Functional analysis of two regulatory regions of the human Na+-dependent vitamin C transporter 2, SLC23A2, in human vascular smooth muscle cells

Uptake of vitamin C occurs through the Na+-dependent vitamin C transporters (SVCT1 and 2), the products of two separate genes. In cultured human vascular smooth muscle cells (hVSMC), we found expression of only the hSVCT2 transcript and identified an additional 5′-UTR transcript variant that we termed exon 1b, in addition to the previously described exon 1a. We cloned and tested the promoter functionality of the two genomic regions of the hSVCT2 upstream of these alternative first exons in hVSMC. Both demonstrated activity, and deletion constructs demonstrated that the minimal promoter regions were within ∼100 bp relative to their adjacent exons.