Ligand and p185c-neu density govern receptor interactions and tyrosine kinase activation

Antibody-drug conjugates targeting HER2 for the treatment of urothelial carcinoma: potential therapies for HER2-positive urothelial carcinoma

Urothelial carcinoma (UC) is a common cancer characterized by high morbidity and mortality rates. Despite advancements in treatment, challenges such as recurrence and low response rates persist. Antibody-drug conjugates (ADCs) have emerged as a promising therapeutic approach for various cancers, although their application in UC is currently limited. This review focuses on recent research regarding ADCs designed to treat UC by targeting human epidermal growth factor receptor 2 (HER2), a surface antigen expressed on tumor cells. ADCs comprise three main components: an antibody, a linker, and a cytotoxic payload. The antibody selectively binds to tumor cell surface antigens, facilitating targeted delivery of the cytotoxic drug, while linkers play a crucial role in ensuring stability and controlled release of the payload. Cleavable linkers release the drug within tumor cells, while non-cleavable linkers ensure stability during circulation. The cytotoxic payload exerts its antitumor effect by disrupting cellular pathways. HER2 is commonly overexpressed in UCs, making it a potential therapeutic target. Several ADCs targeting HER2 have been approved for cancer treatment, but their use in UC is still being tested. Numerous HER2 ADCs have demonstrated significant growth inhibition and induction of apoptosis in translational models of HER2-overexpressing bladder cancer. Ongoing clinical trials are assessing the efficacy and safety of ADCs targeting HER2 in UC, with the aim of determining tumor response and the potential of ADCs as a treatment option for UC patients. The development of effective therapies with improved response rates and long-term effectiveness is crucial for advanced and metastatic UC. ADCs targeting HER2 show promise in this regard and merit further investigation for UC treatment.

Monoclonal Antibodies, Small Molecule Inhibitors and Antibody-drug Conjugates as HER2 Inhibitors

Overexpression of human epidermal growth factor receptor (HER)-2 is found in a variety of cancers, often portending poor clinical outcomes. Therefore, HER2 is an attractive target for treatment. This review describes the research progress of HER2 targeted inhibitors in recent years. Excellent reviews are available, so we focus on the development, mechanisms of action, and structure-activity relationships of different types of inhibitors, including monoclonal antibodies, small molecule inhibitors, and antibody-drug conjugates (ADCs). In addition, the differences among them are compared.

Emergence of ERBB2 Mutation as a Biomarker and an Actionable Target in Solid Cancers

The oncogenic role ERBB2 amplification is well established in breast and gastric cancers. This has led to the development of a well-known portfolio of monoclonal antibodies and kinase inhibitors targeting the ERBB2 kinase. More recently, activating mutations in the ERBB2 gene have been increasingly reported in multiple solid cancers and were shown to play an oncogenic role similar to that of ERBB2 amplification. Thus, ERBB2 mutations define a distinct molecular subtype of solid tumors and serve as actionable targets. However, efforts to target ERBB2 mutation has met with limited clinical success, possibly because of their low frequency, inadequate understanding of the biological activity of these mutations, and difficulty in separating the drivers from the passenger mutations. Given the current impetus to deliver molecularly targeted treatments for cancer, there is an important need to understand the therapeutic potential of ERBB2 mutations. Here we review the distribution of ERBB2 mutations in different tumor types, their potential as a novel biomarker that defines new subsets in many cancers, and current data on preclinical and clinical efforts to target these mutations. IMPLICATIONS FOR PRACTICE: A current trend in oncology is to identify novel genomic drivers of solid tumors and developing precision treatments that target them. ERBB2 amplification is an established therapeutic target in breast and gastric cancers, but efforts to translate this finding to other solid tumors with ERBB2 amplification have not been effective. Recently the focus has turned to targeting activating ERBB2 mutations. The year 2018 marked an important milestone in establishing ERBB2 mutation as an important actionable target in multiple cancer types. There have been several recent preclinical and clinical studies evaluating ERBB2 mutation as a therapeutic target with varying success. With increasing access to next-generation sequencing technologies in the clinic, oncologists are frequently identifying activating ERBB2 mutations in patients with cancer. There is a significant need both from the clinician and bench scientist perspectives to understand the current state of affairs for ERBB2 mutations.

Heterogeneity of ERBB2 in gastric carcinomas: a study of tissue microarray and matched primary and metastatic carcinomas

Trastuzumab in association with systemic cytotoxic chemotherapy is a therapeutic option for patients with advanced or metastatic ERBB2+ gastric carcinoma. The status of the ERBB2 overexpression or gene amplification is an important predictive marker in gastric cancer. However, it is controversial whether the primary tumor is representative of distant metastases in terms of ERBB2 status. Quadruplicated tissue microarrays from formalin-fixed paraffin-embedded tissues from 498 advanced primary gastric carcinomas and 97 matched metastatic lymph nodes were investigated by immunohistochemistry with HercepTest and silver in situ hybridization. For further comparison, another set of 41 paired primary and distant metastatic gastric carcinomas were also tested. Intratumoral heterogeneity was defined as different results between tissue microarray cores. ERBB2-positivity was observed in 52 gastric carcinomas (10%) and was not associated with recurrence of disease or survival of patients. In ERBB2-positive primary gastric carcinomas, heterogeneous ERBB2 overexpression was observed in 21/63 (33%) gastric carcinomas and heterogeneous ERBB2 gene amplification in 14/62 (23%) cases. Repeated immunohistochemistry and silver in situ hybridization in representative paraffin tumor blocks confirmed focal ERBB2 overexpression and ERBB2 gene amplification and did not change the final results. Discrepancies in ERBB2 results between primary and paired metastatic lymph nodes were observed in 11% of cases by immunohistochemistry and 7% by silver in situ hybridization. Out of the 41 paired primary and distant metastases, 5 (12%) cases were ERBB2-positive, and discrepancy was observed in one case. Intratumoral heterogeneity and discrepant ERBB2 results in primary and metastatic tumor are not uncommon in gastric carcinoma. Results of silver in situ hybridization showed less frequent heterogeneity compared with immunohistochemistry. Wherever possible, ERBB2 immunohistochemistry testing should be performed in both primary and distant metastatic sites.

