Association analysis identifies ZNF750 regulatory variants in psoriasis

Abstract

Background: Mutations in the ZNF750 promoter and coding regions have been previously associated with Mendelian forms of psoriasis and psoriasiform dermatitis. ZNF750 encodes a putative zinc finger transcription factor that is highly expressed in keratinocytes and represents a candidate psoriasis gene.

Methods: We examined whether ZNF750 variants were associated with psoriasis in a large case-control population. We sequenced the promoter and exon regions of ZNF750 in 716 Caucasian psoriasis cases and 397 Caucasian controls.

Results: We identified a total of 47 variants, including 38 rare variants of which 35 were novel. Association testing identified two ZNF750 haplotypes associated with psoriasis (p < 0.05). We also identified an excess of rare promoter and 5'untranslated region (UTR) variants in psoriasis cases compared to controls (p = 0.041), whereas there was no significant difference in the number of rare coding and rare 3' UTR variants. Using a promoter functional assay in stimulated human primary keratinocytes, we showed that four ZNF750 promoter and 5' UTR variants displayed a 35-55% reduction of ZNF750 promoter activity, consistent with the promoter activity reduction seen in a Mendelian psoriasis family with a ZNF750 promoter variant. However, the rare promoter and 5' UTR variants identified in this study did not strictly segregate with the psoriasis phenotype within families.

Conclusions: Two haplotypes of ZNF750 and rare 5' regulatory variants of ZNF750 were found to be associated with psoriasis. These rare 5' regulatory variants, though not causal, might serve as a genetic modifier of psoriasis.

Figure 1

ZNF750 gene structure and variants. ZNF750 consists of 3 exons, with the translation start site within exon 2. Narrow boxes indicate 5' and 3' untranslated regions; wider boxes indicate translated regions. ZNF750 contains two nuclear localization sites (NLS) and a C2H2 zinc finger domain (ZNF). Arrows depict the locations of a deleterious frameshift mutation seen in a Jewish Moroccan family (56_57dupCC), promoter and 5' UTR variations examined in this study (c.-625A>C, c.-458G>A, c.-261G>A, c.-233 C>T, c.-232G>A), and start sites of ZNF750 mRNA isoforms A and B.

Figure 2

Luciferase activity of ZNF750 regulatory region in human primary keratinocytes. Bar chart representing luciferase activity of pGL3 constructs containing ZNF750 promoter and 5' UTR variants relative to wild type promoter (WT). Four variants (c.-458G>A, c.-261G>A, c.-233C>T, c.-232G>A) were detected in psoriasis patients in this study, one variant (c.-625A>C) was detected in a psoriasis family in previous study, and a pGL3 basic (empty vector) was used as a negative control. Constructs were co-transfected with Renilla luciferase into primary human keratinocytes and then treated for 24 h with culture medium (A) or culture medium supplemented with 250 ng/ml PMA (B). After 48 h, cells were assayed for luciferase activity. A reduction in luciferase activity is seen for all 4 promoter and 5' UTR variants as well as the c.-625A>C external control. The results represent the means ± SD of three independent experiments. *** p < 0.001 compared to WT by t-test.