Final answer:
Growth factors are proteins that stimulate cell proliferation and differentiation, and PDGF is one such factor that activates the MAP kinase pathway, leading to fibroblast division.
Step-by-step explanation:
Growth factors are proteins that bind to receptors on the cell surface, with the primary result of activating cellular proliferation and/or differentiation. They play a critical role in maintaining normal tissue homeostasis and in promoting wound healing. Many growth factors are quite versatile, stimulating cellular division in numerous different cell types; while others are specific to a particular cell-type.
One well-known growth factor is platelet-derived growth factor (PDGF), which is known to stimulate cell proliferation, migration and adhesion, angiogenesis, and cell division. PDGF achieves these effects by binding to its receptor, PDGF receptor (PDGFR), which is a receptor tyrosine kinase. When PDGF binds to PDGFR, it leads to the activation of the receptor's tyrosine kinase enzymatic activity, which in turn phosphorylates tyrosine residues on itself (autophosphorylation) and on particular downstream proteins. These events trigger a cascade of downstream signaling events that culminate in DNA synthesis and cell division. Specifically, the MAP kinase pathway is a major downstream pathway activated by PDGF, leading to an increase in cell growth and division.