Punicalagin as a novel selective aryl hydrocarbon receptor (AhR) modulator upregulates AhR expression through the PDK1/p90RSK/AP-1 pathway to promote the anti-inflammatory response and bactericidal activity of macrophages.

Aryl hydrocarbon receptor (AhR) plays an important role in inflammation and immunity as a new therapeutic target for infectious disease and sepsis. Punicalagin (PUN) is a Chinese herbal monomer extract of pomegranate peel that has beneficial anti-inflammatory, antioxidant and anti-infective effects. However, whether PUN is a ligand of AhR, its effect on AhR expression, and its signaling pathway remain poorly understood. In this study, we found that PUN was a unique polyphenolic compound that upregulated AhR expression at the transcriptional level, and regulated the AhR nongenomic pathway. AhR expression in lipopolysaccharide-induced macrophages was upregulated by PUN in vitro and in vivo in a time- and dose-dependent manner. Using specific inhibitors and siRNA, induction of AhR by PUN depended on sequential phosphorylation of 90-kDa ribosomal S6 kinase (p90RSK), which was activated by the mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) and phosphoinositide-dependent protein kinase (PDK)1 pathways. PUN promoted p90RSK-mediated activator protein-1 (AP-1) activation. AhR knockout or inhibitors reversed suppression of interleukin (IL)-6 and IL-1ß expression by PUN. PUN decreased Listeria load and increased macrophage survival via AhR upregulation. In conclusion, we identified PUN as a novel selective AhR modulator involved in AhR expression via the MEK/ERK and PDK1 pathways targeting p90RSK/AP-1 in inflammatory macrophages, which inhibited macrophage inflammation and promoted bactericidal activity.

Novel Dichloroacetophenone-Based PDHK1 Inhibitors as Potent Anticancer Agents.

Background: Pyruvate dehydrogenase kinases (PDHKs), important metabolic and abnormally expressed enzymes in cancer cells, are promising targets for cancer therapy, especially for non-small-cell lung cancer (NSCLC). Methods: In this study, a new hit, dichloroacetophenone (DAP) analog 9, was postulated to bind to the PDHK1 allosteric pocket, guided by molecular modeling and kinase biochemical experiments. Based on this binding mode, novel DAP analogs were designed and synthesized to confirm the importance of Phe180, Tyr411, and the hydrophobic core at the bottom of the pocket. Results: This structure-activity relationship (SAR) study led to the discovery of a novel potent hybrid scaffold, dichloroacetophenone biphenylsulfone ether. Dichloroacetophenone biphenylsulfone ether 31 and 32 inhibited PDHK1 with IC50 values of 86 and 140 nM, respectively. Conclusion: Compound 32 with acceptable in vitro metabolic stability, predicted drug-likeness properties and ADME/T profiles, showed promising therapeutic efficacy in a lung cancer xenograft mouse model.

Pdk3's role in RANKL-induced osteoclast differentiation: insights from a bone marrow macrophage model.

Background: Osteoporosis (OP) is a chronic disease characterized by decreased bone mass, loss of skeletal structural integrity and increased susceptibility to fracture. Available studies have shown that the pyruvate dehydrogenase kinase (PDK) family is associated with osteoclastogenesis and bone loss, but the specific role of Pdk3 in bone pathology has not been systematically investigated. Methods: A cell OP model was established in receptor activator for nuclear factor-κB Ligand (RANKL)-induced bone marrow macrophages (BMMs). Hereafter, the expression levels of Pdk3 and osteoclastogenesis feature genes including nuclear factor of activated T cells 1 (Nfatc1), Cathepsin K (Ctsk), osteoclast associated Ig-like receptor (Oscar) in BMMs-derived osteoclasts were examined based on real-time quantitative PCR and western blotting methods. Further, the phosphorylation of ERK, P65 and JAK/STAT and their correlation was Pdk3 was gauged. In particular, changes in the activity of these signaling pathways were observed by silencing experiments of the Pdk3 gene (using small interfering RNA). Finally, the effects of Pdk3 gene silencing on signaling pathway activity, osteoclastogenesis, and related inflammatory and apoptotic indicators were observed by transfection with PDK3-specific siRNA. Results: Following RANKL exposure, the levels of Pdk3 and osteoclastogenesis feature genes were all elevated, and a positive correlation between Pdk3 and osteoclastogenesis feature genes was seen. Meanwhile, ERK, P65 and JAK/STAT phosphorylation was increased by RANKL, and Pdk3 was confirmed to be positively correlated with the phosphorylation of ERK, P65 and JAK/STAT. Additionally, in RANKL-exposed osteoclasts, Pdk3 knockdown diminished the phosphorylation of ERK, P65 and JAK/STAT, reduced the expressions of osteoclastogenesis feature genes. Importantly, knockdown of Pdk3 also reduced the expression of inflammatory cytokines and resulted in elevated levels of Bax and Casp3 expression, as well as downregulation of Bcl2 expression. Conclusion: This study reveals for the first time the role of Pdk3 in RANKL-induced osteoclastogenesis and OP. These findings provide a foundation for future studies on the role of Pdk3 in other bone diseases and provide new ideas for the development of OP therapeutics targeting Pdk3.