Molecular Mechanisms of Trastuzumab-Based Treatment in HER2-Overexpressing Breast Cancer

The past decade of research into HER2-overexpressing breast cancer has provided significant insight into the mechanisms by which HER2 signaling drives tumor progression, as well as potential mechanisms by which cancer cells escape the anticancer activity of HER2-targeted therapy. Many of these preclinical findings have been translated into clinical development, resulting in novel combinations of HER2-targeted therapies and combinations of trastuzumab plus inhibitors of resistance pathways. In this paper, we will discuss proposed mechanisms of trastuzumab resistance, including epitope masking, cross signaling from other cell surface receptors, hyperactive downstream signaling, and failure to induce antibody-dependent cellular cytotoxicity. In addition, we will discuss the molecular mechanisms of action of dual HER2 inhibition, specifically the combination of trastuzumab plus lapatinib or trastuzumab with pertuzumab. We will also discuss data supporting therapeutic combinations of trastuzumab with agents targeted against molecules implicated in trastuzumab resistance. The roles of insulin-like growth factor-I receptor and the estrogen receptor are discussed in the context of resistance to HER2-targeted therapies. Finally, we will examine the major issues that need to be addressed in order to translate these combinations from the bench to the clinic, including the need to establish relevant biomarkers to select for those patients who are most likely to benefit from a particular drug combination.

Engagement of overexpressed Her2 with GEP100 induces autonomous invasive activities and provides a biomarker for metastases of lung adenocarcinoma

Overexpression of Her2/ErbB2/Neu in cancer is often correlated with recurrent distant metastasis, although the mechanism still remains largely elusive. We have previously shown that EGFR, when tyrosine-phosphorylated, binds to GEP100/BRAG2 to activate Arf6, which induces cancer invasion and metastasis. We now show that overexpressed Her2 in lung adenocarcinoma cells also employs GEP100. Like EGFR-GEP100 binding, this association is primarily mediated by the pleckstrin homology (PH) domain of GEP100 and Tyr1139/Tyr1196 of Her2. Tyr1139/Tyr1196 are autonomously phosphorylated, when Her2 is overexpressed. Accordingly, invasive activities mediated by the Her2-GEP100 pathway are not dependent on external factors. Blocking Her2-GEP100 binding, as well as its signaling pathway all inhibit cancer invasive activities. Moreover, our clinical study indicates that co-overexpression of Her2 with GEP100 in primary lung adenocarcinomas of patients is correlated with the presence of their node-metastasis with a statistical significance. Since the GEP100 PH domain interacts with both Her2 and EGFR, targeting this domain may provide novel cancer therapeutics.

The tumor suppressor RECK interferes with HER-2/Neu dimerization and attenuates its oncogenic signaling

Our previous study demonstrates that HER-2/Neu oncogene inhibits a matrix metalloproteinase inhibitor and tumor metastasis suppressor RECK to promote metastasis. Conversely, the effect of RECK on the oncogenic function of HER-2/Neu is unknown. Ectopic expression of RECK in 293T cells and HER-2/Neu-overexpressing breast cancer cells shows that RECK and HER-2/Neu are co-localized and these two proteins can be co-immunoprecipitated. RECK inhibits HER-2/Neu receptor dimerization and autophosphorylation, which causes reduction of ERK and AKT kinase activity and down-regulation of HER-2/Neu target genes. RECK expression is reduced in 58.8% of breast cancer tissues and is associated with lymph node invasion supporting its anti-metastatic role. Collectively, we provide the first evidence that RECK can negatively regulate oncogenic activity of HER-2/Neu by inhibiting receptor dimerization.

Growth factor-induced resistance to tamoxifen is associated with a mutation of estrogen receptor alpha and its phosphorylation at serine 305

Estrogens play a crucial role in breast tumor growth, which is the rationale for the use of antiestrogens, such as tamoxifen, in women with estrogen receptor (ER)-alpha-positive breast cancer. However, hormone resistance is a major clinical problem. Altered growth factor signaling to the ERalpha pathway has been shown to be associated with the development of clinical resistance. We previously have identified a mutation that replaces arginine for lysine at residue 303 (K303R) of ERalpha, which confers hypersensitive growth in low levels of estrogen. To determine if the K303R mutation could participate in the evolution of hormone resistance, we generated MCF-7 breast cancer cells stably transfected with either wild-type (WT) or K303R ERalpha. We found that the mutation confers decreased sensitivity to tamoxifen in the presence of the growth factor heregulin, using anchorage-independent growth assays. K303R ERalpha-expressing cells were hypersensitive to growth factor signals. Our data suggest that phosphorylation of serine 305 within the hinge domain of ERalpha might play a key role in increasing ligand-independent activity of the mutant receptor. We hypothesize that the mutation adapts the receptor for enhanced bidirectional cross-talk with the HER2 growth factor receptor pathway, which then impacts on responsiveness to tamoxifen.

Trastuzumab and Doxorubicin-Related Cardiotoxicity and the Cardioprotective Role of Exercise

Women diagnosed with breast cancer typically undergo a multimodal approach to treating their disease. The treatments used often result in sequelae such as fatigue, hair loss, nausea and vomiting, and functional impairment. Many of these sequelae can be controlled or eliminated with pharmacological, physical, or social interventions. However, 2 effective cytotoxic agents, doxorubicin and trastuzumab, are associated with a potentially life-threatening sequela, cardiotoxicity. Currently, these agents are dosage and duration limited to circumvent cardiac damage. Exercise prior to and during the administration of these agents is emerging as a possible cardioprotective intervention based on the findings of animal model studies. Incorporating exercise into the breast cancer treatment trajectory may eliminate the dosage and duration restrictions of these antineoplastic agents and ultimately affect survival and quality of life. The authors present the pharmacological mechanism for each agent and the exciting results of animal model studies that lay the groundwork for future clinical trials.

Heregulin-beta promotes matrix metalloproteinase-7 expression via HER2-mediated AP-1 activation in MCF-7 cells

It has been reported that HER2 level is strongly correlated with the expression of MMP-7 in some carcinomas. HER2 is a preferred heterodimerization partner of EGFR, HER3, and HER4. HER2 overexpression is believed to enhance the signaling from these receptors in response to binding of their specific ligands. In this study, we show that heregulin-beta (HRG-beta) stimulation remarkably induced MMP-7 promoter activity and significantly enhanced the expression and activity of MMP-7 in MCF-7 cells overexpressing HER2. The expression of c-Jun and c-Fos and the level of the phosphorylated c-Jun were markedly increased after HRG-beta treatment in MCF-7/HER2 cells. Increased MMP-7 promoter activity was observed in MCF-7/c-Jun cells. The activity of the MMP-7 promoter induced by HRG-beta in MCF-7/HER2 cells could be inhibited by a dominant negative c-Jun mutant TAM67 and by the mutagenesis of the AP-1 site. c-Jun binding to MMP-7 promoter was confirmed by ChIP assays. The data indicate a close link among HRG-beta stimulation, HER signaling, and AP-1 activation. Our data suggest that HRG-beta-induced MMP-7 expression was regulated by HER2-mediated AP-1 activation in MCF-7 cells.

