Deadly Insulin Receptors

摘要

A new way of signaling has been detected for one of the most highly studied hormone receptors: the insulin and the related insulin-like growth factor receptors. These receptors, when activated by ligand binding, initiate signaling mechanisms that protect cells from apoptosis and favor cell survival. Thus Boucher et at. were surprised to find that in mouse brown adipose tissue cell lines, the loss of both receptors in the same cell actually made cells resistant to stimuli that normally promote apoptosis. Ligand deprivation of receptor-expressing cells, however, did not cause this effect. This suggests that the receptors, in the absence of hormone binding, are not "turned off" but rather appear to be producing a signal that is permissive for cell death. The receptors thus join a family known as "dependence receptors" because in their presence, a cell is addicted to the presence of growth factor in order to prevent the proapoptotic effect of the unliganded receptor.