Heterogeneous responses to low level death receptor activation are explained by random molecular assembly of the Caspase-8 activation platform

Abstract

Ligand binding to death receptors activates apoptosis in cancer cells. Stimulation of death receptors results in the formation of intracellular multiprotein platforms that either activate the apoptotic initiator Caspase-8 to trigger cell death, or signal through kinases to initiate inflammatory and cell survival signalling. Two of these platforms, the Death-Inducing Signalling Complex (DISC) and the RIPoptosome, also initiate necroptosis by building filamentous scaffolds that lead to the activation of mixed lineage kinase domain-like pseudokinase. To explain cell decision making downstream of death receptor activation, we developed a semi-stochastic model of DISC/RIPoptosome formation. The model is a hybrid of a direct Gillespie stochastic simulation algorithm for slow assembly of the RIPoptosome and a deterministic model of downstream caspase activation. The model explains how alterations in the level of death receptor-ligand complexes, their clustering properties and intrinsic molecular fluctuations in RIPoptosome assembly drive heterogeneous dynamics of Caspase-8 activation. The model highlights how kinetic proofreading leads to heterogeneous cell responses and results in fractional cell killing at low levels of receptor stimulation. It reveals that the noise in Caspase-8 activation—exclusively caused by the stochastic molecular assembly of the DISC/RIPoptosome platform—has a key function in extrinsic apoptotic stimuli recognition.

Theoretical study of the impact of adaptation on cell-fate heterogeneity and fractional killing

“…Moreover, noise-induced fate heterogeneity is the most effective when fluctuating variables are those involved in the positive feedback that triggers death initiation. This requirement is consistent with modeling evidences that variability in diverse regulatory molecules can contribute in very different ways to variability in cell death outcomes 20 and that the main contributions seem to occur in the initial decision commitement phase, whether it is at the level of the fluctuations of short-lived antiapoptotic proteins 22 or the stochastic assembly of DISC/RIPoptosome platform 23 . The manner how cell fate is determined by the impact of these fluctuations at the level of concentration trajectories has been also investigated 24,25,27 .…”

“…An attractive case study is the stochastic fate decision between life and death, commonly termed fractional killing, for which the systematic measure of probabilistic dose-response curves coupled with single-cell analysis of stochastic and dynamical signatures are possible 19 . On this issue, several modelling studies have been devoted to identify which sources of fluctuations and which parts of the apoptotic network could contribute the most to the variability of decision time and outcomes 20 – 23 , while the impact of the transient dynamics has been seldomly addressed 24 . Yet, singe-cell analysis of the temporal trajectories of caspase 8 activity in response to TRAIL has revealed a signature of adaptation dynamics whose transient kinetics determines whether a cell survives or dies 25 .…”

Development of a protein signature to enable clinical positioning of IAP inhibitors in colorectal cancer

“…It is known that downstream of IAP inhibitor treatment, the cytosolic Ripoptosome is the signalling platform required for the activation of initiator caspase, procaspase‐8, thus triggering the extrinsic apoptosis pathway response [33–35]. Moreover, Ripoptosome assembly on its own contributes to a high variability in the cell death response as shown in experimental and mathematical modelling studies [36,37]. Thus, our results suggested that the capacity to initiate extrinsic apoptosis through the Ripoptosome might be a prominent process that is affected by protein expression differences between our cell lines.…”

Modulation of signaling cross-talk between pJNK and pAKT generates optimal apoptotic response

“…However, predicting dynamic cross-talk and its ensuing effects on the long-term phenotypic response requires a detailed kinetic modelling. Recent kinetic modelling showed that TNFα mediated apoptosis is influenced by the TNFα level [ 45 – 47 ] and the overall mitochondrial mass [ 48 ]. These do not reveal the underlying dynamic signaling cross-talk between various intra-cellular intermediate entities.…”