Elsevier

Life Sciences

Volume 234, 1 October 2019, 116771
Life Sciences

MAT1 facilitates the lung metastasis of osteosarcoma through upregulation of AKT1 expression

https://doi.org/10.1016/j.lfs.2019.116771Get rights and content

Abstract

Aims

We aimed to elucidate the effects and mechanisms of MAT1 in the progression of osteosarcoma, especially for its lung metastasis.

Main methods

CCK-8 and flow cytometry assays were carried out to detect the proliferation and apoptosis of osteosarcoma cells. Wound healing and transwell assays were used to determine cell migration and invasion abilities. Real time quantitative PCR (RT-PCR) and western blot technologies were applied to detect the expression levels of RNA and protein, respectively.

Key finds

The results showed that both the mRNA and protein expression levels of MAT1 were elevated in osteosarcoma tissues with lung metastasis and metastatic lung tissues, particularly in the metastatic lung tissues, as compared to the osteosarcoma tissues without lung metastasis. High expression level of MAT1 in osteosarcoma patients showed a negative association with the overall survival. In addition, upregulation of MAT1 induced significant increases in cell growth, migration and invasion and an obvious inhibition in cell apoptosis in osteosarcoma MG63 and 143B cells, as well as elevated AKT1 expression level. Moreover, knockdown of AKT1 obviously impaired MAT1-mediated promotions in cell migration and invasion in vitro, as well as repressed tumor growth and reduced the number of metastatic lung tumors in xenografted nude mice.

Significance

This study reveals that high expression of MAT1 closely related to the poor prognosis and malignant clinical process of osteosarcoma patients. MAT1 serves as a promoter in the lung metastasis of osteosarcoma through increasing AKT1 expression. Our study may provide a potent therapeutic target for the lung metastasis of osteosarcoma.

Introduction

Osteosarcoma is the most common primary malignant bone tumor affecting children and adolescents. It is mainly derived from the metaphysis of long bone and is inclined to local invasion and distant metastases, with lung metastasis as the most common type [[1], [2], [3]]. Despite that patients' prognosis has been improved due to the application of combination therapy of chemoradiotherapy and surgical resection [4,5], the five-year survival rates of patients with lung metastasis are still dim, with ~30% [6]. Therefore, further exploration of the mechanisms underlying the lung metastasis in osteosarcoma is of importance.

It's well documented that cyclin-dependent kinases (CDKs) play important roles in modulating cell proliferation via controlling cell cycle [7]. The phosphorylation of CDKs is executed by CDK-activating kinase (CAK) [8,9], which is a trimeric complex consisting of CDK7 [10], Cyclin H [11], and the accessory protein, MAT1 (MNAT1) [12,13]. MAT1 gathers CAK and determines the substrate specificity of CAK, and then regulates cell cycle G1 exit [14]. Through MAT1, CAK interacts with and phosphorylates retinoblastoma tumor suppressor protein (Rb), a proliferation repressor and a differentiation promoter [15,16]. However, MAT1 deletion impedes the phosphorylation of Rb and induces G1 arrest in osteosarcoma cells [14], suggesting that MAT1 may play a role in the progression of osteosarcoma. Noticeably, inhibition of the expression and phosphorylation of Rb plays an important role in the metastasis of various kinds of cancers. For example, Arima et al. [17] demonstrated that downregulation of Rb with siRNA interference in breast cancer MCF-7 cells destroyed cell-cell adhesion and promoted the epithelial-to-mesenchymal transition (EMT), which was closely implicated in the metastasis of primary tumors. Berman et al. [18] found that mice with Rb and p53 double mutant were viable and displayed multiple characteristics of human osteosarcomas, including high metastasis. These findings suggest that MAT1 might be involved in the metastasis of osteosarcoma.

As a result, this study aimed to explore the effects of MAT1 on the metastasis of osteosarcoma, especially for lung metastasis, as well as reveal its underlying mechanisms.

Section snippets

Patients

All tissue samples used in this study were obtained from osteosarcoma patients who received an osteosarectomy with/without a pneumonectomy. In detail, 8 osteosarcoma tissues were obtained from patients with no pulmonary metastasis; 8 osteosarcoma tissues were acquired from patients with pulmonary metastasis and another 8 lung tissues were gained from patients with pulmonary metastasis. Experiments involving human samples were approved by the ethical committee of the 2nd Xiangya Hospital,

High expression of MAT1 closely associates with osteosarcoma patients' advanced clinical stage and lung metastasis

To explore the effects of MAT1 in the lung metastasis of osteosarcoma, we first divided osteosarcoma patients into two groups, MAT1 high expression group (n = 24) and MAT1 low expression group (n = 23), according to the expression levels of MAT1 obtained from immunohistochemistry staining of MAT1. The results showed that the high expression level of MAT1 closely associated with advanced clinical stage (P = 0.013) and high incidence of lung metastasis (P = 0.002) (Table 1), suggesting that MAT1

Discussion

Human MAT1 gene (ménage trois 1) is located in chromosome 14q23 and codes a 37 kDa-protein that can activates cyclin-associated kinases through threonine phosphorylation [21]. In the present study, we aimed to explore the effects of MAT1 on the lung metastasis of osteosarcoma. The results reveal that MAT1 servers as an inducer of the lung metastasis in osteosarcoma. Our findings may provide a potent therapeutic target of MAT1 for the lung metastasis of osteosarcoma.

Through immunohistochemical

Conclusion

In conclusion, this study clarifies that MAT1 facilitates the lung metastasis of osteosarcoma through increasing AKT1 expression both in vivo and in vitro. Our study provides theoretical basis for serving MAT1 as a new target for preventing and treating osteosarcoma lung metastasis.

Acknowledgements

This study was supported by the Grant of Xiangya famous doctors of Central South University.

Declaration of competing interest

The authors declare that there is no any form of interest conflict.

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