Endophilin A2 Promotes TNBC Cell Invasion and Tumor Metastasis.

Tomas Baldassarre,Mark M Schneider,Jalna Meens,Andrew W Craig,Kathleen Watt,Sandip K Sengupta,Peter Truesdell

doi:10.1158/1541-7786.mcr-14-0573

Abstract

Triple-negative breast cancers (TNBCs) are highly aggressive cancers that lack targeted therapies. However, EGFR is frequently activated in a subset of TNBCs and represents a viable clinical target. Because the endocytic adaptor protein Endophilin A2 (SH3GL1/Endo II) has been implicated in EGFR internalization, we investigated Endo II expression and function in human TNBCs. Endo II expression was high in several TNBC cells compared with normal breast epithelial cells. Stable knockdown (KD) of Endo II was achieved in two TNBC cell lines, and although cell viability was unaffected, defects in receptor-mediated endocytosis were observed. EGFR signaling to Erk and Akt kinases was impaired in Endo II KD cells, and this correlated with reduced rates of EGFR internalization and cell motility. Endo II KD cells also displayed defects in three dimensional (3D) cell invasion, and this correlated with impaired extracellular matrix degradation and internalization of MT1-MMP. Endo II silencing also caused a significant reduction in TNBC tumor growth and lung metastasis in mammary orthotopic tumor xenograft assays. In human breast tumor specimens, Endo II expression was highest in TNBC tumors compared with other subtypes, and at the level of gene expression, high Endo II was associated with reduced relapse-free survival in patients with basal-like breast cancers. Together, these results identify a positive role for Endo II in TNBC tumor metastasis and a potential link with poor prognosis. Endophilin A2 and related adaptor proteins represent important signaling hubs to target in metastatic cancers.

Highlights

Breast cancer continues to be the most prevalent and second most fatal cancer for women within the developed world [1]
Lentiviral shRNA–mediated silencing of Endo II in two Triple-negative breast cancers (TNBCs) cell lines (HCC 1806, MDA-MB-231), resulted in reduced internalization of EGFR, and diminished downstream signaling to Erk and Akt kinases
IB analyses revealed that Endo II was expressed at high levels in HER2 and TNBC cell lines, compared with MCF-10A or luminal cell lines (Fig. 1A; p120RasGAP served as a loading control)

Summary

Introduction

Breast cancer continues to be the most prevalent and second most fatal cancer for women within the developed world [1]. TNBCs are often aggressive with frequent invasion of lymph nodes and development of metastases [2] These properties of TNBCs are often due to activation of EGFR, which leads to downstream activation of signaling pathways promoting cell growth, survival, motility, and invasion through basement membranes [3, 4]. This invasive phenotype is dependent on downstream activation of Erk and Akt kinases [5, 6], which signal to key regulators of cell motility, proliferation, and survival [7].

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Results

Conclusion