Cholesterol content in cell membrane maintains surface levels of ErbB2 and confers a therapeutic vulnerability in ErbB2-positive breast cancer

Jinrui Zhang,Mohamed Y Zaky,Han Liu,Shuyan Liu,Taishu Wang,Duchuang Wang,Lijuan Zou,Yang Zhang,Yueguang Wu,Lu Xu,Shanshan Wang,Shuai Hou,Haixin Lei,Fang Liu,Yingqiu Zhang,Qiong Li,Kun Zou

doi:10.1186/s12964-019-0328-4

Abstract

BackgroundErbB2 overexpression identifies a subset of breast cancer as ErbB2-positive and is frequently associated with poor clinical outcomes. As a membrane-embedded receptor tyrosine kinase, cell surface levels of ErbB2 are regulated dynamically by membrane physical properties. The present study aims to investigate the influence of membrane cholesterol contents on ErbB2 status and cellular responses to its tyrosine kinase inhibitors.MethodsThe cholesterol abundance was examined in ErbB2-positive breast cancer cells using filipin staining. Cellular ErbB2 localizations were investigated by immunofluorescence with altered membrane cholesterol contents. The inhibitory effects of the cholesterol-lowering drug lovastatin were assessed using cell proliferation, apoptosis, immunoblotting and immunofluorescence assays. The synergistic effects of lovastatin with the ErbB2 inhibitor lapatinib were evaluated using an ErbB2-positive breast cancer xenograft mouse model.ResultsMembrane cholesterol contents positively correlated with cell surface distribution of ErbB2 through increasing the rigidity and decreasing the fluidity of cell membranes. Reduction in cholesterol abundance assisted the internalization and degradation of ErbB2. The cholesterol-lowering drug lovastatin significantly potentiated the inhibitory effects of ErbB2 kinase inhibitors, accompanied with enhanced ErbB2 endocytosis. Lovastatin also synergized with lapatinib to strongly suppress the in vivo growth of ErbB2-positive breast cancer xenografts.ConclusionThe cell surface distribution of ErbB2 was closely regulated by membrane physical properties governed by cholesterol contents. The cholesterol-lowering medications can hence be exploited for potential combinatorial therapies with ErbB2 kinase inhibitors in the clinical treatment of ErbB2-positive breast cancer.

Highlights

ErbB2 overexpression identifies a subset of breast cancer as ErbB2-positive and is frequently associated with poor clinical outcomes
We report that cholesterol content modulates the rigidity and fluidity of plasma membranes to maintain the surface levels of ErbB2 in breast cancer cells, while the reduction in cholesterol abundance in plasma membrane facilitates the endocytic degradation of ErbB2 and synergizes with the tyrosine kinase inhibitors against ErbB2 to suppress ErbB2-positive breast cancer growth
Cholesterol content in cell membrane correlates with ErbB2 localization and cell migration Through immunofluorescence examination of ErbB2 localization in ErbB2-positive breast cancer cells, we observed that, in SKBR3 and AU565 cells that possessed round shapes, ErbB2 was almost exclusively distributed to the cell membrane; while in HCC1954 cells that showed flattened and spread-out configurations, ErbB2 formed many intracellular punctae besides surface localizations (Fig. 1a)

Summary

Introduction

ErbB2 overexpression identifies a subset of breast cancer as ErbB2-positive and is frequently associated with poor clinical outcomes. ErbB2, which is called Her or Neu, encodes a receptor tyrosine kinase from the EGFR/ErbB family. Due to the unique conformation of its extracellular domain, this receptor tyrosine kinase is considered as a favorable dimerization partner among ErbB family members [2, 3]. Amplification of ErbB2 gene is frequently observed in cancer patients, which identifies a subgroup of breast cancers called Her2/ErbB2-positive that accounts for 20–30% of breast malignancies. ErbB2 amplification leads to the accumulation of surplus ErbB2 receptors on cell membrane, promoting receptor dimerization and subsequent activation of a wide array of downstream oncogenic signaling circuitries [4, 5]. The overexpression of ErbB2 inversely correlates with patient prognosis, while ErbB2 has proved as a top therapeutic target in breast cancer treatment with multiple ErbB2-targeted therapies received FDA approvals [6,7,8]

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