Insulin-like growth factor and epidermal growth factor independence in human mammary carcinoma cells with c-erbB-2 gene amplification and progressively elevated levels of tyrosine-phosphorylated p185erbB-2

The culture conditions and outputs from breast cancer cell line in vitro experiments

One of the major cancer types that have gained significant importance globally is the breast cancer due to its socio-economic impact. Breast cancer research is an area of considerable importance and several types of material are available for research applications. These include cancer cell lines which can be utilized in several ways. Cell lines are convenient to use and recently about 84 human breast cancer cell lines were classified by molecular sub-typing. These cells lines come under five major molecular subtypes namely the luminal A and B, HER-2⁺, triple^- A and B subtypes. These cell lines have been well characterized and were utilized for understanding various aspects of breast cancers. Also, apart from providing an understanding of the molecular mechanisms associated with breast cancers, these cell lines have contributed significantly to areas such as drug testing. We present in this review the features of these cell lines, the studies conducted using them and the outcome of such studies. Also, the details about the culture conditions and study outcomes of the cell lines grown in 3-dimensional (3D) systems are presented.

Monitoring of receptor dimerization using plasmonic coupling of gold nanoparticles

The dimerization of receptors on the cell membrane is an important step in the activation of cell signaling pathways. Several methods exist for observing receptor dimerization, including coimmunoprecipitation, chemical cross-linking, and fluorescence resonance energy transfer (FRET). These techniques are limited in that only FRET is appropriate for live cells, but even that method suffers from photobleaching and bleed-through effects. In this study, we implement an alternative method for the targeting of HER-2 homodimer formation based on the plasmonic coupling of gold nanoparticles functionalized with HER-2 Ab. In the presented studies, SK-BR-3 cells, known to overexpress HER-2, are labeled with these nanoparticles and receptor colocalization is observed using plasmonic coupling. HER-2 targeted nanoparticles bound to these cells exhibit a peak resonance that is significantly red-shifted relative to those bound to similar receptors on A549 cells, which have significantly lower levels of HER-2 expression. This significant red shift indicates plasmonic coupling is occurring and points to a new avenue for assessing dimerization by monitoring their colocalization. To determine that dimerization is occurring, the refractive index of the nanoenvironment of the labels is assessed using a theoretical analysis based on the Mie coated sphere model. The results indicate scattering by single, isolated nanoparticles for the low HER-2 expressing A549 cell line, but the scattering observed for the HER-2 overexpressing SK-BR-3 cell line may only be explained by plasmonic-coupling of proximal nanoparticle pairs. To validate the conformation of nanoparticles bound to HER-2 receptors undergoing dimerization, discrete dipole approximation (DDA) models are used to assess spectra of scattering by coupled nanoparticles. Comparison of the experimental results with theoretical models indicates that NP dimers are formed for the labeling of SK-BR-3 cells, suggesting that receptor dimerization has been observed.

ErbB2 enhances mammary tumorigenesis, oncogene-independent recurrence and metastasis in a model of IGF-IR-mediated mammary tumorigenesis

Background

The type I insulin-like growth factor receptor (IGF-IR) and ErbB2 (Her-2) are receptor tyrosine kinases implicated in human breast cancer. Both proteins are currently the subject of targeted therapeutics that are used in the treatment of breast cancer or which are in clinical trials. The focus of this study was to utilize our inducible model of IGF-IR overexpression to explore the interaction of these two potent oncogenes.

Results

ErbB2 was overexpressed in our RM11A cell line, a murine tumor cell line that overexpresses human IGF-IR in an inducible manner. ErbB2 conferred an accelerated tumor onset and increased tumor incidence after injection of RM11A cells into the mammary glands of syngeneic wild type mice. This was associated with increased proliferation immediately after tumor cell colonization of the mammary gland; however, this effect was lost after tumor establishment. ErbB2 overexpression also impaired the regression of established RM11A tumors following IGF-IR downregulation and enhanced their metastatic potential.

Conclusion

This study has revealed that even in the presence of vast IGF-IR overexpression, a modest increase in ErbB2 can augment tumor establishment in vivo, mediate resistance to IGF-IR downregulation and facilitate metastasis. This supports the growing evidence suggesting a possible advantage of using IGF-IR and ErbB2-directed therapies concurrently in the treatment of breast cancer.

