Figure 6. Cells overexpressing CERKL showed no mortality increase in a comparison of normal and oxidative stress conditions. A: The histogram shows the mortality (depicted as percentage) of pyknotic nuclei of COS-7 cells. Cells were transfected with either the wild-type CERKL isoforms (named CERKLa to CERKLd), the truncated RP form (R257X), CERK or the empty vector (negative control) and grown in either normal conditions (dotted bars) or treated for 4 h with 200 μM H₂O₂ (solid bars). There was no increase in mortality when the cells were transfected with any of the wt CERKL isoforms. In contrast, there was an increase in mortality in cells transfected with, either the empty vector, a CERK (ceramide kinase) construct or the R257X CERKL mutant. Statistical significance is shown by an asterisk (Mann–Whitney test, p<0.05). B: The histogram shows the mortality fold-increase of H₂O₂-treated versus untreated cells for each construct. Statistically significant differences are shown by asterisks (Mann–Whitney test, p<0.05). More than 500 cells were counted for each construct and condition, in 3 independent replicates.