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Open Access Research article

Functional interaction between mouse erbB3 and wild-type rat c-neu in transgenic mouse mammary tumor cells

Aeree Kim12, Bolin Liu1, Dalia Ordonez-Ercan1, Kathy M Alvarez1, Lynn D Jones1, Christine McKimmey1, Susan M Edgerton1, XiaoHe Yang1 and Ann D Thor1*

Author Affiliations

1 Department of Pathology and College of Medicine, Oklahoma University Health Sciences Center (OUHSC), Oklahoma City, OK, USA

2 Department of Pathology, College of Medicine, Korea University, Seoul, Korea

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Breast Cancer Research 2005, 7:R708-R718  doi:10.1186/bcr1281

Published: 6 July 2005

Abstract

Introduction

Co-expression of several receptor tyrosine kinases (RTKs), including erbB2 and erbB3, is frequently identified in breast cancers. A member of the RTK family, the kinase-deficient erbB3 can activate downstream signaling via heterodimer formation with erbB2. We studied the expression of RTK receptors in mammary tumors from the wild-type (wt) rat c-neu transgenic model. We hypothesized that physical and functional interactions between the wt rat neu/ErbB2 transgene and mouse ErbB3-encoded proteins could occur, activating downstream signaling and promoting mammary oncogenesis.

Methods

Immunohistochemical and Western blot analyses were performed to study the expression of rat c-neu/ErbB2 and mouse erbB3 in mammary tumors and tumor-derived cell lines from the wt rat c-neu transgenic mice. Co-immunoprecipitation methods were employed to quantitate heterodimerization between the transgene-encoded protein erbB2 and the endogenous mouse erbB3. Tumor cell growth in response to growth factors, such as Heregulin (HRG), epidermal growth factor (EGF), or insulin-like growth factor-1 (IGF-1), was also studied. Post-HRG stimulation, activation of the RTK downstream signaling was determined by Western blot analyses using antibodies against phosphorylated Akt and mitogen-activated protein kinase (MAPK), respectively. Specific inhibitors were then used with cell proliferation assays to study the phosphoinositide-3 kinase (PI-3K)/Akt and MAPK kinase (MEK)/MAPK pathways as possible mechanisms of HRG-induced tumor cell proliferation.

Results

Mammary tumors and tumor-derived cell lines frequently exhibited elevated co-expression of erbB2 and erbB3. The transgene-encoded protein erbB2 formed a stable heterodimer complex with endogenous mouse erbB3. HRG stimulation promoted physical and functional erbB2/erbB3 interactions and tumor cell growth, whereas no response to EGF or IGF-1 was observed. HRG treatment activated both the Akt and MAPK pathways in a dose- and time-dependent manner. Both the PI-3K inhibitor LY 294002 and MEK inhibitor PD 98059 significantly decreased the stimulatory effect of HRG on tumor cell proliferation.

Conclusion

The co-expression of wt rat neu/ErbB2 transgene and mouse ErbB3, with physical and functional interactions between these two species of RTK receptors, was demonstrated. These data strongly suggest a role for erbB3 in c-neu (ErbB2)-associated mammary tumorigenesis, as has been reported in human breast cancers.