01-08-2012, 03:02 PM
Growth Factors
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Growth factors are polypeptides that transmit signals to modulate cellular activities. Growth factors can either stimulate or inhibit cellular proliferation, differentiation, migration, adhesion and gene expression. There are several characteristic properties of growth factors. Many cell types can produce the same growth factor and the same growth factor can act on many cell types (pleitropism) with the same or different effects. Furthermore, different growth factors can share the same biological effect (redundancy). Growth factor effects are concentration dependent, often in a complex non-monotonic way.
Growth factors can influence the secretion and action of other growth factors (antagonizes or enhance). Growth factors are not stored as preformed molecules but their secretion is a brief self-limited event and their synthesis is initiated by new gene transcription transient transcriptional activation, and their mRNAs are unstable. There is transient synthesis, rapid release with activity controlled by post-transcriptional mechanisms such as proteolytic release of an active product from an inactive precursor. Most cellular responses to growth factors require new mRNAand protein synthesis.
Growth factors initiate their action by binding to specific receptors on the surface of target cells. Depending on the proximity of their site of synthesis to their site of action, growth factors have been classified as endocrine (target cell is distant),paracrine (target cell is nearby), autocrine (target cell is the same cell that secreted the growth factor), juxtracrine (targetcell is apposed to growth factor/receptor complex) or intracrine(growth factor/receptor complex is internalized). Hundreds of growth factors have been identified, characterized and, based on structural homologies, grouped into at least twenty families and super-families.
Growth factors usually exist as inactive or partially active precursors that require proteolytic activation, and may need to bind to matrix molecules for activity or stabilization. Growth factors have short biological half-lives. Platelet-derived growth factor (PDGF), isolated from platelets, cannot be detected in the circulation and has a half life of less than 2minutes when injected intravenously.
[attachment=29897]
Growth factors are polypeptides that transmit signals to modulate cellular activities. Growth factors can either stimulate or inhibit cellular proliferation, differentiation, migration, adhesion and gene expression. There are several characteristic properties of growth factors. Many cell types can produce the same growth factor and the same growth factor can act on many cell types (pleitropism) with the same or different effects. Furthermore, different growth factors can share the same biological effect (redundancy). Growth factor effects are concentration dependent, often in a complex non-monotonic way.
Growth factors can influence the secretion and action of other growth factors (antagonizes or enhance). Growth factors are not stored as preformed molecules but their secretion is a brief self-limited event and their synthesis is initiated by new gene transcription transient transcriptional activation, and their mRNAs are unstable. There is transient synthesis, rapid release with activity controlled by post-transcriptional mechanisms such as proteolytic release of an active product from an inactive precursor. Most cellular responses to growth factors require new mRNAand protein synthesis.
Growth factors initiate their action by binding to specific receptors on the surface of target cells. Depending on the proximity of their site of synthesis to their site of action, growth factors have been classified as endocrine (target cell is distant),paracrine (target cell is nearby), autocrine (target cell is the same cell that secreted the growth factor), juxtracrine (targetcell is apposed to growth factor/receptor complex) or intracrine(growth factor/receptor complex is internalized). Hundreds of growth factors have been identified, characterized and, based on structural homologies, grouped into at least twenty families and super-families.
Growth factors usually exist as inactive or partially active precursors that require proteolytic activation, and may need to bind to matrix molecules for activity or stabilization. Growth factors have short biological half-lives. Platelet-derived growth factor (PDGF), isolated from platelets, cannot be detected in the circulation and has a half life of less than 2minutes when injected intravenously.