title: The insulin-like growth factor type 1 and insulin-like growth factor type 2/mannose-6-phosphate receptors independently regulate ERK1/2 activity in HEK293 cells.
abstract: Insulin-like growth factor types 1 and 2 (IGF-1; IGF-2) and insulin-like peptides are all members of the insulin superfamily of peptide hormones but bind to several distinct classes of membrane receptor. Like the insulin receptor, the IGF-1 receptor is a heterotetrameric receptor tyrosine kinase, whereas the IGF-2/ mannose 6-phosphate receptor is a single transmembrane domain protein that is thought to function primarily as clearance receptors. We recently reported that IGF-1 and IGF-2 stimulate the ERK1/2 cascade by triggering sphingosine kinase-dependent "transactivation" of G protein-coupled sphingosine-1-phosphate receptors. To determine which IGF receptors mediate this effect, we tested seven insulin family peptides, IGF-1, IGF-2, insulin, and insulin-like peptides 3, 4, 6, and 7, for the ability to activate ERK1/2 in HEK293 cells. Only IGF-1 and IGF-2 potently activated ERK1/2. Although IGF-2 was predictably less potent than IGF-1 in activating the IGF-1 receptor, they were equipotent stimulators of ERK1/2. Knockdown of IGF-1 receptor expression by RNA interference reduced the IGF-1 response to a greater extent than the IGF-2 response, suggesting that IGF-2 did not signal exclusively via the IGF-1 receptor. In contrast, IGF-2 receptor knockdown markedly reduced IGF-2-stimulated ERK1/2 phosphorylation, with no effect on the IGF-1 response. As observed previously, both the IGF-1 and the IGF-2 responses were sensitive to pertussis toxin and the sphingosine kinase inhibitor, dimethylsphingosine. These data indicate that endogenous IGF-1 and IGF-2 receptors can independently initiate ERK1/2 signaling and point to a potential physiologic role for IGF-2 receptors in the cellular response to IGF-2.
authors.affiliation: Department of Medicine, Medical University of South Carolina, Charleston, South Carolina 29425, USA.
authors.forename: Hesham M
authors.initials: HM
authors.lastname: El-Shewy
authors.forename: Mi-Hye
authors.initials: MH
authors.lastname: Lee
authors.forename: Lina M
authors.initials: LM
authors.lastname: Obeid
authors.forename: Ayad A
authors.initials: AA
authors.lastname: Jaffa
authors.forename: Louis M
authors.initials: LM
authors.lastname: Luttrell
mesh_terms: D002460:Cell Line; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D006801:Humans; D007328:Insulin / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D007335:Insulin-Like Growth Factor II; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology*; D019950:Mitogen-Activated Protein Kinase 1 / Q000235:genetics / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism; D011506:Proteins / Q000378:metabolism* / Q000494:pharmacology; D034622:RNA Interference; D017526:Receptor, IGF Type 1 / Q000235:genetics / Q000378:metabolism; D017527:Receptor, IGF Type 2 / Q000235:genetics / Q000378:metabolism*; D049349:Receptors, Lysosphingolipid / Q000235:genetics / Q000378:metabolism; D000099157:Sphingosine Kinase
chemical_list: D007328:Insulin; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D017853:Phosphotransferases (Alcohol Group Acceptor); D011506:Proteins; D017526:Receptor, IGF Type 1; D017527:Receptor, IGF Type 2; D049349:Receptors, Lysosphingolipid; D000099157:Sphingosine Kinase; C035170:IGF2 protein, human