ABSTRACT
BACKGROUND: The insulin-like growth factor (IGF) receptor (IGF1R) is essential for normal development and growth. IGF1R mutations cause IGF-1 resistance resulting in intrauterine and postnatal growth failure. The phenotypic spectrum related to IGF1R mutations remains to be fully understood. METHODS: Auxological and endocrinological data of a patient identified previously were assessed. The patient's fibroblasts were studied to characterize the IGF1R deletion, mRNA fate, protein expression and signalling capabilities. RESULTS: The boy, who carries a heterozygous IGF1R exon 6 deletion caused by Alu element-mediated recombination and a heterozygous SHOX variant (p.Met240Ile), was born appropriate for gestational age but developed proportionate short stature postnatally. IGF-1 levels were low-normal. None of the stigmata associated with SHOX deficiency or sporadically observed in IGF1R mutation carriers were present. Nonsense-mediated mRNA decay led to a substantial decline of IGF1R dosage and IGF-1-dependent receptor autophosphorylation but not impaired downstream signalling. CONCLUSION: We present the first detailed report of an intragenic IGF1R deletion identified in a patient who, apart from short stature, deviates from all established markers that qualify a growth-retarded child for IGF1R analysis. Although such children will usually escape routine clinical mutation screenings, they can contribute to the understanding of factors and mechanisms that cooperate with the IGF1R.
Subject(s)
Alu Elements/physiology , Dwarfism/genetics , Receptor, IGF Type 1/genetics , Recombination, Genetic , Body Height , Child , Growth Charts , Haploinsufficiency , Homeodomain Proteins/genetics , Humans , Male , Pedigree , Short Stature Homeobox ProteinABSTRACT
CONTEXT: The insulin receptor-related receptor (IRR) is an orphan receptor belonging to the insulin receptor (IR) family. Despite its unknown function, the specific tissue expression and the high sequence homology with the IR and the insulin-like growth factor 1 receptor (IGF1R) suggest a biological role in beta-cells. OBJECTIVES: In this study we investigated the influence of a stimulatable IRR-tyrosine kinase on major IR/IGF1R signaling pathways and on proliferation and apoptosis of INS-1E beta-cells. METHODS: INS-1E cells were stably transfected with a colony stimulating factor 1 receptor (CSF1R)/IRR construct activated by a macrophage colony stimulating factor. RESULTS AND CONCLUSION: After stimulation the construct showed time and dose dependent autophosphorylation and transient extracellular signal regulated kinase 1/2 activation. Protein kinase b was not phosphorylated and also an effect on proliferation and apoptosis of INS-1E could not be demonstrated. Thus, no obvious biologic function of the IRR is present in INS-1E beta-cells.
Subject(s)
Insulin-Secreting Cells/metabolism , Mitogen-Activated Protein Kinase 1/metabolism , Mitogen-Activated Protein Kinase 3/metabolism , Proto-Oncogene Proteins c-akt/metabolism , Receptor, Insulin/metabolism , Receptor, Macrophage Colony-Stimulating Factor/metabolism , Animals , Apoptosis/drug effects , Cell Line, Tumor , Cell Proliferation/drug effects , Gene Expression Regulation/drug effects , Humans , Insulin/metabolism , Insulin-Secreting Cells/cytology , Insulin-Secreting Cells/drug effects , Macrophage Colony-Stimulating Factor/pharmacology , Phosphorylation/drug effects , Rats , Receptor, Insulin/chemistry , Receptor, Insulin/genetics , Receptor, Macrophage Colony-Stimulating Factor/chemistry , Receptor, Macrophage Colony-Stimulating Factor/genetics , Signal Transduction/drug effects , Somatomedins/metabolism , Tyrosine/metabolismABSTRACT
Although insulin receptor (InsR) and type I insulin-like growth factor receptor (IGF-IR) elicit different physiological effects in their target tissues, their signaling capabilities are similar to a large extent. In the present work, we investigated the potential of the third member of the family, insulin receptor-related receptor (IRR), to associate with known interaction partners of the InsR and the IGF-I receptor in a yeast two-hybrid assay. Using the intracellular part of the IRR we found no association with any of the tested signaling molecules. Phosphotyrosine detection revealed a lack in the constitutive activation of the IRR described for analogous constructs of the two other members of the family. Replacement of the kinase domain of the IGF-IR or its C-terminal lobe alone into the IRR caused a complete restoration of the tyrosine phosphorylation of the IRR. The reestablishment of autophosphorylation was paralleled by restoration of interaction with a specific range of signaling molecules.
Subject(s)
Receptor, Insulin/chemistry , Receptor, Insulin/metabolism , Signal Transduction , Humans , Phosphorylation , Protein Binding , Protein Structure, Tertiary , Receptor, IGF Type 1/metabolism , Receptor, Insulin/genetics , Saccharomyces cerevisiae/genetics , Saccharomyces cerevisiae/metabolism , Two-Hybrid System TechniquesABSTRACT
The SH2/SH3 adapter proteins of the Crk family are potent signal transducers after receptor tyrosine kinase stimulation with insulin or IGF-1. We have employed a yeast two-hybrid approach and mutational analysis to dissect the capabilities of the insulin receptor and the IGF-I receptor to directly associate with Crk isoforms. Insulin receptor stably recruits full length Crk by association with its SH2 domain in an auto-phosphorylation dependent manner. In contrast, interaction of the IGF-I receptor with the Crk-IISH2 domain was only detectable when Crk-II was truncated in its C-terminal part, indicating the transient nature of this interaction. From these data it can be concluded that members of the insulin receptor family activate Crk proteins in a differential manner.
