Aspergillus thyroiditis: first antemortem case diagnosed by fine-needle aspiration culture in a pediatric stem cell transplant patient

Aspergillus thyroiditis (AT) has historically been considered a postmortem diagnosis in immunocompromised patients; most have disseminated disease. This report summarizes the clinical challenge of diagnosing AT. It also highlights the value of the early use of thyroid fine-needle aspiration culture and the need for a high index of suspicion to reach the final diagnosis before disease dissemination.

Impaired cell death and mammary gland involution in the absence of Dock1 and Rac1 signaling

Throughout life, the tight equilibrium between cell death and the prompt clearance of dead corpses is required to maintain a proper tissue homeostasis and prevent inflammation. Following lactation, mammary gland involution is triggered and results in the death of excessive epithelial cells that are rapidly cleared by phagocytes to ensure that the gland returns to its prepregnant state. Orthologs of Dock1 (dedicator of cytokinesis 1), Elmo and Rac1 (ras-related C3 botulinum toxin substrate 1) in Caenorhabditis elegans are part of a signaling module in phagocytes that is linking apoptotic cell recognition to cytoskeletal reorganization required for engulfment. In mammals, Elmo1 was shown to interact with the phosphatidylserine receptor Bai1 and relay signals to promote phagocytosis of apoptotic cells. Still, the role of the RacGEF Dock1 in the clearance of dying cells in mammals was never directly addressed. We generated two mouse models with conditional inactivation of Dock1 and Rac1 and revealed that the expression of these genes is not essential in the mammary gland during puberty, pregnancy and lactation. We induced mammary gland involution in these mice to investigate the role of Dock1/Rac1 signaling in the engulfment of cell corpses. Unpredictably, activation of Stat3 (signal transducer and activator of transcription 3), a key regulator of mammary gland involution, was impaired in the absence of Rac1 and Dock1 expression. Likewise, failure to activate properly Stat3 was coinciding with a significant delay in the initiation and progression of mammary gland involution in mutant animals. By using an in vitro phagocytosis assay, we observed that Dock1 and Rac1 are essential to mediate engulfment in epithelial phagocytes. In vivo, cell corpses accumulated at late time points of involution in Dock1 and Rac1 mutant mammary glands. Overall, our study demonstrated an unsuspected role for Dock1/Rac1 signaling in the initiation of mammary gland involution, and also suggested a role for this pathway in the clearance of dead cells by epithelial phagocytes.

Abstract P5-18-08: Identification of ErbB2 function in the heart: implication for anti-ErbB2 therapy in breast cancer

The ErbB2 receptor tyrosine kinase is essential for cardiac development during embryogenesis. The importance of its signaling in the adult heart was revealed by an unexpected cardiotoxic side effect of trastuzumab, a monoclonal antibody against ErbB2 used in the treatment of breast cancer. Considering that trastuzumab-associated cardiotoxicity is usually largely reversible, we hypothesized that ErbB2 signaling in the heart is important to maintain cardiac homeostasis.

As genetic experiments showed that ErbB2-deficient embryos die at mid-gestation, whereas conditional inactivation of ErbB2 in the heart leads to early and severe cardiac dysfunction, the role of ErbB2 in the mature heart can not be analyzed in those animal models. Thus, we chose an ErbB2 hypomorph (HP) mouse model in which ErbB2 is expressed at only 10% of its endogenous level to study the role of ErbB2 in the adult heart. Histopathological analyses of the heart in this model revealed that at birth, the ErbB2 HP mice have similar heart mass and cardiomyocite size as the control animals. However, we found that the rapid growth of the heart during early postnatal development is impaired in ErbB2 HP mice, indicating that the heart is unable to increase cell size in order to adapt to the pressure overload that mice face following birth. This incapacity of the ErbB2 HP heart to maintain homeostasis eventually leads to the development of cardiac dysfunction in this model, as characterized by a decrease of the left ventricular function. Microarray and ChIP-seq analyses were applied to identify the ErbB2-responsive pathways which may explain the phenotype observed. Taken together, our results demonstrate that ErbB2 signaling is required for the physiological adaptive response of the mature heart to pressure burden. The results generated by this study reveal the biological function of Erbb2 in the adult heart, but also provide important information for devising strategies to prevent and mitigate the cardiotoxic effects of Trastuzumab treatment, allowing for the potential use of this drug to treat all cancer patients overexpressing ErbB2.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P5-18-08.

eIF4F suppression in breast cancer affects maintenance and progression

Levels of eukaryotic initiation factor 4E (eIF4E) are frequently elevated in human cancers and in some instances have been associated with poor prognosis and outcome. Here we utilize transgenic and allograft breast cancer models to demonstrate that increased mammalian target of rapamycin (mTOR) signalling can be a significant contributor to breast cancer progression in vivo. Suppressing mTOR activity, as well as levels and activity of the downstream translation regulators, eIF4E and eIF4A, delayed breast cancer progression, onset of associated pulmonary metastasis in vivo and breast cancer cell invasion and migration in vitro. Translation of vascular endothelial growth factor (VEGF), matrix metallopeptidase 9 (MMP9) and cyclin D1 mRNAs, which encode products associated with the metastatic phenotype, is inhibited upon eIF4E suppression. Our results indicate that the mTOR/eIF4F axis is an important contributor to tumor maintenance and progression programs in breast cancer. Targeting this pathway may be of therapeutic benefit.

Lipid peroxidation in the freshwater shrimp Caridina nilotica as a biomarker of Roundup(®) herbicide pollution of freshwater systems in South Africa

Glyphosate-based herbicides used to control weeds and invading alien plant species in South Africa ultimately end up in freshwater ecosystems, but no South African environmental water quality guideline exists to regulate these bio-active chemicals. Ecotoxicological tests to assess the possibility of using lipid peroxidation (LPx) in Caridina nilotica as a potential biomarker of Roundup(®), a glyphosate-based herbicide, pollution were conducted. In two separate tests, 40 days post hatch shrimps were exposed to different concentrations of 4.3, 6.7, 10.5, 16.4, 25.6 and 40.0 mg/L in a 96 h acute toxicity test; and 2.2, 2.8, 3.4, 4.3 and 5.4 mg/L in a 21 d chronic toxicity test, using static-non renewal and static-renewal methods, respectively. Shrimp whole body LPx was estimated by thiobarbituric acid reactive species (TBARS) assay, performed by a malondialdehyde (MDA) reaction with 2-thiobarbituric acid (TBA) measured spectrophotometrically. Final MDA concentrations were expressed as nmol MDA produced/mg protein. Results showed that LPx was significantly lower in control animals than in animals exposed to different Roundup(®) concentrations, (p < 0.05). The present work provides an ecotoxicological basis for the possible use of LPx in Caridina nilotica as a biomarker for monitoring Roundup(®) pollution in freshwater ecosystems.

