TMPO

TMPO encodes LAP2 (lamina-associated polypeptide 2), a nuclear protein expressed as three isoforms — alpha (75 kDa), beta (51 kDa) and gamma (39 kDa) — generated by alternative splicing of a single gene, with exon-encoded sequence determining localization: the alpha isoform is distributed diffusely throughout the nucleus via a basic localization motif, whereas beta and gamma are targeted to the nuclear membrane through a hydrophobic membrane-spanning domain (PMID:8530026). At the molecular level, LAP2 isoforms engage chromatin-associated partners and the cell-cycle machinery: the LEM domain mediates association with BAF, the C-terminus contacts the nucleosome-binding protein HMGN5, and LAP2alpha partners with Rb to inhibit E2F1 transcriptional activity, with disease-associated TMPO variants disrupting each of these contacts and impairing proliferation (PMID:36672271). Loss of TMPO restrains proliferation and triggers apoptosis — through downregulation of PCNA, Notch1 and mTOR and caspase-3 cleavage in lung cancer cells (PMID:31648495), and through aberrant nuclear morphology and cancer-selective cell death in triple-negative breast cancer (PMID:38720803). In cancer, TMPO supports malignant phenotypes: 5-FU induces its autolysosome-dependent degradation, which activates ERK-mediated c-Fos phosphorylation and NANOG-driven stemness conferring drug resistance in colon cancer (PMID:38233377), and TMPO drives dissemination and metastasis by enhancing survival under metabolic stress (PMID:41509437). Beyond these contexts, TMPO has been linked to inflammatory signaling via interaction with TMEM35A, restraining MAPK and NF-kB pathways (PMID:34593235), and to TGF-beta/Smad-dependent wound healing (PMID:41321624).

1. 1995 Medium

   Established that a single TMPO gene generates structurally and topologically distinct proteins, defining the isoform architecture that underlies all subsequent functional studies.

   Evidence cDNA cloning, gene structure and alternative splicing analysis with sequence-based localization assignment

   PMID:8530026

   Open questions at the time

   • Localization inferred from sequence and prior data rather than direct imaging of each isoform
   • Molecular partners of each isoform not yet defined
2. 2015 Low

   Addressed the evolutionary origin of the alpha isoform, showing the LAP2alpha-specific domain arose by domestication of a DIRS1-like retrotransposon under purifying selection.

   Evidence Comparative genomics and evolutionary sequence analysis of vertebrate TMPO loci

   PMID:25735770

   Open questions at the time

   • Computational only; no functional experiment on the protein
   • Does not establish the cellular role of the co-opted domain
3. 2019 Medium

   Demonstrated that TMPO is required for cancer cell proliferation, linking its loss to G2/M arrest and apoptosis via Notch1/mTOR signaling.

   Evidence siRNA knockdown in A549 lung cancer cells with proliferation, cell cycle, apoptosis assays and Western blot pathway readouts

   PMID:31648495

   Open questions at the time

   • Single cell line, single lab
   • Mechanistic link between TMPO and Notch1/mTOR not shown to be direct
4. 2021 Medium

   Identified TMEM35A as a physical interactor of TMPO and connected this interaction to suppression of MAPK and NF-kB inflammatory signaling.

   Evidence Co-IP, CRISPR knockdown/overexpression, RNA-seq and proteomics with signaling Western blots in bovine mammary epithelial cells

   PMID:34593235

   Open questions at the time

   • Single non-human cell model
   • Reciprocal validation and interaction interface not defined
   • Direct versus indirect pathway regulation unresolved
5. 2022 Low

   Probed how a TMPO polymorphism modulates lamin interactions, suggesting Arg690Cys destabilizes the LAP2alpha homodimer and lamin AC docking with partial compensation of nuclear morphology defects.

   Evidence Protein modeling/docking and confocal nuclear morphology imaging in leukocytes from a single family

   PMID:36362411

   Open questions at the time

   • No direct biochemical interaction assay; modeling-based prediction
   • Single family, small n
   • Confounded by co-occurring LMNA mutation
6. 2023 Medium

   Resolved molecular consequences of disease variants, mapping specific LAP2 contacts (BAF via LEM domain, HMGN5 at C-terminus, Rb/E2F1 regulation) and tying their disruption to impaired proliferation in cardiomyopathy.

   Evidence Variant expression cellular models with proximity ligation/co-IP, E2F1 reporter assays, immunofluorescence and proliferation assays

   PMID:36672271

   Open questions at the time

   • Single lab
   • Causal link to cardiomyopathy pathophysiology not established in vivo
   • Quantitative contribution of each interaction not separated
7. 2024 Medium

   Established TMPO as an actionable node in cancer therapy resistance, showing 5-FU-induced autolysosomal degradation activates ERK/c-Fos/NANOG to drive stemness and resistance.

   Evidence Western blot of TMPO after 5-FU, autophagy/lysosome inhibitors, ERK phosphorylation, NANOG promoter binding and rescue in colon cancer cells

   PMID:38233377

   Open questions at the time

   • Single lab
   • Mechanism linking TMPO loss to ERK activation not fully defined
   • In vivo relevance untested
8. 2024 Medium

   Defined a cancer-selective dependency, showing TMPO depletion causes aberrant nuclear morphology and death in TNBC cells but spares non-cancerous cells.

   Evidence siRNA knockdown with immunofluorescence, proliferation and apoptosis assays across a TNBC panel versus MCF10A

   PMID:38720803

   Open questions at the time

   • Single lab
   • Basis of cancer selectivity unexplained
   • No in vivo validation
9. 2024 Medium

   Extended TMPO function to fibrotic/regenerative contexts, showing high-glucose-induced TMPO restrains proliferation/migration via TGF-beta/Smad and impairs wound healing.

   Evidence In vitro knockdown under high glucose and in vivo diabetic wound healing mouse model with histology

   PMID:41321624

   Open questions at the time

   • Single study
   • Connection between nuclear LAP2 function and TGF-beta/Smad signaling not mechanistically resolved
10. 2024 Medium

    Implicated TMPO as a driver of metastatic heterogeneity, promoting prostate cancer dissemination by enhancing survival under metabolic stress.

    Evidence Computational systems analysis of CTC organoids from GEMMs with in vivo dissemination and metabolic stress survival assays (preprint)

    PMID:41509437

    Open questions at the time

    • Preprint, single lab
    • Molecular mechanism of stress survival undefined
    • Isoform responsible not specified

• It remains unresolved how the distinct nuclear-envelope/chromatin functions of LAP2 isoforms mechanistically connect to the diverse cytoplasmic signaling outcomes (Notch1/mTOR, ERK/c-Fos, TGF-beta/Smad, MAPK/NF-kB) attributed to TMPO across tissues.
• No unifying mechanism linking nuclear architecture role to cytoplasmic signaling
• Isoform-specific contributions to each phenotype not dissected
• Structural model of LAP2 complexes absent from corpus