Adrenal tumorigenesis targeted by the corticotropin-regulated promoter of the aldo-keto reductase AKR1B7 gene in transgenic mice

Studies of ACTH functions in adrenal steroidogenesis have been facilitated by the availability of immortalized mouse adrenocortical Y1 cells. In order to obtain alternative cell lines with a more differentiated zona fascicula ta (ZF) phenotype we used targeted tumorigenesis strategy. We have generate d transgenic mice expressing the SV40 T antigen under the control of the AC TH-dependent promoter for the AKRIB7/MVDP gene (aldo-keto reductase 1B7/mou se vas deferens protein), which encodes an enzyme responsible for detoxifyi ng isocaproaldehyde, the product of side-chain cleavage of cholesterol gene rated by steroidogenesis. Our previous data indicated that in the mouse adr enal, AKR1B7 expression was restricted to the ZF and that a 0.5-kb promoter region was able to target specific adrenal expression in transgenic mice. In situ hybridization analyses indicate that AKR1B7 expression during fetal and post-natal periods paralleled the onset of glucocorticoid synthesis an d the development of ZF. In transgenic mice, ACTH control and developmental programming of the CAT gene driven by the 0.5-kb promoter followed endogen ous gene regulation. Then transgenic mice harboring the 0.5-kb/SV40 T antig en construct were generated and two founders out of three developed adrenal tumors. Cells derived from the tumor of founder 1 (ATC1) were grown in pre sence of forskolin to maintain ACTH receptor expression and were tested for ACTH responsiveness by immunocychemistry and northern blot analyses. Even after several passages, the ACTH induced AKR1B7 and P450c11 beta mRNAs accu mulations were similar to that observed in mouse primary adrenocortical cel l cultures. Our findings suggest that ATC1 cells have conserved essential f eatures of ZF cells. In order to achieve complete characterization of these cells further analyses are currently performed to investigate their steroi dogenic activity.