SMIM43 (NEMEP, Nodal enhanced mesendoderm micropeptide; formerly annotated as TMEM155) is a 63-amino-acid microprotein with a single N-terminal transmembrane helix, translated from an upstream open reading frame in a transcript previously regarded as non-coding or as encoding a larger, unconfirmed 130-residue protein. In mouse, the orthologous transcript (Gm11549) is a direct target of Nodal/Activin signaling, and the micropeptide localizes to the plasma membrane, where it binds the class I facilitative glucose transporters GLUT1 (SLC2A1) and GLUT3 (SLC2A3) through its transmembrane segment and a short C-terminal motif (His51-Phe57). NEMEP increases cellular glucose uptake and glycolytic flux in a binding-dependent manner, and in mouse embryonic stem cells it is required for mesendoderm differentiation, apparently by supplying the increased glucose uptake that this transition requires. The human protein is translated, shares about 94% identity with the mouse peptide, binds human GLUT1 and GLUT3, and raises glucose consumption and glycolysis when overexpressed in human hepatoma cells; its role in human development has not been examined.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005886 plasma membrane | IEA GO_REF:0000120 | ACCEPT | Summary: Electronic projection of plasma membrane localization from the mouse ortholog, where it rests on immunostaining and membrane fractionation of tagged NEMEP in mouse ES cells. Reason: Consistent with the single transmembrane helix and with the function at the cell surface in complex with GLUT1/GLUT3. The primary data are mouse (tagged, ectopic); no human localization study exists, but the human protein binds the same plasma membrane transporters. Supporting Evidence: PMID:35810171 Immunostaining of ectopically expressed, FLAG-tagged NEMEP in mouse ES cells revealed that NEMEP was localized at the plasma membrane |
| GO:0005886 plasma membrane | ISS GO_REF:0000024 | ACCEPT | Summary: Curator transfer of plasma membrane localization from mouse NEMEP (A0A286YD83, IDA PMID:35810171). Reason: Sound orthology-based transfer (about 94% identity, conserved TM helix and GLUT-binding motif); the correct and specific location for this protein. Supporting Evidence: PMID:35810171 fractionation-based analysis and immunoblotting of mESCs expressing NEMEP-GFP indicated strong accumulation of an NEMEP-GFP fusion protein in the membrane fraction |
| GO:0010828 positive regulation of D-glucose transmembrane transport | IEA GO_REF:0000107 | MODIFY | Summary: Ensembl Compara projection of the mouse IMP annotation. NEMEP loss reduces, and NEMEP expression increases, cellular glucose uptake; human NEMEP overexpression in HepG2 also increases glucose consumption. Reason: The biology is correct and central to the gene, but what was measured is glucose (2-deoxyglucose) uptake into cells via the plasma membrane transporters GLUT1 and GLUT3. The more specific child term GO:0046326 positive regulation of D-glucose import across plasma membrane captures this precisely. Proposed replacements: positive regulation of D-glucose import across plasma membrane Supporting Evidence: PMID:35810171 Compared to WT EBs, the Nemep KO EBs displayed significant reductions in glucose uptake, glycolytic function, and mitochondrial respiration PMID:35810171 the overexpression of human NEMEP in HepG2 cells (Supplementary Fig. 7d) also significantly increased glucose consumption, lactate excretion, glycolysis activity |
| GO:0044325 transmembrane transporter binding | IEA GO_REF:0000107 | ACCEPT | Summary: Ensembl Compara projection of the mouse GLUT1/GLUT3 binding annotations. Reason: Correct and redundant with the direct human IPI annotations below; binding to GLUT1/GLUT3 is the mechanistic basis of NEMEP function. Supporting Evidence: PMID:35810171 Co-immunoprecipitation (co-IP) studies validated that both GLUT1 and GLUT3 do physically interact with NEMEP |
| GO:0044325 transmembrane transporter binding | IPI PMID:35810171 A Nodal enhanced micropeptide NEMEP regulates glucose uptake... | ACCEPT | Summary: Human NEMEP co-immunoprecipitates with human GLUT1 (SLC2A1, P11166) in co-transfected HEK293T cells. Reason: Direct experimental evidence on the human proteins; an informative binding term (not bare protein binding) that names the partner class. Interaction requires the NEMEP TM helix and the H51-F57 motif (mapped in mouse), and is the basis of the glucose-uptake phenotype. Supporting Evidence: PMID:35810171 Then, we confirmed that the homologous human NEMEP protein also interacts with the human GLUT1 and GLUT3 proteins PMID:35810171 These results demonstrate that the TMD domain and NEMEP residues H51-F57 are essential for NEMEP-GLUT1 and -GLUT3 interactions. |
