Molecular cloning and structural characterization of the rat thymosin beta15 gene

Thymosin beta15 is expressed in metastatic variants of Dunning rat prostatic carcinoma but not in a nonmetastatic variant. It is also upregulated in malignant human prostate cancers and was shown to be a predictive marker for patient outcome in prostate cancer. To explore the molecular mechanism of transcriptional regulation of thymosin beta15, we isolated and characterized the rat thymosin beta15 gene. The gene appears to exist as a single copy in the rat genome and to comprise three exons distributed over 2kb. The transcription start site was defined by primer extension analysis at 30 bp upstream of the translation start site. Sequence analysis of the 5'-flanking region of the transcription start site revealed properties consistent with promoter activity. The promoter region is GC rich and contains numerous consensus transcription factor binding sites as well as a GC box, but no TATA box. The transcriptional activity of the 5'-flanking region was analyzed by transient transfection of rat prostate cancer cells with firefly luciferase-encoding gene expression vector constructs. The isolated 5' region showed significant promoter activity. The identification of the thymosin beta15 promoter could aid our understanding of the regulation of this gene and its enhanced expression in human cancer.