LPCAT3

Summary: This is the core enzymatic activity of LPCAT3 (LPCAT = lysophosphatidylcholine acyltransferase). LPCAT3 catalyzes the transfer of acyl groups from acyl-CoA to 1-acyl-lysophosphatidylcholine to form phosphatidylcholine. This activity has been demonstrated directly in multiple biochemical studies (PMID:18195019, PMID:18772128, PMID:18782225).

Reason: This is the primary named enzymatic activity of LPCAT3. Multiple independent studies have demonstrated this activity experimentally. Zhao et al. 2008 showed that "Membranes from HEK293 cells overexpressing LPCAT3 showed significantly increased LPCAT activity" (PMID:18195019). Gijon et al. 2008 confirmed "MBOAT5 prefers lysophosphatidylcholine and lyso-PS to incorporate linoleoyl and arachidonoyl chains" (PMID:18772128). The IBA annotation is phylogenetically supported and consistent with all biochemical evidence.

Summary: IEA annotation for the core LPCAT activity based on UniProt mapping and RHEA reaction cross-references. This duplicates the IBA annotation but from a computational source.

Reason: This is the core enzymatic function of LPCAT3, well-supported by experimental evidence from multiple sources. The IEA mapping is consistent with experimental data.

Summary: Direct biochemical demonstration of LPCAT activity by Matsuda et al. 2008. Over-expression of MBOAT5 in HEK293 cells resulted in great increases in LPC acyltransferase activity using arachidonoyl-CoA as donor.

Reason: Direct experimental evidence from reconstitution studies in HEK293 cells showing LPCAT activity is strongly increased upon MBOAT5/LPCAT3 overexpression.

Summary: Zhao et al. 2008 identified LPCAT3 as the major liver LPCAT and characterized its enzymatic activity with various acyl-CoA substrates, showing preference for unsaturated fatty acids.

Reason: Key primary study identifying LPCAT3 and demonstrating its enzymatic activity directly. Shows LPCAT3 is the major hepatic LPCAT enzyme.

Summary: Gijon et al. 2008 used mass spectrometry-based enzyme assays to characterize MBOAT5/LPCAT3 substrate specificity, showing preference for LPC with linoleoyl and arachidonoyl donors.

Reason: High-quality biochemical characterization using novel MS-based assays confirming LPC acyltransferase activity with PUFA preference.

Summary: Li et al. 2012 showed that LPCAT3 knockdown significantly reduces hepatic LPCAT activity, providing mutant phenotype evidence for this molecular function.

Reason: Important study confirming LPCAT3 as the major hepatic LPCAT isoform through knockdown experiments showing loss of enzymatic activity.

Summary: LPCAT3 is indeed a lysophospholipid acyltransferase with broad substrate specificity encompassing LPC, LPE, and LPS. This broader term correctly captures the enzyme's range of substrates.

Reason: Appropriate parent term that accurately reflects the enzyme's activity on multiple lysophospholipid substrates. Matsuda et al. 2008 demonstrated that MBOAT5 "is a lysophospholipid acyltransferase acting preferentially on LPC, LPS and LPE" (PMID:18782225).

Summary: LPCAT3 has documented LPEAT activity, transferring acyl groups to lysophosphatidylethanolamine. This is a secondary but well-characterized activity.

Reason: LPEAT activity has been experimentally demonstrated, though it is lower than LPCAT activity. UniProt assigns EC 2.3.1.n7 for this activity based on PMID:18772128 and PMID:18782225.

Summary: ISS annotation for LPEAT activity based on mouse ortholog data.

Reason: Sequence similarity annotation is consistent with direct experimental evidence for this activity in human LPCAT3.

Summary: Direct demonstration of LPEAT activity by Gijon et al. 2008 using MS-based enzyme assays.

Reason: Direct experimental evidence showing MBOAT5/LPCAT3 can acylate LPE, though this is a secondary activity compared to LPC.

Summary: Matsuda et al. 2008 demonstrated LPE acyltransferase activity through overexpression studies in HEK293 cells.

Reason: Direct experimental evidence confirming LPEAT activity of MBOAT5/LPCAT3.

Summary: LPCAT3 has documented LPSAT activity, acylating lysophosphatidylserine.

Reason: LPSAT activity is experimentally supported. UniProt assigns EC 2.3.1.n6 based on multiple experimental studies.

Summary: Zhao et al. 2008 demonstrated LPSAT activity in their characterization of LPCAT3.

