KLHL25

KLHL25 is a substrate-recognition adaptor of the CUL3-RING E3 ubiquitin ligase complex that governs translational control and lipid metabolism by targeting specific substrates for proteasomal degradation. The CUL3-KLHL25 complex ubiquitinates hypophosphorylated 4E-BP1, providing homeostatic regulation of eIF4E-dependent translation (PMID:22578813), and also ubiquitinates ATP-citrate lyase (ACLY), thereby inhibiting de novo lipid synthesis (PMID:27664236). During T helper cell differentiation, TGFβ1-induced KLHL25 expression promotes ACLY degradation, reducing malonyl-CoA levels and shifting fatty acid metabolism from synthesis to β-oxidation to support iTreg over Th17 fate; this transcriptional switch is driven by JNK-mediated histone H3S10 phosphorylation at the KLHL25 promoter via NF-YA, and is opposed by IL-6-ERK signaling, which phosphorylates NF-YA to silence KLHL25 (PMID:34491895, PMID:40119138).

1. 2012 High

   Identifying KLHL25 as a CUL3 adaptor that targets hypophosphorylated 4E-BP1 for ubiquitin-dependent degradation established the first known function of the gene: homeostatic regulation of cap-dependent translation via eIF4E.

   Evidence Co-immunoprecipitation, RNAi knockdown, and in vitro ubiquitination assays in cultured cells

   PMID:22578813

   Open questions at the time

   • Structural basis for selectivity toward hypophosphorylated versus phosphorylated 4E-BP1 is unknown
   • Physiological consequence of 4E-BP1 degradation in specific tissue or disease contexts not addressed
   • Whether additional CUL3-KLHL25 substrates exist was unresolved
2. 2016 High

   Demonstrating that CUL3-KLHL25 also ubiquitinates ACLY for proteasomal degradation broadened the complex's substrate repertoire beyond translational control to lipid metabolism and showed tumor-suppressive relevance.

   Evidence Reciprocal co-immunoprecipitation, ubiquitination assays, and xenograft tumor growth assays

   PMID:27664236

   Open questions at the time

   • The degron or binding interface on ACLY recognized by KLHL25 was not mapped
   • Whether KLHL25-dependent ACLY degradation operates in non-tumor cell types was untested
   • Relative contribution of 4E-BP1 versus ACLY degradation to KLHL25 tumor-suppressive activity was unclear
3. 2021 High

   Linking TGFβ1-induced KLHL25-mediated ACLY degradation to a metabolic switch from fatty acid synthesis to oxidation explained how KLHL25 promotes iTreg differentiation by reducing malonyl-CoA and de-repressing CPT1.

   Evidence Ubiquitination assays, malonyl-CoA metabolomics, CPT1 activity measurement, and iTreg differentiation assays with KLHL25 knockdown/overexpression

   PMID:34491895

   Open questions at the time

   • How TGFβ1 signaling upregulates KLHL25 expression was not resolved
   • Whether the 4E-BP1 substrate axis also contributes to T cell fate decisions was not tested
   • In vivo validation in conditional knockout mice was lacking
4. 2025 High

   Elucidating the transcriptional regulation of KLHL25 — activated by TGFβ1-JNK-NF-YA-H3S10ph and repressed by IL-6-ERK-mediated NF-YA phosphorylation — revealed the upstream signaling switch that connects cytokine milieu to KLHL25 expression and iTreg/Th17 cell fate.

   Evidence ChIP for JNK and NF-YA at KLHL25 promoter, NF-YA phosphorylation assays, promoter reporter assays, Th17/iTreg differentiation with pathway inhibitors

   PMID:40119138

   Open questions at the time

   • Whether NF-YA phosphorylation by ERK affects other target genes beyond KLHL25 was not dissected
   • In vivo confirmation of the JNK-NF-YA-H3S10ph axis at the KLHL25 locus in primary human T cells is lacking
   • Structural basis for KLHL25 substrate recognition (BTB-Kelch domain interactions) remains uncharacterized

• How the two known substrates (4E-BP1 and ACLY) are differentially selected by CUL3-KLHL25 in different cellular contexts, and whether additional substrates exist, remain open questions.
• No structural or degron-mapping study for either substrate–KLHL25 interaction
• No conditional knockout mouse model to define in vivo requirements
• Potential role of KLHL25 in tissues beyond immune cells and tumors is unexplored