PTGR1 Human

What is PTGR1 and what is its primary biochemical function?

PTGR1 is a NADPH-dependent alkenal/one oxidoreductase (AOR) that catalyzes the reduction of double bonds in α/β-unsaturated ketones, alkenals, and nitroalkenes. It serves as a rate-limiting enzyme within the arachidonic acid metabolism pathway and plays a crucial role in deactivating certain eicosanoids, including prostaglandins and leukotriene B4 . The enzyme has a broad spectrum of endogenous substrates, making it metabolically versatile. When designing experiments to study PTGR1 function, researchers should consider its involvement in multiple pathways and potentially use metabolomic profiling to capture the full range of its activities.

How is PTGR1 expression regulated in normal and cancer cells?

PTGR1 expression is significantly modulated by the NRF2 pathway, with several NRF2 inducers known to enhance PTGR1 expression, including D3T, resveratrol, and curcumin . In cancer cells, PTGR1 expression is frequently dysregulated, with overexpression observed in hepatocellular carcinoma, lung cancer, prostate cancer, and bladder cancer cell lines . The Super-enhancer (SE) regions of the genome have been identified as playing an important role in controlling PTGR1 expression, particularly in drug-resistant cancer cells. Recent research has identified specific transcription factors, including SRF and RUNX3, that bind to these SEs and significantly increase PTGR1 expression . To investigate PTGR1 regulation, researchers should employ chromatin immunoprecipitation (ChIP) assays to identify transcription factor binding sites and analyze epigenetic modifications around the PTGR1 gene locus.

What is the evidence for PTGR1's role in cancer progression?

Multiple studies have demonstrated that PTGR1 plays a significant role in cancer progression. Knockdown experiments have shown that reducing PTGR1 expression inhibits cell proliferation in multiple cancer cell lines, including triple-negative breast cancer (TNBC) and prostate cancer . In prostate cancer cells, PTGR1 silencing has been shown to increase the expression of key cell cycle inhibitor P21, cleaved-PARP, and caspase 3, while decreasing the expression of cyclin D1 . These findings suggest that PTGR1 supports cancer cell proliferation by regulating cell cycle progression and apoptosis. When investigating PTGR1's role in cancer progression, researchers should employ both genetic knockdown approaches (siRNA, shRNA) and pharmacological inhibition to validate findings through complementary methodologies.

What methods are most effective for detecting and quantifying PTGR1 in clinical samples?

Immunohistochemistry (IHC) has proven effective for detecting PTGR1 in clinical samples, with the AB181131 antibody (Abcam) showing the most reliable staining patterns in validation tissues . When determining PTGR1 positivity by IHC, a mean score threshold of one or above is typically used to indicate positive staining . RNA expression analysis also serves as a valuable quantification method, with a normalized RNA count cutoff of 2,550 achieving an area under the curve (AUC) of 0.9, a sensitivity of 96%, and a specificity of 85% in relation to IHC positivity . For optimal results, researchers should employ both protein (IHC) and RNA expression analyses, as there is a strong correlation between these approaches. When scoring IHC results, multiple assessors should be used to ensure reliability, with Cohen's kappa and Fleiss' kappa statistical methods applied to measure inter-assessor agreement.

What is the potential of PTGR1 as a therapeutic target, and what types of inhibitors are being developed?

PTGR1 has emerged as a potential therapeutic target for cancer, with several inhibitors identified, though none have entered clinical trials to date . Current PTGR1 inhibitors suffer from low potency, with IC50 values in the micromolar range . Research strategies to identify more potent PTGR1 modulators include high-throughput screening, structure-based drug design, and virtual screening approaches . Interestingly, PTGR1 has a dual role in cancer treatment strategies: PTGR1 inhibitors might sensitize cancer cells to ROS-induced cell death, while PTGR1 activators might benefit HMAF (hydroxymethylacylfulvene) anti-cancer treatment by enhancing prodrug activation . This suggests two potential therapeutic approaches: direct PTGR1 inhibition to slow cancer progression or PTGR1 activation to enhance the efficacy of certain prodrugs. For researchers developing PTGR1-targeting agents, assessing both the direct effects on PTGR1 activity and the downstream consequences on cell signaling pathways is essential.

How does PTGR1 influence the efficacy of anticancer prodrugs?

