Thrombospondin signaling through the calreticulin/LDL receptor-related protein co-complex stimulates random and directed cell migration

Abstract

The matricellular extracellular matrix protein thrombospondin-1 (TSP1)stimulates focal adhesion disassembly through a sequence (known as the hep I peptide) in its heparin-binding domain. This mediates signaling through a receptor co-complex involving calreticulin and low-density lipoprotein (LDL)receptor-related protein (LRP). We postulate that this transition to an intermediate adhesive state enhances cellular responses to dynamic environmental conditions. Since cell adhesion dynamics affect cell motility,we asked whether TSP1/hep I-induced intermediate adhesion alters cell migration. Using both transwell and Dunn chamber assays, we demonstrate that TSP1 and hep I gradients stimulate endothelial cell chemotaxis. Treatment with focal adhesion-labilizing concentrations of TSP1/hep I in the absence of a gradient enhances endothelial cell random migration, or chemokinesis,associated with an increase in cells migrating, migration speed, and total cellular displacement. Calreticulin-null and LRP-null fibroblasts do not migrate in response to TSP1/hep I, nor do endothelial cells treated with the LRP inhibitor receptor-associated protein (RAP). Furthermore, TSP1/hep I-induced focal adhesion disassembly is associated with reduced chemotaxis to basic fibroblast growth factor (bFGF) but enhanced chemotaxis to acidic(a)FGF, suggesting differential modulation of growth factor-induced migration. Thus, TSP1/hep I stimulation of intermediate adhesion regulates the migratory phenotype of endothelial cells and fibroblasts, suggesting a role for TSP1 in remodeling responses.

Thrombospondin Induces RhoA Inactivation through FAK-dependent Signaling to Stimulate Focal Adhesion Disassembly

“…Consistent with this, increased focal adhesion formation in FAK knockout fibroblasts results in impaired cell migration, whereas focal adhesion disassembly, such as that stimulated by TSP1/hep I, promotes cell migration (31,57). In addition to the obvious effects on cell motility, transition to the intermediate adhesive state could have profound effects on cell cycle progression, cell survival, and gene expression.…”

“…Thus, analysis of individual phosphorylation sites suggests that TSP1/hep I binding to calreticulin induces a transient increase in FAK kinase activity and a sustained increase in FAK signaling to downstream pathways. culminating in focal adhesion disassembly and increased cell migration (41,42,57). To determine the role of FAK phosphorylation in this pathway, we selectively inhibited these signals and observed the effect on hep I-induced FAK phosphorylation.…”

Intracellular Calreticulin Regulates Multiple Steps in Fibrillar Collagen Expression, Trafficking, and Processing into the Extracellular Matrix

“…From the cell surface, CRT signals multiple cellular processes, including apoptotic clearance of cells, focal adhesion turnover, proliferation, migration, and anoikis resistance (4, 13, 20, 30 -33). Many of these responses to cell surface CRT are mediated by CRT binding to LRP1 (low density lipoprotein receptor-related protein 1) (13,(33)(34)(35).…”

Targeting the hypoxic response in bone tissue engineering: A balance between supply and consumption to improve bone regeneration

“…However, the process of angiogenesis is an inherently slow process (estimates range from 100 mm to 1 mm per day (Mikos et al, 1993;Orr et al, 2003)), and the timely generation of a stable vascular network has long been identified as a fundamental challenge for tissue engineering (Koike et al, 2004). Because of the inherent constraints of vascular ingrowth, constructs of clinically relevant size may progressively become devoid of oxygen and nutrients in their centre upon implantation, which will be detrimental for cellular function and survival (Radisic et al, 2006;Scheufler et al, 2008).…”