New twist in the regulation of cyclin D1

Among the cell cycle-related mammalian cyclins, cyclin D1 is more closely connected with cell proliferation in response to extracellular signals than the cell cycle clock itself. Because both its mRNA and protein are labile, the intracellular abundance of cyclin D1 is thought to be largely regulated at the level of transcription. However, recent findings suggest that, in certain cell types, cyclin D1 is post-translationally regulated, and a disturbance of this regulatory mechanism induces aberrant entry into the cell cycle and proliferation, sometimes leading to diseases such as cancer. In this review, we summarize recent findings and discuss the physiological role and cellular function of the novel mechanism of regulation of cyclin D1 in terms of the control of cell proliferation.