a phosphatidylinositol-3 kinase-sensitive manner. HRG-induced cellular ruffles, loss of intercellular adhesiveness, and increased cell migration could be mimicked by overexpression of a fully functional Tiam1 construct. Furthermore, ectopic expression of Tiam1 or of an active beta-catenin mutant led to potentiation of the beta-catenin-dependent T-cell factor.lymphoid enhancer factor-1 transactivation and invasiveness of HRG-treated cells. We also found preliminary evidence suggesting a close correlation between the status of Tiam1 expression and invasiveness of human breast tumor cells with the degree of progression of breast tumors. Together, these findings suggest that HRG regulate Tiam1 activation and lymphoid enhancer factor/beta-catenin nuclear signaling via phosphatidylinositol-3 kinase in breast cancer cells.

HER2 (neu) signaling increases the rate of hypoxia-inducible factor 1alpha (HIF-1alpha) synthesis: novel mechanism for HIF-1-mediated vascular endothelial growth factor expression

Hypoxia-inducible factor 1 (HIF-1) is a transcriptional activator composed of HIF-1alpha and HIF-1beta subunits. Several dozen HIF-1 targets are known, including the gene encoding vascular endothelial growth factor (VEGF). Under hypoxic conditions, HIF-1alpha expression increases as a result of decreased ubiquitination and degradation. The tumor suppressors VHL (von Hippel-Lindau protein) and p53 target HIF-1alpha for ubiquitination such that their inactivation in tumor cells increases the half-life of HIF-1alpha. Increased phosphatidylinositol 3-kinase (PI3K) and AKT or decreased PTEN activity in prostate cancer cells also increases HIF-1alpha expression by an undefined mechanism. In breast cancer, increased activity of the HER2 (also known as neu) receptor tyrosine kinase is associated with increased tumor grade, chemotherapy resistance, and decreased patient survival. HER2 has also been implicated as an inducer of VEGF expression. Here we demonstrate that HER2 signaling induced by overexpression in mouse 3T3 cells or heregulin stimulation of human MCF-7 breast cancer cells results in increased HIF-1alpha protein and VEGF mRNA expression that is dependent upon activity of PI3K, AKT (also known as protein kinase B), and the downstream kinase FRAP (FKBP-rapamycin-associated protein). In contrast to other inducers of HIF-1 expression, heregulin stimulation does not affect the half-life of HIF-1alpha but instead stimulates HIF-1alpha synthesis in a rapamycin-dependent manner. The 5'-untranslated region of HIF-1alpha mRNA directs heregulin-inducible expression of a heterologous protein. These data provide a molecular basis for VEGF induction and tumor angiogenesis by heregulin-HER2 signaling and establish a novel mechanism for the regulation of HIF-1alpha expression.

A novel role of neuregulin in skeletal muscle. Neuregulin stimulates glucose uptake, glucose transporter translocation, and transporter expression in muscle cells

Neuregulins regulate the expression of acetylcholine receptor genes and induce development of the neuromuscular junction in muscle. In studying whether neuregulins regulate glucose uptake in muscle, we analyzed the effect of a recombinant neuregulin, (r)heregulin-beta1-(177-244) (HRG), on L6E9 muscle cells, which express the neuregulin receptors ErbB2 and ErbB3. L6E9 responded acutely to HRG by a time- and concentration-dependent stimulation of 2-deoxyglucose uptake. HRG-induced stimulation of glucose transport was additive to the effect of insulin. The acute stimulation of the glucose transport induced by HRG was a consequence of the translocation of GLUT4, GLUT1, and GLUT3 glucose carriers to the cell surface. The effect of HRG on glucose transport was dependent on phosphatidylinositol 3-kinase activity. HRG also stimulated glucose transport in the incubated soleus muscle and was additive to the effect of insulin. Chronic exposure of L6E9 cells to HRG potentiated myogenic differentiation, and under these conditions, glucose transport was also stimulated. The activation of glucose transport after chronic HRG exposure was due to enhanced cell content of GLUT1 and GLUT3 and to increased abundance of these carriers at the plasma membrane. However, under these conditions, GLUT4 expression was markedly down-regulated. Muscle denervation is associated with GLUT1 induction and GLUT4 repression. In this connection, muscle denervation caused a marked increase in the content of ErbB2 and ErbB3 receptors, which occurred in the absence of alterations in neuregulin mRNA levels. This fact suggests that neuregulins regulate glucose transporter expression in denervated muscle. We conclude that neuregulins regulate glucose uptake in L6E9 muscle cells by mechanisms involving the recruitment of glucose transporters to the cell surface and modulation of their expression. Neuregulins may also participate in the adaptations in glucose transport that take place in the muscle fiber after denervation.

