OR25-1 Genomic Landscape of Insulin Receptor versus IGF1R Recruitment to Distinct Genomic Targets in Pancreatic Islets

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: OR25-Signaling Originating from Membrane Receptors
Sunday, June 16, 2013: 11:15 AM-12:45 PM
Presentation Start Time: 11:15 AM
Room 133 (Moscone Center)
Shweta Bhatt*1, Rachael Martinez2, Tze Howe Charn3, Michael Molla2 and Rohit N Kulkarni4
1Joslin Diabetes Center and Harvard Medical School, Boston, MA, 2Joslin Diabetes Center, Boston, MA, 3Stanford University, San Francisco, CA, 4Joslin Diabetes Center and Harvard Medical School, Boston, MA
Delineating the unique specificity of growth hormone receptors, such as Insulin Receptor (IR) and Insulin-like Growth Factor 1 Receptor (IGF1R) has been of major scientific interest, but progress has been limited due to their structural and functional homology. We exploited the strikingly different loss-of-function phenotypes in beta-cell specific IR or IGF1R knockout mice to further investigate the specificity of insulin versus IGF-1 receptors. We report, for the first time, the nuclear translocation of these classic trans-membrane receptors in pancreatic beta cells (critical for glucose induced insulin secretion) as confirmed by live cell imaging, immuno-staining and cell-fractionation/western blot analyses (n=3). To explore functional significance, we subjected mouse pancreatic islets to ex-vivo treatment with ligands (glucose and/or insulin, IGF1) followed by (a) genome-wide chromatin immuno-precipitation sequencing (ChIPseq) analysis for IR or IGF1R protein(s) to assess genomic recruitment or (b) microarray gene expression analysis to study transcript regulation (n=3). Indeed, we observed IR recruitment to 9663 genomic binding sites and association with 6778 genes while IGF1R bound 18,016 genomic sequences and associated with 5908 genes, a significant number of which were regulated by ligand and blocked in mouse, human islets or beta cells subjected to shRNA mediated IR or IGF1R knockdown, respectively. Intriguingly, while their binding site enrichment to distal intergenic and intronic regions was a common feature, the two receptors bound only 938 common targets while majority remained unique (5840 for IR and 4970 for IGF1R). Next, we performed transcription factor binding site enrichment analysis -/+100bp of the IR or IGF1R binding site peak to identify potential transcription factors and/or epigenetic regulators. Interestingly, while NeuroD1 (a MODY gene), CTCF (associated with epigenetic regulation/DNA methylation) and AP-1/c-Jun binding sites were commonly enriched in both IR and IGF1R targets, a highly unique enrichment of Pdx-1 binding sites in IR and over-representation of Foxo1 sites at IGF1R targets was observed (p<0.001), a finding that provides mechanistic context to previous reports. In summary, our novel approach identifies previously unknown, distinct molecular signatures of IR versus IGF1R, further investigation of which may enable identification of new pathways and disease mechanism(s) for therapeutic intervention.

Nothing to Disclose: SB, RM, THC, MM, RNK

*Please take note of The Endocrine Society's News Embargo Policy at http://www.endo-society.org/endo2013/media.cfm

Sources of Research Support: NIH RO1 67536
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