ErbB3 is required for ductal morphogenesis in the mouse mammary gland

Amy J Jackson-Fisher,David F Stern,Carmen J Booth,Gary Bellinger,Jerrica L Breindel,Fatteneh A Tavassoli,James K Duong

doi:10.1186/bcr2198

Abstract

IntroductionThe receptor ErbB3/HER3 is often over-expressed in human breast cancers, frequently in conjunction with over-expression of the proto-oncogene ERBB2/HER2/NEU. Although the prognostic/predictive value of ErbB3 expression in breast cancer is unclear, ErbB3 is known to contribute to therapeutic resistance. Understanding ErbB3 functions in the normal mammary gland will help to explain its role in cancer etiology and as a modulator of signaling responses to the mammary oncogene ERBB2.MethodsTo investigate the roles of ErbB3 in mouse mammary gland development, we transplanted mammary buds from ErbB3-/- embryos into the cleared mammary fat pads of wild-type immunocompromised mice. Effects on ductal outgrowth were analyzed at 4 weeks, 7 weeks and 20 weeks after transplantation for total ductal outgrowth, branch density, and number and area of terminal end buds. Sections of glands containing terminal end buds were analyzed for number and epithelial area of terminal end buds. Terminal end buds were also analyzed for presence of mitotic figures, apoptotic figures, BrdU incorporation, and expression of E-cadherin, P-cadherin, α-smooth muscle actin, and cleaved caspase-3.ResultsThe mammary ductal trees developed from ErbB3-/- buds only partly filled the mammary fat pad. In contrast to similar experiments with ErbB2-/- mammary buds, this phenotype was maintained through adulthood, pregnancy, and parturition. In addition, and in contrast to similar work with ErbB4-/- mammary buds, lobuloalveolar development of ErbB3-/- transplanted glands was normal. The ErbB3-/- mammary outgrowth defect was associated with a decrease in the size of the terminal end buds, and with increases in branch density, in the number of terminal end buds, and in the number of luminal spaces. Proliferation rates were not affected by the lack of ErbB3, but there was an increase in apoptosis in ErbB3-/- terminal end buds.ConclusionsEndogenous ErbB3 regulates morphogenesis of mammary epithelium.

Highlights

Introduction The receptorErbB3/HER3 is often overexpressed in human breast cancers, frequently in conjunction with over-expression of the proto-oncogene ERBB2/HER2/ NEU
Proliferation rates were not affected by the lack of ErbB3, but there was an increase in apoptosis in ErbB3-/- terminal end buds
Postnatal development of ErbB3-/- epithelium in ErbB3 wild-type stroma can be analyzed by transplantation

Summary

Introduction

ErbB3/HER3 is often overexpressed in human breast cancers, frequently in conjunction with over-expression of the proto-oncogene ERBB2/HER2/ NEU. The epidermal growth factor receptor (EGFR) family of receptor tyrosine kinases, which consists of EGFR, ErbB2, ErbB3, and ErbB4, is important in many normal developmental processes and is often over-expressed or mutated in human cancer (for review, see [1]). The proto-oncogene product ErbB2 is unique in that it does not bind soluble ligands and requires a heterodimer partner for ligand-dependent activation. BrdU: 5-bromo-2-deoxyuridine; EGFR: epidermal growth factor receptor; H&E: hematoxylin and eosin; IHC: immunohistochemistry; MMP: matrix metalloproteinase; NRG: neuregulin; NSCLC: non-small-cell lung carcinoma; PI3K: phosphatidylinositol 3'-kinase; SD: standard deviation; SMA: αsmooth muscle actin; TEB: terminal end bud. ErbB3 is strongly linked to prosurvival signaling through the phosphatidylinositol 3'-kinase (PI3K)/Akt pathway. The activated Akt is involved in cellular processes including survival, cell growth, and proliferation (for review, see [2])

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