p185, a product of the neu proto-oncogene, is a receptorlike protein associated with tyrosine kinase activity

How much do we know about the metastatic process?

Cancer cells can leave their primary sites and travel through the circulation to distant sites, where they lodge as disseminated cancer cells (DCCs), even during the early and asymptomatic stages of tumor progression. In experimental models and clinical samples, DCCs can be detected in a non-proliferative state, defined as cellular dormancy. This state can persist for extended periods until DCCs reawaken, usually in response to niche-derived reactivation signals. Therefore, their clinical detection in sites like lymph nodes and bone marrow is linked to poor survival. Current cancer therapy designs are based on the biology of the primary tumor and do not target the biology of the dormant DCC population and thus fail to eradicate the initial or subsequent waves of metastasis. In this brief review, we discuss the current methods for detecting DCCs and highlight new strategies that aim to target DCCs that constitute minimal residual disease to reduce or prevent metastasis formation. Furthermore, we present current evidence on the relevance of DCCs derived from early stages of tumor progression in metastatic disease and describe the animal models available for their study. We also discuss our current understanding of the dissemination mechanisms utilized by genetically less- and more-advanced cancer cells, which include the functional analysis of intermediate or hybrid states of epithelial-mesenchymal transition (EMT). Finally, we raise some intriguing questions regarding the clinical impact of studying the crosstalk between evolutionary waves of DCCs and the initiation of metastatic disease.

Exploratory analysis of serum HER2 extracellular domain for HER2 positive gastric cancer treated with SOX plus trastuzumab

BACKGROUND

The aim of this study was to explore the clinical utility of serum HER2 extracellular domain (sHER2 ECD) using data from a clinical trial evaluating trastuzumab combined S-1 plus oxaliplatin (SOX) in HER2 positive gastric cancer.

METHODS

sHER2 ECD were prospectively measured at baseline and subsequent treatment courses. Based on each quantile point of baseline sHER2 ECD levels and its early changes, patients were divided into two groups and compared clinical outcomes.

RESULTS

43 patients were enrolled, and 17 patients (39.5%) were positive for baseline sHER2 ECD. Higher baseline sHER2 ECD levels tended to have lower hazard ratios (HRs). When divided into two groups by baseline sHER2 ECD of 19.1 ng/ml, median progression-free survival (PFS) and overall survival (OS) was longer in the higher group (mPFS: 16.8 vs 8.7 months, p = 0.359. mOS: 35.5 vs 20.6 months, p = 0.270), respectively. After initiation of treatment, sHER2 ECD significantly decreased up until the third cycle. Higher reduction rates of sHER2 ECD within 3 cycles also tended to have lower HRs. When divided into two groups by reduction rate of 42.5%, mPFS and mOS was longer in the higher reduced group (mPFS: 17.2 vs 8.7 months, p = 0.095. mOS: 65.0 vs 17.8 months, p = 0.047), respectively. Furthermore, higher reduction rates could surrogate higher objective response rates (ORR) (ORR: 90% vs 63.2% for 29.5%, p = 0.065. 100% vs 70% for 42.5%, p = 0.085), respectively.

CONCLUSIONS

Baseline sHER2 ECD levels and its early decline may be useful biomarkers for SOX plus trastuzumab efficacy in HER2 positive gastric cancer.

The Role of Tumor-Associated Antigen HER2/neu in Tumor Development and the Different Approaches for Using It in Treatment: Many Choices and Future Directions

The treatment of HER2-positive cancers has changed significantly over the past ten years thanks to a significant number of promising new approaches that have been added to our arsenal in the fight against cancer, including monoclonal antibodies, inhibitors of tyrosine kinase, antibody-drug conjugates, vaccination, and particularly, adoptive-T-cell therapy after its great success in hematological malignancies. Equally important is the new methodology for determining patients eligible for targeted HER2 therapy, which has doubled the number of patients who can benefit from these treatments. However, despite the initial enthusiasm, there are still several problems in this field represented by drug resistance and tumor recurrence that require the further development of new more efficient drugs. In this review, we discuss various approaches for targeting the HER2 molecule in cancer treatment, highlighting their benefits and drawbacks, along with the different mechanisms responsible for resistance to HER2-targeted therapies and how to overcome them.

Exosomes of Mesenchymal Stem Cells as a Proper Vehicle for Transfecting miR-145 into the Breast Cancer Cell Line and Its Effect on Metastasis

Background

Despite recent advances in scientific knowledge and clinical practice, management, and treatment of breast cancer, as one of the leading causes of female mortality, breast cancer remains a major burden. Recently, methods employing stem cells and their derivatives, i.e., exosomes, in gene-based therapies hold great promise. Since these natural nanovesicles are able to transmit crucial cellular information which can be engineered to have robust delivery and targeting capacity, they are considered one of the modes of intercellular communication. miR-145, one of the downregulated microRNAs (miRNAs) in various cancers, can regulate tumor cell invasion, metastasis, apoptosis, and proliferation and stem cell differentiation.

Objectives

The aim of this study was to investigate the role of exosomes secreted from adipose tissue-derived mesenchymal stem cells (MSCs) for miR-145 transfection into breast cancer cells in order to weaken their expansion and metastasis.

Methods

Here, we exploited the exosomes from adipose tissue-derived mesenchymal stem cells (MSC-Exo) to deliver miR-145 in the T-47D breast cancer cell line. Lentiviral vectors of miR-145-pLenti-III-enhanced green fluorescent protein (eGFP) and empty pLenti-III-eGFP as the backbone were used to transfect MSCs and T-47D cells. In order to find the efficiency of exosomes as a delivery vehicle, the expression level of some miR-145 target genes, including Rho-Associated Coiled-Coil Containing Protein Kinase 1 (ROCK1), Erb-B2 Receptor Tyrosine Kinase 2 (ERBB2), Matrix Metalloproteinase 9 (MMP9), and Tumor Protein p53 (TP53), was compared in all treatment groups (T-47D cells treated by miR-145-transfected MSCs and their derivatives or their backbone) and control group (untransfected T-47D cells) using real-time PCR.

Results

The obtained data represented the inhibitory effect of miR-145 on apoptosis induction and metastasis in both direct miR-treated groups. However, exosome-mediated delivery caused an improved anticancer property of miR-145.

Conclusion

Restoration of miR-145 using MSC-Exo can be considered a potential novel therapeutic strategy in breast cancer in the future.

Receptor Tyrosine Kinase Signaling and Targeting in Glioblastoma Multiforme

Glioblastoma multiforme (GBM) is amongst the deadliest of human cancers, with a median survival rate of just over one year following diagnosis. Characterized by rapid proliferation and diffuse infiltration into the brain, GBM is notoriously difficult to treat, with tumor cells showing limited response to existing therapies and eventually developing resistance to these interventions. As such, there is intense interest in better understanding the molecular alterations in GBM to guide the development of more efficient targeted therapies. GBM tumors can be classified into several molecular subtypes which have distinct genetic signatures, and they show aberrant activation of numerous signal transduction pathways, particularly those connected to receptor tyrosine kinases (RTKs) which control glioma cell growth, survival, migration, invasion, and angiogenesis. There are also non-canonical modes of RTK signaling found in GBM, which involve G-protein-coupled receptors and calcium channels. This review uses The Cancer Genome Atlas (TCGA) GBM dataset in combination with a data-mining approach to summarize disease characteristics, with a focus on select molecular pathways that drive GBM pathogenesis. We also present a unique genomic survey of RTKs that are frequently altered in GBM subtypes, as well as catalog the GBM disease association scores for all RTKs. Lastly, we discuss current RTK targeted therapies and highlight emerging directions in GBM research.

Inhibition of ezrin causes PKCα-mediated internalization of erbb2/HER2 tyrosine kinase in breast cancer cells

Unlike other ErbB family members, HER2 levels are maintained on the cell surface when the receptor is activated, allowing prolonged signaling and contributing to its transforming ability. Interactions between HER2, HSP90, PMCA2, and NHERF1 within specialized plasma membrane domains contribute to the membrane retention of HER2. We hypothesized that the scaffolding protein ezrin, which has been shown to interact with NHERF1, might also help stabilize the HER2-PMCA2-NHERF1 complex at the plasma membrane. Therefore, we examined ezrin expression and its relationship with HER2, NHERF1, and PMCA2 levels in murine and human breast cancers. We also used genetic knockdown and/or pharmacologic inhibition of ezrin, HSP90, NHERF1, PMCA2, and HER2 to examine the functional relationships between these factors and membrane retention of HER2. We found ezrin to be expressed at low levels at the apical surface of normal mammary epithelial cells, but its expression is up-regulated and correlates with HER2 expression in hyperplasia and tumors in murine mammary tumor virus-Neu mice, in human HER2-positive breast cancer cell lines, and in ductal carcinoma in situ and invasive breast cancers from human patients. In breast cancer cells, ezrin co-localizes and interacts with HER2, NHERF1, PMCA2, and HSP90 in specialized membrane domains, and inhibiting ezrin disrupts interactions between HER2, PMCA2, NHERF1, and HSP90, inhibiting HER2 signaling and causing PKCα-mediated internalization and degradation of HER2. Inhibition of ezrin synergizes with lapatinib in a PKCα-dependent fashion to inhibit proliferation and promote apoptosis in HER2-positive breast cancer cells. We conclude that ezrin stabilizes a multiprotein complex that maintains active HER2 at the cell surface.