HER-2 signaling, acquisition of growth factor independence, and regulation of biological networks associated with cell transformation

Activated oncogenes are the dominant drivers of malignant progression in human cancer, yet little is known about how the transformation from proto-oncogene to activated oncogene drives the expression of transformed phenotypes. An isogenic model of HER-2-mediated transformation of human mammary epithelial cells was used along with HER-2-amplified human breast cancers to investigate how HER-2 activation alters its properties as a signaling molecule and changes the networks of HER-2-regulated genes. Our results show that full oncogenic activation of HER-2 is the result of a transition in which activated HER-2 acquires dominant signaling properties that qualitatively alter the network of genes regulated by the activated oncogene compared with the proto-oncogene. Consequently, gene expression programs related to invasion, cell stress, and stemness become regulated by HER-2 in a manner not observed in nontransformed cells, even when HER-2 is overexpressed. Our results offer novel insights into biological processes that come under the control of HER-2 after it acquires full oncogenic potential.

Insulin receptor dysfunction impairs cellular clearance of neurotoxic oligomeric a{beta}

Accumulation of amyloid beta (Abeta) oligomers in the brain is toxic to synapses and may play an important role in memory loss in Alzheimer disease. However, how these toxins are built up in the brain is not understood. In this study we investigate whether impairments of insulin and insulin-like growth factor-1 (IGF-1) receptors play a role in aggregation of Abeta. Using primary neuronal culture and immortal cell line models, we show that expression of normal insulin or IGF-1 receptors confers cells with abilities to reduce exogenously applied Abeta oligomers (also known as ADDLs) to monomers. In contrast, transfection of malfunctioning human insulin receptor mutants, identified originally from patient with insulin resistance syndrome, or inhibition of insulin and IGF-1 receptors via pharmacological reagents increases ADDL levels by exacerbating their aggregation. In healthy cells, activation of insulin and IGF-1 receptor reduces the extracellular ADDLs applied to cells via seemingly the insulin-degrading enzyme activity. Although insulin triggers ADDL internalization, IGF-1 appears to keep ADDLs on the cell surface. Nevertheless, both insulin and IGF-1 reduce ADDL binding, protect synapses from ADDL synaptotoxic effects, and prevent the ADDL-induced surface insulin receptor loss. Our results suggest that dysfunctions of brain insulin and IGF-1 receptors contribute to Abeta aggregation and subsequent synaptic loss.

Metastatic potential of 21T human breast cancer cells depends on Akt/protein kinase B activation

Most cancer lethality is caused by metastasis. To gain insight into the molecular basis of tumor progression to metastasis, we used the 21T series of human mammary epithelial cells obtained by successive biopsies from one breast cancer patient. The c-erbB2 gene is amplified and overexpressed in each of three 21T tumor lines. The erbB receptor tyrosine kinase-activated phosphatidylinositol 3-kinase/Akt signaling cascade is crucial for the development and maintenance of epithelial cells, and dysregulation of this pathway is frequently associated with cellular transformation and cancer. For Akt to be fully activated, Ser(473) on its COOH terminus needs to be phosphorylated. We detected more Ser(473) Akt phosphorylation in MT cells, derived from a pleural effusion, compared with cells from the primary tumor. This phosphorylation has recently been shown to be catalyzed by mammalian target of rapamycin (mTOR)/rictor kinase. By using genetic and pharmacologic activators and inhibitors, we showed that Ser(473) Akt phosphorylation is more sensitive to mTOR/rictor inhibition in metastatic tumor cells than normal mammary epithelial and primary tumor cells. The mTOR/rictor kinase activity was indispensable for both Ser(473) Akt phosphorylation and migration of metastatic MT2 cells. In addition, a large decrease of protein phosphatase PH domain leucine-rich repeat protein phosphatase (PHLPP) was found, which could be responsible for the overexpression of Ser(473) Akt in MT cells. Our data indicate that these breast cancer cells acquire new vulnerabilities, rictor and PHLPP, which might provide an Achilles' heel for therapeutic intervention of breast cancer metastasis.

Multiple Interacting Oncogenes on the 8p11-p12 Amplicon in Human Breast Cancer

The 8p11-p12 genomic region is amplified in 15% of breast cancers and harbors several candidate oncogenes. However, functional evidence for a transforming role for these genes is lacking. We identified 21 genes from this region as potential oncogenes based on statistical association between copy number and expression. We further showed that three of these genes (LSM1, BAG4, and C8orf4) induce transformed phenotypes when overexpressed in MCF-10A cells, and overexpression of these genes in combination influences the growth factor independence phenotype and the ability of the cells to grow under anchorage-independent conditions. Thus, LSM1, BAG4, and C8orf4 are breast cancer oncogenes that can work in combination to influence the transformed phenotype in human mammary epithelial cells.

