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Cell Adhesion Regulates CDC25A Expression and Proliferation in Acute Myeloid Leukemia

¹ Centre de Physiopathologie Toulouse-Purpan, Institut National de la Sante et de la Recherche Medicale U563-IFR30, Département "Oncogenèse et Signalisation dans les cellules hématopoïétiques," and ² Service d'Hématologie Biologique, CHU Purpan; ³ Laboratoire de Biologie cellulaire et Moléculaire du Contrôle de la Prolifération, Centre National de la Recherche Scientifique UMR 5088-IFR109, Université Paul Sabatier, Toulouse, France; and ⁴ IPSEN, Institut Henri Beaufour, Les Ulis, France

Requests for reprints: Stéphane Manenti, Centre de Physiopathologie Toulouse-Purpan, Institut National de la Sante et de la Recherche Medicale U563-IFR30, Département "Oncogenèse et Signalisation dans les cellules hématopoïétiques," CHU Purpan, BP3028, 31024 Toulouse Cedex 3, France. Phone: 33-562-74-45-24; Fax: 33-562-74-45-58; E-mail: stephane.manenti{at}toulouse.inserm.fr.

The effects of cell adhesion on leukemia cell proliferation remain poorly documented and somehow controversial. In this work, we investigated the effect of adhesion to fibronectin on the proliferation of acute myeloid leukemia (AML) cell lines (U937 and KG1a) and CD34⁺ normal or leukemic primary cells. We observed an increased rate of proliferation of AML cells when adhered to fibronectin, concomitant with accelerated S-phase entry and accumulation of CDC25A. Conversely, normal CD34⁺ cell proliferation was decreased by adhesion to fibronectin with a concomitant drop in CDC25A expression. Importantly, we showed that both small interfering RNA (siRNA)–mediated CDC25A down-regulation and a recently developed CDC25 pharmacologic inhibitor impaired this adhesion-dependent proliferation, establishing a functional link between CDC25A accumulation and adhesion-dependent proliferation in leukemic cells. CDC25A accumulation was found only slightly dependent on transcriptional regulation and essentially due to modifications of the proteasomal degradation of the protein as shown using proteasome inhibitors and reverse transcription-PCR. Interestingly, CDC25A regulation was Chk1 dependent in these cells as suggested by siRNA-mediated down-regulation of this protein. Finally, we identified activation of the phosphatidylinositol 3-kinase/Akt pathway as an adhesion-dependent regulation mechanism of CDC25A protein expression. Altogether, our data show that in leukemic cells adhesion to fibronectin increases CDC25A expression through proteasome- and Chk1-dependent mechanisms, resulting in enhanced proliferation. They also suggest that these adhesion-dependent proliferation properties of hematopoietic cells may be modified during leukemogenesis. (Cancer Res 2006; 66(14): 7128-35)

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