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Cowan JW, Wang X, Guan R, He K, Jiang J, Baumann G, Black RA, Wolfe MS, Frank SJ. Growth Hormone Receptor Is a Target for Presenilin-dependent γ-Secretase Cleavage. J Biol Chem 2005; 280:19331-42. [PMID: 15743767 DOI: 10.1074/jbc.m500621200] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Growth hormone receptor (GHR) is a cytokine receptor superfamily member that binds growth hormone (GH) via its extracellular domain and signals via interaction of its cytoplasmic domain with JAK2 and other signaling molecules. GHR is a target for inducible metalloprotease-mediated cleavage in its perimembranous extracellular domain, a process that liberates the extracellular domain as the soluble GH-binding protein and leaves behind a cell-associated GHR remnant protein containing the transmembrane and cytoplasmic domains. GHR metalloproteolysis can be catalyzed by tumor necrosis factor-alpha-converting enzyme (ADAM-17) and is associated with down-modulation of GH signaling. We now study the fate of the GHR remnant protein. By anti-GHR cytoplasmic domain immunoblotting, we observed that the remnant induced in response to phorbol ester or platelet-derived growth factor has a reliable pattern of appearance and disappearance in both mouse preadipocytes endogenously expressing GHR and transfected fibroblasts expressing rabbit GHR. Lactacystin, a specific proteasome inhibitor, did not appreciably change the time course of remnant appearance or clearance but allowed detection of the GHR stub, a receptor fragment slightly smaller than the remnant but containing the C terminus of the remnant (receptor cytoplasmic domain). In contrast, MG132, another (less specific) proteasome inhibitor, strongly inhibited remnant clearance and prevented stub appearance. Inhibitors of gamma-secretase, an aspartyl protease, also prevented the appearance of the stub, even in the presence of lactacystin, and concomitantly inhibited remnant clearance in the same fashion as MG132. In addition, mouse embryonic fibroblasts derived from presenilin 1 and 2 (PS1/2) knockouts recapitulated the gamma-secretase inhibitor studies, as compared with their littermate controls (PS1/2 wild type). Confocal microscopy indicated that the GHR cytoplasmic domain became localized to the nucleus in a fashion dependent on PS1/2 activity. These data indicate that the GHR is subject to sequential proteolysis by metalloprotease and gamma-secretase activities and may suggest GH-independent roles for the GHR.
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Affiliation(s)
- Jon W Cowan
- Department of Cell Biology, University of Alabama at Birmingham, Birmingham, Alabama 35294-0012, USA
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Chopin LK, Veveris-Lowe TL, Philipps AF, Herington AC. Co-expression of GH and GHR isoforms in prostate cancer cell lines. Growth Horm IGF Res 2002; 12:126-136. [PMID: 12175650 DOI: 10.1054/ghir.2002.0271] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Prostate cancer is a significant cause of morbidity and mortality in Western males. While it is known that androgens play a central role in prostate cancer development and progression, other hormones and growth factors are also involved in prostate growth. Insulin-like growth factor-I (IGF-I) plasma levels have been associated with prostate cancer risk, and growth hormone (GH), a major factor regulating IGF levels, also appears to have a role in prostate cancer cell growth. Most significantly, GH has been shown to increase the rate of cell proliferation in prostate cancer cell lines. We have now demonstrated the co-expression of GH and GH receptor (GHR) mRNA isoforms in the ALVA41, PC3, DU145, LNCaP prostate cancer cells by reverse transcription polymerase chain reaction. Sequence analysis has confirmed that these cell lines express the pituitary form of GH mRNA and also the placental mRNA isoform. These prostate cancer cell lines also express the full-length mRNA for the GHR and the exon 3 deleted isoform. We have also demonstrated the presence of GH and GHR proteins in these cell lines by immunohistochemistry. GH expression has not been described previously in human prostate cancer cells. The co-expression of GH and its receptor would enable an autocrine-paracrine pathway to exist in the prostate that would be capable of stimulating prostate growth, either directly via the GHR or indirectly via IGF production. The GH axis in the prostate could therefore be an important additional target for the future development of prostate cancer therapies.
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Affiliation(s)
- L K Chopin
- Centre for Molecular Biotechnology, Queensland University of Technology, GPO Box 2434, Brisbane, Q 4001, Australia.