Reason: Direct experimental evidence for LPS acyltransferase activity.

Summary: Gijon et al. 2008 confirmed LPS acyltransferase activity using MS-based assays.

Reason: High-quality MS-based biochemical evidence for LPSAT activity.

Summary: Matsuda et al. 2008 demonstrated LPS acyltransferase activity through overexpression studies.

Reason: Direct experimental evidence for LPSAT activity.

Summary: Reactome annotation for AGPAT-like activity. However, LPCAT3 acts on lysophospholipids (with headgroups like choline, ethanolamine, serine), not on lysophosphatidic acid (LPA). This activity is distinct from true AGPAT/LPAAT activity.

Reason: This term refers to activity on 1-acylglycerol-3-phosphate (lysophosphatidic acid), which is different from the lysophospholipids that LPCAT3 prefers. Matsuda et al. 2008 explicitly showed that MBOAT5 overexpression did NOT increase LPAAT activity (PMID:18782225). The Reactome pathway may be capturing a related reaction step in phospholipid remodeling, but the GO term may be imprecise. Need to verify the exact Reactome reaction definition.

Summary: Second Reactome annotation for AGPAT activity.

Reason: Same concern as above - LPCAT3 lacks significant LPAAT activity according to direct biochemical studies. The Reactome pathway context needs verification.

Summary: Third Reactome annotation for AGPAT activity.

Reason: Same concern - experimental evidence suggests LPCAT3 does not have significant LPAAT activity.

Summary: Reactome annotation for acyltransferase activity at the sn-1 position of 2-acyl-lysophospholipids.

Reason: LPCAT3 primarily acts on 1-acyl-lysophospholipids (re-acylating at sn-2 position), not 2-acyl-lysophospholipids. This annotation may reflect a minor activity or may be pathway modeling that requires verification.

Summary: Second Reactome annotation for 2-AGPAT activity.

Reason: Same concern - primary activity is on 1-acyl-lysophospholipids, not 2-acyl.

Summary: Third Reactome annotation for 2-AGPAT activity.

Reason: Same concern regarding substrate specificity.

Summary: Very general term for transferase activity based on UniProt keyword mapping.

Reason: This term is too general to be informative. LPCAT3 has specific lysophospholipid acyltransferase activities that are captured by more specific terms (GO:0047184, GO:0071617, GO:0106262, GO:0106263).

Proposed replacements: 1-acylglycerophosphocholine O-acyltransferase activity lysophospholipid acyltransferase activity

Summary: General acyltransferase activity term from UniProt keyword mapping.

Reason: This is a broad parent term that doesn't convey the specific substrate preference of LPCAT3. More informative terms exist (GO:0047184, GO:0071617).

Proposed replacements: 1-acylglycerophosphocholine O-acyltransferase activity lysophospholipid acyltransferase activity

Summary: General membrane annotation. LPCAT3 is indeed membrane-localized but this term is too general.

Reason: LPCAT3 is specifically localized to the endoplasmic reticulum membrane (PMID:18195019). The term "membrane" is too general; GO:0005789 (endoplasmic reticulum membrane) is more appropriate and already annotated.

Proposed replacements: endoplasmic reticulum membrane

Summary: IEA annotation for ER membrane localization based on UniProt subcellular location mapping.

Reason: This is the correct and specific localization for LPCAT3, confirmed by direct experimental evidence (PMID:18195019).

Summary: Direct experimental demonstration of ER localization by Zhao et al. 2008.

Reason: Key primary evidence for ER localization from the study that identified LPCAT3 as the major liver LPCAT enzyme.

Summary: Reactome annotation for ER membrane localization in context of PC acyl chain remodeling pathway.

Reason: Consistent with direct experimental evidence for ER localization.

Summary: Reactome annotation for ER membrane localization.

Reason: Consistent with experimental evidence.

Summary: Reactome annotation for ER membrane localization.

Reason: Consistent with experimental evidence.

Summary: Reactome annotation for ER membrane localization.

Reason: Consistent with experimental evidence.

Summary: Reactome annotation for ER membrane localization.

Reason: Consistent with experimental evidence.

Summary: Reactome annotation for ER membrane localization.

Reason: Consistent with experimental evidence.

Summary: High-throughput proteomics study identified LPCAT3 in NK cell membrane preparations.

Reason: While this term is general and the HDA evidence is from a membrane proteomics study, the more specific ER membrane term (GO:0005789) is preferred and already annotated. LPCAT3 is specifically localized to the ER membrane.