Higher levels of AKT-interacting protein in the frontal pole from people with schizophrenia are limited to a sub-group who have a marked deficit in cortical muscarinic M1 receptors.

We are studying the molecular pathology of a sub-group within schizophrenia (∼ 25 %: termed Muscarinic Receptor Deficit subgroup of Schizophrenia (MRDS)) who can be separated because they have very low levels of cortical muscarinic M1 receptors (CHRM1). Based on our transcriptomic data from Brodmann's area ((BA) 9, 10 and 33 (controls, schizophrenia and mood disorders) and the cortex of the CHRM1-/- mouse (a molecular model of aberrant CHRM1 signaling), we predicted levels of AKT interacting protein (AKTIP), but not tubulin alpha 1b (TUBA1B) or AKT serine/threonine kinase 1 (AKT1) and pyruvate dehydrogenase kinase 1 (PDK1) (two AKTIP-functionally associated proteins), would be changed in MRDS. Hence, we used Western blotting to measure AKTIP (BA 10: controls, schizophrenia and mood disorders; BA 9: controls and schizophrenia) plus TUBA1B, AKT1 and PDK1 (BA 10: controls and schizophrenia) proteins. The only significant change with diagnosis was higher levels of AKTIP protein in BA 10 (Cohen's d = 0.73; p = 0.02) in schizophrenia compared to controls due to higher levels of AKTIP only in people with MRDS (Cohen's d = 0.80; p = 0.03). As AKTIP is involved in AKT1 signaling, our data suggests that signaling pathway is particularly disturbed in BA 10 in MRDS.

Identification of STAM-binding protein as a target for the treatment of gemcitabine resistance pancreatic cancer in a nutrient-poor microenvironment.

Pancreatic cancer (PC) is a highly malignant solid tumor whose resistance to gemcitabine (GEM) chemotherapy is a major cause of poor patient prognosis. Although PC is known to thrive on malnutrition, the mechanism underlying its chemotherapy resistance remains unclear. The current study analyzed clinical tissue sample databases using bioinformatics tools and observed significantly upregulated expression of the deubiquitinase STAMBP in PC tissues. Functional experiments revealed that STAMBP knockdown remarkably increases GEM sensitivity in PC cells. Multiple omics analyses suggested that STAMBP enhances aerobic glycolysis and suppresses mitochondrial respiration to increase GEM resistance in PC both in vitro and in vivo. STAMBP knockdown decreased PDK1 levels, an essential regulator of the aerobic glycolytic process, in several cancers. Mechanistically, STAMBP promoted the PDK1-mediated Warburg effect and chemotherapy resistance by modulating E2F1 via direct binding to E2F1 and suppressing its degradation and ubiquitination. High-throughput compound library screening using three-dimensional protein structure analysis and drug screening identified the FDA drug entrectinib as a potent GEM sensitizer and STAMBP inhibitor, augmenting the antitumor effect of GEM in a patient-derived xenograft (PDX) model. Overall, we established a novel mechanism, via the STAMBP-E2F1-PDK1 axis, by which PC cells become chemoresistant in a nutrient-poor tumor microenvironment.

