The growth hormone receptor interacts with its sheddase, the tumour necrosis factor-alpha-converting enzyme (TACE)

Growth hormone proteoformics atlas created to promote predictive, preventive, and personalized approach in overall management of pituitary neuroendocrine tumors

Human growth hormone (GH) is the indispensable hormone for the maintenance of normal physiological functions of the human body, including the growth, development, metabolism, and even immunoregulation. The GH is synthesized, secreted, and stored by somatotroph cells in adenohypophysis. Abnormal GH is associated with various GH-related diseases, such as acromegaly, dwarfism, diabetes, and cancer. Currently, some studies found there are dozens or even hundreds of GH proteoforms in tissue and serum as well as a series of GH-binding protein (GHBP) proteoforms and GH receptor (GHR) proteoforms were also identified. The structure-function relationship of protein hormone proteoforms is significantly important to reveal their overall physiological and pathophysiological mechanisms. We propose the use of proteoformics to study the relationship between every GH proteoform and different physiological/pathophysiological states to clarify the pathogenic mechanism of GH-related disease such as pituitary neuroendocrine tumor and conduct precise molecular classification to promote predictive preventive personalized medicine (PPPM / 3P medicine). This article reviews GH proteoformics in GH-related disease such as pituitary neuroendocrine tumor, which has the potential role to provide novel insight into pathogenic mechanism, discover novel therapeutic targets, identify effective GH proteoform biomarker for patient stratification, predictive diagnosis, and prognostic assessment, improve therapy method, and further accelerate the development of 3P medicine.

Immunomodulatory role of metalloproteinase ADAM17 in tumor development

ADAM17 is a member of the a disintegrin and metalloproteinase (ADAM) family of transmembrane proteases involved in the shedding of some cell membrane proteins and regulating various signaling pathways. More than 90 substrates are regulated by ADAM17, some of which are closely relevant to tumor formation and development. Besides, ADAM17 is also responsible for immune regulation and its substrate-mediated signal transduction. Recently, ADAM17 has been considered as a major target for the treatment of tumors and yet its immunomodulatory roles and mechanisms remain unclear. In this paper, we summarized the recent understanding of structure and several regulatory roles of ADAM17. Importantly, we highlighted the immunomodulatory roles of ADAM17 in tumor development, as well as small molecule inhibitors and monoclonal antibodies targeting ADAM17.

Contribution of ADAM17 and related ADAMs in cardiovascular diseases

A disintegrin and metalloproteases (ADAMs) are key mediators of cell signaling by ectodomain shedding of various growth factors, cytokines, receptors and adhesion molecules at the cellular membrane. ADAMs regulate cell proliferation, cell growth, inflammation, and other regular cellular processes. ADAM17, the most extensively studied ADAM family member, is also known as tumor necrosis factor (TNF)-α converting enzyme (TACE). ADAMs-mediated shedding of cytokines such as TNF-α orchestrates immune system or inflammatory cascades and ADAMs-mediated shedding of growth factors causes cell growth or proliferation by transactivation of the growth factor receptors including epidermal growth factor receptor. Therefore, increased ADAMs-mediated shedding can induce inflammation, tissue remodeling and dysfunction associated with various cardiovascular diseases such as hypertension and atherosclerosis, and ADAMs can be a potential therapeutic target in these diseases. In this review, we focus on the role of ADAMs in cardiovascular pathophysiology and cardiovascular diseases. The main aim of this review is to stimulate new interest in this area by highlighting remarkable evidence.

Growth hormone: does it have a therapeutic role in fracture healing?

BACKGROUND

The role of growth hormone (GH) in augmenting fracture healing has been postulated for over half a century. GH has been shown to play a role in bone metabolism and this can be mediated directly or indirectly through IGF-I.

OBJECTIVES

The use of GH was evaluated as a possible therapeutic agent in augmenting fracture healing.

METHOD

A literature search was undertaken on GH and its effect on bone fracture healing primarily using MEDLINE/OVID (1950 to January 2009). Key words and phrases including 'growth hormone', 'insulin like growth factor', 'insulin like growth factor binding protein', 'insulin like growth factor receptor', 'fracture repair', 'bone healing', 'bone fracture', 'bone metabolism', 'osteoblast' and 'osteoclast' were used in different combinations. Manual searches of the bibliography of key papers were also undertaken.

RESULTS

Current evidence suggests a positive role of GH on fracture healing as demonstrated by in vitro studies on osteoblasts, osteoclasts and the crosstalk between the two. Animal studies have demonstrated a number of factors influencing the effect of GH in vivo such as dose, timing and method of administration. Application of this knowledge in humans is limited but clearly demonstrates a positive effect on fracture healing. Concern has been raised in the past regarding the safety profile of the pharmacological use of GH when used in critically ill patients.

