Recombinant Human Leucine-rich repeat-containing protein 3C (LRRC3C)

What is the genomic location and basic structure of LRRC3C?

LRRC3C is located on chromosome 17q21, neighboring ORMDL3 and other genes including GSDMB, GSDMA, ZPBP2, IKZF3, GRB7, ERBB2, and PGAP3. The gene contains two exons and encodes a 275 amino acid predicted membrane protein with one predicted transmembrane region . The gene is positioned adjacent to ORMDL3, which has been extensively studied in relation to asthma pathogenesis. The chromosome 17q21 locus contains a cluster of nine genes that have been implicated in various inflammatory conditions .

What is the expression pattern of LRRC3C in human tissues?

RNAseq data from normal human tissues demonstrates that LRRC3C has highest expression levels in testis . Interestingly, research has shown that LRRC3C mRNA cannot be detected in human lung tissue, primary bronchial epithelial cells, bronchoalveolar lavage (BAL) macrophages, or peripheral blood mononuclear cells (PBMCs) . This expression pattern differs significantly from neighboring genes like ORMDL3, which is readily detected in lung tissue and multiple cell types relevant to asthma pathogenesis . This tissue-specific expression pattern suggests that LRRC3C may have specialized functions in certain tissues like testis rather than a ubiquitous role.

Which genetic variants of LRRC3C have been associated with disease?

Several single nucleotide polymorphisms (SNPs) within LRRC3C have been linked to inflammatory conditions. The SNP rs4794820, located within LRRC3C, has been significantly associated with severe asthma compared to mild/moderate asthma, as well as with atopic asthma and lower PC20 (a measure of airway hyperresponsiveness) . Another SNP, rs2872507, has been linked to LRRC3C expression in inflammatory bowel disease (IBD) and associated with poor response to inhaled corticosteroids (ICS) in asthma patients . The table below summarizes key genetic variants and their clinical associations:

How does LRRC3C structure compare with other leucine-rich repeat-containing proteins?

While specific structural data for LRRC3C is limited, insights can be drawn from related leucine-rich repeat proteins like LRRK1 and LRRK2, which have been more extensively characterized. LRRK proteins contain leucine-rich repeat domains involved in protein-protein interactions as well as catalytic domains . LRRC3C likely shares structural features common to the leucine-rich repeat family, including a curved solenoid structure formed by tandem LRR motifs. Unlike LRRK1/2, LRRC3C appears to lack kinase domains, suggesting different functional roles . Structural modeling approaches could be employed to predict LRRC3C's three-dimensional conformation based on homology with solved structures of related proteins.

What experimental approaches are most effective for studying LRRC3C expression?

Based on available research, RT-qPCR has been employed to detect LRRC3C mRNA in human tissues with careful validation using positive controls . When studying LRRC3C, researchers should consider:

• Use of highly sensitive RT-qPCR protocols with appropriate primers spanning exon junctions

• Inclusion of positive controls (such as human LRRC3C cDNA clones) across a range of concentrations to establish detection limits

• Parallel detection of housekeeping genes to normalize expression data

• Genotyping of samples for relevant SNPs (such as rs2872507) that may influence expression

• Multiple tissue sampling to account for tissue-specific expression patterns

Research has shown that LRRC3C mRNA was not detectable in lung tissue even when using sensitive RT-qPCR methods that successfully detected control cDNA . This highlights the importance of tissue selection when studying this gene, with testis tissue being potentially more suitable for expression studies.

How might SNPs affect LRRC3C expression and function?

The rs2872507 SNP has been linked to differential expression of LRRC3C in colon tissue, suggesting a regulatory role . Research methodologies to investigate SNP effects on LRRC3C could include:

• Allele-specific expression analysis using samples heterozygous for regulatory SNPs

• CRISPR-Cas9 gene editing to introduce specific SNP variants in cell models

• Reporter assays with constructs containing different SNP variants in the LRRC3C promoter or enhancer regions

• Chromatin immunoprecipitation studies to identify transcription factors whose binding is affected by SNPs

• DNA methylation analysis to determine if SNPs affect epigenetic regulation

The risk allele for rs2872507 (GG) has been detected in 30% of asthma lungs and 61% of control lungs, though LRRC3C expression was not detected in either group . This suggests that while this SNP may be linked to disease risk, additional factors likely influence LRRC3C expression in a tissue-specific manner.

What are the best methods for producing recombinant human LRRC3C protein?

For production of recombinant human LRRC3C, researchers should consider:

• Expression system selection: Mammalian expression systems like HEK293 or CHO cells may be preferable for a transmembrane protein like LRRC3C to ensure proper folding and post-translational modifications.

• Construct design considerations:

  • Inclusion of appropriate affinity tags (His, FLAG, or GST) for purification

  • Signal peptide optimization for secretion or membrane targeting

  • Codon optimization for the selected expression system

  • Optional inclusion of protease cleavage sites for tag removal

• Purification strategy:

  • Detergent selection for membrane protein solubilization (e.g., DDM, CHAPS)

  • Two-step affinity chromatography followed by size exclusion chromatography

  • Validation of protein folding by circular dichroism or limited proteolysis

• Quality control assessments:

  • SDS-PAGE and Western blotting to confirm purity and identity

  • Mass spectrometry to verify sequence integrity

  • Thermal shift assays to assess stability similar to methods used for related proteins

How can researchers investigate the potential role of LRRC3C in inflammatory diseases?