Clinical impact of intratumoral HER2 heterogeneity on trastuzumab efficacy in patients with HER2-positive gastric cancer

BACKGROUND

There is growing interest in the clinical significance of intratumoral HER2 heterogeneity. Its prognostic and predictive impacts on trastuzumab efficacy were demonstrated in breast cancer. However, its clinical significance in gastric cancer is still unclear.

METHODS

Twenty-eight HER2-positive gastric cancer patients who had gastrectomy prior to trastuzumab-based chemotherapy were consecutively enrolled. Intratumoral HER heterogeneity was evaluated using whole-tissue sections by immunohistochemistry. When all tumor cells overexpressed HER2 protein, the tumor was defined as homogeneously HER2 (Homo-HER2)-positive group. The others were defined as heterogeneously HER2 (Hetero-HER2)-positive group.

RESULTS

There was no significant difference in clinicopathological features between the two groups. The median progression-free survival (PFS) and overall survival (OS) in the Homo-HER2-positive group were significantly longer than those in the Hetero-HER2-positive group (PFS; 20.0 months [95% CI 17.8-22.2] vs. 6.0 months [95% CI 2.3-9.7]; HR 0.11; 95% CI 0.03-0.41; p < 0.001, OS; not reached vs. 14.0 months [95% CI 11.9-16.1]; HR 0.18; 95% CI 0.06-0.61; p = 0.003). In the multivariate analysis, these associations remained significant both in PFS (HR 0.12; 95% CI 0.03-0.46, p = 0.002) and OS (HR 0.21; 95% CI 0.06-0.72, p = 0.013). With respect to response rate, no statistical difference was found between two groups. However, deeper tumor shrinkage was obtained in the Homo-HER2-positive group compared with the Hetero-HER2-positive group (p = 0.046).

CONCLUSIONS

Intratumoral HER2 heterogeneity may have robust clinical impact on trastuzumab efficacy in patients with HER2-positive gastric cancer. These findings should be validated by larger independent cohorts and further molecular correlative analyses are warranted.

HER2 signaling regulates HER2 localization and membrane retention

ErbB2/HER2/Neu is a receptor tyrosine kinase that is overexpressed in 25-30% of human breast cancers, usually associated with amplification of the ERBB2 gene. HER2 has no recognized ligands and heterodimers between HER2 and EGFR (ErbB1/HER1) or HER2 and ErbB3/HER3 are important in breast cancer. Unlike other ErbB family members, HER2 is resistant to internalization and degradation, and remains at the cell surface to signal for prolonged periods after it is activated. Although the mechanisms underlying retention of HER2 at the cell surface are not fully understood, prior studies have shown that, in order to avoid internalization, HER2 must interact with the chaperone, HSP90, and the calcium pump, PMCA2, within specific plasma membrane domains that protrude from the cell surface. In this report, we demonstrate that HER2 signaling, itself, is important for the formation and maintenance of membrane protrusions, at least in part, by maintaining PMCA2 expression and preventing increased intracellular calcium concentrations. Partial genetic knockdown of HER2 expression or pharmacologic inhibition of HER2 signaling causes the depletion of membrane protrusions and disruption of the interactions between HER2 and HSP90. This is associated with the ubiquitination of HER2, its internalization with EGFR or HER3, and its degradation. These results suggest a model by which some threshold of HER2 signaling is required for the formation and/or maintenance of multi-protein signaling complexes that reinforce and prolong HER2/EGFR or HER2/HER3 signaling by inhibiting HER2 ubiquitination and internalization.

The scaffolding protein NHERF1 regulates the stability and activity of the tyrosine kinase HER2

We examined whether the scaffolding protein sodium-hydrogen exchanger regulatory factor 1 (NHERF1) interacts with the calcium pump PMCA2 and the tyrosine kinase receptor ErbB2/HER2 in normal mammary epithelial cells and breast cancer cells. NHERF1 interacts with the PDZ-binding motif in PMCA2 in both normal and malignant breast cells. NHERF1 expression is increased in HER2-positive breast cancers and correlates with HER2-positive status in human ductal carcinoma in situ (DCIS) lesions and invasive breast cancers as well as with increased mortality in patients. NHERF1 is part of a multiprotein complex that includes PMCA2, HSP90, and HER2 within specific actin-rich and lipid raft-rich membrane signaling domains. Knocking down NHERF1 reduces PMCA2 and HER2 expression, inhibits HER2 signaling, dissociates HER2 from HSP90, and causes the internalization, ubiquitination, and degradation of HER2. These results demonstrate that NHERF1 acts with PMCA2 to regulate HER2 signaling and membrane retention in breast cancers.

Oncogenic and tumor-suppressive mouse models for breast cancer engaging HER2/neu

The human c-ErbB2 (HER2) gene is amplified in ∼20% of human breast cancers (BCs), but the protein is overexpressed in ∼30% of the cases indicating that multiple different mechanisms contribute to HER2 overexpression in tumors. It has long been used as a molecular marker of BC for subcategorization for the prediction of prognosis and determination of therapeutic strategies. In comparison to ER(+) BCs, HER2-positive BCs are more invasive, but the patients respond to monoclonal antibody therapy with trastuzumab or tyrosine kinase inhibitors at least at early stages. To understand the pathophysiology of HER2-driven carcinogenesis and test HER2-targeting therapeutic agents in vivo, numerous mouse models have been created that faithfully reproduce HER2(+) BCs in mice. They include MMTV-neu (active mutant or wild type, rat neu or HER2) models, neu promoter-driven neuNT-transgenic mice, neuNT-knock-in mice at the neu locus and doxycycline-inducible neuNT-transgenic models. HER2/neu activates the Phosphatidylinositol-3 kinase-AKT-NF-κB pathway to stimulate the mitogenic cyclin D1/Cdk4-Rb-E2F pathway. Of note, overexpression of HER2 also stimulates the cell autonomous Dmp1-Arf-p53 tumor suppressor pathway to quench oncogenic signals to prevent the emergence of cancer cells. Hence tumor development by MMTV-neu mice was dramatically accelerated in mice that lack Dmp1, Arf or p53 with invasion and metastasis. Expressions of neuNT under the endogenous promoter underwent gene amplification, closely recapitulating human HER2(+) BCs. MMTV-HER2 models have been shown to be useful to test humanized monoclonal antibodies to HER2. These mouse models will be useful for the screening of novel therapeutic agents against BCs with HER2 overexpression.

p85α promotes nucleolin transcription and subsequently enhances EGFR mRNA stability and EGF-induced malignant cellular transformation

p85α is a regulatory subunit of phosphatidylinositol 3-kinase (PI3K) that is a key lipid enzyme for generating phosphatidylinositol 3, 4, 5-trisphosphate, and subsequently activates signaling that ultimately regulates cell cycle progression, cell growth, cytoskeletal changes, and cell migration. In addition to form a complex with the p110 catalytic subunit, p85α also exists as a monomeric form due to that there is a greater abundance of p85α than p110 in many cell types. Our previous studies have demonstrated that monomeric p85α exerts a pro-apoptotic role in UV response through induction of TNF-α gene expression in PI3K-independent manner. In current studies, we identified a novel biological function of p85α as a positive regulator of epidermal growth factor receptor (EGFR) expression and cell malignant transformation via nucleolin-dependent mechanism. Our results showed that p85α was crucial for EGFR and nucleolin expression and subsequently resulted in an increase of malignant cellular transformation by using both specific knockdown and deletion of p85α in its normal expressed cells. Mechanistic studies revealed that p85α upregulated EGFR protein expression mainly through stabilizing its mRNA, whereas nucleolin (NCL) was able to bind to egfr mRNA and increase its mRNA stability. Consistently, overexpression of NCL in p85α-/- cells restored EGFR mRNA stabilization, protein expression and cell malignant transformation. Moreover, we discovered that p85α upregulated NCL gene transcription via enhancing C-Jun activation. Collectively, our studies demonstrate a novel function of p85α as a positive regulator of EGFR mRNA stability and cell malignant transformation, providing a significant insight into the understanding of biomedical nature of p85α protein in mammalian cells and further supporting that p85α might be a potential target for cancer prevention and therapy.

