Novel alternatively spliced ADAM8 isoforms contribute to the aggressive bone metastatic phenotype of lung cancer

Abstract

ADAMs (a disintegrin and metalloprotease) are transmembrane proteins involved in a variety of physiological processes and tumorigenesis. Recently, ADAM8 has been associated with poor prognosis of lung cancer. However, its contribution to tumorigenesis in the context of lung cancer metastasis remains unknown. Native ADAM8 expression levels were lower in lung cancer cell lines. In contrast, we identified and characterized two novel spliced isoforms encoding truncated proteins, D18a and D14 0 , which were present in several tumor cell lines and not in normal cells. Overexpression of D18a protein resulted in enhanced invasive activity in vitro. ADAM8 and its D14 0 isoform expression levels were markedly increased in lung cancer cells, in conditions mimicking tumor microenvironment. Moreover, addition of supernatants from D14 0 -overexpressing cells resulted in a significant increase in tartrate-resistant acid phosphatase þ cells in osteoclast cultures in vitro. These findings were associated with increased pro-osteoclastogenic cytokines interleukin (IL)-8 and IL-6 protein levels. Furthermore, lung cancer cells overexpressing D14 0 increased prometastatic activity with a high tumor burden and increased osteolysis in a murine model of bone metastasis. Thus, the expression of truncated forms of ADAM8 by the lung cancer cells may result in the specific upregulation of their invasive and osteoclastogenic activities in the bone microenvironment. These findings suggest a novel mechanism of tumor-induced osteolysis in metastatic bone colonization.

Prognostic and clinical implication of a disintegrin and metalloprotease 8 expression in pediatric medulloblastoma

“…It acts as an active metalloprotease, hydrolyzing myelin basic protein and a variety of peptide substrates based on the cleavage sites of membrane-bound cytokines, growth factors, and receptors [21]. Accumulating evidences have been demonstrated the overexpression of ADAM8 in a variety of human tumors [10][11][12][13][14][15][16]. To our interests on brain malignancies, Wildeboer et al [10] observed maximal ADAM8 mRNA expression in glioblastoma, low-grade oligoastrocytoma, and anaplastic ependymoma.…”

“…Medulloblastoma accounts for nearly 20% of all pediatric tumors in central nervous system and 40% of pediatric posterior fossa tumors [12]. [17].…”

“…ADAM8 is implicated in bone morphogenesis and allergic inflammatory processes [8]. Our special interest is concentrated on АDАМ8 for two reasons: i) In contrast to other proteolytic proteins, АDАМ8 activity is not inhibited by tissue inhibitors of metalloproteinases (TIMPs) [9]; ii) Abberant expression of ADAM8 has been found in multiple malignancies, including gliomas, lung cancer, pancreatic cancer, renal cell carcinomas, prostate carcinomas, and also has been demonstrated to be associated with carcinogenesis [10][11][12][13][14][15]. However, the possible involvement of ADAM8 expression in pediatric medulloblastoma was not fully determined till now.…”

Tumor–stromal interactions of the bone microenvironment: in vitro findings and potential in vivo relevance in metastatic lung cancer models

“…Nevertheless, our in vitro co-culture system does not fully reconstitute the complexity of the tumor-bone microenvironment in vivo, where other cells and/or secreted enzymes could potentially contribute to the extracellular proteolytic activity. In this regard, we have recently shown that ADAM8 (a disintegrin and metalloprotease domain) isoforms contribute to the aggressive bone colonization of lung cancer [25]. Moreover the use of a broad-spectrum inhibitor of MMP and ADAM activities markedly attenuates the development of metastatic lesions [12].…”

“…Fluorescence was determined using 480/520 nm filter set. Experiment was repeated three times, and each condition was done in sixplicate as described previously [25].…”