LZTFL1 Human

What is the genomic location and structure of LZTFL1?

LZTFL1 is a tumor suppressor gene located in chromosomal region 3p21.3, a region frequently deleted in various cancer types including kidney cancer . Structurally, LZTFL1 contains conserved coil-coil and leucine zipper domains that are critical for its function . The full-length cDNA in model organisms such as zebrafish contains 897 base pairs encoding 298 amino acids, with high conservation of functional domains across species . When investigating LZTFL1 structure-function relationships, researchers should consider both the coiled-coil domains that facilitate protein-protein interactions and the leucine zipper motif that may be involved in DNA binding or dimerization.

What are the primary cellular functions of LZTFL1?

LZTFL1 functions in multiple cellular pathways:

• Tumor suppression: LZTFL1 inhibits tumor cell proliferation by destabilizing AKT through the ZNRF1-mediated ubiquitin proteasome pathway, inducing cell cycle arrest at G1 phase .

• Ciliary regulation: As a member of the Bardet-Biedl syndrome (BBS) gene family (also known as BBS17), LZTFL1 interacts with the BBSome protein complex and regulates protein trafficking to primary cilia .

• Signaling pathway modulation: LZTFL1 serves as a negative regulator in hedgehog signaling pathways, which are critical for development and tissue homeostasis .

• Epithelial-mesenchymal transition (EMT) regulation: LZTFL1 inhibits EMT through modulation of Wnt/β-catenin, hedgehog, and TGF-β signaling pathways .

How is LZTFL1 expression regulated in different tissues?

LZTFL1 is widely distributed across various tissues, with particularly strong expression in lung tissue . Within the respiratory system, single-cell RNA sequencing has shown that LZTFL1 is present throughout the respiratory epithelium but is predominantly expressed in ciliated cells . Expression patterns differ among cell types, with the LZTFL1 promoter showing dynamic regulation through tissue-specific enhancers in immune, erythroid, and endothelial cell types . When designing experiments to study LZTFL1, researchers should consider tissue-specific expression patterns and use appropriate positive controls for validation.

How does LZTFL1 contribute to tumor suppression in renal cell carcinoma?

LZTFL1 inhibits kidney tumor cell growth through a specific molecular mechanism involving AKT destabilization:

• LZTFL1 promotes the degradation of AKT (a key oncogenic kinase) via the ZNRF1-mediated ubiquitin proteasome pathway .

• This degradation leads to cell cycle arrest at the G1 phase, inhibiting proliferation of cancer cells .

• LZTFL1 is frequently deleted in clear cell renal cell carcinoma (ccRCC), and its downregulation correlates with poor clinical outcomes .

Experimental evidence from both gain- and loss-of-function studies in kidney tumor cell lines and patient-derived xenograft (PDX) models has validated this tumor-suppressive role . For researchers studying LZTFL1 in cancer contexts, overexpression studies in PDX models via lentiviral delivery have shown promising results in suppressing tumor growth, suggesting potential therapeutic applications .

What is LZTFL1's role in COVID-19 severity?

LZTFL1 has been identified as a candidate effector gene at the 3p21.31 COVID-19 risk locus:

• The risk allele A of SNP rs17713054G>A creates a gain-of-function variant that enhances LZTFL1 expression .

• This genetic variant is associated with a twofold increased risk of respiratory failure in COVID-19 patients .

• LZTFL1 regulates epithelial-mesenchymal transition (EMT), a viral response pathway induced by SARS-CoV-2 infection .

The mechanism likely involves delayed EMT response due to increased LZTFL1 levels, which may prevent the reduction of ACE2 and TMPRSS2 (SARS-CoV-2 entry receptors) and/or slow EMT-driven tissue repair . Methodologically, this connection was established through a combination of chromosome conformation capture techniques, gene expression analysis, and selective spatial transcriptomic analysis of lung biopsies from COVID-19 patients .

How is LZTFL1 involved in Bardet-Biedl syndrome pathogenesis?

As BBS17, LZTFL1 plays a crucial role in ciliary function, with implications for Bardet-Biedl syndrome:

• LZTFL1 interacts with the BBSome protein complex, which functions as a coat complex transporting membrane proteins between plasma and ciliary membranes .

