TENT5A

TENT5A is a non-canonical cytoplasmic poly(A) polymerase that stabilizes target mRNAs by extending their poly(A) tails, thereby controlling the expression of secreted and structural proteins critical for osteogenesis, myogenesis, erythroid differentiation, and immune responses to mRNA vaccines (PMID:33882302, PMID:35137485, PMID:32528962, PMID:40240603). It associates with the endoplasmic reticulum and preferentially polyadenylates mRNAs encoding ER-targeted proteins, including COL1A1, COL1A2, MYC, and myogenin, with its catalytic poly(A) polymerase activity (dependent on an intact PAP/OAS1 domain) being essential for these functions (PMID:33882302, PMID:40240603, PMID:41616089, PMID:35137485). TENT5A physically interacts with Smad1/Smad4 to positively regulate BMP signaling during embryonic development and with RPL35 to negatively regulate mTOR signaling via effects on ribosome biogenesis (PMID:30291163, PMID:39570560). Loss-of-function mutations in TENT5A cause bone fragility and skeletal hypomineralization due to collagen defects, as demonstrated in knockout mice and in patient-derived cells carrying a homozygous p.Ile324Met variant (PMID:33882302, PMID:41908159).

1. 2018 Medium

   Before TENT5A's enzymatic function was characterized, its developmental role was unclear; co-immunoprecipitation in Xenopus showed that Fam46a physically interacts with Smad1/Smad4 and positively regulates BMP signaling, establishing TENT5A as a modulator of a major developmental signaling pathway.

   Evidence Co-immunoprecipitation and morpholino knockdown epistasis in Xenopus embryos

   PMID:30291163

   Open questions at the time

   • Interaction demonstrated only in Xenopus; mammalian confirmation of Smad binding is lacking
   • Whether the poly(A) polymerase activity is required for BMP pathway modulation is unknown
   • Downstream mRNA targets through which BMP signaling is affected are not identified
2. 2020 Medium

   The biochemical identity of TENT5A as an active non-canonical poly(A) polymerase was confirmed by site-directed mutagenesis of catalytic residues, and its subcellular behavior—ER-associated in the cytosol, nucleocytoplasmic shuttling, cell-cycle-dependent proteasomal degradation—was defined, establishing it as a regulated, short-lived enzyme.

   Evidence Site-directed mutagenesis, subcellular fractionation, poly-ubiquitination assays, and overexpression in K562 erythroid cells

   PMID:32528962

   Open questions at the time

   • Single-lab study; independent confirmation of nucleocytoplasmic shuttling not yet available
   • Endogenous mRNA substrates were not identified in this system
   • Structural basis of catalytic activity not resolved
3. 2021 High

   The key physiological question—what mRNAs does TENT5A polyadenylate and what happens without it—was answered by nanopore sequencing and a knockout mouse, revealing that TENT5A polyadenylates collagen and other secreted-protein mRNAs during osteoblast differentiation, and that its loss causes bone fragility and hypomineralization.

   Evidence Nanopore direct RNA sequencing, Tent5a knockout mouse phenotyping, in vitro osteoblast differentiation

   PMID:33882302

   Open questions at the time

   • Whether TENT5A directly binds its osteoblast mRNA substrates or requires cofactors for target selection is not established
   • Mechanism by which poly(A) tail extension increases mRNA stability in this context is not defined
4. 2022 Medium

   Extending TENT5A's functional scope beyond bone, knockdown experiments showed it is required for myoblast proliferation, migration, and type I muscle fiber maturation, acting at least in part by maintaining myogenin mRNA levels.

   Evidence siRNA/shRNA knockdown in C2C12 myoblasts with proliferation, migration, apoptosis, and in vivo muscle fiber assays

   PMID:35137485

   Open questions at the time

   • Direct polyadenylation of myogenin mRNA by TENT5A was not demonstrated
   • Single-lab study without knockout validation
   • Contribution to muscle physiology in vivo in a genetic model is not tested
5. 2024 Medium

   A non-polyadenylation interaction was uncovered: TENT5A binds RPL35 and negatively regulates the mTOR pathway through effects on ribosome biogenesis, while its own transcription is directly activated by EGR1, providing mechanistic context for its tumor-suppressive function in hepatocellular carcinoma.

   Evidence ChIP, dual-luciferase reporter, Co-IP/mass spectrometry, GST pull-down, and Gly122 mutagenesis

   PMID:39570560

   Open questions at the time

   • Whether ribosome biogenesis regulation requires TENT5A's poly(A) polymerase activity or represents a separate function is unknown
   • Single-lab study; RPL35 interaction not validated in non-cancer cell types
   • Mechanism linking RPL35 binding to mTOR suppression is not fully delineated
6. 2025 High

   TENT5A's role was extended to innate immunity: it re-adenylates mRNA vaccine transcripts in macrophages (extending poly(A) tails up to ~200 nt), preferentially acting on ER-targeted mRNAs due to spatial proximity, and its loss reduces vaccine-induced antibody responses.

   Evidence Nanopore direct RNA sequencing of individual vaccine mRNA molecules, TENT5A knockout mouse immunization

   PMID:40240603

   Open questions at the time

   • Whether TENT5A re-adenylates endogenous innate immune mRNAs beyond vaccine transcripts is not established
   • Mechanism of TENT5A induction by mRNA vaccines is not defined
7. 2026 Medium

   TENT5A was shown to directly bind MYC mRNA via its PAP/OAS1 domain and extend its poly(A) tail, stabilizing MYC to drive stemness and chemoresistance in osteosarcoma, revealing a pathological gain-of-function role.

   Evidence Biochemical binding assays, poly(A) tail measurements, orthotopic xenografts, patient-derived organoids, multi-omics

   PMID:41616089

   Open questions at the time

   • Whether MYC mRNA is a physiological target outside osteosarcoma is unknown
   • Selectivity mechanism for MYC mRNA binding versus other transcripts is not defined
8. 2026 Medium

   Human genetic validation came from patient-derived fibroblasts carrying a homozygous TENT5A p.Ile324Met variant, which showed shortened poly(A) tails on COL1A1/COL1A2, reduced collagen expression, and impaired mineralization, confirming TENT5A's role in human bone disease.

   Evidence Nanopore direct RNA sequencing of poly(A) tails, RNA-seq, mineralization assays in patient-derived fibroblasts

   PMID:41908159

   Open questions at the time

   • Single patient/family; broader genotype-phenotype spectrum not established
   • Whether the Ile324Met variant affects catalytic activity, substrate binding, or protein stability is not determined

• The structural basis of TENT5A substrate selectivity—how it distinguishes among the hundreds of ER-proximal mRNAs—and whether its poly(A) polymerase and RPL35-mediated ribosome/mTOR functions are mechanistically separable remain unresolved.
• No crystal or cryo-EM structure of TENT5A or TENT5A–RNA complex is available
• RNA-binding specificity determinants beyond the PAP/OAS1 domain are not mapped
• Relationship between poly(A) polymerase activity and RPL35/mTOR regulation is not dissected