HER2/Neu (ErbB2) Signaling to Rac1-Pak1 Is Temporally and Spatially Modulated by Transforming Growth Factor β

In HER2 (ErbB2)-overexpressing cells, transforming growth factor beta (TGF-beta), via activation of phosphoinositide-3 kinase (PI3K), recruits actin and actinin to HER2, which then colocalizes with Vav2, activated Rac1, and Pak1 at cell protrusions. This results in prolonged Rac1 activation, enhanced motility and invasiveness, Bad phosphorylation, uncoupling of Bad/Bcl-2, and enhanced cell survival. The recruitment of the HER2/Vav2/Rac1/Pak1/actin/actinin complex to lamellipodia was abrogated by actinin siRNAs, dominant-negative (dn) p85, gefitinib, and dn-Rac1 or dn-Pak1, suggesting that the reciprocal interplay of PI3K, HER2 kinase, and Rac GTPases with the actin cytoskeleton is necessary for TGF-beta action in oncogene-overexpressing cells. Thus, by recruiting the actin skeleton, TGF-beta "cross-links" this signaling complex at cell lamellipodia; this prolongs Rac1 activation and increases metastatic properties and survival of HER2-overexpressing cells.

HER2 kinase domain mutation results in constitutive phosphorylation and activation of HER2 and EGFR and resistance to EGFR tyrosine kinase inhibitors

HER2/Neu gene mutations have been identified in lung cancer. Expression of a HER2 mutant containing a G776(YVMA) insertion in exon 20 was more potent than wild-type HER2 in associating with and activating signal transducers, phosphorylating EGFR, and inducing survival, invasiveness, and tumorigenicity. HER2(YVMA) transphosphorylated kinase-dead EGFR(K721R) and EGFR(WT) in the presence of EGFR tyrosine kinase inhibitors (TKIs). Knockdown of mutant HER2 in H1781 lung cancer cells increased apoptosis and restored sensitivity to EGFR TKIs. The HER2 inhibitors lapatinib, trastuzumab, and CI-1033 inhibited growth of H1781 cells and cells expressing exogenous HER2(YVMA). These data suggest that (1) HER2(YVMA) activates cellular substrates more potently than HER2(WT); and (2) cancer cells expressing this mutation remain sensitive to HER2-targeted therapies but insensitive to EGFR TKIs.

Activity of the dual kinase inhibitor lapatinib (GW572016) against HER-2-overexpressing and trastuzumab-treated breast cancer cells

Lapatinib (GW572016) is a selective inhibitor of both epidermal growth factor receptor (EGFR) and HER-2 tyrosine kinases. Here, we explore the therapeutic potential of lapatinib by testing its effect on tumor cell growth in a panel of 31 characterized human breast cancer cell lines, including trastuzumab-conditioned HER-2-positive cell lines. We further characterize its activity in combination with trastuzumab and analyze whether EGFR and HER-2 expression or changes induced in the activation of EGFR, HER-2, Raf, AKT, or extracellular signal-regulated kinase (ERK) are markers of drug activity. We report that concentration-dependent antiproliferative effects of lapatinib were seen in all breast cancer cell lines tested but varied significantly between individual cell lines with up to 1,000-fold difference in the IC(50)s (range, 0.010-18.6 micromol/L). Response to lapatinib was significantly correlated with HER-2 expression and its ability to inhibit HER-2, Raf, AKT, and ERK phosphorylation. Long-term in vivo lapatinib studies were conducted with human breast cancer xenografts in athymic mice. Treatment over 77 days resulted in a sustained and significant reduction in xenograft volume compared with untreated controls. For the combination of lapatinib plus trastuzumab, synergistic drug interactions were observed in four different HER-2-overexpressing cell lines. Moreover, lapatinib retained significant in vitro activity against cell lines selected for long-term outgrowth (>9 months) in trastuzumab-containing (100 microg/mL) culture medium. These observations provide a clear biological rationale to test lapatinib as a single agent or in combination with trastuzumab in HER-2-overexpressing breast cancer and in patients with clinical resistance to trastuzumab.

Overexpression of RasN17 fails to neutralize endogenous Ras in MCF7 breast cancer cells

Receptor tyrosine kinases of the ErbB family have been implicated in the onset/progression of a number of neoplasias. In these diseases, ErbB receptor expression may be accompanied by constitutive activation caused by molecular alterations, overexpression, or ligand binding. An important signaling route activated by these receptors that has been linked to the stimulation of cell proliferation is the Ras route. Here we have investigated the action of a mutant Ras form, H-RasN17, on the proliferation of the breast cancer epithelial cell line MCF7 cells. In these cells expression of RasN17 failed to affect serum or ErbB receptor-stimulated proliferation. Analysis of the action of RasN17 indicated that overexpression of this mutant form of Ras did not affect neuregulin or protein kinase C-induced activation of Erk1/2. In addition, RasN17 failed to prevent activation of endogenous N-Ras and H-Ras even though the levels of the latter were much lower than those of the RasN17 form. The failure of RasN17 to prevent endogenous Ras activation did not appear to be due to deficient processing or sorting of the mutated form. These data indicated that the action of RasN17 as a bona fide inhibitor of Ras depends on the cell type and requires detailed analysis of the biochemical and biological properties of RasN17, particularly with respect to the activation of endogenous Ras.

Targeting ErbB receptor signaling: A pan-ErbB approach to cancer

The ErbB receptors are localized to the cell membrane where they are activated by ligand to trigger a network of signaling pathways. In some cancer cells, dysregulation of ErbB-mediated signaling confers a growth advantage, resulting in cellular transformation and increased metastatic potential. Several agents that inhibit individual ErbB receptors have recently been approved for the treatment of human malignancies, validating ErbB receptors as therapeutic targets. One strategy to improve the efficacy of ErbB-targeted therapies is to inhibit multiple ErbB receptors, thereby interfering with the cooperation that exists between receptors. This minireview addresses the approaches being developed to concurrently inhibit multiple ErbB receptors.