Expression and differential signaling of heregulins in pancreatic cancer cells

The EGF family of ligands and receptors plays an important role in the pathogenesis of pancreatic ductal adenocarcinoma (PDAC) and contributes to its aggressiveness. A number of molecular approaches have been developed to block these pathways, and studies have already proven the clinical benefit of this concept in PDAC. In the present study, we sought to determine the potential role of heregulins (HRGs), a family of EGF-like growth factors, in PDAC. Quantitative RT-PCR analysis revealed that HRGs as well as its signaling ErbB receptors were present in 4 of 4 human pancreatic cancer cell lines (PCCL). HRG-beta1 stimulated the growth of 3 of 4 PCCL, whereas HRG-alpha1 inhibited cell growth in 3 of 4 cell lines. Responses towards HRGs could in part be predicted by ErbB2 and ErbB3 expression levels. HRGs induced phosphorylation of different ErbB receptors as well as activation of MAPK, p38MAPK, JNK and PI3K in a cell- and ligand-specific manner. In vivo, HRG was upregulated in pancreatic cancer tissues and localized predominantly in the cancer cells. High HRG-beta levels but not HRG-alpha levels were associated with decreased patient survival. In conclusion, HRG is expressed by pancreatic cancer cells and influences pancreatic cancer cell growth and patient survival.

Cooperative interactions of HER-2 and HPV-16 oncoproteins in the malignant transformation of human mammary epithelial cells

To better understand the mechanisms of transformation by the oncogene HER-2, we transduced the human mammary epithelial (HME) cell line MCF-10A with HER-2 and developed a cell line that appeared to moderately overexpress HER-2. These MCF-10HER-2 cells were unable to grow in the absence of epidermal growth factor (EGF). However, coexpression of HER-2 with the HPV-16 oncoproteins E6 and E7 resulted in EGF-independent cells that expressed very high levels of constitutively activated HER-2. Interestingly, coexpression of E7 with HER-2 resulted in cells that were EGF-independent for growth but did not express HER-2 to high levels, and coexpression of E6 with HER-2 resulted in cells expressing higher levels of HER-2, which were still dependent on EGF for growth and survival. The MCF-10HER-2E7 and HER-2/E6E7 cells exhibited constitutive activation of a form of epidermal growth factor receptor (EGFR) that had a faster electrophoretic mobility than EGFR activated by exogenous growth factors. Exposure of cells with EGFR activation to ZD1839 (Iressa), at concentrations specific for EGFR, had little or no influence on proliferation of cells with amplified HER-2 but little or no EGFR. These results indicate that HER-2, E6, and E7 cooperate with endogenous EGFR to yield fully transformed cells.

Anti-HER-3 MAbs inhibit HER-3-mediated signaling in breast cancer cell lines resistant to anti-HER-2 antibodies

Two members of the EGF receptor family, HER2 and HER3, act as key oncogenes in breast cancer cells. A MAb against HER2, trastuzumab, interferes with HER2 signaling and istherapeutically effective in humans. Here, we explored the biologic effects of an antibody against HER3 (alpha-HER3ECD) in the invasive breast cancer cell lines MCF-7ADR and MDA-MB-468. Pretreating the breast cancer cells with alpha-HER3ECD prior to Heregulin stimulation caused significant reduction of the migratory and proliferative properties. This reduction is due to a substantial decrease in the tyrosine phosphorylation content of HER2 and to a modification of the HER2/HER3 association, which ultimately inhibits the activity of the downstream effectors phosphatidyinositol-3-OH-kinase and c-jun-terminal kinase. Furthermore, HER3 is internalized and not activated by HRG after pretreatment with alpha-HER3ECD. Our data reinforce the notion that HER3 could be a key target in cancer drug design and show the great potential of anti-HER3 antibodies for the therapy of breast cancer and other malignancies characterized by overexpression of HER3.