Oroxylin A, a broad­spectrum anticancer agent, relieves monocrotaline­induced pulmonary arterial hypertension by inhibiting the Warburg effect in rats.

Pulmonary arterial hypertension (PAH) is a chronic and fatal disease characterized by pulmonary vascular remodeling, similar to the 'Warburg effect' observed in cancer, which is caused by reprogramming of glucose metabolism. Oroxylin A (OA), an active compound derived from Scutellaria baicalensis, which can inhibit glycolytic enzymes [hexokinase 2 (HK2), Lactate dehydrogenase (LDH), and pyruvate dehydrogenase kinase 1 (PDK1) by downregulating aerobic glycolysis to achieve the treatment of liver cancer. To the best of our knowledge, however, the impact of OA on PAH has not been addressed. Consequently, the present study aimed to evaluate the potential protective role and mechanism of OA against PAH induced by monocrotaline (MCT; 55 mg/kg). The mean pulmonary artery pressure (mPAP) was measured using the central venous catheter method; HE and Masson staining were used to observe pulmonary artery remodeling. Non­targeted metabolomics was used to analyze the metabolic pathways and pathway metabolites in MCT­PAH rats. Western Blot analysis was employed to assess the levels of glucose transporter 1 (Glut1), HK2), pyruvate kinase (PK), isocitrate dehydrogenase 2 (IDH2), pyruvate dehydrogenase kinase 1(PDK1), and lactate dehydrogenase (LDH) protein expression in both lung tissue samples from MCT­PAH rats. The results demonstrated that intragastric administration of OA (40 and 80 mg/kg) significantly decreased mPAP from 43.61±1.88 mmHg in PAH model rats to 26.51±1.53 mmHg and relieve pulmonary artery remodeling. Untargeted metabolomic analysis and multivariate analysis indicated abnormal glucose metabolic pattern in PAH model rats, consistent with the Warburg effect. OA administration decreased this effect on the abnormal glucose metabolism. The protein levels of key enzymes involved in glucose metabolism were evaluated by western blotting, which demonstrated that OA could improve aerobic glycolysis and inhibit PAH by decreasing the protein levels of Glut1, HK2, LDH, PDK1 and increasing the protein levels of PK and IDH2. In conclusion, OA decreased MCT­induced PAH in rats by reducing the Warburg effect.

A novel PDHK inhibitor restored cognitive dysfunction and limited neurodegeneration without affecting amyloid pathology in 5xFAD mouse, a model of Alzheimer's disease.

BACKGROUND: Alzheimer's disease (AD) is the most common form of dementia. Although drugs focusing on reducing amyloid ß slow progression, they fail to improve cognitive function. Deficits in glucose metabolism are reflected in FDG-PET and parallel the neurodegeneration and synaptic marker loss closely preceding cognitive decline, but the role of metabolic deficits as a cause or consequence of neurodegeneration is unclear. Pyruvate dehydrogenase (PDH) is lost in AD and an important enzyme connecting glycolysis and the tricarboxylic acid (TCA) cycle by converting pyruvate into acetyl-CoA. It is negatively regulated by pyruvate dehydrogenase kinase (PDHK) through phosphorylation. METHODS: In the present study, we assessed the in vitro/ in vivo pharmacological profile of the novel PDHK inhibitor that we discovered, Compound A. We also assessed the effects of Compound A on AD-related phenotypes including neuron loss and cognitive impairment using 5xFAD model mice. RESULTS: Compound A inhibited human PDHK1, 2 and 3 but had no inhibitory activity on PDHK4. In primary neurons, Compound A enhanced pyruvate and lactate utilization, but did not change glucose levels. In contrast, in primary astrocytes, Compound A enhanced pyruvate and glucose utilization and enhanced lactate production. In an efficacy study using 5xFAD mice, Compound A ameliorated the cognitive dysfunction in the novel object recognition test and Morris water maze. Moreover, Compound A prevented neuron loss in the hippocampus and cerebral cortex of 5xFAD without affecting amyloid ß deposits. CONCLUSIONS: These results suggest ameliorating metabolic deficits by activating PDH by Compound A can limit neurodegeneration and is a promising therapeutic strategy for treating AD.