The Role of Forkhead Box Protein M1 in Breast Cancer Progression and Resistance to Therapy

The Forkhead box M1 (FOXM1) is a transcription factor that has been implicated in normal cell growth and proliferation through control of cell cycle transition and mitotic spindle. It is implicated in carcinogenesis of various malignancies where it is activated by either amplification, increased stability, enhanced transcription, dysfunction of regulatory pathways, or activation of PI3K/AKT, epidermal growth factor receptor, Raf/MEK/MAPK, and Hedgehog pathways. This review describes the role of FOXM1 in breast cancer. This includes how FOXM1 impacts on different subtypes of breast cancer, that is, luminal/estrogen receptor positive (ER+), expressing human epidermal growth factor receptor 2 (HER2), basal-like breast cancer (BBC), and triple negative breast cancer (TNBC). The review also describes different tested preclinical therapeutic strategies targeting FOXM1. Developing clinically applicable therapies that specifically inhibit FOXM1 activity is a logical next step in biomarker-driven approaches against breast cancer but will not be without its challenges due to the unique properties of this transcription factor.

PMCA2 regulates HER2 protein kinase localization and signaling and promotes HER2-mediated breast cancer

In the lactating mammary gland, the plasma membrane calcium ATPase2 (PMCA2) transports milk calcium. Its expression is activated in breast cancers, where high tumor levels predict increased mortality. We find that PMCA2 expression correlates with HER2 levels in breast cancers and that PMCA2 interacts with HER2 in specific actin-rich membrane domains. Knocking down PMCA2 increases intracellular calcium, disrupts interactions between HER2 and HSP-90, inhibits HER2 signaling, and results in internalization and degradation of HER2. Manipulating PMCA2 levels regulates the growth of breast cancer cells, and knocking out PMCA2 inhibits the formation of tumors in mouse mammary tumor virus (MMTV)-Neu mice. These data reveal previously unappreciated molecular interactions regulating HER2 localization, membrane retention, and signaling, as well as the ability of HER2 to generate breast tumors, suggesting that interactions between PMCA2 and HER2 may represent therapeutic targets for breast cancer.

Insulin-like growth factor and epidermal growth factor signaling in breast cancer cell growth: focus on endocrine resistant disease

Breast cancer is the most common type of cancer for women worldwide with a lifetime risk amounting to a staggering total of 10%. It is well established that the endogenous synthesis of insulin-like growth factor (IGF) and epidermal growth factor (EGF) polypeptide growth factors are closely correlated to malignant transformation and all the steps of the breast cancer metastatic cascade. Numerous studies have demonstrated that both estrogens and growth factors stimulate the proliferation of steroid-dependent tumor cells, and that the interaction between these signaling pathways occurs at several levels. Importantly, the majority of breast cancer cases are estrogen receptor- (ER-) positive which have a more favorable prognosis and pattern of recurrence with endocrine therapy being the backbone of treatment. Unfortunately, the majority of patients progress to endocrine therapy resistant disease (acquired resistance) whereas a proportion of patients may fail to respond to initial therapy (de novo resistance). The IGF-I and EGF downstream signaling pathways are closely involved in the process of progression to therapy resistant disease. Modifications in the bioavailability of these growth factors contribute critically to disease progression. In the present review therefore, we will discuss in depth how IGF and EGF signaling participate in breast cancer pathogenesis and progression to endocrine resistant disease.

A kinase inhibitor screen reveals protein kinase C-dependent endocytic recycling of ErbB2 in breast cancer cells

ErbB2 overexpression drives oncogenesis in 20-30% cases of breast cancer. Oncogenic potential of ErbB2 is linked to inefficient endocytic traffic into lysosomes and preferential recycling. However, regulation of ErbB2 recycling is incompletely understood. We used a high-content immunofluorescence imaging-based kinase inhibitor screen on SKBR-3 breast cancer cells to identify kinases whose inhibition alters the clearance of cell surface ErbB2 induced by Hsp90 inhibitor 17-AAG. Less ErbB2 clearance was observed with broad-spectrum PKC inhibitor Ro 31-8220. A similar effect was observed with Go 6976, a selective inhibitor of classical Ca(2+)-dependent PKCs (α, β1, βII, and γ). PKC activation by PMA promoted surface ErbB2 clearance but without degradation, and ErbB2 was observed to move into a juxtanuclear compartment where it colocalized with PKC-α and PKC-δ together with the endocytic recycling regulator Arf6. PKC-α knockdown impaired the juxtanuclear localization of ErbB2. ErbB2 transit to the recycling compartment was also impaired upon PKC-δ knockdown. PMA-induced Erk phosphorylation was reduced by ErbB2 inhibitor lapatinib, as well as by knockdown of PKC-δ but not that of PKC-α. Our results suggest that activation of PKC-α and -δ mediates a novel positive feedback loop by promoting ErbB2 entry into the endocytic recycling compartment, consistent with reported positive roles for these PKCs in ErbB2-mediated tumorigenesis. As the endocytic recycling compartment/pericentrion has emerged as a PKC-dependent signaling hub for G-protein-coupled receptors, our findings raise the possibility that oncogenesis by ErbB2 involves previously unexplored PKC-dependent endosomal signaling.

Review of the adenocarcinoma cell surface receptor for human alpha-fetoprotein; proposed identification of a widespread mucin as the tumor cell receptor

The identification of a tumor cell receptor for alpha-fetoprotein (AFP) has long been sought in the field of medicine. The uptake and endocytosis of AFP by rat tumor cells in 1983 sparked a series of confirmatory reports which were extended to include multiple tumor types in rats, mice, and humans. The following year, French investigators characterized the binding properties of the AFP receptor but they did not purify and characterize the receptor. It was not until 1991-1992 that an AFP receptor was partially purified and characterized from both human monocytes and breast cancer cells. By 1993, monoclonal antibodies had been raised against the "AFP receptor" derived from breast cancer extracts with claims that the receptor was a widespread oncoprotein biomarker for cancer. To date, that receptor has yet to be identified due to its complex multimeric structure and carbohydrate composition. The present report will review the literature of the multiple AFP receptors previously including their cellular uptake, transmembrane passage, and partial biochemical characterization. . In addition, evidence derived from computer modeling, proteolytic/fragmentation cleavage patterns, domain structure analysis, and protein binding software analysis will be presented in a proposed identification of a widespread protein/gene family of transmembrane proteins which fits many, if not most, of the criteria attributed to the AFP receptor. The proposed receptor protein family is tentatively identified as an epithelial cell surface mucin constituting one (or more) of many classes of single-pass transmembrane proteins. Present data do not support the concept that the AFP receptor is a "universal" tumor receptor and/or biomarker, but rather a widespread mucin protein that functions primarily in protecting and lubricating epithelial mucosal layers, and engaging in signal transduction; the mucin only binds AFP as a molecule serving in a subordinate or ancillary function.

The HER2 Receptor in Breast Cancer: Pathophysiology, Clinical Use, and New Advances in Therapy

Human epidermal growth factor receptor 2 (HER2) is overexpressed in around 20-30% of breast cancer tumors. It is associated with a more aggressive disease, higher recurrence rate, and increased mortality. Trastuzumab is a HER2 receptor blocker that has become the standard of care for the treatment of HER2 positive breast cancer. The effectiveness of Trastuzumab has been well validated in research as well as in clinical practice. The addition of Trastuzumab to standard of care chemotherapy in clinical trials has been shown to improve outcomes for early stage as well as metastatic HER2 positive breast cancer. The most clinically significant side effect of Trastuzumab is the risk of cardiac myocyte injury, leading to the development of congestive heart failure. The emergence of patterns of resistance to Trastuzumab has led to the discovery of new monoclonal antibodies and other targeted agents aimed at overcoming Trastuzumab resistance and improving survival in patients diagnosed with HER2 positive breast cancers.

