Selective expression of erg isoforms in human endothelial cells

Erg and Fli-1 are closely related members of the ets family of transcription factors. There are at least five human Erg isoforms (Erg-1, Erg-2, Erg-3/p55(Erg), p49(Erg) and p38(Erg)) produced through differential mRNA splicing and alternative use of translational start codons. However, relatively little is known about the expression or function of these isoforms in vitro or their distribution in vivo. We used RT-PCR to screen a panel of primary and established human cell lines for erg and fli-1 consensus sequences. Whilst fli-1 was expressed in several human cell types, erg was detected mainly in endothelial cells. To identify which erg isoforms are expressed in endothelial cells we used RT-PCR, Northern blotting and 5'-RACE. Erg-3/p55(Erg) and p38(Erg)/p38(Erg)-like transcripts were detected in both microvascular and large vessel endothelial cells affinity-purified from different vascular beds. Moreover, these erg isoforms were present in both freshly isolated, and confluent endothelial cells following several passages in culture, indicating that endothelial erg expression in vitro may be broadly representative of that in vivo. The selective expression of the Erg-3/p55(Erg) and p38(Erg)/p38(Erg)-like isoforms in endothelial cells indicates their involvement in the regulation of endothelial-restricted genes.