Cholesterol-independent interactions with CD47 enhance alphavbeta3 avidity

Area of Science:

• Cell Biology
• Molecular Biology
• Immunology

Background:

• CD47 is a transmembrane protein involved in cell-cell interactions.
• Integrins, such as alpha(v)beta(3), play critical roles in cell adhesion and signaling.
• Cholesterol-rich membrane rafts are specialized domains that compartmentalize signaling molecules.

Purpose of the Study:

• To investigate the role of CD47 and its variants in alpha(v)beta(3) integrin activation and function.
• To determine the involvement of cholesterol-rich rafts in CD47-mediated integrin signaling.
• To elucidate the mechanisms by which CD47 influences alpha(v)beta(3) integrin clustering and adhesion.

Main Methods:

• Expression of wild-type CD47 and CD47 IgV-GPI in OV10 cells.
• Assessment of alpha(v)beta(3) activation using LIBS1 and LIBS6 monoclonal antibodies (mAbs).
• Measurement of cell adhesion to vitronectin and anti-beta(3) antibody AP3.
• Cholesterol depletion using methyl-beta-cyclodextrin.
• Analysis of raft association using detergent-free preparation and chemical cross-linking.

Main Results:

• Expression of CD47 and IgV-GPI enhanced ligand-induced alpha(v)beta(3) activation and increased the pool of "activable" integrin molecules.
• Both CD47 forms promoted alpha(v)beta(3)-mediated adhesion to vitronectin and AP3 through enhanced integrin clustering.
• Cholesterol depletion reduced cell adhesion but CD47 expression conferred partial insulation, with IgV-GPI providing greater protection.
• CD47 and IgV-GPI were found in cholesterol-rich rafts, but only CD47 recruited alpha(v)beta(3) and associated signaling molecules.

Conclusions:

• CD47-alpha(v)beta(3) complexes within cholesterol-rich rafts engage in G(i)-dependent signaling.
• CD47-alpha(v)beta(3) interactions leading to integrin clustering are detergent-resistant and cholesterol-independent.
• The transmembrane region of CD47 is not required for cholesterol-insensitive integrin clustering.