Inhibition of in vivo breast cancer growth by antisense oligodeoxynucleotides to type I insulin-like growth factor receptor mRNA involves inactivation of ErbBs, PI-3K/Akt and p42/p44 MAPK signaling pathways but not modulation of progesterone receptor activity

The present study addresses the effect of targeting type I insulin-like growth factor receptor (IGF-IR) with antisense strategies in in vivo growth of breast cancer cells. Our research was carried out on C4HD tumors from an experimental model of hormonal carcinogenesis in which the synthetic progestin medroxyprogesterone acetate (MPA) induced mammary adenocarcinomas in Balb/c mice. We employed two different experimental strategies. With the first one we demonstrated that direct intratumor injection of phosphorothioate antisense oligodeoxynucleotides (AS[S]ODNs) to IGF-IR mRNA resulted in a significant inhibition of C4HD tumor growth. In the second experimental strategy, we assessed the effect of intravenous (i.v.) injection of AS [S]ODN on C4HD tumor growth. This systemic treatment also resulted in significant reduction in tumor growth. The antitumor effect of IGF-IR AS[S]ODNs in both experimental protocols was due to a specific antisense mechanism, since growth inhibition was dose-dependent and no abrogation of tumor proliferation was observed in mice treated with phosphorothioate sense ODNs (S[S]ODNs). In addition, IGF-IR expression was inhibited in tumors from mice receiving AS[S]ODNs, as compared to tumors from control groups. We then investigated signal transduction pathways modulated in vivo by AS[S]ODNs treatment. Tumors from AS[S]ODN-treated mice of both intratumoral and intravenous protocols showed a significant decrease in the degree of insulin receptor substrate-1 (IRS-1) tyrosine phosphorylation. Activation of two of the main IGF-IR signaling pathways, phosphatidylinositol 3-kinase (PI-3K)/Akt and p42/p44 mitogen-activated protein kinases (MAPK) was abolished in tumors growing in AS[S]ODN-treated animals. Moreover, ErbB-2 tyrosine phosphorylation was blocked by in vivo administration of AS[S]ODNs. On the other hand, we found no regulation of either progesterone receptor expression or activity by in vivo AS[S]ODNs administration. Our results for the first time demonstrated that breast cancer growth can be inhibited by direct in vivo administration of IGF-IR AS[S]ODNs.

Heregulin inhibits proliferation via ERKs and phosphatidyl-inositol 3-kinase activation but regulates urokinase plasminogen activator independently of these pathways in metastatic mammary tumor cells

Heregulin (HRG) and type I receptor tyrosine kinase (RTK) expression was investigated in the highly invasive and metastatic LM3 cell line, our previously described model of metastasis for mammary cancer (Bal de Kier Joffe et al. [1986] Invasion Metastasis 6:302-12; Urtreger et al. [1997] Int J Oncol 11:489-96). Although LM3 cells do not express HRG, they exhibit high levels of ErbB-2 and ErbB-3 as well as moderate expression of ErbB-4. Addition of exogenous HRGbeta1 resulted in inhibition of both proliferation and migration of LM3 cells. HRGbeta1 was also able to decrease the activity of urokinase-type plasminogen activator (uPA) and matrix metalloproteinase 9 (MMP-9), 2 key enzymes in the invasion and metastatic cascade. HRGbeta1 treatment of LM3 cells induced tyrosine phosphorylation of ErbB-2, ErbB-3 and ErbB-4 as well as the formation of ErbB-2/ErbB-3 and ErbB-2/ErbB-4 heterodimers. Assessment of the signaling pathways involved in HRGbeta1 action indicated that the addition of HRGbeta1 to LM3 cells resulted in activation of phosphatidylinositol 3- kinase (PI-3K) and in strong induction of the association of the p85 subunit of PI-3K with ErbB-3. HRGbeta1 also caused the rapid activation of ERK1/ERK2 and Stat3 and Stat5 (signal transducers and activators of transcription [STAT]). This is the first demonstration of the ability of HRGbeta1 to activate STATs in mammary tumor cells. Blockage of PI-3K activity with its chemical inhibitor wortmannin, or of MEK1/ERKs activity with PD98059, resulted in suppression of the ability of HRGbeta1 to inhibit LM3 cell growth. Notwithstanding the suppression of these 2 signaling pathways, HRGbeta1 still proved capable of inhibiting uPA activity. Therefore, our results provide evidence that signaling pathways involved in HRGbeta1-induced proliferation appear to be distinct from those involved in HRGbeta1 regulation of uPA, a protease that plays a pivotal role in invasion and metastasis.

