Recombinant Human RELT-like protein 2 (RELL2)

What is RELL2 and what is its basic structure?

RELL2 (Receptor Expressed in Lymphoid Tissues-Like 2) is a member of the RELT family of proteins, closely associated with the plasma membrane and acting as a modulator for RELT signaling. Structurally, RELL2 is a Type I transmembrane protein encoding a 303 amino acid-long 32.4 kDa protein . Like other RELT family members, RELL2 contains a short extracellular domain (ECD) compared to other TNFRSF members, and lacks the extracellular Cys-rich domains typically used to bind TNFSF ligands . RELL2 is predicted to have a disordered sequence in its carboxy-terminal tail, suggesting that this region may adopt multiple conformations depending on post-translational modifications or interactions with other proteins .

When studying RELL2's structure, researchers should consider that it is distinct from other TNFRSF members in lacking the conserved intracellular "death domain" typical of apoptosis-inducing members such as Fas and TNFR1 .

Where is RELL2 predominantly expressed in human tissues?

RELL2 expression exhibits a tissue-specific pattern that is more restricted than its family member RELL1. Expression data indicates that RELL2 mRNA is predominantly found in hematopoietic tissues such as the thymus and spleen, as well as in immune-privileged sites including the testes, brain, and placenta .

According to the Human Protein Atlas (HPA), high RELL2 expression is observed in various brain regions (including the cerebral cortex and medulla), parathyroid and pituitary glands, placenta, testis, hematopoietic tissues, and peripheral blood leukocytes (PBLs) . Gene expression data from the ARCHS4 platform confirms that RELL2 expression is highest in cell lines of the hematopoietic system with minimal expression in certain tissues such as skeletal muscle . This tissue-specific expression pattern may provide insights into RELL2's physiological functions.

What is known about RELL2's role in cancer biology?

RELL2 expression correlates significantly with tumor stage in multiple cancers, including THCA, KIRP (Kidney Renal Papillary Cell Carcinoma), HNSC (Head and Neck Squamous Cell Carcinoma), COAD (Colon Adenocarcinoma), BRCA (Breast Invasive Carcinoma), and ACC .

How does RELL2 interact with the tumor immune microenvironment and what methodologies are best for studying these interactions?

RELL2 shows significant correlations with various immune components in the tumor microenvironment (TME). Researchers investigating these interactions should employ a multi-faceted approach combining bioinformatic analysis with experimental validation.

For bioinformatic analysis, the ESTIMATE algorithm (Estimation of STromal and Immune cells in MAlignant Tumor tissues using Expression data) is recommended to determine immune and stromal scores across cancer types . This approach revealed that RELL2 expression significantly correlates with immune cells in different cancer types, particularly in KIRC and LIHC (Liver Hepatocellular Carcinoma) .

In KIRC, RELL2 positively and significantly correlates with four immune cell types: CD4+ T cells, dendritic cells (DCs), macrophages, and neutrophils . In LIHC, RELL2 correlates with five immune cell types: B cells, CD4+ T cells, DCs, macrophages, and neutrophils .

When examining RELL2's relationship with immune checkpoints, analysis of over 40 standard checkpoint genes showed significant correlation between RELL2 expression and several checkpoint genes across different cancer types, particularly in KICH, KIRC, and THYM . These findings suggest RELL2 may influence tumor immunity through regulation of these checkpoint genes.

For experimental validation of these bioinformatic findings, flow cytometry, immunohistochemistry, and single-cell RNA sequencing approaches are recommended to characterize the immune cell populations in relation to RELL2 expression.

What methodologies are recommended for studying RELL2 intron retention and its impact on cancer?

Intron retention in RELL2, particularly at intron 4, has been identified as a significant event in cancer, notably in pancreatic ductal adenocarcinoma (PDAC) . To study this phenomenon, researchers should employ a comprehensive approach:

• RNA-Seq Analysis: To identify and quantify intron retention events in RELL2, RNA-seq followed by computational analysis with tools specifically designed to detect alternative splicing is recommended. This approach can help determine the prevalence of intron 4 retention across different cancer types.

• RIP-qPCR: RNA immunoprecipitation followed by quantitative PCR has been successfully used to demonstrate direct interaction between RELL2 and its upstream regulator DHX38 . This technique is valuable for identifying proteins that interact with and potentially regulate RELL2 splicing.

• Functional Validation: To understand the physiological impact of intron retention, researchers should perform in vitro functional assays including cell proliferation, cytotoxicity assays (such as gemcitabine resistance in PDAC), and apoptosis assays with cells expressing normal RELL2 versus the intron-retained variant .