Acetylcholinesterase activity in the freshwater shrimp Caridina nilotica as a biomarker of Roundup(®) herbicide pollution of freshwater systems in South Africa

The use of Caridina nilotica whole-body acetylcholinesterase (AChE) activity as a potential biomarker of Roundup(®) pollution of aquatic ecosystems was investigated. Forty days post hatch (dph) shrimps were exposed to different concentrations of 0.0, 4.3, 6.7, 10.5, 16.4, 25.6 and 40.0 mg/L in a 96 h acute toxicity test; and 0.0, 2.2, 2.8, 3.4, 4.3 and 5.4 mg/L in a 21 d chronic toxicity test. Whole-body AChE activities were determined at the end of the exposure periods by spectrophotometric assay of sample extract; activities were then normalized against protein contents in the samples and expressed in nanomoles of substrate hydrolyzed. Results of both tests showed that AChE activity was concentration-dependent. Mean AChE activities and standard deviations (±SD) for 96 h acute toxicity were 3.6239 (± 0.4185), 3.4157 (± 1.1842), 2.537 (± 1.3989), 2.4253 (± 1.4202), 2.4127 (± 1.9097), 2.0017 (± 1.1080) and 2.316 (± 0.4001) nmol/min/mg protein; while activity levels for 21 d test were 3.6907(± 0.3401), 2.8473 (± 0.713), 2.9134 (± 0.9879), 2.6738 (± 0.7117), 2.3019 (± 0.4464) and 2.1478 (± 0.864) nmol/min/mg protein. Reference basal AChE activity for 40 dph C. nilotica based on the two control groups was estimated as 3.6907 (± 0.3401) nmol/min/mg proteins. The present work provides ecotoxicological basis for the possible use of AChE activity in C. nilotica as a biomarker for monitoring Roundup(®) pollution in freshwater systems.

Integrin-linked kinase has a critical role in ErbB2 mammary tumor progression: implications for human breast cancer

Elevated expression of the integrin-linked kinase (ILK) has been observed in a variety of cancers and has been further correlated with poor clinical outcome. Here, we show that mammary epithelial disruption of ILK results in a profound block in mammary tumor induction. Consistent with these observations, inhibition of ILK function in ErbB2-expressing cells with small molecule inhibitor or RNA interference resulted in profound block in their in vitro invasive properties due to the induction of apoptotic cell death. The rare ILK-deficient tumors that eventually arose overcame this block in tumor induction by an upregulation of ErB3 phosphorylation. These observations provide direct evidence that ILK has a critical role in the initiation phase of ErbB2 tumor induction.

Shc is required for ErbB2-induced inhibition of apoptosis but is dispensable for cell proliferation and disruption of cell polarity

Amplification and overexpression of ErbB2 strongly correlates with aggressive breast cancers. A deeper understanding of pathways downstream of ErbB2 signaling that are required for the transformation of human mammary epithelial cells will identify novel strategies for therapeutic intervention in breast cancer. Using an inducible activation of ErbB2 autophosphorylation qsite mutants and the MCF-10A three-dimensional (3D) culture system, we investigated pathways used by ErbB2 to transform the epithelia. We report that ErbB2 induces cell proliferation and loss of 3D organization by redundant mechanisms, whereas it disrupts apical basal polarity and inhibits apoptosis using Tyr 1201 and Tyr 1226/7, respectively. Signals downstream of Tyr 1226/7 were also sufficient to confer paclitaxel resistance. The Tyr 1226/7 binds Shc, and the knockdown of Shc blocks the ability of ErbB2 to inhibit apoptosis and mediate paclitaxel resistance. Tyr 1226/7 is known to activate the Ras/Erk pathway; however, paclitaxel resistance did not correlate with the activation of Erk or Akt, suggesting the presence of a novel mechanism. Thus, our results show that targeting pathways used by ErbB2 to inhibit cell death is a better option than targeting cell proliferation pathways. Furthermore, we identify a novel function for Shc as a regulator of apoptosis and drug resistance in human mammary epithelial cells transformed by ErbB2.

Effect of laundry activities on in-stream concentrations of linear alkylbenzene sulfonate in a small rural South African river

In many parts of the world clothes are washed near to or in rivers and streams. Little information is available on resulting concentrations of detergent ingredients or on any potential effects caused. In this study, the fate of a commonly used anionic surfactant, linear alkylbenzene sulphonate (LAS) was investigated in a reach of the Balfour River (Eastern Cape Province, South Africa) which was regularly used as a site for laundry activity. Samples of river water were collected upstream of the main washing site and at a number of locations downstream on several occasions in winter and summer. Sediment samples were also collected and analysed. In addition, a household survey was conducted to ascertain the amount of detergent used and the distribution of washing practices. The results of the survey suggested that the use of riverside locations for laundry activities was seasonal. Most washing tended to be done at home during the winter with riverside sites used more frequently during the summer months. The monitoring data showed that LAS concentrations in water were very variable. They were occasionally high in the immediate vicinity of the laundry site (up to 342 microg L(-1)) but were generally very low (<11 microg L(-1)) at downstream monitoring stations, suggesting that LAS was rapidly dissipated by a combination of degradation, hydrodynamic dispersion and dilution. Concentrations in the immediate vicinity of the washing site were lower than expected on the basis of the household survey because most waste water was disposed of on the river bank rather than directly in the river. No ecological effects are expected from LAS emissions at this site.

The Ste20-like kinase SLK is required for ErbB2-driven breast cancer cell motility

The Ste20-like kinase, SLK, is involved in the control of cell motility through its effects on actin reorganization and focal adhesion turnover. Here we investigated the role of SLK in chemotaxis downstream of the tyrosine kinase receptor, HER2/ErbB2/Neu, which is frequently overexpressed in human breast cancers. Our results show that SLK is required for the efficient cell migration of human and mouse mammary epithelial cell lines in the presence of the Neu activator, heregulin, as a chemoattractant. SLK activity is stimulated by heregulin treatment or by overexpression of activated Neu. Phosphorylation of tyrosine 1201 or tyrosines 1226/7 on Neu is a key event for SLK activation and cell migration, and cancer cell invasion mediated by these tyrosines is inhibited by kinase-inactive SLK. Signaling pathway inhibitors show that Neu-mediated SLK activation is dependent on MEK, PI3K, PLCgamma and Shc signaling. Furthermore, heregulin-stimulated SLK activity requires signals from the focal adhesion proteins, FAK and src. Finally, phospho-FAK analysis shows that SLK is required for Neu-dependent focal adhesion turnover. Together, these studies define an interaction between Neu and SLK signaling in the regulation of cancer cell motility.

Deletion of STAT5 prevents HER2/Neu/ErbB2-induced mammary tumor development

Abstract #3045

HER2 (ErbB2/Neu in rodents) is overexpressed in a number of breast cancers and it activates several intracellular signaling pathways by recruiting adaptor proteins. Among them, Shc or Gab2 signaling mediates ErbB2/Neu-induced mammary tumor progression. HER2 activates the transcription factors STAT5A/B but their contribution to the etiology of breast cancer remains to be elucidated. STAT5 mediates signals from a wide variety of cytokine receptors, including the EGFR and ErbB4. Further, constitutive activation of STAT5 has been observed in human breast cancer, leukemia and many solid tumors. To address whether STAT5 mediates HER2/ErbB2/Neu-induced breast cancer progression, both Stat5 genes were deleted specifically in ErbB2/Neu oncogene (known as HER2 in human)-expressing mammary epithelial cells in mice. Briefly, transgenic mice carrying floxed Stat5 alleles (Stat5fl/fl mice) were mated with transgenic MMTV/NIC mice expressing both activated Neu/ErbB2 and Cre recombinase from the same bicistronic transcript due to the presence of an internal ribosome entry site (IRES) between the two cDNA sequences (NIC) under the control of mouse mammary tumor virus (MMTV) long terminal repeat. Whole mount staining of mammary tissue of MMTV/NIC mice demonstrated that mammary glands of control virgin NIC mice (MMTV/NIC;Stat5+/+) exhibited hyperplastic lesions at 5 months of age, while no lesions were detected in NIC mice that lacked STAT5 (MMTV/NIC;Stat5fl/fl). Histological analysis revealed the absence of hyperplastic or neoplastic lesions in MMTV/NIC;Stat5fl/fl mammary glands. These results indicate that inactivation of Stat5 results in the absence of hyperplasias in spite of overexpression of ErbB2/Neu in mammary epithelium and suggest that activation of STAT5 contributes to the development of HER2-induced breast cancer.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 3045.

