A role for Seven in Absentia Homolog (Siah1a) in metabotropic glutamate receptor signaling.
BACKGROUND
The mammalian homologue of Seven in Absentia (Siah) can act in the ubiquitin/proteasome pathway. Recent work has shown that Siah can bind group I metabotropic glutamate receptors (mGluRs), but the functional consequences of this interaction are unknown.


RESULTS
The effects of coexpression of Siah on group I mGluR signaling were examined using heterologous expression in rat sympathetic, superior cervical ganglion neurons. Siah1a attenuated heterologously expressed group I mGluR-mediated calcium current inhibition, but was without effect on group II mGluR- or NE-mediated calcium current modulation via heterologously expressed mGluR2 or native a2 adrenergic receptors, respectively, indicating that the effect of Siah was specific for group I mGluRs. Surface expression and subcellular distribution of group I mGluRs were not detectably altered in the presence of Siah1a as assessed by immunoflourescence experiments with epitope tagged receptors and imaging of a GFP/mGluR fusion construct. In addition, an N-terminal Siah deletion construct, which cannot function in the proteolysis pathway, displayed effects similar to the wild type Siah1a. Finally, coexpression of calmodulin, which competes with Siah1a for binding to the C-terminal tail of group I mGluRs, reversed the effect of Siah1a on mGluR-mediated signaling.


CONCLUSIONS
These data supported the conclusion that the attenuation of mGluR signaling induced by Siah1a expression was likely a direct consequence of Siah/mGluR association rather than a result of targeting of the receptors to the proteosome. In addition, the data suggest that the binding of CaM and Siah may play an important role in the regulation of group I mGluR function.
Kammermeier
P J
PJ
Laboratory of Molecular Physiology, Guthrie Research Institute, Sayre, PA 18840, USA. pkammerm@inet.guthrie.org
Ikeda
S R
SR
D000818:Animals; D002147:Calmodulin / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D003546:Cysteine Endopeptidases / Q000378:metabolism; D018014:Gene Transfer Techniques; D008845:Microinjections; D009097:Multienzyme Complexes / Q000378:metabolism; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D046988:Proteasome Endopeptidase Complex; D011485:Protein Binding / Q000502:physiology; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D051381:Rats; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D017783:Superior Cervical Ganglion / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases; D000098563:Seven in Absentia Proteins
D002147:Calmodulin; D009097:Multienzyme Complexes; D009687:Nuclear Proteins; D020033:Protein Isoforms; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate; C104077:metabotropic glutamate receptor type 1; D044767:Ubiquitin-Protein Ligases; D000098563:Seven in Absentia Proteins; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex