The forkhead transcription factor Foxi1 is a master regulator of vacuolar H-ATPase proton pump subunits in the inner ear, kidney and epididymis.
The vacuolar H(+)-ATPase dependent transport of protons across cytoplasmic membranes in FORE (forkhead related) cells of endolymphatic epithelium in the inner ear, intercalated cells of collecting ducts in the kidney and in narrow and clear cells of epididymis require expression of several subunits that assemble into a functional multimeric proton pump. We demonstrate that expression of four such subunits A1, B1, E2 and a4 all co-localize with the forkhead transcription factor Foxi1 in a subset of epithelial cells at these three locations. In cells, of such epithelia, that lack Foxi1 we fail to identify any expression of A1, B1, E2 and a4 demonstrating an important role for the transcription factor Foxi1 in regulating subunit availability. Promoter reporter experiments, electrophoretic mobility shift assays (EMSA) and site directed mutagenesis demonstrate that a Foxi1 expression vector can trans-activate an a4-promoter reporter construct in a dose dependent manner. Furthermore, we demonstrate using chromatin immunoprecipitation (ChIP) assays that Foxi1-dependent activation to a large extent depends on cis-elements at position -561/-547 in the a4 promoter. Thus, we provide evidence that Foxi1 is necessary for expression of at least four subunits in three different epithelia and most likely is a major determinant for proper assembly of a functional vacuolar H(+)-ATPase complex at these locations.
Vidarsson
Hilmar
H
Center of Medical Genetics, Institute of Biomedicine, The Sahlgrenska Academy, Göteborg University, Göteborg, Sweden.
Westergren
Rickard
R
Heglind
Mikael
M
Blomqvist
Sandra Rodrigo
SR
Breton
Sylvie
S
Enerbäck
Sven
S
D000818:Animals; D002460:Cell Line; D007758:Ear, Inner / Q000166:cytology / Q000378:metabolism*; D004822:Epididymis / Q000166:cytology / Q000378:metabolism*; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D006801:Humans; D007668:Kidney / Q000166:cytology / Q000378:metabolism*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008954:Models, Biological; D011401:Promoter Regions, Genetic; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism*; D006180:Proton-Translocating ATPases / Q000235:genetics / Q000378:metabolism*; D025262:Vacuolar Proton-Translocating ATPases / Q000235:genetics / Q000378:metabolism*
D051858:Forkhead Transcription Factors; C508689:Foxi1 protein, mouse; D021122:Protein Subunits; C490179:Atp6v0a4 protein, mouse; D025262:Vacuolar Proton-Translocating ATPases; D006180:Proton-Translocating ATPases