PTGR1 has been shown to activate certain prodrugs containing α/β-unsaturated ketone structures, such as hydroxymethylacylfulvene (HMAF) . Studies have demonstrated that human HEK293 cells overexpressing PTGR1 were 100 times more sensitive to HMAF than control cells . This correlation has been confirmed across the NCI 60 human tumor cell line panel, with PTGR1 activity positively correlating with HMAF sensitivity . NRF2 inducers that enhance PTGR1 expression, including D3T, resveratrol, and curcumin, have been shown to significantly increase HMAF sensitivity in colon and liver cancer cell lines by 2 to 10-fold . These findings suggest that PTGR1 expression levels could serve as a biomarker for predicting response to HMAF and similar prodrugs. A recent study has identified patients who might be eligible for acylfulvene clinical trials based on PTGR1 expression by IHC staining, demonstrating the translational potential of this research .

What is the relationship between PTGR1 and metformin resistance in prostate cancer?

Recent research has identified a novel role for PTGR1 in metformin resistance in prostate cancer (PCa). In metformin-resistant PCa cells, PTGR1 is upregulated and associated with cell cycle reactivation . Single-cell transcriptome sequencing revealed significantly increased PTGR1 expression in a cluster of cells with metformin resistance . Functional experiments demonstrated that PTGR1 overexpression accelerated cell cycle progression by promoting the transition from G0/G1 to S and G2/M phases, resulting in reduced sensitivity to metformin . This resistance mechanism involves an upstream super-enhancer (SE) that increases PTGR1 expression when bound by transcription factors SRF and RUNX3 . To investigate this mechanism, researchers should consider employing cell cycle analysis techniques (flow cytometry), single-cell RNA sequencing, and chromatin immunoprecipitation sequencing (ChIP-seq) to comprehensively assess the role of PTGR1 in drug resistance.

What are the key considerations when modulating PTGR1 expression in experimental models?

When designing experiments to modulate PTGR1 expression, researchers should consider several approaches, each with distinct advantages and limitations:

• Genetic knockdown: siRNA or shRNA approaches can effectively reduce PTGR1 expression, with previous studies demonstrating significant effects on cancer cell proliferation, cell cycle progression, and apoptosis . For maximum reliability, researchers should use multiple siRNA sequences to rule out off-target effects.

• Overexpression models: Transfection with PTGR1 expression vectors can create gain-of-function models to study enzyme activity and drug sensitivity. Doxycycline-inducible systems offer temporal control over expression levels.

• Pharmacological inhibition: While current PTGR1 inhibitors have relatively low potency (μM range), they can serve as chemical tools to investigate PTGR1 function . Dose-response curves and careful controls are essential when using these compounds.

• NRF2 pathway modulation: Since PTGR1 is regulated by NRF2, compounds like D3T, resveratrol, and curcumin can be used to indirectly increase PTGR1 expression . Researchers should verify that observed effects are specifically due to PTGR1 upregulation rather than other NRF2-regulated genes.

• CRISPR-Cas9 gene editing: For stable knockout models, CRISPR-Cas9 targeting of PTGR1 provides a more complete elimination of protein expression compared to knockdown approaches.

How should researchers approach investigating the complex role of PTGR1 in cancer, given its contradictory effects across different cancer types?

The contradictory effects of PTGR1 across different cancer types present a significant research challenge. To address this complexity, researchers should:

• Use tissue-specific models: When investigating PTGR1, researchers should use models relevant to the specific cancer type of interest, as PTGR1's effects appear highly context-dependent .

• Employ multi-omics approaches: Integrating transcriptomics, proteomics, and metabolomics data can help identify tissue-specific pathways and metabolites through which PTGR1 exerts its effects.

• Consider treatment status: When analyzing PTGR1 expression in relation to cancer survival, it's crucial to account for treatment history, particularly with drugs like irofulven whose efficacy is affected by PTGR1 levels .

• Investigate metabolic products: One hypothesis for PTGR1's contradictory effects is that it might produce metabolites with different effects in different cancer contexts. Identifying these specific metabolites should be a research priority .

• Examine pathway crosstalk: Researchers should investigate how PTGR1 interacts with other cancer-relevant pathways, including oxidative stress responses, which might explain its differential effects across cancer types.

