Angiotensin IV Induces Phosphorylation Of Extracellular Signal‐Regulated Kinase 1/2 Via The AT ₄ Receptor In 3T3‐L1 Adipocytes

Angiotensin II acting via the AT 1 receptor has an inhibitory effect on the insulin‐signaling pathway in adipocytes by activation of extracellular signal‐regulated kinase (ERK 1/2) and subsequent serine phosphorylation of IRS‐1. The objective of this study was to determine if Ang IV is involved in downstream insulin‐signaling pathways by phosphorylation of ERK 1/2 via the AT 4 receptor in 3T3‐L1 adipocytes. We initially confirmed the expression of AT 4 receptors by RT‐PCR in 3T3‐L1 adipocytes. Adipocytes were incubated with various combinations of Ang IV (10 −10 M) for 10 min, AT 4 receptor inhibitor, Norleual (10 −10 M) for 1 hr, and insulin (10 −7 M) for 5 min. Cell lysates were resolved by SDS‐PAGE electrophoresis and immunoblotted with anti‐phospho‐ERK 1/2. Ang IV and insulin alone or in combination increased the phosphorylation of ERK 1/2 as compared with controls. AT 4 induced phosphorylation of ERK 1/2 was reversed by pretreatment with the novel AT 4 receptor antagonist, Norleual. Norleual attenuated Ang IV phosphorylation of ERK1/2, whereas it did not affect ERK 1/2 phosphorylation with insulin or the combination of insulin and Ang IV. This study shows that Ang IV is involved in the insulin‐signaling cascade by increasing phosphorylation of ERK 1/2, which is inhibited by AT 4 receptor blockade and is independent of the insulin receptor in adipocytes.