Evidence for the presence of alpha and beta-related T3 receptors in rat liver mitochondria.
Although the dependence of mitochondrial structure and function on thyroid hormone status is well established, several attempts to demonstrate a direct pathway of T3 action on mitochondria have been made during the last decade without being firmly conclusive. In this study, we present evidence firstly for the presence of specific binding sites for [125I]-T3 in rat liver mitochondria 5 min after injection, as assessed by ultrastructural autoradiography. In the same way, using immunocytological techniques and protein immunoblotting, T3 receptor-like immunoreactivity was revealed mainly in the nucleus and mitochondria of hepatocytes. Whereas the colloidal gold labeling over mitochondria was found to be specific at the ultrastructural level, these results were confirmed biochemically by Western blotting experiments which revealed the presence of two protein bands in mitochondria: a stronger one of 55 kDa and a weaker one of 48 kDa. At the opposite, receptor T3 mRNAs were not detected in mitochondria by ultrastructural in situ hybridization thus confirming that the synthesis of receptor T3 occurs in the cytoplasm and that nuclear-encoded T3 receptors may belong to the bulk of cytosolic precursor polypeptides which are targeted to and imported into mitochondria. These results confirm that a direct pathway of T3 action on mitochondria occurs in situ which could now explain how the rapid activation of several mitochondrial functions can take place within minutes after thyroid hormone injection.
Ardail
D
D
Department of Biochemistry, INSERM CNRS 189, Lyon-Sud Medical School, Oullins/France.
Lerme
F
F
Puymirat
J
J
Morel
G
G
D000818:Animals; D001345:Autoradiography; D001665:Binding Sites; D002467:Cell Nucleus / Q000737:chemistry; D003593:Cytoplasm / Q000737:chemistry; D015151:Immunoblotting; D017403:In Situ Hybridization; D008297:Male; D008854:Microscopy, Electron; D008930:Mitochondria, Liver / Q000737:chemistry* / Q000648:ultrastructure; D015388:Organelles / Q000737:chemistry; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D051381:Rats; D017208:Rats, Wistar; D011988:Receptors, Thyroid Hormone / Q000032:analysis* / Q000235:genetics; D014284:Triiodothyronine / Q000378:metabolism
D012333:RNA, Messenger; D011988:Receptors, Thyroid Hormone; D014284:Triiodothyronine