ARL11 Human

What is ARL11 and what are its key characteristics?

ARL11 (ADP Ribosylation Factor Like GTPase 11) is a protein-coding gene that belongs to the ADP-ribosylation factor (ARF) family of proteins. It is also known by several aliases including ARLTS1 (ADP-Ribosylation Factor-Like Tumor Suppressor Protein 1) . The gene is located on chromosome 13q14.3, a region frequently deleted in various sporadic and hereditary hematopoietic and solid tumors .

The ARL11 protein functions as a small GTP-binding protein that, like other members of the RAS superfamily of small GTPases, acts as a molecular switch cycling between inactive (GDP-bound) and active (GTP-bound) conformations . Gene Ontology annotations related to ARL11 include GTP binding capabilities .

Methodologically, researchers identify ARL11 using specific antibodies targeting the N-terminal region in Western blotting. The mouse ARL11 protein appears at approximately 19 kDa, while the human variant runs at approximately 22 kDa on SDS-PAGE .

What is the normal expression pattern of ARL11 in human tissues?

ARL11 shows a tissue-specific expression pattern with predominance in immune cells. Expression studies have revealed that mammalian ARL11 transcripts are abundantly present in lymphoid tissues including spleen, bone marrow, and lymph nodes .

At the cellular level, the Immunological Genome Project (ImmGen) database analysis demonstrates that ARL11 is predominantly expressed in cells of the innate immune system, with highest expression in:

• Macrophages (highest expression)

• Monocytes (moderate expression)

• Neutrophils (moderate expression)

This expression pattern has been validated experimentally in both human and mouse cell lines. ARL11 protein expression has been confirmed in primary bone marrow-derived mouse macrophages (BMDMs), mouse macrophage cell lines (RAW264.7 and J774), and human monocyte-derived macrophage cell lines (PMA-stimulated THP-1 cells) . Importantly, ARL11 expression is not observed in HeLa cells, which serves as a negative control in experimental settings .

What primary functions has ARL11 been associated with?

ARL11 has been functionally associated with several key cellular processes:

• Apoptosis regulation: ARL11 may play a role in caspase-dependent apoptosis. Overexpression of ARL11 induces apoptotic markers in primary BMDMs, as evidenced by reduced levels of total poly(ADP-ribose) polymerase and increased caspase-3 cleavage .

• Tumor suppression: It functions as a tumor suppressor gene, with its downregulation observed in various cancers .

• Immune cell regulation: ARL11 regulates macrophage activation in response to lipopolysaccharide (LPS) stimulation. It's required for LPS-mediated activation of ERK1/2 and p38 mitogen-activated protein kinases (MAPKs) .

• DNA repair modulation: Recent research indicates that ARL11 facilitates homologous recombination DNA repair by interacting with the RUVBL1/2 complex .

Methodologically, these functions have been established through loss-of-function studies using RNA interference (shRNA, siRNA) and gain-of-function studies through overexpression systems, coupled with functional assays for each respective process .

How does ARL11 expression change during macrophage activation and what are the implications?

ARL11 expression is dynamically regulated during macrophage activation. Upon LPS stimulation of macrophages, ARL11 protein levels show a biphasic response:

• Initial upregulation: ARL11 protein levels increase approximately 1.5-fold after 30 minutes of LPS treatment, further increasing to approximately 2-fold by 4 hours .

• Subsequent downregulation: With prolonged LPS stimulation (12-24 hours), ARL11 expression returns to near-basal levels .

This transient upregulation appears to be specific to TLR signaling rather than a general stress response, as treatment with ER stress inducer thapsigargin or oxidative stress inducer hydrogen peroxide does not significantly alter ARL11 expression .

Methodologically, these temporal dynamics are best studied through time-course experiments with Western blotting and densitometric analysis. The specificity can be verified using different stress inducers and comparing the expression patterns.

The transient nature of ARL11 upregulation likely serves as a regulatory mechanism, as sustained high levels of ARL11 can promote apoptosis. Indeed, experimental overexpression of ARL11 in primary BMDMs induces apoptotic markers and can override the anti-apoptotic effects of LPS stimulation .

What role does ARL11 play in cancer biology and how is it being investigated?

ARL11's role in cancer is multifaceted and appears to be context-dependent:

• Tumor suppressor function: ARL11 was first identified in a screening for putative tumor suppressor genes at chromosome location 13q14.3, a region frequently deleted in various tumors . Downregulation of ARL11 expression has been reported in several sporadic lung cancer and ovarian tumors, attributed to promoter methylation and loss of heterozygosity .

