Protein kinase C-dependent antilipolysis by insulin in rat adipocytes

Recently, we have shown that protein kinase C (PKC) activated by phorbol 12-myristate 13-acetate (PMA) attenuates the β1-adrenergic receptor (β1-AR)-mediated lipolysis in rat adipocytes. Stimulation of cells by insulin, angiotensin II, and α1-AR agonist is known to cause activation of PKC. In this study, we found that lipolysis induced by the β1-AR agonist dobutamine is decreased and is no longer inhibited by PMA in adipocytes that have been treated with 20 nM insulin for 30 min followed by washing out insulin. Such effects on lipolysis were not found after pretreatment with angiotensin II and α1-AR agonists. The rate of lipolysis in the insulin-treated cells was normalized by the PKCα- and β-specific inhibitor Gö 6976 and PKCβ-specific inhibitor LY 333531. In the insulin-treated cells, wortmannin increased lipolysis and recovered the lipolysis-attenuating effect of PMA. Western blot analysis revealed that insulin slightly increases membrane-bound PKCα, βI, and δ, and wortmannin decreases PKCβI, βII, and δ in the membrane fraction. These results indicate that stimulation of insulin receptor induces a sustained activation of PKC-dependent antilipolysis in rat adipocytes.