Novel nuclear localization and potential function of insulin-like growth factor-1 receptor/insulin receptor hybrid in corneal epithelial cells

• Published in: PloS one Vol. 7; no. 8; p. e42483
• Main Authors: Wu, Yu-Chieh, Zhu, Meifang, Robertson, Danielle M
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 03.08.2012; Public Library of Science (PLoS)
• Subjects: AKT protein; Biology; Cancer; Cell activation; Cell adhesion & migration; Cell culture; Cell cycle; Cell growth; Cell Nucleus - drug effects; Cell Nucleus - metabolism; Cell proliferation; Cell Proliferation - drug effects; Chromatin; Cluster Analysis; Cornea; Diabetes; Epidermal growth factor; Epithelial cells; Epithelial Cells - cytology; Epithelial Cells - drug effects; Epithelial Cells - metabolism; Epithelium; Epithelium, Corneal - cytology; Gene Knockdown Techniques; Genes; Homology; Humans; Immunoblotting; Immunofluorescence; Immunoprecipitation; Insulin; Insulin resistance; Insulin-like growth factor I; Insulin-Like Growth Factor I - metabolism; Insulin-like growth factors; Kinases; Ligands; Localization; Lysates; Medical research; Medicine; Molecular Sequence Annotation; Nuclei; Nuclei (cytology); Pathways; Phosphatidylinositol 3-Kinases - metabolism; Phosphorylation - drug effects; Protein Multimerization - drug effects; Protein Transport - drug effects; Proteins; Proto-Oncogene Proteins c-akt - metabolism; Receptor, IGF Type 1 - metabolism; Receptor, Insulin - metabolism; Ribonucleic acid; RNA; RNA, Small Interfering - metabolism; Rodents; Signal transduction; Signal Transduction - drug effects; Signaling; siRNA; Software; Subcellular Fractions - drug effects; Subcellular Fractions - metabolism; Target recognition; Telomere - metabolism; United States > US; Texas
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0042483

Type I insulin-like growth factor receptor (IGF-1R) and insulin receptor (INSR) are highly homologous molecules, which can heterodimerize to form an IGF-1R/INSR hybrid (Hybrid-R). The presence and biological significance of the Hybrid-R in human corneal epithelium has not yet been established. In addition, while nuclear localization of IGF-1R was recently reported in cancer cells and human corneal epithelial cells, the function and profile of nuclear IGF-1R is unknown. In this study, we characterized the nuclear localization and function of the Hybrid-R and the role of IGF-1/IGF-1R and Hybrid-R signaling in the human corneal epithelium. IGF-1-mediated signaling and cell growth were examined in a human telomerized corneal epithelial (hTCEpi) cell line using co-immunoprecipitation, immunoblotting and cell proliferation assays. The presence of Hybrid-R in hTCEpi and primary cultured human corneal epithelial cells was confirmed by immunofluorescence and reciprocal immunoprecipitation of whole cell lysates. We found that IGF-1 stimulated Akt and promoted cell growth through IGF-1R activation, which was independent of the Hybrid-R. The presence of Hybrid-R, but not IGF-1R/IGF-1R, was detected in nuclear extracts. Knockdown of INSR by small interfering RNA resulted in depletion of the INSR/INSR and preferential formation of Hybrid-R. Chromatin-immunoprecipitation sequencing assay with anti-IGF-1R or anti-INSR was subsequently performed to identify potential genomic targets responsible for critical homeostatic regulatory pathways. In contrast to previous reports on nuclear localized IGF-1R, this is the first report identifying the nuclear localization of Hybrid-R in an epithelial cell line. The identification of a nuclear Hybrid-R and novel genomic targets suggests that IGF-1R traffics to the nucleus as an IGF-1R/INSR heterotetrameric complex to regulate corneal epithelial homeostatic pathways. The development of novel therapeutic strategies designed to target the IGF-1/IGF-1R pathway must take into account the modulatory roles IGF-1R/INSR play in the epithelial cell nucleus.