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Zhang Y, Guan R, Jiang J, Kopchick JJ, Black RA, Baumann G, Frank SJ. Growth hormone (GH)-induced dimerization inhibits phorbol ester-stimulated GH receptor proteolysis. J Biol Chem 2001; 276:24565-73. [PMID: 11309389 DOI: 10.1074/jbc.m101281200] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Growth hormone (GH) initiates its cellular action by properly dimerizing GH receptor (GHR). A substantial fraction of circulating GH is complexed with a high-affinity GH-binding protein (GHBP) that in many species can be generated by GHR proteolysis and shedding of the receptor's ligand-binding extracellular domain. We previously showed that this proteolysis 1) can be acutely promoted by the phorbol ester phorbol 12-myristate 13-acetate (PMA), 2) requires a metalloprotease activity, 3) generates both shed GHBP and a membrane-associated GHR transmembrane/cytoplasmic domain remnant, and 4) results in down-regulation of GHR abundance and GH signaling. Using cell culture model systems, we now explore the effects of GH treatment on inducible GHR proteolysis and GHBP shedding. In human IM-9 lymphocytes, which endogenously express GHRs, and in Chinese hamster ovary cells heterologously expressing wild-type or cytoplasmic domain internal deletion mutant rabbit GHRs, brief exposure to GH inhibited PMA-induced GHR proteolysis (receptor loss and remnant accumulation) by 60-93%. PMA-induced shedding of GHBP from Chinese hamster ovary transfectants was also inhibited by 70% in the presence of GH. The capacity of GH to inhibit inducible GHR cleavage did not rely on JAK2-dependent GH signaling, as evidenced by its continued protection in JAK2-deficient gamma2A rabbit GHR cells. The GH concentration dependence for inhibition of PMA-induced GHR proteolysis paralleled that for its promotion of receptor dimerization (as monitored by formation of GHR disulfide linkage). Unlike GH, the GH antagonist, G120K, which binds to but fails to properly dimerize GHRs, alone did not protect against PMA-induced GHR proteolysis; G120K did, however, antagonize the protective effect of GH. Our data suggest that GH inhibits PMA-induced GHR proteolysis and GHBP shedding by inducing GHR dimerization and that this effect does not appear to be related to GH site 1 binding, GHR internalization, or GHR signaling. The implications of these findings with regard to GH signaling and GHR down-regulation are discussed.
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Affiliation(s)
- Y Zhang
- Department of Medicine, Division of Endocrinology and Metabolism, University of Alabama at Birmingham, Birmingham, AL 35294, USA
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Zhang Y, Jiang J, Black RA, Baumann G, Frank SJ. Tumor necrosis factor-alpha converting enzyme (TACE) is a growth hormone binding protein (GHBP) sheddase: the metalloprotease TACE/ADAM-17 is critical for (PMA-induced) GH receptor proteolysis and GHBP generation. Endocrinology 2000; 141:4342-8. [PMID: 11108241 DOI: 10.1210/endo.141.12.7858] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The GH binding protein (GHBP), which exists in many vertebrates, is a circulating high affinity binding protein corresponding to the extracellular domain of the GH receptor (GHR). In humans, rabbits, and several other species, the GHBP is generated by proteolysis of the GHR and shedding of its extracellular domain. We previously showed that GHBP shedding is inducible by the phorbol ester phorbol 12-myristate,13-acetate (PMA) and inhibited by the metalloprotease inhibitor, Immunex Corp. Compound 3 (IC3). The metzincin metalloprotease, tumor necrosis factor-alpha (TNF-alpha)-converting enzyme (TACE), catalyzes the shedding of TNF-alpha from its transmembrane precursor, a process that is also inhibitable by IC3. TACE may hence be a candidate for GHBP sheddase. In this study, we reconstitute fibroblasts derived from a TACE knockout mouse (Null cells) with either the rabbit (rb) GHR alone (Null/R) or rbGHR plus murine TACE (Null/R+T). Although GHR in both cells was expressed at similar abundance, dimerized normally and caused JAK2 activation in response to GH independent of TACE expression, PMA was unable to generate GHBP from Null/R cells. In contrast, PMA caused ample GHBP generation from TACE reconstituted (Null/R + T) cells, and this GHBP shedding was substantially inhibited by IC3 pretreatment. Corresponding to the induced shedding of GHBP from Null/R + T cells, PMA treatment caused a significant loss of immunoblottable GHR in Null/R+T, but not in Null/R cells. We conclude that TACE is an enzyme required for PMA-induced GHBP shedding and that PMA-induced down-regulation of GHR abundance may in significant measure be attributable to TACE-mediated GHR proteolysis.