Chronic Corticosterone Treatment Decreases Extracellular pH and Increases Lactate Release via PDK4 Upregulation in Cultured Astrocytes.

The pathogenesis of stress-related disorders involves aberrant glucocorticoid secretion, and decreased pH and increased lactate in the brain are common phenotypes in several psychiatric disorders. Mice treated with glucocorticoids develop these phenotypes, but it is unclear how glucocorticoids affect brain pH. Therefore, we investigated the effect of corticosterone (CORT), the main glucocorticoid in rodents, on extracellular pH and lactate release in cultured astrocytes, which are the main glial cells that produce lactate in the brain. CORT treatment for one week decreased the extracellular pH and increased the extracellular lactate level via glucocorticoid receptors. CORT also increased the intracellular pyruvate level and upregulated pyruvate dehydrogenase kinase 4 (PDK4), while PDK4 overexpression increased extracellular lactate and decreased the extracellular pH. Furthermore, PDK4 inhibition suppressed the increase in extracellular lactate and the decrease in extracellular pH induced by CORT. These results suggest that increased lactate release via accumulation of intracellular pyruvate in astrocytes by chronic glucocorticoid exposure contributes to decreased brain pH.

Capturing Autoinhibited PDK1 Reveals the Linker's Regulatory Role, Informing Innovative Inhibitor Design.

PDK1 is crucial for PI3K/AKT/mTOR and Ras/MAPK cancer signaling. It phosphorylates AKT in a PIP3-dependent but S6K, SGK, and RSK kinases in a PIP3-independent manner. Unlike its substrates, its autoinhibited monomeric state has been unclear, likely due to its low population time, and phosphorylation in the absence of PIP3 has been puzzling too. Here, guided by experimental data, we constructed models and performed all-atom molecular dynamics simulations. In the autoinhibited PDK1 conformation that resembles autoinhibited AKT, binding of the linker between the kinase and PH domains to the PIF-binding pocket promotes the formation of the Glu130-Lys111 salt bridge and weakens the association of the kinase domain with the PH domain, shifting the population from the autoinhibited state to states accessible to the membrane and its kinase substrates. The interaction of the substrates' hydrophobic motif and the PDK1 PIF-binding pocket facilitates the release of the autoinhibition even in the absence of PIP3. Phosphorylation of the serine-rich motif within the linker further attenuates the association of the PH domain with the kinase domain. These suggest that while the monomeric autoinhibited state is relatively stable, it can readily shift to its active, catalysis-prone state to phosphorylate its diverse substrates. Our findings reveal the PDK1 activation mechanism and discover the regulatory role of PDK1's linker, which lead to two innovative linker-based inhibitor strategies: (i) locking the autoinhibited PDK1 through optimization of the interactions of AKT inhibitors with the PH domain of PDK1 and (ii) analogs (small molecules or peptidomimetics) that mimic the linker interactions with the PIF-binding pocket.

The activity of therapeutic molecular cluster Ag5 is dependent on oxygen level and HIF-1 mediated signalling.

Regions of hypoxia occur in most solid tumours and are known to significantly impact therapy response and patient prognosis. Ag5 is a recently reported silver molecular cluster which inhibits both glutathione and thioredoxin signalling therefore limiting cellular antioxidant capacity. Ag5 treatment significantly reduces cell viability in a range of cancer cell lines with little to no impact on non-transformed cells. Characterisation of redox homeostasis in hypoxia demonstrated an increase in reactive oxygen species and glutathione albeit with different kinetics. Significant Ag5-mediated loss of viability was observed in a range of hypoxic conditions which mimic the tumour microenvironment however, this effect was reduced compared to normoxic conditions. Reduced sensitivity to Ag5 in hypoxia was attributed to HIF-1 mediated signalling to reduce PDH via PDK1/3 activity and changes in mitochondrial oxygen availability. Importantly, the addition of Ag5 significantly increased radiation-induced cell death in hypoxic conditions associated with radioresistance. Together, these data demonstrate Ag5 is a potent and cancer specific agent which could be used effectively in combination with radiotherapy.

