Protein phosphorylation in isolated human adipocytes-- adrenergic control of the phosphorylation of hormone-sensitive lipase

The effect of adrenergic agents on protein phosphorylation in human adipocytes was examined. Freshly isolated human fat cells were incubated with ³²PO₄ in order to label intracellular ATP, then treated with a variety of adrenergic and other pharmacologic agents. Treatment with the β-adrenergic agonist isoproterenol led to a significant increase in phosphate content of at least five protein bands (M_r 52, 53, 63, 67, 84 kDa). The increase in phosphate content of at least five partially inhibited by the α-2 agonist clonidine. Epinephrine, a combined α and β agonist, was less effective at increasing phosphate content of the proteins than was isoproterenol. Neither insulin nor the α-1 agonist phenylephrine had any discernible effect on the pattern of protein phosphorylation. The 84 kDa phosphorylated peptide band appears to contain hormone-sensitive lipase, a key enzyme in the lipolytic pathway which is activated by phosphorylation. These results are somewhat different than previously reported results for rat adipocytes, and represent the first report of overall pattern and adrenergic modulation of protein phosphorylation in human adipocytes.