Tropomyosin isoform Tpm2.1 regulates collective and amoeboid cell migration and cell aggregation in breast epithelial cells.

Hyerim Shin,David M Helfman,Dayoung Kim

doi:10.18632/oncotarget.19182

Hyerim Shin, David M Helfman + Show 1 more

Open Access

https://doi.org/10.18632/oncotarget.19182

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Abstract

Metastasis dissemination is the result of various processes including cell migration and cell aggregation. These processes involve alterations in the expression and organization of cytoskeletal and adhesion proteins in tumor cells. Alterations in actin filaments and their binding partners are known to be key players in metastasis. Downregulation of specific tropomyosin (Tpm) isoforms is a common characteristic of transformed cells. In this study, we examined the role of Tpm2.1 in non-transformed MCF10A breast epithelial cells in cell migration and cell aggregation, because this isoform is downregulated in primary and metastatic breast cancer as well as various breast cancer cell lines. Downregulation of Tpm2.1 using siRNA or shRNA resulted in retardation of collective cell migration but increase in single cell migration and invasion. Loss of Tpm2.1 is associated with enhanced actomyosin contractility and increased expression of E-cadherin and β-catenin. Furthermore, inhibition of Rho-associated kinase (ROCK) recovered collective cell migration in Tpm2.1-silenced cells. We also found that Tpm2.1-silenced cells formed more compacted spheroids and exhibited faster cell motility when spheroids were re-plated on 2D surfaces coated with fibronectin and collagen. When Tpm2.1 was downregulated, we observed a decrease in the level of AXL receptor tyrosine kinase, which may explain the increased levels of E-cadherin and β-catenin. These studies demonstrate that Tpm2.1 functions as an important regulator of cell migration and cell aggregation in breast epithelial cells. These findings suggest that downregulation of Tpm2.1 may play a critical role during tumor progression by facilitating the metastatic potential of tumor cells.

Highlights

Metastasis is the major cause of cancer-associated mortality
We examined the role of Tpm2.1 in non-transformed MCF10A breast epithelial cells in cell migration and cell aggregation, because this isoform is downregulated in primary and metastatic breast cancer as well as various breast cancer cell lines
Tpm2.1 was detected only in non-transformed breast epithelial cells and undetectable in various breast cancer cell lines including MCF7, T47D, BT-474, SK-BR-3, BT-20, MDA-MB-231, and MDA-MB-468 (Figure 1A). This is in agreement with previous studies showing Tpm2.1 is downregulated in breast cancer cell lines [15, 21, 22]

Summary

Introduction

Metastasis is the major cause of cancer-associated mortality. Metastasis dissemination is due to various processes including cell migration and cell aggregation. Metastatic cells are known for their ability to migrate and invade into the microvasculature of the lymph and blood systems, survive from detachment before entering distant tissues and adapting to the foreign microenvironment for colonization. Cells exhibit different types of motility including amoeboid, collective, and mesenchymal or single cell migration. Cells travel through the circulation before entering secondary sites, where they extravasate to the distant organ [1,2,3]. In order to understand and prevent metastasis, a detailed understanding of the mechanisms underlying metastasis is essential

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