Heterogeneity in the processing defect of SLC26A4 mutants.
BACKGROUND
Mutations in the SLC26A4 gene are responsible for Pendred syndrome and non-syndromic hearing loss (DFNB4). This study analysed non-synonymous SLC26A4 mutations newly identified in East Asians, as well as three common mutations in Caucasians, to characterise their molecular pathogenic mechanisms and to explore the possibility of rescuing their processing defects.


METHODS
A total of 11 non-synonymous disease associated mutations were generated and their effects on protein processing and on ion transporting activities were examined.


RESULTS
Most of the mutations caused retention of the SLC26A4 gene product (pendrin) in the intracellular region, while wild-type pendrin reached the plasma membrane. Accordingly, these mutations abolished complex glycosylation and Cl(-)/HCO(3)(-) exchange activities of pendrin. However, significant heterogeneity in the processing of mutant pendrin molecules was observed. Each mutant protein exhibited a different cellular localisation, a different degree of N-glycosylation, and a different degree of sensitivity to the treatments that rescue processing defects. For example, H723R-pendrin, the most common mutation in East Asians, was mostly expressed in endoplasmic reticulum (ER), and its defects in protein processing and ion transporting activities were restored considerably by low temperature incubation. On the other hand, L236P-pendrin, the most common mutation in Caucasians, was mainly in the centrosomal region and was temperature insensitive.


CONCLUSIONS
These results indicate that the processing of pendrin mutant protein is determined by mutant specific mechanisms, and that a mutant specific method would be required to rescue the conformational defects of each folding mutant.
Yoon
J S
JS
Department of Pharmacology and Brain Korea 21 Project for Medical Science, Yonsei University College of Medicine, Seoul, Korea.
Park
H-J
HJ
Yoo
S-Y
SY
Namkung
W
W
Jo
M J
MJ
Koo
S K
SK
Park
H-Y
HY
Lee
W-S
WS
Kim
K H
KH
Lee
M G
MG
D027963:Chloride-Bicarbonate Antiporters / Q000378:metabolism; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D014644:Genetic Variation; D006367:HeLa Cells; D006319:Hearing Loss, Sensorineural / Q000235:genetics*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D015151:Immunoblotting; D026901:Membrane Transport Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D016133:Polymerase Chain Reaction; D000076988:Sulfate Transporters; D014162:Transfection
D027963:Chloride-Bicarbonate Antiporters; D018076:DNA, Complementary; D026901:Membrane Transport Proteins; C085609:SLC26A4 protein, human; D000076988:Sulfate Transporters