Kruppel-like factor 5 (Klf5) regulates expression of mouse T1R1 amino acid receptor gene (Tas1r1) in C2C12 myoblast cells

T1R1 and T1R3 are receptors expressed in taste buds that detect L-amino acids. These receptors are also expressed throughout diverse organ systems, such as the digestive system and muscle tissue, and are thought to function as amino acid sensors. The mechanism of transcriptional regulation of the mouse T1R1 gene (Tas1r1) has not been determined; therefore, in this study, we examined the function of Tas1r1 promoter in the mouse myoblast cell line, C2C12. Luciferase reporter assays showed that a 148-bp region upstream of the ATG start codon of Tas1r1 had a promoter activity. The GT box in the Tas1r1 promoter was conserved in the dog, human, mouse, and pig. Site-directed mutagenesis of this GT box significantly reduced the promoter activation. The GT box in promoters is a recurring motif for Sp/KLF family members. RNAi-mediated depletion of Sp4 and Klf5 decreased Tas1r1 expression, while overexpression of Klf5, but not Sp4, significantly increased Tas1r1 expression. The ENCODE data of chromatin immunoprecipitation and sequencing (ChIP-seq) showed that Klf5 bound to the GT box during the myogenic differentiation. Furthermore, the Klf5 knockout cell lines led to a considerable decrease in the levels of Tas1r1 expression. Collectively, these results showed that Klf5 binds to the GT box in the Tas1r1 promoter and regulates Tas1r1 expression in C2C12 cells.