• Clinical significance in breast cancer: Recent clinical data analysis from The Cancer Genome Atlas (TCGA) demonstrates that ARL11 expression is significantly elevated in breast cancer patients compared to healthy controls. Moreover, higher expression correlates with poorer prognosis .

• PARP inhibitor resistance: A genome-wide CRISPR activation screen identified ARL11 as a top candidate gene that, when upregulated, confers resistance to olaparib (a PARP inhibitor) in BRCA-wild-type breast cancer cells .

Research methodologies to investigate ARL11's role in cancer include:

• Genome-wide CRISPR activation screens to identify genes conferring drug resistance

• In vitro validation experiments using cell line models with ARL11 overexpression or knockdown

• In vivo xenograft models to assess the effect of ARL11 expression on tumor growth and drug response

• Clinical database analysis (e.g., TCGA) to correlate ARL11 expression with patient outcomes

• Mechanistic studies to elucidate how ARL11 influences various cellular pathways relevant to cancer

What are the key mechanisms through which ARL11 influences PARP inhibitor resistance?

Recent research has identified ARL11 as a critical determinant of resistance to PARP inhibitors (PARPi). The mechanisms underlying this resistance are dual-faceted:

• Enhancement of innate immune responses: ARL11 interacts with Stimulator of Interferon Genes (STING) to enhance innate immune responses, creating a positive feedback loop with type I interferon production .

• Facilitation of homologous recombination (HR) DNA repair: ARL11 interacts with the RUVBL1/2 complex to facilitate HR DNA repair, which can bypass the DNA damage caused by PARP inhibitors .

These mechanisms were elucidated through a comprehensive experimental approach:

• Initial genome-wide CRISPR activation screen identified ARL11 as a top candidate conferring resistance to olaparib

• Validation experiments demonstrated that ARL11 overexpression significantly reduced cancer cell sensitivity to multiple PARPi drugs and other DNA-damaging agents both in vitro and in vivo

• Protein-protein interaction studies revealed ARL11's physical association with STING and the RUVBL1/2 complex

• Functional assays assessed the impact of these interactions on interferon signaling and DNA repair capacity

These findings suggest that simultaneously targeting RUVBL1/2 with specific inhibitors might be a strategy to overcome ARL11-mediated PARP inhibitor resistance in cancer therapy .

How does ARL11 regulate macrophage effector functions and what signaling pathways are involved?

ARL11 plays a crucial role in regulating multiple aspects of macrophage effector functions through its involvement in key signaling pathways:

• Morphological changes during activation: ARL11 depletion suppresses the typical pseudopodia formation observed in LPS-stimulated macrophages, which is associated with macrophage maturation and activation .

• Phagocytic capacity: ARL11-silenced macrophages show significantly reduced phagocytic capacity (approximately 2.5-fold lower) compared to control cells under both normal and LPS-stimulated conditions .

• Pro-inflammatory cytokine production: ARL11 silencing leads to significantly lower IL-6 and TNFα production upon LPS stimulation, as determined by quantitative RT-PCR and enzyme-linked immunoassay .

• Nitric oxide production: Nitric oxide production (measured as nitrite concentration) is significantly lower in ARL11-depleted macrophages .

The key signaling pathway involved is the MAPK pathway:

• ARL11 is required for LPS-stimulated activation of extracellular signal–regulated kinase (ERK) and p38 mitogen-activated protein kinase (MAPK)

• LPS-stimulated activation of ERK and p38 MAPK is substantially compromised in ARL11-silenced macrophages

• Increased expression of ARL11 leads to constitutive ERK1/2 phosphorylation, resulting in macrophage exhaustion

• ARL11 forms a complex with phospho-ERK in macrophages within minutes of LPS stimulation

Methodologically, these findings were established through:

• RNA interference to deplete ARL11 expression

• Phagocytosis assays using fluorescently labeled E. coli bioparticles

• Cytokine production measurements via ELISA and qRT-PCR

• Western blotting for signaling pathway activation

• Co-immunoprecipitation to detect protein-protein interactions

• Immunofluorescence microscopy to visualize protein localization

What experimental approaches are most effective for studying ARL11 function?