PDK4-mediated metabolic reprogramming is a potential therapeutic target for neovascular age-related macular degeneration.

Age-related macular degeneration (AMD) causes severe blindness in the elderly due to choroidal neovascularization (CNV), which results from the dysfunction of the retinal pigment epithelium (RPE). While normal RPE depends exclusively on mitochondrial oxidative phosphorylation for energy production, the inflammatory conditions associated with metabolic reprogramming of the RPE play a pivotal role in CNV. Although mitochondrial pyruvate dehydrogenase kinase (PDK) is a central node of energy metabolism, its role in the development of CNV in neovascular AMD has not been investigated. In the present study, we used a laser-induced CNV mouse model to evaluate the effects of Pdk4 gene ablation and treatment with pan-PDK or specific PDK4 inhibitors on fluorescein angiography and CNV lesion area. Among PDK isoforms, only PDK4 was upregulated in the RPE of laser-induced CNV mice, and Pdk4 gene ablation attenuated CNV. Next, we evaluated mitochondrial changes mediated by PDK1-4 inhibition using siRNA or PDK inhibitors in inflammatory cytokine mixture (ICM)-treated primary human RPE (hRPE) cells. PDK4 silencing only in ICM-treated hRPE cells restored mitochondrial respiration and reduced inflammatory cytokine secretion. Likewise, GM10395, a specific PDK4 inhibitor, restored oxidative phosphorylation and decreased ICM-induced upregulation of inflammatory cytokine secretion. In a laser-induced CNV mouse model, GM10395 significantly alleviated CNV. Taken together, we demonstrate that specific PDK4 inhibition could be a therapeutic strategy for neovascular AMD by preventing mitochondrial metabolic reprogramming in the RPE under inflammatory conditions.

Hypoxia-induced downregulation of PGK1 crotonylation promotes tumorigenesis by coordinating glycolysis and the TCA cycle.

Protein post-translational modifications (PTMs) are crucial for cancer cells to adapt to hypoxia; however, the functional significance of lysine crotonylation (Kcr) in hypoxia remains unclear. Herein we report a quantitative proteomics analysis of global crotonylome under normoxia and hypoxia, and demonstrate 128 Kcr site alterations across 101 proteins in MDA-MB231 cells. Specifically, we observe a significant decrease in K131cr, K156cr and K220cr of phosphoglycerate kinase 1 (PGK1) upon hypoxia. Enoyl-CoA hydratase 1 (ECHS1) is upregulated and interacts with PGK1, leading to the downregulation of PGK1 Kcr under hypoxia. Abolishment of PGK1 Kcr promotes glycolysis and suppresses mitochondrial pyruvate metabolism by activating pyruvate dehydrogenase kinase 1 (PDHK1). A low PGK1 K131cr level is correlated with malignancy and poor prognosis of breast cancer. Our findings show that PGK1 Kcr is a signal in coordinating glycolysis and the tricarboxylic acid (TCA) cycle and may serve as a diagnostic indicator for breast cancer.

Identification of programmed cell death-related genes and diagnostic biomarkers in endometriosis using a machine learning and Mendelian randomization approach.

Background: Endometriosis (EM) is a prevalent gynecological disorder frequently associated with irregular menstruation and infertility. Programmed cell death (PCD) is pivotal in the pathophysiological mechanisms underlying EM. Despite this, the precise pathogenesis of EM remains poorly understood, leading to diagnostic delays. Consequently, identifying biomarkers associated with PCD is critical for advancing the diagnosis and treatment of EM. Methods: This study used datasets from the Gene Expression Omnibus (GEO) to identify differentially expressed genes (DEGs) following preprocessing. By cross-referencing these DEGs with genes associated with PCD, differentially expressed PCD-related genes (DPGs) were identified. Enrichment analyses for KEGG and GO pathways were conducted on these DPGs. Additionally, Mendelian randomization and machine learning techniques were applied to identify biomarkers strongly associated with EM. Results: The study identified three pivotal biomarkers: TNFSF12, AP3M1, and PDK2, and established a diagnostic model for EM based on these genes. The results revealed a marked upregulation of TNFSF12 and PDK2 in EM samples, coupled with a significant downregulation of AP3M1. Single-cell analysis further underscored the potential of TNFSF12, AP3M1, and PDK2 as biomarkers for EM. Additionally, molecular docking studies demonstrated that these genes exhibit significant binding affinities with drugs currently utilized in clinical practice. Conclusion: This study systematically elucidated the molecular characteristics of PCD in EM and identified TNFSF12, AP3M1, and PDK2 as key biomarkers. These findings provide new directions for the early diagnosis and personalized treatment of EM.