At the crossroads: EGFR and PTHrP signaling in cancer-mediated diseases of bone

The epidermal growth factor receptor is a well-established cancer therapeutic target due to its stimulation of proliferation, motility, and resistance to apoptosis. Recently, additional roles for the receptor have been identified in growth of metastases. Similar to development, metastatic spread requires signaling interactions between epithelial-derived tumor cells and mesenchymal derivatives of the microenvironment. This necessitates reactivation of developmental signaling molecules, including the hypercalcemia factor parathyroid hormone-related protein. This review covers the variations of epidermal growth factor receptor signaling in cancers that produce bone metastases, regulation of parathyroid hormone-related protein, and evidence that the two molecules drive cancer-mediated diseases of bone.

Testing for HER2 in Breast Cancer: A Continuing Evolution

Human epidermal growth factor receptor 2 (HER2) is an important prognostic and predictive factor in breast cancer. HER2 is overexpressed in approximately 15%–20% of invasive breast carcinomas and is associated with earlier recurrence, shortened disease free survival, and poor prognosis. Trastuzumab (Herceptin) a “humanized” monoclonal antibody targets the extracellular domain of HER2 and is widely used in the management of HER2 positive breast cancers. Accurate assessment of HER2 is thus critical in the management of breast cancer. The aim of this paper is to present a comprehensive review of HER2 with reference to its discovery and biology, clinical significance, prognostic value, targeted therapy, current and new testing modalities, and the interpretation guidelines and pitfalls.

Increasing CD44+/CD24(-) tumor stem cells, and upregulation of COX-2 and HDAC6, as major functions of HER2 in breast tumorigenesis

Background

Cancer cells are believed to arise primarily from stem cells. CD44⁺/CD24^- have been identified as markers for human breast cancer stem cells. Although, HER2 is a well known breast cancer oncogene, the mechanisms of action of this gene are not completely understood. Previously, we have derived immortal (M13SV1), weakly tumorigenic (M13SV1R2) and highly tumorigenic (M13SV1R2N1) cell lines from a breast epithelial cell type with stem cell phenotypes after successive SV40 large T-antigen transfection, X-ray irradiation and ectopic expression of HER2/C-erbB2/neu. Recently, we found that M13SV1R2 cells became non-tumorigenic after growing in a growth factor/hormone-deprived medium (R2d cells).

Results

In this study, we developed M13SV1R2N1 under the same growth factor/hormone-deprived condition (R2N1d cells). This provides an opportunity to analyze HER2 effect on gene expression associated with tumorigenesis by comparative study of R2d and R2N1d cells with homogeneous genetic background except HER2 expression. The results reveal distinct characters of R2N1d cells that can be ascribed to HER2: 1) development of fast-growing tumors; 2) high frequency of CD44⁺/CD24^- cells (~50% for R2N1d vs. ~10% for R2d); 3) enhanced expression of COX-2, HDAC6 mediated, respectively, by MAPK and PI3K/Akt pathways, and many genes associated with inflammation, metastasis, and angiogenesis. Furthermore, HER2 expression can be down regulated in non-adhering R2N1d cells. These cells showed longer latent period and lower rate of tumor development compared with adhering cells.

Conclusions

HER2 may induce breast cancer by increasing the frequency of tumor stem cells and upregulating the expression of COX-2 and HDAC6 that play pivotal roles in tumor progression.

MMTV mouse models and the diagnostic values of MMTV-like sequences in human breast cancer

Mouse mammary tumor virus (MMTV) long terminal repeat (LTR)-driven transgenic mice are excellent models for breast cancer as they allow for the targeted expression of various oncogenes and growth factors in neoplastic transformation of mammary glands. Numerous MMTV-LTR-driven transgenic mouse models of breast cancer have been created in the past three decades, including MMTV-neu/ErbB2, cyclin D1, cyclin E, Ras, Myc, int-1 and c-rel. These transgenic mice develop mammary tumors with different latency, histology and invasiveness, reflecting the oncogenic pathways activated by the transgene. Recently, homologous sequences of the env gene of MMTV have been identified in approximately 40% of human breast cancers, but not in normal breast or other types of cancers, suggesting possible involvement of mammary tumor virus in human breast carcinogenesis. Accumulating evidence demonstrates the association of MMTV provirus with progesterone receptor, p53 mutations and advanced-stage breast cancer. Thus, the detection of MMTV-like sequences may have diagnostic value to predict the clinical outcome of breast cancer patients.

Production and characterisation of monoclonal antibodies against RAI3 and its expression in human breast cancer

Background

RAI3 is an orphan G-protein coupled receptor (GPCR) that has been associated with malignancy and may play a role in the proliferation of breast cancer cells. Although its exact function in normal and malignant cells remains unclear and evidence supporting its role in oncogenesis is controversial, its abundant expression on the surface of cancer cells would make it an interesting target for the development of antibody-based therapeutics. To investigate the link with cancer and provide more evidence for its role, we carried out a systematic analysis of RAI3 expression in a large set of human breast cancer specimens.

Methods

We expressed recombinant human RAI3 in bacteria and reconstituted the purified protein in liposomes to raise monoclonal antibodies using classical hybridoma techniques. The specific binding activity of the antibodies was confirmed by enzyme-linked immunosorbent assay (ELISA), western blot and immunocytochemistry. We carried out a systematic immunohistochemical analysis of RAI3 expression in human invasive breast carcinomas (n = 147) and normal breast tissues (n = 44) using a tissue microarray. In addition, a cDNA dot blot hybridisation assay was used to investigate a set of matched normal and cancerous breast tissue specimens (n = 50) as well as lymph node metastases (n = 3) for RAI3 mRNA expression.

Results

The anti-RAI3 monoclonal antibodies bound to recombinant human RAI3 protein with high specificity and affinity, as shown by ELISA, western blot and ICC. The cDNA dot blot and immunohistochemical experiments showed that both RAI3 mRNA and RAI3 protein were abundantly expressed in human breast carcinoma. However, there was no association between RAI3 protein expression and prognosis based on overall and recurrence-free survival.

Conclusion

We have generated a novel, highly-specific monoclonal antibody that detects RAI3 in formaldehyde-fixed paraffin-embedded tissue. This is the first study to report a systematic analysis of RAI3 expression in normal and cancerous human breast tissue at both the mRNA and protein levels.

Clathrin-independent endocytosis of ErbB2 in geldanamycin-treated human breast cancer cells

The epidermal growth factor (EGF)-receptor family member ErbB2 is commonly overexpressed in human breast cancer cells and correlates with poor prognosis. Geldanamycin (GA) induces the ubiquitylation, intracellular accumulation and degradation of ErbB2. Whether GA stimulates ErbB2 internalization is controversial. We found that ErbB2 was internalized constitutively at a rate that was not affected by GA in SK-BR-3 breast cancer cells. Instead, GA treatment altered endosomal sorting, causing the transport of ErbB2 to lysosomes for degradation. In contrast to earlier work, we found that ErbB2 internalization occurred by a clathrin- and tyrosine-kinase-independent pathway that was not caveolar, because SK-BR-3 cells lack caveolae. Similar to cargo of the glycosylphosphatidylinositol (GPI)-anchored protein-enriched early endosomal compartment (GEEC) pathway, internalized ErbB2 colocalized with cholera toxin B subunit, GPI-anchored proteins and fluid, and was often seen in short tubules or large vesicles. However, in contrast to the GEEC pathway in other cells, internalization of ErbB2 and fluid in SK-BR-3 cells did not require Rho-family GTPase activity. Accumulation of ErbB2 in vesicles containing constitutively active Arf6-Q67L occurred only without GA treatment; Arf6-Q67L did not slow transport to lysosomes in GA-treated cells. Further characterization of this novel clathrin-, caveolae- and Rho-family-independent endocytic pathway might reveal new strategies for the downregulation of ErbB2 in breast cancer.

ERBB3/HER3 and ERBB2/HER2 duet in mammary development and breast cancer

ERBB3/HER3 is one of the four members of the epidermal growth factor receptor (ERBB) family. It is activated by binding to ligands Neuregulin-1 and Neuregulin-2. Since ERBB3 lacks intrinsic kinase activity, signal transduction occurs through formation of heterodimers with EGFR, ERBB2, and ERBB4. ERBB3 is a signaling specialist since it has six binding sites for the p85 SH2 adapter subunit of phosphoinositide 3' kinases. These lipid kinases coordinate regulation of metabolism, cell size, proliferation, survival, and angiogenesis. Not surprisingly, ERBB3 signaling has been linked to cancer etiology and progression. In breast cancer, the partnership of ERBB2 and ERBB3 may be crucial for the aggressive properties of cancers with ERBB2 amplification, and may contribute to pre-existing and acquired resistance to therapy. This partnership creates opportunities for improving efficacy of ERBB-targeted pharmaceuticals, by interfering with coupling of ERBB2 to ERBB3 through dimerization inhibitors, and by use of therapeutic compounds that target AKT-dependent pathways activated through ERBB3. Additional therapeutic opportunities may be identified through better understanding of how ERBBs are regulated and deployed in normal mammary gland processes. Work using mouse models has identified the main processes regulated by each of the four ERBBs, which has practical implications in understanding breast cancer etiology, and eventual development of better prognostic, predictive, and therapeutic tools.