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Affiliation(s)
- Y Zhang
- Department of Cell Biology, University of Alabama at Birmingham, 35294, USA
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Vleurick L, Kühn ER, Decuypere E, Burnside J, Pezet A, Edery M. Generation of chicken growth hormone-binding proteins by proteolysis. Gen Comp Endocrinol 1999; 113:283-9. [PMID: 10082631 DOI: 10.1006/gcen.1998.7202] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A soluble protein that specifically bound growth hormone (GH) was characterized in culture medium of a COS-7 cell line transfected with the cDNA of the full-length chicken GH receptor (cGHR). Incubation of culture medium with 125I-labeled human GH resulted in the formation of a single specific complex with high affinity (KD = 0.36 nM) and apparent molecular weight of 75 kDa. The production of large quantities of GH-binding protein (GHBP) amounting to, per hour, 23% of the cell's GHR, points to the importance of partial proteolysis for GHR turnover. Considerable amounts of GHBP were also detected in a cytosolic fraction. These results strongly suggest that in chicken, as in rabbit and monkey, the GHBP is generated, at least partially, by proteolytic cleavage of the membrane-anchored GHR.
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Affiliation(s)
- L Vleurick
- Faculté de Médecine Necker, INSERM U344, 156 rue de Vaugirard, Paris Cedex 15, F-75730, France
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Alele J, Jiang J, Goldsmith JF, Yang X, Maheshwari HG, Black RA, Baumann G, Frank SJ. Blockade of growth hormone receptor shedding by a metalloprotease inhibitor. Endocrinology 1998; 139:1927-35. [PMID: 9528979 DOI: 10.1210/endo.139.4.5906] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
GH, an important growth-promoting and metabolic hormone, exerts its biological effects by interacting with cell surface GH receptors (GHRs). The GHR is a single membrane-spanning protein that binds GH via its extracellular domain. The high affinity GH-binding protein (GHBP), which corresponds to a soluble form of the GHR extracellular domain, carries a substantial fraction of the GH in the circulation of various species and probably has a role in modulation of the hormone's bioavailability. Although in rodents, it is believed that the GHBP is largely derived by translation of an alternatively spliced GHR messenger RNA, in humans and rabbits, proteolytic cleavage of the membrane-anchored receptor releases the GHR extracellular domain, which is believed to thereby become the GHBP. In this study, we used human IM-9 lymphocytes and GHR antibodies to study this proteolytic shedding of the GHBP. As determined by immunoblotting with anti-GHR cytoplasmic domain serum, addition of phorbol 12-myristate 13-acetate (PMA; 1 microg/ml) to serum-starved cells led to rapid loss (roughly 60% decline after 1 h; t(1/2) = approximately 5 min) of mature GHRs (115-140 kDa) from either total cell or detergent-soluble extracts. Loss of full-length GHRs was accompanied by accumulation of four proteins (65-68 kDa), each reactive with the cytoplasmically directed antiserum. The pattern of appearance of these GHR ctyoplasmic domain proteins, the electrophoretic and immunological characteristics of which are similar to those of a recombinant rabbit GHR mutant that lacks the extracellular domain, was such that progressively faster migrating forms were evident between 5-60 min of PMA exposure. Treatment with N-ethylmaleimide (NEM; 5 mM), an agent known to cause GHBP shedding from IM-9 cells, promoted a similar rapid loss of full-length GHRs and an accumulation of GHR cytoplasmic domain remnant proteins. PMA-induced, but not NEM-induced, GHR proteolysis was blocked by the protein kinase C inhibitor, GF109203X. Both PMA- and NEM-induced receptor proteolysis were, however, inhibited by the metalloprotease inhibitor, Immunex Compound 3 (minimum effective concentration, 10 microM). Notably, PMA and NEM also promoted shedding of GHBP into the conditioned medium of the cells, as determined by a chromatographic [125I]human GH binding assay; this GHBP shedding was also inhibited by Immunex Compound 3. These results strongly implicate a member(s) of the metalloprotease family as a potential GHBP-generating enzyme.