Sam68 haploinsufficiency delays onset of mammary tumorigenesis and metastasis

The Src-associated substrate in mitosis Sam68 is a KH type RNA-binding protein known to be a substrate of numerous tyrosine kinases, and often referred to as a STAR (signal transduction activator of RNA) protein. Herein, we observed that Sam68-null mice display mammary gland and the uterine development defects. Moreover, we report that Sam68 haploinsufficiency impedes mammary tumor onset in vivo driven by the potent mammary-targeted polyoma middle T-antigen (MMTV-PyMT) oncogene. The effect was cell autonomous as the Sam68 knockdown in PyMT-transformed cell lines also delayed tumorigenesis and metastasis formation in nude mice. Interestingly, tumor extracts isolated from PyMT/Sam68(+/-) mice compared with PyMT/Sam68(+/+) mice contained activated Src and FAK kinases. These findings suggest that Sam68 may be a modulator of tyrosine kinase activity in vivo and a signaling requirement for mammary tumorigenesis and metastasis.

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

The phosphatidyl inositol 3-kinase (PI3K)/Akt pathway is activated downstream of a variety of extracellular signals and activation of this signaling pathway impacts a number of cellular processes including cell growth, proliferation and survival. The alteration of components of this pathway, through either activation of oncogenes or inactivation of tumor suppressors, disrupts a signaling equilibrium and can thus lead to cellular transformation. The frequent dysregulation of the PI3K/Akt pathway in human cancer has made components of this pathway attractive for therapeutic targeting; however, a more comprehensive understanding of the signaling intricacies is necessary to develop pharmacological agents to target not only specific molecules, but also specific functions. Here, we review a series of experiments examining the contribution of molecules of this signaling network including PI3K, phosphatase and tensin homolog deleted on chromosome 10, integrin-linked kinase and Akt and address the significance to human breast cancer.

Role of Gab2 in mammary tumorigenesis and metastasis

Overexpression of the adaptor/scaffolding protein Gab2 has been detected in primary human breast cancer cells and cell lines, although its functional significance in breast carcinogenesis is not fully understood. Here, we show a requirement for Gab2 in promoting mammary tumor metastasis. Although Gab2 expression levels were elevated in mammary tumors induced by the Neu (ErbB-2) oncogene, homozygous deletion of Gab2 in mice had only a modest effect on the initiation of Neu-induced mammary tumors. Notably, ablation of Gab2 severely suppressed lung metastasis. Gab2-deficient cancer cells displayed normal Akt activities, and their proliferative rate in vitro was similar to control cells. However, Gab2(-/-) cancer cells exhibited decreased migration and impaired Erk activation, and the defects were rescued by re-introduction of Gab2 into Gab2(-/-) cells. These findings suggest that although Gab2 overexpression may confer growth advantage to tumor cells, the functional requirement for Gab2 in mammary tumor initiation/growth may be dispensable, and that Gab2 may have a prominent role in promoting mammary tumor metastasis.

Intratumoral administration of an adenovirus expressing a kinase dead form of ErbB-2 inhibits tumor growth

ErbB-2 is amplified or overexpressed in a number of different cancers including breast, ovarian, lung, prostate and stomach. This overexpression leads to enhanced receptor dimer formation and stabilization allowing the receptor to remain in an active state. The clinical consequences of ErbB-2 overexpression include increased tumor aggressiveness, poor prognosis, decreased patient survival and resistance to chemotherapy. As a result, a variety of different strategies are being examined to inhibit its function or expression. In this study, we explored the efficacy of a type 5 recombinant adenovirus encoding a kinase dead form of ErbB-2, AderbB-2 Delta tk, as a potential therapeutic agent for breast cancer using a murine breast model expressing constitutively active ErbB-2. Co-expression in tumor cells of the kinase dead form of ErbB-2 inhibits receptor activity and induces the death of cells expressing constitutively active ErbB-2. In addition, AderbB-2 Delta tk exhibits antitumor activity in both immune-competent and immune-deficient animals with increased antitumor activity in the immune-competent animals. The results suggest both immune and non-immune mechanisms contribute to the antitumor efficacy of this vector.

The pea3 subfamily ets genes are required for HER2/Neu-mediated mammary oncogenesis

BACKGROUND

The PEA3 Ets transcription factor is overexpressed in the vast majority of human breast tumors and in nearly all of those of the HER2/Neu-positive subclass. PEA3 is also overexpressed in various transgenic mouse models of this disease. Whether PEA3 plays an essential role in HER2/Neu-mediated oncogenesis has heretofore not been addressed.

RESULTS

Here, we report that each of the three highly related ets genes of the pea3 subfamily (pea3, er81, and erm) were coordinately overexpressed in mammary tumors of MMTV-neu transgenic mice. Other ets genes normally expressed in the mammary gland were not upregulated in these tumors. Expression of a dominant-negative pea3 transgene under the control of the MMTV promoter in mammary epithelial cells of MMTV-neu transgenic mice dramatically delayed the onset of mammary tumors and reduced the number and size of such tumors in individual mice. Those tumors that arose in bitransgenic mice expressed the MMTV-neu transgene, but not the MMTV-dominant-negative pea3 transgene.

CONCLUSIONS

These findings imply that one or more of the PEA3 subfamily Ets proteins or other Ets proteins with related DNA binding specificity play an essential role in Neu-mediated mammary oncogenesis. Hence, agents that inhibit the expression or activity of the PEA3 subfamily proteins may prove efficacious in the treatment of breast cancer.

Mammary epithelial-specific expression of the integrin-linked kinase (ILK) results in the induction of mammary gland hyperplasias and tumors in transgenic mice

The integrin linked kinase (ILK) is a cytoplasmic effector of integrin receptors, involved in the regulation of integrin binding properties as well as the activation of cell survival and proliferative pathways, including those involving MAP kinase, PKB/Akt and GSK-3beta. Overexpression of ILK in cultured intestinal and mammary epithelial cells has been previously shown to induce changes characteristic of oncogenic transformation, including anchorage-independent growth, invasiveness, suppression of anoikis and tumorigenicity in nude mice. In order to determine if ILK overexpression can result in the formation of mammary tumors in vivo, we generated transgenic mice expressing ILK in the mammary epithelium, under the transcriptional control of the mouse mammary tumor virus (MMTV) long terminal repeat (LTR). By the age of 6 months, female MMTV/ILK mice developed a hyperplastic mammary phenotype, which was accompanied by the constitutive phosphorylation of PKB/Akt, GSK-3beta and MAP kinase. Focal mammary tumors subsequently appeared in 34% of the animals at an average age of 18 months. Given the focal nature and long latency of the tumors, however, additional genetic events are likely required for tumor induction in the MMTV/ILK mice. These results provide the first direct demonstration of a potential oncogenic role for ILK, which is upregulated in human tumors and tumor cell lines.

