Abstract
Apoptotic cell death can be initiated through the extrinsic and intrinsic signaling pathways. While cell cycle progression promotes the responsiveness to intrinsic apoptosis induced by genotoxic stress or spindle poisons, this has not yet been studied conclusively for extrinsic apoptosis. Here, we combined fluorescence-based time-lapse monitoring of cell cycle progression and cell death execution by long-term time-lapse microscopy with sampling-based mathematical modeling to study cell cycle dependency of TRAIL-induced extrinsic apoptosis in NCI-H460/geminin cells. In particular, we investigated the interaction of cell death timing and progression of cell cycle states. We not only found that TRAIL prolongs cycle progression, but in reverse also that cell cycle progression affects the kinetics of TRAIL-induced apoptosis: Cells exposed to TRAIL in G1 died significantly faster than cells stimulated in S/G2/M. The connection between cell cycle state and apoptosis progression was captured by developing a mathematical model, for which parameter estimation revealed that apoptosis progression decelerates in the second half of the cell cycle. Similar results were also obtained when studying HCT-116 cells. Our results therefore reject the null hypothesis of independence between cell cycle progression and extrinsic apoptosis and, supported by simulations and experiments of synchronized cell populations, suggest that unwanted escape from TRAIL-induced apoptosis can be reduced by enriching the fraction of cells in G1 phase. Besides novel insight into the interrelation of cell cycle progression and extrinsic apoptosis signaling kinetics, our findings are therefore also relevant for optimizing future TRAIL-based treatment strategies.
Highlights
The cell cycle regulates the expression of numerous proteins [1, 2], and affects various cellular processes, including for example glycolysis and oxidative phosphorylation [3]
Using sample-based modeling, we demonstrate that times required to commit apoptotic cell death depend on the cell cycle position at the time of TRAIL exposure, with delays manifesting during S phase, around a time that can be defined as a point of apoptosis deceleration (PAD)
Canonical extrinsic apoptosis requires the activation of death receptors, such as TRAIL receptors 1 and 2, which is followed by a signaling cascade that leads to cleavage of executioner caspases (-3, -6 and -7) and subsequent cell death
Summary
The cell cycle regulates the expression of numerous proteins [1, 2], and affects various cellular processes, including for example glycolysis and oxidative phosphorylation [3]. Since de novo synthesis of proteins subsequent to TRAIL exposure is not required for apoptosis induction, independence between extrinsic apoptosis and cell cycle progression could be expected. Expression, phosphorylation and localization of several proteins involved in signal transduction is controlled in a cell cycle-dependent manner [14,15,16]. To study if both dynamical processes, extrinsic apoptosis and cell cycle progression, are coupled, and due to substantial cell-to-cell heterogeneities even in isogenic cell populations [12, 17], the development and application of mathematical models and appropriate statistical tools is inevitable. We focused on statistical methods and phenomenological models to study the relationship of extrinsic apoptosis and cell cycle progression in NCI-H460/ geminin cells [24] and HCT-116/geminin cells when these were exposed to a 2nd generation hexavalent TRAIL receptor agonist (IZI1551) [25]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
