Recognition of the N-terminal Modules of Thrombospondin-1 and Thrombospondin-2 by α6β1 Integrin

Abstract

In addition to its recognition by ␣ 3 ␤ 1 and ␣ 4 ␤ 1 integrins, the N-terminal pentraxin module of thrombospondin-1 is a ligand for ␣ 6 ␤ 1 integrin. ␣ 6 ␤ 1 integrin mediates adhesion of human microvascular endothelial and HT-1080 fibrosarcoma cells to immobilized thrombospondin-1 and recombinant N-terminal regions of thrombospondin-1 and thrombospondin-2. ␣ 6 ␤ 1 also mediates chemotaxis of microvascular cells to thrombospondin-1 and thrombospondin-2. Using synthetic peptides, LALERKDHSG was identified as an ␣ 6 ␤ 1 -binding sequence in thrombospondin-1. This peptide inhibited ␣ 6 ␤ 1 -dependent cell adhesion to thrombospondin-1, thrombospondin-2, and the E8 fragment of murine laminin-1. The Glu residue in this peptide was required for activity, and the corresponding residue (Glu 90 ) in the N-terminal module of thrombospondin-1 was required for its recognition by ␣ 6 ␤ 1 , but not by ␣ 4 ␤ 1 . ␣ 6 ␤ 1 was also expressed in human umbilical vein endothelial cells; but in these cells, only certain agonists could activate the integrin to recognize thrombospondins. Selective activation of ␣ 6 ␤ 1 integrin in microvascular endothelial cells by the anti-␤ 1 antibody TS2/16 therefore accounts for their adhesion responses to thrombospondins and explains the distinct functions of ␣ 4 ␤ 1 and ␣ 6 ␤ 1 integrins as thrombospondin receptors in microvascular and large vessel endothelial cells.

Identification of Novel β1 Integrin Binding Sites in the Type 1 and Type 2 Repeats of Thrombospondin-1

“…Three Domains of TSP1 Are Recognized by ␤ 1 Integrins-In addition to the three known ␤ 1 integrin binding sites in the N-module of TSP1 (3,8,9), a survey of cell adhesion to other recombinant regions of TSP1 in the absence or presence of a ␤ 1 integrin-activating antibody revealed that the type 1 and type 2 repeats contain ␤ 1 integrin-dependent adhesion sites (Fig. 1).…”

“…␣ 3 ␤ 1 recognizes a sequence near the carboxyl end of the N-module containing the motif NVR (8), but a truncated recombinant N-module lacking this site retains binding to ␣ 6 ␤ 1 and ␣ 4 ␤ 1 (3,9). Mutation of Glu (90) abolishes ␣ 6 ␤ 1 but not ␣ 4 ␤ 1 binding to this region of TSP1 (9). Binding to the latter integrin is at least partially mediated by an LDVP sequence (3).…”

“…At least three ␤ 1 integrins recognize distinct sites in the N-terminal pentraxin-like domain of TSP1. ␣ 3 ␤ 1 recognizes a sequence near the carboxyl end of the N-module containing the motif NVR (8), but a truncated recombinant N-module lacking this site retains binding to ␣ 6 ␤ 1 and ␣ 4 ␤ 1 (3,9). Mutation of Glu (90) abolishes ␣ 6 ␤ 1 but not ␣ 4 ␤ 1 binding to this region of TSP1 (9).…”

Involvement of MAPK signaling molecules and Runx2 in the NELL1‐induced osteoblastic differentiation

“…The laminin G domain serves in the interaction with integrins and a 67-kDa laminin receptor [26]. Mutational analyses of TSP1 and TSP2 have demonstrated that a Glu residue (Glu-90) between b-strands D and E is important for the interaction with integrin a6b1, which is conserved in the similar positions of hNELL1 [22] (Fig. 1).…”

Pneumococcal Adhesins PavB and PspC Are Important for the Interplay with Human Thrombospondin-1

“…Human TSP-1 is a 420-kDa homotrimeric multidomain glycoprotein with multiple, often tissue-specific functions, which includes cell adhesion, signaling, proliferation, and angiogenesis of different cell types as well as immune regulation (17)(18)(19)(20). Human TSP-1 monomers consist thereby of a globular N-terminal heparin binding domain, a von Willebrand factor binding domain, three properdin-like type I repeats, three epidermal growth factor-like type II repeats, eight calcium binding type III repeats, and a globular C-terminal domain (21,22).…”