C-myc transcript is induced in rat liver at a very early stage of regeneration or by cycloheximide treatment

Abstract

In rats, partial hepatectomy induces reasonably synchronized DNA replication in the remaining liver after approximately 20 h¹. Events occurring during the earlier stages of liver regeneration are of Interest because they may tell us how cells in vivo respond when they move from a differentiated resting state (G₀ phase) to a proliferative state. We report here that the expression of the C-myc oncogene is increased up to 10–15-fold of the normal level within 1–3 h after partial hepatectomy. This expression begins to decrease rapidly after 4 h and has returned to less than double the normal level after 8 h, at which time replicative DNA synthesis has still not begun. A still larger increase in c-myc transcription (∼600-fold) is observed in the liver when protein synthesis is inhibited by an injection of cycloheximide. These findings suggest the existence of a short-lived protein that is synthesized soon after partial hepatectomy, and which suppresses the expression of c-myc.