Abstract
The present study, utilizing the hormone-responsive rat thyroid cell line FRTL-5, presents evidence establishing the regulatory role of thyrotropin in modulating mRNA for beta-galactoside alpha 2,6-sialytransferase, the enzyme responsible for the expression of alpha 2,6-linked sialic acid. Both the cell surface membrane and the thyroglobulin secreted by cells grown in the presence of this hormone exhibit a marked decrease in the level of alpha 2,6-bound sialic acid with little or no change in the number of alpha 2,3-sialic acid residues. An additional, and unexpected, sequel is the finding of a coordinated decrease in all of the core monosaccharide constituents of the secreted thyroglobulin. Both of the above phenomenological changes appear to be at some variance with previously described systems wherein thyrotropin was deemed to increase glycosylation. It is anticipated that further resolution of this apparent difference may provide a clearer definition for the role of the carbohydrate moiety in affecting the biological function of thyroglobulin.
Highlights
The present study, utilizing the hormone-responsive rat thyroid cell lineFRTL-5, presents evidence establishing the regulatory role of thyrotropin in modulating mRNA for &galactoside cr2,6-sialyltransferase,the enzyme responsible for the expression of a2,6-linked sialic acid
Both the cell surface membrane and the thyroglobulin secreted by cells grown in the presence of this hormone exhibit a marked decrease in the level of a2,6-bound sialic acid with littleor no change in the number ofa2,3-sialic acid residues
In order to pursue these observations in an lation (1).Thyroglobulin (Tg),’ the major and unique secre- experimentalsystem responsive tohormonal influence, we tory protein synthesized by this organ, is an heterogeneous chose to study a rat thyroid cell line, FRTL-5, that grows in glycoprotein with a molecular mass of 660,000 Da (2)
Summary
The present study, utilizing the hormone-responsive rat thyroid cell lineFRTL-5, presents evidence establishing the regulatory role of thyrotropin in modulating mRNA for &galactoside cr2,6-sialyltransferase,the enzyme responsible for the expression of a2,6-linked sialic acid. Both the cell surface membrane and the thyroglobulin secreted by cells grown in the presence of this hormone exhibit a marked decrease in the level of a2,6-bound sialic acid with littleor no change in the number ofa2,3-sialic acid residues. Cells were grown in 100-mm culture dishes (Costar) in 5% CO,,95% air, 37 “C atmosphere using Coon’s modified Ham’s F-12 medium (Sigma)supplementedwith 5% calf serum(GIBCO/BRL.
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