ADAM12 Transmembrane and Secreted Isoforms Promote Breast Tumor Growth: A DISTINCT ROLE FOR ADAM12-S PROTEIN IN TUMOR METASTASIS

Roopali Roy,Scott Rodig,Diane Bielenberg,David Zurakowski,Marsha A Moses

doi:10.1074/jbc.m110.216036

Roopali Roy, Scott Rodig + Show 3 more

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https://doi.org/10.1074/jbc.m110.216036

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Abstract

Increased levels of ADAM12 have been reported in a variety of human cancers. We have previously reported that urinary ADAM12 is predictive of disease status in breast cancer patients and that ADAM12 protein levels in urine increase with progression of disease. On the basis of these findings, the goal of this study was to elucidate the contribution of ADAM12 in breast tumor growth and progression. Overexpression of both the ADAM12-L (transmembrane) and ADAM12-S (secreted) isoforms in human breast tumor cells resulted in a significantly higher rate of tumor take and increased tumor size. Cells expressing the enzymatically inactive form of the secreted isoform, ADAM12-S, had tumor take rates and tumor volumes similar to those of wild-type cells, suggesting that the tumor-promoting activity of ADAM12-S was a function of its proteolytic activity. Of the two isoforms, only the secreted isoform, ADAM12-S, enhanced the ability of tumor cells to migrate and invade in vitro and resulted in a higher incidence of local and distant metastasis in vivo. This stimulatory effect of ADAM12-S on migration and invasion was dependent on its catalytic activity. Expression of both ADAM12 isoforms was found to be significantly elevated in human malignant breast tissue. Taken together, our results suggest that ADAM12 overexpression results in increased tumor take, tumor size, and metastasis in vivo. These findings suggest that ADAM12 may represent a potential therapeutic target in breast cancer.

Highlights

Human ADAM12 is expressed as two alternatively spliced forms, a membrane-anchored long form (ADAM12-L) and a short secreted form (ADAM12-S) [1]
ADAM12 Expression Is Elevated in Human Malignant Breast Tissue and Metastatic Lymph Nodes—To assess the distinct roles of ADAM12 isoforms in breast tumor growth and progression, we conducted a comprehensive analysis of arrays of malignant human breast tissue and adjacent normal tissue for ADAM12 protein and mRNA expression by immunohistochemistry (IHC) and real-time RT-PCR, respectively
Of the matched sets of primary tumor tissue and metastatic lymph nodes (LN) (n ϭ 53) analyzed in this study, ϳ80% had a positive expression of ADAM12 in both the primary tumor and matched LN, ϳ13% were negative for ADAM12 in the primary tumor but had positive staining in the LN, and only ϳ1% of the primary tumors were positive for ADAM12 expression, whereas their matched LN were negative (Fig. 1D), suggesting that ADAM12 expression may be essential for primary tumor growth as well as promoting and/or maintaining distant metastasis

Summary

Introduction

Human ADAM12 (meltrin ␣, MCMP) is expressed as two alternatively spliced forms, a membrane-anchored long form (ADAM12-L) and a short secreted form (ADAM12-S) [1]. The catalytic domain of ADAM12 contains the consensus HEXGHXXGXXHD zinc-binding motif, and both isoforms are active proteases. ADAM12 mRNA and protein are highly expressed in a variety of malignant tumor tissues and tumor cell lines including breast, brain, bladder, gastric, colon, lung, laryngeal, and hepatocellular carcinomas We have utilized an in vivo orthotopic tumor model that reliably recapitulates human breast tumor growth to investigate the role of the two distinct isoforms of ADAM12 in the development of invasive breast cancer. We show that overexpression of both ADAM12 isoforms in breast tumor cells promotes tumor growth and that only ADAM12-S expression stimulates their migration and invasion in vitro and local and distant invasion in vivo as a function of its proteolytic activity. Tel.: 617-919-2207; Fax: 617-730-0231; E-mail: marsha.moses@ childrens.harvard.edu

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