The Disintegrin ADAM9 Indirectly Contributes to the Physiological Processing of Cellular Prion by Modulating ADAM10 Activity

Abstract

The cellular prion protein (PrP c ) is physiologically cleaved in the middle of its 106 -126 amino acid neurotoxic region at the 110/ 1112112 peptidyl bond, yielding an N-terminal fragment referred to as N1. We recently demonstrated that two disintegrins, namely ADAM10 and ADAM17 (TACE, tumor necrosis factor alpha converting enzyme) participated in both constitutive and protein kinase C-regulated generation of N1, respectively. These proteolytic events were strikingly reminiscent of those involved in the socalled "␣-secretase pathway" that leads to the production of secreted sAPP␣ from ␤APP. We show here, by transient and stable transfection analyses, that ADAM9 also participates in the constitutive secretion of N1 in HEK293 cells, TSM1 neurons, and mouse fibroblasts. Decreasing endogenous ADAM9 expression by an antisense approach drastically reduces both N1 and sAPP␣ recoveries. However, we establish that ADAM9 was unable to increase N1 and sAPP␣ productions after transient transfection in fibroblasts depleted of ADAM10. Accordingly, ADAM9 is unable to cleave a fluorimetric substrate of membrane-bound ␣-secretase activity in ADAM10 ؊/؊ fibroblasts. However, we establish that co-expression of ADAM9 and ADAM10 in ADAM10-deficient fibroblasts leads to enhanced membrane-bound and released fluorimetric substrate hydrolyzing activity when compared with that observed after ADAM10 cDNA transfection alone in ADAM10 ؊/؊ cells. Interestingly, we demonstrate that shedded ADAM10 displays the ability to cleave endogenous PrP c in fibroblasts. Altogether, these data provide evidence that ADAM9 is an important regulator of the physiological processing of PrP c and ␤APP but that this enzyme acts indirectly, likely by contributing to the shedding of ADAM10. ADAM9 could therefore represent, besides ADAM10, another potential therapeutic target to enhance the breakdown of the 106 -126 and A␤ toxic domains of the prion and ␤APP proteins.Spongiform encephalopathies are fatal neurodegenerative diseases involving a highly protease-resistant protein referred to as prion scrapie (PrP sc ) 4 (1, 2). Human prion diseases include, among others, Creutzfeldt-Jakob disease, familial transmissible spongiform encephalopathies, new variant of Creutzfeldt-Jakob disease, as well as a few cases of iatrogenic transmission (3-5). PrP sc corresponds to the abnormal conformation of an ubiquitous glycosylphosphatidylinositol-anchored protein called cellular prion (PrP c ) that is mainly synthesized in the central nervous system (6, 7). The mechanisms by which PrP c is converted into PrP sc are not fully understood. However, it appears clearly that inoculation of PrP sc triggers pathology and ultimately cell death in mice only when PrP c is present in the host animal. Thus, PrP c null mice resist infection and toxicity exhibited by scrapie-enriched inoculates (8 -10). On the other hand, it appears that depletion of PrP c is relatively innocuous (11,12). Therefore, all strategies aimed at lowering endogenous PrP c are potential therapeutic approaches. Clas...

New insights into cellular prion protein (PrPc) functions: The “ying and yang” of a relevant protein

“…However, a protein similar to F35 is generated in the healthy human brain when PrP c is endoproteolized into 110/111 residues through ADAMs in a Protein kinase C (PKC)-dependent way, thereby generating a C-terminal fragment termed C1 (Cisse et al, 2005;Chen et al, 1995;Harris et al, 1993;Vincent et al, 2000;Vincent et al, 2001). A shorter fragment, within the OR region (residues 90/91), the C2, is generated in pathological conditions and poor data have yet been provided about this cleavage (Chen et al, 1995).…”

M1and M3Muscarinic Receptors Control Physiological Processing of Cellular Prion by Modulating ADAM17 Phosphorylation and Activity

“…We also showed that ADAM9 indirectly participated in N1 formation, by modulating ADAM10 activity (Alfa Cissé et al, 2005). The mechanisms by which ADAM17 is modulated by PKC and upregulates N1 formation remained to be established.…”

Prion and TNFα: TAC(E)it agreement between the prion protein and cell signaling

“…This was achieved by stimulating serotonergic and noradrenergic neurons with antibodymediated PrP C cross-linking that, by triggering Fyn-dependent NADPH oxidase two distinct endo-proteolytic events, termed α-and β-cleavage, of which the α-cleavage implicates ADAM9, ADAM10 and ADAM17 (TACE). [33][34][35] Although the latter report has recently been questioned, 32 the patho-physiologic relevance of PrP C shedding and of the endo-proteolytic processes remains unclear.…”