title: Growth hormone internalization in mitochondria decreases respiratory chain activity.
abstract: Growth hormone (GH) is a signaling molecule regulating cell proliferation, differentiation and metabolism via activation of specific cell surface receptors and subsequent triggering of signal transduction pathways. This is associated with GH/GH receptor internalization and accumulation of GH in several subcellular compartments, including mitochondria. To assess the functional relevance of such mitochondrial accumulation, we first confirmed the occurrence of mitochondrial GH uptake ex vivo as early as 10 min after (125)I-GH injection to the rats. We next showed that intact (125)I-GH accumulates in mitochondrial fractions in vitro in a specific, rapid and saturable manner with an apparent affinity (K(d)) of 1.44 nM. At the electron-microscopic level, immunoreactive GH density within mitochondria increased after in vitro hormone incubation, without any modification of the sub-mitochondrial distribution pattern. The presence of GH in the inter-membrane space and at the inner membrane seen by electron microscopy was confirmed by SDS-PAGE and autoradiography after mitochondrial fractioning thus suggesting the involvement of GH in the respiration control. To test this hypothesis further, we performed polarographic and spectrophotometric assays on isolated mitochondria. These assays pointed to a direct, selective and dose-dependent effect of GH on the inhibition of succinate dehydrogenase and cytochrome C oxidase activities. The latter inhibition was in contrast with indirect, GH receptor-initiated stimulation of cytochrome C oxidase activity observed in GH-treated whole BRL cells transfected to express this receptor. Altogether, these data show that GH is specifically imported in mitochondria, where it operates a direct metabolic effect, independently of cell surface receptors and signal transduction.
authors.affiliation: IFR 41, CNRS UMR 5123, Physiologie Intégrative Cellulaire et Moléculaire, Université de Lyon, Villeurbanne, France.
authors.forename: Dominique
authors.initials: D
authors.lastname: Ardail
authors.forename: Aude
authors.initials: A
authors.lastname: Debon
authors.forename: Cécile
authors.initials: C
authors.lastname: Perret-Vivancos
authors.forename: Marie-Claire
authors.initials: MC
authors.lastname: Biol-N'Garagba
authors.forename: Slavika
authors.initials: S
authors.lastname: Krantic
authors.forename: Peter E
authors.initials: PE
authors.lastname: Lobie
authors.forename: Gérard
authors.initials: G
authors.lastname: Morel
mesh_terms: D000818:Animals; D002460:Cell Line; D004579:Electron Transport / Q000502:physiology*; D003576:Electron Transport Complex IV / Q000378:metabolism; D013006:Growth Hormone / Q000378:metabolism*; D007457:Iodine Radioisotopes; D008099:Liver / Q000378:metabolism / Q000648:ultrastructure; D008297:Male; D008930:Mitochondria, Liver / Q000378:metabolism* / Q000648:ultrastructure; D051336:Mitochondrial Membranes / Q000378:metabolism / Q000648:ultrastructure; D051381:Rats; D017208:Rats, Wistar; D011986:Receptors, Somatotropin / Q000378:metabolism; D013385:Succinate Dehydrogenase / Q000378:metabolism; D013997:Time Factors
chemical_list: D007457:Iodine Radioisotopes; D011986:Receptors, Somatotropin; D013006:Growth Hormone; D013385:Succinate Dehydrogenase; D003576:Electron Transport Complex IV