Alternative promoters and oct-1 gene tissue-specific regulation

Murine oct-1 gene contains exons 1U and 1L at 5'-end, which are alternatively presented in oct-1 mRNA. 1U exon is presented in oct-1 mRNA expressed in all tissues whereas lymphoid cells of mouse and human express mRNA containing alternatively 1U or 1L exon. Upstream of these exons there are U and L promoters, respectively, which are separated by 67 kb in mice otf-1 locus. Nucleotide sequences located upstream 1U and 1L exons are very different: 1U region contains a number of Sp1 sites and I L region contains many homeo-specific sites and two octamers AT-GCAAAT recognized by transcription factors Oct-1, Oct-2 and other POU-domain containing proteins. Oct-1 sites may participate in oct-1 gene autoregulation. The role of U- and L-promoter fragments in oct-1 gene regulation was studied by transfection of luc-containing constructs in lymphoid (NS/0) and non-lymphoid cells. It was shown that L-promoter efficiency is much higher in lymphoid cells than in fibroblast cell line 10/1. U-promoter is active in both types of the cells. Upstream of 1L-exon there is the inhibitory nucleotide sequence which elimination increases the expression level by many times. This silencing element is located between initiation starts of transcription and translation. The obtained data suggest that oct-1 gene contains at least two alternative promoters. It seems that U-promoter promises the constitutive synthesis of Oct-1 protein whereas L-promoter is tissue-specific and putatively is inducible and autoregulated.