• Wed. Feb 12th, 2025

Furthermore, a number of studies have proposed that calpain-mediated degradation of NMDAR could act as an initial defense mechanism by reducing the number of functional NMDAR molecules, and consequently decreasing the extent of Ca2+ influx [30C32]

Byacusticavisual

Oct 28, 2024

Furthermore, a number of studies have proposed that calpain-mediated degradation of NMDAR could act as an initial defense mechanism by reducing the number of functional NMDAR molecules, and consequently decreasing the extent of Ca2+ influx [30C32]. activity without affecting the amount of the protease originally associated to NMDAR. In all the conditions examined, resident calpain 1 specifically cleaves NR2B at Rabbit Polyclonal to 5-HT-1E the C-terminal region, leading to its internalization together with NR1 subunit. While in basal conditions intracellular membranes include small amounts of NMDAR containing the calpain-digested NR2B, upon NMDAR stimulation nearly all the receptor molecules are internalized. We here propose that resident calpain 1 is involved in NMDAR turnover, and following an increase in Ca2+ influx, the activated protease, by promoting the removal of NMDAR from the plasma membranes, can decrease Ca2+ entrance through this channel. Due to the absence of calpastatin in such cluster, the activity of resident calpain 1 may be under the control of HSP90, whose levels are directly related to the activation of this protease. Observations of different HSP90/calpain 1 ratios in different ultrasynaptic compartments support this conclusion. Introduction Multiple lines of evidence indicate that the Ca2+-dependent protease calpain plays critical roles in both physiological and pathological conditions [1C6]. In particular, in brain tissue, calpain activation is normally mediated by Ca2+ entry via stimulation Cucurbitacin I of NMDAR, and whose NR2A and NR2B subunits are both calpain substrates [7C10]. Moreover, it is well known that following receptor stimulation, these NMDAR subunits, involved in the anchoring of NMDAR to the cytoskeleton by protein-protein interactions [11C22], participate to the activation of downstream intracellular signaling pathways. The direct functional correlation between calpain and NMDAR Cucurbitacin I has been extensively investigated and the data obtained have often suggested different conclusions. In particular the major controversial problem concerns the hypothesis that calpain activation, induced by extensive stimulation of NMDAR, is directly responsible for excitotoxicity and cell death [23C28]. A second issue concerns the fate of NMDAR after the digestion of NR2 subunits [9, 29]. Furthermore, a number of studies have proposed that calpain-mediated degradation of NMDAR could act as an initial defense mechanism by reducing the number of functional NMDAR molecules, and consequently reducing the degree of Ca2+ influx [30C32]. More recently it has been reported the activation of calpain 1 coupled with synaptic NMDAR can exert a role in neuroprotection, whereas the activation of calpain 2 coupled with extrasynaptic NMDAR is definitely involved in neurodegeneration [33]. From our recent observations [34] an additional contribution to the understanding of the mechanism and the biological role of the proteolytic control of NMDAR emerges. Our data show that, in SKNBE neuroblastoma cells, the chaperone HSP90 takes on a specific part in the control of the dynamic activation of calpain 1 and that the chaperone can assist the protease during its recruitment in the multiprotein NMDAR cluster [34]. These observations are consistent with the finding that calpain 1, but not calpain 2, resides in small but saturating amounts in the NMDAR complex together with a large excess of HSP90 [34]. To obtain additional information on the mechanism and the physiological significance of the relationship between calpain 1 and NMDAR, we have investigated the part of resident calpain 1 in the proteolytic processing of NMDAR. We here Cucurbitacin I demonstrate that, in human being neuroblastoma SKNBE cells, the NR2B subunit of NMDAR, mainly indicated in these cells [35, 36], undergoes a selective in situ proteolytic digestion in the C-terminal region, by resident calpain 1. We observed that NR2B proteolysis normally happens at limited degree in resting cells and at a much higher rate following cell activation with non-toxic NMDA concentrations. In both conditions NMDAR, comprising the digested NR2B Cucurbitacin I subunit, undergoes internalization into membrane vesicles. On the basis of these observations, we are now proposing that in basal conditions calpain 1 resident in the NMDAR complex is definitely involved.