title: Feedback inhibition by RALT controls signal output by the ErbB network.
abstract: The ErbB-2 interacting protein receptor-associated late transducer (RALT) was previously identified as a feedback inhibitor of ErbB-2 mitogenic signals. We now report that RALT binds to ligand-activated epidermal growth factor receptor (EGFR), ErbB-4 and ErbB-2.ErbB-3 dimers. When ectopically expressed in 32D cells reconstituted with the above ErbB receptor tyrosine kinases (RTKs) RALT behaved as a pan-ErbB inhibitor. Importantly, when tested in either cell proliferation assays or biochemical experiments measuring activation of ERK and AKT, RALT affected the signalling activity of distinct ErbB dimers with different relative potencies. RALT deltaEBR, a mutant unable to bind to ErbB RTKs, did not inhibit ErbB-dependent activation of ERK and AKT, consistent with RALT exerting its suppressive activity towards these pathways at a receptor-proximal level. Remarkably, RALT deltaEBR retained the ability to suppress largely the proliferative activity of ErbB-2.ErbB-3 dimers over a wide range of ligand concentrations, indicating that RALT can intercept ErbB-2.ErbB-3 mitogenic signals also at a receptor-distal level. A suppressive function of RALT deltaEBR towards the mitogenic activity of EGFR and ErbB-4 was detected at low levels of receptor occupancy, but was completely overcome by saturating concentrations of ligand. We propose that quantitative and qualitative aspects of RALT signalling concur in defining identity, strength and duration of signals generated by the ErbB network.
authors.affiliation: Regina Elena Cancer Institute, Via Delle Messi d'Oro, 156, Rome 00158, Italy.
authors.forename: Sergio
authors.initials: S
authors.lastname: Anastasi
authors.forename: Loredana
authors.initials: L
authors.lastname: Fiorentino
authors.forename: Monia
authors.initials: M
authors.lastname: Fiorini
authors.forename: Rocco
authors.initials: R
authors.lastname: Fraioli
authors.forename: Gianluca
authors.initials: G
authors.lastname: Sala
authors.forename: L
authors.initials: L
authors.lastname: Castellani
authors.forename: Stefano
authors.initials: S
authors.lastname: Alemà
authors.forename: Maurizio
authors.initials: M
authors.lastname: Alimandi
authors.forename: Oreste
authors.initials: O
authors.lastname: Segatto
mesh_terms: D016475:3T3 Cells; D000818:Animals; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism*; D002455:Cell Division; D002460:Cell Line; D004247:DNA / Q000378:metabolism; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066246:ErbB Receptors / Q000378:metabolism*; D005982:Glutathione Transferase / Q000378:metabolism; D007120:Immunochemistry; D007150:Immunohistochemistry; D047908:Intracellular Signaling Peptides and Proteins; D008024:Ligands; D051379:Mice; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008957:Models, Genetic; D009154:Mutation; D010982:Platelet-Derived Growth Factor / Q000378:metabolism; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D020794:Receptor Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism*; D066247:Receptor, ErbB-4; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction; D014162:Transfection
chemical_list: D002352:Carrier Proteins; D004247:DNA; D004791:Enzyme Inhibitors; D066246:ErbB Receptors; D005982:Glutathione Transferase; D047908:Intracellular Signaling Peptides and Proteins; D008024:Ligands; D020928:Mitogen-Activated Protein Kinases; D010982:Platelet-Derived Growth Factor; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D020794:Receptor Protein-Tyrosine Kinases; D018719:Erb-b2 Receptor Tyrosine Kinases; D066247:Receptor, ErbB-4; D011993:Recombinant Fusion Proteins; C475819:Errfi1 protein, mouse; C587690:Erbb4 protein, mouse