Regulation of basal core promoter activity of human organic cation transporter 1 (OCT1/SLC22A1).
Human organic cation transporter 1 (OCT1/SLC22A1) plays important roles in the hepatic uptake of cationic drugs. The functional characteristics of this transporter have been well evaluated, but molecular information regarding transcriptional regulation is limited. In the present study, therefore, we examined the gene regulation of OCT1 gene focusing on basal core expression. An approximately 2.5-kb fragment of the OCT1 promoter region was isolated, and promoter activity was measured by luciferase assay in the human liver cell lines Huh7 and HepG2. Deletion analysis suggested that the region spanning -141/-69 was essential for the basal core transcriptional activity and that this region contained the sequence of a cognate E-box (CACGTG). The E-box is known to be bound by the basal transcription factors, upstream stimulating factors (USFs), and the functional involvements of USF1 and USF2 were confirmed by a transactivation effect, a mutational analysis of the E-box, and an electrophoretic mobility shift assay. The transactivation effect of USFs on the OCT1 promoter was further stimulated by hepatocyte nuclear factor 4alpha, a liver-enriched transcription factor. There were no polymorphisms in the proximal promoter region (about 400 bp) of OCT1 gene (n = 109). These findings indicated that both USF1 and USF2 bind to an E-box sequence located in the OCT1 core promoter region and are required for the basal gene expression of this transporter.
Kajiwara
Moto
M
Department of Pharmacy, Kyoto University Hospital, Faculty of Medicine, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
Terada
Tomohiro
T
Asaka
Jun-ichi
J
Aoki
Masayo
M
Katsura
Toshiya
T
Ikai
Iwao
I
Inui
Ken-ichi
K
D001483:Base Sequence; D045744:Cell Line, Tumor; D004252:DNA Mutational Analysis; D024721:E-Box Elements / Q000235:genetics; D005786:Gene Expression Regulation; D051557:Hepatocyte Nuclear Factor 4; D006801:Humans; D008969:Molecular Sequence Data; D050811:Octamer Transcription Factor-1 / Q000235:genetics*; D020641:Polymorphism, Single Nucleotide; D011401:Promoter Regions, Genetic / Q000235:genetics*; D024363:Transcription Initiation Site; D051720:Upstream Stimulatory Factors / Q000502:physiology*
C496592:HNF4A protein, human; D051557:Hepatocyte Nuclear Factor 4; D050811:Octamer Transcription Factor-1; C494165:POU2F1 protein, human; C497181:USF1 protein, human; C497184:USF2 protein, human; D051720:Upstream Stimulatory Factors