Expression of genes involved in initiation, regulation, and execution of apoptosis in human neutrophils and during neutrophil differentiation of HL-60 cells

Neutrophils possess a very short lifespan, dying by apoptosis. HL-60 cells undergo apoptosis after neutrophil differentiation with dimethyl sulfoxide (DMSO). We have found that the onset of apoptosis in neutrophil-differentia tion,a HL-60 cells correlates with the achievement of an apoptosis-related gene expression pattern similar to that of peripheral blood mature neutroph ils. Using reverse transcriptase-polymerase chain reaction, cloning, and se quencing techniques, we have found that HL-60 cells express bak, bik, bax, bad, bcl-2, bcl-x(L), bcl-w, bfl-1, fas, and caspases 1-4 and 7-10. After D MSO treatment, bak, brl-tr,, bfl-1, fas, and caspases 1 and 9 were up-regul ated, whereas bik, bcl-2, and caspases 2, 3, and 10 were down-regulated at different degrees, achieving mRNA expression levels that correlated with th ose detected in peripheral blood neutrophils. Caspase-2 mRNA and protein ex pression was drastically reduced after HL-60 cell differentiation, being ab sent in both HL-60-differentiated neutrophils and mature neutrophils, where as caspase-3 and -10 mRNA and protein expression were diminished upon HL-60 cell differentiation until achieving the respective levels found in mature neutrophils. Bak and bfl-1 mRNA levels were largely increased during DMSO- induced differentiation of HL-60 cells, and these genes were the bcl-2 fami ly members that were expressed most abundantly in mature neutrophils. Bcl-2 overexpression or caspase inhibition prevented differentiation-induced apo ptosis in HL-60 cells, hut not their differentiation capability. Neutrophil spontaneous apoptosis was also blocked by the caspase inhibitor z-Asp-2,6- dichlorobenzoyloxymethylketone. Peripheral blood neutrophils expressed bat, bad, bcl-w, bfl-1, fas, and caspases 1, 3, 4, and 7-10, hut hardly express ed bcl-2, bcl-x(L), bik, bax, and caspase-2. These results suggest that the above gene expression changes in neutrophil-differentiating HL-60 cells ma y play a role in the acquisition of the neutrophil apoptotic features.