• LZTFL1 regulates ciliary trafficking of this complex and affects the transport of signaling proteins such as Smoothened, a hedgehog signal transducer .

• Defects in LZTFL1 can lead to BBS characteristics including blindness, obesity, and kidney anomalies .

LZTFL1-null mice exhibit phenotypes consistent with ciliopathies, including obesity, retinal degeneration, and abnormal cilia development . When investigating BBS-related mechanisms, researchers should examine both LZTFL1's direct role in protein trafficking and its indirect effects on signaling pathways crucial for development and tissue maintenance.

What are the optimal methods for studying LZTFL1 protein interactions?

Several complementary approaches are recommended for investigating LZTFL1 protein interactions:

• Tandem affinity purification (TAP): This method has successfully identified novel LZTFL1 interactions, as demonstrated in studies using transgenic mice expressing BBSome subunits to discover LZTFL1 as a BBSome-interacting protein .

• Co-immunoprecipitation (Co-IP): Essential for validating protein-protein interactions in different cellular contexts and conditions.

• Proximity-dependent biotin identification (BioID): Useful for identifying transient or weak interactions in the native cellular environment.

• Chromosome conformation capture techniques: Methods like Micro Capture-C (MCC) have been used to identify interactions between the rs17713054 enhancer and the LZTFL1 promoter .

When designing interaction studies, researchers should consider cellular localization of LZTFL1, which has been shown to be primarily cytoplasmic in zebrafish expression systems .

How can LZTFL1 expression be effectively modulated in experimental systems?

Both gain- and loss-of-function approaches have been successfully employed to study LZTFL1:

• Overexpression systems: Lentiviral delivery of LZTFL1 has shown successful overexpression in patient-derived xenograft models, suppressing tumor growth . Researchers should optimize vector design to ensure proper expression level and subcellular localization.

• RNA interference (RNAi): Knockdown of LZTFL1 has demonstrated that reduction of LZTFL1 can restore BBSome trafficking to cilia in BBS3 and BBS5 depleted cells .

• CRISPR-Cas9 gene editing: Deletion of the rs17713054 enhancer has been used to study LZTFL1 expression regulation, although some experiments showed no effect on expression (suggesting compensatory mechanisms) .

• Animal models: LZTFL1-null mice exhibit phenotypes of obesity, retinal degeneration, and abnormal cilia development, providing valuable in vivo systems for studying LZTFL1 function .

What are the best model systems for investigating LZTFL1 function?

Multiple model systems have proven valuable for LZTFL1 research, each with specific advantages:

• Zebrafish: Widely considered a powerful model for understanding LZTFL1 functions related to obesity, disease, and cancer. Zebrafish LZTFL1 shows conserved domains and subcellular localization patterns similar to mammalian LZTFL1 .

• Mouse models: LZTFL1-null mice exhibit phenotypes consistent with BBS, making them valuable for studying ciliopathies and related conditions .

• Cell lines: Kidney tumor cell lines have been used for studying LZTFL1's role in cancer progression and tumor suppression . HeLa cells have been employed for ectopic expression and localization studies .

• Patient-derived xenografts (PDX): Particularly useful for cancer-related studies, allowing assessment of LZTFL1's effects on tumor growth in a more physiologically relevant context .

• Chlamydomonas: This model organism has been used to study LZTFL1's role in mediating phototaxis through ciliary function regulation .

How do genetic variants in LZTFL1 affect its function in different cellular contexts?

The impact of LZTFL1 genetic variants appears to be context-dependent:

• rs17713054G>A variant: In lung epithelial cells, this variant creates a gain-of-function by adding a second CEBPB binding motif, enhancing transcription through augmentation of an epithelial-endothelial-fibroblast enhancer .

• Deletion variants: In cancer contexts, downregulation of LZTFL1 due to chromosomal deletions in region 3p21.3 is associated with poor prognosis in clear cell renal cell carcinoma .

