Increased Expression of Secreted Form A Disintegrin and Metalloproteinase 28 (ADAM28s) in Esophageal Squamous Cell Carcinoma: Implication for Carcinoma Cell Proliferation via Interleukin 6 Receptor Shedding

A disintegrin and metalloproteinase 28 (ADAM28), which comprises membrane-anchored form (ADAM28m) and short-secreted form (ADAM28s), is overexpressed by carcinoma cells and involved in cancer cell proliferation and metastasis in several cancers. However, little is known about the implications of ADAM28 in esophageal squamous cell carcinoma (ESCC). In this study, we investigated the expression and clinical implication of ADAM28 in ESCC and examined the molecular mechanism of ADAM28-mediated ESCC cell proliferation. Immunoblotting analysis demonstrated that ADAM28s is overexpressed in active forms of 42 and/or 40 kDa in ESCC tissues compared with nonneoplastic esophageal tissues. Immunohistochemistry and deep learning artificial intelligence showed that ADAM28s is expressed mainly by carcinoma cells in the ESCC tissue, and the 5-year overall survival and disease-specific survival rates in cases with extensive immunostaining are significantly worse than those in low immunostaining cases. Among several factors examined, interleukin 6 (IL-6) enhanced ADAM28s expression in ESCC cell lines (TE-1 and KYSE-140), which exhibited ADAM28 expression but not in a cell line without the expression (TE-8). Proliferation of TE-1 and KYSE-140 cells under IL-6 stimulation was effectively inhibited by treatment with anti-ADAM28 antibody or siRNA-mediated downregulation of ADAM28, whereas no such effect was observed in TE-8 cells. In mouse ESCC cell xenografts, tumor growth of KYSE-140^ffLuc-cp156 cells was significantly reduced by treatment with the anti-ADAM28 antibody compared with the control immunoglobulin G–treated group. These results show that ADAM28s is overexpressed as active forms in ESCC cells and suggest that ADAM28s is involved in cell proliferation probably through the IL-6 signaling pathway.