Demonstration of a Ca2+ requirement for thyroglobulin dimerization and export to the golgi complex.
We have examined the effects of depleting the endoplasmic reticulum Ca2+ store on the maturation of newly synthesized thyroglobulin molecules, their export to the Golgi complex, and their secretion by FRTL-5 cells. An inhibitor of the endoplasmic reticulum Ca2+ pump, thapsigargin, and the Ca2+ ionophore A23187 depleted the endoplasmic reticulum Ca2+ store and strongly inhibited thyroglobulin secretion in cells chased in medium containing 0.1 mM Ca2+. Inhibition of thyroglobulin secretion was caused by a block in the export of newly synthesized thyroglobulin molecules from the endoplasmic reticulum to the Golgi complex, as shown by cell-fractionation experiments and the intracellular accumulation of endoH-sensitive thyroglobulin. The thyroglobulin molecules retained in the endoplasmic reticulum of cells treated with the drugs were found to assemble more slowly into dimers than thyroglobulin in control cells. Protease-sensitivity experiments demonstrated that thyroglobulin dimers assembled in the presence of thapsigargin had a different conformation with respect to dimers assembled in controls cells.
Di Jeso
B
B
Centro di Endocrinologia ed Oncologia Sperimentale del CNR and Dipartimento di Biologia e Patologia Cellulare e Molecolare, Università Federico II Medical School, Napoli, Italy.
Pereira
R
R
Consiglio
E
E
Formisano
S
S
Satrustegui
J
J
Sandoval
I V
IV
D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D002499:Centrifugation, Density Gradient; D019281:Dimerization; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006031:Glycosylation; D006056:Golgi Apparatus / Q000378:metabolism*; D007700:Kinetics; D009844:Oligosaccharides / Q000378:metabolism; D011487:Protein Conformation; D051381:Rats; D019284:Thapsigargin / Q000494:pharmacology; D013954:Thyroglobulin / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D013961:Thyroid Gland / Q000378:metabolism*
D009844:Oligosaccharides; D000001:Calcimycin; D019284:Thapsigargin; D013954:Thyroglobulin; D002118:Calcium