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Thyroid hormone is a critical determinant for the regulation of the cochlear motor protein prestin.

ABSTRACT: The most impressive property of outer hair cells (OHCs) is their ability to change their length at high acoustic frequencies, thus providing the exquisite sensitivity and frequency-resolving capacity of the mammalian hearing organ. Prestin, a protein related to a sulfate/anion transport protein, recently has been identified and proposed as the OHC motor molecule. Homology searches of 1.5 kb of genomic DNA 5' of the coding region of the prestin gene allowed the identification of a thyroid hormone (TH) response element (TRE) in the first intron upstream of the prestin ATG codon. Prestin(TRE) bound TH receptors as a monomer or presumptive heterodimer and mediated a triiodothyronine-dependent transactivation of a heterologous promotor in response to triiodothyronine receptors alpha and beta. Retinoid X receptor-alpha had an additive effect. Expression of prestin mRNA and prestin protein was reduced strongly in the absence of TH. Although prestin protein typically was redistributed to the lateral membrane before the onset of hearing, an immature pattern of prestin protein distribution across the entire OHC membrane was noted in hypothyroid rats. The data suggest TH as a first transcriptional regulator of the motor protein prestin and as a direct or indirect modulator of subcellular prestin distribution.

SUBMITTER: Weber T

PROVIDER: S-EPMC122445 | biostudies-literature | 2002 Mar

REPOSITORIES: biostudies-literature

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Thyroid hormone is a critical determinant for the regulation of the cochlear motor protein prestin.

Weber Thomas T Zimmermann Ulrike U Winter Harald H Mack Andreas A Köpschall Iris I Rohbock Karin K Zenner Hans-Peter HP Knipper Marlies M

Proceedings of the National Academy of Sciences of the United States of America 20020226 5

The most impressive property of outer hair cells (OHCs) is their ability to change their length at high acoustic frequencies, thus providing the exquisite sensitivity and frequency-resolving capacity of the mammalian hearing organ. Prestin, a protein related to a sulfate/anion transport protein, recently has been identified and proposed as the OHC motor molecule. Homology searches of 1.5 kb of genomic DNA 5' of the coding region of the prestin gene allowed the identification of a thyroid hormone ...[more]

PMID: 11867734

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Project description:Cochlear outer hair cells change their length in response to variations in membrane potential. This capability, called electromotility, is believed to enable the sensitivity and frequency selectivity of the mammalian cochlea. Prestin is a transmembrane protein required for electromotility. Homozygous prestin knockout mice are profoundly hearing impaired. In humans, a single nucleotide change in SLC26A5, encoding prestin, has been reported in association with hearing loss. This DNA sequence variation, IVS2-2A>G, occurs in the exon 3 splice acceptor site and is expected to abolish splicing of exon 3.To further explore the relationship between hearing loss and the IVS2-2A>G transition, and assess allele frequency, genomic DNA from hearing impaired and control subjects was analyzed by DNA sequencing. SLC26A5 genomic DNA sequences from human, chimp, rat, mouse, zebrafish and fruit fly were aligned and compared for evolutionary conservation of the exon 3 splice acceptor site. Alternative splice acceptor sites within intron 2 of human SLC26A5 were sought using a splice site prediction program from the Berkeley Drosophila Genome Project.The IVS2-2A>G variant was found in a heterozygous state in 4 of 74 hearing impaired subjects of Hispanic, Caucasian or uncertain ethnicity and 4 of 150 Hispanic or Caucasian controls (p = 0.45). The IVS2-2A>G variant was not found in 106 subjects of Asian or African American descent. No homozygous subjects were identified (n = 330). Sequence alignment of SLC26A5 orthologs demonstrated that the A nucleotide at position IVS2-2 is invariant among several eukaryotic species. Sequence analysis also revealed five potential alternative splice acceptor sites in intron 2 of human SLC26A5.These data suggest that the IVS2-2A>G variant may not occur more frequently in hearing impaired subjects than in controls. The identification of five potential alternative splice acceptor sites in intron 2 of human SLC26A5 suggests a potential mechanism by which expression of prestin might be maintained in cells carrying the SLC26A5 IVS2-2A>G DNA sequence variation. Additional studies are needed to evaluate the effect of the IVS2-2A>G transition on splicing of SLC26A5 transcripts and characterize the hearing status of individuals homozygous for the IVS2-2A>G variant.

Project description:1. The effect of thyroidectomy on turnover rates of liver, kidney and brain mitochondrial proteins was examined. 2. In the euthyroid state, liver and kidney mitochondria show a synchronous turnover with all protein components showing more or less identical half-lives compared with the whole mitochondria. The brain mitochondrial proteins show asynchronous turnover, the soluble proteins having shorter half-lives. 3. Mitochondrial DNA (m-DNA) of liver and kidney has half-lives comparable with that of whole mitochondria from these tissues. 4. Thyroidectomy results in increased half-lives of liver and kidney mitochondria, with no apparent change in the half-life of brain mitochondria. 5. A detailed investigation of the turnover rates of several protein components revealed a significant decrease in the turnover rates of mitochondrial insoluble proteins from the three tissues under study. 6. The turnover rates of m-DNA of liver and kidney show a parallel decrease. 7. Thus it is apparent that thyroid hormone(s) may have a regulatory role in maintaining the synchrony of turnover of liver and kidney mitochondria in the euthyroid state. Turnover of brain mitochondria may perhaps be regulated by some other factor(s) in addition to thyroid hormone(s). 8. It seems likely that during mitochondrial turnover m-DNA and insoluble proteins may constitute a major unit. 9. The mitochondrial protein contents of the three tissues are not affected by thyroidectomy. 10. No correlation was seen between the turnover rate of mitochondria and cathepsin activity in any of the tissues under study in normal or thyroidectomized animals. 11. On the other hand, mitochondrial proteinase activity shows good correlation with the turnover rates of mitochondria in normal animals, and a parallel decrease in activity comparable with the decreased rates of turnover is observed after thyroidectomy. 12. It is concluded that mitochondrial proteinase activity may play a significant role in their protein turnover.

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Thyroid hormone is a critical determinant for the regulation of the cochlear motor protein prestin.

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Thyroid hormone is a critical determinant for the regulation of the cochlear motor protein prestin.

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