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Epigenetic inactivation of the CIP/KIP cell-cycle control pathway in acute leukemias

C S Chim1, A S Y Wong, Y L Kwong

  • 1University Department of Medicine, Queen Mary Hospital, Hong Kong.

American Journal of Hematology
|November 30, 2005
PubMed

Insights

Gene promoter hypermethylation rarely inactivates the cell cycle regulators p21, p27, and p57 in leukemia. This study investigated methylation in leukemic cell lines and patient samples, finding infrequent gene silencing.

Area of Science:

  • Oncology
  • Molecular Biology
  • Epigenetics

Background:

  • Cell cycle dysregulation is a hallmark of cancer, including leukemia.
  • The cyclin E/CDK/RB pathway, regulated by CIP/KIP family proteins (p21, p27, p57), is crucial for cell cycle control.
  • Gene promoter hypermethylation is a known mechanism for tumor suppressor gene inactivation.

Purpose of the Study:

  • To investigate the frequency of inactivation of p21, p27, and p57 genes by promoter hypermethylation in leukemic cell lines and patient samples.
  • To assess the role of methylation in the cyclin E/CDK/RB pathway in oncogenesis of leukemia.
  • To compare findings with existing literature and explore reasons for variability.

Main Methods:

  • Methylation-specific polymerase chain reaction (MSP) was employed using primers for methylated (M-MSP) and unmethylated (U-MSP) alleles.
  • The study analyzed five human leukemic cell lines.
  • Fifty acute myeloid leukemia (AML) and twenty-five acute lymphoblastic leukemia (ALL) patient samples at diagnosis were examined.

Main Results:

  • In cell lines, p21 showed hemizygous methylation in Raji and Jurkat. p27 was hemizygously methylated in Raji. p57 was methylated in Raji and NB4, and hemizygously methylated in U937.
  • In patient samples, p21 methylation was not detected in AML or ALL.
  • p27 methylation was found in 2% of AML and 4% of ALL patients. p57 methylation occurred in 2% of AML and 4% of ALL patients.

Conclusions:

  • Methylation-mediated inactivation of the INK4/CDK/RB pathway, specifically involving p21, p27, and p57, is infrequent in acute leukemias.
  • The observed low frequency suggests other mechanisms may be more dominant in leukemia development.
  • Variations in reported methylation frequencies in the literature may stem from differences in detection methodologies.

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