In normal cells, cyclin D1 is induced by growth factors and promotes progression through the
G 1 phase of the cell cycle. Cyclin D1 is also an oncogene that is thought to act primarily by
bypassing the requirement for mitogens during the G 1 phase. Studies of clinical tumors
have found that cyclin D1 overexpression is associated with chromosome abnormalities,
although a causal effect has not been established in experimental systems. In this study, we
found that transient expression of cyclin D1 in normal hepatocytes in vivo triggered …