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Affiliation(s)
- J Alele
- Department of Medicine, University of Alabama, Birmingham 35294, USA
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Dastot F, Duquesnoy P, Sobrier ML, Goossens M, Amselem S. Evolutionary divergence of the truncated growth hormone receptor isoform in its ability to generate a soluble growth hormone binding protein. Mol Cell Endocrinol 1998; 137:79-84. [PMID: 9607731 DOI: 10.1016/s0303-7207(97)00232-3] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The soluble growth hormone binding protein (GHBP), which is encoded by the GH receptor (GHR) gene, is generated by several mechanisms. In rabbits (rb) and humans (h), it is derived by proteolytic cleavage of the full-length membrane-bound receptor molecules (GHR-fl), whereas in rats (r) and mice, it results from an alternative splice excluding the transmembrane domain. Furthermore, in all these species, alternative splicing in the cytoplasmic domain results in a truncated isoform (GHR-tr), that, in humans, produces large amounts of GHBP through proteolysis. To further characterize the species specificity of the mechanism underlying GHBP generation, rbGHR-tr and rGHR-tr expressed in COS-7 cells were assayed for their ability to produce a GHBP in comparison with the corresponding full-length receptors. Large amounts of GHBP were secreted by cells expressing the rabbit constructs, the rbGHR-tr isoform being more efficient in GHBP generation than rbGHR-fl. In contrast, no GHBP was detected from cells expressing rGHR-tr, the cytoplasmic deletion having no effect on GHBP release from membrane receptors. These data further demonstrate evolutionary divergence in the mechanism by which GHBP is generated and provide new clues to decipher the molecular process underlying the cleavage step.
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Affiliation(s)
- F Dastot
- Laboratoire de Génétique moléculaire, Institut National de la Santé et de la Recherche Médicale U, 468, Hôpital Henri Mondor, Créteil, France
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Amit T, Bergman T, Dastot F, Youdim MB, Amselem S, Hochberg Z. A membrane-fixed, truncated isoform of the human growth hormone receptor. J Clin Endocrinol Metab 1997; 82:3813-7. [PMID: 9360546 DOI: 10.1210/jcem.82.11.4358] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Previously, we reported the identification of a new human GH receptor (hGHR) messenger RNA species that encodes a smaller hGHR isoform, termed hGHRtr. Its messenger RNA is expressed in several human tissues and predicts a severely truncated GHR protein that lacks 97.5% of the intracellular domain. Because these two hGHR isoforms, which display similar binding affinity, are coexpressed in several tissues, they may reside side by side and, therefore, interrelate. To further characterize the biological properties of hGHRtr in comparison with hGHR, we generated Chinese hamster ovary (CHO) cell lines stably expressing each of these hGHR isoforms. Cross-linking of [125I]hGH to CHO/hGHRtr cells revealed a majored specific complex with apparent Mr of approximately 100 kDa, which would indicate the hGHRtr to be in molecular mass form of about 80 kDa. When compared with CHO/hGHR, CHO/hGHRtr cells secreted higher amounts of soluble GH-binding protein (GHBP). In contrast to CHO/hGHR cells, CHO/hGHRtr cells did not exhibit any GH-induced receptor down-regulation, and internalization was markedly reduced. Analysis of the constitutive turnover of cellular hGHR and soluble GHBP showed that incubation of CHO/hGHR cells with cycloheximide caused parallel disappearance of hGHR and GHBP. This contrasted with the stability of GHRtr, which showed no decline after cycloheximide treatment for up to 4 h, suggesting that the bulk GHRtr and GHBP may be derived from preformed proteins. Thus, in contrast to hGHR, hGHRtr is fixed at the cell membrane; it undergoes minimal internalization, no down-regulation by hGH, no constitutive turnover for as long as 4 h, but increased capacity to generate a soluble GHBP. Because hGHRtr failed to undergo ligand-induced internalization, the source of the continuous, undisturbed GHBP released into the medium may be from an intracellular storage pool. The relative abundance of these two hGHR isoforms, through regulation of splicing, could be of critical importance in modulating the biological effects of GH.
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Affiliation(s)
- T Amit
- Department of Pharmacology, Bruce Rappaport Faculty of Medicine, Technion, Haifa, Israel
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