CO-IMMUNOPRECIPITATION AS A STRATEGY TO EVALUATE RECEPTOR-RECEPTOR OR RECEPTOR-PROTEIN INTERACTIONS

Immunoprecipitation is a useful method for isolating proteins of interest from cellular ex-tracts using specific antibodies. Following immunoprecipitation of a protein of interest, itcan be determined via Western blot whether any other proteins have co-immunoprecipi-tated. This method has been routinely used over the past several decades to study pro-tein–protein interactions and thereby elucidate cellular signaling pathways.The interactions of G protein-coupled receptors (GPCRs) with a variety of proteinpartners have proven tractable to analysis via co-immunoprecipitation. For example, it isin some cases possible to co-immunoprecipitate G proteins with GPCRs (Matesic et al.,1989; Law et al., 1991; Matesic et al., 1991; Law and Reisine, 1992; Okuma and Reisine,1992; Georgoussi et al., 1995; Sidhu et al., 1998; Chalecka-Franaszek et al., 2000). Thishas been a useful method for helping to characterize the specificity of G protein couplingfor certain receptors. The associations of arrestins with GPCRs have also been effectivelystudied via co-immunoprecipitation (Luttrell et al., 1999; Cheng et al., 2000; Cen et al.,2001; Chen et al., 2002; Conlan et al., 2002; Kishi et al., 2002; Perry et al., 2002), as haveinteractions between GPCRs and various other cytoplasmic proteins (Table 9.1). Finally,co-immunoprecipitation has been an effective method for studying GPCR dimerization(Table 9.2). Receptor–receptor interactions characterized via co-immunoprecipitation