Lactase persistence DNA variant enhances lactase promoter activity in vitro: functional role as a cis regulatory element

Abstract

Lactase persistence is a heritable, autosomal dominant, condition that results in a sustained ability to digest the milk sugar lactose throughout adulthood. The majority of the world's human population experiences a decline in production of the digestive enzyme lactase-phlorizin hydrolase during maturation. However, individuals with lactase persistence continue to express high levels of the lactase gene into adulthood. Lactase persistence has been strongly correlated with single nucleotide genetic variants, C/T_(13910) and G/A_(22018), located 13.9 and 22 kb upstream from the lactase structural gene. We aimed to characterize a functional role for the polymorphisms in regulating lactase gene transcription. DNA in the region of the C/T_(13910) or G/A_(22018) human lactase variants was cloned upstream of the 3.0 kb rat lactase gene promoter in a luciferase reporter construct. Human intestinal Caco-2 cells were transfected with the lactase variant/promoter-reporter constructs and assayed for promoter activity. A 200 bp region surrounding the C_(13910) variant, associated with lactase non-persistence, results in a 2.2-fold increase in lactase promoter activity. The T_(13910) variant, associated with lactase persistence, results in an even greater 2.8-fold increase. The DNA sequence of the C/T_(13910) variants differentially interacts with intestinal cell nuclear proteins on EMSAs. AP2 co-transfection results in a similar repression of the C/T_(13910) variant/promoter-reporter constructs. The DNA region of the C/T_(13910) lactase persistence/non-persistence variant functions in vitro as a cis element capable of enhancing differential transcriptional activation of the lactase promoter. Such differential regulation by the C and T variants is consistent with a causative role in the mechanism specifying the lactase persistence/non-persistence phenotypes in humans.

The genetic variant of lactase persistence C (−13910) T as a risk factor for type I and II diabetes in the Finnish population

“…Functional evidence for the nonpersistent C À13910 allele and persistent T À13910 allele has recently been obtained by relative quantitation of the expressed LPH alleles that show several times higher expression of LPH mRNA in the intestinal mucosa in individuals with the T À13910 allele compared to that found in individuals with the C À13910 allele, suggesting regulation of the LPH gene at the transcriptional level (Kuokkanen et al, 2003). This is in agreement with recent functional studies reporting greater increase in lactase promoter activity by the T À13910 variant using Luciferase reporter constructs (Olds & Sibley, 2003;Troelsen et al, 2003).…”

Associations of the lactase persistence allele and lactose intake with body composition among multiethnic children

“…The ''T'' variant disrupts this binding motif and allows lactase production to occur at a rapid pace. Thus, the presence of a ''T'' variant is associated with unhindered gene transcription and lactase production, whereas a homozygous genotype for the ''C'' variant is associated with dysfunctional lactase production which results in lactose intolerance (Enattah et al 2002;Olds and Sibley 2003).…”

The Reluctant Calf

“…However, it is at least reassuring that persistence and dairying-history correlations are found elsewhere in the world, 6,10,14 and that European lactose intolerance is specifically associated with the tolerance allele. And there's yet more to this story.…”

“…A few exceptions have been claimed, of lactose-tolerant Europeans without the expected T allele. 6,10 This may indicate genetic heterogeneity, but a new study has found a pattern of chromosomal haplotype-sharing that extends much farther around the LCT gene, raising the possibility that the T mutation arose on a larger haplotype subsequent to some other undiscovered mutation that was already present and is the truly causal one. 11 And there is circumstantial evidence in some African dairying populations that the T allele may not be as frequent as selective arguments would predict.…”