L4: Growth factor receptors Flashcards
what are growth factors
Cells signal to on eanother in various ways
Two major ways of signalling. 2 cells touching as one cell expresses ligand, other-receptor so localised signalling between signalling and target cell. Other, paracrine signalling. Local signalling but signal in cell expressing ligand and target cells expressing receptor. Signalling cell expresses ligand not receptor vise versa. So c ontrol in paracrine signalling over who is talking to who. Growth factors are one of the key ligands beng secreted by cells in that paracrine signalling in tissues.
What are
growth factors?
Proteins, generally protein chains, polypeptides/
Oncogenes alter gf/gf receptors as gf signalling drives key cellularp processes like cellular dfifferentiation, movement, cell division.
In normal: drives a huge amount of embyrogenesis. In adult tissue- tissue repair, cell turnover homeostasis.
Growth factors are grouped into families based on sequence homology and receptor interaction.
PDGF
Platelet-derived growth factor (PDGF)
PDGF ONE OF THE FIRST GF TO BE DISCOVERED. RESEARCHERS WERE TRYING TO CULTURE CELLS IN VITRO. But could not keep the cells alive. Started to test whether adding serum could help. Culturing the cells. Tested plasma serum- no platelets and whole blood serum- platelets and platlet secretions present. Plasma serum= no help. Blood serum could elavate proliferation of the cells. Suggested there were factors that could promot ethe cells to stay alive and proliferate.
4 diff isoforms of pdgf: PDGF-A, B,C,D. Expressed by diff tissues *table on slide 9. Restricted expression of pdgf-d suggests specific functions/ driving specific processes in a smaller subset of cells.
All the pdgf polypeptide chains have a cpmmmon reigion called the gf somain- 100 aa which contains conserved cysteine residues. Across all of the isoforms.
Disulphide bonds form between the cysteine residues. Isoforms form as homo or heterodimers . the four pdgf chains assemble into disulphide bonded dimers via homo or heterodimerization and there are 5 known isiofmr.s no heterodimers for pdgf-c and pdgf-d chains have been described.
biological activities of PDGF
Parricularly active in vasculature. In terms of contrstriction and relazation.
Potent stimulator of wound healing, triggers chemotaxis of fibroblasts, white blood cells, smooth muscle cells,
Stimulatres prod of matrix: molecules inovolved in the healing process
Embroynic development: kidney, bv, lung central nervous system.
Adult blood vessels – constriction and relaxation effects
Wound healing – a) stimulates the directed migration (chemotaxis) of fibroblasts,
white blood cells and smooth
muscle cells
b) stimulates production of matrix
molecules involved in the healing process
Very powerful signalling molecules. Response by interaction of growth factor with receptor. Can elicit very large cellular responses through their signalling pathways.
EGFR superfamily
These molecules collectively comprise the EGF super family
Epidermal growth factor (EGF)
Transforming growth factor-α (TGF-α)
Amphiregulin (AR)
Heparin binding-EGF (HB-EGF)
Epigen
Epiregulin (EPR)
Betacellulin (BTC)
Neurogulins 1-4 (NRG 1-4)
Terato carcinoma derived growth factor
EGF: The explanation was that the salivary gland extract contained a growth factor.
The team termed this substance epidermal growth factor (EGF) because it could stimulate the proliferation of epithelial cells in skin and cornea.
We now know that salivary gland cells produce and secrete EGF as do cells at the site of a wound, and cells during embryonic development.
amino acid sequence alignment of the conserved egf motif
Highly conserved cysteine residues that gen loops that form disulphide bonds. This 3d structure of the growth factor delivers specificity between gf and its receptor.
Each member of the EGF super family contains at least one characteristic EGF motif.
An EGF motif contains 6 cysteine residues that generate 3 peptide loops through the formation of disulphide bonds
making active egf
EGF is directed to the plasma membrane via the signal sequence
The proteins are then inserted into the plasma membrane. Have a signal that directs the protein after its been made to the plasma membrane.
The transmembrane protein is then cleaved by cell surface proteases. Cleaveage event by proteases that are secreted outside of the cell. Doesnt actually get activated until out sticking out of membrane. The bit containing egf motif is the functional signalling ligand that binds to the receptor.
The cleaved protein is now a mature growth factor that can bind to the receptor on the target cell.
biological activities of egf
EGF is known to be involved in wound healing responses promoting the regeneration of the epidermis
EGF is a strong chemoattractant (attracts cells) for fibroblasts and epithelial cells
In vivo EGF is known to be involved in embryonic development and stimulate the proliferation of embryonic cells
Cells in wound heling respond by proliferating and migrating to fill that gap and that response is mediated by egf and its receptor?
biosynthesis of tgf-beta
Mature tgf-beta actually active, signalling bit. Fused to LAP (latency-associated protein). signal sequence sends it into golgi, in golgi disulphide bonds gen homodimer but still fused to lap. Secreted out of cell into ecm.
Still inactive at this point. That lap is bound to latenttgf-beta binding protein with ecm binding sites so sticks ot ecm outside of the cell. All of this is nw outside of cell held in ecm.
One way active tgf-beta released is through activation of plasmin in ecm. Plasmin can cleave tgf-beta and release the active part that can bind to tgf-beta receptor.
LAP contains RGD sequence. Bind to proteins called integrins which are expressed on surface of cells.
Those integrins bind to ecm proteins. Adherence. Sequences they recognise in ecm proteins are rgd sequence. Lap is basically mimicing an ecm protein. Now know alot of activation of tgf-beta is by: as cell moves or shift within tissue the integrin pulls on the lap and mechanical release of tgf-beta. Requires mechanica activity.
tgf-beta signalling effects + diseases
epithelial and endothelial cells:phenotypic transitions, restricted proliferation, balanced differentiation, paracrine secretomes
fibroblasts, bone, connective tissue cells: proliferation, activiation, ecm production, migration
innate and adaptive immune cells: resitricted proliferation, restricted effector functions, inflammation suppression
neural cells: migration, survival
diseases: developmental: connective, bone, cardiovascular tissues: aortic aneurysms, craniofacial anomalies, brittle skin
fibrosis- lung, liver, kidney
cancer
how do gf interact with their receptors
How RTKs work (receptor tyrosine kinase)
Binding of the ligand promotes dimerisation of
the receptor either because the ligand is a dimer or one ligand binds both monomers
Dimerisation allows trans-phosphorylation and or autophosphorylation of the catalytic domains which induces activation.
The receptor can then phosphorylate other intracellular substrates.
Proteins which contain a Src homology 2
(SH2) domain bind to tyrosine phosphorylated residues.
SH2 containing proteins are recruited to the
phosphorylated receptor and form one of the first steps in the signal transduction process
Proteins containing PTB (phosphotyrosine binding domains) can also be recruited to/ dock with the phosphorylated receptor
Ligand in this case is growth factor
Binds to receptor
Dimerisation in plasma m
Phosphorylation event in tail of receptor danglign down in cytoplasm.
Inside of receptor dangling down into cytoplasm inside cell outside ready to recieve ligand
Either trans or autophosphorylation
In tyrosine kinase receptor phosphorylated trysoine. This docks to sh2 domain. Sh2 domain recognises phosphorylated tyrosine so now first step in intracellular signalling pathway. How a gf sitting on outside of cell starts signal pathway inside cell by causing recruitment of sh2.?
Receptors like gf also form these 3d diff structures so very good binding specificity.
Regulated
