{"type":"root","children":[{"type":"paragraph","children":[{"type":"text","value":"Cyclins are a family of proteins involved in the progression of cells through the cell cycle. Cyclins form a complex with their partner, cyclin-dependent kinase (Cdk), which activates the latter’s protein kinase function. Cyclins are so named because they are produced or degraded as needed in order to drive the cell through the different stages of the cell cycle. When its concentrations in the cell are low, the cyclin detaches from the Cdk, inhibiting the enzyme’s activity, probably by causing a protein chain to block the enzymatic site."}]},{"type":"paragraph","children":[{"type":"text","value":"Cyclin D1 or PRAD-1 or bcl-1 is one of the key cell-cycle regulators, and functions in association with Cdk4 and/or Cdk6 by phosphorylating the Rb protein. It is a putative proto-oncogene overexpressed in a wide variety of human neoplasms including Mantle Cell Lymphomas. Cyclin D1 has been found to be overexpressed in breast carcinoma."}]}]}