Activation of ErbB-2 via a hierarchical interaction between ErbB-2 and type I insulin-like growth factor receptor in mammary tumor cells

The present study focused on interactions between signaling pathways activated by progestins and by type I and II receptor tyrosine kinases (RTKs) in mammary tumors. An experimental model in which the synthetic progestin medroxyprogesterone acetate (MPA) induced mammary adenocarcinomas in Balb/c mice was used. MPA-stimulated proliferation, both in vivo and in vitro, of progestin-dependent tumors induced up-regulation of ErbB-2 protein levels and tyrosine phosphorylation of this receptor. Combinations of antisense oligodeoxynucleotides (ASODNs) directed to ErbB-2 mRNA with ASODNs directed to the insulin-like growth factor-I receptor (IGF-IR) were used to study the effect of the simultaneous block of these receptors on the MPA-induced proliferation of epithelial cells from the progestin-dependent C4HD line. Neither synergistic nor additive effects on the inhibition of MPA-induced proliferation of C4HD cells were observed as a result of the combination of these ASODNs. Suppression of IGF-IR expression by ASODNs resulted in complete abrogation of MPA-induced phosphorylation of ErbB-2 in C4HD cells, whereas blockage of ErbB-2 did not affect IGF-IR phosphorylation. These results show the existence of a hierarchical interaction between IGF-IR and ErbB-2, by means of which IGF-IR directs ErbB-2 phosphorylation. We demonstrated, for the first time, that this hierarchical interaction involves physical association of both receptors, resulting in the formation of a heteromeric complex. Furthermore, confocal laser microscopy experiments demonstrated that MPA was able to induce co-localization of ErbB-2 and IGF-IR. This hetero-oligomer was also found in MCF-7 human breast cancer cells in which association of IGF-IR and ErbB-2 was induced by heregulin and IGF-I. Oncogene (2001) 20, 34 - 47.

Coexpression patterns of EGFR, HER2, HER3 and HER4 in non-melanoma skin cancer

The receptor tyrosine kinases (RTKs) epidermal growth factor receptor (EGFR), HER2, HER3 and HER4 are involved in the pathogenesis of multiple human malignant neoplasias. However, their role in the carcinogenesis of basal cell carcinomas (BCC) and squamous cell carcinomas (SCC) remains to be elucidated. In order to further define the role of these RTKs, 56 human skin tissue samples of normal skin, BCC and SCC were studied by conventional and differential and quantitative reverse transcriptase-polymerase chain reaction (rtPCR). EGFR and HER3 were predominantly expressed in the BCCs and SCCs, while HER2 was ubiquitously expressed. HER4 was not expressed in any sample. Since in vitro studies have provided compelling evidence that heterodimer formation of these receptors are associated with different signal transduction processes, coexpression patterns might be decisive for the induction and maintenance of a malignant phenotype. These results confirm this concept: isolated HER2 expression and EGFR/HER2 were predominantly found in normal skin, while HER2/HER3 and the triple expression of EGFR/HER2/HER3 were seen more frequently in the BCCs and SCCs compared with normal skin (50% and 40% compared with 26%, respectively). The activation of HER3, in addition to EGFR and HER2, might therefore be associated with the malignant phenotype. However, due to the small numbers in this study, further confirmation of the patterns is needed.

Heregulin-beta is especially potent in activating phosphatidylinositol 3-kinase in nontransformed human mammary epithelial cells

