Growth Factors, Receptors, and Cancer Chapter 5 PDF

Growth Factors, Receptors, and Cancer Chapter 5  Why do cells communicate? What did you no;ce about the ;ssue response a=er injury? What were your observa;ons as to how cells interacted? – Groups of cells were involved in the response (i.e. red blood cells, platelets, fibroblas...

Growth Factors, Receptors, and Cancer Chapter 5  Why do cells communicate? What did you no;ce about the ;ssue response a=er injury? What were your observa;ons as to how cells interacted? – Groups of cells were involved in the response (i.e. red blood cells, platelets, fibroblasts) – The cells needed to “talk” to each other in order to repair the wound!  How do cells communicate? The extra- and intra-cellular spaces are separated by the lipid bilayer. The plasma membrane is a barrier that blocks the movement of almost all molecules. – How have cells managed to solve the problem of passing signals through the membrane that is impermeable? – How can inside the cell “know” what is going on in the extracellular space? Normal cells control each other’s lives How can we determine if cells depend on each other to make a “decision?” Experiment: – Cells extracted from ;ssue and placed in Petri dish – Liquid medium contains all nutrients but not sufficient to induce prolifera;on… – Thus, serum is required and added to culture to cause cells to proliferate. – Why do you think serum would cause this (serum is naturally present and produced when blood is allowed to clot)? GROWTH FACTORS! – What would happen if serum was not added to cel culture? Normal cells control each other’s lives Where would such signals come from in the process of wound healing? Oncogene-encoded proteins: responsible for enabling cells to sense the presence of GFs in their surroundings, to convey this informa;on within the cell, and to process the informa;on Oncoproteins are able to “delude” a cell to think that it has encountered GFs in its surroundings – What do you think would be the consequence of this? Let’s first understand how signaling works in normal cells…  Normal cell signaling Key features of cellular signaling: – Specificity conferred by ligand-protein and protein-protein interac;ons – Signal amplifica;on by ac;vated enzymes – Capacity for pathway convergence (mul;ple signals affec;ng the same messenger) and/or divergence (mul;ple pathways developing form a single component) – Signal termina;on by decrease in concentra;on of ac;va;ng ligand along with de-phosphoryla;on and/or receptor internaliza;on  Normal cell signaling Four basic mechanisms used to transduce signals – Enzyme-coupled receptors – G-protein coupled receptors (GPCRs) – Ligand-gated ion channel receptors – Receptors within cell to respond to steroid hormones  Normal cell signaling Enzyme-coupled receptors – Receptor tyrosine kinases (RTKs)?  Normal cell signaling Receptor tyrosine kinases (RTKs) – The receptors Ectodomain Intracellular domain  Normal cell signaling Receptor tyrosine kinases (RTKs) – The intracellular proteins: adaptors and enzymes Adaptor proteins interact with other proteins to mediate the forma;on of protein complexes or to draw proteins to specific loca;ons ( ~molecular Velcro) Enzymes, most commonly phosphatases or kinases, may also func;on as adaptors These proteins have two major types of domains responsible for protein binding to phosphorylated tyrosines: – Src homology 2 (SH2) – Phosphotyrosine binding (PTB) Normal cell signaling Fig. 11-7c Signaling Ligand-binding site molecule (ligand) Signaling molecule α Helix Tyr Tyr Tyr Tyr Tyr Tyr Tyrosines Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Receptor tyrosine kinase proteins Dimer CYTOPLASM 1 2 AcDvated relay proteins Cellular Tyr Tyr P Tyr Tyr P Tyr Tyr P response 1 P Tyr Tyr P Tyr Tyr P P Tyr Tyr P Tyr Tyr P Tyr Tyr P P Tyr Tyr P Cellular 6 ATP 6 ADP response 2 AcDvated tyrosine Fully acDvated receptor kinase regions tyrosine kinase InacDve relay proteins 3 4  Normal cell signaling Receptor tyrosine kinases (RTKs) – EGFR, PDGFR, FGFR, and IR Non-Receptor Tyrosine Kinases (NRTKs) – SRC, ABL, FAK, and Janus kinase (JAK) Normal cell signaling EGF receptor func;ons as tyrosine kinase Structure and func;on of EGF and EGF-R EGF receptor func;ons as tyrosine kinase Structure and func;on of EGF and EGF-R EGF receptor func;ons as tyrosine kinase Structure and func;on of EGF and EGF-R PDGF receptor func;ons as tyrosine kinase Structure and func;on of PDGF and PDGF-R PDGF receptor func;ons as tyrosine kinase Structure and func;on of PDGF and PDGF-R GFs and RTKs o=en involved in tumor pathogenesis Depending on growth factor binding to its receptor mul;ple responses may take place such as, cell growth, division, cell shape, cell survival, and mo;lity.  