USP38 Antibody

What is USP38 and what are its primary biological functions?

USP38 is a ubiquitin-specific peptidase that belongs to the Peptidase C19 protein family. It functions primarily as a deubiquitinating enzyme that removes ubiquitin chains from target proteins. USP38 plays critical roles in several cellular processes including: negative regulation of type I IFN signaling through dynamic ubiquitin editing of TBK1 in response to viral infection; maintenance of genome integrity through DNA damage response pathways; and modulation of inflammatory responses. The protein is highly expressed in skeletal muscle and has been implicated in cancer cell resistance to DNA-damaging therapy and viral defense mechanisms .

What are the structural characteristics and molecular details of the USP38 protein?

The canonical human USP38 protein consists of 1042 amino acid residues with a calculated molecular weight of approximately 117 kDa. Up to two different isoforms have been reported for this protein. USP38 contains functional domains including a C-terminal domain (401-1004aa) that is critical for its interactions with target proteins, such as the Zika virus envelope protein. The protein's deubiquitinase activity resides in its catalytic domain, which contains essential residues (C454, H857, and D918) that are crucial for its enzymatic function. Mutation of these residues (C454A/H857A/D918N) abolishes its deubiquitinase activity and associated biological functions .

What applications can USP38 antibodies be used for in research settings?

USP38 antibodies have been validated for multiple research applications as shown in the following table:

These applications enable researchers to study USP38 expression, localization, interaction with other proteins, and functional roles in various biological contexts .

What are the optimal conditions for using USP38 antibodies in Western blotting experiments?

For Western blotting applications, USP38 antibodies should be used at a dilution range of 1:200-1:1000, with the optimal dilution being sample-dependent. The antibody detects human USP38 at approximately 117 kDa, which corresponds to its calculated molecular weight. Positive detection has been confirmed in HEK-293T cells, making these cells suitable as positive controls for Western blot experiments. It's recommended to use freshly prepared protein lysates and to titrate the antibody in each testing system to obtain optimal results. Common detection methods including ECL and fluorescence-based systems are compatible with USP38 antibodies, but optimization may be required based on the specific experimental conditions .

How can I validate the specificity of USP38 antibodies in my experimental system?

To validate USP38 antibody specificity, several approaches should be considered:

• Use USP38 knockout or knockdown cell lines as negative controls. Multiple publications have utilized USP38 knockdown (using shRNA targeting USP38) and knockout systems to confirm antibody specificity.

• Perform overexpression experiments using tagged USP38 constructs (such as HA-USP38 or Flag-USP38) to compare with endogenous protein detection.

• Conduct peptide competition assays using the immunogen peptide (USP38 fusion protein Ag12172) to block specific binding.

• Compare reactivity patterns across multiple cell lines with known USP38 expression levels, such as HEK-293T and K-562 cells which have demonstrated positive reactivity.

• Consider cross-validation using multiple antibodies targeting different epitopes of USP38 to confirm consistent results .

What considerations are important when designing immunoprecipitation experiments with USP38 antibodies?

When designing immunoprecipitation (IP) experiments with USP38 antibodies, researchers should consider:

• Use 0.5-4.0 μg of antibody per 1.0-3.0 mg of total protein lysate as recommended for optimal results.

• K-562 cells have been validated for IP applications with USP38 antibodies and can serve as positive controls.

• For Co-IP experiments investigating USP38 interaction partners, such as HDAC1 or viral proteins, mild lysis conditions are recommended to preserve protein-protein interactions.

• When studying USP38's deubiquitinating activity on target proteins, include ubiquitin detection in the experimental design using antibodies that can distinguish between different ubiquitin linkages (K48, K63).

• Consider including appropriate controls such as IgG control, input samples, and where possible, USP38 knockout/knockdown samples to verify specificity of the interactions detected .

How does USP38 function in DNA damage response and genome stability?

USP38 plays a critical role in maintaining genome integrity through regulation of DNA damage response (DDR) pathways, particularly non-homologous end joining (NHEJ). The molecular mechanism involves:

• In response to DNA damage, USP38 interacts with HDAC1 and specifically removes K63-linked ubiquitin chains from HDAC1, which promotes its deacetylase activity.

• Activated HDAC1 then deacetylates histone H3K56, a critical step in chromatin remodeling during DNA repair.

• USP38 deletion results in persistent focal accumulation of NHEJ factors at DNA damage sites and impaired NHEJ efficiency.

• This impairment leads to genomic instability and increased sensitivity to genotoxic agents.

• USP38 knockout mice exhibit hypersensitivity to irradiation and shortened survival.

These findings highlight USP38's importance in genome stability maintenance and suggest that its dysregulation may contribute to tumorigenesis. USP38 has been observed to be expressed at low levels in certain cancers, including renal cell carcinoma, further supporting its potential role in cancer biology .

