When the IRE1[alpha] -XBP1 pathway is induced in response to ER-stress, sXBP1 regulates downstream genes such as BiP, GRP94, Herpud1, and HRD1 [7,13,17].
Although horse HRD1 and EDEM1 do not contain UPRE, their expression was not altered to the same degree as BiP and GRP94, suggesting that 4 h of heat shock is not a sufficient duration to induce the ERAD system (Figure 4C).
Human HRD1 promoter carries a functional unfolded protein response element to which XBP1 but not ATF6 directly binds.
Human HRD1 protects against ER stress-induced apoptosis through ER-associated degradation.
(C) Expression of HRD1 (one-way ANOVA, 1 h heat shock: p = 0.4513, 4 h heat shock: p = 0.3608) and eDeM1 (one-way ANOVA, 1 h heat shock: p = 0.7198, 4 h heat shock: p = 0.7406) were investigated by real-time qPCR.
showed that HRD1 protein was insolubilized by oxidative stress but not by other AD-related molecules and stressors, such as amyloid-[beta], tau, and ER stress.
Quite recently, HRD1 ubiquitin ligase, previously reported to favor APP degradation , was also identified as a negative regulator of tau phosphorylation in AD .
Fang et al., "Hrd1 facilitates tau degradation and promotes neuron survival," Current Molecular Medicine, vol.
pCDNA3.1 vectors expressing an myc tagged version of either wildtype Hrd1-mycHis or a dominant negative form of Hrd1 (C240A-) mycHis were gifts from Dr.
293T were transfected with siRNA against Hrd1 (ON-TARGETplus SMARTpool Human SYVN1, Dharmacon) or a negative control siRNA (AllStars Neg.
Ubiquitination of WT-TCR[alpha] is known to require Hrd1 12,13], an E3 ubiquitin ligase of the RING finger family that mediates degradation of many ER substrates .
In our system, we observe that when present, lysines residues are the preferred targets of Hrd1-mediated ubiquitination, while in the absence of lysine residues, Hrd1 is capable of conjugating ubiquitin to nonlysine residues.