PPARα Enhances Cancer Cell Chemotherapy Sensitivity by Autophagy Induction

IGF2BP3 modified GLI2 transcriptionally regulates SYVN1 and facilitates sepsis liver injury through autophagy

Autophagy enhancement in septic liver injury can play a protective role. Nerveless, the mechanism of autophagy-mediated septic liver injury needs further investigation. Our study demonstrated that in septic condition, GLI Family Zinc Finger 2 (GLI2) was elevated, whereas peroxisome-proliferator-activated receptor α (PPARα) was downregulated. Suppressing GLI2 or synovialapoptosis inhibitor 1 (SYVN1) in LPS-exposed cells increased PPARα levels, enhanced cell viability and autophagy, while inhibiting apoptosis. LPS enhanced the GLI2-SYVN1 promoter binding. SYVN1 fostered ubiquitin-mediated degradation of PPARα. IGF2BP3 stabilized GLI2 mRNA by targeting its m6A site. Silencing IGF2BP3 led to decreased GLI2 and SYVN1 but increased PPARα levels, promoting cell survival and autophagy, while repressing apoptosis. This was counteracted by SYVN1 overexpression. In cecal ligation and puncture mice, IGF2BP3, SYVN1, or GLI2 knockdown ameliorated liver damage and augmented autophagy. In summary, IGF2BP3 enhanced GLI2 stability, overexpressed GLI2 subsequent promoted SYVN1 levels by interacting with its promoter, leading to ubiquitinated degradation of PPARα, thereby inhibiting PPARα-mediated autophagy and then exacerbating liver injury in sepsis.

Nuclear Receptor PPARα as a Therapeutic Target in Diseases Associated with Lipid Metabolism Disorders

Lipid metabolic diseases have substantial morbidity and mortality rates, posing a significant threat to human health. PPARα, a member of the peroxisome proliferator-activated receptors (PPARs), plays a crucial role in lipid metabolism and immune regulation. Recent studies have increasingly recognized the pivotal involvement of PPARα in diverse pathological conditions. This comprehensive review aims to elucidate the multifaceted role of PPARα in metabolic diseases including liver diseases, diabetes-related diseases, age-related diseases, and cancers, shedding light on the underlying molecular mechanisms and some regulatory effects of natural/synthetic ligands of PPARα. By summarizing the latest research findings on PPARα, we aim to provide a foundation for the possible therapeutic exploitation of PPARα in lipid metabolic diseases.

The role of peroxisome proliferator-activated receptors in the tumor microenvironment, tumor cell metabolism, and anticancer therapy

Peroxisome proliferator-activated receptors (PPARs) have been extensively studied for over 3 decades and consist of three isotypes, including PPARα, γ, and β/δ, that were originally considered key metabolic regulators controlling energy homeostasis in the body. Cancer has become a leading cause of human mortality worldwide, and the role of peroxisome proliferator-activated receptors in cancer is increasingly being investigated, especially the deep molecular mechanisms and effective cancer therapies. Peroxisome proliferator-activated receptors are an important class of lipid sensors and are involved in the regulation of multiple metabolic pathways and cell fate. They can regulate cancer progression in different tissues by activating endogenous or synthetic compounds. This review emphasizes the significance and knowledge of peroxisome proliferator-activated receptors in the tumor microenvironment, tumor cell metabolism, and anti-cancer treatment by summarizing recent research on peroxisome proliferator-activated receptors. In general, peroxisome proliferator-activated receptors either promote or suppress cancer in different types of tumor microenvironments. The emergence of this difference depends on various factors, including peroxisome proliferator-activated receptor type, cancer type, and tumor stage. Simultaneously, the effect of anti-cancer therapy based on drug-targeted PPARs differs or even opposes among the three peroxisome proliferator-activated receptor homotypes and different cancer types. Therefore, the current status and challenges of the use of peroxisome proliferator-activated receptors agonists and antagonists in cancer treatment are further explored in this review.

The pleiotropic peroxisome proliferator activated receptors: Regulation and therapeutics

The Peroxisome proliferator-activated receptors (PPARs) are key regulators of metabolic events in our body. Owing to their implication in maintenance of homeostasis, both PPAR agonists and antagonists assume therapeutic significance. Understanding the molecular mechanisms of each of the PPAR isotypes in the healthy body and during disease is crucial to exploiting their full therapeutic potential. This article is an attempt to present a rational analysis of the multifaceted therapeutic effects and underlying mechanisms of isotype-specific PPAR agonists, dual PPAR agonists, pan PPAR agonists as well as PPAR antagonists. A holistic understanding of the mechanistic dimensions of these key metabolic regulators will guide future efforts to identify novel molecules in the realm of metabolic, inflammatory and immunotherapeutic diseases.

