Shed Phosphatase Promotes Migration

Abstract

The protein tyrosine phosphatase SHP-1 and the transmembrane protein SHPS-1 (SHP substrate 1) are involved in cell migration. SHPS-1 interacts with the cell surface protein CD47 to mediate cell migration signals related to cell-cell contact. Ohnishi et al. report that SHPS-1 is shed from the surface of cultured cells [both transfected Chinese hamster ovary (CHO) cells and primary hippocampal neurons and mouse macrophages] in response to treatments that stimulate protein kinase C (PKC) and release of the ectodomain was blocked by metalloproteinase inhibitors. The shed ectodomain of SHPS-1 did not inhibit the interaction between CD47-expressing cells and recombinant SHPS-1 fused to the Fc portion of human immunoglobulin G (IgG) (SHPS-1-Fc). In vitro, SHPS-1-Fc was cleaved by metalloproteinases MMP-1 or MMP-9. The cleavage site was mapped to the juxtamembrane region of SHPS-1. CHO cells expressing a juxtamembrane mutant version of SHPS-1 that was not a substrate for MMPs were defective in a cell migration assay and did not spread when plated on fibronectin and showed reduced numbers of focal adhesions compared with cells expressing wild-type SHPS-1. (In both cases, the cells were also overexpressing an active form of H-Ras, which promotes cell migration.) The juxtamembrane mutant of SHPS-1 was tyrosine phosphorylated and did interact with SHP-2. CHO cells transfected with only SHPS-1 or the juxtamembrane mutant, but not overexpressing Ras, were also compared, and the SHPS-1 mutant-expressing cells were impaired in migration and cell spreading. The defects in migration and spreading were less pronounced in these CHO cells compared with the Ras-expressing cells, but the amount of SHPS-1 was lower than in the CHO-Ras-SHPS-1-expressing cells. The results suggest that stimulated ectodomain shedding of SHPS-1 may be important for the action of SHPS-1 in regulating cell migration. H. Ohnishi, H. Kobayashi, H. Okazawa, Y. Ohe, K. Tomizawa, R. Sato, T. Matozaki, Ectodomain shedding of SHPS-1 and it role in regulation of cell migration. J. Biol. Chem. 279 , 27878-27887 (2004). [Abstract] [Full Text]