Functional analysis of promoter variants in the microsomal triglyceride transfer protein (MTTP) gene.
The microsomal triglyceride transfer protein (MTTP) is required for the assembly and secretion of apolipoprotein B (apoB)-containing lipoproteins from the intestine and liver. According to this function, polymorphic sites in the MTTP gene showed associations to low-density lipoprotein (LDL) cholesterol and related traits of the metabolic syndrome. Here we studied the functional impact of common MTTP promoter polymorphisms rs1800804:T>C (-164T>C), rs1800803:A>T (-400A>T), and rs1800591:G>T (-493G>T) using gene-reporter assays in intestinal Caco-2 and liver Huh-7 cells. Significant results were obtained in Huh-7 cells. The common MTTP promoter haplotype -164T/-400A/-493G showed about two-fold lower activity than the rare haplotype -164C/-400T/-493T. MTTP promoter mutant constructs -164T/-400A/-493T and -164T/-400T/-493T exhibited similar activity than the common haplotype. Activities of mutants -164C/-400A/-493G and -164C/-400A/-493T resembled the rare MTTP promoter haplotype. Electrophoretic mobility shift assays (EMSAs) revealed higher binding capacity of the transcriptional factor Sterol regulatory element binding protein1a (SREBP1a) to the -164T probe in comparison to the -164C probe. In conclusion, our study indicates that the polymorphism -164T>C mediates different activities of common MTTP promoter haplotypes via SREBP1a. This suggested that the already described SREBP-dependent modulation of MTTP expression by diet is more effective in -164T than in -164C carriers.
Rubin
Diana
D
Institute of Physiology and Biochemistry of Nutrition, Federal Research Center for Nutrition and Food, Kiel, Germany. diana.rubin@bfel.de
Schneider-Muntau
Alexandra
A
Klapper
Maja
M
Nitz
Inke
I
Helwig
Ulf
U
Fölsch
Ulrich R
UR
Schrezenmeir
Jürgen
J
Döring
Frank
F
D000483:Alleles; D001665:Binding Sites; D018938:Caco-2 Cells; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D002478:Cells, Cultured; D014644:Genetic Variation; D006239:Haplotypes; D006801:Humans; D008862:Microsomes, Liver / Q000378:metabolism; D020641:Polymorphism, Single Nucleotide; D011401:Promoter Regions, Genetic; D051780:Sterol Regulatory Element Binding Protein 1 / Q000378:metabolism; D024363:Transcription Initiation Site; D014162:Transfection
D002352:Carrier Proteins; D051780:Sterol Regulatory Element Binding Protein 1; C106092:microsomal triglyceride transfer protein