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Cholesterol in Receptor Complex Assembly

Beginning on page 673, Green et al. describe the elucidation of a role for cholesterol in the recruitment of integrin-associated protein (IAP) to a receptor signaling complex. Though previous work had shown that cholesterol is required for signaling in several cell types, the new study is the first demonstration of a specific role for cholesterol in receptor complex assembly and the regulation of integrin function. IAP seems to regulate some of the functions of a v b 3 integrin receptors and has been shown to form a signaling complex with a v b 3 and trimeric G proteins. The authors show that depletion of cholesterol from the cell membrane prevents the formation of this complex and blocks downstream signaling. Depleting cholesterol from IAP also causes a change in the antigenicity of the protein, and expression of chimeric forms of IAP demonstrates that the multiple membrane-spanning domain is required for both cholesterol binding and complex assembly. “We postulate that cholesterol is directly involved in creating the transmembrane complex that signals,” says Eric Brown, senior author on the study. In this model, cholesterol binding to the multiple membrane-spanning domain of IAP produces a protein conformation that can interact with a v b 3, and this entity in turn associates with the trimeric G protein to form the signaling complex.