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p21 Cip1 (alternatively p21 Waf1), also known as cyclin-dependent kinase inhibitor 1 or CDK-interacting protein 1, is a cyclin-dependent kinase inhibitor (CKI) that is capable of inhibiting all cyclin/CDK complexes, [5] though is primarily associated with inhibition of CDK2.
p53, also known as Tumor protein P53, cellular tumor antigen p53 (UniProt name), or transformation-related protein 53 (TRP53) is a regulatory protein that is often mutated in human cancers. The p53 proteins (originally thought to be, and often spoken of as, a single protein) are crucial in vertebrates , where they prevent cancer formation. [ 5 ]
P14ARF is a central actor of the cell cycle regulation process as it participates to the ARF-MDM2-p53 pathway and the Rb-E2F-1 pathway. [15] It is the physiological inhibitor of MDM2, an E3 ubiquitin ligase controlling the activity and stability of P53, and loss of P14ARF activity may have a similar effect as loss of P53. [ 16 ]
Human cells contain many different cyclins that bind to different CDKs. CDKs and cyclins appear and activate at specific cell cycle phases. Seven cyclin-dependent kinase inhibitor proteins have been identified. They are p15, p16, p18, p19, p21, p27, and p57. [7]
Both of these pathways are activated in response to cellular stressors and lead to cell cycle inhibition. p53 activates p21 which deactivates cyclin-dependent kinase 2(Cdk 2). Without Cdk 2, retinoblastoma protein (pRB) remains in its active, hypophosphorylated form and binds to the transcription factor E2F1, an important cell cycle regulator. [34]
Rb and p53 regulate the transition between G1 and S phase, arresting the cell cycle before DNA replication until the appropriate checkpoint inputs, such as DNA damage repair, are completed. [ 20 ] p53 regulates the p21 gene, which produces a protein which binds to the Cyclin D-Cdk4/6 complex. [ 21 ]
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Mutated p53 is also involved in the pathophysiology of leukemias, lymphomas, sarcomas, and neurogenic tumors. Abnormalities of the p53 gene can be inherited in Li-Fraumeni syndrome (LFS), which increases the risk of developing various types of cancers. BCL2. BCL2 is a family of proteins that are involved in either inducing or inhibiting ...