• Tissue-specific effects: The impact of variants may differ across tissues due to the presence of tissue-specific enhancers and different interaction profiles of the LZTFL1 promoter .

When investigating genetic variants, researchers should consider employing both bioinformatics approaches (such as colocalization analysis to determine if GWAS and eQTL associations result from a single variant or distinct variants) and experimental validation through enhancer deletion or mutation studies .

What is the interplay between LZTFL1 and signaling pathways in ciliary function?

LZTFL1 regulates multiple signaling pathways relevant to ciliary function:

• Hedgehog signaling: LZTFL1 serves as a negative regulator in hedgehog signaling pathways and affects ciliary trafficking of Smoothened, a key hedgehog signal transducer .

• BBSome-mediated trafficking: LZTFL1 interacts with the BBSome complex and regulates its ciliary trafficking. Reduction of LZTFL1 can restore BBSome trafficking to cilia in cells depleted of BBS3 and BBS5 .

• Epithelial-mesenchymal transition pathways: LZTFL1 regulates EMT through Wnt/β-catenin, hedgehog, and TGF-β signaling, with increased levels inhibiting EMT and decreased levels promoting it .

To study these interactions, researchers should employ both genetic manipulation approaches (overexpression, knockdown) and pharmacological interventions targeting specific pathway components, followed by assessment of ciliary trafficking using microscopy techniques.

How might targeting LZTFL1 be developed as a therapeutic strategy?

Based on current research, LZTFL1 represents a potential therapeutic target in multiple contexts:

• Cancer therapy: Re-expression of LZTFL1 in tumors where it is downregulated may provide a therapeutic strategy against clear cell renal cell carcinoma. Lentiviral delivery of LZTFL1 has shown promising results in suppressing patient-derived xenograft growth .

• COVID-19 treatment: Since the 3p21.31 COVID-19 risk locus is associated with a gain-of-function variant causing increased expression of LZTFL1, inhibiting LZTFL1 might be a potential therapeutic approach .

• Ciliopathy management: Modulating LZTFL1 function might help address conditions related to ciliary dysfunction, as demonstrated by the restoration of BBSome trafficking to cilia in BBS3 and BBS5 depleted cells when LZTFL1 is reduced .

Development of therapeutic strategies requires careful consideration of tissue-specific expression patterns and potential off-target effects. Small molecule screening approaches targeting LZTFL1 protein-protein interactions or antisense oligonucleotides modulating LZTFL1 expression might be promising avenues for investigation.

How does LZTFL1 contribute to epithelial-mesenchymal transition in diverse pathological contexts?

LZTFL1's role in EMT extends beyond COVID-19 to other pathological conditions:

• Cancer progression: In malignancy contexts, increased levels of LZTFL1 inhibit EMT, whereas decreased LZTFL1 promotes EMT, affecting tumor invasiveness and metastatic potential .

• Tissue injury response: EMT plays a key role in the innate immune response and is involved in both development and resolution of pneumonitis, suggesting LZTFL1 may influence inflammatory lung conditions beyond COVID-19 .

• Developmental processes: Given LZTFL1's role in ciliary function and signaling pathway regulation, its impact on EMT may also affect normal developmental processes dependent on cell migration and differentiation.

Research approaches should include analysis of EMT markers in LZTFL1-manipulated systems, assessment of cellular reorganization, and evaluation of signaling pathway activation states through phosphoprotein analysis.

What is the significance of LZTFL1's interaction with the BBSome in non-ciliated cells?

While LZTFL1's interaction with the BBSome is well-established in ciliated cells, its function in non-ciliated cells remains an important research question:

• The BBSome functions as a coat complex transporting membrane proteins, suggesting potential roles in vesicular trafficking beyond cilia .

• LZTFL1's widespread tissue distribution indicates it may have functions independent of ciliary regulation .

• The interaction between LZTFL1 and the BBSome may influence signaling pathways relevant to cell proliferation and differentiation even in the absence of cilia.

Researchers investigating this question should consider comparative studies between ciliated and non-ciliated cell types, subcellular localization analysis of LZTFL1 and BBSome components, and identification of cell type-specific interaction partners through proteomics approaches.