Tight correlation between expression of the Forkhead transcription factor FOXM1 and HER2 in human breast cancer

Background

FOXM1 regulates expression of cell cycle related genes that are essential for progression into DNA replication and mitosis. Consistent with its role in proliferation, elevated expression of FOXM1 has been reported in a variety of human tumour entities. FOXM1 is a gene of interest because recently chemical inhibitors of FOXM1 were described to limit proliferation and induce apoptosis in cancer cells in vitro, indicating that FOXM1 inhibitors could represent useful anticancer therapeutics.

Methods

Using immunohistochemistry (IHC) we systematically analysed FOXM1 expression in human invasive breast carcinomas (n = 204) and normal breast tissues (n = 46) on a tissue microarray. Additionally, using semiquantitative realtime PCR, a collection of paraffin embedded normal (n = 12) and cancerous (n = 25) breast tissue specimens as well as benign (n = 3) and malignant mammary cell lines (n = 8) were investigated for FOXM1 expression. SPSS version 14.0 was used for statistical analysis.

Results

FOXM1 was found to be overexpressed in breast cancer in comparison to normal breast tissue both on the RNA and protein level (e.g. 8.7 fold as measured by realtime PCR). We found a significant correlation between FOXM1 expression and the HER2 status determined by HER2 immunohistochemistry (P < 0.05). Univariate survival analysis showed a tendency between FOXM1 protein expression and unfavourable prognosis (P = 0.110).

Conclusion

FOXM1 may represent a novel breast tumour marker with prognostic significance that could be included into multi-marker panels for breast cancer. Interestingly, we found a positive correlation between FOXM1 expression and HER2 status, pointing to a potential role of FOXM1 as a new drug target in HER2 resistant breast tumour, as FOXM1 inhibitors for cancer treatment were described recently. Further studies are underway to analyse the potential interaction between FOXM1 and HER2, especially whether FOXM1 directly activates the HER2 promoter.

[Molecular protocol for HER2/neu analysis in breast carcinoma]

BACKGROUND

The HER2/neu proto-oncogene is frequently over-expressed in breast cancer and serves as a biological target for trastuzumab therapy. However, there is no consensus regarding the technical aspects to be used to define HER2/neu status in clinical practice.

METHODS

The present study was conducted to address this critical issue by prospectively analysing a large cohort of breast cancer patients (n = 222) and using a variety of methods. To define HER2/neu expression, detection of its encoded protein (p185) was performed by comparative immunohistochemical (IHC) analysis using two mouse monoclonal antibodies (mAb CB11 and mAb TAB250). To assess HER2/neu gene amplification, fluorescent in situ hybridisation (FISH) assays with gene-specific probes were conducted. All procedures were applied to de-paraffinised tissue sections of breast tumour samples.

RESULTS

Results showed that mAb CB11 had increased sensitivity and specificity (62.5% and 93.4%, respectively) compared to mAb TAB250 (40% and 76.4%, respectively) in defining HER2/neu amplification. We conclude that HER2/neu measurement by IHC using mAb CB11 is an appropriate strategy which provides a high negative predictive value (95.5%) for HER2/neu amplification in cases with low or undetectable p185 expression. Conversely, mAb CB11 has a high positive predictive value (96.2%) for HER2/neu amplification in cases with p185 overexpression. However, cases with moderate p185 expression need to be considered as inconclusive. In such cases, it is necessary to use FISH measurement to evaluate HER2/neu amplification. It is also advisable to conduct FISH if there is discordance between p185 expression and the histopathology classification of the lesion, or molecular profile of the tumour. Finally, even though the false positive rate of IHC assay is <5%, the toxicity and cost of trastuzumab therapy suggest that FISH be used systematically prior to implementation of treatment.

CONCLUSION

We suggest the use of a molecular protocol for HER2/neu analysis in this type of tumor.

c-erbB2 and topoisomerase IIalpha protein expression independently predict poor survival in primary human breast cancer: a retrospective study

Introduction

c-erbB2 (also known as HER-2/neu) and topoisomerase IIα are frequently overexpressed in breast cancer. The aim of the study was to analyze retrospectively whether the expression of c-erbB2 and topoisomerase IIα protein influences the long-term outcome of patients with primary breast cancer.

Methods

In this study c-erbB2 and topoisomerase IIα protein were evaluated by immunohistochemistry in formalin-fixed paraffin-embedded tissue from 225 samples of primary breast cancer, obtained between 1986 and 1998. The prognostic value of these markers was analyzed.

Results

Of 225 primary breast tumor samples, 78 (34.7%) showed overexpression of either c-erbB2 (9.8%) or topoisomerase IIα protein (24.9%), whereas in 21 tumors (9.3%) both proteins were found to be overexpressed. Patients lacking both c-erbB2 and topoisomerase IIα overexpression had the best long-term survival. Overexpression of either c-erbB2 or topoisomerase IIα was associated with shortened survival, whereas patients overexpressing both c-erbB2 and topoisomerase IIα showed the worst disease outcome (P < 0.0001). Treatment with anthracyclines was not capable of reversing the negative prognostic impact of topoisomerase IIα or c-erbB2 overexpression.

Conclusion

The results of this exploratory study suggest that protein expression of c-erbB2 and topoisomerase IIα in primary breast cancer tissues are independent prognostic factors and are not exclusively predictive factors for anthracycline response in patients with primary breast cancer.

Her2/neu overexpression in differentiated thyroid carcinomas predicts metastatic disease

To investigate the prognostic value of Her2/neu expression in differentiated thyroid carcinomas 103 patients were retrospectively investigated. All of them received surgical and an identical follow-up treatment. The patients with papillary and follicular thyroid cancer were further separated into two groups concerning their clinical development, including one group without distant metastasis (follow-up of minimum 8 years). The second group presented with distant metastases as a sign of an aggressive behaviour. Her2/neu was immunohistochemically detected on sections from formalin-fixed, paraffin-embedded tissues using c-erbB-2/Her-2/neu oncoprotein Ab-17 monoclonal antibody (mAb). In statistical analysis using the Mann-Whitney U-test and chi(2) test, Her2/neu protein overexpression was significantly correlated with prognosis. Both tumour entities without distant metastases showed significantly less cytoplasmic immunostaining than patients with development of metastases. Concerning the clinical outcome, Her2/neu overexpression may be regarded as a prognostic factor in differentiated thyroid carcinomas. Moreover, in addition to standard radio-iodine elimination therapy, application of Herceptin could lead to new successful therapeutic concepts for a number of patients with progressive thyroid cancer.

Evaluation of HER-2/neu gene amplification and protein expression in non-small cell lung carcinomas

HER-2/neu gene amplification and cell surface overexpression are important factors in breast cancer for prognosis and prediction of sensitivity to anti-HER-2/neu monoclonal antibody therapy. In lung cancer, the clinical significance of HER-2/neu expression is currently under evaluation. We investigated 238 non-small lung carcinomas for HER-2/neu protein overexpression by immunohistochemistry using the HercepTest. We found 2+ or 3+ overexpression in 39 patients (16%), including 35% in adenocarcinomas and 20% in large cell carcinomas, but only 1% of squamous cell carcinomas. Marked (3+) overexpression was uncommon (4%). The association between protein expression and gene copy number per cell, as determined by fluorescence in situ hybridisation assay, was investigated in 51 of these NSCLC tumours. Twenty-seven tumours (53%) were negative by both tests. Marked (3+) protein expression and gene amplification were present in only 4% of samples. In 11 tumours (21%), gene gain was accompanied by chromosomal aneusomy and did not result in high protein levels while in 7 (14%) the score 2+ was associated with maximum number of signals per cell <9. The prognostic implication of HER-2/neu protein expression was studied in 187 surgically resected tumours. No statistical difference in survival was observed comparing patients with positive (2+/3+) and negative tumours (0/1+), although 3+ patients showed a tendency to shorter survival. The therapeutic implications of protein expression and gene amplification in lung cancer need to be examined in prospective clinical trials.

