title: Regulation of glucose transport and c-fos and egr-1 expression in cells with mutated or endogenous growth hormone receptors.
abstract: To identify mechanisms by which GH receptors (GHR) mediate downstream events representative of growth and metabolic responses to GH, stimulation by GH of c-fos and egr-1 expression and glucose transport activity were examined in Chinese hamster ovary (CHO) cells expressing mutated GHR. In CHO cells expressing wild-type GHR(GHR(1-638)), GH stimulated the expression of c-fos and egr-1, and stimulated 2-deoxyglucose uptake, responses also mediated by endogenous GHR in 3T3-F442A cells. Deletion of the proline-rich box 1 of GHR (GHR(deltaP)) abrogated all of these responses to GH, indicating that box 1, a site of association of GHR with the tyrosine kinase JAK2, is crucial for these GH-stimulated responses. As the C-terminal half of the cytoplasmic domain of GHR is required for GH-stimulated calcium flux and for stimulation of spi-2.1 transcription, GHR lacking this sequence (GHR(1-454)) were examined. Not only did GHR(1-454) mediate stimulation of c-fos and egr-1 expression and 2-deoxyglucose uptake, but they also mediated GH-stimulated transcriptional activation via Elk-1, a transcription factor associated with the c-fos Serum Response Element. Thus, the C-terminal half of the cytoplasmic domain of GHR is not required for GH-stimulated c-fos transcription, suggesting that increased calcium is not required for GH-stimulated c-fos expression. In CHO cells lacking all but five N-terminal residues of the cytoplasmic domain (GHR(1-294)), GH did not induce c-fos or egr-1 expression or stimulate 2-deoxyglucose uptake. Further, in 3T3-F442A fibroblasts with endogenous GHR, GH-stimulated c-fos expression and 2-deoxyglucose uptake were reduced by the tyrosine kinase inhibitors herbimycin A, staurosporine, and P11. Herbimycin A and staurosporine inhibit JAK2 and tyrosyl phosphorylation of all proteins stimulated by GH, whereas P11 inhibits the GH-dependent tyrosyl phosphorylation of only some proteins, including extracellular signal regulated kinases ERK1 and -2, but not JAK2. Taken together, these results implicate association of GHR with JAK2 and GH-stimulated tyrosyl phosphorylation of an additional cellular protein in GH-stimulated glucose transport and c-fos and egr-1 expression. These studies also indicate that, in contrast to spi-2.1, the N-terminal half of the cytoplasmic domain of GHR is sufficient to mediate stimulation of c-fos and egr-1 expression and Elk-1 activation, supporting multiple mechanisms for GH signaling to the nucleus.
authors.affiliation: Department of Physiology, University of Michigan Medical School, Ann Arbor 48109-0622, USA.
authors.forename: T W
authors.initials: TW
authors.lastname: Gong
authors.forename: D J
authors.initials: DJ
authors.lastname: Meyer
authors.forename: J
authors.initials: J
authors.lastname: Liao
authors.forename: C L
authors.initials: CL
authors.lastname: Hodge
authors.forename: G S
authors.initials: GS
authors.lastname: Campbell
authors.forename: X
authors.initials: X
authors.lastname: Wang
authors.forename: N
authors.initials: N
authors.lastname: Billestrup
authors.forename: C
authors.initials: C
authors.lastname: Carter-Su
authors.forename: J
authors.initials: J
authors.lastname: Schwartz
mesh_terms: D016475:3T3 Cells / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D016466:CHO Cells; D006224:Cricetinae; D004268:DNA-Binding Proteins / Q000235:genetics*; D003847:Deoxyglucose / Q000378:metabolism*; D051766:Early Growth Response Protein 1; D004791:Enzyme Inhibitors / Q000494:pharmacology; D017353:Gene Deletion; D005786:Gene Expression Regulation / Q000187:drug effects*; D016762:Genes, fos / Q000235:genetics*; D013006:Growth Hormone / Q000494:pharmacology*; D017874:Immediate-Early Proteins; D051379:Mice; D016296:Mutagenesis; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D051381:Rats; D011986:Receptors, Somatotropin / Q000235:genetics / Q000502:physiology*; D011994:Recombinant Proteins; D014157:Transcription Factors / Q000235:genetics*
chemical_list: D004268:DNA-Binding Proteins; D051766:Early Growth Response Protein 1; C486109:Egr1 protein, mouse; C486110:Egr1 protein, rat; D004791:Enzyme Inhibitors; D017874:Immediate-Early Proteins; D011986:Receptors, Somatotropin; D011994:Recombinant Proteins; D014157:Transcription Factors; D013006:Growth Hormone; D003847:Deoxyglucose; D011505:Protein-Tyrosine Kinases