Caspase activation in human neuroblastoma cells: mechanisms and spatiotemporal aspects

Sammanfattning: Apoptosis is one of the modes of programmed cell death, in which several members of the caspase family of proteases play the central role. However, activation of apoptotic caspases does not necessarily lead to cell death. Instead, these caspases may mediate, for instance, differentiation or synaptic plasticity, if their activity is restricted in space and time. Such localized caspase activation has been also implicated in the initial stages of neurodegeneration. In order to assess this kind of events at a subcellular level, our research group has previously constructed tau-anchored FRET-based caspase sensors (tAFSs). Here, we demonstrate that localization of tAFSs to the cytoskeleton results in enrichment of the sensors in neuritic processes and enables increased spatiotemporal resolution for live cell imaging of caspase activation, as compared to soluble FRET sensors. This feature is particularly beneficial for investigation of neurodegeneration-related processes.tAFSs were further employed for investigation of caspase activation in neuroblastoma, an extracranial solid pediatric tumor. Tumor necrosis factor-related apoptosis inducing factor (TRAIL) is a promising candidate for cancer treatment due to its ability to selectively trigger apoptosis malignant cells. However, many cancer cells, including neuroblastoma, acquire resistance to TRAIL. Here, we show that in S-type neuroblastoma cell lines, TRAIL resistance is dependent on incomplete activation of apoptotic caspase-3. Sensitization to TRAIL was achieved with protein kinase C (PKC)-inhibiting compounds, suggesting a role for this kinase in blocking the apoptotic response to TRAIL. This effect of PKC could possibly involve stabilization of XIAP, an endogenous caspase inhibitor, as PKC inhibition, in combination with TRAIL treatment, led to downregulation of XIAP.