title: Differential regulation of thyrotropin subunit apoprotein and carbohydrate biosynthesis by thyroid hormone.
abstract: The regulation of TSH apoprotein and carbohydrate biosynthesis by thyroid hormone was studied by incubating pituitaries from normal and hypothyroid (3 weeks post-thyroidectomy) rats in medium containing [14C]alanine and [3H] glucosamine. After 6 h, samples were sequentially treated with anti-TSH beta to precipitate TSH and free TSH beta, anti-LH beta to clear the sample of LH and free LH beta, then anti-LH alpha to precipitate free alpha-subunit. Total proteins were acid precipitated. All precipitates were subjected to electrophoresis on sodium dodecyl sulfate-polyacrylamide gels, which were then sliced and assayed by scintillation spectrometry. In hypothyroid pituitaries plus medium, [14C]alanine incorporation in combined and free beta-subunits was 26 times normal (P less than 0.001) and considerably greater than the 3.4-fold increase seen in total protein (P less than 0.05); combined and free alpha-subunits showed no specific increase in apoprotein synthesis. [3H]Glucosamine incorporation in combined alpha- and beta-subunits in hypothyroid samples was 13 and 21 times normal, respectively, and was greater than the 1.9-fold increase in total protein (P less than 0.05); free alpha-subunit showed no specific increase in carbohydrate synthesis. The glucosamine to alanine ratio, reflecting relative glycosylation of newly synthesized molecules, was increased in hypothyroidism for combined alpha-subunits (P less than 0.001), but not for combined beta-subunits, free alpha-subunits, or total proteins. In summary, short term hypothyroidism selectively stimulated TSH beta apoprotein synthesis and carbohydrate synthesis of combined alpha- and beta-subunits. Hypothyroidism also increased the relative glycosylation of combined alpha-subunit. Thus, thyroid hormone deficiency appears to alter the rate-limiting step in TSH assembly (i.e. beta-subunit synthesis) as well as the carbohydrate structure of TSH, which may play important roles in its biological function.
mesh_terms: D000818:Animals; D001059:Apoproteins / Q000096:biosynthesis*; D002241:Carbohydrates / Q000096:biosynthesis*; D002250:Carbon Radioisotopes; D008297:Male; D010902:Pituitary Gland / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D011863:Radioimmunoassay; D051381:Rats; D011919:Rats, Inbred Strains; D013963:Thyroid Hormones / Q000502:physiology*; D013972:Thyrotropin / Q000096:biosynthesis* / Q000378:metabolism; D014316:Tritium
chemical_list: D001059:Apoproteins; D002241:Carbohydrates; D002250:Carbon Radioisotopes; D011506:Proteins; D013963:Thyroid Hormones; D014316:Tritium; D013972:Thyrotropin