Evidence for a Critical Role of the Tumor Necrosis Factor α Convertase (TACE) in Ectodomain Shedding of the p75 Neurotrophin Receptor (p75NTR)

Abstract

Protein ectodomain shedding, the proteolytic release of the extracellullar domain of membrane-tethered proteins, can dramatically affect the function of cell surface receptors, growth factors, cytokines, and other proteins. In this study, we evaluated the activities involved in ectodomain shedding of p75 NTR , a neurotrophin receptor with critical roles in neuronal differentiation and survival. p75 NTR is shed in a variety of cell types, including dorsal root ganglia cells and PC12 cells. In Chinese hamster ovary cells, inhibitors of the MEK/ERK and p38 MAP kinase pathways uncovered distinct signaling pathways required for the constitutive and stimulated shedding of p75 NTR . Stimulated p75 NTR shedding is abrogated in M2 mutant Chinese hamster ovary cells that lack functional tumor necrosis factor-␣ converting enzyme (TACE, also referred to as ADAM17) and in cells isolated from adam17؊/؊ mice, but not in cells from adam9/12/15؊/؊ or adam10؊/؊ mice. Stimulated p75 NTR shedding is strongly reduced by deletion of 15 amino acid residues in its extracellular membrane-proximal stalk domain. However, similar to other shed proteins, point mutations and overlapping shorter deletions within this region have little or no effect on shedding. Because ectodomain shedding of p75 NTR releases a soluble ectodomain and could also be a prerequisite for its regulated intramembrane proteolysis, these findings may have important implications for the functional regulation of p75 NTR .Protein ectodomain shedding is emerging as an important post-translational mechanism for regulating the function of membrane-anchored proteins. Shedding involves the proteolytic processing of membrane-tethered proteins leading to the release of their extracellular-or ectodomain (reviewed in Refs. 1-4). About 2-4% of the proteins on the cell surface are released by metalloproteases in response to phorbol ester stimulation (5). These molecules comprise a variety of structurally and functionally distinct proteins, including epidermal growth factor receptor ligands such as TGF␣ 1 and HB-EGF, TNF family members, and other cytokines, receptors such as the p55 and p75 TNF receptors and the interleukin-6 receptor, and several other proteins, including the amyloid precursor protein, Notch, and Delta (see Ref. 3 and references therein). Ectodomain shedding has been shown to be essential for proper signaling via epidermal growth factor receptor ligands (6 -15), Notch-mediated lateral inhibition (16 -23), limiting TNFR-mediated inflammatory reactions (24), and regulating axonal guidance (25)(26)(27). Even if the functional consequences of ectodomain release remain to be evaluated for most shed proteins, it seems likely that ectodomain shedding will affect the function of the majority of its substrate proteins.Despite the growing number of proteins that are known to undergo ectodomain shedding, much remains to be learned about the mechanisms underlying this process and the responsible proteases. The TNF␣ convertase (TACE) is one of the first proteases shown to be in...

BDNF transcripts, proBDNF and proNGF, in the cortex and hippocampus throughout the life span of the rat

“…Our preliminary data revealed an increase by 30 % of ADAM-10 mRNA expression in the cortex of 12-month-old animals that returned to the control level in aged animals (data not shown). On the other hand, the 55-kDa p75ECD fragment detected in our study was reported as a complete p75NTR ectodomain cleaved by γ-secretase in response to NGF (Weskamp et al 2004). The presence of this fragment in middle-aged animals implies that γ-secretase-dependent ectodomain shedding occurs as well, and that shedding efficiency is lost during aging.…”

TrkA Receptor Activation by Nerve Growth Factor Induces Shedding of the p75 Neurotrophin Receptor Followed by Endosomal γ-Secretase-mediated Release of the p75 Intracellular Domain

“…The observed cell type-specific regulation of p75 shedding by neurotrophins might be related to the cell typespecific expression and distribution of metalloproteases; for instance those belonging to the ADAM family, and to the signal transduction system by which these metalloproteases are regulated. For example, the enzymatic activity of ADAM17, a prominent p75 sheddase (35,66,67), is regulated through phosphorylation by ERK1/2, kinases known to be activated by TrkA (68). Thus, TrkA activation may indirectly regulate ADAM17 activity.…”

Targeting MMPs in Acute and Chronic Neurological Conditions

“…In support, MMPs can shed the extracellular portion of the Nogo receptor (NgR) 32 and of the p75NTR, 33 molecules that are involved in inhibiting axonal growth. After experimental spinal cord injury (SCI), the MMP-2 activity that increases between 7 to 14 days after the insult is associated with the clearance of proteoglycans that retard axonal regrowth correlating with functional recovery.…”