2 PREPROENDOTHELIN-1 MESSENGER-RNAS TRANSCRIBED BY ALTERNATIVE PROMOTERS

Endothelin-1, initially identified as potent vasoconstrictor secreted by vascular endothelial cells, was subsequently found to have many effects on both vascular and nonvascular tissues. We have identified from a human placenta cDNA library a clone (cDNA-2) which corresponds to a novel 5'-extended preproendothelin 1 (preproET-1 ) mRNA. Comparison with the known preproET-1 mRNA (cDNA-1 ), showed that the two molecules share the same coding sequence but differ in the 5'-untranslated region. Interestingly, cDNA-2 extends upstream of promoter regions previously shown to be essential for full preproET-1 expression. Primer extension and PCR analysis of human placenta RNA demonstrated the presence of additional transcription initiation sites located upstream of the previously identified preproET-1 CAP site. Moreover, the two mRNAs show different pattern of expression. To elucidate the mechanisms controlling the production of alternative transcripts we transfected COS-1 cells with a series of preproET-1 promoter deletion mutants. This analysis revealed that the human preproET-1 gene can be transcribed from a proximal and a distal promoter element which has hitherto been undetected. In addition, we demonstrate the presence of a region in the down-epithelial specific expression.