The neu differentiation factors/heregulins (HRGs) comprise a family of polypeptide growth factors that activate p185(erbB-2) through direct binding to either erbB-3 or erbB-4 receptor tyrosine kinases. We have previously shown that HRG-beta is mitogenic for various human mammary epithelial cell lines that coexpress c-erbB-2 and c-erbB-3. Phosphatidylinositol 3-kinase (PI3K) is activated by p185(erbB-2) /erbB-3 heterodimers in cells stimulated by HRG, and PI3K is constitutively activated by p185(erbB-2) /erbB-3 in breast carcinoma cells that overexpress c-erbB-2. To better understand the relative abilities of HRGs, epidermal growth factor (EGF), or insulin to activate PI3K under normal physiological conditions, we compared the levels of recruitment of the 85-kDa regulatory subunit of PI3K when activated by the type I (erbB) or type II [insulin-like growth factor (IGF)] receptor tyrosine kinases in two different nontransformed human mammary epithelial cell lines. The nontransformed H16N-2 cells isolated from normal tissue express EGFR, p185(erbB-2), and erbB-3, and are highly responsive to the mitogenic effects of HRG-beta as well as to the combination of EGF and insulin in serum-free culture. We measured the stoichiometry of p85 recruited by tyrosine-phosphorylated proteins induced in H16N-2 cells by either the alpha or the beta isoform of HRG. HRG-beta was greater than 10-fold more potent in inducing p85 recruitment than was the less biologically active HRG-alpha isoform. HRG-beta was also a more potent inducer of p85 recruited by tyrosine-phosphorylated proteins than was either EGF, insulin, or EGF and insulin combined. Furthermore, erbB-3 principally mediated the direct recruitment of p85 in cells stimulated by HRG or EGF, indicating that, in addition to the high-level activation of PI3K by p185(erbB-2) / erbB-3, EGFR/erbB-3 heterodimer interaction is essential for the weak but significant level of PI3K activated by EGF in cells that express normal EGFR levels. Studies using the PI3K inhibitor wortmannin also indicated that PI3K activation was required for the proliferation of H16N-2 cells induced by either HRG-beta or EGF and insulin in serum-free culture. Finally, HRG-beta was also an especially potent inducer of PI3K in the nontransformed MCF-10A cells, which were derived spontaneously from normal reduction mammoplasty tissue. These data show, for the first time, a side-by-side quantitative comparison of the relative degree of PI3K activated by different growth factors in nontransformed growth factor-dependent cells under precisely defined conditions in culture.

ERBB-2 overexpression confers PI 3' kinase-dependent invasion capacity on human mammary epithelial cells

Amplification and overexpression of ERBB-2 in human breast cancer is thought to play a significant role in the progression of the disease; however, its precise role in the aetiology of altered phenotypes associated with human breast cancer is unknown. We have previously shown that exogenous overexpression of ERBB-2 conferred growth factor independence on human mammary epithelial cells. In this study, we show that ERBB-2 overexpression also causes the cells to acquire other characteristics exhibited by human breast cancer cells, such as anchorage-independent growth and invasion capabilities. ERBB-2-induced invasion is dependent on fibronectin and correlates with the down-regulation of cell surface alpha4 integrin. In addition ERBB-2 co-immunoprecipitates with focal adhesion kinase (FAK) in these cells. We have also shown, by use of exogenously expressed PTEN and by treatment with the PI3'-kinase inhibitor LY294002, that ERBB-2-induced invasion is dependent on the PI3'-kinase pathway; however, PTEN does not dephosphorylate FAK in these cells.

Molecular cytogenetic analysis of 11 new breast cancer cell lines

We describe a survey of genetic changes by comparative genomic hybridization (CGH) in 11 human breast cancer cell lines recently established in our laboratory. The most common gains took place at 8q (73%), 1 q (64%), 7q (64%), 3q (45%) and 7p (45%), whereas losses were most frequent at Xp (54%), 8p (45%), 18q (45%) and Xq (45%). Many of the cell lines displayed prominent, localized DNA amplifications by CGH. One-third of these loci affected breast cancer oncogenes, whose amplifications were validated with specific probes: 17q12 (two cell lines with ERBB2 amplifications), 11q13 (two with cyclin-D1), 8p11-p12 (two with FGFR1) and 10q25 (one with FGFR2). Gains and amplifications affecting 8q were the most common genetic alterations in these cell lines with the minimal, common region of involvement at 8q22-q23. No high-level MYC (at 8q24) amplifications were found in any of the cell lines. Two-thirds of the amplification sites took place at loci not associated with established oncogenes, such as 1q41-q43, 7q21-q22, 7q31, 8q23, 9p21-p23, 11p12-p14, 15q12-q14, 16q13-q21, 17q23, 20p11-p12 and 20q13. Several of these locations have not been previously reported and may harbour important genes whose amplification is selected for during cancer development. In summary, this set of breast cancer cell lines displaying prominent DNA amplifications should facilitate discovery and functional analysis of genes and signal transduction pathways contributing to breast cancer development.

erbB-2 overexpression in human mammary epithelial cells confers growth factor independence