Akt, MAPK (Erk1/2), and p38 act in concert to promote apoptosis in response to ErbB receptor family inhibition

The ErbB receptor family is implicated in the malignant transformation of several tumor types and is overexpressed frequently in breast, ovarian, and other tumors. The mechanism by which CI-1033 and gemcitabine, either singly or in combination, kill tumor cells was examined in two breast lines, MDA-MB-453 and BT474; both overexpress the ErbB-2 receptor. CI-1033, a potent inhibitor of the ErbB family of receptor tyrosine kinases, reduced levels of activated Akt in MDA-MB-453 cells. This effect alone, however, did not induce apoptosis in these cells. Gemcitabine treatment resulted in a moderate increase in the percentage of apoptotic cells that was accompanied by activation of p38 and MAPK (ERK1/2). CI-1033 given 24 h after gemcitabine produced a significant increase in the apoptotic fraction over treatment with either drug alone. During the combined treatment p38 remained activated, whereas Akt and activated MAPK were suppressed. Substitution of CI-1033 with the phosphatidylinositol 3-kinase inhibitor LY294002 and the MAPK/ERK kinase inhibitor PD 098059 in combination with gemcitabine produced the same results as the combination of CI-1033 and gemcitabine. p38 suppression by SB203580 prevented the enhanced cell kill by CI-1033. In contrast to MDA-MB-453, BT474 cells exhibited activated p38 under unstressed conditions as well as activated Akt and MAPK. Treatment of BT474 cells with CI-1033 inhibited both the phosphorylation of Akt and MAPK and resulted in a 47% apoptotic fraction. Gemcitabine did not cause apoptosis in the BT474 cells. These data indicate that suppression of Akt and MAPK in the presence of activated p38 results in cell death and a possible mechanism for the enhanced apoptosis produced by the combination of CI-1033 and gemcitabine in MDA-MB-453 cells. Furthermore, tumors that depend on ErbB receptor signaling for survival and exhibit activated p38 in the basal state may be susceptible to apoptosis by CI-1033 as a single agent.

Syk: a new player in the field of breast cancer

Breast tumor development and progression are thought to occur through a complex, multistep process, including oncogene activation (eg HER2/neu) and mutation or loss of tumor suppressor genes (eg p53). Determining the function of genetic alterations in breast carcinoma tumorigenesis and metastasis has been the focus of intensive research efforts for several decades. One group of proteins that play a critical role in breast cancer cell signaling pathways are tyrosine kinases. Overexpression of the tyrosine kinase HER2/neu is observed in many human breast cancers and is positively correlated with enhanced tumorigenesis. Recently, another tyrosine kinase, Syk, has been implicated as an important inhibitor of breast cancer cell growth and metastasis. This recent finding was unexpected, since Syk function has been predominantly linked to hematopoietic cell signaling, and is discussed further in this commentary.