What is the role of USP38 in viral defense, particularly against Zika virus infection?

USP38 exhibits antiviral activity against Zika virus (ZIKV) through direct interaction with viral components:

• USP38 binds to the ZIKV envelope (E) protein through its C-terminal domain (401-1004aa) and co-localizes with it in the cytoplasm.

• USP38 attenuates both K48-linked and K63-linked polyubiquitination of the E protein.

• Overexpression of USP38 in HeLa cells inhibits ZIKV invasion, leading to reduced production of viral proteins (E and NS5) and viral RNA.

• Conversely, knockdown of USP38 using shRNA significantly enhances ZIKV invasion and increases viral protein production and RNA levels.

• The deubiquitinase activity of USP38 is essential for this antiviral function; mutants lacking deubiquitinase activity (C454A/H857A/D918N) lose their ability to inhibit ZIKV infection.

Importantly, USP38 does not affect ZIKV attachment to cells but rather influences post-attachment stages of the viral life cycle. This mechanism represents a novel host defense strategy against ZIKV infection and potentially identifies USP38 as a therapeutic target for ZIKV-associated diseases .

How does USP38 contribute to inflammatory processes and cardiac pathophysiology?

USP38 plays a significant role in regulating inflammation, particularly in the context of cardiac pathophysiology:

• In a mouse myocardial infarction (MI) model, USP38 exacerbates atrial inflammation and fibrosis, increasing susceptibility to atrial fibrillation.

• Cardiac-specific overexpression of USP38 (USP38-TG) significantly increases expression of inducible nitric oxide synthase (iNOS) in macrophages following MI.

• USP38 overexpression enhances the expression of pro-inflammatory cytokines IL-1β and IL-6 at both mRNA and protein levels in cardiac tissue.

• Conversely, cardiac-conditional knockout of USP38 (USP38-CKO) reduces atrial inflammation after MI.

• USP38 may regulate inflammation through modulation of IL-33R ubiquitination levels and by forming a chromatin-modifying complex with KDM5B to selectively inhibit pro-inflammatory cytokines.

These findings suggest that USP38 is an important regulator of inflammatory responses in the heart and could represent a promising therapeutic target for treating atrial fibrillation following myocardial infarction .

How can I investigate USP38's deubiquitinase activity in different experimental contexts?

To study USP38's deubiquitinase activity effectively:

• Utilize ubiquitin chain-specific constructs: Employ plasmids encoding different ubiquitin linkages (e.g., Myc-UB, Myc-K48, Myc-K48R, Myc-K63, and Myc-K63R) to determine the specificity of USP38's deubiquitinating activity.

• Generate enzymatically inactive mutants: Create USP38(C454A/H857A/D918N) mutants that lack deubiquitinase activity to serve as negative controls in functional studies.

• Conduct in vitro deubiquitination assays: Purify recombinant USP38 protein and incubate it with ubiquitinated substrate proteins to directly assess its deubiquitinating function.

• Perform ubiquitination status analysis: Use immunoprecipitation followed by Western blotting with ubiquitin-specific antibodies to assess changes in target protein ubiquitination in the presence or absence of USP38.

• Compare wild-type vs. domain mutants: Analyze the contributions of different domains to USP38's activity by generating and testing N-terminal (1-400aa) and C-terminal (401-1004aa) domain constructs separately .

What approaches can be used to identify and characterize novel USP38 substrates and interaction partners?

To identify and characterize novel USP38 substrates and interactors:

• Immunoprecipitation-mass spectrometry (IP-MS): Perform IP of USP38 followed by mass spectrometry to identify proteins that co-precipitate with it under different cellular conditions.

• Proximity labeling techniques: Use BioID or APEX2 fused to USP38 to label proteins in close proximity to USP38 in living cells.

• Yeast two-hybrid screening: Screen for potential interactors using USP38 or its domains as bait against cDNA libraries.

• Co-localization studies: Use immunofluorescence with USP38 antibodies combined with markers for different cellular compartments or potential interacting proteins to identify spatial relationships.

• Validation approaches: Confirm interactions using reciprocal Co-IP, pulldown assays with recombinant proteins, and functional assays examining the effect of USP38 on the ubiquitination status of potential substrates.

• Domain mapping: Use truncated versions of USP38 (such as the N-terminal domain (1-400aa) and C-terminal domain (401-1004aa)) to determine which regions are responsible for specific protein interactions .

What current experimental models are available for studying USP38 function in vivo?