Proposed replacements: endoplasmic reticulum membrane

Summary: LPCAT3 participates in PE acyl-chain remodeling as part of the Lands cycle through its LPEAT activity.

Reason: LPCAT3 has demonstrated LPEAT activity (PMID:18772128, PMID:18782225), enabling it to participate in PE remodeling. This is a core function related to the Lands cycle.

Summary: IEA annotation based on Ensembl Compara orthology to mouse.

Reason: Consistent with direct experimental evidence for LPEAT activity.

Summary: Reactome pathway annotation for PE acyl-chain remodeling.

Reason: Consistent with LPEAT activity of LPCAT3.

Summary: Matsuda et al. 2008 showed that MBOAT5 knockdown impairs PUFA incorporation into PE.

Reason: Direct mutant phenotype evidence from knockdown experiments.

Summary: Gijon et al. 2008 demonstrated LPEAT activity in neutrophils.

Reason: Direct biochemical evidence for PE remodeling activity.

Summary: LPCAT3 contributes to PC biosynthesis through the Lands cycle remodeling pathway, converting LPC to PC.

Reason: While the de novo Kennedy pathway is the primary biosynthetic route, the Lands cycle (which LPCAT3 catalyzes) is responsible for remodeling >50% of cellular PC and can be considered biosynthetic in the sense that it produces the final PC species. This is a core function.

Summary: LPCAT3 modifies lipids by reacylating lysophospholipids.

Reason: This is a correct general parent term for the acyl-chain remodeling activities of LPCAT3. The Lands cycle fundamentally involves lipid modification.

Summary: Core function of LPCAT3 in the Lands cycle - remodeling PC acyl chains.

Reason: This is the primary biological process of LPCAT3. The enzyme remodels PC by incorporating PUFAs at the sn-2 position.

Summary: Reactome pathway annotation for PC acyl-chain remodeling.

Reason: Core function consistent with experimental evidence.

Summary: Matsuda et al. 2008 showed knockdown of MBOAT5 reduced PUFA incorporation into PC.

Reason: Direct mutant phenotype evidence for PC remodeling function.

Summary: Zhao et al. 2008 directly demonstrated PC remodeling by LPCAT3.

Reason: Key primary evidence for PC remodeling function.

Summary: Gijon et al. 2008 demonstrated PC remodeling in neutrophils.

Reason: Direct biochemical evidence for PC remodeling.

Summary: ISS annotation based on mouse ortholog.

Reason: Consistent with direct experimental evidence.

Summary: LPCAT3 has LPSAT activity enabling PS remodeling.

Reason: Consistent with demonstrated LPSAT activity (PMID:18195019, PMID:18772128, PMID:18782225).

Summary: Reactome pathway annotation for PS acyl-chain remodeling.

Reason: Consistent with LPSAT activity.

Summary: Knockdown of MBOAT5 reduced PUFA incorporation into PS.

Reason: Direct mutant phenotype evidence.

Summary: Zhao et al. 2008 demonstrated LPSAT activity.

Reason: Direct biochemical evidence.

Summary: Gijon et al. 2008 demonstrated PS remodeling activity.

Reason: Direct MS-based biochemical evidence.

Summary: Very general term for lipid metabolism from UniProt keyword mapping.

Reason: This term is too general. More specific terms like GO:0036151 (phosphatidylcholine acyl-chain remodeling) better capture LPCAT3's function.

Proposed replacements: phosphatidylcholine acyl-chain remodeling

Summary: LPCAT3 contributes to phospholipid production through the Lands cycle.

Reason: While technically LPCAT3 is involved in remodeling rather than de novo biosynthesis, the Lands cycle produces the final phospholipid species with appropriate acyl chains. This general term is acceptable as a parent annotation.

Summary: General phospholipid metabolism term from UniPathway mapping.

Reason: LPCAT3 is centrally involved in phospholipid metabolism through the Lands cycle. This is a correct general parent term.

Summary: LPCAT3 in intestine provides PC for chylomicron surface assembly.

Reason: While this is a documented physiological role in enterocytes (primarily from mouse studies), it is a downstream consequence of LPCAT3's core phospholipid remodeling function rather than the core molecular function. Intestine-specific Lpcat3 knockout in mice impairs chylomicron secretion.

Summary: ISS annotation based on mouse ortholog data.

Reason: Downstream physiological consequence in intestine, not core molecular function.

Summary: LPCAT3 in liver provides PC for VLDL assembly.