Overexpression of ErbB2 in cancer and ErbB2-targeting strategies

This past decade has witnessed the remarkable advances in the understanding of the role of the erbB2 gene in cancers and the stunning progress in developing targeted therapies for erbB2-overexpressing cancers. Activation of the ErbB2 receptor signaling pathways can enhance various metastasis-associated properties that lead to an increase of cancer metastasis. Additionally, ErbB2 overexpression confers therapeutic resistance via receptor-mediated antiapoptotic signals. To limit these disastrous effects of the overexpressed ErbB2, various ErbB2-blocking strategies have been developed in the laboratories and several have been tested in clinical trials or approved as therapies for ErbB2 overexpressing cancers. In this article, we will discuss the detrimental effects of the erbB2 gene in cancers, with a focus on breast cancer. We will also outline ErbB2-targeting strategies as potential therapies for ErbB2-overexpressing cancers. Progress in understanding the molecular biology of ErbB2 and in molecular-based treatment of ErbB2-overexpressing tumors will bring great benefits to cancer patients.

Transgenic mouse models of human breast cancer

The pathogenesis of human breast cancer is thought to involve multiple genetic events, the majority of which fall into two categories, gain of function mutations in proto-oncogenes such as c-myc, cyclin D1, ErbB-2 and various growth factors which are involved in supporting cell growth, division and survival, and loss of function mutations in so called 'tumor suppressor' genes, such as p53, which are involved in preventing unrestrained cellular growth. A number of mouse systems exist to address the significance of these mutations in the pathogenesis of breast cancer including transgenic mice expressing high levels of a specific gene in target tissues and knockout mice in which specific genes have been ablated via homologous recombination. More recently, the combination of these techniques to create bigenics as well as the use of 'knockin' and conditional tissue specific gene targeting strategies have allowed the models more reflective of the human disease to be devised. Studies with these models have not only implicated particular genetic events in the progression of the disease but have emphasized the complex, multi-step nature of breast cancer progression. These models also provide the opportunity to study various aspects of the pathogenesis of this disease, from hormonal effects to responses to chemotherapeutic drugs. It is hoped that through the combined use of these models, and the further development of more relevant models, that a deeper understanding of this disease and the generation of new therapeutic agents will result.

Serine phosphorylation of paxillin by heregulin-beta1: role of p38 mitogen activated protein kinase

The mechanisms through which heregulin (HRG) regulates the progression of breast cancer cells to a more invasive phenotype are currently unknown. Recently we have shown that HRG treatment of breast cancer cells leads to the formation of lamellipodia/filopodia, and increased cell migration and invasiveness through the phosphatidylinositol 3-kinase (PI-3 kinase). Since the process of cell migration must involve changes in adhesion, we explored the potential HRG regulation of paxillin, a major cytoskeletal phosphoprotein of focal adhesion. We report that HRG stimulation of non-invasive breast cancer cells resulted in stimulation of p38 mitogen-activated protein kinase (p38MAPK), extracellular signal-regulated kinases (ERK) and PI-3K, and a concurrent unexpected increase in the level of paxillin phosphorylation on serine residue which was sensitive to protein-phosphatase 2b but not to protein tyrosine phosphatase 1. In addition, HRG triggered a rapid redistribution of paxillin to the perinuclear regions from the tyrosine-phosphorylated focal adhesions, and increased cell scattering. There was no effect of HRG on the state of phosphorylation and localization of focal adhesion kinase. The HRG-induced increase in serine phosphorylation of paxillin and cell scattering were selectively inhibited by a specific inhibitor of p38MAPK or a dominant-negative p38MAPK mutant, but not by inhibitors of p42/44MAPK or PI-3 kinase pathways. For the first time our results have shown that HRG, a potent migratory growth factor stimulates serine phosphorylation of paxillin. These findings suggest a role of p38MAPK-dependent signal transduction pathway(s) in serine phosphorylation and disassembly of the paxillin from the focal complexes during HRG-induced cell shape alterations and motility.

ErbB4 signaling in the mammary gland is required for lobuloalveolar development and Stat5 activation during lactation

Signaling by members of the epidermal growth factor receptor family plays an important role in breast development and breast cancer. Earlier work suggested that one of these receptors, ErbB4, is coupled to unique responses in this tissue. To determine the function of ErbB4 signaling in the normal mouse mammary gland, we inactivated ErbB4 signaling by expressing a COOH terminally deleted dominant-negative allele of ErbB4 (ErbB4DeltaIC) as a transgene in the mammary gland. Despite the expression of ErbB4DeltaIC from puberty through later stages of mammary development, an ErbB4DeltaIC-specific phenotype was not observed until mid-lactation. At 12-d postpartum, lobuloalveoli expressing ErbB4DeltaIC protein were condensed and lacked normal lumenal lactation products. In these lobuloalveoli, beta-casein mRNA, detected by in situ hybridization, was normal. However, whey acidic protein mRNA was reduced, and alpha-lactalbumin mRNA was undetectable. Stat5 expression was detected by immunohistochemistry in ErbB4DeltaIC-expressing tissue. However, Stat5 was not phosphorylated at Y694 and was, therefore, probably inactive. When expressed transiently in 293T cells, ErbB4 induced phosphorylation of Stat5. This phosphorylation required an intact Stat5 SH2 domain. In summary, our results demonstrate that ErbB4 signaling is necessary for mammary terminal differentiation and Stat5 activation at mid-lactation.

The HER-2/neu receptor tyrosine kinase gene encodes a secreted autoinhibitor

HER-2/neu (erbB-2) encodes an 185-kDa orphan receptor tyrosine kinase that is constitutively active as a dimer and displays potent oncogenic activity when overexpressed. Here we describe a secreted protein of approximately 68 kDa, designated herstatin, as the product of an alternative HER-2 transcript that retains intron 8. This alternative transcript specifies 340 residues identical to subdomains I and II from the extracellular domain of p185HER-2 followed by a unique C-terminal sequence of 79 aa encoded by intron 8. The recombinant product of the alternative transcript specifically binds to HER-2-transfected cells with a K(D) of approximately 14 nM and was chemically crosslinked to p185HER-2, whereas the intron encoded sequence alone also binds with high affinity to transfected cells and associates with p185 solubilized from cell extracts. The herstatin mRNA is expressed in normal human fetal kidney and liver, but is at reduced levels relative to p185HER-2 mRNA in carcinoma cells that contain an amplified HER-2 gene. Herstatin appears to be an inhibitor of p185HER-2, because it disrupts dimers, reduces tyrosine phosphorylation of p185, and inhibits the anchorage-independent growth of transformed cells that overexpress HER-2.

Expression of dominant-negative ErbB2 in the mammary gland of transgenic mice reveals a role in lobuloalveolar development and lactation

Overexpression of the receptor tyrosine kinase ErbB2/HER2/Neu (ErbB2) occurs in 15-40% of human breast cancers. To determine the function of ErbB2 signaling during normal mouse mammary gland development, we expressed a carboxyl-terminal truncated dominant negative allele of ErbB2 (ErbB2deltaIC) in the developing mouse mammary gland. Despite ErbB2deltaIC expression within mammary glands of pubescent virgin and pregnant mice, a phenotype was not observed until late in pregnancy. At 1 day post-partum, lactationally active, distended lobuloalveoli failed to form. This phenotype was exaggerated in multiparous females expressing ErbB2deltaIC. Immunohistochemical staining for ErbB2deltaIC revealed a concordance between high levels of ErbB2deltaIC protein expression and the absence of lactational products within the lumens of ErbB2deltaIC stained lobuloalveoli. These results demonstrate that ErbB2 signaling is required for proper mammary development and lactation at parturition.

Activation of Neu (ErbB-2) mediated by disulfide bond-induced dimerization reveals a receptor tyrosine kinase dimer interface

Receptor dimerization is a crucial intermediate step in activation of signaling by receptor tyrosine kinases (RTKs). However, dimerization of the RTK Neu (also designated ErbB-2, HER-2, and p185(neu)), while necessary, is not sufficient for signaling. Earlier work in our laboratory had shown that introduction of an ectopic cysteine into the Neu juxtamembrane domain induces Neu dimerization but not signaling. Since Neu signaling does require dimerization, we hypothesized that there are additional constraints that govern signaling ability. With the importance of the interreceptor cross-phosphorylation reaction, a likely constraint was the relative geometry of receptors within the dimer. We have tested this possibility by constructing a consecutive series of cysteine substitutions in the Neu juxtamembrane domain in order to force dimerization along a series of interreceptor faces. Within the group that dimerized constitutively, a subset had transforming activity. The substitutions in this subset all mapped to the same face of a predicted alpha helix, the most likely conformation for the intramembrane domain. Furthermore, this face of interaction aligns with the projected Neu* V664E substitution and with a predicted amphipathic interface in the Neu juxtamembrane domain. We propose that these results identify an RTK dimer interface and that dimerization of this RTK induces an extended contact between juxtamembrane and intramembrane alpha helices.

