Identification of a distal regulatory sequence of the human IGFBP-1 gene promoter and regulation by the progesterone receptor in a human endometrial adenocarcinoma cell line.

The activity of the insulin-like growth factor binding protein-1 (IGFBP-1) gene promoter was studied in the human endometrial adenocarcinoma cell line HEC-1B. Basal promoter activity was directed by the region +68 to -207 bp, similar to observations in the hepatoma HepG2 cell line. A distal regulatory sequence approximately -2.6 kb from the transcription initiation site strongly enhanced the activity of the IGFBP-1 gene promoter in HEC-1B cells, but not in HepG2 cells. Sequence analysis revealed that this active region resides in 105 bp between -2,628 to -2,732 bp (the Rsa I-Cla I fragment). This region contains many putative active motifs homologous to known cis elements. Additional deletion and mutation in the Rsa I-Cla I fragment showed that the activity was confined to a 58-bp DNA fragment. In cells treated with progestin and co-transfected with progesterone receptor vector hPR1, the CAT activity derived from constructs containing the Rsa I-Cla I fragment was reduced in a dose-dependent manner. The active DNA fragment also stimulated the activity of the heterologous TK/CAT promoter in HEC-1B cells, while the PR complex inhibited this activity by 50%. These observations indicate that most of the regulation of the IGFBP-1 gene in HEC-1B cells is derived from the distal promoter region confined to the Rsa I-Cla I fragment and that the same region mediates an inhibitory effect from the progesterone receptor.