Cooperation of C1q Receptors and Integrins in C1q-Mediated Endothelial Cell Adhesion and Spreading

Abstract

The interaction of C1q with endothelial cells elicits a multiplicity of biologic responses. Although these responses are presumed to be mediated by the interaction of C1q with endothelial cell surface proteins, the identity of the participants is not known. In this study we examined the roles of two C1q binding proteins, cC1q-R/calreticulin and gC1q-R/p33, in C1q-mediated adhesion and spreading of human dermal microvascular endothelial cells (HDMVEC). When HDMVEC were cultured in microtiter plate wells coated with concentrations of C1q ranging from 0 to 50 μg/ml, a specific and dose-dependent adhesion and spreading was observed. The extent of adhesion and spreading was similar to the adhesion seen on collagen-coated wells. Spreading (68 ± 12%) and to a moderate extent adhesion (47 ± 9%) were inhibited by anti-gC1q-R mAb 60.11. Similar effects were noted with polyclonal anti-cC1q-R but not with control nonimmune IgG. The two Abs had a slight additive effect (75 ± 13% inhibition) when mixed together in the proportion of 100 μg/ml anti-gC1q-R and 30 μg/ml anti-cC1q-R. More importantly, a 100% inhibition of spreading, but not adhesion, to C1q-coated wells was observed when HDMVEC were cultured in the presence of 30 μM of the peptide GRRGDSP but not GRRGESP. Furthermore, while anti-β1 integrin Ab blocked both adhesion and spreading, anti-α5 integrin blocked only spreading and not adhesion. Ag capture ELISA of endothelial cell membrane proteins using polyclonal anti-gC1q-R showed the presence of not only β1 and α5 integrins but also CD44. Taken together these results suggest that endothelial cell adhesion and spreading require the cooperation of both C1qRs and β1 integrins and possibly other membrane-spanning molecules.

Anthrax Toxin Receptor 1/Tumor Endothelium Marker 8 Mediates Cell Spreading by Coupling Extracellular Ligands to the Actin Cytoskeleton

“…Furthermore, many extracellular ligands and transmembrane proteins cooperate with ␤1 integrins to promote cell spreading: immobilized ADAM12 binds to syndecan-1 to trigger cell spreading through ␤1 integrins (37), as well as uPAR (reviewed in Ref. 38)) and C1q (39). Transmembrane proteins such as tetraspanins and IAP (reviewed in Refs.…”

Cutting Edge: Proliferating Fibroblasts Respond to Collagenous C1q with Phosphorylation of p38 Mitogen-Activated Protein Kinase and Apoptotic Features

“…Given that CRT lacks a transmembrane domain, we favor, instead, an alternative explanation that functional HF receptors for C1q tails consist of complexes of immunologically distinct proteins, some of which possess membrane-spanning regions (4,8,24). For instance, surface CRT signals on macrophages through engagement of CD91 (32), and on endothelial cells through association with both receptor for globular heads of C1q (gC1qR)/p33 and ␤ 1 integrin (33). Integrins participate in CRT-mediated adhesion of HF to substrate-bound C1q tails (14), and ␤ 1 integrin mediates p38 MAPK activation of epithelial cells (34).…”

C1q as a unique player in angiogenesis with therapeutic implication in wound healing

“…For example, C1q can target ECs by binding to the receptors for the collagen-like tail (cC1qR) and the globular head of the molecule (gC1qR) as well as to other ligands such as heparan sulfate. As a result of these interactions, C1q induces adhesion and spreading of ECs and stimulates expression of adhesion molecules (18) and release of the chemotactic factors IL-8 and monocyte chemoattractant protein-1 and IL-6 (19). C1q has also been reported to recognize apoptotic ECs (20) and to stimulate expression of genes in neurons that are associated with neuroprotection-enhancing neurite outgrowth and limiting neuronal stress and inflammation (21).…”