title: Exposure of neuroblastoma cell lines to imatinib results in the upregulation of the CDK inhibitor p27(KIP1) as a consequence of c-Abl inhibition.
abstract: Imatinib mesylate is a tyrosine kinase inhibitor with selectivity for abelson tyrosine-protein kinase 1 (c-Abl), breakpoint cluster region (Bcr)-Abl fusion protein (Bcr-Abl), mast/stem cell growth factor receptor Kit (c-Kit), and platelet-derived growth factor receptor (PDGFR). Previous studies demonstrated that imatinib in the low micromolar range exerted antiproliferative effects on neuroblastoma cell lines. However, although neuroblastoma cells express c-Kit and PDGFR, the imatinib concentrations required to achieve significant growth inhibitory effects (≥ 10 μM) are substantially higher than those required for inhibition of ligand-induced phosphorylation of wild type c-Kit and PDGFR (≤ 1 μM), suggesting that additional mechanisms are responsible for the antitumor activity of imatinib on these cells. In this study, we show that treatment of neuroblastoma cell lines with 1-15 μM imatinib resulted in a dose dependent inhibition of 5-bromo-2'-deoxyuridine (BrdU) incorporation into newly synthesized DNA. The antiproliferative effect of imatinib was dependent on the upregulation of the cyclin-dependent kinase (CDK) inhibitor p27(KIP1) in the nuclear compartment as a result of increased p27(KIP1) protein stability. We demonstrate that the mechanism of p27(KIP1) stabilization relied on inhibition of p27(KIP1) phosphorylation on tyrosine residues by c-Abl. We provide evidence that in neuroblastoma cell lines a significant fraction of cellular c-Abl is phosphorylated on Tyr-245, consistent with an open and active conformation. Notably, exposure to imatinib did not affect Tyr-245 phosphorylation. Given the low affinity of active c-Abl for imatinib, these data provide a molecular explanation for the relatively high imatinib concentrations required to inhibit neuroblastoma cell proliferation.
authors.affiliation: Department of Oncology, School of Medicine, University of Torino, Italy.
authors.forename: Elisa
authors.initials: E
authors.lastname: Lupino
authors.affiliation: Department of Oncology, School of Medicine, University of Torino, Italy.
authors.forename: Cristina
authors.initials: C
authors.lastname: Ramondetti
authors.affiliation: Department of Oncology, School of Medicine, University of Torino, Italy.
authors.forename: Barbara
authors.initials: B
authors.lastname: Buccinnà
authors.affiliation: Department of Oncology, School of Medicine, University of Torino, Italy. Electronic address: marco.piccinini@unito.it.
authors.forename: Marco
authors.initials: M
authors.lastname: Piccinini
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D001549:Benzamides / Q000494:pharmacology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects / Q000502:physiology; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000096:biosynthesis*; D004305:Dose-Response Relationship, Drug; D016313:Genes, abl / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D000068877:Imatinib Mesylate; D009447:Neuroblastoma / Q000378:metabolism*; D010879:Piperazines / Q000494:pharmacology*; D011743:Pyrimidines / Q000494:pharmacology*; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology
chemical_list: D000970:Antineoplastic Agents; D001549:Benzamides; C436291:CDKN1B protein, human; D010879:Piperazines; D011743:Pyrimidines; D050760:Cyclin-Dependent Kinase Inhibitor p27; D000068877:Imatinib Mesylate
keywords: 5-bromo-2′-deoxyuridine (PubChem CID: 6035); CDK2; Cycloheximide (PubChem CID: 6197); Hoechst 33258 (PubChem CID: 16218619); Imatinib; Imatinib (PubChem CID: 123596); Neuroblastoma; c-Abl; p27(KIP1); pRb