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International audience; Human and animal cell lines are important laboratory tools that can be used for studying a variety of cell functions. Some cell lines are blocked at a certain step of maturation and can be used in order to study the mechanisms involved in cell maturation. Because such cell lines can be differentiated toward a more mature-like phenotype after the addition of agents, they can replace primary cells in large screening experiments preventing daily isolation. The human promyelocytic HL-60 leukemia cell line is an attractive model for studying the events which occur in myeloid cells. Interestingly, these cells can be differentiated toward monocytes, macrophages, or granulocytes as described in the present chapter.

Tightly controlled proteolysis is a defining feature of apoptosis and caspases are critical in this regard. Significant roles for non-caspase proteases in cell death have been highlighted. Staurosporine causes a rapid induction of apoptosis in virtually all mammalian cell types. Numerous studies demonstrate that staurosporine can activate cell death under caspase-inhibiting circumstances. The aim of this study was to investigate the proteolytic mechanisms responsible for cell death under these conditions. To that end, we show that inhibitors of serine proteases can delay cell death in one such system. Furthermore, through profiling of proteolytic activation, we demonstrate, for the first time, that staurosporine activates a chymotrypsin-like serine protease-dependent cell death in HL-60 cells independently, but in parallel with the caspase controlled systems. Features of the serine protease-mediated system include cell shrinkage and apoptotic morphology, regulation of caspase-3, altered nuclear morphology, generation of an endonuclease and DNA degradation. We also demonstrate a staurosporine-induced activation of a putative 16 kDa chymotrypsin-like protein during apoptosis.