Mechanism of action of anti-HER2 monoclonal antibodies: scientific update on trastuzumab and 2C4

The HER family of transmembrane tyrosine kinase receptors is composed of four members, BER1 to HER4. HER2 is a ligand-orphan receptor expressed in many human tumors and overexpressed in 25-30% of breast cancers. HER2 amplifies the signal provided by other receptors of the HER family by forming heterodimers. The essential role of HER2 in the HER signaling network led to the development of anti-HER2 monoclonal antibodies (MAbs) for cancer therapy. In particular, the humanized MAb trastuzumab (Herceptin) has antitumor activity against HER2-overexpressing human breast tumor cells and is widely used for the treatment of women with HER2 overexpressing breast cancers. Trastuzumab induces HER2 receptor downmodulation and, as a result, inhibits critical signalling pathways (i.e. ras-Raf-MAPK and PI3K/Akt) and blocks cell cycle progression by inducing the formation of p27/Cdk2 complexes. Trastuzumab also inhibits HER2 cleavage, preceding antibody-induced receptor downmodulation, and this effect might contribute to its antitumor activity in some cancers. In vivo, trastuzumab inhibits angiogenesis and induces antibody-dependent cellular cytotoxicity. A limitation of trastuzumab is that its activity is largely restricted to breast cancers with the highest level of HER2 overexpression or HER2 gene amplification. However, there is a large population of breast cancers and of many other tumors that have low or moderate HER2 expression. In such tumors, HER2 functions as a preferred coreceptor to form heterodimers with HER1 (EGFR), HER3 or HER4. For this reason, a humanized monoclonal antibody, called 2C4, that targets the role of HER2 as a coreceptor is under active development. 2C4 binds to a different epitope of HER2 ectodomain than trastuzumab and sterically hinders HER2 recruitment in heterodimers with other HER receptors. This results in the inhibition of signalling by HER2-based heterodimers both in cells with low and high HER2 expression. In vitro and in vivo antitumor activity has been reported in a range of breast and prostate tumor models. Therefore, 2C4 may have potential against a wide variety of solid tumors. Phase I trials are underway.

Cooperation of the ErbB2 receptor and transforming growth factor beta in induction of migration and invasion in mammary epithelial cells

MCF10A mammary epithelial cells form growth-arrested structures when cultured in three-dimensional basement membrane gels. Activation of the receptor tyrosine kinase ErbB2 induces formation of proliferative structures that share properties with noninvasive early stage lesions. We conducted a genetic screen to identify cDNAs that can cooperate with ErbB2 to induce migration in these cells, with the hypothesis that they would represent candidate "second hits" in the development of invasive breast carcinomas. We found that expression of transforming growth factor (TGF)beta1 and TGFbeta3 in cells expressing activated ErbB2 induces migration in transwell chambers and invasive behavior in both basement membrane cultures and invasion chambers. The ability of ErbB2 to cooperate with TGFbeta correlated with sustained, elevated activation of extracellular signal-regulated kinase (Erk)-mitogen-activated protein kinase. Pharmacological reduction of Erk activity inhibited the cooperative effect of TGFbeta and ErbB2 on migration and expression of activated Erk kinase was sufficient to cooperate with TGFbeta to induce migration and invasion, suggesting that sustained Erk activation is critical for ErbB2/TGFbeta cooperation. In addition, we show that costimulation of ErbB2 and TGFbeta induces autocrine secretion of factors that are sufficient to induce migration, but not invasion, by means of both epidermal growth factor receptor-dependent and -independent processes. These results support the role of TGFbeta as a pro-invasion factor in the progression of breast cancers with activated ErbB2 and suggest that activation of the Erk and epidermal growth factor receptor pathways are key in mediating these events.

Immunologic principles and immunotherapeutic approaches in ovarian cancer

Ovarian cancer is an immunogenic tumor, and numerous antigens have been identified in recent years. Several of these antigens are important in regulating tumor growth and may be ideal targets for the development of immune-based strategies. In the absence of immunologic intervention, tumors evade the immune system by several mechanisms, most notably tolerance and immunosuppression. As understanding of the immune response improves, strategies are being designed to circumvent T-cell tolerance to self-antigens through modulation of APC function. In addition, techniques are being developed to identify reverse ovarian cancer-induced immune evasion tactics. The type of the immune-based therapy to apply varies with disease burden. It is hoped that discoveries at the bench along with lessons learned in prior clinical trials soon will allow clinicians to develop rationally based immunologic strategies to treat and prevent ovarian cancer.

ErbB2 and bone sialoprotein as markers for metastatic osteosarcoma cells

Osteosarcoma is the most common malignant bone neoplasia occurring in young patients in the first two decades of life, and represents 20% of all primitive malignant bone tumours. At present, treatment of metastatic osteosarcoma is unsatisfactory. High-dose chemotherapy followed by CD34+ leukapheresis rescue may improve these poor results. Neoplastic cells contaminating the apheresis may, however, contribute to relapse. To identify markers suitable for detecting osteosarcoma cells in aphereses we analysed the expression of bone-specific genes (Bone Sialoprotein (BSP) and Osteocalcin) and oncogenes (Met and ErbB2) in 22 patients with metastatic osteosarcoma and six healthy stem cell donors. The expression of these genes in aphereses of patients affected by metastatic osteosarcoma was assessed by RT-PCR and Southern blot analysis. Met and Osteocalcin proved to be not useful markers since they are positive in aphereses of both patients with metastatic osteosarcoma and healthy stem cell donors. On the contrary, BSP was expressed at significant levels in 85% of patients. Moreover, 18% of patients showed a strong and significantly positive (seven to 16 times higher than healthy stem cell donors) ErbB2 expression. In all positive cases, neoplastic tissue also expressed ErbB2. Our data show that ErbB2 can be a useful marker for tumour contamination in aphereses of patients affected by ErbB2-expressing osteosarcomas and that analysis of Bone Sialoprotein expression can be an alternative useful marker.

