ARL11

ARL11 (ARLTS1) is a small GTPase with two distinct, context-dependent roles: a pro-apoptotic tumor suppressor in epithelial cancers and a positive regulator of innate immune signaling in macrophages and microglia (PMID:15843669, PMID:29618517). As a tumor suppressor, re-expression of wild-type ARL11 in lung and ovarian cancer cells that have lost it induces caspase-dependent apoptosis, inhibits growth, and suppresses xenograft tumor formation, whereas a truncating Trp149Stop variant shows attenuated activity; loss of expression in tumors is driven in part by promoter methylation (PMID:15843669, PMID:17699778, PMID:17079447). In immune cells, ARL11 acts downstream of LPS/TLR4 to drive pro-inflammatory activation: it forms a complex with phospho-ERK within minutes of stimulation and facilitates ERK1/2 and p38 MAPK activation, promoting cytokine production and control of intracellular Salmonella, while its overexpression causes constitutive ERK phosphorylation and macrophage exhaustion (PMID:29618517). It further amplifies inflammatory signaling by binding JAK2/phospho-JAK2 to modulate their degradation and activate JAK2/STAT1 in atherosclerosis, and its expression is transcriptionally activated by ELF1 binding to its promoter in microglial neuroinflammation (PMID:39312826, PMID:39307293). ARL11 also interacts with STING to amplify type I interferon responses and with the RUVBL1/RUVBL2 complex to facilitate homologous-recombination DNA repair, conferring PARP-inhibitor resistance (PMID:40123001). How a single GTPase reconciles tumor-suppressive apoptosis with pro-survival immune and DNA-repair functions, and whether nucleotide-dependent GTPase cycling governs these roles, has not been resolved in the available corpus.

1. 2005 Medium

   Established that ARL11 has an intrinsic pro-apoptotic tumor-suppressor function and that a natural truncating variant impairs it, distinguishing wild-type from variant activity.

   Evidence Transfection of full-length vs Trp149Stop ARLTS1 into A549 lung cancer cells with apoptosis assays and xenograft tumor formation

   PMID:15843669

   Open questions at the time

   • No molecular mechanism for how the GTPase triggers apoptosis
   • Effector and nucleotide-state dependence not defined
2. 2006 Medium

   Showed that ARL11 silencing in tumors occurs via promoter methylation and that restoring it is sufficient to induce apoptosis and reduce tumorigenicity in ovarian cancer.

   Evidence Promoter methylation analysis and adenoviral restoration in TOV-112 ovarian cells with apoptosis and xenograft assays

   PMID:17079447

   Open questions at the time

   • Downstream apoptotic effectors not identified
   • Generality of methylation silencing across tumor types unestablished
3. 2007 Medium

   Confirmed tumor-suppressor rescue across multiple lung cancer lines and broadened the affected transcriptional program.

   Evidence Adenoviral transduction of A549 and H1299 cells, growth/apoptosis assays, nude mouse xenografts, microarray profiling

   PMID:17699778

   Open questions at the time

   • ~650 differentially expressed transcripts not resolved into direct vs indirect targets
   • No physical effector linked to the apoptotic phenotype
4. 2010 Low

   Connected ARL11 re-expression to chemosensitization and specific apoptotic regulators caspase-3 and bcl-2.

   Evidence Stable transfection of SKOV3 ovarian cells, MTT, flow cytometry, Western blot for caspase-3 and bcl-2

   PMID:19292033 PMID:21153650

   Open questions at the time

   • Single cell line, no in vivo validation
   • Whether bcl-2/caspase-3 changes are direct or downstream is unknown
5. 2012 Low

   Provided the first candidate physical partners (CRABP2, PGAM1) for ARL11, raising the question of which interactions are functional.

   Evidence In-frame cDNA library screen with split-reporter protein complementation assay

   PMID:23272234

   Open questions at the time

   • Single method, no functional validation of either interaction
   • No reciprocal confirmation or cellular consequence demonstrated
6. 2018 High

   Defined a positive signaling role distinct from tumor suppression: ARL11 drives LPS/TLR4-induced MAPK activation in macrophages by complexing with phospho-ERK.

   Evidence siRNA knockdown, LPS stimulation, phospho-ERK/p38 immunoblotting, reciprocal co-IP of ARL11 with phospho-ERK, Salmonella replication and overexpression assays

   PMID:29618517

   Open questions at the time

   • Whether ARL11 binds phospho-ERK directly or via an adaptor not established
   • Role of GTPase activity in the interaction undefined
7. 2024 Medium

   Extended pro-inflammatory function to JAK2/STAT1 signaling and atherosclerosis, and placed ELF1 as a direct transcriptional activator of ARL11 in neuroinflammation.

   Evidence Co-IP of ARL11 with JAK2/p-JAK2, siRNA knockdown, ApoE-/- and SCI mouse models, ChIP/promoter binding for ELF1

   PMID:39307293 PMID:39312826

   Open questions at the time

   • Mechanism by which ARL11 modulates JAK2 degradation not resolved
   • Whether MAPK and JAK2 pathways are engaged independently is unclear
8. 2025 Medium

   Identified two new interaction-based functions—STING-mediated type I IFN amplification and RUVBL1/2-dependent homologous recombination—linking ARL11 to PARP-inhibitor resistance.

   Evidence Genome-wide CRISPR activation screen, co-IP of ARL11 with STING and with RUVBL1/2, DNA damage and HR repair assays

   PMID:40123001

   Open questions at the time

   • Limited mutagenesis/reconstitution depth for either interaction
   • Direct vs indirect nature of RUVBL1/2 and STING binding not dissected

• How a single GTPase reconciles tumor-suppressive apoptosis with pro-survival immune signaling and DNA-repair functions, and whether nucleotide-dependent GTPase cycling controls these roles, remains unresolved.
• No structural or nucleotide-state characterization of ARL11
• No identified GEF/GAP or canonical effector
• Context determinants switching between tumor-suppressor and pro-inflammatory roles unknown