Catecholamine-Stimulated Protein Phosphorylation in 3T3-L1 Preadipocytes and Adipocytes

Abstract

The endogenous protein phosphorylation stimulated by catecholamines was compared in 3T3-L1 preadipocytes and adipocytes. Phosphorylation of a protein with an approximate molecular weight of 57, 000 was stimulated both in preadipocytes and adipocytes of 3T3-L1. Stimulated phosphorylation of four other proteins with approximate molecular weights of 90, 000, 62, 000, 48, 000, and 32, 000 was observed only in 3T3-L1 adipocytes. All of these proteins appeared to be localized in the microsomal fraction. Phosphorylation of these proteins was stimulated by norepinephrine, epinephrine, isoproterenol, dibutyryl cyclic AMP, theophylline, or 1-methyl-3-isobutylxanthine, but not by A23187. Among the phosphorylated proteins in 3T3-L1 adipocytes, the 62, 000 dalton protein was most evident. Using this protein as a marker, it appeared that epinephrine and norepinephrine were effective in stimulating the phosphorylation at the same concentration range. This result was in clear contrast to the different affinities of these catecholamines for β-receptors of 3T3-L1 adipocytes reported by Lai, Rosen, and Rubin (J. Biol. Chem. (1982) 257, 6691-6696). The phosphorylation of the 62, 000 dalton protein in 3T3-L1 adipocytes was observed 1min after the addition of norepinephrine, and dephosphorylation was observed within 10min aster the addition of propranolol.