Detection of Genome-Wide IGF-1R Recruitment to Enhancer and Promoter Regions of Chromatin in Clinical Prostate Cancers

Introduction: Nuclear insulin-like growth factor-1 receptor (IGF-1R) undergoes IGF-induced recruitment to cancer cell chromatin in vitro and associates with advanced prostate cancer (PCa) stage in clinical tissue, prompting this investigation of IGF-1R chromatin recruitment in vivo. Methods: Human tissues surplus to diagnostic need were obtained from consenting patients undergoing transurethral resection of the prostate (TURP) or radical prostatectomy (RP). Initial tissue samples were processed for H3K4me1-positive control ChIP to optimise homogenisation, fixation and ChIP conditions. Following successful method optimization, IGF-1R and H3K4me1 ChIP-seq was performed on six treatment-naïve localized PCa samples, along with parallel IGF-1R immunohistochemistry analysis. MACS2 and LanceOtron peak callers were used to identify binding sites from ChIP-seq data and MEME Suite was used to identify an IGF-1R binding motif. In vitro chromatin immunoprecipitation qPCR (ChIP-qPCR) was used for ChIP-seq data validation. Results: We identified 5743 unique IGF-1R binding sites, with 37% within 3 kb of gene transcription start sites (TSSs). Of these sites, 72.3% coincided with enhancer mark H3K4me1, suggesting regulatory function. Motif analysis identified an IGF-1R consensus binding motif for the first time, with a sequence resembling that of the insulin receptor and PITX2 transcription factor binding motifs, supporting functional similarities. In vitro ChIP-qPCR confirmed IGF-1R recruitment to a site identified in vivo in the RRM2 TSS, a gene involved in DNA replication and repair and regulated by the IGF-axis, highlighting potential regulatory function of nuclear IGF-1R. Conclusion: Overall, these data represent the first characterization of genome-wide IGF-1R recruitment in PCa tissue and are consistent with a transcriptional regulatory role, further elucidating the contribution of nuclear IGF-1R to advanced clinical stage.