• Gene Knockdown/Overexpression Studies: Manipulating the expression of upstream splicing regulators (such as DHX38) and observing the effects on RELL2 intron retention can provide insights into the regulatory mechanisms. This approach demonstrated that altered expression of DHX38 results in corresponding changes in intron 4 retention of RELL2 .

• Analysis of Nonsense-Mediated mRNA Decay (NMD): Since intron retention often leads to premature termination codons that trigger NMD, researchers should assess the stability of intron-retained RELL2 transcripts and determine if they undergo NMD, which ultimately affects RELL2 protein levels .

How can researchers effectively design experiments to analyze RELL2 as a pan-cancer biomarker?

Developing RELL2 as a robust pan-cancer biomarker requires a systematic experimental approach:

What are the recommended protocols for producing and purifying recombinant RELL2 for functional studies?

Based on established approaches for similar proteins, researchers can consider the following protocol for producing recombinant RELL2:

• Expression Construct Design:

  • For full-length RELL2: Clone the complete coding sequence (303 amino acids)

  • For the extracellular domain: Consider using a construct similar to that used for ANGPTL2, which includes a C-terminal 6-His tag for purification

  • For structural studies: Focus on the specific domains of interest (e.g., the extracellular domain or the fibrinogen-like domain)

• Expression System Selection:

  • Mammalian expression systems (such as HEK293 cells) are recommended for producing properly folded and post-translationally modified RELL2, given that recombinant RELL1 (a related protein) shows evidence of significant post-translational modifications

  • For structural studies, consider expression in simpler systems like E. coli, following approaches used for similar proteins like RuvBL2

• Purification Strategy:

  • Immobilized metal affinity chromatography (IMAC) using the His-tag

  • Follow with size exclusion chromatography to ensure homogeneity

  • Consider additional purification steps if needed, based on protein purity

• Functional Validation:

  • Verify protein activity through established assays such as cell-based functional tests

  • For a His-tagged construct, verify that the tag does not interfere with protein function

  • Consider analyzing oligomerization state, as RELL family proteins are known to form complexes and interact with each other

• Storage and Stability:

  • Determine optimal buffer conditions for long-term stability

  • Assess freeze-thaw stability and consider single-use aliquots

When designing these experiments, researchers should note that RELL2, like other RELT family proteins, binds to other family members as demonstrated by co-immunoprecipitation experiments. Co-expression of recombinant RELT family members results in co-localization at the plasma membrane of cells .

How can researchers effectively analyze RELL2 genetic alterations in cancer samples?

For comprehensive analysis of RELL2 genetic alterations in cancer, researchers should employ the following multi-platform approach:

• Somatic Mutation Analysis:

  • Utilize cancer genomics databases like COSMIC (Catalogue Of Somatic Mutations In Cancer) to identify mutations across RELL2

  • Implement visualization tools that display mutations at the amino acid level across the full length of the gene

  • Focus analysis on specific regions of interest using filters or sliders to highlight particular domains

  • Categorize mutations by type (single base substitutions, complex mutations, insertions, deletions)

  • Switch between peptide view and cDNA coordinates for comprehensive analysis

• Copy Number Variation Analysis:

  • Analyze CNV data in conjunction with gene expression data

  • Link to sample and study information for contextual understanding

  • Utilize visualization tools like ChromoView to examine CNVs across the whole chromosome containing RELL2

• Expression Analysis Across Cancer Types:

  • Compare RELL2 expression between cancer tissues and adjacent normal tissues using analytical packages like edgeR

  • Combine data from multiple databases (TCGA, GTEx, CCLE) to expand cancer types and sample sizes

  • Implement statistical approaches like the Kruskal-Wallis test to analyze differences between various tissues

  • Visualize results using violin plots through R packages like ggplot

• Correlation with Clinical Parameters:

  • Stratify analysis by clinical factors such as tumor stage, grade, and patient demographics

  • Employ univariate and multivariate Cox regression analyses to assess prognostic significance

  • Generate Kaplan-Meier survival curves for high and low RELL2 expression groups

• Integration with Other Molecular Data:

  • Correlate RELL2 alterations with other molecular features such as microsatellite instability (MSI) and tumor mutational burden (TMB)

  • Analyze relationships with DNA methylation patterns by examining associations with methyltransferases (DNMT3B, DNMT3A, DNMT2, and DNMT1)

  • Investigate potential interactions with DNA repair genes

This comprehensive approach will provide researchers with a thorough understanding of RELL2 alterations across cancer types and their potential clinical implications.

What experimental approaches can elucidate the mechanism by which RELL2 influences apoptosis?

