Mammalian G₁ cyclins

D- and E-type cyclins regulate the progression of mammalian cells through the G₁ phase of the cell cycle. The mechanisms responsible for the accumulation and activation of kinases dependent on cyclins D and E in both normal and cancerous cells have recently been uncovered. Overexpression of cyclin D1 protein as a consequence of genetic rearrangements, and deletions or mutations of the p16^INK4 gene have been demonstrated in a large variety of human cancers, including breast and esophageal carcinomas, lymphomas, bladder carcinoma, pancreatic adenocarcinoma and familial melanoma.