The EGF receptor family as targets for cancer therapy

Human carcinomas frequently express high levels of receptors in the EGF receptor family, and overexpression of at least two of these receptors, the EGF receptor (EGFr) and closely related ErbB2, has been associated with a more aggressive clinical behavior. Further, transfection or activation of high levels of these two receptors in nonmalignant cell lines can lead to a transformed phenotype. For these reasons therapies directed at preventing the function of these receptors have the potential to be useful anti-cancer treatments. In the last two decades monoclonal antibodies (MAbs) which block activation of the EGFr and ErbB2 have been developed. These MAbs have shown promising preclinical activity and 'chimeric' and 'humanized' MAbs have been produced in order to obviate the problem of host immune reactions. Clinical activity with these antibodies has been documented: trastuzumab, a humanized anti-ErbB2 MAb, is active and was recently approved in combination with paclitaxel for the therapy of patients with metastatic ErbB2-overexpressing breast cancer; IMC-C225, a chimeric anti-EGFr MAb, has shown impressive activity when combined with radiation therapy and reverses resistance to chemotherapy. In addition to antibodies, compounds that directly inhibit receptor tyrosine kinases have shown preclinical activity and early clinical activity has been reported. A series of phase III studies with these antibodies and direct tyrosine kinase inhibitors are ongoing or planned, and will further address the role of these active anti-receptor agents in the treatment of patients with cancer.

Grb2 downregulation leads to Akt inactivation in heregulin-stimulated and ErbB2-overexpressing breast cancer cells

ErbB2 can be activated by its own overexpression or be transactivated by the heregulin polypeptide growth factor. Activation of ErbB2 leads to breast cancer cell proliferation, presumably by inducing the activation of extracellular signal-regulated kinases 1,2 (Erk1,2) and Akt. We have previously reported that the growth factor receptor bound protein-2 (Grb2) is required for the proliferation of ErbB2-overexpressing breast cancer cells. We investigated here whether Grb2 protein plays a role in heregulin-stimulated proliferation. Grb2 protein inhibition led to growth inhibition of heregulin-stimulated breast cancer cells, but not Erk1,2 inactivation. These findings are similar to our earlier observations in ErbB2-overexpressing cells. Since Akt can also be activated by heregulin, the effects of Grb2 inhibition on Akt were examined. Akt was inactivated following Grb2 downregulation in heregulin-stimulated breast cancer cells. We then examined the effects of Grb2 downregulation on Akt in ErbB2-overexpressing cells in the absence of heregulin. Similar to heregulin-stimulated cells, Grb2 inhibition also led to Akt inactivation in ErbB2-overexpressing breast cancer cells. Our results indicate that the activation of ErbB2 by heregulin or by its overexpression requires Grb2 to stimulate the Akt pathway to propagate mitogenic signals.

Molecular mechanisms underlying ErbB2/HER2 action in breast cancer

Overexpression of ErbB2, a receptor-like tyrosine kinase, is shared by several types of human carcinomas. In breast tumors the extent of overexpression has a prognostic value, thus identifying the oncoprotein as a target for therapeutic strategies. Already, antibodies to ErbB2 are used in combination with chemotherapy in the treatment of metastasizing breast cancer. The mechanisms underlying the oncogenic action of ErbB2 involve a complex network in which ErbB2 acts as a ligand-less signaling subunit of three other receptors that directly bind a large repertoire of stroma-derived growth factors. The major partners of ErbB2 in carcinomas are ErbB1 (also called EGFR) and ErbB3, a kinase-defective receptor whose potent mitogenic action is activated in the context of heterodimeric complexes. Why ErbB2-containing heterodimers are relatively oncopotent is a function of a number of processes. Apparently, these heterodimers evade normal inactivation processes, by decreasing the rate of ligand dissociation, internalizing relatively slowly and avoiding the degradative pathway by returning to the cell surface. On the other hand, the heterodimers strongly recruit survival and mitogenic pathways such as the mitogen-activated protein kinases and the phosphatidylinositol 3-kinase. Hyper-activated signaling through the ErbB-signaling network results in dysregulation of the cell cycle homeostatic machinery, with upregulation of active cyclin-D/CDK complexes. Recent data indicate that cell cycle regulators are also linked to chemoresistance in ErbB2-dependent breast carcinoma. Together with D-type cyclins, it seems that the CDK inhibitor p21waf1 plays an important role in evasion from apoptosis. These recent findings herald a preliminary understanding of the output layer which connects elevated ErbB-signaling to oncogenesis and chemoresistance.