title: Increased p21 expression and complex formation with cyclin E/CDK2 in retinoid-induced pre-B lymphoma cell apoptosis.
abstract: Cip/Kip family protein p21, a cyclin-dependent kinase (CDK) inhibitor, is directly transactivated by retinoic acid receptor alpha (RARalpha) upon retinoic acid (RA):RARalpha binding. Yet the role of p21 upregulation by RA in lymphoma cells remains unknown. Here, we show that, in human pre-B lymphoma Nalm6 cells, RA-induced proliferation inhibition results from massive cell death characterized by apoptosis. Upregulated p21 by RA accompanies caspase-3 activation and precedes the occurrence of apoptosis. p21 induction leads to increased p21 complex formation with cyclin E/CDK2, which occurs when cyclin E and CDK2 levels remain constant. CDK2 can alternatively promote apoptosis, but the mechanisms remain unknown. Data presented here suggest a novel RA-signaling, by which RA-induced p21 induction and complex formation with cyclin E/CDK2 diverts CDK2 function from normally driving proliferation to alternatively promoting apoptosis.
authors.affiliation: Division of Hematology/Oncology, Childrens Hospital Los Angeles Saban Research Institute, Los Angeles, CA 90027, USA.
authors.forename: George C
authors.initials: GC
authors.lastname: Bao
authors.forename: Jian-Guang
authors.initials: JG
authors.lastname: Wang
authors.forename: Ambrose
authors.initials: A
authors.lastname: Jong
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D045744:Cell Line, Tumor; D019927:Cyclin E / Q000378:metabolism*; D051357:Cyclin-Dependent Kinase 2 / Q000378:metabolism*; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D016393:Lymphoma, B-Cell / Q000378:metabolism* / Q000473:pathology*; D046912:Multiprotein Complexes / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D018168:Receptors, Retinoic Acid / Q000378:metabolism; D000072482:Retinoic Acid Receptor alpha; D014212:Tretinoin / Q000494:pharmacology*
chemical_list: D019927:Cyclin E; D050759:Cyclin-Dependent Kinase Inhibitor p21; D046912:Multiprotein Complexes; C000607071:RARA protein, human; D018168:Receptors, Retinoic Acid; D000072482:Retinoic Acid Receptor alpha; D014212:Tretinoin; D051357:Cyclin-Dependent Kinase 2