 In conditions of prolonged stress, the goal of the UPR changes from being one that promotes cellular survival to one that commits the cell to a pathway of apoptosis.Proteins downstream of all 3 UPR receptor pathways have been identified as having pro-apoptotic roles.However, the point at which the 'apoptotic switch' is activated has not yet been determined, but it is a logical consideration that this should be beyond a certain time period in which resolution of the stress has not been achieved.