Human brain carboxypeptidase B, which cleaves β‐amyloid peptides in vitro, is expressed in the endoplasmic reticulum of neurons

Abstract

Intracellular localization of novel human brain carboxypeptidase B (HBCPB) was investigated in human hippocampus, using immunohistochemistry by confocal laser microscopy and biochemical purification of the homogenate by density gradient ultracentrifugation. The former revealed that the majority of HBCPB was expressed in the endoplasmic reticulum, in which the HBCPB-specific C14-module immunoreactivity was colocalized with GRP78 immunoreactivity, a stress 70 heat shock protein specifically expressed in the endoplasmic reticulum. The latter showed that anti-C14-module immunoreactivity and prepro-HBCPB immunoreactivity were both enriched in the microsome fraction, especially in that of the endoplasmic reticulum-density fraction of normal human hippocampal homogenates from various sources. However, HBCPB prepared from human hippocampus showed exopeptidase activity for synthetic beta-amyloid 1-42 peptide, in which Abeta X-42 C-terminus immunoreactivity was decreased in a fashion dose-dependent of the amount of the protease added. These findings indicate that HBCPB, which is expressed in the endoplasmic reticulum of a group of neuronal perikarya, may play an important physiological role in degradation of beta-amyloid 1-42, which is specifically generated in the endoplasmic reticulum of human and rodent neurons and is also regarded as the most pathogenic and aggregatable species among all beta-amyloid peptides.

Identification of Novel Genes That Modify Phenotypes Induced by Alzheimer's β-Amyloid Overexpression in Drosophila

“…In our studies we have identified carboxypeptidase D, which belongs to a family of enzymes that proteolytically process peptides in the secretory pathway (Arolas et al 2007), as a modifier of Ab toxicity. Previous reports have identified carboxypeptidase B as an enzyme that may degrade Ab intracellularly (Matsumoto et al 2001) by processing its carboxy terminus (Hamazaki 1998). The C terminus of Ab plays an important role in the formation of Ab fibrils (CerdaCosta et al 2007), suggesting that the processing by carboxypeptidases may have an important function in the toxicity of Ab.…”

Aluminum inhibits proteolytic degradation of amyloid β peptide by cathepsin D: A potential link between aluminum accumulation and neuritic plaque deposition

“…Several proteases have been shown to be capable of cleaving Ab peptide. There are number of candidate proteases, including trypsin and a-chymotrypsin [27], insulin degrading enzyme [28][29][30], endothelin-converting enzyme [31], carboxypeptidase B [32], angiotensin-converting enzyme [33], plasmin [34,35], neprilysin [36] and cathepsin D [20,21]. However, the enzyme definitively responsible for the physiological degradation of Ab peptide is thus far unclear.…”

“…3B and 4B. Although Ab 1- 19 and Ab [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] were confirmed in the eluent from Ab 1-40 peptide, only Ab 1-19 was identified from Ab 1-42 peptide under our HPLC conditions in order to quantify the amount of residual Ab 1-40 or Ab 1-42 peptide. However, when the each Ab peptide was pretreated with Al, Fe, or Zn (at a level about 0.25 mM), the degradation of Ab 1-40 and Ab 1-42 peptides by cathepsin D was significantly inhibited by pretreatment of Al above 0.25 mM (Figs.…”

“…Earlier studies have suggested that Al inhibited calpain-mediated proteolysis of human neurofilament [3] and also inhibited trypsin and a-chymotrypsin proteolytic activity [4]. Korchazhkina et al [5] recently reported that Al was able to inhibit plasmin degradation of the Ab peptide (Ab [25][26][27][28][29][30][31][32][33][34][35] ). Their results indicated that inhibitory effect of Al was caused by a direct interaction between Al and plasmin.…”

Brain‐specific carboxypeptidase B: selective down‐regulation in ependymal cell by irradiation and altered β‐amyloid processing

“…HBCPB is expressed in a group of neuronal perikarya and ependymal cells in normal brains. In brains of sporadic Alzheimer's disease patients, however, expression of HBCPB in neuronal perikarya is decreased, and the immunorea~tivity is detected in about one third of senile plaque and a portion of activated microglia (2,3). The expression of HBCPB is confined in brain, and is basically divided into two groups: (i) endoplasmi~ reticulum of a group of neurons such as On the other hand, it is recently clarified that ependymal cells are stem cells for particular neurons and glias (4).…”