ErbB-2 signaling is involved in regulating PSA secretion in androgen-independent human prostate cancer LNCaP C-81 cells

The expression and secretion of prostate-specific antigen (PSA) are regulated by androgens in normal prostate secretory epithelial cells. In prostate cancer patients, the serum PSA level is usually elevated and cancer cells are initially responsive to androgens. However, those cancer cells become androgen-independent after androgen ablation therapy. In hormone-refractory cancer patients, even in an androgen-deprived environment, the circulation level of PSA rebounds and is constitutively elevated through a yet unknown mechanism. Tyrosine phosphorylation of ErbB-2 is involved in regulating the androgen-responsive phenotype of prostate cancer cells, and it is at least partly regulated by the cellular form of prostatic acid phosphatase (PAcP), a prostate-unique protein tyrosine phosphatase. We investigated the ErbB-2 signal pathway in androgen-independent PSA secretion. LNCaP C-81 cells, which are androgen-independent LNCaP cells lacking endogenous PAcP expression with a hypertyrosine phosphorylated ErbB-2, secreted a higher level of PSA in conditioned media than did androgen-sensitive LNCaP C-33 parental cells. A restored expression of cellular PAcP in C-81 cells was concurrent with a decrease in tyrophosphorylation of ErbB-2 and reduction of PSA secretion. Moreover, transient transfection of C-33 cells with the wild-type ErbB-2 or a constitutively active mutant of MEK1 cDNA resulted in an increased level of secreted PSA. The elevation of secreted PSA level by the forced expression of ErbB-2 was inhibited by an MEK inhibitor, PD98059. In C-81 cells, the expression of a dominant negative mutant of ErbB-2 reduced the secreted level of PSA. The inhibition of ErbB-2 or mitogen-activated protein (MAP) kinases by specific inhibitors AG879, AG825, or PD98059 led to a decrease in PSA secretion. Taken together, our data clearly indicate that the ErbB-2 signal pathway via MAP kinases (ERK1/2) is involved in regulating the secretion of PSA by androgen-independent human prostate cancer LNCaP C-81 cells in an androgen-depleted environment.

Trastuzumab, an appropriate first-line single-agent therapy for HER2-overexpressing metastatic breast cancer

Overexpression of the HER2/Neu (ErbB2) proto-oncogene is associated with breast cancer progression and poor patient prognosis. Herceptin (trastuzumab) is a humanized IgG1 against the ectodomain of the HER2 receptor. In combination with chemotherapy, it induces regression of HER2-overexpressing metastatic breast tumors and prolongs patient survival. Single-agent Herceptin in patients with HER2-amplified breast tumors also induces a definite objective response and clinical benefit rates, and is well tolerated. These data suggest that Herceptin is an effective first-line single-agent therapy for a predictable cohort of metastatic breast cancers and can therefore be used as a platform for therapeutic discovery against tumors that overexpress HER2.

CD157 undergoes ligand-independent dimerization and colocalizes with caveolin in CHO and MCA102 fibroblasts

CD157, a glycosylphosphatidylinositol (GPI)-anchored glycoprotein, has recently been shown to induce protein tyrosine phosphorylation in monocytes differentiated from HL-60 cells (mHL-60) in a ligand-dependent manner, but in a ligand-independent manner in stable CD157-transfected CHO (CHO/CD157) and MCA102 (MCA/CD157) fibroblasts [Cell Signal. 11 (1999) 891-897.]. Many GPI-anchored proteins need to be clustered by their ligands or antibodies to induce redistribution to caveolae and a concomitant activation of the associated signal-transducing proteins [Nature 387 (1997) 569-572.]. Here, we demonstrate that CD157, independent of antibody crosslinking, undergoes dimerization with disulfide bond formation and localization in caveolae in CHO/CD157 and MCA/CD157 fibroblasts. However, the native CD157 induced in mHL-60 cells remains a monomer form. The structural integrity of caveolae is required for the association of CD157 with caveolin and CD157-mediated tyrosine kinase signalling in the fibroblasts. We propose that an overexpression of CD157 could lead to its dimerization and relocation to caveolae and to further result in the initiation of signalling processes.

ErbB2/Neu-induced, cyclin D1-dependent transformation is accelerated in p27-haploinsufficient mammary epithelial cells but impaired in p27-null cells

ErbB2/Neu destabilizes the cyclin-dependent kinase (Cdk) inhibitor p27 and increases expression of cyclin D1. Therefore, we studied the roles of p27 and cyclin D1 in ErbB2-mediated mammary epithelial cell transformation. Overexpression of ErbB2 or cyclin D1 in p27(+/-) primary murine mammary epithelial cells resulted in increased proliferation, cyclin D1 nuclear localization, and colony formation in soft agar compared to those in p27(+/+) cells. In contrast, ErbB2- or cyclin D1-overexpressing p27(-/-) cells displayed reduced proliferation, anchorage-independent growth, Cdk4 activity, cyclin D1 expression, and cyclin D1 nuclear localization compared to wild-type cells. A cyclin D1 mutation in its nuclear export sequence (T286A) partially rescued nuclear localization of cyclin D1 in p27(-/-) cells but did not increase proliferation or Cdk4 kinase activity. Overexpression of E2F1, however, increased proliferation to the same degree in p27(+/+), p27(+/-), and p27(-/-) cells. Mammary glands from MMTV (mouse mammary tumor virus)-neu/p27(+/-) mice exhibited alveolar hyperplasia, enhanced proliferation, decreased apoptosis, and accelerated tumor formation compared to MMTV-neu/p27(+/+) glands. However, MMTV-neu/p27(-/-) glands showed decreased proliferation, cyclin D1 expression, and Cdk4 activity, as well as markedly prolonged tumor latency, compared to MMTV-neu/p27(+/+) glands. These results suggest that p27(+/-) mammary epithelium may be more susceptible to oncogene-induced tumorigenesis, whereas p27-null glands, due to severely impaired cyclin D1/Cdk4 function, are more resistant to transformation.

Comparison of the biochemical and kinetic properties of the type 1 receptor tyrosine kinase intracellular domains. Demonstration of differential sensitivity to kinase inhibitors

Epidermal growth factor receptor (EGFR), ErbB-2, and ErbB-4 are members of the type 1 receptor tyrosine kinase family. Overexpression of these receptors, especially ErbB-2 and EGFR, has been implicated in multiple forms of cancer. Inhibitors of EGFR tyrosine kinase activity are being evaluated clinically for cancer therapy. The potency and selectivity of these inhibitors may affect the efficacy and toxicity of therapy. Here we describe the expression, purification, and biochemical comparison of EGFR, ErbB-2, and ErbB-4 intracellular domains. Despite their high degree of sequence homology, the three enzymes have significantly different catalytic properties and substrate kinetics. For example, the catalytic activity of ErbB-2 is less stable than that of EGFR. ErbB-2 uses ATP-Mg as a substrate inefficiently compared with EGFR and ErbB-4. The three enzymes have very similar substrate preferences for three optimized peptide substrates, but differences in substrate synergies were observed. We have used the biochemical and kinetic parameters determined from these studies to develop an assay system that accurately measures inhibitor potency and selectivity between the type 1 receptor family. We report that the selectivity profile of molecules in the 4-anilinoquinazoline series can be modified through specific aniline substitutions. Moreover, these compounds have activity in whole cells that reflect the potency and selectivity of target inhibition determined with this assay system.

