GRINA

GRINA (TMBIM3) is a multi-transmembrane ER-membrane protein that governs ER calcium homeostasis, the unfolded protein response, and apoptotic cell fate (PMID:22240901, PMID:31683519). It is transcriptionally induced by the PERK branch of the UPR and limits ER calcium release through physical interaction with inositol-1,4,5-trisphosphate receptors, synergizing with TMBIM6/BI-1 to provide ER stress protection (PMID:22240901, PMID:31683519). In ischemic injury, GRINA restrains the pro-apoptotic PERK arm of the UPR and suppresses caspase-9-dependent neuronal death; its loss enlarges infarct volume and abolishes erythropoietin-mediated neuroprotection (PMID:31211943, PMID:31683519). GRINA also assembles a GRINA-HRD1-ATF6 complex that catalyzes ATF6 polyubiquitination and proteasomal degradation, thereby suppressing ER-phagy and protecting hepatocytes from ischemia-reperfusion injury (PMID:39855351). Beyond the ER, GRINA directly binds CaV2.2 (N-type) voltage-gated calcium channels and inhibits their current in a manner mimicking G-protein βγ modulation (PMID:30991297). In cancer cells GRINA supports PI3K/Akt/mTOR signaling and glycolytic metabolism and restrains apoptosis and ferroptosis (PMID:30541591, PMID:40011365).

1. 2011 Medium

   Established GRINA as a defined gene product by characterizing it as an ~38 kDa seven-transmembrane protein enriched in brain, providing the structural and expression baseline for later functional studies.

   Evidence Biochemical fractionation, sequence analysis, immunohistochemistry, and knockout mouse generation

   PMID:21614515

   Open questions at the time

   • No molecular function assigned at this stage
   • Basal knockout had no obvious phenotype, leaving physiological role undefined
   • Topology was predicted, not structurally resolved
2. 2012 High

   Placed GRINA within ER stress biology by showing it is induced via the PERK arm of the UPR and physically engages IP3Rs to control ER calcium and apoptosis, defining its core ER-protective function.

   Evidence Reciprocal Co-IP for IP3R interaction plus loss-of-function in Drosophila and zebrafish and calcium homeostasis assays

   PMID:22240901

   Open questions at the time

   • Mechanism by which GRINA suppresses IP3R-mediated calcium release not resolved at molecular level
   • Relationship between PERK induction and downstream survival not yet defined
   • No mammalian disease context established
3. 2019 High

   Demonstrated GRINA directly inhibits CaV2.2 voltage-gated calcium channels, extending its calcium-regulatory role to the plasma-membrane channel level.

   Evidence Co-IP and whole-cell patch clamp electrophysiology in a heterologous co-expression system with action-potential-like protocols

   PMID:30991297

   Open questions at the time

   • Whether GRINA modulates CaV2.2 in native neurons not shown
   • Structural basis of the βγ-like inhibition unknown
   • Physiological consequence of channel inhibition not established in vivo
4. 2019 High

   Defined GRINA's neuroprotective function in vivo by showing its loss exacerbates ischemic stroke through derepression of the caspase-9 apoptotic pathway and the pro-apoptotic PERK arm of the UPR, linking it to EPO-mediated survival signaling.

   Evidence GRINA knockout mice in tMCAo focal ischemia, primary neuron OGD, pharmacological UPR inhibitors, overexpression rescue, Western blotting, and mRNA analysis

   PMID:31211943 PMID:31683519

   Open questions at the time

   • How GRINA biases UPR signaling away from PERK and toward IRE1α mechanistically unresolved
   • Direct molecular link between GRINA and caspase-9 not defined
   • EPO-to-GRINA induction pathway not mapped
5. 2018 Medium

   Connected GRINA to oncogenic metabolism by showing it is a c-Myc transcriptional target supporting PI3K/Akt/mTOR signaling, glycolysis, and apoptosis resistance in gastric cancer.

   Evidence siRNA knockdown with glycolysis, proliferation, apoptosis assays and pathway/transcriptional analysis

   PMID:30541591

   Open questions at the time

   • Single-lab, single cancer type
   • Mechanism linking GRINA to PI3K/Akt/mTOR not defined
   • No direct molecular interaction with pathway components shown
6. 2025 High

   Revealed a new biochemical mechanism: GRINA scaffolds a HRD1-ATF6 complex to drive ATF6 polyubiquitination and degradation, suppressing ER-phagy and protecting hepatocytes from ischemia-reperfusion injury.

   Evidence Co-IP, ubiquitination assays, mass spectrometry, hepatocyte-specific Grina knockout and transgenic mice, RNA-seq, and pharmacological ATF6 inhibition

   PMID:39855351

   Open questions at the time

   • How GRINA recruits HRD1 to ATF6 structurally unknown
   • Whether this complex operates outside hepatocytes not established
   • Integration with the IP3R/PERK functions not resolved
7. 2025 Medium

   Extended GRINA's anti-death function to ferroptosis by showing its knockdown raises iron and ROS and causes mitochondrial abnormalities in HCC cells.

   Evidence siRNA knockdown with ROS assays, iron quantification, mitochondrial morphology, and proliferation/colony formation assays

   PMID:40011365

   Open questions at the time

   • Single-lab, single endpoint per readout
   • Molecular mechanism of ferroptosis suppression unknown
   • Link to GRINA's ER calcium/UPR functions not made

• How GRINA's distinct activities — IP3R/CaV2.2 channel modulation, UPR arm biasing, and HRD1-ATF6-mediated ER-phagy control — are integrated into a single coherent molecular mechanism remains unresolved.
• No structural model unifying its transmembrane topology with its multiple binding partners
• Unclear whether channel modulation and ATF6 degradation occur in the same cellular context
• Relative contribution of each activity to cytoprotection not quantified