Given the genetic association of LRRC3C with inflammatory bowel disease and the contrasting lack of expression in asthmatic lungs, researchers might employ these methodological approaches:

• Tissue-specific expression analysis:

  • Compare LRRC3C expression in intestinal tissues from IBD patients versus controls

  • Correlate expression levels with genotype at rs2872507 and clinical parameters

  • Single-cell RNA sequencing to identify specific cell types expressing LRRC3C

• Functional studies:

  • CRISPR-Cas9 knockout or knockdown studies in relevant cell types

  • Overexpression studies with wild-type and mutant LRRC3C

  • Protein interaction studies using proximity labeling or co-immunoprecipitation

  • Phosphorylation site mapping similar to approaches used for LRRK proteins

• Animal models:

  • Generation of LRRC3C knockout mice and assessment of susceptibility to induced colitis

  • Humanized mouse models carrying human LRRC3C variants

What approaches can be used to identify potential interaction partners of LRRC3C?

Leucine-rich repeat domains typically mediate protein-protein interactions. To identify LRRC3C binding partners, researchers might consider:

• Affinity purification-mass spectrometry (AP-MS):

  • Expression of tagged LRRC3C in relevant cell types

  • Crosslinking prior to lysis to capture transient interactions

  • Quantitative comparison between wild-type and mutant LRRC3C

• Proximity-based labeling techniques:

  • BioID or TurboID fusion proteins to label proximal proteins

  • APEX2 fusion for temporal control of labeling

  • Spatial-specific labeling in different cellular compartments

• Yeast two-hybrid screening:

  • Using the LRR domain or full-length LRRC3C as bait

  • Screening against tissue-specific libraries (e.g., testis or intestinal)

• In silico prediction of interaction partners:

  • Structural modeling followed by protein-protein docking simulations

  • Analysis of co-expression patterns across tissues and conditions

How does LRRC3C function compare with neighboring genes in the 17q21 locus?

The chromosome 17q21 locus contains several genes including ORMDL3, GSDMB, GSDMA, and ZPBP2 that have been implicated in inflammatory conditions . Unlike ORMDL3, which is expressed in lung tissue and associated specifically with asthma pathogenesis, LRRC3C appears not to be expressed in lung tissue but is associated with both asthma and IBD through genetic studies .

Comparative research approaches could include:

• Parallel expression profiling of all 17q21 genes across multiple tissues and disease states

• Investigation of potential co-regulation mechanisms through shared enhancers or insulator elements

• Analysis of evolutionary conservation patterns of these genes across species

• Functional studies comparing phenotypic effects of gene knockdown/knockout

• Epistasis analysis to determine genetic interactions between 17q21 genes

ORMDL3 has established roles affecting airway smooth muscle, sphingolipid metabolism, and inflammatory pathways, while LRRC3C function remains largely uncharacterized . The different expression patterns suggest distinct biological roles despite their genomic proximity.

What structural and functional similarities exist between LRRC3C and other leucine-rich repeat family proteins?

LRRC3C belongs to the leucine-rich repeat protein family, which includes the better-characterized LRRK1 and LRRK2 proteins. While LRRK1/2 contain multiple functional domains including kinase domains, LRRC3C appears to be a simpler protein with primarily LRR domains and a transmembrane region .

Structural comparisons between LRRC3C and related proteins could investigate:

• Conservation of key residues in the leucine-rich repeat motifs

• Differences in interdomain interactions that regulate protein function

• Presence of regulatory motifs such as phosphorylation sites

• Membrane association mechanisms

In LRRK proteins, interactions between domains are critical for regulating kinase activity . For example, specific residues in the LRRK1 αC helix form contacts with the COR-B domain that are crucial for kinase function . While LRRC3C lacks kinase domains, similar interdomain interactions might regulate its function.

What are the most promising approaches for elucidating LRRC3C function?

Given the current knowledge gaps regarding LRRC3C function, several research directions appear promising:

• Tissue-specific functional genomics:

  • Focused studies in testis tissue where LRRC3C expression is highest

  • Single-cell transcriptomics to identify specific cell populations expressing LRRC3C

  • Conditional knockout models to assess tissue-specific phenotypes

• Disease-relevant functional studies:

  • Investigation of LRRC3C function in intestinal epithelial cells relevant to IBD

  • Assessment of how disease-associated SNPs affect expression in specific tissues

  • Examination of potential roles in inflammatory signaling pathways

• Structural biology approaches:

  • Cryo-EM or X-ray crystallography studies of LRRC3C structure

  • Mapping of protein interaction surfaces through mutagenesis

  • Comparative structural analysis with related proteins

How might understanding LRRC3C function contribute to therapeutic approaches for inflammatory diseases?

While current evidence suggests LRRC3C may be more relevant to intestinal inflammatory conditions than respiratory diseases , further investigation could reveal therapeutic applications:

• Target validation studies:

  • Determine if modulating LRRC3C expression or function affects inflammatory processes

  • Investigate whether disease-associated SNPs create druggable differences in protein function

  • Assess whether LRRC3C-dependent pathways intersect with established drug targets

• Biomarker development:

  • Evaluation of LRRC3C genetic variants as predictive biomarkers for treatment response

  • Assessment of whether the rs2872507 SNP could predict corticosteroid responsiveness in larger cohorts

• Therapeutic approaches:

  • If functional studies confirm a role in disease pathogenesis, development of inhibitors or activators

  • Investigation of whether existing drugs affecting related pathways modulate LRRC3C function

  • Generation of tissue-specific delivery strategies based on expression patterns