HMGA1 controls transcription of insulin receptor to regulate cyclin D1 translation in pancreatic cancer cells.

The HMGA1 proteins act as architectural transcription factors and are involved in the regulation of genes important in the process of carcinogenesis. Although HMGA1 proteins are overexpressed in most types of cancer, signaling circuits regulated by HMGA1 are not clarified in detail. In this study, we show that HMGA1 proteins promote proliferation of pancreatic cancer cells by accelerating G(1) phase progression. Transfection of HMGA1-specific small interfering RNA (siRNA) activates the RB-dependent G(1)-phase checkpoint due to the impaired expression of cyclin D1. Down-regulation of cyclin D1 after the HMGA1 knockdown is due to translational control and involves the repressor of the eukaryotic translation initiation factor 4E (eIF4E) 4E-BP1. We show that 4E-BP1 and cyclin D1 act downstream of the insulin receptor (IR) in pancreatic cancer cells. At the molecular level transcription of the IR is controlled by a CAAT/enhancer binding protein beta (C/EBPbeta)/HMGA1 complex. Together, this work defines a novel pathway regulated by HMGA1, which contributes to the proliferation of pancreatic cancer cells.