D - Glucose Modulates Intestinal Niemann - Pick C 1 Like 1 ( NPC 1 L 1 ) Gene 1 Expression via Transcriptional Regulation

44 The expression of intestinal NPC1L1 cholesterol transporter has been shown to be 45 elevated in patients with diseases associated with hypercholesterolemia such as 46 diabetes mellitus. High levels of glucose were shown to directly increase the expression 47 of NPC1L1 in intestinal epithelial cells but the underlying mechanisms are not fully 48 defined. The current studies were, therefore, undertaken to examine the transcriptional 49 regulation of NPC1L1 expression in human intestinal Caco2 cells in response to glucose. 50 Removal of glucose from the culture medium of Caco2 cells for 24 h significantly 51 decreased the NPC1L1 mRNA, protein expression as well as the promoter activity. 52 Glucose replenishment significantly increased the promoter activity of NPC1L1 in a dose 53 dependent manner as compared to control cells. Exposure of Caco2 cells to non54 metabolizeable form of glucose, 3-O-methyl-D-glucopyranose (OMG) had no effect on 55 NPC1L1 promoter activity indicating that the observed effects are dependent on glucose 56 metabolism. Further, glucose-mediated increase in promoter activity was abrogated in 57 the presence of okadiac acid suggesting the involvement of protein phosphatases. 58 Glucose effects on several deletion constructs of NPC1L1 promoter demonstrated that 59 cis-elements mediating the effects of glucose are located in the region between -291 and 60 +56 of NPC1L1 promoter. Consistent with the effects of glucose removal on NPC1L1 61 expression in Caco2 cells, 24 h fasting resulted in a significant decrease in the relative 62 expression of NPC1L1 in mouse jejunum. In conclusion, glucose appears to directly 63 modulate NPC1L1 expression via a transcriptional mechanisms and the involvement of 64 phosphatase-dependent pathways. 65