E2-25K/Hip-2 regulates caspase-12 in ER stress–mediated Aβ neurotoxicity

Abstract

Amyloid-β (Aβ) neurotoxicity is believed to contribute to the pathogenesis of Alzheimer's disease (AD). Previously we found that E2-25K/Hip-2, an E2 ubiquitin-conjugating enzyme, mediates Aβ neurotoxicity. Here, we report that E2-25K/Hip-2 modulates caspase-12 activity via the ubiquitin/proteasome system. Levels of endoplasmic reticulum (ER)–resident caspase-12 are strongly up-regulated in the brains of AD model mice, where the enzyme colocalizes with E2-25K/Hip-2. Aβ increases expression of E2-25K/Hip-2, which then stabilizes caspase-12 protein by inhibiting proteasome activity. This increase in E2-25K/Hip-2 also induces proteolytic activation of caspase-12 through its ability to induce calpainlike activity. Knockdown of E2-25K/Hip-2 expression suppresses neuronal cell death triggered by ER stress, and thus caspase-12 is required for the E2-25K/Hip-2–mediated cell death. Finally, we find that E2-25K/Hip-2–deficient cortical neurons are resistant to Aβ toxicity and to the induction of ER stress and caspase-12 expression by Aβ. E2-25K/Hip-2 is thus an essential upstream regulator of the expression and activation of caspase-12 in ER stress–mediated Aβ neurotoxicity.

Amyloid-β42signals tau hyperphosphorylation and compromises neuronal viability by disrupting alkylacylglycerophosphocholine metabolism

“…We next assessed ER stress responses. In murine neurons, A␤ 42 activates both calpains and ER-associated caspase-12 (20). The human homolog of caspase-12 has a frameshift mutation resulting in a premature stop codon and an amino acid substitution within a critical site for caspase enzymatic activity, rendering it catalytically inactive (21).…”

FcγRIIb mediates amyloid-β neurotoxicity and memory impairment in Alzheimer’s disease

“…Conversely, overexpressed FcγRIIb, but not the I232T FcγRIIb mutant, induced similar ER stress responses in HT22 cells (Supplemental Figure 5D). Of particular note, Aβ 1-42 -induced activation of caspase-12, a key player in ER stress-and Aβ-mediated apoptosis (12,31), was abrogated in Fcgr2b KO cortical neurons (Supplemental Figure 5C). Furthermore, ectopic expression of the caspase-12 active site mutant (C298S) significantly suppressed FcγRIIb-mediated HT22 cell death, while caspase-12 significantly enhanced it (Supplemental Figure 5E).…”

“…We previously isolated a cytosolic mediator of Aβ neurotoxicity, E2-25K/Hip-2, based on a global analysis of the genes expressed in the primary cortical neurons exposed to Aβ (11,12). Using the same approach, we found that Aβ strongly upregulated the expression of FcγRIIb in the cortical neurons.…”

“…To construct the rFcγRIIb(ED)-CD40 chimera, the extracellular domain of rFcγRIIb and the transmembrane and cytosolic domains of CD40 were subcloned into pEGFP-N1 using the primers (FcγRIIb-ED-5′-NheI, 5′-GCTAGCGC-TATGGACAGCAACAGGACT-3′; FcγRIIb-ED-3′-HindIII, 5′-AAGCTTGG-GAGGCAACGAACTGCTGGATTT-3′; CD40-TM+cyto-5′-HindIII, 5′-CCCAAGCTTGGGGCCCTGGTGGTGATCCCCATC-3; and CD40-TM+cyto-3′-KpnI, 5′-CGGGTACCATTCACTGTCTCTCCTGCA C-3′). Caspase-12 GFP and its active site mutant (C298S) have been described previously (12). The promoter (-537 to +43) of the human FcγRIIb (22) was amplified by PCR and subcloned into pGL2-basic vectors.…”

Genesis of ER stress in Huntington’s Disease

“…PERK and phosphorylated eIF2α were also upregulated [134,135] and there was a decrease in Sigma-1R [136]. Amyloid β increases PERK activation and CHOP expression in neurons in culture [137][138][139]. Expression of mutant presenilin 1, linked to familial AD, also alters the PERK, IRE1 and ATF6 pathways [140,141] and increases CHOP expression [142].…”