Here, we report that an E-box element located within the human topoisomerase IIIα (hTOP3α) gene promoter acts as a cell type-specific enhancer. The upstream stimulatory factor (USF) was shown to specifically recognize the mutationally sensitive E-box element. When assayed by transient transfection with hTOP3α promoter-dependent reporter genes, USF is transcriptionally active in HeLa cells but lacks transcriptional activity in Saos-2 cells. The hTOP3α mRNA level in Saos-2 cells was reduced to about 30% of the level observed for HeLa cells, suggesting that the inactivity of USF in hTOP3α promoter activity may be the cause of the marked reduction of hTOP3α mRNA levels in Saos-2 cells. Using transient transfection assays in HeLa cells, we demonstrated that ectopically expressed USF2, but not USF1, was capable of activating hTOP3α transcription through the E-box element. However, USF2 did not stimulate hTOP3α promoter activity in Saos-2 cells. This cell type-specific regulation of promoter activity by USF2 may provide a mechanism for the differential expression of hTOP3α in various tissues and during developmental stages.
Bibliographical noteFunding Information:
We are very grateful to Dr. R. Roeder for the gift of USF1 and USF2 expression vectors, and to Dr. M. Sawadogo for the gift of U2ΔUSR vector. This work was supported in part by Grant 98-MM-02-01-A-01 from the Molecular Medicine Research Group Program, MOST, and Grant 2000-2-0610 from the Korea Science and Engineering Foundation through the Protein Network Research Center at Yonsei University.
All Science Journal Classification (ASJC) codes
- Structural Biology
- Molecular Biology
- Cell Biology