LGALS3 Human

What is LGALS3 and what protein does it encode?

LGALS3 is a human gene located on chromosome 14, locus q21-q22, that encodes Galectin-3 protein . Galectin-3 (also known as Gal-3) is a member of the lectin family of proteins, specifically belonging to the beta-galactoside-binding protein family . It is approximately 30 kDa in size and contains a carbohydrate-recognition-binding domain (CRD) of about 130 amino acids that enables specific binding to β-galactosides . Galectin-3 is one of 14 identified mammalian galectins and is distinguished by its chimeric structure consisting of a single CRD linked to a non-lectin domain .

What are the primary biological functions of Galectin-3?

Galectin-3 exhibits remarkable functional versatility, participating in numerous cellular processes:

• Cell adhesion and cell-matrix interactions

• Cell activation and chemoattraction

• Cellular migration, polarity, and chemotaxis

• Cell growth, proliferation, and differentiation

• Cell cycle regulation

• Apoptosis (programmed cell death)

• Inflammation and inflammatory responses

• Angiogenesis and metastasis processes

These diverse functions are made possible through Galectin-3's ability to bind to specific carbohydrate structures and interact with various cellular components . Additionally, it demonstrates antimicrobial activity against bacteria and fungi . Galectin-3 can function both intracellularly and extracellularly, with different roles depending on its cellular localization .

Where is Galectin-3 expressed and localized in human cells?

Galectin-3 exhibits a ubiquitous expression pattern in adults under physiological conditions . Its cellular distribution is remarkably versatile, as it can be found in multiple cellular compartments:

• Nucleus

• Cytoplasm

• Mitochondrion

• Cell surface

• Extracellular space

This broad distribution pattern underlies its diverse functionality . Interestingly, galectins including Galectin-3 lack a known signal peptide typically required for classical secretion pathways. Instead, they are primarily found in cytosolic compartments where they fulfill intracellular roles, but can also be secreted via one or more unknown non-classical secretory pathways to function extracellularly .

What standard laboratory methods are available for measuring Galectin-3?

For researchers seeking to quantify Galectin-3 in experimental or clinical samples, several methodological approaches are available:

ELISA (Enzyme-Linked Immunosorbent Assay):

• Commercial kits such as the Human Galectin-3 ELISA Kit (LGALS3) provide sensitive detection with a reported sensitivity of 13.3 pg/ml

• SimpleStep ELISA format allows for rapid 90-minute protocols using a mix-wash-read approach

• Colorimetric detection at 450nm provides compatibility with standard plate readers

Recombinant Protein Standards:

• Highly pure recombinant Human Galectin-3/LGALS3 proteins are available as standards for multiple applications

• These are typically expressed in E. coli expression systems

Additional Methods:

• Western blotting

• Immunohistochemistry

• PCR-based gene expression analysis

The selection of appropriate detection methods should be guided by the specific research question, sample type, and required sensitivity.

How is LGALS3 gene expression regulated at the epigenetic level?

The regulation of LGALS3 transcription involves complex epigenetic mechanisms, particularly in response to injurious stimuli:

BRG1-Dependent Regulation:
Research has identified Brahma-related gene-1 (BRG1) as a critical mediator in injury-induced galectin-3 transcription in hepatocytes. BRG1 facilitates several epigenetic modifications on the LGALS3 promoter :

• DNA Methylation Dynamics:

  • Removal of 5-methylcytosine (5mC) and acquisition of 5-hydroxymethylcytosine (5hmC) on the galectin-3 promoter parallel its activation

  • BRG1 depletion reverses these changes, indicating its essential role in DNA demethylation

• Histone Modifications:

  • Injurious stimuli lead to slight up-regulation of active transcription markers (acetylated histone H3 and trimethylated H3K4)

  • More importantly, significant down-regulation of repressive histone marks (dimethylated H3K9) occurs upon injury

  • BRG1 knockdown abolishes the erasure of these repressive marks

• TET1 Recruitment Mechanism:

  • BRG1 interacts with and recruits TET1 (Ten-Eleven Translocation 1) dioxygenase to the galectin-3 promoter

  • This recruitment is essential for DNA demethylation and subsequent galectin-3 expression

  • Co-immunoprecipitation experiments confirmed BRG1-TET1 interaction in hepatocytes

This epigenetic pathway represents a novel mechanism contributing to injury-associated activation of galectin-3 transcription, where the removal of repressive epigenetic traits appears to be the rate-limiting step for its transactivation.

What is the role of transcription factors in LGALS3 expression during cellular stress?

Transcription factor dynamics play a crucial role in mediating LGALS3 expression in response to cellular stress and injurious stimuli:

AP-1 and BRG1 Interplay:
Research has identified that BRG1 relies on Activator Protein 1 (AP-1) to activate galectin-3 transcription:

• Promoter Analysis:

  • Deletion analysis identified an AP-1 binding site as essential for BRG1-mediated galectin-3 promoter activation

  • Mutation of this AP-1 site abrogated the induction of galectin-3 promoter activity

• Temporal Recruitment Pattern:

  • Under injurious stimuli, both AP-1 and BRG1 are recruited to the same region of the galectin-3 promoter with comparable kinetics

  • Depletion of AP-1 significantly diminishes BRG1 binding to the galectin-3 promoter

• Protein-Protein Interactions:

  • Co-immunoprecipitation assays confirmed direct interaction between BRG1 and AP-1

  • Re-ChIP assays detected a BRG1-AP-1 complex on the galectin-3 promoter specifically under stimulation conditions

This mechanistic understanding provides insight into how stress signals are translated into transcriptional activation of LGALS3, highlighting a coordinated action between transcription factors and chromatin remodelers.

What experimental models are effective for studying Galectin-3's role in liver injury?