CONCLUSION

The optimal dose and method of administration is still to be determined, and the safety profile of this novel use of GH needs to be investigated prior to establishing its widespread use as a fracture-healing agent.

Endocytic regulation of Notch activation and down-regulation (Review)

Notch receptor signalling plays a central role in development and its misfunction has been linked to a number of diseases. In the cannonical Notch signalling pathway, ligand binding to Notch activates a series of proteolytic cleavages that release the Notch intracellular domain for trafficking to the nucleus, where it activates the transcription factor, Suppressor of Hairless (Su(H)). A number of recent papers have demonstrated the importance of endocytic trafficking of Notch and its ligands for both the activation and the down-regulation of the Notch receptor. These reports highlight uncertainty regarding the whereabouts in the cell where Notch activation occurs, and the form of the ligand that can induce signalling. In this review we speculate that, decision points between alternative trafficking pathways represent important regulatory nodes that may allow Notch signalling levels to be modulated by other developmental signals, providing context-dependency to Notch activation. We also review data that suggest that key proteolytic events, associated with Notch activation, may occur within the endocytic pathway or require prior endocytosis and recycling of Notch and its ligands to the cell surface. Sorting within the endocytic pathway, regulated by several different ubiquitin ligase proteins, may be involved in ensuring whether ligand and receptor are competent to signal. Furthermore, the utilisation of an alternative mechanism of Notch signalling, independent of Su(H), may depend on driving endocytic Notch into a specific compartment, in response to the activity of the ring finger domain protein, Deltex.

The ADAM metalloproteinases

The ADAMs (a disintegrin and metalloproteinase) are a fascinating family of transmembrane and secreted proteins with important roles in regulating cell phenotype via their effects on cell adhesion, migration, proteolysis and signalling. Though all ADAMs contain metalloproteinase domains, in humans only 13 of the 21 genes in the family encode functional proteases, indicating that at least for the other eight members, protein–protein interactions are critical aspects of their biological functions. The functional ADAM metalloproteinases are involved in “ectodomain shedding” of diverse growth factors, cytokines, receptors and adhesion molecules. The archetypal activity is shown by ADAM-17 (tumour necrosis factor-α convertase, TACE), which is the principal protease involved in the activation of pro-TNF-α, but whose sheddase functions cover a broad range of cell surface molecules. In particular, ADAM-17 is required for generation of the active forms of Epidermal Growth Factor Receptor (EGFR) ligands, and its function is essential for the development of epithelial tissues. Several other ADAMs have important sheddase functions in particular tissue contexts. Another major family member, ADAM-10, is a principal player in signalling via the Notch and Eph/ephrin pathways. For a growing number of substrates, foremost among them being Notch, cleavage by ADAM sheddases is essential for their subsequent “regulated intramembrane proteolysis” (RIP), which generates cleaved intracellular domains that translocate to the nucleus and regulate gene transcription. Several ADAMs play roles in spermatogenesis and sperm function, potentially by effecting maturation of sperm and their adhesion and migration in the uterus. Other non-catalytic ADAMs function in the CNS via effects on guidance mechanisms. The ADAM family are thus fundamental to many control processes in development and homeostasis, and unsurprisingly they are also linked to pathological states when their functions are dysregulated, including cancer, cardiovascular disease, asthma, Alzheimer’s disease. This review will provide an overview of current knowledge of the human ADAMs, discussing their structure, function, regulation and disease involvement.

Differential regulation of membrane associated-growth hormone binding protein (MA-GHBP) and growth hormone receptor (GHR) expression by growth hormone (GH) in mouse liver

Growth hormone (GH) binding to GH receptor (GHR) is the initial step that leads to the physiological functions of the hormone. Proteolytical cleavage of the GHR in humans and rabbits and alternative processing of the GHR transcript in rodents generates circulating growth hormone binding protein (GHBP). Moreover, other GHR truncated forms that result from alternative processing of the GHR mRNA transcript have been described. These GHR short forms are inserted in the plasma membrane but they are unable to transduce the signal. In rodents, membrane associated-GHBP (MA-GHBP), which accounts for a significant proportion of liver GH binding capacity, represents the main GHR short form found in membranes, and may therefore function as a negative form of the receptor. In the present study, GHR and MA-GHBP content in liver were analyzed using mutant and transgenic mice expressing different concentrations of growth hormone to evaluate the correlation between GH levels, body weight (BW), GHR and MA-GHBP expression. It was found that GH deficiency was associated with diminished BW, GHR and MA-GHBP expression, while increased GH concentration led to increased BW, GHR and MA-GHBP expression, but MA-GHBP upregulation was more pronounced than the observed increase in GHR expression. Since GHR and MA-GHBP both contribute to liver GH binding capacity, GH-induced enrichment of the dominant negative form would represent a compensatory mechanism triggered by high levels of the hormone. This attempt to attenuate the effects of supraphysiological concentrations of GH may be critical to reduce or prevent their plausible damaging effects on the organism.

