Blastemal/stromal expression of IGF1R in Wilms tumours is driven by increased copy number and correlates with relapse
Authors: Rachael Natrajan, Suzanne E. Little, Jorge S. Reis-Filho, William Warren, Boo Messahel, Marie-Anne Brundler, Gordan Vujanic, Kathy Pritchard-Jones, Chris Jones
Journal: Cancer Research (2006)

Proc Amer Assoc Cancer Res, Volume 47, 2006

4196 

Wilms tumor is the most common paediatric renal malignancy, affecting approximately 1 in 10,000 children before the age of 15 years. Most Wilms tumors are of low stage, have a favourable histology, and with improved multimodality therapy the overall survival is high. Despite this, there remains a group of relapsing patients for whom intensive salvage regimens result in survival of only 50%. We have carried out microarray-based comparative genomic hybridization (aCGH) on a series of 118 Wilms tumor samples, enriched for cases which recurred, in order to identify changes in DNA copy number associated with clinical outcome. Fitting a COX proportional hazards model for each of the 4583 clones on our array with respect to relapse-free survival time, we identified a significant correlation between increased copy number at chromosome 15q26.3 and Wilms tumor relapse (p < 0.01). End-sequencing and FISH mapping confirmed that these clones mapped to the insulin-like growth factor 1 receptor (IGF1R) locus. Approximately 10% of Wilms tumors exhibited a low level gain corresponding to 3-4 copies of the gene by aCGH analysis, while high mRNA levels were detected in 15% Wilms tumors by quantitative real-time RT-PCR, which was also found to correspond with relapse (p < 0.05, Fishers exact test). Those tumors exhibiting both increased copies and overexpression (∼8%) showed a highly significant shorter time to tumor relapse (p < 0.001, log rank test). IGF1R protein expression by IHC was observed in the developing tubules, but not the metanephric blastema of foetal kidney. In the mature kidney, it is seen to be localized to the epithelial cells of the proximal tubules. In tissue arrays consisting of 245 Wilms tumors, IGF1R expression was observed to be predominantly restricted to the epithelial component, however up to 15% of Wilms tumors were found to express IGF1R in the blastemal and/or stromal cells. Blastemal/stromal IGF1R protein expression was associated with shorter relapse-free survival time (p < 0.05, log-rank test). Chromogenic in situ hybridization (CISH) using a specific IGF1R probe demonstrated that expression of IGF1R in blastemal/stromal cells is associated with increased gene copy number (3–4 copies). Intriguingly, as well as membrane localization of the receptor, in a number of Wilms tumors (approximately 6%), IGF1R expression was localized to “perinuclear dots” in the blastemal cells. This aberrant localization has not to our knowledge been previously reported either for IGF1R (in any tumor type) or in Wilms tumor (for any protein), and raises the possibility of abrogated post-translational packaging, or even the presence of IGF1R mutations. Ongoing work in the lab is involved with investigating whether the receptor is activated in these cases using an anti-phosphorylated IGF1R antibody, and whether this increase in copy number/expression is associated with an activating mutation.