Cytoplasmic mislocalization of p27Kip1 protein is associated with constitutive phosphorylation of Akt or protein kinase B and poor prognosis in acute myelogenous leukemia.
Cyclin-dependent kinase inhibitor p27Kip1 functions at the nuclear level by binding to cyclin E/cyclin-dependent kinase-2. It was shown that Akt or protein kinase B (Akt/PKB)-dependent phosphorylation of p27Kip1 led to the cytoplasmic mislocalization of p27Kip1, suggesting the potential abrogation of its activity. Here, we evaluated the localization of p27Kip1 protein in leukemic blasts in relation to Akt/PKB phosphorylation and clinical outcomes in acute myelogenous leukemia (AML). Western blot analysis of the nuclear and cytoplasmic fractions revealed a heterogenous localization pattern of p27Kip1 in AML. Cytoplasmic mislocalization of p27Kip1 was significantly associated with the constitutive serine(473) Akt/PKB phosphorylation in AML cells (P < 0.05). Transfection of U937 cells with an expression construct encoding the constitutively active form of Akt/PKB resulted in a remarkable increase in the levels of cytoplasmic p27Kip1. Whereas the transfection of U937 cells with a construct encoding dominant-negative Akt/PKB resulted in a recovery of nuclear localization of p27Kip1. Both the disease-free survival and overall survival are significantly shorter in AML cases with high cytoplasmic to nuclear ratio of p27Kip1 localization compared with the cases with low cytoplasmic to nuclear ratio (P = 0.0353, P = 0.0023, respectively). Multivariate analysis indicated that the cytoplasmic to nuclear ratio of p27Kip1 localization was an independent prognostic variable for both disease-free survival and overall survival (P = 0.043, P = 0.008, respectively). These findings additionally extend our understanding of the role of p27Kip1 in AML, and buttress the case of p27Kip1 mislocalization as a prognostic indicator and Akt/PKB/p27Kip1 pathway as a ready target for antileukemia therapy.
Min
Yoo Hong
YH
Department of Internal Medicine, Yonsei University College of Medicine, Seodaemun-ku Shinchon-dong 134, Seoul 120-752, Korea. minbrmmd@yumc.yonsei.ac.kr
Cheong
June-Won
JW
Kim
Ji Yeon
JY
Eom
Ju In
JI
Lee
Seung Tae
ST
Hahn
Jee Sook
JS
Ko
Yun Woong
YW
Lee
Mark Hong
MH
D000208:Acute Disease; D000293:Adolescent; D000328:Adult; D000368:Aged; D014408:Biomarkers, Tumor; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D050760:Cyclin-Dependent Kinase Inhibitor p27; D003593:Cytoplasm / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000378:metabolism*; D005260:Female; D005799:Genes, Dominant; D016147:Genes, Tumor Suppressor; D006801:Humans; D007951:Leukemia, Myeloid / Q000378:metabolism* / Q000473:pathology / Q000628:therapy; D008297:Male; D008875:Middle Aged; D010766:Phosphorylation; D011379:Prognosis; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D021381:Protein Transport; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D013347:Subcellular Fractions; D015996:Survival Rate; D025521:Tumor Suppressor Proteins / Q000378:metabolism*; D020298:U937 Cells
D014408:Biomarkers, Tumor; D018797:Cell Cycle Proteins; D004791:Enzyme Inhibitors; D011518:Proto-Oncogene Proteins; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D011505:Protein-Tyrosine Kinases; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt