Abstract 416: ADAM12 long and short isoforms promote breast tumor growth and metastasis via distinct mechanisms

Abstract

Abstract Human ADAM12 is expressed as two alternatively spliced forms, a transmembrane form (ADAM12-L), and a secreted form (ADAM12-S). ADAM12 transcript and protein levels are elevated in several types of 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. In this study, our goal was to elucidate the contribution of the isoforms of ADAM12 in breast tumor growth and progression. We engineered stable MCF-7 clones that overexpress ADAM12-L or ADAM12-S and characterized their properties in vitro as well as in an orthotopic breast tumor model. Overexpression of both the transmembrane ADAM12-L and the secreted ADAM12-S isoforms in breast tumor cells resulted in a significantly higher rate of tumor take and increased tumor size. ADAM12-S-expressing tumors also displayed a significantly higher incidence of lymph node and lung metastasis as compared to ADAM12-L and WT MCF-7 tumors respectively. ADAM12-S expression enhanced the ability of tumor cells to migrate and invade in vitro based on its catalytic function, whereas both isoforms conferred estrogen-independent growth capabilities to hormone responsive MCF-7 cells. In ADAM12-L-expressing breast tumor cells, this enhanced proliferation was a direct result of increased EGFR expression and activation and downstream MAPK signaling. This was confirmed when treatment with EGFR inhibitors AG1478 or PD15035 or the MAPK inhibitor U0126 resulted in complete abrogation of estrogen-independent growth in these cells. However, for ADAM12-S-expressing cells, the increased activation of MAPK and proliferation may be due to an alternate mechanism. We have also determined that ADAM12 protein and mRNA expression is elevated in malignant tissue as compared to normal breast tissue via analysis of human breast tissue arrays. Interestingly, there appears to be a differential expression pattern of the transmembrane and secreted isoforms during breast tumor progression. Taken together, our results suggest that ADAM12-S, via its catalytic function enhances the ability of malignant cells to locally invade and form distant metastasis. Expression of both ADAM12 isoforms may confer a proliferative advantage to breast tumor cells in the absence of estrogen stimulation, although via distinct mechanisms, resulting in increased tumor take, tumor size and metastasis in vivo. These findings highlight the therapeutic potential of targeting ADAM12, given that hormone independence is a hallmark of aggressive breast cancer. [The authors acknowledge the support of NIH PO1 CA45548, The JoAnn Webb Fund for Angiogenesis Research and The Fortin Foundation] Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 416.