ABRACL Human

What is ABRACL and what is its basic molecular structure?

ABRACL (ABRA C-terminal like) is a non-typical winged-helix protein with a positively charged surface on one side, a negatively charged surface on the other side, and a hydrophobic groove that facilitates protein-protein interactions . It belongs to a family of low-molecular weight proteins involved in actin dynamics and cell motility . The human ABRACL gene (Gene ID: 58527) is also known by synonyms COSTARS, PRO2013, C6ORF115, and HSPC280 .

How is ABRACL expression regulated across different tissue types?

ABRACL expression varies considerably across tissue types and developmental stages. Expression profiling from the Allen Brain Atlas indicates differential ABRACL expression patterns in human and mouse brain tissues . Functional association analysis has shown that ABRACL has 3,025 functional associations with biological entities spanning 8 categories extracted from 67 datasets . These categories include molecular profiles, organisms, functional terms, chemicals, diseases, phenotypes, structural features, cell types, and gene/protein interactions, suggesting complex regulatory mechanisms influenced by tissue-specific factors.

What are the primary cellular functions of ABRACL?

ABRACL primarily functions as a modulator of actin dynamics, influencing the polymerization state of actin in cells . Research has demonstrated that ABRACL promotes the distribution of cellular actin to the polymerized fraction (F-actin) . It plays a significant role in cell migration and morphological changes, particularly in response to external stimuli such as growth factors like EGF . ABRACL physically and functionally interacts with cofilin, an actin-binding protein, inhibiting cofilin-stimulated actin disassembly, thereby regulating actin filament turnover .

What are the recommended methods for detecting and quantifying ABRACL expression?

For comprehensive ABRACL expression analysis, researchers should employ multiple complementary techniques:

Studies have successfully used immunohistochemistry data from the Human Protein Atlas to compare ABRACL expression between normal and cancerous gastric tissues . For subcellular analysis, immunofluorescence microscopy with co-staining for actin has revealed ABRACL's distribution patterns, particularly at the leading edge of migrating cells .

What genetic manipulation techniques are most effective for ABRACL functional studies?

Several genetic manipulation approaches have proven effective for studying ABRACL function:

• CRISPR/Cas9-mediated genome editing has successfully generated ABRACL-knockout cell lines in cancer models, providing complete ablation of protein expression .

• RNA interference using shRNA-expressing lentiviruses targeting ABRACL (specifically Sh295 and Sh484 constructs) has created stable knockdown models with partial reduction in expression .

• For overexpression studies, transient transfection with HA-tagged or GFP-tagged ABRACL constructs allows for both functional analysis and visualization of the protein .

• Rescue experiments expressing RNAi-resistant ABRACL variants in knockdown cells have confirmed phenotype specificity, demonstrating that migration defects were directly attributable to reduced ABRACL expression .

What methods best demonstrate ABRACL's interactions with actin and associated proteins?

To investigate ABRACL's interactions with actin and regulatory proteins, several methods have been successfully employed:

• F-actin/G-actin fractionation assays reveal ABRACL's influence on the equilibrium between filamentous and globular actin in cellular contexts .

• In vitro actin polymerization and depolymerization assays using purified recombinant ABRACL and pyrene-labeled actin quantitatively assess direct effects on actin dynamics .

• Proximity ligation assays (PLA) have confirmed physical interactions between ABRACL and cofilin in situ .

• Co-localization studies using immunofluorescence have demonstrated spatial overlap of ABRACL and cofilin signals, particularly at lamellipodia of migrating cells .

• F-actin co-sedimentation assays have determined whether ABRACL affects the binding of cofilin to actin filaments .

How does ABRACL expression correlate with cancer progression and patient outcomes?

ABRACL expression shows significant correlations with cancer progression and clinical outcomes:

These findings indicate that ABRACL is upregulated in various cancer tissues compared to normal tissues and that high expression correlates with poor prognosis . The mechanism likely involves ABRACL's role in promoting cell migration, as evidenced by reduced migratory capacity in ABRACL-knockout or knockdown cancer cells .

