Anti-Human Retinoblastoma (Rb-1) - Purified

The Rb antigen is a phosphoprotein that is expressed in most normal cells of vertebrates. It is a tumor suppressor gene which functions as a negative regulator of the cell cycle by interacting with transcription factors including E2F1, PU1, ATF2, UBF, Elf1 and cAbl (1, 2). This ability of Rb to alter transcription is regulated by phosphorylation catalyzed by the cyclin dependent protein kinases (cdks) (3, 4). Rb is phosphorylated on serine and threonine, but not on tyrosine residues. The active, underphosphorylated form of Rb (Rb or pRb) is primarily found in resting or fully differentiated cells. The hyperphosphorylated form (ppRb) is primarily found in proliferating cells. The underphosphorylated form of Rb may bind to viral oncogenes such as SV40 large T Ag, adenoviral EIA and HPV-E7, which may contribute to the transforming activity of these viral oncoproteins. Recent evidence shows that the Rb protein is cleaved by caspases. A caspase-resistant Rb can attenuate the death response to tumor necrosis factor–α, suggesting that Rb degradation contributes to the activation of cell-death pathway (5). Rb also stabilizes constitutive heterochromatin to maintain the overall chromatin structure. Aberrations in the Rb gene have been implicated in cancers of breast, colon, prostate, bladder, kidney, nasopharynx and leukemia, as well as the childhood cancer retinoblastoma (RB) (6).