RELL2 overexpression has been shown to induce the activation of MAPK14/p38 cascade and apoptosis . To elucidate this mechanism, researchers should consider the following experimental approaches:

• Signaling Pathway Analysis:

  • Western blot analysis to detect phosphorylation status of MAPK14/p38 and downstream signaling molecules upon RELL2 overexpression or knockdown

  • Small molecule inhibitors of the p38 pathway to determine if RELL2-induced apoptosis is dependent on this pathway

  • Co-immunoprecipitation studies to identify direct binding partners of RELL2 in the signaling cascade

• Domain Function Analysis:

  • Generate truncation or deletion mutants of RELL2 to identify domains essential for apoptosis induction

  • Site-directed mutagenesis to modify key residues in RELL2's structure

  • Given that RELL2 lacks the classic "death domain" found in other apoptosis-inducing TNFRSF members , determine which structural elements are responsible for its pro-apoptotic function

• Cell Death Assays:

  • Annexin V/PI staining followed by flow cytometry to quantify apoptotic cells

  • TUNEL assay to detect DNA fragmentation

  • Caspase activity assays to determine which caspases are activated in RELL2-induced apoptosis

  • Mitochondrial membrane potential assays to assess involvement of the intrinsic apoptotic pathway

• Comparative Analysis with RELT Family Members:

  • Since RELL2 functions as a modulator for RELT signaling , compare apoptotic mechanisms between RELL2 and other RELT family members

  • Co-expression studies to determine if interactions between RELT family members affect apoptotic signaling

  • Analysis of RELL2 localization at the plasma membrane, as this is where it likely initiates signaling cascades

• Context-Dependent Effects:

  • Given RELL2's varied prognostic implications across cancer types , investigate cell type-specific responses to RELL2 expression

  • Determine if the tumor microenvironment influences RELL2's apoptotic function

  • Explore whether RELL2's effects on apoptosis differ between normal and cancer cells

These approaches will provide a comprehensive understanding of RELL2's role in apoptotic signaling and may reveal potential therapeutic strategies for cancers where RELL2 expression is altered.

How does intron retention in RELL2 affect its function in cancer and what techniques can be used to study this phenomenon?

Intron retention in RELL2, particularly at intron 4, has been identified as a significant event in pancreatic ductal adenocarcinoma (PDAC) with potential implications for cancer progression . To study this complex phenomenon, researchers should employ the following integrated approaches:

• Mechanism of Intron Retention Regulation:

  • Identify upstream regulators of RELL2 splicing, such as DHX38 (DEAH-Box Helicase 38), which has been shown to directly interact with RELL2

  • Perform RNA immunoprecipitation followed by quantitative PCR (RIP-qPCR) to confirm direct interactions between splicing factors and RELL2 mRNA

  • Manipulate expression of potential splicing regulators (e.g., DHX38) and observe effects on RELL2 intron 4 retention

• Functional Consequences Analysis:

  • Characterize the RELL2 protein product resulting from intron 4 retention (if translated) or determine if the transcript undergoes nonsense-mediated decay

  • Compare functional properties of cells expressing wild-type RELL2 versus the intron 4-retained variant through:

    • Cell proliferation assays

    • Chemotherapy resistance assays (e.g., gemcitabine cytotoxicity in PDAC cells)

    • Apoptosis assays

    • Migration and invasion assays to assess metastatic potential

• Clinical Correlation Studies:

  • Analyze patient samples to determine the prevalence of RELL2 intron 4 retention across different stages of cancer progression

  • Correlate intron 4 retention with patient outcomes, including response to therapy and survival

  • Develop RT-PCR assays specifically designed to detect the intron 4-retained variant in clinical samples

• Targeted Modulation Approaches:

  • Design antisense oligonucleotides (ASOs) that can specifically target and modify the splicing of RELL2 intron 4

  • Test whether modulation of RELL2 splicing affects cancer cell phenotypes and response to therapy

  • Investigate whether combinatorial approaches targeting both RELL2 splicing and other cancer pathways show synergistic effects

• Genome-wide Context Analysis:

  • Determine if RELL2 intron retention is part of a broader splicing program in cancer by identifying other genes with altered splicing patterns

  • Perform RNA-seq analysis to identify genome-wide splicing changes associated with the factors regulating RELL2 intron retention

  • Investigate whether global splicing modulators (like DHX38) could be potential therapeutic targets in cancers exhibiting RELL2 intron retention

This comprehensive approach will provide valuable insights into how RELL2 intron retention contributes to cancer progression and may identify novel therapeutic strategies for PDAC and potentially other cancer types where similar splicing alterations occur.