What experimental models best demonstrate ABRACL's role in cancer cell migration?

Several experimental models have effectively demonstrated ABRACL's role in cancer cell migration:

Additionally, wound closure (scratch) assays with ABRACL-knockout MDA-MB-231 cells have revealed ABRACL's importance specifically in EGF-stimulated directional migration, while having less effect on basal migration capacity .

How does ABRACL contribute to EGF-stimulated cancer cell migration?

ABRACL plays a crucial role in EGF-stimulated cancer cell migration through several mechanisms:

• In MDA-MB-231 breast cancer cells, ABRACL is required for EGF-induced migration enhancement, as ABRACL-knockout cells show significantly decreased migration in response to EGF compared to parental control cells .

• The EGFR-PI3K-Akt signaling pathway, which underlies EGF-induced migration, is activated in both parental and ABRACL-knockout cells (as evidenced by Akt phosphorylation), indicating ABRACL functions downstream of initial EGF signaling .

• ABRACL is specifically required for EGF-induced morphological changes, as EGF treatment resulted in well-spread morphology in parental cells but failed to induce cell spreading in ABRACL-knockout clones .

• The mechanism likely involves ABRACL's effect on actin dynamics at the leading edge of migrating cells, as ABRACL co-localizes with F-actin signals at lamellipodia .

How does ABRACL influence actin polymerization dynamics in vitro versus in cellular contexts?

ABRACL exhibits context-dependent effects on actin dynamics:

These findings reveal an apparent discrepancy between ABRACL's in vitro and cellular effects . In purified protein assays, ABRACL inhibits actin polymerization, while in cellular contexts, ABRACL promotes actin distribution to the polymerized fraction . This paradox is likely explained by ABRACL's interactions with other actin-regulating proteins, particularly cofilin, as ABRACL inhibits cofilin-stimulated actin disassembly in cells .

How does ABRACL interact with cofilin to regulate actin dynamics?

ABRACL physically and functionally interacts with cofilin to regulate actin dynamics:

• Physical interaction is supported by immunofluorescence co-localization studies showing overlap of ABRACL and cofilin signals at lamellipodia of migrating cells .

• Proximity ligation assay (PLA) has confirmed the physical interaction between ABRACL and cofilin in situ .

• Functionally, ABRACL hinders cofilin-stimulated pyrene F-actin fluorescence decay in vitro, indicating that ABRACL inhibits cofilin's ability to promote actin disassembly .

• F-actin co-sedimentation assays demonstrate that ABRACL does not prevent cofilin from binding to F-actin, suggesting that ABRACL modulates cofilin's activity after it binds to actin filaments .

• The net effect in cells is that ABRACL promotes F-actin stability by counteracting cofilin's severing and depolymerizing activities .

What signaling pathways regulate or are affected by ABRACL function?

Evidence suggests ABRACL interfaces with growth factor signaling pathways:

• In MDA-MB-231 cells, EGF stimulation enhances cell migration in an ABRACL-dependent manner, suggesting a functional connection between EGFR signaling and ABRACL .

• The EGFR-PI3K-Akt pathway is activated by EGF regardless of ABRACL status (as confirmed by Akt phosphorylation), indicating ABRACL functions downstream of or parallel to this pathway .

• ABRACL is specifically required for EGF-induced morphological changes, suggesting it may be a crucial effector that translates growth factor signaling into cytoskeletal remodeling .

• The localization of ABRACL at lamellipodia, regions of active actin remodeling during directional migration, further supports its role in translating external signals into cytoskeletal responses .

How might the structural features of ABRACL determine its functional interactions?

ABRACL's unique structural features—a non-typical winged-helix protein with polarized surface charges and a hydrophobic groove—are likely critical determinants of its functional interactions . The positively charged surface may facilitate interactions with negatively charged phospholipids or the acidic regions of proteins, while the hydrophobic groove could serve as a binding pocket for specific protein partners. Understanding how these structural elements contribute to ABRACL's function requires advanced structural biology approaches, including:

• X-ray crystallography or cryo-electron microscopy of ABRACL in complex with cofilin and/or actin

• Structure-guided mutagenesis to identify critical residues for protein-protein interactions

• Molecular dynamics simulations to predict conformational changes upon binding to partners

What factors might explain the contradictory effects of ABRACL on actin dynamics in different experimental contexts?

