Mechanism of the inhibitory effect of EGF on cAMP-stimulated amino acid transport.

EGF inhibits the cAMP stimulation of amino acid transport in primary cultures of rat hepatocytes. This effect is not observed in freshly isolated cells incubated in suspension but only in cells that have been allowed to attach to culture dishes. Sequential addition of cAMP and EGF to monolayer cultures of hepatocytes revealed that EGF does not affect the half-life of the carrier proteins induced by cAMP but rather prevents the induction of new amino acid transport proteins. The EGF effect is inhibited by drugs interfering with protein synthesis. These results indicate that EGF promotes the synthesis of specific proteins that are able to prevent the cAMP induction of amino acid carriers.