Nuclear translocation and retention of growth hormone.
We have previously demonstrated that GH is subject to rapid receptor-dependent nuclear translocation. Here, we examine the importance of ligand activation of the GH-receptor (GHR)-associated Janus kinase (JAK) 2 and receptor dimerization for hormone internalization and nuclear translocation by use of cells stably transfected with cDNA for the GHR. Staurosporine and herbimycin A treatment of cells did not affect the ability of GH to internalize but resulted in increased nuclear accumulation of hormone. Similarly, receptor mutations, which prevent the association and activation of JAK2, did not affect the ability of the hormone to internalize or translocate to the nucleus but resulted in increased nuclear accumulation of GH. These results were observed both by nuclear isolation and confocal laser scanning microscopy. Staurosporine treatment of cells in which human GH (hGH) was targeted to the cytoplasm (removal of secretion sequence) or to the nucleus (addition of the nuclear localization sequence of SV40 large T antigen) resulted in preferential accumulation of hGH in the nucleus. We further investigated the requirement of receptor dimerization for GH nuclear translocation using the non-receptor-dimerizing hGH antagonist, hGH-G120R, conjugated to fluorescein isothiocyanate. Confocal laser scanning microscopy demonstrated efficient internalization of both hGH and hGH-G120R but lack of nuclear translocation of hGH-G120R. Thus, we conclude that activation of JAK2 kinase and the subsequent tyrosine phosphorylation is not required for nuclear translocation of GH but is pivotal for the removal of the hormone from the nucleus, and that GH translocates into the nucleus in a GHR dimerized-dependent fashion.
Mertani
Hichem C
HC
Centre National de la Recherche Scientifique, Unité Mixte de Recherche 5123 Physiologie Energetique Cellulaire et Moléculaire, Université Claude Bernard, 69622 Lyon I, France.
Raccurt
Mireille
M
Abbate
Aude
A
Kindblom
Jenny
J
Törnell
Jan
J
Billestrup
Nils
N
Usson
Yves
Y
Morel
Gérard
G
Lobie
Peter E
PE
D021581:Active Transport, Cell Nucleus / Q000502:physiology*; D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D002467:Cell Nucleus / Q000378:metabolism; D006224:Cricetinae; D003593:Cytoplasm / Q000378:metabolism; D018076:DNA, Complementary; D019281:Dimerization; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay; D017353:Gene Deletion; D013006:Growth Hormone / Q000378:metabolism*; D053614:Janus Kinase 2; D008024:Ligands; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D016296:Mutagenesis; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D051381:Rats; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011986:Receptors, Somatotropin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019311:Staurosporine / Q000494:pharmacology; D014162:Transfection
D018076:DNA, Complementary; D004791:Enzyme Inhibitors; D008024:Ligands; D011518:Proto-Oncogene Proteins; D011956:Receptors, Cell Surface; D011986:Receptors, Somatotropin; D013006:Growth Hormone; D011505:Protein-Tyrosine Kinases; C507924:JAK2 protein, human; C507927:Jak2 protein, rat; D053614:Janus Kinase 2; D019311:Staurosporine