SLC16A12
Monocarboxylate transporter 12 (MCT 12) (Creatine transporter 2) (CRT2) (Solute carrier family 16 member 12) [MCT12]
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SLC16A12 encodes an orphan member of the monocarboxylate transporter family, MCT12. A nonsense mutation in SLC16A12 (c.643C>T; p.Q215X) causes juvenile cataract with a dominant inheritance pattern. In the present study, in vitro and in vivo experimental models were used to gain insight into how the SLC16A12 (c.643C>T) mutation leads to cataract formation. MCT12 peptide antibodies were generated and used to examine the expression of MCT12 in the lens using immuno-confocal microscopy. To determine whether loss of Slc16a12 resulted in cataract formation, a Slc16a12 hypomorphic rat generated by transposon insertional mutagenesis was characterized using RT-PCR, slit lamp microscopy and histologic methods. Exogenous expression of MCT12 and MCT12:214Δ, a mimic of the mutant allele, were used to assess protein expression and trafficking. MCT12 protein was detected in the lens epithelium and secondary fiber cells at postnatal day 1. In the Slc16a12(TKO) rat, complete loss of MCT12 did not result in any detectable ocular phenotype. Exogenous expression of MCT12-GFP and MCT12:214Δ-GFP revealed that the full-length protein was trafficked to the plasma membrane (PM), whereas the truncated protein was retained in the endoplasmic reticulum (ER). When both MCT12 and MCT12:214Δ were coexpressed, to mimic the heterozygous patient genotype, the truncated protein was retained in the ER whereas full-length MCT12 was trafficked to the PM. Furthermore, MCT12 was identified as another MCT isoform that requires CD147 for trafficking to the cell surface. These data support a model whereby the SLC16A12 (c.643C>T) mutation causes juvenile cataract by a defect in protein trafficking rather than by haploinsufficiency.
MeSH Terms
- Aging
- Animals
- Animals, Newborn
- Cataract
- Cell Membrane
- Cells, Cultured
- DNA
- Disease Models, Animal
- Epithelium
- Gene Expression
- Genotype
- Immunoblotting
- Immunoprecipitation
- Lens, Crystalline
- Mice
- Mice, Inbred C57BL
- Microscopy, Acoustic
- Microscopy, Confocal
- Microscopy, Electron, Scanning
- Monocarboxylic Acid Transporters
- Mutation
- Protein Transport
- Rats
- Rats, Inbred F344
- Reverse Transcriptase Polymerase Chain Reaction
PURPOSE. Knowledge of genetic factors predisposing to age-related cataract is very limited. The aim of this study was to identify DNA sequences that either lead to or predispose for this disease. METHODS. The candidate gene SLC16A12, which encodes a solute carrier of the monocarboxylate transporter family, was sequenced in 484 patients with cataract (134 with juvenile cataract, 350 with age-related cataract) and 190 control subjects. Expression studies included luciferase reporter assay and RT-PCR experiments. RESULTS. One patient with age-related cataract showed a novel heterozygous mutation (c.-17A>G) in the 5'untranslated region (5'UTR). This mutation is in cis with the minor G-allele of the single nucleotide polymorphism (SNP) rs3740030 (c.-42T/G), also within the 5'UTR. Using a luciferase reporter assay system, a construct with the patient's haplotype caused a significant upregulation of luciferase activity. In comparison, the SNP G-allele alone promoted less activity, but that amount was still significantly higher than the amount of the common T-allele. Analysis of SLC16A12 transcripts in surrogate tissue demonstrated striking allele-specific differences causing 5'UTR heterogeneity with respect to sequence and quantity. These differences in gene expression were mirrored in an allele-specific predisposition to age-related cataract, as determined in a Swiss population (odds ratio approximately 2.2; confidence intervals, 1.23-4.3). CONCLUSIONS. The monocarboxylate transporter SLC16A12 may contribute to age-related cataract. Sequences within the 5'UTR modulate translational efficiency with pathogenic consequences.
MeSH Terms
- 5' Untranslated Regions
- Aged
- Aging
- Cataract
- Cell Line
- Cloning, Molecular
- DNA Primers
- Female
- Gene Expression Regulation
- Genetic Predisposition to Disease
- Genetic Vectors
- Humans
- Monocarboxylic Acid Transporters
- Muscle, Smooth, Vascular
- Mutation
- Plasmids
- Polymorphism, Single Nucleotide
- Radial Artery
- Reverse Transcriptase Polymerase Chain Reaction