Apoptosis-induced structural changes in leukemia cells identified by IR spectroscopy

Abstract

Apoptotic changes induced in the leukemia cell line CEM by treatment with the chemical etoposide were investigated by IR spectroscopy. Characteristic band alterations were identified in the apoptotic cells arising from cellular protein, lipid and DNA. Besides general changes such as an increase in lipid content and a decrease in the amount of detectable DNA, there were specific changes that affected the secondary structure of proteins in the apoptotic leukemia cells, i.e. the dominant protein structure shifts from β-sheet in the control cells to unordered coil in the apoptotic cells. The student's t-test was applied to the spectral range 1500–1700cm−1 in order to determine the significant differences of protein structure between control and etoposide treated cells at various time points. A temporal relationship was found between the spectrally significant differences of the protein structure in the apoptotic cells and the severity of apoptosis. The IR spectral changes of protein structure also correlate well with the activity of caspase-3, an important proteolytic enzyme in apoptosis. This preliminary study suggests that IR spectroscopy could possibly be used to monitor and quantitate apoptosis in leukemia cells.