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 HNF3 alpha and HNF3 beta 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 HNF3 alpha. Gene transfer experiments into Drosophila Schneider cells that lack many mammalian transcription factor homologs revealed that HNF3 alpha and HNF3 beta on their own cannot activate the uteroglobin/CC10 promoter. However, HNF3 alpha and HNF3 beta strongly enhanced Sp1-mediated promoter activation. Synergistic activation by HNF3 alpha 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 HNF3 alpha. 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 HNF3 alpha and the ubiquitous factor Sp1.