The effect of 3,5,3'-triiodothyronine on leucine uptake and incorporation into protein in cultured neurons and subcellular fractions of rat central nervous system.
Previous studies have shown that nuclear thyroid hormone receptors in rat brain are preferentially localized within neurons. These cells also synthesize protein at a high rate, and the aim of the present study was to investigate any relationship between these two characteristics. In this paper we have shown that T3 stimulates leucine uptake and incorporation into protein in primary cell cultures of neurons. Stimulation was apparent with concentrations of hormone as low as 1.25 nM and increased in a dose-dependent manner up to 10 nM T3. However, the rapidity of the effect (evident at 25 min, and significant at 40 min) suggests that protein synthesis is stimulated at the level of translation, rather than transcription. More detailed study with 5 nM T3, revealed that incorporation into both soluble (cytoplasmic) and insoluble (membrane-associated) protein fractions was stimulated to similar degrees, and therefore the effect on protein synthesis was general. Furthermore, T3-mediated stimulation of leucine uptake into neurons was completely abolished in the presence of the protein synthesis inhibitors, actinomycin D and cycloheximide, and therefore the effect on leucine uptake was attributed to an increased requirement for the amino acid in protein synthesis (pleiotrophic effect). Parallel studies conducted with synaptosomes and mitochondria isolated from the central nervous system of adult euthyroid animals revealed that 5 nM T3 was without effect on leucine uptake and incorporation into protein. Possible reasons for this lack of effect are discussed.
Pickard
M R
MR
Department of Molecular Endocrinology, Middlesex Hospital Medical School, London, United Kingdom.
Sinha
A K
AK
Gullo
D
D
Patel
N
N
Hubank
M
M
Ekins
R P
RP
D000818:Animals; D001921:Brain / Q000196:embryology / Q000378:metabolism*; D002478:Cells, Cultured; D005333:Fetus; D007700:Kinetics; D007930:Leucine / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000096:biosynthesis*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013574:Synaptosomes / Q000378:metabolism; D014284:Triiodothyronine / Q000494:pharmacology*
D009419:Nerve Tissue Proteins; D014284:Triiodothyronine; D007930:Leucine