Multiple ErbB-2/Neu Phosphorylation Sites Mediate Transformation through Distinct Effector Proteins

Amplification of the type I receptor tyrosine kinase ErbB-2 (HER2/Neu) is observed in 20-30% of human mammary carcinomas, correlating with a poor clinical prognosis. We have previously demonstrated that four (Tyr(1144), Tyr(1201), Tyr(1226/1227), or Tyr(1253)) of the five known Neu/ErbB-2 autophosphorylation sites can independently mediate transforming signals. The transforming potential of at least two of these autophosphorylation sites (Tyr(1144) and Tyr(1226/1227)) has been further correlated with their ability to associate with Grb2 and Shc adapter proteins, respectively. To confirm the specificity of these interactions, we have created a series of second site mutants in these phosphorylation sites. The results showed that Grb2 recruitment to site 1144 is absolutely required for transforming signal from this autophosphorylation site, whereas association of Shc-mediated transformation is dependent on conservation of the NPXY motif spanning Tyr(1227). A stretch of amino acid identity around tyrosines 1201 (ENPEYLTP)and 1253 (ENPEYLDL) exists, and mutation of key residues within this motif reveals distinct requirements for an intact protein tyrosine-binding protein (NPXY). We show that DOK-R, a protein tyrosine-binding site-containing protein implicated in Ras signaling, interacts with Neu/ErbB-2 at Tyr(1253) as do two unidentified proteins, p150 and p34, the latter correlating with transformation. Together these data argue that ErbB-2/Neu is capable of mediating transformation through distinct effector pathways.

Preliminary observations on the effects of hydrocortisone and sodium methohexital on development of Sarcophaga (Curranea) tibialis Macquart (Diptera: Sarcophagidae), and implications for estimating post mortem interval

Larvae of Sarcophaga (Curranea) tibialis (S. tibialis) were reared at constant temperature on chicken liver treated with a steroid or a barbiturate at concentrations that would be lethal, half-lethal and twice-lethal doses for humans. Trends to greater mortality at higher drug concentrations were not statistically significant. Larvae exposed to either drug took significantly longer to reach pupation compared to those in the control, while larvae exposed to sodium methohexital passed through pupation significantly faster than those in the control. No systematic relationship was found between drug concentration and development time of larvae or pupae. The total developmental period from hatching to eclosion did not differ between treatments, implying that estimates of post mortem intervals- (PMI) based on the emergence of adult flies will not be affected by the involvement of these drugs in a case. On the other hand, anomalous pupation spans may indicate the presence of barbiturates. These findings are compared with patterns found in another fly fed other contaminants.

Scavenging of extracellular H2O2 by catalase inhibits the proliferation of HER-2/Neu-transformed rat-1 fibroblasts through the induction of a stress response

High levels of reactive oxygen species (ROS) are associated with cytotoxicity. Alternatively, nontoxic levels of ROS like hydrogen peroxide (H(2)O(2)) can mediate the transmission of many intracellular signals, including those involved in growth and transformation. To identify pathways downstream of endogenous cellular H(2)O(2) production, the response of Rat-1 fibroblasts exhibiting differential HER-2/Neu receptor tyrosine kinase activity to removal of physiological H(2)O(2) concentrations was investigated. The proliferation of all cells was abolished by addition of the H(2)O(2) scavenger catalase to the culture medium. HER-2/Neu activity was not significantly affected by catalase treatment, suggesting that the target(s) of the H(2)O(2) signal lie downstream of the receptor in our model. ERK1/2 phosphorylation was blocked by catalase in fibroblasts expressing wild type Neu, however such a response did not occur in cells possessing activated mutant Neu. This indicates that the ERK1/2 response contributes little to the growth inhibition observed. By contrast, JNK1 activity increased following the addition of catalase or H(2)O(2), regardless of Neu activity or level of cell transformation. Phosphorylation of p38 MAPK was induced by H(2)O(2) but not by catalase. These observations suggest that scavenging of H(2)O(2) from the cellular environment blocks Rat-1 proliferation primarily through the activation of stress pathways.

Activation of Akt (protein kinase B) in mammary epithelium provides a critical cell survival signal required for tumor progression

Activation of Akt by the phosphatidylinositol 3'-OH kinase (PI3K) results in the inhibition of proapoptotic signals and the promotion of survival signals (L. P. Kane et al., Curr. Biol. 9:601-604, 1999; G. J. Kops et al., Nature 398:630-634, 1999). Evidence supporting the importance of the PI3K/Akt signaling pathway in tumorigenesis stems from experiments with transgenic mice bearing polyomavirus middle T antigen under the control of the mouse mammary tumor virus long terminal repeat promoter. Mammary epithelium-specific expression of polyomavirus middle T antigen results in the rapid development of multifocal metastatic mammary tumors, whereas transgenic mice expressing a mutant middle T antigen decoupled from the phosphatidylinositol 3'-OH kinase (MTY315/322F) develop extensive mammary gland hyperplasias that are highly apoptotic. To directly assess the role of Akt in mammary epithelial development and tumorigenesis, we generated transgenic mice expressing constitutively active Akt (HAPKB308D473D or Akt-DD). Although expression of Akt-DD interferes with normal mammary gland involution, tumors were not observed in these strains. However, coexpression of Akt-DD with MTY315/322F resulted in a dramatic acceleration of mammary tumorigenesis correlated with reduced apoptotic cell death. Furthermore, coexpression of Akt-DD with MTY315/322F resulted in phosphorylation of the FKHR forkhead transcription factor and translational upregulation of cyclin D1 levels. Importantly, we did not observe an associated restoration of wild-type metastasis levels in the bitransgenic strain. Taken together these observations indicate that activation of Akt can contribute to tumor progression by providing an important cell survival signal but does not promote metastatic progression.

Grb2 and Shc adapter proteins play distinct roles in Neu (ErbB-2)-induced mammary tumorigenesis: implications for human breast cancer

Amplification of the Neu (ErbB-2 or HER-2) receptor tyrosine kinase occurs in 20 to 30% of human mammary carcinomas, correlating with a poor clinical prognosis. We have previously demonstrated that four (Y1144 Y1201, Y1227 and Y1253) of the five known Neu autophosphorylation sites can independently mediate transforming signals. The transforming potential of two of these mutants correlates with their capacity to recruit Grb2 directly to Y1144 (YB) or indirectly through Shc to Y1227 (YD). Here, we demonstrate that these transformation-competent neu mutants activate extracellular signal-regulated kinases and stimulate Ets-2-dependent transcription. Although the transforming potential of three of these mutants (YB, YD, and YE) was susceptible to inhibition by Rap1A, a genetic antagonist of Ras, the transforming potential of YC was resistant to inhibition by Rap1A. To further address the significance of these ErbB-2-coupled signaling molecules in induction of mammary cancers, transgenic mice expressing mutant Neu receptors lacking the known autophosphorylation sites (NYPD) or those coupled directly to either Grb2 (YB) or Shc (YD) adapter molecules were derived. In contrast to the NYPD strains, which developed focal mammary tumors after a long latency period with low penetrance, all female mice derived from YB and YD strains rapidly developed mammary tumors. Although female mice from several independent YB or YD lines developed mammary tumors, the YB strains developed lung metastases at substantially higher rates than the YD strains. These observations argue that Grb2 and Shc play important and distinct roles in ErbB-2/Neu-induced mammary tumorigenesis and metastasis.