The apparent contradiction between ABRACL's effects on actin dynamics in vitro (inhibition of polymerization) versus in cells (promotion of F-actin formation) requires careful consideration . Several hypotheses might explain this discrepancy:

• In cells, ABRACL's primary function may be to inhibit cofilin-mediated actin disassembly rather than directly affecting actin polymerization, resulting in a net increase in F-actin content.

• ABRACL may require cofactors present in the cellular environment but absent in purified protein assays.

• Post-translational modifications might alter ABRACL's activity in cellular contexts.

• ABRACL may have concentration-dependent effects, with different outcomes at physiological versus experimental concentrations.

• The temporal dynamics of actin turnover in cells might be affected differently than what static in vitro assays can capture.

Resolving this contradiction requires reconstitution experiments with multiple purified components and advanced live-cell imaging techniques.

How might ABRACL contribute to tissue-specific cellular functions beyond cancer?

While ABRACL has been primarily studied in cancer contexts, its expression in normal tissues suggests broader physiological roles . Given its involvement in actin dynamics, ABRACL likely contributes to various processes requiring cytoskeletal remodeling:

• Neuronal development and synaptic plasticity - differential expression in brain regions suggests potential roles in neuronal function .

• Immune cell function - processes like leukocyte migration and immunological synapse formation require precise actin regulation.

• Embryonic development - cell migration and tissue morphogenesis during development rely heavily on cytoskeletal dynamics.

• Wound healing - cell migration during tissue repair involves extensive actin remodeling.

• Specialized cell functions - processes like endocytosis, vesicle trafficking, and cell division all require actin dynamics regulation.

Understanding these potential functions requires tissue-specific conditional knockout models and single-cell analyses to identify cell types with high ABRACL expression.

What is the current evidence for ABRACL as a prognostic biomarker in cancer?

Evidence supporting ABRACL as a prognostic biomarker includes:

To establish ABRACL as a clinically useful biomarker would require validation in large, prospective patient cohorts with standardized assessment methods and multivariate analyses to determine its independent prognostic value.

What therapeutic strategies could target ABRACL or its interactions?

Several potential therapeutic strategies could be developed to target ABRACL:

• Small molecule inhibitors designed to disrupt ABRACL-cofilin interaction, identified through structure-based drug design or high-throughput screening.

• Peptide-based inhibitors that mimic critical binding interfaces between ABRACL and its partners.

• RNA interference approaches (siRNA, shRNA) to downregulate ABRACL expression.

• Combination therapies targeting both ABRACL and associated signaling pathways such as EGFR-PI3K-Akt.

• Antibody-drug conjugates specifically targeting cancer cells with high ABRACL expression.

Development of these approaches requires thorough understanding of ABRACL's structure, interaction interfaces, and cancer-specific vulnerabilities to ensure therapeutic efficacy while minimizing off-target effects.

What considerations are important for developing ABRACL as a clinical target?

Developing ABRACL as a clinical target requires addressing several key considerations:

• Patient stratification - identifying patients with high ABRACL expression who would most likely benefit from ABRACL-targeted therapies.

• Tissue specificity - understanding ABRACL's functions in normal tissues to predict potential side effects of systemic inhibition.

• Resistance mechanisms - determining whether cancer cells might develop resistance to ABRACL-targeted therapies through compensatory pathways.

• Delivery challenges - developing effective delivery methods for ABRACL-targeting molecules, particularly for RNA-based therapeutics.

• Companion diagnostics - creating standardized, clinically validated assays to measure ABRACL expression or activity in patient samples.

• Combination strategies - identifying synergistic combinations with existing therapies to enhance efficacy and overcome potential resistance.