Recombinant Bovine RELT-like protein 2 (RELL2)

What is Bovine RELL2 and how does it relate to the RELT family of proteins?

Bovine RELL2 (RELT-like protein 2) is a member of the RELT family of proteins (RELTfms), which includes RELT (Receptor Expressed in Lymphoid Tissues, a Tumor Necrosis Factor Superfamily member) and RELL1. RELL2 is a Type I transmembrane protein that shares significant homology with RELT and RELL1, particularly in the transmembrane and intracellular domains.

The three proteins collectively termed RELTfms have gained research interest due to their association with various biological processes including cytokine signaling and pathways that either promote cell death or survival. Unlike RELT, which contains extracellular Cys-rich domains characteristic of TNFRSF members, RELL2 has a shorter extracellular domain (ECD) without these Cys-rich domains .

What is the expression pattern of RELL2 in bovine tissues?

RELL2 mRNA expression in bovine tissues follows a tissue-restricted pattern similar to that observed in other species. It is predominantly expressed in:

• Hematopoietic tissues (thymus, spleen)

• Immune-privileged sites (testes, brain, placenta)

• Peripheral blood leukocytes (PBLs)

According to gene expression data from the ARCHS4 platform, RELL2 expression is highest in cell lines of the hematopoietic system, whereas minimal RELL2 expression is found in certain tissues such as skeletal muscle . The tissue specificity of RELL2 expression suggests it may play specialized roles in immune function and development in cattle.

What is the protein structure of recombinant Bovine RELL2?

Bovine RELL2 encodes a 303 amino acid-long protein with a predicted molecular weight of approximately 32.4 kDa. Its structure includes:

• A short extracellular domain (ECD) compared to other TNFRSF members

• No extracellular Cys-rich domains (which are typically used to bind TNFSF ligands)

• A single transmembrane domain

• A cytoplasmic region with predicted disordered sequences in its carboxy-terminal tail

The disordered sequences in the carboxy-terminus suggest that this region may adopt multiple conformations depending on post-translational modifications or protein binding partners. This structural flexibility is a common feature among all RELTfms and likely contributes to their functional versatility .

How does Bovine RELL2 interact with other RELT family proteins?

Bovine RELL2, like its human counterpart, can interact with other RELT family proteins as demonstrated through co-immunoprecipitation (co-IP) experiments. Key aspects of these interactions include:

• All RELTfms (RELT, RELL1, and RELL2) can bind to each other

• Co-expression of recombinant RELTfms results in co-localization at the plasma membrane

• While RELT alone tends to localize predominantly in cytosolic compartments, co-expression with either RELL1 or RELL2 enhances its localization to the plasma membrane

These protein-protein interactions suggest that RELL2 may modulate the signaling capabilities of other RELT family members, potentially creating functional diversity through heteromeric complex formation .

What methods are available for producing recombinant Bovine RELL2?

Based on established protocols for similar proteins, recombinant Bovine RELL2 can be produced using several expression systems:

Bacterial Expression System:

• Advantages: High yield, cost-effective, relatively simple process

• Challenges: Lack of post-translational modifications, potential protein misfolding

• Implementation: The coding sequence for Bovine RELL2 can be cloned into vectors such as pET or pGEX systems for expression in E. coli strains like BL21(DE3)

Mammalian Expression System:

• Advantages: Proper protein folding and post-translational modifications

• Challenges: Lower yield, higher cost, longer production time

• Implementation: Expression in HEK293 or CHO cells using vectors like pcDNA3.1

Insect Cell Expression System:

• Advantages: Higher yield than mammalian cells with better post-translational modifications than bacteria

• Implementation: Baculovirus expression systems in Sf9 or S2 cells, similar to methods used for other recombinant bovine proteins

What are the optimal experimental conditions for expressing soluble recombinant Bovine RELL2?

