Crosstalk and specificity in signalling - Are we crosstalking ourselves into general confusion?

The numerous examples of "crosstalk" between signal transduction pathways r eported in the biochemical literature seem to imply a general common respon se of cells to different stimuli, even when these stimuli act initially on different cascades. This contradicts our knowledge of the specificity of ac tion of extracellular signals in different cell types. Th is discrepancy is explained by the restricted occurrence of crosstalks in any cell type and by several categories of cell specificity mechanisms. for instance, the spe cific qualitative and quantitative expression of the various subtypes of si gnal transduction proteins, the combinatorial control of the cascades with specific sets of regulatory factors and the compartmentation of signal tran sduction cascades or their elements. (C) 2001 Elsevier Science Inc. All rig hts reserved.