Abstract
Apoptosis-inducing factor (AIF) is a mitochondrial flavoprotein which mediates staurosporine (STS) - induced cell death. AIF cleavage and translocation to the cytosol is thought to be calpain-1-dependent as calpain inhibitors reduce AIF proteolysis; however, many calpain inhibitors also inhibit matrix metalloproteinase-2 (MMP-2) activity, an intracellular and extracellular protease implicated in apoptosis. Here we investigated whether MMP-2 activity is affected in response to STS and if it contributes to AIF cleavage. Human fibrosarcoma HT1080 cells were treated with STS (0.1 µM, 0.25-24 h). A significant increase in cellular MMP-2 activity was seen by gelatin zymography after a 6 h STS treatment, prior to induction of cell necrosis. Western blot showed the time-dependent appearance of two forms of AIF (∼60 and 45 kDa) in the cytosol which were significantly increased at 6 h. Surprisingly, knocking down MMP-2 or inhibiting its activity with MMP-2 preferring inhibitors ARP-100 or ONO-4817, or inhibiting calpain activity with ALLM or PD150606, did not prevent the STS-induced increase in cytosolic AIF. These results show that although STS rapidly increases MMP-2 activity, the cytosolic release of AIF may be independent of the proteolytic activities of MMP-2 or calpain.