Erk5 participates in neuregulin signal transduction and is constitutively active in breast cancer cells overexpressing ErbB2

The four receptor tyrosine kinases of the ErbB family play essential roles in several physiological processes and have also been implicated in tumor generation and/or progression. Activation of ErbB1/EGFR is mainly triggered by epidermal growth factor (EGF) and other related ligands, while activation of ErbB2, ErbB3, and ErbB4 receptors occurs by binding to another set of EGF-like ligands termed neuregulins (NRGs). Here we show that the Erk5 mitogen-activated protein kinase (MAPK) pathway participates in NRG signal transduction. In MCF7 cells, NRG activated Erk5 in a time- and dose-dependent fashion. The action of NRG on Erk5 was dependent on the kinase activity of ErbB receptors but was independent of Ras. Expression in MCF7 cells of a dominant negative form of Erk5 resulted in a significant decrease in NRG-induced proliferation of MCF7 cells. Analysis of Erk5 in several human tumor cell lines indicated that a constitutively active form of this kinase was present in the BT474 and SKBR3 cell lines, which also expressed activated forms of ErbB2, ErbB3, and ErbB4. Treatments aimed at decreasing the activity of these receptors caused Erk5 inactivation, indicating that the active form of Erk5 present in BT474 and SKBR3 cells was due to a persistent positive stimulus originating at the ErbB receptors. In BT474 cells expression of the dominant negative form of Erk5 resulted in reduced proliferation, indicating that in these cells Erk5 was also involved in the control of proliferation. Taken together, these results suggest that Erk5 may play a role in the regulation of cell proliferation by NRG receptors and indicate that constitutively active NRG receptors may induce proliferative responses in cancer cells through this MAPK pathway.

ErbB2, but not ErbB1, reinitiates proliferation and induces luminal repopulation in epithelial acini

Both ErbB1 and ErbB2 are overexpressed or amplified in breast tumours. To examine the effects of activating ErbB receptors in a context that mimics polarized epithelial cells in vivo, we activated ErbB1 and ErbB2 homodimers in preformed, growth-arrested mammary acini cultured in three-dimensional basement membrane gels. Activation of ErbB2, but not that of ErbB1, led to a reinitiation of cell proliferation and altered the properties of mammary acinar structures. These altered structures share several properties with early-stage tumours, including a loss of proliferative suppression, an absence of lumen, retention of the basement membrane and a lack of invasive properties. ErbB2 activation also disrupted tight junctions and the cell polarity of polarized epithelia, whereas ErbB1 activation did not have any effect. Our results indicate that ErbB receptors differ in their ability to induce early stages of mammary carcinogenesis in vitro and this three-dimensional model system can reveal biological activities of oncogenes that cannot be examined in vitro in standard transformation assays.

Overexpression of ErbB2 in cancer and ErbB2-targeting strategies

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

Role of erbB2 in breast cancer chemosensitivity

The erbB2 gene, which encodes a transmembrane growth factor receptor, is overexpressed in approximately 30% of breast cancers. Overexpressing this gene makes breast cancers resistant to certain chemotherapeutic agents. In this article, we review what is known about ErbB2-mediated chemoresistance and the controversies surrounding it. We also examine the antiapoptotic function of erbB2 as one of the molecular mechanisms of ErbB2-mediated Taxol resistance and describe several emerging strategies for overcoming intrinsic ErbB2-mediated chemoresistance. Finally, we discuss future avenues for studies of chemosensitivity in ErbB2-overexpressing breast cancers that may lead to the development of effective biology-based treatment strategies.

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.

Role of the amnioserosa in germ band retraction of the Drosophila melanogaster embryo

As the germ band shortens in Drosophila melanogaster embryos, cell shape changes cause segments to narrow anteroposteriorly and to lengthen dorsoventrally. One of the genes required for this retraction process is the hindsight (hnt) gene. hnt encodes a nuclear Zinc-finger protein that is expressed in the extraembryonic amnioserosa and the endodermal midgut prior to and during germ band retraction (M. L. R. Yip, M. L. Lamka, and H. D. Lipshitz, 1997, Development 124, 2129-2141). Here we show, through analysis of hnt genetic mosaic embryos, that hnt activity in the amnioserosa-particularly in those cells that are adjacent to the epidermis-is necessary for germ band retraction. In hnt mutant embryos the amnioserosa undergoes premature cell death (L. C. Frank and C. Rushlow, 1996, Development 122, 1343-1352). We demonstrate that prevention of premature apoptosis in hnt mutants does not rescue retraction. Thus, failure of this process is not an indirect consequence of premature amnioserosal apoptosis; instead, hnt must function in a pathway that controls germ band retraction. We show that the Krüppel gene is activated by hnt in the amnioserosa while the Drosophila insulin receptor (INR) functions downstream of hnt in the germ band. We present evidence against a physical model in which the amnioserosa "pushes" the germ band during retraction. Rather, it is likely that the amnioserosa functions in production, activation, or presentation of a diffusible signal required for retraction.

Epidermal growth factor stimulates 3-hydroxy-3-methylglutaryl-coenzyme A reductase expression via the ErbB-2 pathway in human breast adenocarcinoma cells

HMG-CoA reductase is the key enzyme for the biosynthesis of isoprenoid compounds essential for cell growth and differentiation. Its tyrosine kinase-dependent modulation has recently been suggested and described in the ErbB-2 overexpressing cell line SKBR-3 [Asslan et al. (1998) Biochem. J. 330, 241-246]. Epidermal growth factor (EGF) increased the HMG-CoA reductase activity, protein, and mRNA levels only in ErbB-2-expressing cells (SKBR-3 and MCF-7) but not in MDA-MB-468 cells that do not express ErbB-2 even though their EGF receptor was efficiently phosphorylated. Tyrphostin AG 879, a specific inhibitor of ErbB-2 tyrosine kinase activity, decreased HMG-CoA reductase activity only in cells that expressed ErbB-2. A functional EGF receptor appeared to be necessary since its inhibition by the specific tyrphostin AG 1478 abolished the EGF effects. Phosphatidylinositol 3-kinase (PI 3-kinase) might be a crucial enzyme in the signaling pathway since the specific inhibitor, LY 294002, was shown to inhibit HMG-CoA reductase activity and to completely abolish the stimulation by EGF in SKBR-3 cells.

