Generation of transgenic fibroblasts expressing pancreas‑specific and doxycycline-inducible ICER Iγ for the establishment of a porcine model of human diabetes mellitus.

Inducible cyclic AMP (cAMP) early repressor (ICER) Iγ acts as an endogenous inhibitor and disrupts the transcriptional regulation of cAMP response element binding protein (CREBP) responsive genes. Since the overexpression of ICER Iγ induces severe diabetes in a transgenic mouse model, with characteristics similar to human diabetes mellitus, an ICER Iγ construct containing an adjustable pancreas tissue specific promoter was utilized in the present study. Using the human insulin promoter region, a doxycycline (dox)‑inducible ICER Iγ expression system was established using the tetracycline (tet)-controlled transactivator (tTA) with a TA response element (TRE) promoter. A unitary tet-on system that combined a tet-on activator cassette was also developed and was controlled by the human insulin promoter with a responder cassette containing genes encoding ICER Iγ regulated by the TRE promoter. To determine whether dox-enhanced ICER Iγ expression affected insulin production, the unitary tet-on ICER Iγ vector was introduced into a mouse pancreatic β-cell line and then the cells were treated with 0.1-1 mg/ml dox. The results revealed a robust increase in ICER Iγ expression and decreased insulin production. Therefore, this in vitro system may be useful for studying human diabetes mellitus and pre-diabetes using tissue-specific promoters and a dox-inducible transgene. In addition, porcine transgenic fibroblasts containing dox-inducible ICER Iγ were generated. These fibroblasts may serve as a cell source for somatic cell nuclear transfer to generate a porcine model of human diabetes mellitus.