Isolation and Functional Characterization of the Human 90K Promoter

Abstract

90K is a secreted protein thought to be involved in the body's defense against pathogens and cancer. To elucidate its transcriptional regulation, the promoter of human 90K (HGMW-approved symbol LGAL S3BP) was isolated and characterized. Analysis of the 3.3-kb 5′-flanking region revealed that it is a TATA-less promoter, but neither GC-rich nor dependent on SP1 sites. RNase protection assays detected one major transcription start site (+1) and several minor transcription start sites upstream and downstream. Deletion studies defined a minimal promoter (−103 → −49) and indirectly suggested positive synergism between different elements within it. Consistent with the proposed function of 90K, its promoter activity could be stimulated by poly(I) · poly(C), mimicking viral infection. Two regions mediating induction by poly(I) · poly(C) (−171 → −112, −32 → 46) were identified by deletion mutants. A small region around the minimal promoter (−99 → −12) was highly homologous between human and mouse. While both human and mouse minimal promoters contained an interferon-responsive element (IRF-E), the human minimal promoter was not inducible by poly(I) · poly(C) in contrast to that of the mouse. Point mutations 30 bp upstream of the IRF-E, however, conferred inducibility to the human minimal promoter, suggesting interaction between different promoter elements.