The localization of caspase-3 in the present studies does not distinguish between the proenzyme and the mature activated forms of the enzyme, but inhibitors of caspase-3 activity have been used to prevent apoptosis in granulosa cells, which suggests that the enzyme is activated during granulosa cell death. Apoptosis of granulosa cells following gonadotropin withdrawal might therefore be a consequence of both increased expression of caspase-3 and activation of the protease by an apoptogenic signal. In this regard, we have recently demonstrated that both Fas and Fas ligand (FasL) expression were increased in granulosa cells of atretic follicles after anti-eCG antiserum induced gonadotropin withdrawal. FasL binding to Fas causes apoptosis by activating a cascade of proteolysis resulting in the cleavage and activation of caspase-3. buy ampicillin
In order to study the activation of caspase-3 during ovarian apoptosis, we examined the cleavage of PARP and actin, two substrates of caspase-3. Actin (42 kDa) can be cleaved in vitro by recombinant caspase-1 to produce both a 30-kDa and a 41-kDa fragment, or by caspase-3 to produce a 30-kDa product. The cleavage pattern of actin during PGF2c,-induced luteal regression demonstrated that both caspase-1 and caspase-3 might have been activated during apoptosis in luteal cells. This is consistent with the cascade of proteolysis during apoptosis, which can result in the activation of several different members of the caspase family.