Differential functions of ERK1 and ERK2 in lung metastasis processes in triple-negative breast cancer

Maria Gagliardi,Hiroko Masuda,Naoto T Ueno,Rachel M Sammons,Gaurav Chauhan,Debu Tripathy,Kimie Kondo,Xuemei Xie,Mary Kathryn Pitner,Huiqin Chen,Hitomi Saso,Chandra Bartholomeusz,Kevin N Dalby,Bisrat G Debeb,Caimiao Wei,Richard A Larson,Jihyun Park

doi:10.1038/s41598-020-65250-3

Abstract

Triple-negative breast cancer (TNBC) is an aggressive form of breast cancer characterized by metastasis, drug resistance and high rates of recurrence. With a lack or targeted therapies, TNBC is challenging to treat and carries a poor prognosis. Patients with TNBC tumors expressing high levels of ERK2 have a poorer prognosis than those with low ERK2-expressing tumors. The MAPK pathway is often found to be highly activated in TNBC, however the precise functions of the ERK isoforms (ERK1 and ERK2) in cancer progression have not been well defined. We hypothesized that ERK2, but not ERK1, promotes the cancer stem cell (CSC) phenotype and metastasis in TNBC. Stable knockdown clones of the ERK1 and ERK2 isoforms were generated in SUM149 and BT549 TNBC cells using shRNA lentiviral vectors. ERK2 knockdown significantly inhibited anchorage-independent colony formation and mammosphere formation, indicating compromised self-renewal capacity. This effect correlated with a reduction in migration and invasion. SCID-beige mice injected via the tail vein with ERK clones were employed to determine metastatic potential. SUM149 shERK2 cells had a significantly lower lung metastatic burden than control mice or mice injected with SUM149 shERK1 cells. The Affymetrix HGU133plus2 microarray platform was employed to identify gene expression changes in ERK isoform knockdown clones. Comparison of gene expression levels between SUM149 cells with ERK2 or ERK1 knockdown revealed differential and in some cases opposite effects on mRNA expression levels. Those changes associated with ERK2 knockdown predominantly altered regulation of CSCs and metastasis. Our findings indicate that ERK2 promotes metastasis and the CSC phenotype in TNBC.

Highlights

Triple-negative breast cancer (TNBC), is an aggressive subtype that accounts for 10–15% of all breast cancers
Previous reports have shown that ERK2, but not ERK1, plays an essential role in the epithelial-mesenchymal transition (EMT), which is required for the acquisition of stem cell-like properties[11,12]
We found that high ERK1 mRNA expression correlated with improved overall survival (OS) and distant-metastasis-free survival (DMFS) (Fig. 1A), whereas high ERK2 mRNA expression significantly correlated with poor OS and DMFS (Fig. 1B)

Summary

Introduction

Triple-negative breast cancer (TNBC), is an aggressive subtype that accounts for 10–15% of all breast cancers. Aberrant activity in the MAPK pathway (RAS-MEK-ERK) is important in the initiation and progression of cancer. Activation of this pathway is a marker of breast cancer metastasis and is clinically associated with shorter disease-free survival[2,3,4,5]. Previous reports have shown that ERK2, but not ERK1, plays an essential role in the epithelial-mesenchymal transition (EMT), which is required for the acquisition of stem cell-like properties[11,12]. TNBC is characterized by EMT and is highly associated with stem cell markers, which have been linked to biological aggressiveness[15]

Methods

Results

Conclusion