Collagen-homology domain 1 deletion mutant of Shc suppresses transformation mediated by neu through a MAPK-independent pathway

Shc proteins are implicated in coupling receptor tyrosine kinase to the mitogen-activated protein kinase (MAPK) pathway by recruiting Grb2/SOS to the plasma membrane. To better understand the role of Shc in the oncogenesis by point-mutation activated neu (p185*), we transfected a Shc mutant (ShcdeltaCHI), which lacks the Grb2 binding site Y317 by deletion of collagen-homology domain 1, into p185*-transformed NIH3T3 cells. The cellular transformation phenotypes were found to be largely suppressed by expression of ShcdeltaCH1. Although ShcdeltaCH1 still retained another Grb2 binding site (Y239/240), we did not detect its physical association with Grb2. We also found that ShcdeltaCH1 could associate with p185*; however, this association did not interfere with the endogenous Shc-p185* interaction or the Shc-Grb2 interaction. In addition, p185*-mediated MAPK and Elk activation likewise were not inhibited by ShcdeltaCH1 expression. Taken together, these data demonstrate that ShcdeltaCH1 suppresses the transformation induced by activated neu through a MAPK-independent pathway, indicating that Shc may be involved in other signal pathway(s) critical for cellular transformation in addition to the MAPK pathway.

ErbB-2 amplification inhibits down-regulation and induces constitutive activation of both ErbB-2 and epidermal growth factor receptors

ErbB-2/HER2 is an important signaling partner for the epidermal growth factor receptor (EGFR). Overexpression of erbB-2 is also associated with poor prognosis in breast cancer. To investigate how erbB-2 amplification affects its interactions with the EGFR, we used a human mammary epithelial cell system in which erbB-2 expression was increased 7-20-fold by gene transfection. We found that amplification of erbB-2 caused constitutive activation of erbB-2 as well as ligand-independent activation of the EGFR. Overexpression of erbB-2 strongly inhibited erbB-2 down-regulation following transactivation by EGFR. Significantly, down-regulation of activated EGFR was also inhibited by erbB-2 amplification, resulting in enhanced ligand-dependent activation of the EGFR. The rate of EGFR endocytosis was not affected by erbB-2 overexpression, but the rate of lysosomal targeting was significantly reduced. In addition, erbB-2 overexpression promoted rapid recycling of activated EGFR back to the cell surface and decreased ligand dissociation from the EGFR. Our data suggest that overexpression of erbB-2 inhibits both its down-regulation and that of the EGFR. The net effect is increased signaling through the EGFR system.

Domain-specific interactions between the p185(neu) and epidermal growth factor receptor kinases determine differential signaling outcomes

We expressed the epidermal growth factor receptor (EGFR) along with mutant p185(neu) proteins containing the rat transmembrane point mutation. The work concerned the study of the contributions made by various p185(neu) subdomains to signaling induced by a heterodimeric ErbB complex. Co-expression of full-length EGFR and oncogenic p185(neu) receptors resulted in an increased EGF-induced phosphotyrosine content of p185(neu), increased cell proliferation to limiting concentrations of EGF, and increases in both EGF-induced MAPK and phosphatidylinositol 3-kinase (PI 3-kinase) activation. Intracellular domain-deleted p185(neu) receptors (T691stop neu) were able to associate with full-length EGFR, but induced antagonistic effects on EGF-dependent EGF receptor down-regulation, cell proliferation, and activation of MAPK and PI 3-kinase pathways. Ectodomain-deleted p185(neu) proteins (TDelta5) were unable to physically associate with EGFR, and extracellular domain-deleted p185(neu) forms failed to augment activation of MAPK and PI 3-kinase in response to EGF. Association of EGFR with a carboxyl-terminally truncated p185(neu) mutant (TAPstop) form did not increase transforming efficiency and phosphotyrosine content of the TAPstop species, and proliferation of EGFR.TAPstop-co-expressing cells in response to EGF was similar to cells containing EGFR only. Thus, neither cooperative nor inhibitory effects were observed in cell lines co-expressing either TDelta5 or TAPstop mutant proteins. Unlike the formation of potent homodimer assemblies composed of oncogenic p185(neu), the induction of signaling from p185(neu).EGFR heteroreceptor assemblies requires the ectodomain for ligand-dependent physical association and intracellular domain contacts for efficient intermolecular kinase activation.

Conversion of a radioresistant phenotype to a more sensitive one by disabling erbB receptor signaling in human cancer cells

Inhibition of cell growth and transformation can be achieved in transformed glial cells by disabling erbB receptor signaling. However, recent evidence indicates that the induction of apoptosis may underlie successful therapy of human cancers. In these studies, we examined whether disabling oncoproteins of the erbB receptor family would sensitize transformed human glial cells to the induction of genomic damage by gamma-irradiation. Radioresistant human glioblastoma cells in which erbB receptor signaling was inhibited exhibited increased growth arrest and apoptosis in response to DNA damage. Apoptosis was observed after radiation in human glioma cells containing either a wild-type or mutated p53 gene product and suggested that both p53-dependent and -independent mechanisms may be responsible for the more radiosensitive phenotype. Because cells exhibiting increased radiation-induced apoptosis were also capable of growth arrest in serum-deprived conditions and in response to DNA damage, apoptotic cell death was not induced simply as a result of impaired growth arrest pathways. Notably, inhibition of erbB signaling was a more potent stimulus for the induction of apoptosis than prolonged serum deprivation. Proximal receptor interactions between erbB receptor members thus influence cell cycle checkpoint pathways activated in response to DNA damage. Disabling erbB receptors may improve the response to gamma-irradiation and other cytotoxic therapies, and this approach suggests that present anticancer strategies could be optimized.

Immunologic approaches to inhibiting cell-surface-residing oncoproteins in human tumors

The erbB family of receptor tyrosine kinases are growth factor receptors that are overexpressed or mutated in a large variety of human cancers. Studies of erbB-mediated signal transduction will lead to an understanding of the role played by this family of receptors in normal and transformed cells. In this article, we discuss the contemporary understanding of the structure and function of these receptors, and how these features might be exploited in immunologic strategies of receptor-based growth inhibition. The first part of this article details the structure of erbB receptors as it relates to the process of transformation of cells and the malignant phenotype in human tumors. In the second part of this article, we discuss immunologic approaches to therapy for cancers in which surface-residing erbB receptors are overexpressed or mutated, with an emphasis on studies targeting the p185neu/c-erbB2 oncoprotein. The potential for antireceptor immunity and the evolution of small molecules for receptor-based immunotherapy are discussed. These studies provide a basis for the application of receptor-based strategies of growth inhibition in erbB-expressing human cancers.

