Connective tissue growth factor is a substrate of ADAM28

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 lung and breast carcinomas. However, information about substrates of ADAM28 is limited. We screened interacting molecules of ADAM28 in human lung cDNA library by yeast two-hybrid system and identified connective tissue growth factor (CTGF). Binding of CTGF to proADAM28 was demonstrated by yeast two-hybrid assay and protein binding assay. ADAM28 cleaved CTGF in dose- and time-dependent manners at the Ala181–Tyr182 and Asp191–Pro192 bonds in the hinge region of the molecule. ADAM28 selectively digested CTGF in the complex of CTGF and vascular endothelial growth factor165 (VEGF165), releasing biologically active VEGF165 from the complex. RT-PCR and immunohistochemical analyses demonstrated that ADAM28, CTGF and VEGF are commonly co-expressed in the breast carcinoma tissues. These data provide the first evidence that CTGF is a novel substrate of ADAM28 and suggest that ADAM28 may promote VEGF165-induced angiogenesis in the breast carcinomas by the CTGF digestion in the CTGF/VEGF165 complex.

Research highlights
► The hyper-variable region in the cysteine-rich domain of ADAM28 binds to C-terminal domain of CTGF.
► ADAM28 cleaves CTGF alone and CTGF in the CTGF/VEGF165 complex.
► CTGF digestion by ADAM28 releases biologically active VEGF165 from the complex.
► ADAM28, CTGF and VEGF165 are commonly co-expressed by carcinoma cells in human breast carcinoma tissues.
► These suggest that ADAM28 promotes VEGF165-induced angiogenesis in the breast carcinomas by selective CTGF digestion in the CTGF/VEGF165 complex.