Distinct tyrosine autophosphorylation sites mediate induction of epithelial mesenchymal like transition by an activated ErbB-2/Neu receptor

Tight control of cell proliferation and morphogenesis is required to ensure normal tissue patterning and prevent cancer formation. Overexpression of the ErbB-2/Neu receptor tyrosine kinase is associated with increased progression in human breast cancer, yet in breast explant cultures, the ErbB-2/Neu receptor contributes to alveolar differentiation. To examine the consequence of deregulated ErbB-2/Neu activation on epithelial morphogenesis, we have expressed a constitutively activated mutant of ErbB-2/Neu in a Madin-Darby canine kidney (MDCK) epithelial cell model. Using two-dimensional cultures we demonstrate that activated ErbB-2/Neu induces breakdown of cell-cell junctions, increased cell motility and dispersal of epithelial colonies. This correlates with reorganization of the actin cytoskeleton and focal adhesions and loss of insoluble cell-cell junction complexes involving E-cadherin. Interestingly, a constitutively activated ErbB-2/Neu receptor promotes an invasive morphogenic program in MDCK cells in a three-dimensional matrix. We show that two tyrosines in the carboxy-terminal tail of ErbB-2/Neu, involved in the phosphorylation of the Shc adapter protein, are each sufficient to promote epithelial-mesenchymal like transition and enhanced cell motility in two-dimensional culture and cell invasion rather than a morphogenic response in matrix culture. This provides a model system to investigate ErbB-2/Neu induced signaling pathways required for epithelial cell dispersal and invasion versus morphogenesis.

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.

Matrix metalloproteinase 9 promoter activity is induced coincident with invasion during tumor progression

Matrix metalloproteinase 9 (MMP-9, also known as gelatinase B or 92-kd Type IV collagenase) is overexpressed in many human and murine cancers. We induced carcinomas in mice carrying a transgene that links the MMP-9 promoter to the reporter ss-galactosidase so that activation of the MMP-9 promoter would be indicated by ss-galactosidase. Mammary carcinomas were induced by mating the MMP-9 promoter reporter transgenic mice with mice carrying a transgene for murine mammary tumor virus promoter linked to polyoma middle T antigen, a transgene that leads to rapid development of mammary tumors in female mice. None of the hyperplastic mammary glands and none of the carcinomas in situ expressed ss-galactosidase. However, all invasive tumors had evidence of ss-galactosidase expression. In addition to the breast carcinomas, a malignant teratoma in a female and a papillary adenocarcinoma in the pelvic region of a male arose and were also ss-galactosidase positive. We also induced skin tumors in the mice with the MMP-9 reporter transgene with 7, 12-dimethylbenz[a]anthracene (DMBA) treatment followed by phorbol 12 myristate 13-acetate (TPA). None of the papillomas or in situ carcinomas showed any ss-galactosidase expression, but expression was seen in invasive carcinoma. Although normal skin epithelial cells did not express ss-galactosidase, we did find staining in a few cells at the duct of the sebaceous gland at the base of the hair follicles. The MMP-9 reporter transgene did not lead to expression in the alveolar macrophages, confirming that additional upstream sequences are required for expression in macrophages. These experiments have revealed that MMP-9 promoter activity is induced coincident with invasion during tumor progression. Furthermore, this indicates that the more proximal upstream elements of the promoter are sufficient for MMP-9 transcription during tumor progression.

HER-2/neu is a tumor rejection target in tolerized HER-2/neu transgenic mice

HER-2/neu (neu-N) transgenic mice, which express the nontransforming rat proto-oncogene, develop spontaneous focal mammary adenocarcinomas beginning at 5-6 months of age. The development and histology of these tumors bears a striking resemblance to what is seen in patients with breast cancer. We have characterized the immunological responses to HER-2/neu (neu) in this animal model. neu-positive tumor lines, which were derived from spontaneous tumors that formed in neu-N animals, are highly immunogenic in parental, FVB/N mice. In contrast, a 100-fold lower tumor challenge is sufficient for growth in 100% of transgenic animals. Despite significant tolerance to the transgene, neu-specific immune responses similar to those observed in breast cancer patients can be demonstrated in neu-N mice prior to vaccination. Both cellular and humoral neu-specific responses in transgenic mice can be boosted with neu-specific vaccination, although to a significantly lesser degree than what is observed in FVB/N mice, indicating that the T cells involved are less responsive than in the nontoleragenic parental strain. Using irradiated whole-cell and recombinant vaccinia virus vaccinations we are able to protect neu-N mice from a neu-expressing tumor challenge. T-cell depletion experiments demonstrated that the observed protection is T cell dependent. The vaccine-dependent neu-specific immune response is also sufficient to delay the onset of spontaneous tumor formation in these mice. These data suggest that, despite tolerance to neu in this transgenic model, it is possible to immunize neu-specific T cells to achieve neu-specific tumor rejection in vivo. These transgenic mice provide a spontaneous tumor model for identifying vaccine approaches potent enough to overcome mechanisms of immune tolerance that are likely to exist in patients with cancer.

Mammary gland neoplasia: insights from transgenic mouse models

Current theories of breast cancer progression have been greatly influenced by the development and refinement of mouse transgenic and gene targeting technologies. Early transgenic mouse models confirmed the involvement of oncogenes, previously implicated in human breast cancer, by establishing a causal relationship between overexpression or activation of these genes and mammary tumorigenesis. More recently, the importance of genes located at sites of loss of heterozygosity in human breast cancer have been examined in mice by their targeted disruption via homologous recombination. The union of these two approaches allows the generation of complex animal models that more accurately reflect the multistep nature of human breast cancer. This review will examine how the study of transgenic mice has increased our understanding of the molecular events responsible for oncogenic transformation of the mammary gland. BioEssays 22:554-563, 2000.

Amplification of the neu/erbB-2 oncogene in a mouse model of mammary tumorigenesis

The neu (c-erbB-2, Her-2) protooncogene is amplified and overexpressed in 20-30% of human breast cancers. Although transgenic mouse models have illustrated the role of Neu in the induction of mammary tumors, Neu expression in these models is driven by a strong viral promoter of questionable relevance to the human disease. To ascertain whether expression of activated Neu under the control of the endogenous promoter in the mammary gland could induce mammary tumors we have generated mice that conditionally express activated Neu under the transcriptional control of the intact endogenous Neu promoter. Expression of oncogenic neu in the mammary gland resulted in accelerated lobulo-alveolar development and formation of focal mammary tumors after a long latency period. However, expression of activated Neu under the normal transcriptional control of the endogenous promoter was not sufficient for the initiation of mammary carcinogenesis. Strikingly, all mammary tumors bear amplified copies (2-22 copies) of the activated neu allele relative to the wild-type allele and express highly elevated levels of neu transcript and protein. Thus, like human erbB-2-positive breast tumors, mammary tumorigenesis in this mouse model requires the amplification and commensurate elevated expression of the neu gene.

Oncogenic activating mutations in the neu/erbB-2 oncogene are involved in the induction of mammary tumors

Amplification and overexpression of erbB-2/neu is an important determinant in the initiation and progression of human breast cancer. Indeed, transgenic mice that over-express the neu proto-oncogene heritably develop mammary adenocarcinomas. Tumorigenesis in these transgenic strains is associated with activation of the intrinsic catalytic activity of Neu. In many of these tumors, activation of Neu occurs as a result of somatic mutations located within the transgene itself. Examination of the altered neu transcripts revealed the presence of in-frame deletions that encode aberrant Neu receptors lacking 5 to 12 amino acids within the extracellular domain proximal to the transmembrane region of Neu. In addition to these deletion mutants we have also detected single point mutations within this juxta-transmembrane region. The majority of the mutations analyzed affect the one of several conserved cysteine residues present within this region. Introduction of these activating mutations into the wild-type neu cDNA results in its oncogenic conversion. Taken together, these observations suggest that this cysteine-rich region plays an important role in regulating the catalytic activity of Neu.

