The p21WAF1/CIP1 (hereafter referred to as p21), a member of the cyclin-dependent kinase (cdk) inhibitor family, has also been identified as a target of p53 tumor-suppressor in response to DNA damage. p21 plays multiple roles not only as a cell-cycle regulator, but also as a regulator of transcription, cell motility, apoptosis, and DNA repair [1] and [2]. The role of p21 in apoptosis remains controversial [3]. It is mostly known to protect
Torin 1 from apoptosis, however, overexpression of p21 protein in some cases enhances apoptosis of cancer cells or in response to DNA damage. It has been suggested that the role of p21 is associated with its subcellular localization [2]. The inhibitory activity of p21 on
cell cycle progression correlates with its nuclear localization [4] and [5], while cytoplasmic p21 confers resistance to apoptosis by forming a complex with apoptosis-signaling kinase 1 (ASK1) and procaspase 3 [6] and [7]. The mechanism that regulates cellular localization of p21 is being elucidated [8], [9] and [10].