For optimal expression of soluble recombinant Bovine RELL2, researchers should consider the following experimental design parameters:

For Bacterial Expression:

• Induction conditions: Using experimental design approaches similar to those employed for other recombinant proteins, optimal parameters include:

  • IPTG concentration: 0.1-1.0 mM

  • Induction temperature: 16-25°C (lower temperatures often improve solubility)

  • Induction time: 4-16 hours

  • OD600 at induction: 0.6-0.8

• Solubility enhancement strategies:

  • Fusion tags: GST, MBP, or SUMO tags can enhance solubility

  • Co-expression with chaperones: GroEL/GroES, DnaK/DnaJ/GrpE

  • Solubility-enhancing additives: 5-10% glycerol, 50-300 mM NaCl, 0.1-1% Triton X-100

The design of experiment (DoE) methodology, as applied for other recombinant proteins, can be used to optimize these conditions systematically rather than using a trial-and-error approach .

How can researchers verify the functional activity of recombinant Bovine RELL2?

Verifying the functional activity of recombinant Bovine RELL2 involves multiple complementary approaches:

Structural verification:

• Circular Dichroism (CD) spectroscopy to confirm proper secondary structure

• Size Exclusion Chromatography (SEC) to verify oligomeric state

• Western blotting using antibodies against RELL2 or epitope tags

Functional assays:

• Protein-protein interaction studies:

  • Co-immunoprecipitation (co-IP) with other RELT family members

  • Surface Plasmon Resonance (SPR) to measure binding kinetics with potential partners

  • Proximity ligation assays in bovine cell lines

• Signaling pathway analysis:

  • Monitoring NF-κB pathway activation using reporter assays

  • Phosphorylation studies of downstream effectors

  • Analysis of cellular responses (apoptosis, proliferation) in transfected bovine cells

• Localization studies:

  • Immunofluorescence microscopy to confirm proper membrane localization

  • Co-localization with RELT and RELL1 in membrane fractions

What role might Bovine RELL2 play in immune regulation based on its expression pattern?

Based on its expression pattern predominantly in hematopoietic tissues, RELL2 likely plays significant roles in bovine immune regulation:

• B lymphocyte function:

  • RELL2 may influence B cell maturation processes similar to how other RBPs regulate germinal center (GC) B-cell responses

  • It could be involved in class-switching recombination (CSR) and somatic hypermutation

  • Potential roles in regulating cellular proliferation and survival, similar to TIA1 and TIAL1 proteins that sustain long-term GC responses

• T cell regulation:

  • Given the high expression in thymus, RELL2 may influence T cell development

  • Potential modulation of T cell responses against tumors, similar to effects observed with RELT

  • Possible involvement in inflammatory cytokine production regulation

• Immunosuppressive mechanisms:

  • RELL2 might contribute to establishing immunosuppressive environments, as suggested for RELT

  • Expression in immune-privileged sites (brain, testes) suggests potential roles in limiting inflammation in these tissues

Investigation of RELL2 expression during bovine immune challenges, particularly viral or bacterial infections, would provide valuable insights into its specific immunoregulatory functions.

What transcriptomic approaches can be used to study Bovine RELL2 expression patterns in different physiological conditions?

Advanced transcriptomic approaches for studying Bovine RELL2 expression include:

High-throughput real-time PCR:
This approach has been successfully used to monitor expression profiles of genes in bovine somatic cells under different conditions, such as rbST treatment. A similar methodology could be applied to study RELL2 expression:

• Multiple timepoints sampling to capture temporal expression changes

• Analysis of expression across diverse bovine tissues and cell types

• Statistical analysis using both univariate and multivariate methods to identify significant changes in expression patterns

RNA-Seq analysis:

• Whole transcriptome sequencing to examine RELL2 expression in relation to other genes

• Identification of alternative splicing events affecting RELL2

• Differential expression analysis across conditions (disease, development, treatment)

Single-cell RNA sequencing:

• Cell type-specific expression patterns in heterogeneous tissue samples

• Identification of specific immune cell populations expressing RELL2

• Developmental trajectories of RELL2 expression

Alternative splicing analysis:
Given the importance of alternative splicing in immune regulation, analysis of RELL2 splicing variants should be considered using:

• PCR with isoform-specific primers

• Long-read sequencing technologies (PacBio, Nanopore)

• Computational prediction of functional differences between isoforms

How does post-translational modification affect Bovine RELL2 function and stability?