Reason: This is a downstream physiological consequence of LPCAT3's ER membrane PC remodeling activity. LPCAT3 knockdown affects VLDL production through altered LPC/PC levels and MTP expression (PMID:22511767).

Summary: ISS annotation based on mouse ortholog.

Reason: Downstream physiological consequence in liver, not core molecular function.

Summary: Mouse studies suggest LPCAT3 regulates intestinal stem cell function through cholesterol metabolism.

Reason: A pleiotropic downstream effect in intestine rather than the core molecular function, but properly evidenced. The intestinal-stemness work that Rong et al. cite as their reference 31 is PMID:29395055 (Wang et al. 2018), now fetched and cited here in place of the hepatic lipogenesis paper that had been attached. Intestine-specific Lpcat3 knockout drives ISC proliferation, and the effect is cholesterol-mediated: blocking cholesterol synthesis normalizes it.

Summary: ISS annotation from mouse ortholog.

Reason: Pleiotropic downstream effect, not core function. Same basis as the IEA row: PMID:29395055 is the study that actually establishes the intestinal stem cell phenotype, and it replaces the hepatic paper previously attached here.

Summary: LPCAT3-mediated ER membrane remodeling affects SREBP processing and cholesterol/lipid biosynthesis.

Reason: Indirect regulation through ER membrane composition rather than a direct molecular function of LPCAT3 -- but the annotation is sound, and is now cited correctly. It traces to mouse Lpcat3, where UniProt made it IMP from PMID:29395055 (Wang et al. 2018): loss of Lpcat3 raises membrane saturation, which activates SREBP-2 and drives cholesterol synthesis, and blocking cholesterol synthesis pharmacologically reverses the resulting crypt hyperproliferation. The paper previously attached here, DOI:10.1172/jci93616, was simply the wrong one. It reports that LPCAT3 loss is selective for SREBP-1c targets with no effect on Hmgcr, Hmgcs or Sqs, so it reads as a refutation of this term. The two studies do not actually conflict: Rong is liver and the SREBP-1c lipogenic branch, Wang is intestine and the SREBP-2 cholesterol branch -- and Wang is in fact Rong's own reference 31.

Summary: ISS annotation from mouse ortholog.

Reason: Indirect regulatory effect, not core function. Same basis as the IEA row for this term: the mouse source annotation is IMP from PMID:29395055, now cited here in place of the wrongly-attached DOI:10.1172/jci93616.

Summary: Mouse studies show LPCAT3 in enterocytes affects cholesterol absorption.

Reason: Tissue-specific downstream effect in intestine through membrane remodeling affecting passive diffusion of cholesterol.

Summary: ISS annotation from mouse ortholog.

Reason: Tissue-specific downstream effect, not core function.

Summary: LPCAT3 may down-regulate inflammation by limiting arachidonic acid availability for inflammatory eicosanoid synthesis.

Reason: This is an indirect effect of LPCAT3-dependent PUFA incorporation into ER phospholipids, reported mainly in mouse liver, where it acts by mitigating ER stress rather than by limiting free arachidonic acid. The arachidonate-limiting mechanism previously asserted here is not what the cited review says: it states the opposite, that LPCAT3 activity supports production of inflammatory lipid mediators such as prostaglandin E2.

Summary: ISS annotation from mouse ortholog.

Reason: Indirect effect of ER phospholipid remodeling, not core function. Note that the anti-inflammatory effect reported for LPCAT3 runs through mitigation of ER stress, not through limiting arachidonic acid availability.

Summary: LPCAT3-mediated phospholipid remodeling affects ER membrane composition and properties.

Reason: While LPCAT3 certainly affects ER membrane composition through its remodeling activity, "membrane organization" as a biological process is an indirect consequence rather than a core function.

Summary: ISS annotation from mouse ortholog.

Reason: Indirect effect of phospholipid remodeling activity.

Summary: Mouse studies suggest LPCAT3 counteracts lipid-induced ER stress.

Reason: Indirect effect through ER membrane composition. Lpcat3 deficiency in mice exacerbates NASH partly through ER stress mechanisms.

Summary: ISS annotation from mouse ortholog.

Reason: Indirect effect through membrane composition.

Summary: LPCAT3 affects TG transport through effects on lipoprotein assembly.

Reason: Indirect effect through lipoprotein biogenesis (chylomicron, VLDL).

Summary: ISS annotation from mouse ortholog.

Reason: Indirect effect through lipoprotein metabolism.