Suppression of tumor growth and metastasis in Mgat5-deficient mice

Golgi beta1,6N-acetylglucosaminyltransferase V (MGAT5) is required in the biosynthesis of beta1,6GlcNAc-branched N-linked glycans attached to cell surface and secreted glycoproteins. Amounts of MGAT5 glycan products are commonly increased in malignancies, and correlate with disease progression. To study the functions of these N-glycans in development and disease, we generated mice deficient in Mgat5 by targeted gene mutation. These Mgat5-/- mice lacked Mgat5 products and appeared normal, but differed in their responses to certain extrinsic conditions. Mammary tumor growth and metastases induced by the polyomavirus middle T oncogene was considerably less in Mgat5-/- mice than in transgenic littermates expressing Mgat5. Furthermore, Mgat5 glycan products stimulated membrane ruffling and phosphatidylinositol 3 kinase-protein kinase B activation, fueling a positive feedback loop that amplified oncogene signaling and tumor growth in vivo. Our results indicate that inhibitors of MGAT5 might be useful in the treatment of malignancies by targeting their dependency on focal adhesion signaling for growth and metastasis.

Signal transduction in mammary tumorigenesis: a transgenic perspective

A number of genes have been implicated in breast cancer development, yet few have been demonstrated to play causative roles in mammary tumor formation. The advent of transgenic mouse and embryonic stem cell technologies now permits manipulation of the mouse genome in such a way as to temporally and spatially control a gene product's expression. Thus, the basic researcher now can directly assess the involvement of particular genes in tumorigenesis and disease progression and, in the process, to develop mouse models of human genetic disease. The utility of such technologies is emphasized in transgenic mice expressing genes thought to play important roles in the initiation and progression of mammary carcinomas. As these transgenic strains have been the subject of several reviews, here we focus on two mouse mammary tumor models, Polyomavirus middle T antigen and the Neu/ErbB-2 receptor tyrosine kinase, which are most amenable to study specific signaling pathways in process of mammary tumorigenesis.

Cyclin D1 is required for transformation by activated Neu and is induced through an E2F-dependent signaling pathway

The neu (c-erbB-2) proto-oncogene encodes a tyrosine kinase receptor that is overexpressed in 20 to 30% of human breast tumors. Herein, cyclin D1 protein levels were increased in mammary tumors induced by overexpression of wild-type Neu or activating mutants of Neu in transgenic mice and in MCF7 cells overexpressing transforming Neu. Analyses of 12 Neu mutants in MCF7 cells indicated important roles for specific C-terminal autophosphorylation sites and the extracellular domain in cyclin D1 promoter activation. Induction of cyclin D1 by NeuT involved Ras, Rac, Rho, extracellular signal-regulated kinase, c-Jun N-terminal kinase, and p38, but not phosphatidylinositol 3-kinase. NeuT induction of the cyclin D1 promoter required the E2F and Sp1 DNA binding sites and was inhibited by dominant negative E2F-1 or DP-1. Neu-induced transformation was inhibited by a cyclin D1 antisense or dominant negative E2F-1 construct in Rat-1 cells. Growth of NeuT-transformed mammary adenocarcinoma cells in nude mice was blocked by the cyclin D1 antisense construct. These results demonstrate that E2F-1 mediates a Neu-signaling cascade to cyclin D1 and identify cyclin D1 as a critical downstream target of neu-induced transformation.

Tyrosine kinase signalling in breast cancer: tyrosine kinase-mediated signal transduction in transgenic mouse models of human breast cancer

The ability of growth factors and their cognate receptors to induce mammary epithelial proliferation and differentiation is dependent on their ability to activate a number of specific signal transduction pathways. Aberrant expression of specific receptor tyrosine kinases (RTKs) has been implicated in the genesis of a significant proportion of sporadic human breast cancers. Indeed, mammary epithelial expression of activated RTKs such as ErbB2/neu in transgenic mice has resulted in the efficient induction of metastatic mammary tumours. Although it is clear from these studies that activation these growth factor receptor signalling cascades are directly involved in mammary tumour progression, the precise interaction of each of these signalling pathways in mammary tumourigenesis and metastasis remains to be elucidated. The present review focuses on the role of several specific signalling pathways that have been implicated as important components in RTK-mediated signal transduction. In particular, it focuses on two well characterized transgenic breast cancer models that carry the polyomavirus middle T(PyV mT) and neu oncogenes.

Accelerated mammary tumor development in mutant polyomavirus middle T transgenic mice expressing elevated levels of either the Shc or Grb2 adapter protein

The Grb2 and Shc adapter proteins play critical roles in coupling activated growth factor receptors to several cellular signaling pathways. To assess the role of these molecules in mammary epithelial development and tumorigenesis, we have generated transgenic mice which individually express the Grb2 and Shc proteins in the mammary epithelium. Although mammary epithelial cell-specific expression of Grb2 or Shc accelerated ductal morphogenesis, mammary tumors were rarely observed in these strains. To explore the potential role of these adapter proteins in mammary tumorigenesis, mice coexpressing either Shc or Grb2 and a mutant form of polyomavirus middle T (PyV mT) antigen in the mammary epithelium were generated. Coexpression of either Shc or Grb2 with the mutant PyV mT antigen resulted in a dramatic acceleration of mammary tumorigenesis compared to parental mutant PyV mT strain. The increased rate of tumor formation observed in these mice was correlated with activation of the epidermal growth factor receptor family and mitogen-activated protein kinase pathway. These observations suggest that elevated levels of the Grb2 or Shc adapter protein can accelerate mammary tumor progression by sensitizing the mammary epithelial cell to growth factor receptor signaling.

The role of the epidermal growth factor receptor family in mammary tumorigenesis and metastasis

A number of receptor systems have been implicated to play an important role in the development and progression of many human cancers. The epidermal growth factor (EGF) receptor tyrosine kinase family has been found to consistently play a leading role in tumor progression. Indeed, in human breast cancer cases the prognosis of a patient is inversely correlated with the overexpression and/or amplification of this receptor family. Furthermore, downstream signaling components such as the Src kinases, PI3'K, and the Ras pathway display evidence of deregulation that can accelerate tumor progression. The transgenic mouse system has been ideal in elucidating the biological significance of this receptor family in mammary tumorigenesis. Molecular events involved in mammary tumorigenesis such as ligand binding, receptor dimerization, and the activation of downstream pathways have been addressed using this system. Although there are many molecular steps that appear to drive each stage of tumor development, the EGF receptor family appears to play a causal role in the progression to a transformed phenotype.

