Combinatorial action of HNF3 and Sp family transcription factors in the activation of the rabbit uteroglobin/CC10 promoter.

It has been reported that respiratory epithelium-specific transcription is mediated by thyroid transcription factor 1 and members of the HNF3/forkhead family of transcription factors. Here, we show that the uteroglobin/Clara cell 10-kDa promoters from rabbit and man are regulated by HNF3alpha and HNF3beta but not by HFH-4 and TTF-1. We have identified two HNF3-responsive elements in the rabbit uteroglobin/CC10 promoter located around 95 and 130 base pairs upstream of the transcriptional start site. Both elements contribute to promoter activity in H441 cells expressing uteroglobin/CC10 and HNF3alpha. Gene transfer experiments into Drosophila Schneider cells that lack many mammalian transcription factor homologs revealed that HNF3alpha and HNF3beta on their own cannot activate the uteroglobin/CC10 promoter. However, HNF3alpha and HNF3beta strongly enhanced Sp1-mediated promoter activation. Synergistic activation by HNF3alpha and Sp1 was absolutely dependent on the integrity of two Sp1 sites located at around -65 and -230. We show further that multiple activation domains of Sp1 are required for cooperativity with HNF3alpha. These studies demonstrate that transcription from the rabbit uteroglobin/CC10 promoter in lung epithelium is controlled by the combinatorial action of the cell-specific factor HNF3alpha and the ubiquitous factor Sp1.