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The SQUU-B cell line spreads its metastatic properties to nonmetastatic clone SQUU-A from the same patient through exosomes

https://doi.org/10.1016/j.job.2015.10.001Get rights and content

Abstract

Emerging evidence indicates that cancer-derived exosomes increase the tumorigenic potential of tumor cells by reprogramming the cells associated with the tumor microenvironment. Our aim was to examine the cross talk via exosomes between two oral squamous cell carcinoma (OSCC) clones from the same patient. Our data showed that exosomes derived from highly metastatic SQUU-B cells conferred metastatic ability to nonmetastatic SQUU-A cells and subsequently reduced mRNA expression of cytokeratin 13, which is strongly linked to malignant transformation of OSCCs. The results suggest that multiple cell clones secrete their unique exosomes within the malignant tumor mass, which mediate paracrine interactions with other cell clones and affect clinical prognosis.

Introduction

Local invasion is a central process of the metastatic cascade [1]. Many reports have shown that there are extracellular modulators in the tumor microenvironment that can influence the invasive potential [2]. Among them, exosomes recently emerged as crucial components of cell-to-cell and cell-to-matrix communication related to invasive and metastatic processes [3], [4]. Exosomes are small membrane vesicles of endocytic origin that are released from various types of cells into the extracellular environment after fusion of multivesicular bodies with the plasma membrane [5]. Recent evidence highlights the ability of tumor-released exosomes to stimulate invasion and migration in various cancer models [4], [5], [6], [7]. Nevertheless, the majority of these studies have been focused on the activity of tumor-related exosomes toward stromal cells or malignant cells from another patient.

Oral squamous cell carcinoma (OSCC) is a type of invasive epithelial cancer that carries a high risk of lymph node metastasis and shows poor prognosis [8]. Our aim was to examine the cross talk via exosomes between two OSCC clones from the same patient. We demonstrated that a highly metastatic OSCC clone (SQUU-B) conferred metastatic potential to a nonmetastatic OSCC clone (SQUU-A) derived from the same tumor microenvironment. Our findings provide new insights into the function of tumor-derived exosomes: the cross talk among different malignant cell clones in the same tumor microenvironment.

Section snippets

Cell culture

The cell lines SQUU-A and SQUU-B (established from local recurrence events of a tongue cancer [9]) were maintained in Dulbecco’s modified Eagle′s medium (DMEM; Nacalai Tesque Inc., Kyoto, Japan) supplemented with 10% fetal bovine serum (BioWest, Nuaillé, France) at 37 °C in a humidified atmosphere containing 5% of CO2.

The cell invasion assay

The hardware for the assay was assembled from 8-μm-pore Transwell inserts (Corning Inc., Corning, NY) as upper chambers and 24-well plates as lower chambers. The cell culture

Verification and characterization of SQUU-A and SQUU-B cells

First, we successfully confirmed that cytokeratin (CK) 13 and CK17 expression levels in SQUU-A cells were significantly higher than those in SQUU-B cells (Fig. 1A), in line with other studies [9], [10]. We next performed cell invasion assays based on the migratory ability of invasive and metastatic cancer cells [11]. As shown in Fig. 1B, the invasive ability of SQUU-B cells was markedly greater than that of SQUU-A cells. Given that the migratory and invasive abilities of cancer cells are

Conclusions

Our study shows the spread of the metastatic potential between OSCC cell clones (derived from the same tumor mass) via exosomes. Our findings suggest that there is an exosome-mediated system of interaction among tumor cell clones, and this system may affect clinical prognosis.

Ethical approval

The study did not require any ethical approval.

Conflict of interest

The authors have no conflicts of interest to disclose.

References (15)

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