AKAP8L

AKAP8L (HAP95/NAKAP95) is a nucleocytoplasmic shuttling protein that participates in both nuclear RNA export and cytoplasmic growth-signaling control (PMID:10748171, PMID:32312749). In the nucleus it binds the C-terminal nuclear transport domain of RNA helicase A (RHA) and, through its own RHA-binding and nuclear localization domains plus a novel nuclear export signal, synergizes with RHA to drive CTE-mediated nuclear export of unspliced mRNA (PMID:10748171, PMID:11402034). This RHA partnership is co-opted during HIV-1 replication, where AKAP8L associates with the reverse transcriptase region of Pol and inhibits RHA helicase activity in vitro to protect annealed tRNA-Lys3 on viral RNA (PMID:25034436). In the cytoplasm, its N-terminal region directly binds mTORC1 to promote mTORC1-mediated translation, cell growth, and proliferation, with rescue requiring the intact N-terminal mTORC1-binding region (PMID:32312749); in high-glucose-treated microglia this same interaction acts upstream of mTORC1 to suppress autophagy and promote neuroinflammation (PMID:39033121). AKAP8L additionally stabilizes SCD1 mRNA in an IGF2BP1-dependent manner to support cancer cell stemness and chemoresistance (PMID:36522343), and supports erythroid lineage commitment of hematopoietic stem cells (PMID:32457162). Although it is a structural homolog of the A-kinase anchoring protein AKAP8 and can anchor the PKA regulatory subunit Iα, it lacks the canonical RII-binding motif of AKAP8 (PMID:10697960, PMID:32312749).

1. 2000 Medium

   Established AKAP8L as a nuclear shuttling protein that acts on retroviral RNA export by binding RNA helicase A, defining its first molecular function.

   Evidence RHA C-terminus binding, shuttling assays, and CTE reporter gene assays

   PMID:10748171

   Open questions at the time

   • Binding region on AKAP8L not yet mapped
   • Specificity for CTE versus Rev/RRE export explained only at the phenotypic level
2. 2000 Medium

   Defined AKAP8L's genomic and structural relationship to AKAP8, showing it shares NLS and zinc-finger motifs but lacks the RII-binding motif, distinguishing it from a canonical AKAP.

   Evidence cDNA cloning, chromosomal mapping, and sequence alignment

   PMID:10697960

   Open questions at the time

   • Absence of RII binding inferred from sequence, not biochemically tested
   • Functional consequence of zinc-finger motifs unknown
3. 2001 Medium

   Mapped the domains underlying export function, showing both RHA-binding and nuclear localization domains are required for CTE activation and that AKAP8L synergizes with RHA for unspliced mRNA export.

   Evidence Truncation/deletion mutagenesis with CTE reporter and nuclear export assays

   PMID:11402034

   Open questions at the time

   • Mechanism of synergy with RHA at the molecular level unresolved
   • Endogenous cellular RNA substrates not identified
4. 2008 Medium

   Identified AKAP8L as an RNF43-interacting protein subject to proteasomal turnover, while excluding RNF43 as its ubiquitin ligase.

   Evidence Yeast two-hybrid, co-IP, MG132 treatment, and ubiquitylation assay

   PMID:18313049

   Open questions at the time

   • The responsible E3 ligase remains unidentified
   • Functional significance of the RNF43 interaction unknown
5. 2014 Medium

   Extended the RHA partnership to a viral mechanism, showing AKAP8L associates with HIV-1 Pol and inhibits RHA helicase activity to protect tRNA-Lys3 annealing.

   Evidence siRNA knockdown, Pol co-IP, and in vitro helicase assay with purified GST-AKAP8L

   PMID:25034436

   Open questions at the time

   • Single lab; helicase inhibition shown in vitro only
   • Whether this role applies to host RNAs not addressed
6. 2020 High

   Discovered a distinct cytoplasmic role: the N-terminal region binds mTORC1 to drive translation, growth, and proliferation, with domain-specific rescue establishing causality.

   Evidence Co-IP, pulldown, deletion/rescue, and translation/growth/proliferation assays

   PMID:32312749

   Open questions at the time

   • Direct mTORC1 subunit contacted not pinpointed
   • How nuclear export and mTORC1 roles are coordinated unknown
7. 2020 Medium

   Linked AKAP8L to a developmental process, showing it is required for erythroid lineage commitment and proliferation of hematopoietic stem cells.

   Evidence Knockdown with differentiation/apoptosis assays guided by single-cell transcriptomics

   PMID:32457162

   Open questions at the time

   • No molecular mechanism beyond the cellular phenotype
   • Connection to its mTORC1 or RNA roles untested
8. 2022 Medium

   Defined an RNA-stabilizing function through IGF2BP1, showing AKAP8L stabilizes SCD1 mRNA to promote cancer stemness and chemoresistance.

   Evidence Co-IP, RNA-IP, mRNA stability assays, and in vitro/in vivo perturbation in gastric cancer cells

   PMID:36522343

   Open questions at the time

   • Generality of the IGF2BP1 partnership beyond SCD1 unknown
   • Relationship to nuclear RNA export role unclear
9. 2024 Medium

   Connected the mTORC1 interaction to a disease-relevant pathway, showing AKAP8L acts upstream of mTORC1 in microglia to suppress autophagy and drive neuroinflammation.

   Evidence Co-IP, PLA, knockdown, rapamycin comparator, and behavioral/autophagy assays in STZ-diabetic mice

   PMID:39033121

   Open questions at the time

   • Mechanism by which AKAP8L activates mTORC1 not defined
   • Single lab/disease model

• How AKAP8L coordinates its nuclear RNA-export functions with its cytoplasmic mTORC1-anchoring and PKA-anchoring roles, and what governs its compartment-specific partner selection, remains unresolved.
• No unifying model linking RNA-binding and growth-signaling functions
• Structural basis of mTORC1 and RHA contacts not determined
• PKA-anchoring role not functionally dissected