Prediction of recurrence by quantification of p185neu protein in non-small-cell lung cancer tissue

The concentration of c-erbB-2 oncogene-encoded protein (p185neu) in fresh tumour samples obtained at the time of surgery from 94 non-small-cell lung cancer patients (NSCLC) was determined by an enzyme immunoassay. The relative prognostic importance was estimated, and the influence of other predictors was assessed by means of a Cox's proportional regression model. Median concentration of p185 in tumour tissues was 206 U mg(-1) (range 21-1050 U mg(-1)). p185 level did not differ significantly among subgroups defined by TNM classification, histological type, sex and age. Categorization of patients by p185 level, with 206 U mg(-1) and 343 U mg(-1) taken as cut-off values (corresponding to the 50th and 80th percentiles of the frequency distribution), showed that the recurrence rate, cumulative disease-free likelihood at the 36-month follow-up and median time from surgery to the diagnosis of recurrence worsened progressively as the level of p185 increased. Multivariate analysis confirmed the independent prognostic value of p185 level. Risk of recurrence increased by 1.304 for every increase of 100 units in p185 concentration (95% CI 1.141-1.490) (P<0.001). These findings encourage the inclusion of p185 concentration assay in a future predictive multifactorial prognostic index in NSCLC.

Epidermal growth factor receptor expression in pancreatic lesions induced in the rat by azaserine

In the present study, the expression of the epidermal growth factor receptor (EGFR) was investigated in putative preneoplastic and neoplastic acinar cell lesions induced in the rat pancreas by azaserine, using Northern blotting, in situ hybridisation (ISH) and immunohistochemistry. EGFR protein levels were decreased in putative preneoplastic eosinophilic acinar cell lesions (atypical acinar cell nodules, AACN) in comparison with normal acinar cells of the pancreas. However, EGFR mRNA expression correlated positively with the volume of AACN in pancreatic homogenates and ISH showed equal or stronger EGFR mRNA expression in AACN than in the surrounding normal acinar cells. Neither EGFR protein nor EGFR mRNA was detected in more advanced lesions such as acinar adenocarcinomas (in situ). Moreover, EGFR protein expression showed an inverse relationship with the mitotic rate of the acinar cells. These findings suggest that down-regulation of EGFR at the protein level may abrogate negative constraints on cell growth, which may stimulate the development of putative preneoplastic AACN to more advanced lesions and, ultimately, acinar adenocarcinomas.

Cell cycle-dependent regulation of p185neu: a relationship between disruption of this regulation and transformation

Structure and function of p185neu receptor tyrosine kinase were found to be regulated in a cell cycle-dependent manner. In M phase, p185neu is hyperphosphorylated at serine and/or threonine residues. The phosphotyrosine [Tyr(P)] content of p185neu is at its highest level in G0/G1 phase, decreases through S and G2 phases, and reaches its lowest level in M phase. Phospholipase C-gamma (PLC-gamma) and GTPase-activating protein (GAP), substrates of p185neu, also have a similar profile of Tyr(P) content during the cell cycle. These results, along with in vitro immune complex kinase assays, suggest that the tyrosine kinase activity of p185neu is least active in M phase. Interestingly, the mutation-activated neu oncogene (neu*)-encoded protein product, p185neu* escaped from cell cycle regulation. Taken together, we demonstrate in this report that the structure and function of p185neu are regulated in a cell cycle-dependent manner, yet p185neu* escapes from this regulation and remains active through the cell cycle. Disruption of this cell cycle regulation may define a mechanism for p185neu*-mediated cellular transformation.

Differential responses of human tumor cell lines to anti-p185HER2 monoclonal antibodies

The HER2 protooncogene encodes a receptor tyrosine kinase, p185HER2. The overexpression of p185HER2 has been associated with a worsened prognosis in certain human cancers. In the present work we have screened a variety of different tumor cell lines for p185HER2 expression using both enzyme-linked immunosorbent and fluorescence-activated cell sorting assays employing murine monoclonal antibodies directed against the extracellular domain of the receptor. Increased levels of p185HER2 were found in breast (5/9), ovarian (1/6), stomach (2/3) and colorectal (5/16) carcinomas, whereas all kidney and submaxillary adenocarcinoma cell lines tested were negative. Some monoclonal antibodies directed against the extracellular domain of p185HER2 inhibited growth in monolayer culture of breast and ovarian tumor cell lines overexpressing p185HER2, but had no effect on the growth of colon or gastric adenocarcinomas expressing increased levels of this receptor. The most potent growth-inhibitory anti-p185HER2 monoclonal antibody in monolayer culture, designated mumAb 4D5 (a murine IgG1 kappa antibody), was also tested in soft-agar growth assays for activity against p185HER2-overexpressing tumor cell lines of each type, with similar results. In order to increase the spectrum of tumor types potentially susceptible to monoclonal antibody-mediated anti-p185HER2 therapies, to decrease potential immunogenicity issues with the use of murine monoclonal antibodies for human therapy, and to provide the potential for antibody-mediated cytotoxic activity, a mouse/human chimeric 4D5 (chmAb 4D5) and a "humanized" 4D5 (rhu)mAb 4D5 HER2 antibody were constructed. Both engineered antibodies, in combination with human peripheral blood mononuclear cells, elicited antibody-dependent cytotoxic responses in accordance with the level of p185HER2 expression. Since this cytotoxic activity is independent of sensitivity to mumAb 4D5, the engineered monoclonal antibodies expand the potential target population for antibody-mediated therapy of human cancers characterized by the overexpression of p185HER2.

Neural expression and chromosomal mapping of Neu differentiation factor to 8p12-p21

Neu differentiation factor (NDF/heregulin) is a 44-kDa glycoprotein that interacts with the Neu/ErbB-2 receptor tyrosine kinase to increase its phosphorylation on tyrosine residues. In vitro NDF promotes differentiation of certain mammary tumor cell lines to milk-producing cells. As a first step toward understanding the physiological role of NDF, we performed in situ hybridization analyses to determine mRNA distribution in the mouse embryo and to map the gene to human karyotypes. In 14.5-day-postcoitum mouse embryos, NDF expression is confined predominantly to the central and peripheral nervous system, including the neuroepithelium that lines the lateral ventricles of the brain, the ventral horn of the spinal cord, and the intestinal as well as dorsal root ganglia. Other tissues that contain NDF transcripts are the adrenal gland, liver, and distinct cell layers of the dermis and germinal ridge. In situ hybridization of a 3H-labeled probe to human metaphase spreads localized the NDF gene to the short arm of chromosome 8 at bands p12-p21.

Antiserum raised against a synthetic phosphotyrosine-containing peptide selectively recognizes p185neu/erbB-2 and the epidermal growth factor receptor

Rabbits were immunized with a synthetic phosphopeptide corresponding to a major autophosphorylation site of p185neu/erbB2 to determine the feasibility of producing tyrosine-phosphopeptide-specific antibodies. A series of adsorption and affinity chromatography steps were used to select antibodies with the desired reactivity. Immunoblot experiments showed that the resulting serum is highly specific for tyrosine-phosphorylated forms of p185 and the related epidermal growth factor receptor. The serum recognized these two receptors selectively when compared to five other receptor tyrosine kinases and several phosphorylated substrates. The serum is compatible with tissue-based assays since it detected tyrosine phosphorylation of the epidermal growth factor receptor in immunofluorescence experiments on permeabilized cells. The generality of the procedures used means that similar anti-tyrosine phosphopeptide sera can be produced that recognize other tyrosine kinases and substrates. Such sera will have numerous applications in research and clinical settings.

Negative autoregulation of the neu gene is mediated by a novel enhancer

In an attempt to study potential feedback regulation of the neu oncogene, we have found that the neu oncogene product specifically represses its own promoter activity. Deletion analysis indicated a 140-bp region (nucleotides -312 to -173 relative to the ATG initiation codon) in the rat neu promoter responsible for neu autorepression. Gel shift assays and methylation interference analysis further demonstrated that a GGTGGGGGGG sequence (nucleotides -243 to -234 relative to the ATG initiation codon) in this 140-bp region interacts with specific protein complexes. The GGTGGGGGGG sequence (GTG element), which functions as an enhancer, is sufficient to cause neu-mediated repression in a heterologous promoter. Furthermore, it produces different gel shift patterns with nuclear extracts from neu-transformed cell lines and their parental lines, suggesting that a transcriptional factor(s) interacting with this enhancer element has been perturbed by the introduction of neu. Taken together, the data presented in this report show that (i) the neu oncogene product autorepresses its own promoter, (ii) the neu promoter contains a novel enhancer, and (iii) neu autorepression is mediated through this enhancer, likely by inhibition of the enhancer activity.