Previously, we demonstrated that human breast cancer cells with progressively elevated levels of constitutively tyrosine phosphorylated erbB-2 are independent of growth factors required by normal human mammary epithelial (HME) cells for proliferation in serum-free medium. To determine whether erbB-2 overexpression alone is sufficient to confer the growth factor-independence phenotype in HME cells, the spontaneously immortalized MCF-10A cell line and the HPV-16-immortalized H16N2 cell line were infected with the bicistronic retroviral vector pTPerbB-2 and tested for their ability to grow in the absence of specific factors. Selection of infected cells in G418-containing medium resulted in moderate levels of erbB-2 overexpression in approximately 40% of cells. The subpopulation of erbB-2 overexpressing cells could be selected for by culturing the cells in medium devoid of insulin. When MCF-10A or H16N2 cells were infected with pTPerbB-2 and directly selected in growth factor-deficient medium over long periods of time, populations of both cell lines emerged that expressed levels of erbB-2 protein equivalent to levels expressed by breast cancer cells with an erbB-2 gene amplification. Furthermore, overexpressed p185(erbB-2) was constitutively tyrosine phosphorylated in these cells. The levels of tyrosine phosphorylated p185(erbB-2) differed in the two recipient lines, with H16N2-erbB-2 cells having higher levels of activated receptor than MCF-10AerbB-2 cells. Furthermore, only the H16N2-erbB-2 cells were independent of both insulin and epidermal growth factor for growth in serum-free medium. Overexpression of erbB-2 also resulted in progressively increasing levels of tyrosine-phorphorylated erbB-3, without any significant changes in p180(erbB-3) levels. These studies demonstrate a direct relationship between the level of expression and activation of p185(erbB-2) and the requirements of HME cells for insulin-like and epidermal growth factor-like growth factors. The results also suggest that genetic alterations present in breast cancer cells, or mediated by HPV-16-induced alterations in pRb and p53, can influence the expression level and activation status of erbB-2 as well as erbB-3 and, in turn, their degree of growth factor independence.

A new member of the tumor necrosis factor/nerve growth factor receptor family inhibits T cell receptor-induced apoptosis

By comparing untreated and dexamethasone-treated murine T cell hybridoma (3DO) cells by the differential display technique, we have cloned a new gene, GITR (glucocorticoid-induced tumor necrosis factor receptor family-related gene) encoding a new member of the tumor necrosis factor/nerve growth factor receptor family. GITR is a 228-amino acids type I transmembrane protein characterized by three cysteine pseudorepeats in the extracellular domain and similar to CD27 and 4-1BB in the intracellular domain. GITR resulted to be expressed in normal T lymphocytes from thymus, spleen, and lymph nodes, although no expression was detected in other nonlymphoid tissues, including brain, kidney, and liver. Furthermore, GITR expression was induced in T lymphocytes upon activation by anti-CD3 mAb, Con A, or phorbol 12-myristate 13-acetate plus Ca-ionophore treatment. The constitutive expression of a transfected GITR gene induced resistance to anti-CD3 mAb-induced apoptosis, whereas antisense GITR mRNA expression lead to increased sensitivity. The protection toward T cell receptor-induced apoptosis was specific, because other apoptotic signals (Fas triggering, dexamethasone treatment, or UV irradiation) were not modulated by GITR transfection. Thus, GITR is a new member of tumor necrosis factor/nerve growth factor receptor family involved in the regulation of T cell receptor-mediated cell death.

Roles of ErbB-3 and ErbB-4 in the physiology and pathology of the mammary gland

ErbB-3 and ErbB-4 are the most recently discovered and least characterized of the class I tyrosine kinase receptors. ErbB-3 is noteworthy for its low tyrosine kinase activity, suggesting that it may function more as an adaptor in signaling than as a kinase. Heregulin serves as a ligand for both receptors. A primary mechanism of heregulin action involves heterodimerization of its targeted receptors with other members of the class I family to promote cross-phosphorylation and cellular responses. Betacellulin also acts as a ligand for ErbB-4 to stimulate its kinase activity in both homo- and hetero-dimers. A new ligand (ASGP-2) for ErbB-2 has been discovered which operates by an intramembrane mechanism and may be able to modulate external ligand-dependent ErbB-3 or ErbB-4 heterodimeric interactions with ErbB-2. Heterodimerization stimulated by the ligands is a key feature of mitogenic signaling in mammary epithelial cells and tumors. Characterization of the signaling pathways for these receptors is still incomplete, but phosphatidylinositol 3-kinase and SHC have been implicated. Heregulin synthesized by the mesenchyme has been implicated in mammary development, modulated by systemic hormones. Observations on cultured mammary cells and mammary tumors have suggested linkages of ErbB-3 and ErbB-4 to proliferation and differentiation, respectively, but further work is needed to establish their definitive roles.