Diacylglycerol treatment rapidly decreases the affinity of the epidermal growth factor receptors of Swiss 3T3 cells

Abstract

The synthetic diacylglycerol 1‐oleoyl‐2‐acetyl glycerol (OAG) and phorbol esters activate protein kinase C in intact cells. We report here that OAG inhibits the binding of ¹²⁵I‐labelled epidermal growth factor (¹²⁵I‐EGF) to Swiss 3T3 cells. The inhibition was detected as early as 1 min after treatment at 37°C and persisted for at least 120 min. The effect of OAG was reversed upon removal of this diacylglycerol. Detailed Scatchard analysis of ¹²⁵I‐EGF binding to Swiss 3T3 cells at 4°C after a 1 h incubation with a saturating dose of OAG at 37°C, demonstrates that this OAG pretreatment does not change the apparent number of EGF receptors but causes a marked decrease in their apparent affinity for the ligand. Prolonged treatment (40 h) of the cells with phorbol dibutyrate (PBt₂) which causes a marked decrease in the number of phorbol ester binding sites and in the activity of protein kinase C, prevented the inhibition of ¹²⁵I‐EGF binding by both PBt₂ and OAG. The results support the possibility that protein kinase C plays a role in the transmodulation of the EGF receptor in intact cells.