Nw. Lo et Jty. Lau, TRANSCRIPTION OF THE BETA-GALACTOSIDE ALPHA-2,6-SIALYLTRANSFERASE GENE IN B-LYMPHOCYTES IS DIRECTED BY A SEPARATE AND DISTINCT PROMOTER, Glycobiology, 6(3), 1996, pp. 271-279
A single human gene, SIAT1, encodes the beta-galactoside alpha 2,6-sia
lyltransferase from which multiple mRNA isoforms are generated, In rat
, expression of the hepatic mRNA isoform (Form I) has been defined wit
h respect to the transcriptional initiation site and promoter region,
We show here that a similar hepatic SIAT1 mRNA isoform exists in human
, Another human mRNA isoform, a mature B-cell-specific mRNA isoform (F
orm 2), was previously reported, Here, we used 5'-RACE and S1 nuclease
protection analysis to define the 5'-untranslated region of Form 2 hu
man SIAT1 mRNA. We demonstrate conclusively that Form 2 mRNA is initia
ted from a point completely distinct from that of Form I mRNA, A numbe
r of cis-acting regulatory elements residing immediately 5' of the For
m 2 initiation site includes AP-1, AP-2, NF-kappa B, NF-IL6, C/EBP, an
d CREB, A TATAA box is also present 29 bp 5' of the transcriptional in
itiation site. CAT reporter gene expression from serially-truncated se
gments of the 5'-flanking region of the Form 2 initiation site indicat
es that the segment between (-)784 and (+)125 was sufficient to promot
e high level CAT expression in Louckes, a mature B-cell line, The 5'-f
lanking region to the human Form I initiation site is competent in exp
ression of CAT upon transfection of the fusion construct into HepG2 a
human hepatoma cell line, Cellular specificity of expression is appare
ntly retained, Louckes cells expressed CAT efficiently from Form 2 pro
moter but only marginally from the Form I promoter, In contrast, CAT e
xpression from Form I promoter is more efficient than from the Form 2
promoter in HepG2 cells.