Cell function intracellular signaling

Holmes, K., Roberts, O.L., Thomas, A.M., Cross, M.J. Vascular endothehal growth factor receptor-2 structure, function, intracellular signalling and therapeutic inhibition. Cell. Signal. 19(10), 2003-2012 (2007)... 

Three phases of receptor-mediated signaling can be identified 178 Four distinct molecular mechanisms that link agonist occupancy of cell-surface receptors to functional responses have been identified 178 Cross-talk can occur between intracellular signaling pathways 179 Signaling molecules can activate gene transcription 181 Nitric oxide acts as an intercellular signaling molecule in the central nervous system 181... 

Cellular signals converge at the level of protein phosphorylation pathways. Individual intracellular messenger pathways, such as cAMP, Ca2+ and MAPK pathways, are often drawn as distinct biochemical cascades that operate in parallel in the control of cell function. While this is useful for didactic purposes, it is now well established that these various pathways function as complex webs, with virtually every conceivable type of interaction seen among them. 

Another reason for complexity of cell-activation mechanisms resides in the end response of neutrophils - that is, the delivery of cytotoxic products. Whilst these products are highly lethal towards pathogens, they can also attack and destroy host tissues, and this can have deleterious effects on tissue function. Complex intracellular signalling mechanisms to activate these cytotoxic pathways also guards against non-specific activation, which could lead to host tissue damage. 

---