CERKL, a Retinal Disease Gene, Encodes an mRNA-Binding Protein That Localizes in Compact and Untranslated mRNPs Associated with Microtubules

Alihamze Fathinajafabadi,Erwin Knecht,Roser Gonzàlez-Duarte,Marina Riera,Eva Pérez-Jiménez

doi:10.1371/journal.pone.0087898

Abstract

The function of CERKL (CERamide Kinase Like), a causative gene of retinitis pigmentosa and cone-rod dystrophy, still awaits characterization. To approach its cellular role we have investigated the subcellular localization and interaction partners of the full length CERKL isoform, CERKLa of 532 amino acids, in different cell lines, including a photoreceptor-derived cell line. We demonstrate that CERKLa is a main component of compact and untranslated mRNPs and that associates with other RNP complexes such as stress granules, P-bodies and polysomes. CERKLa is a protein that binds through its N-terminus to mRNAs and interacts with other mRNA-binding proteins like eIF3B, PABP, HSP70 and RPS3. Except for eIF3B, these interactions depend on the integrity of mRNAs but not of ribosomes. Interestingly, the C125W CERKLa pathological mutant does not interact with eIF3B and is absent from these complexes. Compact mRNPs containing CERKLa also associate with microtubules and are found in neurites of neural differentiated cells. These localizations had not been reported previously for any member of the retinal disorders gene family and should be considered when investigating the pathogenic mechanisms and therapeutical approaches in these diseases.

Highlights

Retinitis pigmentosa (RP) is the most common form of retinal dystrophies and is characterized by night blindness and progressive loss of vision due to photoreceptor degeneration [1]
CERKL localizes to stress granules (SGs) and P-bodies Upon transient transfection, CERKL was found in COS-7 cells both in the cytoplasm and in the nucleus
These aggregates containing CERKL were partially found around the nuclear envelope and endoplasmic reticulum and they were absent from the Golgi complex, mitochondria, early, late and recycling endosomes, clathrin-coated vesicles, lysosomes and autophagosomes (Fig. S1)

Summary

Introduction

Retinitis pigmentosa (RP) is the most common form of retinal dystrophies (prevalence of 1:4,000) and is characterized by night blindness and progressive loss of vision due to photoreceptor degeneration [1]. RP is a hereditary disorder with extremely high genetic heterogeneity and to date more than fifty causative genes have been identified. CERKL (CERamide Kinase Like) was first identified in a RP Spanish family [2] and later was shown to promote cone-rod dystrophy (CRD), a retinal disorder associated with a more severe phenotype [3]. CERKL encodes a protein abundant in cones and present in rods and at the inner nuclear layer and ganglion cell layer [4,5]. Of the many isoforms reported in human and mouse retina [6], only CERKLa (hereafter called CERKL), the full length protein that encompasses all thirteen exonic regions and comprises 532 amino acids, is conserved in vertebrates [7]

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Results

Conclusion