Negative autoregulation of the neu gene is mediated by a novel enhancer

In an attempt to study potential feedback regulation of the neu oncogene, we have found that the neu oncogene product specifically represses its own promoter activity. Deletion analysis indicated a 140-bp region (nucleotides -312 to -173 relative to the ATG initiation codon) in the rat neu promoter responsible for neu autorepression. Gel shift assays and methylation interference analysis further demonstrated that a GGTGGGGGGG sequence (nucleotides -243 to -234 relative to the ATG initiation codon) in this 140-bp region interacts with specific protein complexes. The GGTGGGGGGG sequence (GTG element), which functions as an enhancer, is sufficient to cause neu-mediated repression in a heterologous promoter. Furthermore, it produces different gel shift patterns with nuclear extracts from neu-transformed cell lines and their parental lines, suggesting that a transcriptional factor(s) interacting with this enhancer element has been perturbed by the introduction of neu. Taken together, the data presented in this report show that (i) the neu oncogene product autorepresses its own promoter, (ii) the neu promoter contains a novel enhancer, and (iii) neu autorepression is mediated through this enhancer, likely by inhibition of the enhancer activity.

Expression and characterization of kinase-active v-erbB protein using a baculovirus vector system

The v-erbB gene is an oncogene of the avian erythroblastosis virus encoding a protein that is a truncated version of the epidermal growth factor receptor. The v-erbB protein was expressed alone or as polyhedrin-erbB fusion proteins using the Bombyx mori nuclear polyhedrosis virus vector. The expression level of the fusion protein whose polyhedrin portion consisted of only 8 amino-terminal amino acids was more than ten times higher than that of the non-fusion protein. Studies with tunicamycin showed that the recombinant v-erbB proteins were glycosylated. The recombinant protein autophosphorylated tyrosine residues, and phosphorylated a synthetic tyrosine-containing peptide and lipocortin I. These observations indicate that functional v-erbB protein can be expressed in silkworm-derived cells, and furthermore, that this system can be used for large-scale production.

Down-regulation of cellular platelet-derived growth factor receptors induced by an activated neu receptor tyrosine kinase

The functional integration of growth factor signaling occurs at several levels in target cells. One of the most proximal mechanisms is receptor transmodulation, by which one activated receptor can regulate the expression of other receptors in the same cells. Well-established transregulatory loops involve platelet-derived growth factor (PDGF) down-regulation of epidermal growth factor (EGF) receptors and beta-type transforming growth factors modulation of PDGF receptors. We have studied the relationship between neu tyrosine kinase activation and the expression of the PDGF receptors in transfected NIH/3T3 cells. Expression of the neu oncogene, but not of the neu proto-oncogene, was associated with a decrease of PDGF alpha- and beta-receptors on the cell surface, as measured by [125-I]PDGF-AA and -BB binding. These results were corroborated by metabolic labeling and immunoprecipitation of the PDGF beta-receptors. PDGF alpha- and beta-receptor mRNAs were strongly decreased in the neu oncogene-transformed cells in comparison with control cells expressing the neu proto-oncogene. Down-regulation of the PDGF receptors and their mRNAs was also observed after EGF treatment of cells expressing a chimeric EGF receptor/neu receptor, where the neu tyrosine kinase is activated by EGF binding. These results show that the neu tyrosine kinase can down-modulate PDGF receptor expression, and the effect is mediated via decreased PDGF receptor mRNA levels.

Regulation of phosphorylation of the c-erbB-2/HER2 gene product by a monoclonal antibody and serum growth factor(s) in human mammary carcinoma cells

Monoclonal antibody (MAb) 4D5 was used to analyze the phosphorylation of p185HER2, the gene product of c-erbB-2/HER2, in SK-BR-3 cells. Culture in the continuous presence of 4D5 reduced the in vivo steady-state levels of p185HER2 phosphorylation by 80% in a dose-dependent manner, suggesting that MAb 4D5 may have interfered with the activation of phosphorylation of p185HER2. The observed MAb-mediated reduction of p185HER2 phosphorylation could not be completely accounted for by down-regulation. When cultures were grown under serum-free conditions, the steady-state levels of p185HER2 phosphorylation were reduced by 56%, and addition of 4D5 further inhibited phosphorylation to 20% of steady-state levels. With continuous exposure to increasing concentrations of newborn calf serum in these cultures, there was a linear increase in tyrosine-specific phosphorylation of p185HER2, reaching a 5.4-fold increase with 10% newborn calf serum. Phosphorylation of p185HER2 in the presence of newborn calf serum was not attributable to stimulation of the epidermal growth factor receptor by epidermal growth factor or by transforming growth factor-alpha. Extension of these observations to two other mammary carcinoma cell lines. MDA-MB-453 and BT-474, also demonstrated a significant capacity of serum to induce p185HER2 phosphorylation. The demonstration of antibody-mediated partial inhibition of phosphorylation under serum-free conditions suggests that mammary carcinoma cells may also produce and secrete a factor or factors which may activate p185HER2. Our observation that growth-inhibitory MAb 4D5 is able to reduce the phosphorylation of p185HER2 by newborn calf serum and by a cellular-derived factor(s) suggests the existence of a growth factor(s) which uses phosphorylation of p185HER2 as a signal transduction pathway to regulate cell proliferation.

Spk1, a new kinase from Saccharomyces cerevisiae, phosphorylates proteins on serine, threonine, and tyrosine

A Saccharomyces cerevisiae lambda gt11 library was screened with antiphosphotyrosine antibodies in an attempt to identify a gene encoding a tyrosine kinase. A subclone derived from one positive phage was sequenced and found to contain an 821-amino-acid open reading frame that encodes a protein with homology to protein kinases. We tested the activity of the putative kinase by constructing a vector encoding a glutathione-S-transferase fusion protein containing most of the predicted polypeptide. The fusion protein phosphorylated endogenous substrates and enolase primarily on serine and threonine. The gene was designated SPK1 for serine-protein kinase. Expression of the Spk1 fusion protein in bacteria stimulated serine, threonine, and tyrosine phosphorylation of bacterial proteins. These results, combined with the antiphosphotyrosine immunoreactivity induced by the kinase, indicate that Spk1 is capable of phosphorylating tyrosine as well as phosphorylating serine and threonine. In in vitro assays, the fusion protein kinase phosphorylated the synthetic substrate poly(Glu/Tyr) on tyrosine, but the activity was weak compared with serine and threonine phosphorylation of other substrates. To determine if other serine/threonine kinases would phosphorylate poly(Glu/Tyr), we tested calcium/calmodulin-dependent protein kinase II and the catalytic subunit of cyclic AMP-dependent protein kinase. The two kinases had similar tyrosine-phosphorylating activities. These results establish that the functional difference between serine/threonine- and tyrosine-protein kinases is not absolute and suggest that there may be physiological circumstances in which tyrosine phosphorylation is mediated by serine/threonine kinases.

The transforming potential of the c-erbB-2 protein is regulated by its autophosphorylation at the carboxyl-terminal domain

The mutant c-erbB-2 protein with Glu instead of Val-659 exhibited transforming activity in NIH 3T3 cells. This protein showed enhanced tyrosine kinase activity in vitro and enhanced autophosphorylation at Tyr-1248 located proximal to the carboxyl terminus. Enhanced tyrosine phosphorylation of several cellular proteins was detected in cells expressing the Glu-659 c-erbB-2 protein. Introduction of an additional mutation at the ATP-binding site (Lys-753 to Met) of this protein resulted in abolition of its transforming ability. These data indicate that the transforming potential of c-erbB-2 is closely correlated with elevated tyrosine kinase activity of the gene product. To investigate the role of autophosphorylation in cell transformation, we introduced an additional mutation at the autophosphorylation site of the Glu-659 c-erbB-2 protein (Tyr-1248 to Phe). This mutant protein exhibited lower tyrosine kinase activity and lower transforming activity. On the other hand, when the carboxyl-terminal 230 amino acid residues were deleted from the c-erbB-2 protein, the tyrosine kinase activity and cell-transforming activity of the protein were enhanced. Thus, the carboxyl-terminal domain, which contains the major autophosphorylation site, Tyr-1248, may regulate cellular transformation negatively and autophosphorylation may eliminate this negative regulation.