What is the significance of PTGR1 in relation to DNA repair mechanisms and cancer therapy?

Recent research has begun to explore connections between PTGR1 expression and DNA repair mechanisms, particularly nucleotide excision repair (NER) deficiency. In a study of bladder cancer patients, 13% of the cohort was identified as both NER-deficient (having mutations in ERCC1, ERCC2, ERCC3, ERCC4) and PTGR1-positive . This co-occurrence may have implications for therapeutic strategies, as cancers with defective DNA repair mechanisms often show increased sensitivity to certain chemotherapeutics. For researchers investigating this relationship, comprehensive genomic profiling should be employed to identify mutations in NER pathway genes alongside PTGR1 expression analysis. DNA damage assays (such as comet assay or γH2AX foci detection) can provide functional validation of repair deficiencies, while drug sensitivity testing with agents targeting cells with compromised DNA repair (like platinum compounds) may reveal synthetic lethal interactions with PTGR1 status.

How can multi-omics data integration advance our understanding of PTGR1's role in cancer metabolism?

PTGR1's involvement in metabolic pathways and its differential effects across cancer types suggest that a multi-omics approach could significantly enhance our understanding of its functions. Researchers should consider:

• Integrated transcriptomics and metabolomics: Correlating PTGR1 expression levels with global metabolite profiles can identify specific metabolic pathways affected by PTGR1 activity.

• Lipidomics: Given PTGR1's role in eicosanoid metabolism, detailed lipidomic profiling before and after PTGR1 modulation could identify specific lipid species regulated by this enzyme.

• Epigenomic analysis: H3K27ac ChIP-Seq has already identified super-enhancers regulating PTGR1 expression . Further epigenomic profiling could reveal additional regulatory mechanisms.

• Single-cell approaches: As demonstrated in metformin resistance research, single-cell RNA sequencing can identify specific cell populations with altered PTGR1 expression , potentially revealing functional heterogeneity within tumors.

• Proteomics: Interactome studies using co-immunoprecipitation followed by mass spectrometry could identify PTGR1 protein-protein interactions that influence its function in different cellular contexts.

What are the most promising strategies for developing more potent and selective PTGR1 modulators?

Current PTGR1 inhibitors lack potency and have not advanced to clinical trials . To develop improved PTGR1 modulators, researchers should consider:

• Structure-based drug design: Utilizing crystallographic data of PTGR1 to design compounds with improved binding affinity and selectivity.

• Fragment-based screening: Identifying small molecular fragments that bind to PTGR1 and subsequently optimizing these into lead compounds.

• Allosteric modulators: Exploring binding sites beyond the catalytic center that might alter enzyme activity through conformational changes.

• Targeted protein degradation: Developing PROTAC (proteolysis targeting chimera) molecules that could induce selective degradation of PTGR1 rather than just inhibiting its activity.

• Combination approaches: As suggested by research, exploring the potential of combining PTGR1 modulators with other agents, such as ROS-inducing compounds or standard chemotherapeutics .

How might understanding temporary, non-mutational resistance mechanisms involving PTGR1 impact cancer treatment strategies?

Research on metformin resistance in prostate cancer has revealed that PTGR1-mediated resistance appears to be a temporary, non-mutational phenotype. After 30 days of drug withdrawal, metformin-resistant cells regained sensitivity to the drug . This finding has important implications for cancer treatment strategies:

• Drug holiday approaches: Understanding the dynamics of PTGR1-mediated resistance could inform the design of intermittent dosing schedules that prevent or delay resistance development.

• Adaptive therapy: Rather than aiming for maximum tumor cell killing, adaptive therapy approaches that maintain a stable population of drug-sensitive cells might prevent the emergence of resistant populations with elevated PTGR1.

• Sequential therapy strategies: Targeting the PTGR1 pathway during drug holidays could potentially eliminate resistant cells and restore sensitivity to the primary therapy.

• Biomarker-guided treatment decisions: Monitoring PTGR1 expression levels during treatment could guide clinical decision-making about when to switch therapies or implement drug holidays.

• Epigenetic modifiers: Since the resistance mechanism appears to be non-mutational and potentially epigenetic in nature, combining primary therapy with epigenetic modifiers might prevent or reverse PTGR1-mediated resistance.