Isolation and characterization of NUC70, a cytoplasmic, hematopoietic apoptotic endonuclease

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Apoptosis, or programmed cell death, is characterized by endonucleolytic DNA fragmentation.
• Identifying the specific enzymes involved in this process is crucial for understanding cell death mechanisms.

Purpose of the Study:

• To identify and characterize the endonuclease responsible for DNA fragmentation during drug-induced apoptosis in human hematopoietic cells.
• To elucidate the activation mechanism and cellular localization of this novel endonuclease.

Main Methods:

• Purification of the 70-kDa endonuclease (NUC70) to homogeneity.
• Biochemical characterization including Ca2+/Mg2+ dependence and pH activity range.
• Western immunoblotting and DNA-SDS-polyacrylamide gel electrophoresis to assess expression and activity.
• Inhibition studies using specific chemical agents and caspase inhibitors.
• Immunostaining to determine cellular localization.

Main Results:

• NUC70 was identified as a Ca2+/Mg2+-dependent endonuclease active at pH 6-8, capable of inducing internucleosomal DNA fragmentation.
• NUC70 expression and activity were found to be specific to human hematopoietic cells, not detected in epithelial cells or murine hematopoietic cells.
• NUC70 activation appears to be regulated by posttranslational modification rather than changes in expression levels.
• Caspase inhibitors significantly reduced NUC70 activity, indicating a caspase-dependent activation mechanism.
• NUC70 is a cytoplasmic endonuclease that translocates to the nucleus during apoptosis.

Conclusions:

• NUC70 is a key endogenous endonuclease involved in DNA fragmentation during apoptosis of human hematopoietic cells.
• Its activation is caspase-dependent and involves translocation from the cytoplasm to the nucleus.
• NUC70 represents a specific target for understanding and potentially modulating apoptosis in hematopoietic malignancies.