Seven in absentia homolog 1A mediates ubiquitination and degradation of group 1 metabotropic glutamate receptors

Abstract

Seven in absentia homolog 1A (Siah1A) is a member of the RING-finger-containing E3 ubiquitin ligases and has been shown to bind to the Siah-interacting domain (SID) at the carboxyl-terminal tails of the long splice forms of group 1 metabotropic glutamate receptors (mGluR1a and mGluR5). We examined the function of Siah1A in ubiquitination and degradation of group 1 mGluRs in heterologously expressing cell lines. Coexpression of Siah1A markedly decreased the SID-containing splice forms of group 1 mGluRs but not the SID-lacking mGluR1b splice form or the SID-deleted mGluR1a mutant. The decrease of mGluR1a resulted from accelerated protein turnover, as revealed by pulse-chase experiments. The Siah1A-mediated degradation of group 1 mGluRs was abrogated by not only mutations at the RING-finger domain of Siah1A but also treatment with a proteasome inhibitor. Siah1A coexpression induced strong ubiquitination of group 1 mGluRs. Replacements of lysine residues with arginine showed that Siah1A-mediated ubiquitination occurs at multiple lysine residues spanning both the seven-transmembrane region and carboxyl-terminal tail of mGluR5. In situ hybridization histochemistry showed a widespread distribution of Siah1 mRNAs, with high expression in the hippocampal pyramidal neurons and cerebellar Purkinje cells. Group 1 mGluRs play critical roles in the neural plasticity in both the hippocampal neurons and Purkinje cells. This investigation indicates that Siah1A serves as a selective ubiquitin ligase that mediates ubiquitination-dependent degradation of long splice variants of group 1 mGluRs and would contribute to posttranslational down-regulation of group 1 mGluRs.

Mediation of Af4 protein function in the cerebellum by Siah proteins

“…Both Siah-1a and Siah-2 are expressed widely in embryonic and adult mouse tissues (16), and a recent study using a nonspecific Siah-1a͞b probe demonstrated that pyramidal neurons of the hippocampus as well as Purkinje cells express high levels of Siah-1 mRNAs (17). To determine whether Siah-1a has an expression profile similar to that of Af4, in situ hybridization was carried out on adult brain sections using a riboprobe designed from the 3Ј UTR to avoid crossreactivity with Siah-1b (16).…”

Synphilin-1A Inhibits Seven in Absentia Homolog (SIAH) and Modulates α-Synuclein Monoubiquitylation and Inclusion Formation

“…In agreement, both proteins were previously shown to be widely expressed in the brain and to be present at the presynapse (25, 35, 36). In addition, SIAH interacts with and promotes the degradation of different synaptic proteins, including the group 1 metabotropic glutamate receptor and the synaptic vesicle protein synaptophysin (36,37). Moreover, endogenous SIAH was shown to be present and to co-localize with synaptophysin in neuritic processes of neuronally differentiated PC12 cells (37).…”

Proteasome Targeted Therapies in Rheumatoid Arthritis

“…Proteasome inhibitors can cause cellular apoptosis in proliferating cancer cells by affecting various short-lived proteins, resulting in inhibition of NF-ĸB activity, increased activity of p53 and Bax proteins, and accumulation of cyclin-dependent kinase inhibitors p27 and p21 [Moriyoshi et al, 2004;Van Waes et al, 2007]. Preclinical studies show that malignant, transformed, and proliferating cells are more susceptible to proteasome inhibition than cells in a resting state Sherr, 1996].…”

“…UPS regulates synaptic functions by controlling levels of pre-synaptic proteins [Speese et al, 2003]. At the post-synaptic levels, the UPS regulates the surface expression and internalization of NMDA-and AMPA-glutamate receptors [Moriyoshi et al, 2004]. It has been implicated that mechanical allodynia and hyperalgesia can be prevented with NMDAreceptor antagonists [Laughlin et al, 1997].…”