N-α-acetyltransferase 10 protein promotes metastasis by stabilizing matrix metalloproteinase-2 protein in human osteosarcomas

Highlights

• Naa10p promotes invasion and metastasis of osteosarcoma cells.

• Naa10p promotes metastasis via increasing MMP-2 expression in osteosarcoma cells.

• Naa10p acetylates MMP-2 and prevents its degradation via NatA activity.

Abstract

N-α-Acetyltransferase 10 protein (Naa10p) mediates N-terminal acetylation of nascent proteins. Oncogenic or tumor suppressive roles of Naa10p were reported in cancers. Here, we report an oncogenic role of Naa10p in promoting metastasis of osteosarcomas. Higher NAA10 transcripts were observed in metastatic osteosarcoma tissues compared to non-metastatic tissues and were also correlated with a worse prognosis of patients. Knockdown and overexpression of Naa10p in osteosarcoma cells respectively led to decreased and increased cell migratory/invasive abilities. Re-expression of Naa10p, but not an enzymatically inactive mutant, relieved suppression of the invasive ability in vitro and metastasis in vivo imposed by Naa10p-knockdown. According to protease array screening, we identified that matrix metalloproteinase (MMP)-2 was responsible for the Naa10p-induced invasive phenotype. Naa10p was directly associated with MMP-2 protein through its acetyltransferase domain and maintained MMP-2 protein stability via NatA complex activity. MMP-2 expression levels were also significantly correlated with Naa10p levels in osteosarcoma tissues. These results reveal a novel function of Naa10p in the regulation of cell invasiveness by preventing MMP-2 protein degradation that is crucial during osteosarcoma metastasis.

Introduction

Osteosarcomas are the most common primary malignant tumor of the bone in children and adolescents [1]. Although clinical management of osteosarcomas, including surgery and chemotherapy, has significantly improved long-term survival over the past few decades, outcomes for those patients with metastatic or recurrent osteosarcoma remain dismally poor and, therefore, novel therapeutic strategies are urgently required [2].

Matrix metalloproteinases (MMPs) play important roles in the progression of several types of cancer by increasing tumor growth, migration, invasion, and metastasis and are associated with poor disease prognosis [3]. Tumor growth of osteosarcomas is accompanied by both enhanced local bone destruction and bone formation, two processes that are dependent on proteolytic enzymes. Indeed, many MMPs were found to be expressed in primary and metastatic osteosarcoma tissues [4]. MMP-2, -9, and -14 as well as tissue inhibitor of matrix metalloproteinase (TIMP)-1 were shown to be associated with a poor prognosis of osteosarcomas [5,6]. Intense immunostaining for MMP-2 and -9 was also detected in metastatic lesions from osteosarcomas [4,7]. However, MMP-2 was recently considered to be a more-important MMP involved in osteosarcoma progression. A shift from MMP-9 to predominant MMP-2 activity was observed in zymographic screening of cryo-preserved osteosarcoma biopsies and was associated with a poor response to chemotherapy [8].

N-α-acetyltransferase 10 protein (Naa10p) is the catalytic subunit of a heterodimeric complex, NatA, which co-translationally acetylates N termini of small side-chain amino acids such as Ser, Ala, Thr, Gly, Val, and Cys, after the initiator methionine has been cleaved from nascent polypeptides [9,10]. Despite being debated, Naa10p was also found to acetylate proteins at internal lysine residues of diverse targets [11]. Through N-α or N-ε acetylation, Naa10p regulates protein stability [12], protein activity [13], and protein-protein interactions [14,15] in a variety of target proteins. Non-acetylation-dependent functions of Naa10p were also documented in regulating cell behaviors [16,17]. Thus, Naa10p seems to be a diverse protein with different capacities for executing its effects on target proteins. This diversity also reflects the identified roles of Naa10p in cancer cells. Dependent on the cell context, Naa10p is involved in regulating cell proliferation, apoptosis, autophagy, metastasis, and chemosensitivity of different cancer cells [9]. Naa10p overexpression was reported in breast [18], colorectal [19], liver [20], and lung cancers [21], while low expression in non-small cell lung cancer (NSCLC) was also documented [12]. Furthermore, loss of heterozygosity at Naa10p gene loci was also found in tumors including lung, breast, pancreatic, and ovarian cancers [12]. Considering the diverse targets Naa10p may regulate in different types of cancer cells or in different stages during cancer development, identifying cancer-type specific targets may help to understand the role of Naa10p in a particular cancer type.

Recently, Naa10p was found to participate in controlling osteoblast differentiation and bone formation as a feedback regulator of Runx2 [22]. Naa10p transgenic mice showed delayed calvarial bone development, while Naa10p-knockout mice showed facilitated calvarial bone development. Naa10p-knockdown also augmented the healing of rat calvarial defects. These results highlight a negative role of Naa10p in osteoblast differentiation and bone development. However, whether Naa10p is involved in the formation or progression of osteosarcomas is completely unknown. Herein, we showed that Naa10p is functionally involved in the invasion and metastasis of osteosarcomas. Naa10p is highly expressed in late-stage osteosarcomas and was correlated with shorter survival in patients. Mechanistic studies revealed that Naa10p directly interacts with MMP-2. Naa10p increases MMP-2 protein stability in an N-α-acetylation-dependent manner and thus increases the invasive ability of osteosarcoma cells. Our findings highlight the potential of targeting Naa10p-MMP2 regulation in therapeutic applications against osteosarcomas.