Related Experiment Videos
Metalloproteinases and the modulation of GH signaling
1Center for Endocrinology, Metabolism and Molecular Medicine, Department of Medicine, Northwestern University Medical School, 303 E Chicago Avenue, Chicago, IL 60611, USA.
Abstract:
The metzincin metalloproteinase, tumor necrosis factor-alpha-converting enzyme (TACE), also known as ADAM (a disintegrin and metalloproteinase) 17, has recently been identified as an important enzyme for cleavage of the GH receptor (GHR) and shedding of GH-binding protein (GHBP). Proteolysis can be induced by phorbol esters, platelet-derived growth factor and serum; it is dependent on protein kinase C and partially on MAP kinase pathways. Proteolysis occurs at the cell surface, leading to extracellular release of GHBP and intracellular GHR remnant accumulation. The GHR remnant is further processed by gamma-secretase activity, possibly leading to biologically active products. TACE-dependent GHR proteolysis can be inhibited by GH as the dimerized GHR is resistant to cleavage. The cleavage site lies within a short juxtamembranous stem region that extends between the transmembrane helix and the globular dimerization domain of the GHR. GHR proteolysis leads to downregulation of functional GHRs at the cell surface, and has complex secondary effects on GH action via GHBP and GHR remnant generation.
Insights
Tumor necrosis factor-alpha-converting enzyme (TACE), or ADAM 17, cleaves the GH receptor (GHR), releasing GH-binding protein (GHBP). This process downregulates functional GHRs and impacts GH action.
Area of Science:
- Biochemistry
- Cell Biology
- Endocrinology
Background:
- The growth hormone receptor (GHR) mediates growth hormone (GH) action.
- Proteolytic cleavage of cell surface receptors is a mechanism for regulating their function.
- Tumor necrosis factor-alpha-converting enzyme (TACE), also known as ADAM 17, is a metalloproteinase implicated in ectodomain shedding.
Purpose of the Study:
- To investigate the role of TACE/ADAM 17 in GHR cleavage and GH-binding protein (GHBP) shedding.
- To elucidate the signaling pathways involved in TACE-mediated GHR proteolysis.
- To understand the consequences of GHR proteolysis on GH signaling.
Main Methods:
- Cell-based assays using phorbol esters, platelet-derived growth factor, and serum to induce proteolysis.
- Western blotting and ELISA to detect GHR cleavage and GHBP shedding.
- Pharmacological inhibition of protein kinase C (PKC) and mitogen-activated protein kinase (MAPK) pathways.
- Gamma-secretase inhibition to study GHR remnant processing.
Main Results:
- TACE/ADAM 17 mediates the cleavage of GHR at the cell surface, releasing GHBP into the extracellular space.
- GHR proteolysis is induced by phorbol esters, growth factors, and serum, and is dependent on PKC and partially on MAPK signaling.
- The GHR remnant is further processed by gamma-secretase, potentially generating biologically active fragments.
- GH binding to GHR induces dimerization, rendering the receptor resistant to TACE-mediated cleavage.
- GHR proteolysis results in the downregulation of cell surface GHRs and affects GH signaling.
Conclusions:
- TACE/ADAM 17 plays a critical role in GHR regulation through proteolysis.
- GHR cleavage by TACE/ADAM 17 is a regulated process influenced by signaling pathways and GH itself.
- The shedding of GHBP and processing of GHR remnants have significant implications for GH action and endocrine signaling.