Post-translational modifications (PTMs) likely play crucial roles in regulating Bovine RELL2 function and stability:

Predicted PTMs for RELL2:

• Phosphorylation:

  • The disordered carboxy-terminal region likely contains multiple phosphorylation sites

  • Phosphorylation may regulate protein-protein interactions and signaling capabilities

  • Key kinases potentially involved: MAPK, PKC, CK2

• Glycosylation:

  • N-linked glycosylation sites may be present in the extracellular domain

  • Glycosylation could affect protein stability and trafficking to the plasma membrane

  • Analysis of recombinant protein should include glycosidase treatments to assess glycan content

• Ubiquitination:

  • May regulate protein turnover and abundance

  • Could affect signaling capacity and half-life

Experimental approaches to study PTMs:

• Mass spectrometry-based proteomics for comprehensive PTM mapping

• Site-directed mutagenesis of predicted modification sites

• Pharmacological inhibition of specific modification pathways

• Comparison of PTM patterns between recombinant and native Bovine RELL2

The observed migration of recombinant RELL proteins at positions larger than predicted molecular weights, with multiple bands apparent, suggests significant post-translational modifications .

What are the challenges in studying RELL2 protein-protein interactions in bovine cells?

Studying RELL2 protein-protein interactions in bovine cells presents several methodological challenges:

Technical challenges:

• Antibody availability:

  • Limited availability of bovine-specific antibodies against RELL2

  • Cross-reactivity issues when using antibodies developed for human RELL2

  • Solution: Production of custom antibodies or use of epitope-tagged recombinant proteins

• Low endogenous expression:

  • Natural expression levels may be insufficient for certain detection methods

  • Tissue-specific expression patterns may necessitate working with specialized cell types

  • Solution: Development of sensitive detection methods or controlled overexpression systems

• Membrane protein complexes:

  • Membrane proteins like RELL2 require special solubilization conditions

  • Detergent selection can affect protein-protein interactions

  • Solution: Optimization of membrane protein extraction protocols with mild detergents

Methodological approaches:

• Proximity-based methods:

  • BioID or TurboID fusion proteins to identify proximal interacting proteins

  • FRET/BRET assays for live-cell interaction studies

  • Recently developed CRISPR-based RNA proximity proteomics (CBRPP)

• Advanced co-IP strategies:

  • Crosslinking prior to lysis to stabilize transient interactions

  • Tandem affinity purification for higher purity

  • Mass spectrometry identification of co-precipitated proteins

• Interactome analysis:

  • Enhanced interactome capture (eRIC)

  • Chemistry-assisted interactome capture (CARIC)

  • Total RNA-associated protein purification (TRAPP)

How might Bovine RELL2 be involved in livestock disease processes based on our understanding of similar proteins?

Based on RELL2's expression pattern and its family relationship to RELT, several potential roles in livestock disease processes can be hypothesized:

Infectious diseases:

• Bovine Leukemia Virus (BLV) infection:

  • Given RELL2's expression in hematopoietic tissues, it may influence BLV infectivity or host response

  • BLV causes enzootic bovine leukosis with high prevalence (30-90%) in dairy cattle worldwide

  • RELL2 could be investigated in the context of persistent lymphocytosis characterized by polyclonal expansion of CD5+ B-cells

• Mycobacterial infections:

  • RELL2 may participate in immune responses against Mycobacterium bovis

  • Its expression in lymphoid tissues suggests possible roles in granuloma formation or maintenance

  • Research could explore RELL2 expression changes during infection or vaccination

Oncological conditions:

• Potential involvement in bovine lymphosarcoma development

• Possible roles in regulating apoptosis, similar to how Nrf2 up-regulates anti-apoptotic protein Bcl-2

• Expression changes in neoplastic versus healthy tissues could provide insights

Immune dysregulation:

• RELL2 may influence inflammatory responses in bovine tissues

• Potential involvement in cytokine signaling networks

• Roles in balancing pro-inflammatory and immunosuppressive mechanisms

Research investigating RELL2 expression during these disease processes, particularly using transcriptomic approaches comparing healthy and affected tissues, would provide valuable insights into its pathophysiological relevance.

How can CRISPR/Cas9 technology be applied to study Bovine RELL2 function?

