Cyclin D1 is a nuclear protein required for cell cycle progression in G1.

TLDR

Growth factor addition to quiescent mammalian cells triggers a cascade that restarts proliferation by driving the G0/G1 to S‑phase transition. Cyclin D1, a putative G1 cyclin, was studied in normal diploid human fibroblasts. Cyclin D1 accumulates in the nucleus before S‑phase, disappears as cells enter S‑phase, and inhibition of cyclin D1 blocks S‑phase entry, demonstrating that it is required earlier than cyclin A and is a critical target of proliferative signals in G1.

Abstract

A cascade of events is triggered upon the addition of growth factor to quiescent mammalian cells, which ultimately restarts proliferation by inducing the transition from G0/G1 to S-phase. We have studied cyclin D1, a putative G1 cyclin, in normal diploid human fibroblasts. Cyclin D1 accumulated and reached a maximum level before S-phase upon the addition of serum to quiescent cells. The protein was localized to the nucleus, and it disappeared from the nucleus as cells proceeded into S-phase. Microinjection of anti-cyclin D1 antibodies or antisense plasmid prevented cells from entering S-phase, and the kinetics of inhibition showed that cyclin D1 is required at a point in the cell cycle earlier than cyclin A. These results demonstrate that cyclin D1 is a critical target of proliferative signals in G1.