Transcription factor CAAT/enhancer-binding protein is involved in regulation of expression of sterol carrier protein x in Spodoptera litura.

The Spodoptera litura sterol carrier protein x (SlSCPx) gene is expressed in various tissues throughout the life cycle and plays important role in sterol absorption and transport. In this study, the effects of insect hormones (20-hydroexcdysone and juvenile hormone) and lipids (arachidonic acid, cholesterol) on the expression of SlSCPx was analysed by reverse-transcriptase PCR. The results showed that none of these substances significantly induced the expression of SlSCPx in Spodoptera litura-221 (Spli-221) cells. To identify the transcription factors responsible for regulation of SlSCPx expression, a 3311-bp promoter sequence of the gene was cloned. Transcriptional activity of the promoter was studied using an in vivo promoter/reporter system and a 29-bp sequence between -1000 and -1029 nucleotides (nt) upstream of this gene was found to be responsible for the up-regulation of the gene. Over-expression of CAAT/enhancer-binding protein (C/EBP) in Spli-221 cells increased the promoter activity 5.57-fold. An electrophoretic mobility shift assay showed that two nuclear proteins bound to this sequence. Recombinant C/EBP specifically bound with a putative cis-regulatory element (CRE). Mutation of the C/EBP CRE abolished the binding of the C/EBP with the CRE. These results suggest that the transcription factor C/EBP may regulate the expression of SlSCPx by binding to the CRE in the promoter of this gene.