PPAR-α Modulators as Current and Potential Cancer Treatments

Cancer is one of the leading causes of mortality worldwide. PPAR modulators may hold great potential for the management of cancer patients. Indeed, PPARs are critical sensors and regulators of lipid, and they are able to promote eNOS activation, regulate immunity and inflammation response, and affect proliferation and differentiation of cancer cells. Cancer, a name given to a group of diseases, is characterized by multiple distinctive biological behaviors, including angiogenesis, abnormal cell proliferation, aerobic glycolysis, inflammation, etc. In the last decade, emerging evidence has shown that PPAR-α, a nuclear hormone receptor, can modulate carcinogenesis via exerting effects on one or several characteristic pathological behaviors of cancer. Therefore, the multi-functional PPAR modulators have substantial promise in various types of cancer therapies. This review aims to consolidate the functions of PPAR-α, as well as discuss the current and potential applications of PPAR-α agonists and antagonists in tackling cancer.

All-trans-retinoic acid inhibits the malignant behaviors of hepatocarcinoma cells by regulating autophagy

Hepatocellular carcinoma is the fourth leading cause of cancer-related deaths due to its high rate of recurrence and metastasis. All-trans-retinoic acid (ATRA) can inhibit the malignant behaviors of hepatocarcinoma cells. Autophagy is reportedly involved in the migration and metastasis of various cancer cells. This study aimed to investigate the effect of autophagy on the function of ATRA on hepatocarcinoma cells, and to explore its possible underlying mechanism. Hepatocarcinoma cell lines, Hepa1-6 and HepG2, were treated with ATRA and autophagy inhibitors, including 3-methyladenine (3-MA) and Bafilomycin (Baf). Transmission electron microscopy, laser scanning, western blot, and real-time PCR demonstrated that ATRA induces autophagy in hepatocarcinoma cells. Trypan blue staining, a wound healing assay, and a transwell assay showed that 3-MA and Baf reverses the inhibitory functions of ATRA on the proliferation, migration, and invasion of hepatocarcinoma cells. Flow cytometry, Hoechst staining, periodic acid-Schiff staining, and indocyanine green uptake validated that 3-MA and Baf reverses the function of ATRA on apoptosis and the differentiation of hepatocarcinoma cells. Real-time PCR, western blot, and an immunofluorescence assay demonstrated that the reversal of the epithelial-mesenchymal transition (EMT) process by ATRA is weakened when autophagy is inhibited. Additionally, we confirmed that Bcl-2 is associated with the induction of ATRA-induced autophagy instead of the PI3K/Akt/mTOR pathway. These findings suggest that ATRA induces autophagy and autophagic cell death through the Bcl-2/Beclin1 pathway. Furthermore, ATRA-induced autophagy is involved in the inhibitory effect of ATRA on the malignant behaviors of hepatocarcinoma cells by reversing the EMT process.

PPARδ is a regulator of autophagy by its phosphorylation

In response to nutrient deficiency, autophagy degrades cytoplasmic materials and organelles in lysosomes, which is nutrient recycling, whereas activation of EGFR mediates autophagy suppression in response to growth factors. It is unclear whether PPARδ could be the regulator of autophagy in response to active EGFR. Here we found that EGFR induced PPARδ phosphorylation at tyrosine-108 leading to increased binding of LC3 to PPARδ by its LIR (LC3 interacting region) motif, consequently, inhibited autophagic flux. Conversely, EGFR inhibitor treatment reversed this event. Furthermore, EGFR-mediated PPARδ phosphorylation at tyrosine-108 led to autophagy inhibition and tumor growth. These findings suggest that PPARδ serves as a regulator of autophagy by its phosphorylation.

PPARα agonist alleviates tumor growth and chemo-resistance associated with the inhibition of glucose metabolic pathway

As a nuclear receptor, peroxisome-proliferator-activated receptor α (PPARα) plays a critical role in regulation of metabolism and cancer, while the effect of PPARα agonist on cancer cell glucose metabolism-linked tumor growth is still unclear. Here we found that PPARα agonist (Wy14,643) decreased Glut1 (Glucose transporter 1) gene and protein expressions of colorectal cancer cell lines in response to normoxia or hypoxia. Dual-luciferase analysis showed that Wy14,643 inhibited Glut1 transcription activity. Importantly, ChIP-qPCR analysis showed that Wy14,643 increased the binding of PPARα to Glut1 promoter region. Wy14,643 suppressed Glut1 transcription activity resulting in reduced influx of glucose in cancer cells in response to normoxia or hypoxia. Further analysis showed that Wy14,643-mediated inhibition of tumor growth and chemo-resistance was associated with inhibition of mTOR pathway. Taken together, PPARα agonist Wy14,643 suppressed Glut1 transcription activity, glucose uptake and mTOR pathway in colorectal cancer cells, which was involved in reduced tumor growth and chemo-resistance. These findings provided a novel therapy strategy for cancer progression.