Aqp1 expression in erythroleukemia cells: genetic regulation of glucocorticoid and chemical induction

The aquaporin-1 (AQP1) water channel protein is expressed in multiple mammalian tissues by several different developmental programs; however, the genetic regulation is undefined. The proximal promoter of mouse Aqp1 contains multiple putative cis-acting regulatory elements, and mouse erythroleukemia (MEL) cells are a well-characterized model for erythroid differentiation. Corticosteroid or dimethyl sulfoxide (DMSO) exposure induces AQP1 protein expression in MEL cells, and transcriptional regulation was investigated by transient transfections with Aqp1 promoter-reporter constructs. Dexamethasone induction is abrogated by deletion of two glucocorticoid response elements -0.5 kilobases (kb) from the transcription initiation site. Mutation of the GATA element at -0.62 kb has no effect, whereas mutation of the CACCC site at -37 bp significantly reduces DMSO-induced promoter activity. Hydroxyurea induces expression of AQP1 protein without acting through the proximal promoter. The MEL cell line is a reproducible erythroid model system for studying transcriptional regulation of the Aqp1 gene while determining the consequences on AQP1 protein biosynthesis.