Vascular and Tumor Biology P5.1 ADAM28 expression in oncogene-transformed cells and human carcinoma cells

ADAM28, a member of the ADAM (a disintegrin and metalloproteinase) gene family, is over-expressed by carcinoma cells and the expression correlates with carcinoma cell proliferation and progression in human non-small cell lung and breast carcinomas. To study the molecular mechanisms of ADAM28 gene expression in carcinoma cells, we examined the expression of ADAM28 in MadinDurby canine kidney (MDCK) epithelial cells transformed by oncogenes, and found that transformation by v-Src, but not LMP1, ErbB2, Ha-Ras or c-Fos, induces ADAM28 expression together with a round morphology without cell-to-cell contacts. Immunocytochemistry and immunoelectron microscopy demonstrated ADAM28 expression in cytoplasm and on cell membrane of v-Src-transformants. Implantation of v-Src-transformants in subcutaneous tissue of immunodeficient mice showed progressively growing tumor, which expressed ADAM28 protein, and the growth was significantly reduced by local injections of neutralizing anti-ADAM28 antibody. ADAM28 expression in v-Src-transformants was suppressed by treatment with inhibitors to Src kinase, mitogen-activated protein kinase kinase (MEK), phosphatidylinositol 3-kinase (PI3K) or mTOR. Simultaneous treatment of v-Src-transformants with inhibitors of MEK and PI3K showed complete inhibition of ADAM28 expression. Human cell lines of the lung, breast, ovarian, kidney and colon carcinomas expressed ADAM28 mRNA and protein, which showed a positive correlation to phosporylation of c-Src (phosphoSrc). ADAM28 expression in human carcinoma cells was efficiently suppressed by treatment with inhibitors to Src kinase, MEK or PI3K, and almost completely by simultaneous treatment with inhibitors of MEK and PI3K. In addition, co-expression of ADAM28 and phospho-Src was immunohistochemically shown in neoplastic cells of the breast, lung, ovarian and colon carcinomas and some adenomas of the colon, whereas negligible expression was seen in non-neoplastic colon mucosa. Our data provide, to the best of our knowledge, the first evidence that Src is an inducer of ADAM28 gene expression through the MEK/ ERK and PI3K/mTOR pathways in v-Src-transformants and human carcinoma cells. P5.2 Oral presentation