Different cell types vary greatly in the ratio of PDGF isoforms and PDGFRs expressed.

Different external stimuli such as inflammation, embryonic development or differentiation modulate cellular receptor expression allowing binding of some PDGFs but not others.

Tyrosine phosphorylation sites in growth factor receptors serve two major purposes—to control the state of activity of the kinase and to create binding sites for downstream signal transduction molecules, which in many cases also are substrates for the kinase.

The specificity of these interactions appears to be very high, since mutant receptors carrying phenylalanine residues in one or several of the different phosphorylation sites generally lack the capacity to bind the targeted signal transduction molecule.

Activated MAPK phosphorylates a variety of cytoplasmic substrates, as well as transcription factors, when translocated into the nucleus.

MAPK family members have been found to regulate various biological functions by phosphorylation of particular target molecules (such as transcription factors, other kinases etc.)

Similarly to other SH2 domain-containing proteins, PI-3 kinase forms a complex with PY sites on activated receptors.

The major biological functions of Akt activation can be classified into three categories – survival, proliferation and cell growth.

Ca 2+ then binds to calmodulin, which subsequently activates a family of calmodulindependent protein kinases (CamKs).

The second messengers generated by PtdIns(4,5)P2 hydrolysis stimulate a variety of intracellular processes such as proliferation, angiogenesis, cell motility.