| GO:0044325 transmembrane transporter binding | IPI PMID:35810171 A Nodal enhanced micropeptide NEMEP regulates glucose uptake... | ACCEPT | Summary: Human NEMEP co-immunoprecipitates with human GLUT3 (SLC2A3, P11169) in co-transfected HEK293T cells. Reason: Direct experimental evidence on the human proteins, as for GLUT1. Supporting Evidence: PMID:35810171 Then, we confirmed that the homologous human NEMEP protein also interacts with the human GLUT1 and GLUT3 proteins |
| GO:0048382 mesendoderm development | IEA GO_REF:0000107 | KEEP AS NON CORE | Summary: Ensembl Compara projection of the mouse IMP annotation (Nemep frameshift knockout mESCs fail to induce mesendoderm transcription factors in embryoid bodies). Reason: The mouse genetic evidence is solid, but it is in vitro (mESC embryoid bodies) and shows necessity, with the proposed mechanism being metabolic support (glucose uptake) rather than a developmental signaling or specification activity of NEMEP itself. It has not been tested in human cells or in embryos. Retained as a contextual, non-core process. Supporting Evidence: PMID:35810171 The absence of NEMEP in EBs dramatically impaired the expression of well-known mesendoderm LDTFs including Gsc, Mixl1, T, Eomes, Foxa2, and Sox17 |
| GO:0048382 mesendoderm development | ISS GO_REF:0000024 | KEEP AS NON CORE | Summary: Curator transfer from mouse NEMEP (IMP, PMID:35810171). Reason: As for the IEA row; valid orthology transfer of a mouse in vitro finding, non-core relative to the glucose-transporter activating function. Supporting Evidence: PMID:35810171 We discovered that NEMEP is essential for mesendoderm differentiation in mESCs |
| GO:0141109 transporter activator activity | ISS GO_REF:0000024 | NEW | Summary: Proposed molecular function. NEMEP binds GLUT1/GLUT3 and increases glucose transporter activity, and binding-deficient mutants (TMD deletion, H51-F57 deletion) fail to do so, including in cells overexpressing GLUT1 or GLUT3. Reason: This is the only molecular activity that describes what NEMEP does, rather than what it binds; transmembrane transporter binding alone does not convey the direction of the effect. It parallels the regulator-type MFs used for the SERCA-regulating microproteins (DWORF GO:0008047 enzyme activator activity; SLN and PLN GO:0004857 enzyme inhibitor activity). Caveats: the evidence is cell-based and largely mouse (human only by HepG2 overexpression), the authors say "likely", and a direct effect on transporter kinetics has not been shown in a reconstituted system, so confidence is moderate. Coded as ISS from mouse NEMEP (A0A286YD83), because the direction-giving experiments (binding-deficient TMD and H51-F57 mutants in mESCs) are mouse; the human data in the same paper are a HEK293T co-IP with GLUT1/GLUT3 (binding only) and HepG2 glycolytic flux, which corroborate but do not themselves assay transporter activity. Supporting Evidence: PMID:35810171 the expression of WT NEMEP but not TMD-deletion NEMEP or H51-F57-deletion NEMEP in mESCs overexpressing GLUT1 or GLUT3 resulted in significantly higher glucose uptake compared to the GLUT1 or GLUT3 overexpressing mESCs PMID:35810171 Therefore, NEMEP’s boosting glucose uptake likely through interactions with the known glucose transporters GLUT1 and GLUT3. |
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Download this section (compressed HTML)Q: Does NEMEP change the intrinsic kinetics (Vmax, Km) of GLUT1/GLUT3, or does it act by increasing their surface abundance or stability? This decides between transporter activator activity and a trafficking/stabilization role.
Q: Is SMIM43 expressed and required during human gastrulation-stage differentiation (e.g. hESC-derived mesendoderm), and is it Nodal/Activin-responsive in human cells?
Q: What is the function of TMEM155/SMIM43 upregulation reported in immune-cell transcriptomic studies (acute HIV infection PBMCs), given that previous annotations were based on an incorrect 130-residue ORF?
Experiment: Reconstitute GLUT1 or GLUT3 in proteoliposomes with and without synthetic NEMEP (WT versus H51-F57 deletion) and measure glucose transport kinetics.
Type: in vitro reconstitution transport assay
Experiment: Knock out SMIM43 in human ES cells and assay 2-deoxyglucose uptake and mesendoderm marker induction after Activin A treatment, together with surface biotinylation of GLUT1/GLUT3.
Type: CRISPR knockout in hESCs
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