Several experimental models have been developed for studying USP38 function in vivo:

• Genetic mouse models:

  • Cardiac-conditional USP38 knockout (USP38-CKO) mice generated using the Cre-loxP system

  • USP38 cardiac-specific transgenic (USP38-TG) mice for overexpression studies

  • These models have been used to study USP38's role in cardiac inflammation and fibrosis following myocardial infarction

• Cell line models:

  • Stable USP38 knockdown cell lines using shRNA (validated in HeLa cells)

  • CRISPR/Cas9-mediated USP38 knockout cell lines

  • Cells stably expressing wild-type or mutant USP38 constructs

• Viral infection models:

  • Zika virus infection in USP38-manipulated cell systems to study antiviral functions

• DNA damage models:

  • Irradiation treatment of USP38 knockout mice to assess radiation sensitivity

  • Genotoxic agent treatment of USP38-manipulated cancer cell lines

These models enable the comprehensive investigation of USP38's function in different physiological and pathological contexts .

What common issues arise when using USP38 antibodies and how can they be resolved?

When working with USP38 antibodies, researchers may encounter several common issues:

• Weak or no signal in Western blot:

  • Optimize antibody concentration (try the upper end of the recommended dilution range: 1:200)

  • Increase protein loading (USP38 may be expressed at low levels in some tissues)

  • Extend primary antibody incubation time (overnight at 4°C)

  • Use enhanced detection systems (high-sensitivity ECL substrates)

  • Ensure sample preparation preserves protein integrity (use fresh protease inhibitors)

• High background in immunostaining:

  • Increase blocking time and concentration (5% BSA or 10% normal serum)

  • Optimize antibody dilution (more dilute than for Western blotting)

  • Include additional washing steps with increased detergent concentration

  • Pre-absorb antibody with blocking protein to reduce non-specific binding

• Unsuccessful immunoprecipitation:

  • Increase antibody amount (up to 4.0 μg per 1.0-3.0 mg of total protein)

  • Optimize lysis conditions to ensure proper protein extraction

  • Extend incubation time with the antibody (overnight at 4°C)

  • Consider using protein A/G beads instead of protein A or protein G alone

• Inconsistent results across experiments:

  • Use a standardized protocol with controlled conditions

  • Prepare larger antibody aliquots to minimize freeze-thaw cycles

  • Include appropriate positive controls (HEK-293T cells for WB, K-562 cells for IP) .

How can detection of USP38 be optimized in challenging tissue samples?

For optimizing USP38 detection in challenging tissue samples:

• Sample preparation:

  • For formalin-fixed tissues, optimize antigen retrieval methods (test both heat-induced and enzymatic retrieval)

  • For frozen tissues, optimize fixation time to preserve both antigen integrity and tissue morphology

  • Use specialized lysis buffers for fibrous tissues to improve protein extraction

• Signal amplification:

  • Employ tyramide signal amplification (TSA) for immunohistochemistry applications

  • Use biotin-streptavidin systems for signal enhancement

  • Consider multiplex fluorescent detection with spectral unmixing to distinguish USP38 signal from autofluorescence

• Background reduction:

  • Include tissue-specific blocking agents (e.g., mouse-on-mouse blocking for mouse tissues)

  • Conduct autofluorescence quenching steps when using fluorescent detection

  • Employ automated staining platforms for more consistent results

• Validation approaches:

  • Compare multiple fixation and embedding methods to determine optimal preservation

  • Use USP38 overexpression or knockout tissues as positive and negative controls

  • Consider dual staining with antibodies targeting different epitopes of USP38 .

What are the best practices for analyzing USP38 in the context of ubiquitination studies?

When analyzing USP38 in ubiquitination studies:

• Experimental design:

  • Include controls for specific ubiquitin linkages (K48, K63) using linkage-specific antibodies

  • Use ubiquitin mutants (K48R, K63R) to verify linkage specificity

  • Include the enzymatically inactive USP38 mutant (C454A/H857A/D918N) as a negative control

  • Consider using N-ethylmaleimide (NEM) in lysis buffers to inhibit deubiquitinases and preserve ubiquitination

• Sample preparation:

  • Use denaturing conditions when analyzing ubiquitination to disrupt non-covalent interactions

  • Inhibit proteasomal degradation with MG132 treatment to accumulate ubiquitinated proteins

  • Consider using tandem ubiquitin binding entities (TUBEs) to enrich ubiquitinated proteins

• Analysis approaches:

  • Perform sequential immunoprecipitation (IP of target protein followed by ubiquitin detection)

  • Consider mass spectrometry-based approaches to identify specific ubiquitination sites

  • Use in vitro deubiquitination assays with purified components to directly assess USP38 activity

• Data interpretation:

  • Distinguish between direct deubiquitination by USP38 and indirect effects through intermediate factors

  • Consider the kinetics of deubiquitination by performing time-course experiments

  • Evaluate the physiological relevance of observed deubiquitination by correlating with functional outcomes .