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 kinasedependent "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.The insulin superfamily family of peptide hormones, consisting of insulin, insulin-like growth factor type 1 (IGF-1), 2 insu- Although all members of the insulin superfamily share structural homology, their signals are transmitted through binding to a number of structurally dissimilar receptors. IGF-1 and IGF-2 are single chain polypeptides, with sequences 62% identical to that of proinsulin. Both contain a short D domain that is not present in insulin, and unlike insulin, they do not undergo post-translational proteolysis, such that the A and B domains remain linked in the mature peptide by a C domain analogous to the C peptide of insulin (1, 2). IGF-1 and IGF-2 bind two structurally distinct types of receptor, referred to as the IGF-1 and IGF-2/mannose-6-phosphate (M6P) receptors. The IGF-1 receptor is heterotetrameric transmembrane receptor tyrosine kinase that is structurally and functionally related to the insulin receptor. It is composed of two extracellular ␣-subunits that contain the ligand-binding domain and two transmembrane ␤-subunits that possess intrinsic ligand-stimulated tyrosine kinase activity (3,4). Ligand binding to the ␣-subunit activates the ␤-subunit tyrosine kinase, resulting in tyrosine phosphorylation of intracellular adapter proteins, such as insulin receptor substrate (IRS)-1 and IRS-2, Shc, and...

Musashi1 Modulates Mammary Progenitor Cell Expansion through Proliferin-Mediated Activation of the Wnt and Notch Pathways

“…PLF1 is a ligand for the Gi proteincoupled IGF2R (25,36), which mediates prolactin-induced alveolar development in the mammary gland through activation of ERK and Jak2 (6,27). Receptor activation by PLF1 activates ERK (20,25) and transcription factor AP-1 (63) and is blocked by pertussis toxin (20,25), which catalyzes ADPribosylation of the Gi␣ subunit to prevent its interaction with cell membrane receptors (8). This mechanism is consistent with the inhibitory effect of pertussis toxin on PLF1-mediated ERK activation by COMMA/Msi-conditioned medium, as well as inhibition of ERK activation by PLF1 depletion from COMMA/Msi1-conditioned medium.…”

Insulin-Like Growth Factor-I Regulation of Immune Function: A Potential Therapeutic Target in Autoimmune Diseases?

“…Two distinct binding sites accommodate IGF-II and mannose-6-phosphate (Braulke, 1999). Type I and II receptors may mediate Erk 1/2 phosphorylation provoked by IGF-I and IGF-II, respectively (El-Shewy et al, 2007). By knocking down type I IGF-IR, the activation of Erk p42/44 elicited by IGF-I is substantially abrogated, whereas that of IGF-II persists.…”

“…In contrast, interfering with the type II receptor had little effect on IGF-I signaling to Erk, whereas the activities of IGF-II on the activation of this kinase were reduced. Thus, type I and II receptors might function independently with regard to Erk activation, and IGF-II might exert at least some of its actions through the type II receptor (El-Shewy et al, 2007). The signaling initiated through IGF-IR begins with a conformational change provoked by receptor ligation and involves a number of well used pathways in tissues in which IGF-I exerts its actions.…”

Cooperative Repression of Insulin-Like Growth Factor Type 2 Receptor Translation by MicroRNA 195 and RNA-Binding Protein CUGBP1

“…Several studies have also shown that IGF2R is expressed in many tissues, including the gut epithelium, and its expression is known to be altered in response to stressful environments such as after SBR and during the inhibition of intestinal mucosal growth (1, 2). Interestingly, the levels of mucosal miR-195 and CUGBP1 decrease in the small intestine after SBR, along with stimulation of mucosal regeneration, but their levels increase dramatically after food starvation or polyamine depletion, which is associated with an inhibition of intestinal mucosal growth (18,25,44). Moreover, IGF2R also regulates cellular processes and functions by (i) activating IGF2 signaling (42,45); (ii) promoting the cellular uptake and degradation of peptides such as proliferin, leukemia inhibitory factor, and transforming growth factor beta (TGF-␤) (4, 6); and (iii) regulating extracellular signal-regulated kinase 1/extracellular signal-regulated kinase 2 (ERK1/2) activity (32).…”

“…Biotin-labeled miRNA-195 was custom-made by Dharmacon (Lafayette, CO). The IEC-6 cell line (normal rat intestinal crypt cells) was purchased from the American Type Culture Collection (ATCC) at passage 13 and was maintained under standard culture conditions as described previously (44,46). Plasmid construction.…”