Full-length IGF-1R and subunits undergo nuclear import following clathrin-dependent endocytosis. nucleus. Nuclear IGF-1R is phosphorylated in response to ligand, and undergoes IGF-induced interaction with chromatin, suggesting direct engagement in transcriptional regulation. The IGF-dependence of these phenomena indicate a requirement for the receptor kinase, and indeed IGF-1R nuclear import and chromatin binding can be blocked by a novel IGF-1R kinase inhibitor. Nuclear IGF-1R is detectable in primary renal cancer cells, formalin-fixed tumors, preinvasive lesions in the breast, and nonmalignant tissues characterized by a high proliferation rate. In clear cell renal cancer, nuclear IGF-1R is associated with adverse prognosis. Our findings suggest that IGF-1R nuclear import has biological significance, may contribute directly to IGF-1R function, and may influence the efficacy of IGF-1R inhibitory drugs. == Introduction == The IGF-1R mediates proliferation and cell survival, and is recognized as an attractive cancer treatment target (1). Following co-translational insertion into the endoplasmic reticulum (ER) as a 220kDa proreceptor, the IGF-1R is cleaved in the trans-Golgi network to generate mature (135kDa) and (98kDa) subunits linked by disulfide bonds (2). After trafficking to the plasma membrane, IGF-1Rs are activated by IGFs, and then internalized and degraded, or recycled to the cell surface (3,4). While other receptor tyrosine kinases (RTKs) are known to undergo nuclear translocation (5-8), nuclear IGF-1R has not been reported in human cancers, although was detected in hamster kidney cells (9). Building on our studies of IGF signaling in prostate and renal cell cancer (RCC) (10-13), we hypothesized that this IGF-1R undergoes nuclear translocation in these tumors. == Methods == Human DU145 prostate cancer, 786-0/EV (RCC) and MCF7 (breast cancer) cells were from Cancer Research UK (CRUK; Hertfordshire UK). IGF-1R null murine fibroblasts (R cells) and isogenic R+ cells expressing human IGF-1R were from Renato Baserga (Philadelphia, AZD9567 US). Primary RCC cultures were generated by disaggregation of fresh tumors, and stained for pancytokeratin (Abcam, Cambridge UK). Cells were transfected with IGF-1R (#SI00017521), caveolin (#SI00027720), or control (#1022076) siRNAs (Qiagen, Crawley UK) using Oligofectamine (Invitrogen, Paisley UK). IGF-1R antibody MAB391 was from R&D Systems (Abingdon UK). AZ12253801 (from Elizabeth Anderson, AstraZeneca UK), is an ATP-competitive IGF-1R tyrosine kinase inhibitor that show ~10-fold selectivity over the insulin receptor (IR). IC50values for inhibition of IGF-1R and IR phosphorylationin vitroare 2.1nM and 19 nM respectively. The IC50for inhibition of IGF-1R-driven proliferation in 3T3 mouse fibroblasts transfected with human IGF-1R is 17nM, whereas the IC50for EGFR-driven proliferation is 440nM. AZ12253801 has been tested against a wide range of other relevant kinases, where AZD9567 IC50s are generally AZD9567 >1M or the compound has little or no inhibitory activity at 10M. == Immunofluorescence == Cells were cultured in complete medium, or serum-starved overnight and treated with long-R3 IGF-I (SAFC Biosciences, Andover UK), IGF-II, insulin (Sigma-Aldrich) or solvent. Some cultures were pre-treated with solvent (DMSO), 300nM dibenzazepine (DBZ; Calbiochem, Nottingham UK), 300M dansylcadaverine (Sigma-Aldrich, Gillingham UK), 30M dynasore(Sigma-Aldrich), or AZ12253801. Immunostaining used antibodies to IGF-1R carboxy-terminus (#3027, Cell Signaling Technology, CST), IGF-1R amino-terminus (H-60, Santa Cruz), IGF-1R (24-31 from Ken Siddle, Cambridge UK, or IR3, #GR11L, Calbiochem), calnexin, nucleolin or RNA polymerase II (Abcam). Images were acquired on a LSM 510 confocal microscope (Zeiss, Welwyn Garden City UK). Photomicrographs show mid-slice confocal images through the nucleus, 63 magnification unless stated otherwise. Fluorescence was quantified using ImageJ software in 20-30 cells for each condition, and statistical analysis utilized GraphPad Prism v5. == Cell fractionation, immunoblotting, immunoprecipitation == Whole cell extracts were prepared in RIPA buffer (14). Nuclear extraction used Nuclear Extraction reagents (Panomics, CA), to disrupt cells in hypotonic Buffer A, and release nuclear proteins with Buffer B (high salt with detergent). Whole cell, non-nuclear and nuclear fractions and chromatin extracts were analyzed by SDS-PAGE and immunoblotting for IGF-1R (Santa Cruz), IGF-1R (CST), phosphorylated IGF-1R (Y1135-6, CST), lamin, calnexin (Abcam), golgin-84 (BD Biosciences), EpCAM (clone AUA1, Rabbit Polyclonal to hnRNP H CRUK), -tubulin (Sigma-Aldrich), and Hes1 (gift of Dr. Tatsuo Sudo, Kamakura, Japan). Extracts were immunoprecipitated with IGF-1R antibody (#3027, CST) or rabbit IgGs (Sigma-Aldrich); seeSupplementary Information. == Immunohistochemistry == Human tissue was used under National Research Ethics studies 04/Q1606/96, 07/H0606/120 and 09/H0606/5. Formalin-fixed whole mount and tissue microarray (TMA) sections were immunostained for IGF-1R – (#3027, CST) and – (24-31). IGF-1R intensity and distribution were scored as described (10,13,15). Contingency tables were analysed using Pearsons Chi-square test to assess relationships between IGF-1R and clinical parameters. Survival was measured from nephrectomy to death or last follow-up, and survival curves were.