Cytokine and growth factor receptors in the nucleus: what's up with that?

Signaling via cell surface receptors that are anchored by a single transmembrane domain is a well-established paradigm. Ligand binding to the extracellular domain of the receptor facilitates receptor dimerization, which juxtaposes the intracellular domains, typically activating intrinsic or associated kinases. Two large families of tyrosine kinase activating receptors have been particularly well characterized: the receptor-type protein tyrosine kinases and the receptors for the alpha-helical cytokines, which activate non-covalently bound JAK family tyrosine kinases. Despite the well-established function of these receptors at the cell surface, both intact and cleaved receptors belonging to these families have been repeatedly detected in the nucleus. Furthermore, there is evidence that some of these receptors or receptor fragments function directly in modulating gene transcription. In this essay, I examine how close we are to demonstrating that direct translocation of receptors, or receptor fragments, from the cell surface to the nucleus is a physiologically relevant means of intracellular signaling that can supplant or complement canonical signaling cascades.

Nectin-4, a new serological breast cancer marker, is a substrate for tumor necrosis factor-alpha-converting enzyme (TACE)/ADAM-17

Serum markers are extensively used in diagnostic and follow-up of cancer patients. We recently described Nectin-4, a 66-kDa adhesion molecule of the Nectin family, which is a valuable new histological and serological marker for breast carcinoma. In vivo, Nectin-4 is re-expressed in breast carcinoma, and a circulating form of Nectin-4 is detected in the sera of patients with metastatic breast cancer. In vitro, a soluble form of Nectin-4 is produced in the supernatant of breast tumor cell lines (S. Fabre-Lafay, C. Ginestier, S. Garrido-Urbani, C. Berruyer, R. Sauvan, N. Reymond, J. Adelaide, J. Geneix, P. Dubreuil, J. Jacquemier, D. Birnbaum, and M. Lopez, manuscript in preparation). We have investigated the mechanisms that regulate the production of this soluble form. It was found that the soluble form of Nectin-4 detected in the sera of patients and the supernatant of breast tumor cell lines share similar biochemical and immunological features. The soluble Nectin-4 form (43 kDa) is formed by the entire Nectin-4 ectodomain. Nectin-4 shedding is constitutive, strongly enhanced by 12-O-tetradecanoylphorbol-13-acetate activation, and reduced tumor necrosis factor-alpha protease inhibitor TAPI-1 or by the tissue inhibitor of metalloproteinase-3 (TIMP-3). TAPI-1 and TIMP-3 are inhibitors of the endoprotease tumor necrosis factor-alpha-converting enzyme (TACE)/ADAM-17. Overexpression or small interfering RNA-mediated silencing of TACE enhanced or reduced Nectin-4 shedding, respectively. Nectin-4 is not shed when expressed in TACE-deficient fibroblasts. Interestingly, the active form of TACE is overexpressed in breast tumors and may indicate that TACE is responsible for Nectin-4 shedding not only in vitro but also in vivo.

Proteasome inhibition activates the transport and the ectodomain shedding of TNF-α receptors in human endothelial cells

Binding of tumor necrosis factor-α (TNF-α) to its transmembrane receptors (TNFRs) mediates proinflammatory, apoptotic and survival responses in several cell types including vascular endothelial cells. Because ectodomain shedding of cell surface molecules can be modified by proteasome activity, we studied in human endothelial cells whether the TNF-α–TNFRs axis can be regulated by the cleavage of their transmembrane forms in a proteasome-dependent manner. We show that proteasome inhibition increases the release of TNF-α and TNFRs from human endothelial cells and decreases their cellular and cell surface expression. This phenomenon involves the transient activation of mitogen-activated protein kinase p42/p44 that triggers the dispersion of TNF-α and TNFRs from their intracellular Golgi-complex-associated pool towards the plasma membrane. This results in their enhanced cleavage by TNF-α converting enzyme (TACE) because it is reduced by synthetic metalloprotease inhibitors, recombinant TIMP-3 and by a dominant negative form of TACE. In the presence of TACE inhibitor, proteasome inhibition increases the cell surface expression of TNFRs and enhances the sensitivity of these cells to the proapoptotic effect of recombinant TNF-α.

In conclusion, our data provide evidence that proteasome inhibitors increase TACE-dependent TNFR-shedding in endothelial cells, supporting the use of these molecules in inflammatory disorders. In association with TACE inhibitor, proteasome inhibitors increase the amount of TNFRs at the cell surface and enhance the sensitivity to the proapoptotic effect of TNF-α, which might be of interest in the antitumor therapy.