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Impaired intracellular transport contributes to partial thyroxine-binding globulin deficiency in a Japanese family

Impaired intracellular transport contributes to partial thyroxine-binding globulin deficiency in... Abstract We have previously reported a Japanese family manifesting partial TBG deficiency (TBG-PDJ). This variant was characterized by a decreased level of serum TBG concentration, heat lability, and normal isoelectric focussing pattern, but the affinity to iodothyronine is unknown. The TBG-PDJ gene possesses a single nucleotide substitution replacing the normal Pro363(CCT) with Leu(CTT); however, the precise mechanism that results in the reduction of the TBG concentration in the serum of the subjects harboring this mutation remains unknown. This was investigated in the current communication by expressing the complementary DNAs of TBG-PDJ and the common type TBG (TBG-C) in COS-1 cells. Pulse-chase experiments revealed impaired secretion of TBG-PDJ. TBG-C secretion into the medium was evident during 60 min of the pulse period and was almost completed by 12 h. On the other hand, TBG-PDJ was secreted slowly and continued to accumulate between 12-24 h of the chase period. The molecular mass of TBG-PDJ in the cell lysate was identical to that of TBG-C when estimated by gel electrophoresis (54 kilodaltons). The content of TBG-PDJ in the cell lysate decreased less rapidly than that of TBG-C, indicating that impaired TBG-PDJ secretion accounts for the partial TBG deficiency. Oligosaccharide units of intracellular TBG-C were resistant to endoglycosidase-H, but half of those of TBG-PDJ were sensitive to the enzyme digestion, suggesting partial retention of TBG-PDJ within the rough endoplasmic reticulum. Northern blot analysis revealed abundant messenger ribonucleic acid for the glucose-regulated protein-78, the level of which was 3.54-fold greater in the cells transfected with TBG-PDJ than in nontransfected COS-1 cells, whereas that in TBG-C-transfected cells was same as that in the nontransfected cells. Increased expression of glucose-regulated protein-78 together with the sensitivity to endoglycosidase-H suggests impairment of intracellular processing of TBG-PDJ. Our results indicate that the impaired intracellular transport of the TBG-PDJ molecule is the main cause of the reduced concentration of immunoreactive TBG in the serum of subjects harboring this TBG variant. This content is only available as a PDF. Copyright © 1994 by The Endocrine Society http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Clinical Endocrinology and Metabolism Oxford University Press

Impaired intracellular transport contributes to partial thyroxine-binding globulin deficiency in a Japanese family

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References (25)

Publisher
Oxford University Press
Copyright
Copyright © 1994 by The Endocrine Society
ISSN
0021-972X
eISSN
1945-7197
DOI
10.1210/jcem.79.3.8077354
Publisher site
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Abstract

Abstract We have previously reported a Japanese family manifesting partial TBG deficiency (TBG-PDJ). This variant was characterized by a decreased level of serum TBG concentration, heat lability, and normal isoelectric focussing pattern, but the affinity to iodothyronine is unknown. The TBG-PDJ gene possesses a single nucleotide substitution replacing the normal Pro363(CCT) with Leu(CTT); however, the precise mechanism that results in the reduction of the TBG concentration in the serum of the subjects harboring this mutation remains unknown. This was investigated in the current communication by expressing the complementary DNAs of TBG-PDJ and the common type TBG (TBG-C) in COS-1 cells. Pulse-chase experiments revealed impaired secretion of TBG-PDJ. TBG-C secretion into the medium was evident during 60 min of the pulse period and was almost completed by 12 h. On the other hand, TBG-PDJ was secreted slowly and continued to accumulate between 12-24 h of the chase period. The molecular mass of TBG-PDJ in the cell lysate was identical to that of TBG-C when estimated by gel electrophoresis (54 kilodaltons). The content of TBG-PDJ in the cell lysate decreased less rapidly than that of TBG-C, indicating that impaired TBG-PDJ secretion accounts for the partial TBG deficiency. Oligosaccharide units of intracellular TBG-C were resistant to endoglycosidase-H, but half of those of TBG-PDJ were sensitive to the enzyme digestion, suggesting partial retention of TBG-PDJ within the rough endoplasmic reticulum. Northern blot analysis revealed abundant messenger ribonucleic acid for the glucose-regulated protein-78, the level of which was 3.54-fold greater in the cells transfected with TBG-PDJ than in nontransfected COS-1 cells, whereas that in TBG-C-transfected cells was same as that in the nontransfected cells. Increased expression of glucose-regulated protein-78 together with the sensitivity to endoglycosidase-H suggests impairment of intracellular processing of TBG-PDJ. Our results indicate that the impaired intracellular transport of the TBG-PDJ molecule is the main cause of the reduced concentration of immunoreactive TBG in the serum of subjects harboring this TBG variant. This content is only available as a PDF. Copyright © 1994 by The Endocrine Society

Journal

Journal of Clinical Endocrinology and Metabolism – Oxford University Press

Published: Sep 1, 1994

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