Specificity in signaling and modulators: the Homers

Abstract

The literature on signal transduction is very confusing. Besides the use of misnomers such as ‘crosstalk’, it can give the impression that all extracellular signals activate all cascades. In fact, in a given cell type at a given stage, only a few signals are active, and their effects are very specific. Among the various factors that confer this specificity, intracellular targeting of the proteins involved, and the cell-specific complement of ‘modulators’ of the cascade, are important. We call modulators proteins or other factors that modulate the level of activity of a cascade without belonging to its direct causal sequence. This is well illustrated by recent work from Bockaert's group on the modulator Homer proteins of the seven-transmembrane metabotropic glutamate receptors mGlu R1 and mGlu R5 [1,2].