{"type":"root","children":[{"type":"paragraph","children":[{"type":"text","value":"The retinoblastoma protein (Rb) is a tumor-suppressor protein that is dysfunctional in many types of cancer. One highly studied function of Rb is to prevent excessive cell growth by inhibiting cell-cycle progression until a cell is ready to divide. Rb prevents the cell from replicating damaged DNA by preventing its progression along the cell cycle through G1 into S."}]},{"type":"paragraph","children":[{"type":"text","value":"Should an oncogenic protein (such as that produced by cells infected with high-risk types of human papillomaviruses, SV40 or Adenoviruses) bind and inactivate Rb, this can lead to cancer. Rb protein may act by regulating transcription; loss of its function leads to uncontrolled cell growth. Aberrations in the Rb gene have been implicated in cancers of breast, colon, prostate, kidney, nasopharynx, and Leukemia."}]}]}