The ErbB-2/HER2 oncogenic receptor of adenocarcinomas: from orphanhood to multiple stromal ligands

Extensive clinical and biochemical evidence implicates ErbB-2, a transmembrane tyrosine kinase related to growth factor receptors, in the development, metastasis, and resistance to therapy of multiple, common human carcinomas. Previous attempts to uncover an ErbB-2-specific ligand led to isolation of the neuregulin (NRG) family, but these ligands, like all other growth factors with an EGF-like motif, only indirectly active ErbB-2. On the other hand, biochemical and genetic evidence suggest a non-autonomous function of ErbB-2 in an interactive ErbB signaling network. Accordingly, the oncoprotein acts as a shared signaling subunit of primary growth factor receptors. By stabilizing heterodimers with other ErbB proteins, ErbB-2 prolongs and enhances signal transduction by a large group of stroma-derived growth factors. Furthermore, we have proposed a model in which all ErbB-2 ligands are bivalent and bind to ErbB-2 with low affinity, following high affinity binding to a primary receptor with which ErbB-2 is heterodimerized. Thus the presence of ErbB-2 in relevant ErbB heterodimeric structures on the surfaces of certain epithelial tumor cells can amplify signals arising from the binding of stromal ErbB ligands. This effect, in turn, may promote the growth of carcinoma cells.

Bivalence of EGF-like ligands drives the ErbB signaling network

Signaling by epidermal growth factor (EGF)-like ligands is mediated by an interactive network of four ErbB receptor tyrosine kinases, whose mechanism of ligand-induced dimerization is unknown. We contrasted two existing models: a conformation-driven activation of a receptor-intrinsic dimerization site and a ligand bivalence model. Analysis of a Neu differentiation factor (NDF)-induced heterodimer between ErbB-3 and ErbB-2 favors a bivalence model; the ligand simultaneously binds both ErbB-3 and ErbB-2, but, due to low-affinity of the second binding event, ligand bivalence drives dimerization only when the receptors are membrane anchored. Results obtained with a chimera and isoforms of NDF/neuregulin predict that each terminus of the ligand molecule contains a distinct binding site. The C-terminal low-affinity site has broad specificity, but it prefers interaction with ErbB-2, an oncogenic protein acting as a promiscuous low-affinity subunit of the three primary receptors. Thus, ligand bivalence enables signal diversification through selective recruitment of homo- and heterodimers of ErbB receptors, and it may explain oncogenicity of erbB-2/HER2.

Mitosis-specific negative regulation of epidermal growth factor receptor, triggered by a decrease in ligand binding and dimerization, can be overcome by overexpression of receptor

The function of epidermal growth factor receptor (EGFR) was found to be negatively regulated in M phase in which it showed less phosphotyrosine content and reduced intrinsic kinase activity accompanied by retarded electrophoretic mobility owing to total hyperphosphorylation. Ligand-induced autophosphorylation and downstream signaling of EGFR were tightly suppressed in M phase due to a decrease in ligand binding affinity and the inability of epidermal growth factor (EGF) to induce receptor dimerization. There was no change in the number of surface-exposed EGF receptors between G0/G1 and M phases of the cell cycle. Hyperphosphorylation (due to serine and/or threonine phosphorylation) correlates with the unresponsiveness of cells to EGF-mediated stimulation of tyrosine phosphorylation in cells that express the normal or basal level of EGFR. This M phase-specific negative regulation was overcome by overexpression of EGFR, which was responsive to ligand throughout the cell cycle and revealed ligand-induced signaling in the M phase. These findings indicate that EGFR does not respond to ligand stimulation in M phase and suggest that a negative regulation of ligand-receptor interactions in M phase may control the normal function of receptor tyrosine kinase and that receptor overexpression will disrupt this cell cycle-dependent regulation of receptor tyrosine kinases.

Expression of neu and Neu differentiation factor in the olfactory mucosa of rat

The growth and differentiation of olfactory sensory neurons are regulated tightly. We had shown previously, by immunohistochemistry, that transforming growth factor-alpha (TGF-alpha) and epidermal growth factor (EGF) receptor are present in the olfactory epithelium of untreated adult rats and that TGF-alpha is a potent mitogen of olfactory epithelium in vitro. Expression of EGF receptor and TGF-alpha was detected primarily in horizontal basal cells and supporting cells but rarely in globose basal cells, which suggested that EGF receptor is not a likely candidate for the mitotic regulator of sensory neurons. In order to expand the search for candidate regulators, we have now examined other members of the EGF family of receptors and ligands. By utilizing reverse transcriptase-polymerase chain reaction (RT-PCR) methodology, we have detected the messenger RNA encoding the protein of the neu gene (p185neu) and Neu differentiation factor (NDF) isoforms in the olfactory mucosa. Immunohistochemical localization of p185neu and NDF indicates expression of these proteins in the olfactory epithelium of adult rats in regions where globose basal cells and immature sensory neurons are found, as well as in the ensheathing cells of the olfactory nerve. The presence of neu and NDF transcripts in the olfactory tissue and the localization of their encoded polypeptides to proliferative regions of the epithelium suggest involvement of these gene products in the regulated proliferation/differntiation of the sensory neurons.

Laminin activates the p185HER2 oncoprotein and mediates growth inhibition of breast carcinoma cells

The interaction between laminin and the oncoprotein encoded by the c-erbB-2 oncogene was studied in vitro and in vivo in human breast carcinomas. In vitro analysis of breast carcinoma cell lines overexpressing p185HER2 revealed that laminin, but not fibronectin, induced tyrosine phosphorylation and down-modulation of oncoprotein membrane expression. Laminin also specifically inhibited growth of p185HER2-positive cell lines. No direct binding between the recombinant extracellular domain of p185HER2 and laminin was found. Induction of oncoprotein down-modulation by anti-integrin antibodies and coprecipitation of the oncoprotein with the beta 4 integrin subunit indicate that the interaction between p185HER2 and laminin occurs through integrin molecules. The relevance of this in vitro observation was verified in vivo by analysing the prognostic value of p185HER2 overexpression as a function of laminin production on archival paraffin-embedded sections of 887 primary breast tumours. The results revealed an association between p185HER2 overexpression and unfavourable prognosis in tumours negative for laminin production, whereas in laminin-producing tumours, the oncoprotein overexpression was not associated with tumour aggressiveness.