Based on the research literature, several complementary experimental approaches have proven effective for studying ARL11 function:

• Genetic manipulation techniques:

  • RNA interference (siRNA, shRNA) for loss-of-function studies

  • CRISPR-Cas9 gene editing for knockout models

  • CRISPR activation (CRISPRa) for gain-of-function screens

  • Overexpression systems using plasmid-based approaches

• Protein detection and localization:

  • Western blotting using specific antibodies targeting the N-terminal region of ARL11

  • Immunofluorescence microscopy to visualize subcellular localization

  • Co-immunoprecipitation to identify protein-protein interactions

• Functional assays:

  • Apoptosis assays measuring caspase activation and PARP cleavage

  • Phagocytosis assays using fluorescently labeled particles

  • Cytokine production measurements (ELISA, qRT-PCR)

  • Cell proliferation assays (e.g., alamarBlue® dye reduction)

  • Bacterial infection models to assess immune cell function (e.g., Salmonella control)

• Signaling pathway analysis:

  • Phosphorylation state analysis of MAPK pathways

  • Inhibitor studies to dissect pathway components

  • Time-course analyses to capture dynamic changes

• In vivo models:

  • Xenograft models for cancer studies

  • Potentially knockout or conditional knockout mice (though not explicitly mentioned in the search results)

• Clinical correlation:

  • Analysis of public databases (TCGA, ImmGen)

  • Expression correlation with clinical outcomes

When selecting experimental approaches, researchers should consider:

• The specific aspect of ARL11 function being studied

• The cellular context (cancer cells vs. immune cells)

• The need to validate findings across multiple methodologies

• The temporal dynamics of ARL11 expression and activation

How might ARL11 be targeted for therapeutic purposes in cancer treatment?

Based on current research findings, several strategies for targeting ARL11 in cancer therapy can be considered:

• For cancers with ARL11 downregulation (acting as tumor suppressor):

  • Epigenetic modifiers to reverse promoter methylation and restore ARL11 expression

  • Gene therapy approaches to reintroduce functional ARL11

  • Small molecules that mimic ARL11 tumor suppressor function

• For cancers with ARL11 upregulation (mediating drug resistance):

  • Direct inhibition of ARL11 function through small molecule inhibitors

  • Targeting ARL11's interaction partners, such as the RUVBL1/2 complex

  • Combination therapy approaches that counteract ARL11-mediated resistance pathways

• For targeting ARL11 in the tumor microenvironment:

  • Modulating ARL11 function in tumor-associated macrophages to enhance anti-tumor immune responses

  • Combining immune checkpoint inhibitors with approaches that target ARL11-mediated immunomodulation

Recent research specifically suggests that simultaneously targeting RUVBL1/2 with specific inhibitors might be an effective strategy to overcome ARL11-mediated PARP inhibitor resistance . This approach would disrupt the ability of ARL11 to facilitate homologous recombination DNA repair, thereby restoring sensitivity to PARP inhibitors.

Methodologically, drug development approaches might include:

• High-throughput screening for small molecule inhibitors of ARL11 or its interactions

• Structure-based drug design based on ARL11's GTP-binding domain

• Peptide-based inhibitors targeting specific protein-protein interaction domains

• Antibody-based approaches for targeting ARL11 in accessible compartments

What are the current limitations in ARL11 research and how might they be addressed?

Current ARL11 research faces several limitations that need to be addressed for comprehensive understanding:

• Limited structural information:

  • No crystal structure of ARL11 appears to be available in the literature

  • Solution: Structural biology approaches including X-ray crystallography, cryo-EM, or NMR spectroscopy to determine ARL11's structure, especially in different nucleotide-bound states

• Incomplete understanding of tissue-specific functions:

  • While ARL11's role in macrophages and certain cancer cells is being elucidated, its function in other cell types remains unclear

  • Solution: Single-cell transcriptomics to identify additional cell types expressing ARL11, followed by cell-type-specific functional studies

• Limited in vivo models:

  • The search results don't mention knockout mouse models

  • Solution: Development of constitutive and conditional knockout models to study ARL11 function in different tissues and disease contexts

• Unclear GTPase cycle regulation:

  • The factors that regulate ARL11's GDP/GTP exchange and GTP hydrolysis are not well defined

  • Solution: Biochemical studies to identify guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs) for ARL11

• Limited clinical correlation studies:

  • More comprehensive analyses of ARL11 expression across cancer types and correlation with treatment responses are needed

  • Solution: Larger clinical studies correlating ARL11 expression/mutation status with treatment outcomes

• Technological challenges in studying small GTPases:

  • Monitoring the activation state of ARL11 in live cells remains challenging

  • Solution: Development of FRET-based biosensors or other live-cell imaging techniques to monitor ARL11 activation dynamics

Addressing these limitations will require interdisciplinary approaches combining structural biology, biochemistry, cell biology, genetics, and clinical research to fully elucidate ARL11's function and therapeutic potential.