ADAM8 expression in invasive breast cancer promotes tumor dissemination and metastasis

Abstract

The transmembrane metalloprotease-disintegrin ADAM8 mediates cell adhesion and shedding of ligands, receptors and extracellular matrix components. Here, we report that ADAM8 is abundantly expressed in breast tumors and derived metastases compared to normal tissue, especially in triple-negative breast cancers (TNBCs). Furthermore, high ADAM8 levels predicted poor patient outcome. Consistently, ADAM8 promoted an aggressive phenotype of TNBC cells in culture. In a mouse orthotopic model, tumors derived from TNBC cells with ADAM8 knockdown failed to grow beyond a palpable size and displayed poor vascularization. Circulating tumor cells and brain metastases were also significantly reduced. Mechanistically, ADAM8 stimulated both angiogenesis through release of VEGF-A and transendothelial cell migration via β1-integrin activation. In vivo, treatment with an anti-ADAM8 antibody from the time of cell inoculation reduced primary tumor burden and metastases. Furthermore, antibody treatment of established tumors profoundly decreased metastases in a resection model. As a non-essential protein under physiological conditions, ADAM8 represents a promising novel target for treatment of TNBCs, which currently lack targeted therapies and frequently progress with fatal dissemination.Subject Category Cancer

N-Glycosylation Regulates ADAM8 Processing and Activation

“…Large increases were seen in the levels of the proform, active, and remnant forms of ADAM8 in MDA-MB-231 cells under hypoxic conditions ( Fig. 2A, left panel), consistent with our previous findings (7). Similarly, hypoxia resulted in substantial increases in ADAM8 proform and active form in the SUM-149 line ( Fig.…”

“…Site-directed mutagenesis supports the conclusion that human ADAM8 is N-glycosylated at four sites. Mutation of two of these sites: Asn-91 (located in the prodomain) and Asn-612 (located between the CRD and ELD), reduced the processing of ADAM8 and its localization at the cell surface, two events required for ADAM8 to promote breast tumor growth and metastatic dissemination (7). N-Glycosylation at the Asn-91 was required for ADAM8 exit from the Golgi, while an inability to N-glycosylate ADAM8 on Asn-612 resulted in localization of ADAM8 in the endoplasmic reticulum.…”

“…For growth under hypoxic conditions, cells were incubated at 1% oxygen, 95% nitrogen, and 5% carbon dioxide for 24 h at 37°C. Stable clones of MDA-MB-231 with ADAM8-specific shRNA (shA8) or control shRNA (shCtrl) were kindly provided by Joerg Bartsch (Philipps-University Marburg, Department of Neurosurgery, Marburg, Germany) and maintained as described (7).…”

“…Thus, endogenous ADAM8 is subjected to N-glycosylation in ER␣-negative but not in ER␣-positive breast cancer cells. Recently we demonstrated that when MDA-MB-231 cells were grown under hypoxic conditions, the levels of ADAM8 were induced and its processing was enhanced (7). Thus, we next tested the effects of hypoxia on N-glycosylation and processing of ADAM8 in ER␣-negative versus -positive breast cancer lines.…”

“…their metastases, particularly in Triple-Negative breast cancers (TNBCs) (7). Furthermore, ADAM8 was implicated in various steps of breast tumorigenesis and validated as a target for antibody-based targeted treatment of mammary tumors derived from TNBCs.…”