Title

The proto-oncogene c-Maf is a transcriptional activator of the CD13 promoter in endothelial cells

Date of Completion

January 2008

Keywords

Biology, Cell|Health Sciences, Oncology

Degree

Ph.D.

Abstract

CD13/APN is a marker of the tumor vasculature. Its inhibition abrogates endothelial morphogenesis in vitro and tumor growth in vivo. Growth factors, such as bFGF and VEGF, activate transcription of CD13 in endothelial cells by signaling through Ras/MAPK pathways. The region between–153bp and –70bp of the CD13 gene, i.e. the proximal promoter, is essential for CD13 promoter activity in endothelial cells. The Ets2 transcription factor is phosphorylated by ERK and activates CD13 promoter activity through a motif in this region between –153bp and –115bp of the proximal promoter. Because of the complex regulation of tissue-specific gene expression and the significant homology within this region of the promoter across mammalian species, we have explored other transcription factors important in vascular biology that regulate the expression of CD13. While CD13 has been established as a marker of tumor endothelium, the role of the Maf proteins has not yet been studied in endothelial cells. We found that the overexpression of c-Maf activates transcription of the proximal promoter of CD13 in endothelial cells. Furthermore we established that c-Maf is expressed by endothelial cell and directly interacts with an atypical Maf response element within the first 153bp of the proximal promoter of the the CD13 gene to induce its activity. While the literature regarding the regulation of Maf proteins is complicated and contradictory, the Ras/MAPK signal pathway appears to regulate c-Maf activity in endothelial cells. Therefore we made site-directed mutations of c-Maf to assay the role of putative phosphorylation sites (serines 15 and 70) on c-Maf's ability to activate transcription. We found that the S15A mutation reduces c-Mars activity in endothelial cells, while the S15A, S70A, and S15A/S70A mutations increase c-Maf activity in liver cells. Further elucidation of the role c-Maf in angiogenesis is necessary for determining whether it may serve as a therapeutic target in pathologic adult angiogenesis. ^