A p75 tumor necrosis factor receptor-specific mutant of murine tumor necrosis factor alpha expressed from an adenovirus vector induces an antitumor response with reduced toxicity

The toxic effects of tumor necrosis factor alpha (TNFalpha) have greatly limited its use in tumor therapy. Recently, clear evidence has been obtained linking the p55 TNF receptor (TNFR) to the induction of systemic toxicity. We have generated a p75 murine TNFR (mTNFR)-specific mutant of mTNFalpha (D142N-A144R), cloned this gene into a recombinant adenovirus vector (Ad-75), and studied its efficacy for tumor immunotherapy of a murine transgenic breast cancer model. Cell culture supernatants from Ad-75-transduced cells showed no cytotoxic activity on L929 cells, but retained the ability to induce proliferation of a murine T-cell line (CT6); this activity was not blocked by soluble p55 mTNFR. Furthermore, it was shown that the mutant form of mTNFalpha was able to coimmunoprecipitate only with the p75 mTNFR and not with the p55 mTNFR. Tumors injected with Ad-75 became necrotic, and mice injected with < or =1 x 10(9) plaque-forming units showed no mortality, whereas both wild-type murine and human TNF vectors induced lethality at doses of 1 and 5 x 10(8) plaque-forming units. All Ad-TNF vectors induced partial or permanent tumor regressions, with cured mice showing immune memory against the tumor. These results demonstrate that a p75 mTNFR agonist expressed from a recombinant adenovirus vector does not induce mortality at doses that cause tumor regression.

Tenascin-C modulates tumor stroma and monocyte/macrophage recruitment but not tumor growth or metastasis in a mouse strain with spontaneous mammary cancer

The local growth of tumors and their ability to metastasize are crucially dependent on their interactions with the surrounding extracellular matrix. Tenascin-C (TNC) is an extracellular matrix protein which is highly expressed during development, tissue repair and cancer. Despite the high levels of TNC in the stroma of primary and metastatic tumors, the function of TNC is not known. In the present study we have crossed TNC-null mice with a mouse strain where both female and male mice spontaneously develop mammary tumors followed by metastatic disease in the lungs. We report that the absence of TNC had no effect on the temporal occurrence of mammary tumors and their metastatic dissemination in lungs. Furthermore, the number and size of tumors, the number and size of metastatic foci in the lungs, the proliferation rate and apoptosis of tumor cells and tumor angiogenesis were not altered in the absence of TNC. Histological examination revealed that the tumor organisation, however, was modulated by TNC. In the presence of TNC both primary as well as metastatic tumors were organised in large tumor cell nests surrounded by thick layers of extracellular matrix proteins. In the absence of TNC these tumor cell nests were smaller but still separated from each other by extracellular matrix proteins. In addition, the TNC-null stromal compartment contained significantly more monocytes/macrophages than tumor stroma from TNC wild-type mice. Using in vitro coculture experiments we show that TNC-null tumor cells were still able to activate the TNC gene in fibroblasts which express low basal levels of TNC. Altogether these data indicate that TNC has a very limited role during the spontaneous development and growth of mamary tumors and their metastasis to the lungs.

Elevated expression of activated forms of Neu/ErbB-2 and ErbB-3 are involved in the induction of mammary tumors in transgenic mice: implications for human breast cancer

To assess the importance of Neu activation during mammary tumorigenesis, altered receptors harboring in-frame deletions within the extracellular domain were expressed in transgenic mice. Females from several independent lines develop multiple mammary tumors that frequently metastasize to the lung. Tumor progression in these strains was associated with elevated levels of tyrosine-phosphorylated Neu and ErbB-3. Consistent with these observations, a survey of primary human breast tumors revealed frequent co-expression of both erbB-2 and erbB-3 transcripts. The ability of altered Neu receptors to induce mammary tumorigenesis in transgenic mice prompted us to examine whether similar mutations occurred in ErbB-2 during human breast cancer progression. Interestingly, an alternatively spliced form of erbB-2, closely resembling spontaneous activated forms of neu, was detected in human breast tumors. The ErbB-2 receptor encoded by this novel transcript harbors an in-frame deletion of 16 amino acids in the extracellular domain and can transform Rat-1 fibroblasts. Together, these observations argue that co-expression of ErbB-2 and ErbB-3 may play a critical role in the induction of human breast tumors, and raise the possibility that activating mutations in the ErbB-2 receptor may also contribute to this process.

Adenoviral vectors expressing lymphotactin and interleukin 2 or lymphotactin and interleukin 12 synergize to facilitate tumor regression in murine breast cancer models

We have previously demonstrated that intratumoral injection with Ad vectors expressing IL-2 or IL-12 can induce regression in a murine breast cancer model. These IL-2- or IL-12-induced antitumor responses were mainly mediated by Ag-specific T cells. Lymphotactin is a novel lymphocyte chemokine that can cause local accumulation of CD4+, CD8+, and NK cells. We hypothesized that addition of lymphotactin may enhance the antitumor immune responses induced by locally produced IL-2 and IL-12 as we have previously shown. To this end we constructed two double-recombinant adenoviral vectors expressing lymphotactin along with either IL-2 (Ad5 Lym/IL-2) or IL-12 (Ad5 Lym/IL-12). Subcutaneous injection of polyoma middle T (PyMT) or Neu (8142) transgenically derived breast adenocarcinoma cells, in the hind flank of FVB/n mice, results in the formation of tumor nodules in 14-21 days. We show that these constructs elicit potent antitumor responses when administered intratumorally. The antitumor responses are long lasting as determined by rechallenge experiments and hence demonstrate a protective immunity. These observations indicate that by augmenting the antitumor response with adenoviral vectors expressing lymphotactin in combination with IL-2 or IL-12 is a novel way to enhance immunotherapeutic approaches.

pp60(v-src) induction of cyclin D1 requires collaborative interactions between the extracellular signal-regulated kinase, p38, and Jun kinase pathways. A role for cAMP response element-binding protein and activating transcription factor-2 in pp60(v-src) signaling in breast cancer cells

The cyclin D1 gene is overexpressed in breast tumors and encodes a regulatory subunit of cyclin-dependent kinases that phosphorylate the retinoblastoma protein. pp60(c-src) activity is frequently increased in breast tumors; however, the mechanisms governing pp60(c-src) regulation of the cell cycle in breast epithelium are poorly understood. In these studies, pp60(v-src) induced cyclin D1 protein levels and promoter activity (48-fold) in MCF7 cells. Cyclin D1-associated kinase activity and protein levels were increased in mammary tumors from murine mammary tumor virus-pp60(c-src527F) transgenic mice. Optimal induction of cyclin D1 by pp60(v-src) involved the extracellular signal-regulated kinase, p38, and c-Jun N-terminal kinase members of the mitogen-activated protein kinase family. Cyclin D1 promoter activation by pp60(v-src) involved a cAMP response element-binding protein (CREB)/activating transcription factor 2 (ATF-2) binding site. Dominant negative mutants of CREB and ATF-2 but not c-Jun inhibited pp60(v-src) induction of cyclin D1. pp60(v-src) induction of CREB was blocked by the p38 inhibitor SB203580 or by mutation of CREB at Ser133. pp60(v-src) induction of ATF-2 was abolished by the c-Jun N-terminal kinase inhibitor JNK-interacting protein-1 or by mutation of ATF-2 at Thr69 and Thr71. CREB and ATF-2, which bind to a common pp60(v-src) response element, are transcriptionally activated by distinct mitogen-activated protein kinases. Induction of cyclin D1 activity by pp60(v-src) may contribute to breast tumorigenesis through phosphorylation and inactivation of the retinoblastoma protein.

