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Expression of DNA-dependent protein kinase in human granulocytes

Annahita Sallmyr1, Anna Miller, Aida Gabdoulkhakova

  • 1Department of Medical Microbiology, Lund University, Malmo University Hospital, S-205 02 Malmo, Sweden.

Cell Research
|September 9, 2004
PubMed

Insights

Human polymorphonuclear leukocytes (PMN) have reduced DNA-dependent protein kinase (DNA-PK) expression, not a complete absence, during myeloid differentiation. This finding corrects previous assumptions about DNA repair mechanisms in mature white blood cells.

Area of Science:

  • Molecular Biology
  • Cellular Biology
  • Immunology

Background:

  • Human polymorphonuclear leukocytes (PMN) were previously thought to lack DNA-dependent protein kinase (DNA-PK), crucial for DNA repair.
  • Promyelocytic HL-60 cells exhibit a variant Ku protein, leading to increased radiation sensitivity.
  • This raised questions about the efficiency of nonhomologous end-joining (NHEJ) in myeloid differentiation.

Purpose of the Study:

  • To investigate the expression and integrity of DNA-PK in human PMN and HL-60 cells.
  • To determine if the previously reported absence of DNA-PK in PMN is accurate.
  • To clarify the role of DNA-PK in myeloid differentiation and DNA repair.

Main Methods:

  • Analysis of DNA-PK and Ku protein expression in PMN and HL-60 cell extracts.
  • Investigation of a potential DNA-PK-degrading protease in these cells.
  • Utilization of a protease-resistant whole cell assay to detect intact DNA-PK components.

Main Results:

  • Confirmed the absence of intact DNA-PK in PMN protein extracts and the presence of a truncated Ku86 variant in HL-60 cells.
  • Identified a DNA-PK-degrading protease in both PMN and HL-60 cells.
  • Demonstrated the presence of Ku86 and DNA-PKcs in PMN using a protease-resistant assay, indicating reduced, not absent, expression.
  • Observed significantly lower levels of Ku86 and DNA-PKcs in PMN compared to lymphocytes, and elevated levels in HL-60 cells.

Conclusions:

  • The absence of DNA-PK in human PMN is an artifact caused by a protease.
  • Mature myeloid differentiation is characterized by reduced, rather than depleted, DNA-PK expression.
  • These findings have implications for understanding DNA repair efficiency during myeloid cell maturation.

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