Final Report Summary - REMITODED (Regulating the Mitochondrial Decision to Die)
During our research we developed a new way to detect mitochondrial permeabilisation making use of fluorescent fusion proteins. In this method, GFP re-localises onto RFP labelled mitochondria when they are permeabilised, this leads to mitochondria turning yellow – we can detect this by microscopy.
Using this approach we have found that sub-lethal stresses can engage mitochondrial permeabilisation in a minority of mitochondria, a process we call minority MOMP. Importantly minority MOMP does not lead to cell death but instead triggers DNA-damage. These data argue that apoptosis signalling is not always anti-cancer per se and instead may promote cancer in some circumstances – we are investigating this further.
Intense interest surrounds that targeting of proteins, called Bcl-2 proteins, that prevent mitochondrial permeabilisation. Indeed, recently developed drugs called BH3-mimetics target Bcl-2 proteins and in doing so, sensitise to apoptosis. The BH3-mimetic compound called Venetoclax has recently been clinically approved for the treatment of specific type of leukaemia. Unfortunately, the Bcl-2 protein family is relatively diverse such that no-one inhibitor can inhibit them all – this represents a source of resistance. The ability to screen for specific new inhibitors, as well as investigate resistance mechanisms is therefore key. Driven by this, and the desire to develop a clean-system to trigger mitochondrial apoptosis we developed a method we call “mito-priming” 2 . In this we co-express a pair of proteins, one a pro-apoptotic killer BH3- only protein the other an anti-apoptotic Bcl-2 protein. Cells expressing this combination are viable but highly sensitive to the addition of BH3-mimetic compounds. Following treatment, cells rapidly succumb to cell death. The specific combination of killer and protector can be altered. This method serves both as a powerful research tool as well as a means to rapidly screen for new and specific Bcl-2 targeting inhibitors.