Retinopathy mutations in the bZIP protein NRL alter phosphorylation and transcriptional activity.
The transcription factor neural retina leucine zipper (NRL) is required for rod photoreceptor differentiation during mammalian retinal development. NRL interacts with CRX, NR2E3, and other transcription factors and synergistically regulates the activity of photoreceptor-specific genes. Mutations in the human NRL gene are associated with retinal degenerative diseases. Here we report functional analyses of 17 amino acid variations and/or mutations of NRL. We show that 13 of these lead to changes in NRL phosphorylation. Six mutations at residues p.S50 (c.148T>A, c.148T>C, and c.149C>T) and p.P51 (c.151C>A, c.151C>T, and c.152C>T), identified in patients with autosomal dominant retinitis pigmentosa, result in a major NRL isoform that exhibits reduced phosphorylation but enhanced activation of the rhodopsin promoter. The truncated NRL mutant proteins-p.L75fs (c.224_225insC) and p.L160fs (c.459_477dup)-do not localize to the nucleus because of the absence of bZIP domain. The p.L160P (c.479T>C), p.L160fs, and p.R218fs (c.654delC) mutant proteins do not bind to the NRL-response element, as revealed by electrophoretic mobility shift assays. These three and p.S225N (c.674G>A) mutant show reduced transcriptional activity and may contribute to recessive disease. The p.P67S (c.199C>T) and p.L235F (c.703C>T) variations in NRL do not appear to directly cause retinitis pigmentosa, while p.E63K (c.187G>A), p.A76V (c.227C>T), p.G122E (c.365G>A), and p.H125Q (c.375C>G) are of uncertain significance. Our results support the notion that gain-of-function mutations in the NRL gene cause autosomal dominant retinitis pigmentosa while loss-of-function NRL mutations lead to autosomal recessive retinitis pigmentosa. We propose that differential phosphorylation of NRL fine-tunes its transcriptional regulatory activity, leading to a more precise control of gene expression.
Kanda
Atsuhiro
A
Department of Ophthalmology and Visual Sciences, W.K. Kellogg Eye Center, University of Michigan, Ann Arbor, Michigan 48105, USA.
Friedman
James S
JS
Nishiguchi
Koji M
KM
Swaroop
Anand
A
D021581:Active Transport, Cell Nucleus / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D050976:Basic-Leucine Zipper Transcription Factors / Q000235:genetics* / Q000378:metabolism; D019556:COS Cells; D002460:Cell Line; D002522:Chlorocebus aethiops; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D005136:Eye Proteins / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation; D005799:Genes, Dominant; D005808:Genes, Recessive; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D012162:Retinal Degeneration / Q000235:genetics*; D012174:Retinitis Pigmentosa / Q000235:genetics*; D012243:Rhodopsin / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D015533:Transcriptional Activation / Q000235:genetics; D014162:Transfection
D050976:Basic-Leucine Zipper Transcription Factors; D004268:DNA-Binding Proteins; D005136:Eye Proteins; C490037:NRL protein, human; D004247:DNA; D012243:Rhodopsin