Clone REA691 recognizes the human retinoblastoma (Rb) antigen phosphorylated at serines 807 and 811. The Rb protein is a tumor suppressor that plays a pivotal role in the negative control of the cell cycle and in tumor progression. It has been shown that Rb is responsible for a major G1 checkpoint, blocking S-phase entry, and cell growth. Loss of Rb functions may induce cell cycle deregulation, leading to a malignant phenotype. Rb negatively regulates transcription by forming complexes with members of the E2F transcription factor family. These complexes, when bound to E2F sites within certain target genes, actively repress transcription through a variety of mechanisms including physical interaction with adjacent transcriptional activation domains and recruitment of proteins that directly, or indirectly, lead to histone deacetylation. Rb function is, in turn, modulated by phosphorylation mediated by cyclin-dependent kinases. Phospho-Rb is described as being hyperphosphorylated and when in this state, it is unable to complex E2F and therefore, unable to restrict progression from the G1 phase to the S phase of the cell cycle. During the M-to-G1 transition, phospho-Rb is progressively dephosphorylated by PP1, returning to its growth-suppressive hypophosphorylated state.

Additional information: Clone REA691 displays negligible binding to Fc receptors.