DISC-dependent versus DISC-independent aspects of non-apoptotic TRAIL signalling
Creators: name: Prieske, Silvia
Publisher: name: Imperial College London
Year: 2012

description: The Tumour Necrosis Factor (TNF) superfamily member TNF-related apoptosis- inducing ligand (TRAIL) can selectively induce apoptosis in a wide variety of tumour cells in vivo without causing toxicity to normal cells. Consequently, these findings have triggered the design of novel TRAIL-based cancer therapies. Yet, in recent years it has become apparent that human primary tumour cells are often resistant to TRAIL- mediated apoptosis. However, treatment with chemotherapeutics or other biological agents can sensitise these cells to TRAIL-induced cell death whilst leaving normal cells largely unaffected. Importantly, our laboratory has previously shown that TRAIL can act as a specific suppressor of metastasis in types of cancer in which detachment induces sensitisation of TRAIL-resistant tumour cells to TRAIL-induced apoptosis. Conversely however, our laboratory has also contributed to the discovery that human and murine colorectal cancer cell lines in which the Kirsten rat sarcoma viral oncogene homolog ue (KRas) is endogenously mutated were not only resistant to TRAIL - and CD95L -mediated apoptosis induction but tha t stimulation by these ligands also increased motility and membrane ruffling in these cells. Although TRAIL and CD95L have so far only been described to form one type of membrane -associated signalling complex, the so called death -inducing signalling comple x (DISC), which results in the activation of the initiator caspases 8 and 10, the increase in motility was not dependent on caspases or the formation of the DISC. Based on these findings, the aim of this thesis was to delineate the differences between DISC -dependent and DISC - independent non -apoptotic signals triggered by TRAIL receptors (TRAIL -Rs), and to specifically investigate the DISC -independent migration -inducing pathway downstream of TRAIL -Rs in cancer cells bearing endogenously mutated KRas. In this thesis, TRAIL -induced activation of NF -ĸB and S rc kinase phosphorylation is found to be DISC -dependent. Furthermore, it is demonstrated that TRAIL triggering of the DISC leads to a caspase -dependent, but Src -independent, loss of E -cadherin in epithelial cancer cell lines. Investigating the DISC -independent induction of migration it is demonstrated that KRas -mutated cancer cell lines derived from different tissues do not rely on exogenous stimulus for induction of migration but, instead, employ endogenous TRAIL for autocrine TRAIL/TRAIL -R2 signalling. Intriguingly, this ligand -receptor interaction is required for the entire gain of migratory capacity afforded to cancer cells by oncogenic mutation of endogenous KRas. Migration induced by autocrine TRAIL/TRAIL -R2 signalling does not require caspases and DISC formation, but instead depends on activation of the family of Rho -GTPases. Importantly, inhibition of the kinases ROCKI/II increases the migratory capacity of cancer cells that express wild- type KRas, and this increase in motility is entirely dependent on TRAIL-R2. This identifies naturally occurring ROCK suppression in KRas-mutated cells as the molecular switch that enables endogenous TRAIL and TRAIL-R2 to induce migration rather than apoptosis.