Cone photoreceptor cyclic nucleotide-gated (CNG) channel is essential for central and color vision and visual acuity. Mutations in the cone channel subunits CNGA3 and CNGB3 are linked to achromatopsia and progressive cone dystrophy in humans. Over 50 mutations have been identified in the CNGA3 subunit. The R277C and R283W substitutions are among the most frequently occurring mutations. This study investigated the defects of these two mutations using a heterologous expression system. The wild type and mutant CNGA3 were expressed in HEK293 cells, the channel’s expression and cellular localization were examined by immunoblotting and immunofluorecences labeling, and activity of the channel was evaluated by ratiometric [Ca2+]i measurements and by electrophysiological recordings. By using this model system we observed dysfunction of the mutant channels. Co-expression of the mutant channel with the wild type subunit did not affect the wild type channel’s activity. Immunoflurescence labeling showed apparent cytosol aggregation of the immunoreactivity in cells expressing the mutants. Thus these disease-causing mutations appear to induce loss of function by impairing the channel cellular trafficking and plasma membrane targeting. Therapeutic supplementation of the wild type transgene may help correct the visual disorders caused by these two mutations.
This is a preview of subscription content, log in to check access
This work was supported by grants from the National Center For Research Resources (P20RR017703), the National Eye Institute (P30EY12190), the American Health Assistance Foundation, and the Presbyterian Health Foundation. We thank Dr. Benjamin Kaupp for providing the monoclonal anti-CNGA3 antibody.
Ding XQ, Fitzgerald JB, Matveev AV et al (2008) Functional activity of photoreceptor cyclic nucleotide-gated channels is dependent on the integrity of cholesterol- and sphingolipid-enriched membrane domains. Biochemistry 47:3677–3687CrossRefPubMedGoogle Scholar
Faillace MP, Bernabeu RO, Korenbrot JI (2004) Cellular processing of cone photoreceptor cyclic GMP-gated ion channels: a role for the S4 structural motif. J Biol Chem 279:22643–22653CrossRefPubMedGoogle Scholar
Fitzgerald JB, Malykhina AP, Al-Ubaidi MR et al (2008) Functional expression of cone cyclic nucleotide-gated channel in cone photoreceptor-derived 661 W cells. Adv Exp Med Biol 613:327–334CrossRefPubMedGoogle Scholar
Kohl S, Marx T, Giddings I et al (1998) Total colourblindness is caused by mutations in the gene encoding the alpha-subunit of the cone photoreceptor cGMP-gated cation channel. Nat Genet 19:257–259CrossRefPubMedGoogle Scholar
Liu C, Varnum MD (2005) Functional consequences of progressive cone dystrophy-associated mutations in the human cone photoreceptor cyclic nucleotide-gated channel CNGA3 subunit. Am J Physiol Cell Physiol 289:C187–C198CrossRefPubMedGoogle Scholar
Malykhina AP, Qin C, Greenwood-van Meerveld B et al (2006) Hyperexcitability of convergent colon and bladder dorsal root ganglion neurons after colonic inflammation: mechanism for pelvic organ cross-talk. Neurogastroenterol Motil 18:936–948CrossRefPubMedGoogle Scholar
Matveev AV, Quiambao AB, Fitzgerald JB et al (2008) Native cone photoreceptor cyclic nucleotide-gated channel is a heterotetrameric complex comprising both CNGA3 and CNGB3: a study using the cone-dominant retina of Nrl–/– mice. J Neurochem 106(5):2042–2055PubMedGoogle Scholar
Nishiguchi KM, Sandberg MA, Gorji N et al (2005) Cone cGMP-gated channel mutations and clinical findings in patients with achromatopsia, macular degeneration, and other hereditary cone diseases. Hum Mutat 25:248–258CrossRefPubMedGoogle Scholar
Patel KA, Bartoli KM, Fandino RA et al (2005) Transmembrane S1 mutations in CNGA3 from achromatopsia 2 patients cause loss of function and impaired cellular trafficking of the cone CNG channel. Invest Ophthalmol Vis Sci 46:2282–2290CrossRefPubMedGoogle Scholar