Several experimental models have proven valuable for investigating Galectin-3's functions in liver pathology:

In Vivo Models:

• Hepatocyte-Specific Conditional Knockout Models:

  • Hepatocyte conditional BRG1 knockout (CKO) mice provide valuable insights into regulatory mechanisms

  • These models allow for tissue-specific evaluation of galectin-3 expression and function

• Chemical Injury Models:

  • CCl₄ (carbon tetrachloride) administration - induces hepatic fibrosis and up-regulation of galectin-3

  • Models of drug overdose (e.g., acetaminophen)

  • Diet-induced liver injury models (e.g., high-fat diet, methionine-choline deficient diet)

In Vitro Models:

• Cell Culture Systems:

  • HepG2 hepatocellular carcinoma cells provide a tractable system for molecular studies

  • Primary hepatocytes isolated from wild-type and CKO mice allow for comparative analyses

• Stimulation Protocols:

  • Combined LPS (lipopolysaccharide) plus palmitate treatment - mimics inflammatory and metabolic stress

  • This combination effectively induces galectin-3 expression in hepatocytes

• Reporter Assay Systems:

  • Galectin-3 promoter-luciferase constructs enable detailed analysis of transcriptional regulation

  • Progressive deletion constructs allow identification of critical regulatory elements

When selecting experimental models, researchers should consider the specific aspect of galectin-3 biology under investigation and the relevance of the model to human pathophysiology.

How does Galectin-3 function as an "alarmin" in cellular stress responses?

Galectin-3 has been identified as a potential "alarmin" that mediates cellular stress responses:

Expression Pattern Changes:
Unlike many constitutively expressed proteins, galectin-3 expression is dynamically regulated in response to injurious stimuli in a cell type and signal-specific manner . This conditional up-regulation in the context of injury supports its classification as an alarmin or damage-associated molecular pattern (DAMP).

Tissue Injury Response:
Multiple studies have reported that hepatic galectin-3 expression is up-regulated in different animal models of liver injury, including:

• Toxin-induced injury

• Drug overdose

• Dietary challenges

• Inflammatory conditions

Cellular Stress Response Functions:
As an alarmin, Galectin-3 participates in numerous stress-related processes:

• Acute inflammatory responses including neutrophil activation

• Adhesion and chemoattraction of monocytes/macrophages

• Opsonization of apoptotic neutrophils

• Activation of mast cells

• Autophagy regulation in response to membrane damage

Mechanism of Action:
Recent research indicates that Galectin-3 cooperates with TRIM16 to coordinate recognition of membrane damage with mobilization of core autophagy regulators (ATG16L1 and BECN1) in response to damaged endomembranes . This positions Galectin-3 as a sensor and mediator of cellular stress responses.

Understanding Galectin-3's role as an alarmin provides insight into how cells detect and respond to injurious stimuli, potentially offering therapeutic opportunities for modulating stress responses in various pathological conditions.

What methodological approaches can be used to study Galectin-3's protein interactions?

Investigating Galectin-3's diverse interactions requires sophisticated methodological approaches:

Protein-Protein Interaction Analyses:

• Co-Immunoprecipitation (Co-IP):

  • Used to confirm interactions between Galectin-3 and partner proteins

  • Successfully demonstrated interactions between BRG1 and AP-1, as well as BRG1 and TET1 in hepatocytes

• Chromatin Immunoprecipitation (ChIP):

  • Reveals DNA binding patterns of Galectin-3 and its regulatory proteins

  • Identifies binding regions and occupancy on target gene promoters

• Re-ChIP (Sequential ChIP):

  • Detects protein complexes on specific DNA regions

  • Confirmed BRG1-AP-1 and BRG1-TET1 complexes on the galectin-3 promoter under stimulation conditions

Functional Interaction Studies:

• RNA Interference:

  • siRNA knockdown of TET1 demonstrated its essential role in galectin-3 induction

  • Provides functional validation of protein interaction significance

• Promoter-Reporter Assays:

  • Galectin-3 promoter-luciferase constructs with progressive deletions

  • Site-directed mutagenesis of specific binding sites (e.g., AP-1 site)

  • Enables functional assessment of specific regulatory elements

• Recombinant Protein Techniques:

  • Expression of recombinant Galectin-3 for binding studies

  • Analysis of carbohydrate recognition domain (CRD) interactions

These methodological approaches provide complementary information about Galectin-3's interactions, from physical binding to functional consequences, enabling comprehensive characterization of its molecular networks.

What is the significance of Galectin-3 in various disease processes and how can it be targeted therapeutically?

Galectin-3 has been implicated in numerous pathological conditions, presenting both diagnostic and therapeutic opportunities:

Disease Associations:
Galectin-3 plays crucial roles in multiple diseases including:

• Cancer (particularly in metastasis processes)

• Inflammatory disorders and autoimmune conditions

• Fibrotic diseases across multiple organs

• Heart failure and cardiovascular remodeling

• Stroke and neurological conditions

• Congenital polycystic kidney disease

Mechanistic Involvement:
In heart failure specifically, Galectin-3 contributes to:

• Myofibroblast proliferation

• Fibrogenesis and tissue repair

• Inflammatory responses

• Ventricular remodeling

In cancer progression, Galectin-3 influences:

• Cell adhesion and migration

• Metastatic potential

• Immune evasion

• Angiogenesis

Therapeutic Targeting Strategies:

Diagnostic Applications:
Galectin-3 serum levels serve as a biomarker in various conditions:

• Heart failure prognosis and risk stratification

• Fibrosis progression monitoring

• Cancer progression monitoring

The multifaceted involvement of Galectin-3 in disease processes makes it an attractive target for therapeutic intervention, with ongoing research focusing on developing specific modulators that can alter its activity in pathological contexts.