Comparison of the effectiveness of adenovirus vectors expressing cyclin kinase inhibitors p16INK4A, p18INK4C, p19INK4D, p21(WAF1/CIP1) and p27KIP1 in inducing cell cycle arrest, apoptosis and inhibition of tumorigenicity

Cell cycle regulatory proteins are important candidates for therapeutic tumour suppressors. Adenovirus vectors were constructed to overexpress cyclin kinase inhibitors p16INK4A, p18INK4C, p19INK4D, p21(WAF1/CIP1) and p27KIP1 under the control of the murine cytomegalovirus immediate early gene promoter. These vectors directed the efficient expression of each of the cyclin kinase inhibitors and induced growth arrest, inhibited DNA synthesis, and prevented phosphorylation of the retinoblastoma protein (pRb) in cell lines expressing functional pRb. In pRb-deficient cells, expression of the cyclin kinase inhibitors was not effective in inhibiting DNA replication or growth arrest. Interestingly, three of the cyclin kinase inhibitors, p16, p18 and p27 were found to induce apoptotic death in transduced HeLa and A549 cells. When the vectors were tested for their ability to inhibit tumorigenicity in a polyomavirus middle T antigen model of murine breast carcinoma, expression of the cyclin kinase inhibitors resulted in a delay in tumour formation that varied from several weeks for the p19 expressing vector to greater than 25 weeks for the p27 expressing vector. When tumours were injected directly with the adenovirus vectors expressing the cyclin kinase inhibitors, only treatment with the vector expressing p16 resulted in a delay in tumour growth.

Mammalian Grb2 regulates multiple steps in embryonic development and malignant transformation

Proteins with SH2 and SH3 domains link tyrosine kinases to intracellular pathways. To investigate the biological functions of a mammalian SH2/SH3 adaptor, we have introduced a null mutation into the mouse gene for Grb2. Analysis of mutant embryonic stem cells, embryos, and chimeras reveals that Grb2 is required during embyrogenesis for the differentiation of endodermal cells and formation of the epiblast. Grb2 acts physiologically as an adaptor, since replacing the C terminus of the Ras activator Sos1 with the Grb2 SH2 domain yields a fusion protein that largely rescues the defects caused by the Grb2 mutation. Furthermore, Grb2 is rate limiting for mammary carcinomas induced by polyomavirus middle T antigen. These data provide genetic evidence for a mammalian Grb2-Ras signaling pathway, mediated by SH2/SH3 domain interactions, that has multiple functions in embryogenesis and cancer.

The matrix metalloproteinase matrilysin influences early-stage mammary tumorigenesis

Overexpression of the epithelial specific matrix metalloproteinase matrilysin (MAT) has been correlated with enhanced tumorigenicity and tumor cell invasion using in vitro model systems. We have determined the effects of MAT expression on the development of mammary tumorigenesis using transgenic mice that express human MAT under the control of the mouse mammary tumor virus (MMTV)-long terminal repeat promoter/enhancer. Examination of mammary glands from multiparous MMTV-MAT animals revealed the development of premalignant hyperplastic alveolar nodules in 50% of aged females. MMTV-MAT mice were mated with MMTV-neu transgenic mice to determine the effect of MAT on neu-induced mammary tumorigenesis. Bigenic MMTV-MAT/neu female offspring developed primary mammary tumors approximately 13 weeks earlier than did MMTV-neu controls. The mechanism of enhanced neu-induced tumorigenesis was explored. No discernible difference in Neu receptor dimerization or activation was detected in MMTV-MAT/neu tumors or mammary glands compared to MMTV-neu controls. A similar percentage of MMTV-MAT/neu and MMTV-neu tumors acquired deletions in the neu transgene, which have previously been shown to result in constitutive receptor activation. The presence of premalignant nodules and the accelerated development of oncogene-induced mammary tumors suggest that expression of MAT in the mammary epithelium contributes to early-stage mammary tumorigenesis.

Active signaling by Neu in transgenic mice

Transgenic mice engineered to overexpress the HER-2/neu/erbB-2 protooncogene under the control of a mammary-specific promoter develop mammary tumors and are a model for human breast cancer. Signal transduction by Neu was examined in situ in the tumors of these transgenic mice. This was accomplished using the PN2A monoclonal antibody, which recognizes Neu only in the phosphorylated, and therefore actively signaling, state. Immunohistochemistry using PN2A demonstrated that Neu actively signals in the tumors of Neu transgenic mice. Expression of Neu was always accompanied by co-overexpression of the endogenous epidermal growth factor receptor. Qualitatively similar results were found in mammary tumors from mice bitransgenic for the neu and transforming growth factor-alpha genes (both driven by the mouse mammary tumor virus promoter). Early mammary lesions demonstrated distinctive patterns of Neu activation relative to expression levels. Overexpression and activation were separable both temporally and spatially. These results refine the multi-step model for the role of Neu in mammary neoplasia and establish phosphorylation-state specific antibodies as a powerful tool for investigating tumor progression.

Intratumoral coinjection of adenoviral vectors expressing IL-2 and IL-12 results in enhanced frequency of regression of injected and untreated distal tumors

We have studied the ability of adenoviral (Ad) vectors expressing the cytokines IL-2 or IL-12 to mediate regression of established tumors in a mouse model of mammary adenocarcinoma. Previous results indicated that intratumoral injection of vectors expressing IL-2 (AdCAIL-2), or IL-12 (AdmIL-12.1) induced complete tumor regression in approximately 30-40% of treated animals. In the current studies, we investigated the mechanism of tumor killing in responding animals and the efficacy of AdIL-2 and AdIL-12 vector administration in combination compared with the use of either vector alone. Animals bearing subcutaneous mammary tumors were injected intratumorally with Ad vectors expressing IL-2 or IL-12 or were coinjected with both vectors. Animals receiving the combination treatment responded substantially better than animals which had received either vector alone, with 65% of animals treated with both vectors undergoing complete tumor regression. In all three treatment regimens, tumor regression was associated with the presence of specific antitumor antigen cytotoxic T-lymphocytes (CTLs), which secreted elevated levels of IFN-gamma. Consistent with circulating CTLs being involved in regression, when animals bearing bilateral tumors were inoculated in a single tumor with IL-2 or IL-12 expressing vectors, both tumors regressed in many cases. Again, treatment with both AdCAIL-2 and AdmIL-12.1 was most effective, with 63% of animals undergoing complete regression of both treated and untreated tumors, compared to 18 or 22% of animals injected with either AdCAIL-2 or AdmIL-12.1 alone. These data indicate that the combination of IL-2 and IL-12 is a more effective inducer of antitumor immune responses than either one alone, and that the resulting antitumor responses are effective in mediating the regression of distal untreated tumors, a property which may aid in the treatment of metastatic disease.

Down regulation of major histocompatibility complex class I expression in mammary carcinoma of HER-2/neu transgenic mice

Transgenic mice carrying the HER-2/neu proto-oncogene under tissue-specific transcriptional control of a mammary tumor virus long terminal repeat (Tg-MMTVneu mice) spontaneously develop mammary carcinomas. HER-2/neu is a tumor antigen that can be recognized by cytotoxic T lymphocytes if tumor cells present the appropriate major histocompatibility complex (MHC) class I glycoproteins. The purpose of this work was to assess whether mammary carcinomas arising in Tg-MMTVneu mice correctly expressed MHC (H-2q) class I gene products. We analyzed by flow cytometry 51 primary tumors from 19 transgenic mice. About one-half of the tumors showed a reduced expression of class I antigens. All tumors were highly positive for membrane neu. Some mice had multiple mammary carcinomas with widely different MHC expression levels, and most mice had at least one tumor with a low expression. Treatment with gamma-interferon of carcinoma cells cultured in vitro induced a strong reexpression of H-2q antigens. Our results suggest that the immune response activated in vivo by HER-2/neu-positive tumors can lead to the emergence of escape variants characterized by a down-regulation of MHC class I products.