The Src protein: a tyrosine kinase What is Src? – Cell adhesion, growth, movement, and differen;a;on – Associates with membranes: plasma membrane, perinuclear membrane, and endosomal membrane – At plasma membrane, Src transduces signals from receptors to internal pathways to relay the signal to the nucleus, cytoskeleton, or other cellular components – May act through growth factor receptors to affect cell growth and prolifera;on The Src protein: a tyrosine kinase The Src protein: a tyrosine kinase The Src protein: a tyrosine kinase Altered GF receptor can func;on as an oncoprotein In 1984, sequence of EGF receptor was found to be closely related to oncogene erbB – erbB oncogene was first discovered in the genome of avian erythroblastosis virus (AEV) – In avian, the erbB oncogene altered by AEV induces a leukemia of the red blood cell precursors-- erythromleukemia – ErbB is a closely related type of EGFR – Normally, in avian, ErbB protein “senses” the presence of a GF in its surroundings, but the AEV coverts the gene into a potent retrovirus-encoded oncoprotein! – The modified ErbB oncoprotein was found to lack sequences in the N-terminal ectodomain… Altered GF receptor can func;on as an oncoprotein Other tumor types were found to have this common truncated region of EGF receptors: – Glioblastomas – Breast cancer Causes for deregula;on of receptor firing... Altered GF receptor can func;on as an oncoprotein Altered GF receptor can func;on as an oncoprotein Altered GF receptor can func;on as an oncoprotein Altered GF receptor can func;on as an oncoprotein GF gene can become an oncogene: sis In 1983, the sequence of PDGF was found similar to that of an oncoprotein encoded by the v-sis oncogene of simian sarcoma virus. – When this virus infects a cell, its sis oncogene causes the infected cell to release large amounts of PDGF-like Sis protein in extracellular space – These Sis proteins then bind to PDGFR on the same cell resul;ng in strong, constant ac;va;on of PDGFR signaling – Only a specific type of cell(s) would be transformed by this virus (e.g. fibroblasts and not epithelial cells) GF gene can become an oncogene: sis  Transphosphoryla;on of RTKs Ligands and receptors interact to promote signals within the cell, but the ques;on s;ll remains: – How do growth factor receptors use their tyrosine kinase domains to relay signals upon ligand binding? A=er numerous studies, a simple model developed… Transphosphoryla;on of RTKs  Transphosphoryla;on of RTKs How would overexpression of receptors cause over-ac;va;on of signaling pathway in absence of ligand?  Transphosphoryla;on of RTKs Gene fusions can also cause cons;tu;vely ac;ve dimerized receptors  Transphosphoryla;on of RTKs Gene fusions can also cause cons;tu;vely ac;ve dimerized receptors Other receptors and signaling pathways Other signaling factors – Cytokine receptors interac;ng with Janus kinase (Jaks): controls development of hematopoie;c cell types; kinase that interacts with cytoplasmic domains of receptors for erythropoie;n (EPO) and thrombopoie;n (TPO) Other receptors and signaling pathways Other signaling factors – Transforming growth factor-β (TGF-β) that bind to heterodimer receptors Other receptors and signaling pathways Other signaling factors – Notch receptor signaling Other receptors and signaling pathways Other signaling factors – Patched receptor signaling Other receptors and signaling pathways Other signaling factors – Wnt signaling: canonical Other receptors and signaling pathways Other signaling factors – Wnt signaling: non-canonical  Ras protein func;ons as a G protein Ras proteins were iden;fied to be a component of the GF signaling machinary – ras oncogene found to cause the same outcome as cells that were transformed by either src, erbB, or sis – This suggested that they may exist in the same signaling pathway or the signaling pathways converge on the same target Ras found to bind and cleave guanosine nucleo;des, similar to G proteins: – Binds GDP in its inac;ve state – Releases GDP once ac;vated by a factor upstream – Replaces GDB with GTP – Shi=s into an ac;ve, signal-eminng state – Cleaves its own GTP a=er short period of ;me and rever;ng back to inac;ve state Ras protein func;ons as a G protein  Ras protein func;ons as a G protein Ras oncoprotein, encoded by Harvey sarcoma virus, exists as a result of point-muta;on on ras oncogene – Ras oncoprotein can bind GTP but loses GTPase ac;vity (GTP fails to revert back to GDP) – This causes Ras oncoprotein to be in an ac;ve state for a prolonged (probably indefinite) period of ;me – Only point muta;ons at the 12th, 13th, and 61st amino acid residues have been shown to deac;vate Ras’ GTPase ac;vity Other receptors and signaling pathways Nuclear receptors – Some ligands are hydrophobic and able to pass through plasma membrane – These ligands will be able to get to the nucleus and either bind or ac;vated nuclear DNA-proteins that act as transcrip;on factors – Receptors commonly found to bind steroid hormones such as, estrogen, progesterone, and androgens – Commonly found in human malignancies such as breast, ovarian, and prostate carcinomas Other receptors and signaling pathways Nuclear receptors  Chapter 5 Learning Outcomes Understand the general pathway of cell signaling, specifically, RTKs; in what ways can deregula;on of this pathway lead to cancer? Understand the general structure and func;on of the two examples of RTK pathways: EGF-R and PDGF-R; think of ways different muta;ons can result in fatal consequences in the pathway Understand the structure and func;on of Src What is the difference between oncoproteins and oncogenes? Know and understand the examples provided. Understand how a faulty ligand and receptor (including its kinase domain) result in tumorgensis Understand and know the other signaling pathways discussed: cytokine receptors, TGF-beta, Patched, Notch, Wnt, and nuclear receptors Understand and know the func;on of Ras (a G-protein). What is a G-protein? Primary func;on of G-protein-coupled receptors?