title: Nucleoside analogs induce proteasomal down-regulation of p21 in chronic lymphocytic leukemia cell lines.
abstract: Nucleoside analogs (NAs) represent an important class of anticancer agents that induce cell death after conversion to triphosphate derivatives. One of their most important mechanisms of action is the activation of p53, leading to apoptosis through the intrinsic pathway. Classically, the activation of p53 also induces p21 accumulation, which leads to cell cycle arrest at the G1/S transition. In previous work, we observed that 2-chloro-2'-deoxyadenosine (CdA), a NA with high activity in lymphoid disorders, including chronic lymphocytic leukemia (CLL), promotes the G1/S transition in the CLL cell line EHEB at cytotoxic concentrations. This finding led us to investigate the p21 response to NAs in these cells. We show here that CdA, but also fludarabine, gemcitabine, and cytarabine, strongly reduced the p21 protein level in EHEB cells as well as in JVM-2 cells, another CLL cell line. This p21 depletion occurred despite induction of p53 and increase of p21 mRNA and was prevented by proteasome inhibitors. Increase of proteasomal degradation caused by NAs appeared to be ubiquitin-independent. Also, NAs induced in these cells an increase of cyclin-dependent kinase (Cdk2) activity and a monoubiquitination of cell proliferating nuclear antigen (PCNA), two processes that are negatively regulated by p21. These changes were not observed with other p53 activators, like etoposide and nutlin-3a that increased the p21 protein level. In conclusion, our study reveals that NAs can induce an alternative pattern of cellular response in some cell models.
authors.affiliation: Laboratory of Physiological Chemistry, de Duve Institute and Université catholique de Louvain, B-1200 Brussels, Belgium.
authors.forename: L
authors.initials: L
authors.lastname: Bastin-Coyette
authors.forename: S
authors.initials: S
authors.lastname: Cardoen
authors.forename: C
authors.initials: C
authors.lastname: Smal
authors.forename: E
authors.initials: E
authors.lastname: de Viron
authors.forename: A
authors.initials: A
authors.lastname: Arts
authors.forename: R
authors.initials: R
authors.lastname: Amsailale
authors.forename: E
authors.initials: E
authors.lastname: Van Den Neste
authors.forename: F
authors.initials: F
authors.lastname: Bontemps
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D045744:Cell Line, Tumor; D017338:Cladribine / Q000494:pharmacology; D051357:Cyclin-Dependent Kinase 2 / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000096:biosynthesis*; D015536:Down-Regulation; D004789:Enzyme Activation; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000378:metabolism*; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D011684:Purine Nucleosides / Q000494:pharmacology*; D016159:Tumor Suppressor Protein p53 / Q000096:biosynthesis*; D054875:Ubiquitination; D015854:Up-Regulation; D014740:Vidarabine / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D000970:Antineoplastic Agents; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018809:Proliferating Cell Nuclear Antigen; D011684:Purine Nucleosides; D016159:Tumor Suppressor Protein p53; D017338:Cladribine; D051357:Cyclin-Dependent Kinase 2; D046988:Proteasome Endopeptidase Complex; D014740:Vidarabine; C024352:fludarabine