BCR-ABL induces the expression of Skp2 through the PI3K pathway to promote p27Kip1 degradation and proliferation of chronic myelogenous leukemia cells.
Chronic myelogenous leukemia (CML) is characterized by the expression of the BCR-ABL tyrosine kinase, which results in increased cell proliferation and inhibition of apoptosis. In this study, we show in both BCR-ABL cells (Mo7e-p210 and BaF/3-p210) and primary CML CD34+ cells that STI571 inhibition of BCR-ABL tyrosine kinase activity results in a G(1) cell cycle arrest mediated by the PI3K pathway. This arrest is associated with a nuclear accumulation of p27(Kip1) and down-regulation of cyclins D and E. As a result, there is a reduction of the cyclin E/Cdk2 kinase activity and of the retinoblastoma protein phosphorylation. By quantitative reverse transcription-PCR we show that BCR-ABL/PI3K regulates the expression of p27(Kip1) at the level of transcription. We further show that BCR-ABL also regulates p27(Kip1) protein levels by increasing its degradation by the proteasome. This degradation depends on the ubiquitinylation of p27(Kip1) by Skp2-containing SFC complexes: silencing the expression of Skp2 with a small interfering RNA results in the accumulation of p27(Kip1). We also demonstrate that BCR-ABL cells show transcriptional up-regulation of Skp2. Finally, expression of a p27(Kip1) mutant unable of being recognized by Skp2 results in inhibition of proliferation of BCR-ABL cells, indicating that the degradation of p27(Kip1) contributes to the pathogenesis of CML. In conclusion, these results suggest that BCR-ABL regulates cell cycle in CML cells at least in part by inducing proteasome-mediated degradation of the cell cycle inhibitor p27(Kip1) and provide a rationale for the use of inhibitors of the proteasome in patients with BCR-ABL leukemias.
Andreu
Enrique J
EJ
Division of Cancer, Area of Cell Therapy and Hematology Service, Clinica Universitaria/School of Medicine, Foundation for Applied Medical Research, University of Navarra, Pamplona, Spain.
Lledó
Elisa
E
Poch
Enric
E
Ivorra
Carmen
C
Albero
M Pilar
MP
Martínez-Climent
José Angel
JA
Montiel-Duarte
Cristina
C
Rifón
José
J
Pérez-Calvo
Javier
J
Arbona
Cristina
C
Prósper
Felipe
F
Pérez-Roger
Ignacio
I
D001549:Benzamides; D002352:Carrier Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D002453:Cell Cycle / Q000187:drug effects; D048708:Cell Growth Processes / Q000502:physiology; D050760:Cyclin-Dependent Kinase Inhibitor p27; D016044:Fusion Proteins, bcr-abl / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D000068877:Imatinib Mesylate; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000201:enzymology / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D010879:Piperazines; D011743:Pyrimidines / Q000494:pharmacology; D016160:Retinoblastoma Protein / Q000378:metabolism; D044786:S-Phase Kinase-Associated Proteins / Q000096:biosynthesis* / Q000378:metabolism; D014158:Transcription, Genetic
D001549:Benzamides; C436291:CDKN1B protein, human; D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D010879:Piperazines; D011743:Pyrimidines; D016160:Retinoblastoma Protein; D044786:S-Phase Kinase-Associated Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D000068877:Imatinib Mesylate; D019869:Phosphatidylinositol 3-Kinases; D016044:Fusion Proteins, bcr-abl