Growth hormone receptor ubiquitination, endocytosis, and degradation are independent of signal transduction via Janus kinase 2.
The ubiquitin-proteasome system is required in growth hormone receptor (GHR) endocytosis. For cytokine receptors, which lack intrinsic tyrosine kinase activity, signal transduction is initiated by the activation of a member of the Janus kinase (JAK) family. Previously, we have shown that GHR and JAK2 tyrosine (de) phosphorylation are regulated via the ubiquitin system. In this study, we examined the role of JAK2-mediated signal transduction in GHR internalization and down-regulation. Mutation of the attachment site for JAK2, box-1, in the GHR cytoplasmic tail resulted in the complete absence of GHR and JAK2 phosphorylation. This modification did not alter the rate and extent of receptor-bound growth hormone internalization as compared with a functional GHR, nor did it change its turnover and transport to the plasma membrane. In addition, the receptor was still normally ubiquitinated and remained dependent on both an intact ubiquitin system and proteasomal action for its internalization. Thus, GHR ubiquitination, endocytosis, and degradation occur independently of GHR signal transduction via JAK2. We conclude that whereas endocytosis and degradation require the ubiquitin system, they are independent of GHR signal transduction.
Alves dos Santos
C M
CM
Department of Cell Biology, University Medical Center Utrecht, Utrecht, The Netherlands.
ten Broeke
T
T
Strous
G J
GJ
D000818:Animals; D001692:Biological Transport; D002460:Cell Line; D006224:Cricetinae; D004705:Endocytosis; D019382:Human Growth Hormone / Q000493:pharmacokinetics / Q000494:pharmacology; D006801:Humans; D053614:Janus Kinase 2; D007700:Kinetics; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins; D011817:Rabbits; D011986:Receptors, Somatotropin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D014162:Transfection; D014452:Ubiquitins / Q000378:metabolism*
D011518:Proto-Oncogene Proteins; D011986:Receptors, Somatotropin; D011994:Recombinant Proteins; D014452:Ubiquitins; D019382:Human Growth Hormone; D019000:Phosphotyrosine; D011505:Protein-Tyrosine Kinases; C507924:JAK2 protein, human; D053614:Janus Kinase 2