Expression, Purification and Functional Identification of Extracellular Part of Discoidin Domain Receptor 2

Discoidin domain receptor 2 (DDR2) is a new type of receptor tyrosine kinases, and was thought to be involved in the metastasis of some tumors. Its ligand is fibrillar collagen. The activation of DDR2 induced by collagen mediates the over-expression of matrix metalloproteinase 1 (MMP-1) in cells. A specific inhibitor of DDR2 was necessary for the study of DDR2 function. Theoretically, a soluble receptor could possibly be used as specific inhibitor for the native receptor on cell membrane. In this report, a fragment (DB) of extracellular part of DDR2 was cloned and expressed for the use as potential inhibitor. This DB fragment corresponded to the polypeptide from the 23rd amino acid residue to the 293rd amino acid residue of DDR2. The fragment was amplified by RT-PCR from human lung cancer tissue, and the product was cloned into pMD18-T vector. After identification by sequence analysis, the fragment was sub-cloned into pGEX-4T-1 vector. Fusion protein of GST-DB was expressed in JM109 E.coli cells as expected and the soluble part accounted for about 13% of the total fusion protein. The soluble fusion protein was then purified with glutathione affinity resin, and GST-DB with purity of 86.1% was obtained. Competitive combination inhibitory test showed that the purified GST-DB inhibited the interaction between collagen II and DDR2 on the surface of RA synovial fibroblasts. Zymography analysis showed that the level of MMP-1 of both NIH 3T3 cell and RA synovial fibroblasts with collagen II-stimulation decreased after adding GST-DB fusion protein. The results indicated that the fusion protein GST-DB could inhibit the function of DDR2 on cells, and DDR2 might mediate collagen II-induced over-expression of MMP-1 in these cells.