Cytoskeletal Reorganization Induced by Engagement of the NG2 Proteoglycan Leads to Cell Spreading and Migration

Abstract

Cells expressing the NG2 proteoglycan can attach, spread, and migrate on surfaces coated with NG2 mAbs, demonstrating that engagement of NG2 can trigger the cytoskeletal rearrangements necessary for changes in cell morphology and motility. Engagement of different epitopes of the proteoglycan results in distinct forms of actin reorganization. On mAb D120, the cells contain radial actin spikes characteristic of filopodial extension, whereas on mAb N143, the cells contain cortical actin bundles characteristic of lamellipodia. Cells that express NG2 variants lacking the transmembrane and cytoplasmic domains are unable to spread or migrate on NG2 mAb-coated surfaces, indicating that these portions of the molecule are essential for NG2-mediated signal transduction. Cells expressing an NG2 variant lacking the C-terminal half of the cytoplasmic domain can still spread normally on mAbs D120 and N143, suggesting that the membraneproximal cytoplasmic segment is responsible for this process. In contrast, this variant migrates poorly on mAb D120 and exhibits abnormal arrays of radial actin filaments decorated with fascin during spreading on this mAb. The C-terminal portion of the NG2 cytoplasmic domain, therefore, may be involved in regulating molecular events that are crucial for cell motility.

Pathological angiogenesis is reduced by targeting pericytes via the NG2 proteoglycan

“…Thus other factors that we have not yet investigated, such as decreased cell motility or increased apoptosis, may contribute to the large decrease in pericyte number relative to that of endothelial cells. While a specific role for NG2 in apoptosis has not been explored, there are numerous indications of NG2 involvement in cytoskeletal reorganization and cell motility [23][24][25][26][27][28]. In future work it will therefore be important for us to investigate the impact of NG2 on these processes in the context of neovascularization.…”

“…In addition, NG2 appears to mediate signal transduction events that lead to increased cell spreading and motility [23][24][25][26][27]. This combination of properties, coupled with the high level of NG2 expression on nascent microvascular pericytes during developmental angiogenesis [19], has led us to investigate the functional role of the proteoglycan in neovascularization.…”

Phosphorylation of NG2 Proteoglycan by Protein Kinase C-α Regulates Polarized Membrane Distribution and Cell Motility

“…These include sequestration of growth factors (5,8), modulation of the activity of kringle domain proteins (9,10) and matrix metalloproteinases (11), and interaction with other cell surface molecules or with extracellular matrix components that regulate signaling pathways involved in cell proliferation and motility (12)(13)(14)(15). NG2 engagement has been shown to result in activation of the small GTPases cdc42 and rac (15,16) and in ␤ 1 integrin-dependent activation of focal adhesion kinase and ERK-1/2 1 (17,18).…”

Expression of NG2 proteoglycan during endochondral and intramembranous ossification

“…As a membrane-spanning molecule, NG2 has the capability of interacting with both extracellular and cytoplasmic components and, therefore, of mediating communication between the extracellular and intracellular environments. Various pieces of evidence have suggested roles for NG2 in cell proliferation (Grako and Stallcup, 1995;Nishiyama et al, 1996b;Burg et al, 1998;Grako et al, 1999) and cell morphology/motility (Iida et al, 1995;Burg et al, 1997;Fang et al, 1999;Eisenmann et al, 1999;Stallcup and Dahlin-Huppe, 2001). NG2-mediated spreading and migration require the presence of the NG2 cytoplasmic domain (Fang et al, 1999) and appear to occur through activation of the small GTPases cdc42 and rac (Eisenmann et al, 1999;Majumdar et al, 2002).…”