CRISPR/Cas9 technology offers powerful approaches to investigate Bovine RELL2 function:

Genome editing strategies:

• Gene knockout:

  • Complete RELL2 deletion to assess loss-of-function phenotypes

  • Target guide RNA design to early exons for maximum disruption

  • Verification through sequencing, RT-PCR, and Western blotting

• Domain-specific mutations:

  • Precise editing of key domains (transmembrane, cytoplasmic regions)

  • Introduction of point mutations to disrupt specific protein-protein interactions

  • Creation of truncation mutants to study domain functions

• Regulatory element editing:

  • Modification of RELL2 promoter regions to study expression regulation

  • Targeting potential enhancer elements identified through epigenomic profiling

  • Analysis of transcription factor binding sites involvement

Experimental approaches:

• In vitro cellular models:

  • Editing in bovine cell lines (e.g., MDBK cells, BL3.1 B lymphocyte line)

  • Phenotypic analysis of edited cells (proliferation, apoptosis, cytokine responses)

  • Transcriptomic and proteomic profiling of knockout vs. wild-type cells

• CRISPR activation/inhibition:

  • CRISPRa (dCas9-activator) to upregulate RELL2 expression

  • CRISPRi (dCas9-repressor) to downregulate expression without genomic changes

  • Temporal control using inducible systems

• CRISPR screening:

  • Genome-wide screens to identify genetic interactors of RELL2

  • Focused screens targeting immune pathways

  • Analysis of synthetic lethal/viable interactions

This approach has been successfully applied in studying immune factors in bovine cells, revealing that critical immune factors including IFNAR2 and IL2RB are transcriptionally regulated by specific enhancer elements .

What are the potential roles of Bovine RELL2 in signaling pathways based on structural predictions?

Structural predictions suggest several potential roles for Bovine RELL2 in signaling pathways:

Predicted signaling activities:

• NF-κB pathway interactions:

  • The homology between RELL2 and RELT suggests potential interactions with TRAF proteins

  • RELT has been shown to bind the adaptor protein TRAF-1 and activate the NF-κB pathway

  • RELL2 may modulate this signaling, either enhancing or inhibiting NF-κB activation

• MAPK signaling:

  • The disordered carboxy-terminal domain may interact with components of MAPK cascades

  • Similar to RELT, RELL2 might influence p38 and JNK signaling

  • Potential roles in stress responses and apoptosis regulation

• Cytokine signaling modulation:

  • Potential interaction with IL2RB signaling pathways based on genomic proximity

  • Possible roles in IL2 and IL15 signaling regulation

  • Influence on JAK/STAT pathways in immune cells

Structural determinants of signaling:

• The disordered C-terminal region likely contains multiple protein-protein interaction motifs

• The transmembrane domain may participate in receptor clustering

• Co-localization with other RELTfms at the plasma membrane suggests potential for heteromeric signaling complexes

Research using phosphoproteomic analysis following RELL2 activation or inhibition would help elucidate its specific signaling roles and targets in bovine cells.

How does alternative splicing affect RELL2 expression and function in bovine tissues?

Alternative splicing (AS) likely plays a significant role in regulating RELL2 expression and function in bovine tissues:

Predicted splicing regulation:

• Tissue-specific isoforms:

  • Different bovine tissues may express distinct RELL2 isoforms with specialized functions

  • Hematopoietic versus non-hematopoietic tissues might utilize different splicing patterns

  • Developmental stages may feature transitions between isoforms

• Regulatory mechanisms:

  • RNA-binding proteins like RBFOX2, SRSF1, and HNRNPM may regulate RELL2 splicing

  • RBFOX2 binds the consensus sequence (U)GCAUG and affects exon inclusion/skipping

  • SRSF proteins recognize exonic splicing enhancers to promote inclusion

• Functional consequences:

  • Isoforms may differ in cellular localization (membrane vs. cytoplasmic)

  • Alternative C-termini could alter protein interaction capabilities

  • Variations in the extracellular domain might affect ligand binding properties

Experimental approaches to study AS:

• RT-PCR with isoform-specific primers across bovine tissues

• RNA-Seq analysis with focus on splice junction reads

• Minigene assays to test splicing regulation mechanisms

• Expression of individual isoforms to assess functional differences

Given the importance of AS in immune regulation, and considering that 64% of alternative splicing events affected by RBFOX2 deletion are directly bound by RBFOX2 , investigation of similar mechanisms for RELL2 could reveal important regulatory pathways in bovine immune cells.