| Claim/topic | Key findings | Model/system | Publication (authors, journal) | Date (month/year) | URL/DOI |
|---|---|---|---|---|---|
| Identity, ER localization, SAM-domain oligomerization | Human SAMD8 encodes SMSr, an ER-resident multi-pass member of the sphingomyelin synthase family that produces small amounts of CPE in the ER lumen. The N-terminal SAM domain mediates homotypic oligomerization; crosslinking detected trimers and hexamers, and oligomerization-defective mutants partially redistributed from ER to Golgi, while SAM deletion caused stronger Golgi relocalization (pqac-00000001, pqac-00000002, pqac-00000022). | Human cells; heterologous systems; confocal microscopy, native gels, crosslinking | Cabukusta et al., *Scientific Reports* | 01/2017 | https://doi.org/10.1038/srep41290 |
| Regulation during apoptosis; caspase-6 cleavage | SMSr is an ER-resident CPE synthase and suppressor of ceramide-mediated apoptosis. During apoptosis, caspase-6 cleaves SMSr primarily at Asp120 (secondary Asp118), generating an ~33 kDa V5-tagged fragment; cleavage was induced by staurosporine/FasL, reproduced with recombinant caspase-6, and reduced by z-VEID-fmk or caspase-6 knockdown (pqac-00000000, pqac-00000003, pqac-00000006). | HeLa cells; wheat-germ cell-free reconstitution; recombinant caspases | Cabukusta et al., *Bioscience Reports* | 07/2017 | https://doi.org/10.1042/BSR20170867 |
| Enzymatic activity, tissue abundance, knockout phenotypes | SMSr is a monofunctional CPE synthase, whereas SMS2 is bifunctional for SM and CPE. In mouse tissues, CPE is ~300- to 1,500-fold lower than SM; absolute CPE reaches ~0.020 mol% of total phospholipid in testis/brain and ~0.002–0.005 mol% in heart/liver. Catalytic inactivation of SMSr mainly reduced brain CPE (e.g., 40–60% reduction in short-chain CPE species; ~30% lower total CPE in forebrain/cerebellum) but did not measurably raise tissue ceramide, disrupt organelle morphology, or impair survival/development; combined SMSr/SMS2 inactivation reduced but did not abolish tissue CPE (pqac-00000012, pqac-00000013, pqac-00000016, pqac-00000018). | Mouse tissues and mutant lines; lipidomics; EM | Bickert et al., *Journal of Lipid Research* | 04/2015 | https://doi.org/10.1194/jlr.M055269 |
| Recent reinterpretation of activity; NAFLD/NASH role | SMSr was reported as a phosphatidylethanolamine phospholipase C (PE-PLC) in vivo. Smsr knockout reduced hepatic PE-PLC activity and increased liver PE, whereas adenoviral SMSr increased PE-PLC activity and lowered PE. In a 16-week HFD+fructose model, Smsr deficiency attenuated body-weight gain, hyperlipidemia, hepatic TG accumulation, fatty liver/NASH, fibrosis, and tumorigenesis; inflammatory cytokines were reduced by ~30%, and genes including Fsp27, PPARγ2, FAS, Tnfα, and Timp1 were decreased (pqac-00000008, pqac-00000009, pqac-00000010). | Mouse knockout and adenoviral overexpression; liver homogenate PE-PLC assay; NAFLD/NASH models; human NASH liver staining | Chiang et al., *Journal of Biological Chemistry* | 09/2023 | https://doi.org/10.1016/j.jbc.2023.105162 |
| SAM-domain interaction with DGKδ; DAG/PA signaling | SMSr physically and functionally interacts with DGKδ via their SAM domains. Co-immunoprecipitation showed strong SAMD-dependent association; deletion of SMSr SAMD reduced DGKδ co-precipitation by ~75%. In COS-7 cells, SMSr overexpression with DGKδ increased total PA by ~20% and enriched 16:0/16:1-related PA species, including 30:0, 32:1, 32:0, 34:1, and 34:2 PA; SMSr also raised total DG by ~14%, supporting a model in which SMSr supplies DG species upstream of DGKδ (pqac-00000025, pqac-00000026, pqac-00000027, pqac-00000029, pqac-00000032). | COS-7 overexpression; co-IP; purified proteins; LC-MS/MS lipidomics | Murakami et al., *Journal of Biological Chemistry* | 03/2020 | https://doi.org/10.1074/jbc.RA119.012369 |
| Authoritative review / current consensus and controversy | Review consensus places SMSr/SAMD8 as the third SMS-family member, a ~414 aa ER-localized six-pass membrane protein with a SAM domain and conserved catalytic His-His-Asp motif. The review notes established in vitro CPE synthase activity and highlights an emerging reinterpretation of SMSr as a PE-PLC-like enzyme that generates DAG in the absence of ceramide, while emphasizing unresolved physiology because mouse knockout studies showed minimal overt phenotypes despite cell-based reports of ER ceramide regulation (pqac-00000019, pqac-00000020, pqac-00000021, pqac-00000023, pqac-00000024). | Narrative review synthesizing biochemical and genetic studies | Jiang & Chiang, *Advances in Experimental Medicine and Biology* | 01/2022 | https://doi.org/10.1007/978-981-19-0394-6_7 |


*Table: This table summarizes the main primary studies and a key review on human SAMD8/SMSr, covering identity, localization, enzymatic activity, regulation, and phenotypes. It highlights where the literature is consistent and where recent work has introduced mechanistic controversy, especially around CPE synthase versus PE-PLC activity.*