Cyclin D1 is a key regulatory protein involved in cell cycle progression. It belongs to the cyclin family, which is essential for the control of the cell cycle at the G1/S (start) transition. Cyclin D1 forms a complex with cyclin-dependent kinase (CDK) 4 or CDK6, and this complex phosphorylates the retinoblastoma protein (Rb), leading to the release of E2F transcription factors and the subsequent progression of the cell cycle.