Decreased AMPK/SIRT1/PDK4 induced by androgen excess inhibits human endometrial stromal cell decidualization in PCOS.

Polycystic ovary syndrome (PCOS) is a complex common endocrine disorder affecting women of reproductive age. Ovulatory dysfunction is recognized as a primary infertile factor, however, even when ovulation is medically induced and restored, PCOS patients continue to experience reduced cumulative pregnancy rates and a higher spontaneous miscarriage rate. Hyperandrogenism, a hallmark feature of PCOS, affects ovarian folliculogenesis, endometrial receptivity, and the establishment and maintenance of pregnancy. Decidualization denotes the transformation that the stromal compart of the endometrium must undergo to accommodate pregnancy, driven by the rising progesterone levels and local cAMP production. However, studies on the impact of hyperandrogenism on decidualization are limited. In this study, we observed that primary endometrial stromal cells from women with PCOS exhibit abnormal responses to progesterone during in vitro decidualization. A high concentration of testosterone inhibits human endometrial stromal cells (HESCs) decidualization. RNA-Seq analysis demonstrated that pyruvate dehydrogenase kinase 4 (PDK4) expression was significantly lower in the endometrium of PCOS patients with hyperandrogenism compared to those without hyperandrogenism. We also characterized that the expression of PDK4 is elevated in the endometrium stroma at the mid-secretory phase. Artificial decidualization could enhance PDK4 expression, while downregulation of PDK4 leads to abnormal decidualization both in vivo and in vitro. Mechanistically, testosterone excess inhibits IGFBP1 and PRL expression, followed by phosphorylating of AMPK that stimulates PDK4 expression. Based on co-immunoprecipitation analysis, we observed an interaction between SIRT1 and PDK4, promoting glycolysis to facilitate decidualization. Restrain of AR activation resumes the AMPK/SIRT1/PDK4 pathway suppressed by testosterone excess, indicating that testosterone primarily acts on decidualization through AR stimulation. Androgen excess in the endometrium inhibits decidualization by disrupting the AMPK/SIRT1/PDK4 signaling pathway. These data demonstrate the critical roles of endometrial PDK4 in regulating decidualization and provide valuable information for understanding the underlying mechanism during decidualization.

CD39 is induced by nutrient deprivation in colorectal cancer cells and contributes to the tolerance to hypoxia.

Rapid tumor growth and insufficient blood supply leads to the development of a hypoxic and nutrient deprived microenvironment. To survive, tumor cells need to tolerate these adverse conditions. Here we found the expression of CD39 was enhanced in necrotic regions distant from blood vessels. We speculate that this is a strategy for tumor cells to actively adapt to the hostile environment. Further studies showed that CD39 was induced by nutrient deprivation through the AMPK signalling pathway. We next explored the significance of CD39 for tumor cells. Our results showed that CD39 reduced cellular oxygen consumption, which could be significant for tumor cells if the available oxygen is limited. Metabolomics analysis showed that overexpression of CD39 significantly altered cellular metabolism, and tricarboxylic acid (TCA) cycle was identified as the most impacted metabolic pathway. In order to explore the molecular mechanism, we performed RNA-seq analysis. The results showed that CD39 significantly up-regulated the expression of pyruvate dehydrogenase kinase isozyme 2 (PDK2), thus inhibiting the activity of pyruvate dehydrogenase (PDH) and TCA cycle. Finally, CD39 was shown to protect tumor cells from hypoxia-induced cell death and reduce intratumoral hypoxia levels. CD39 has attracted a great deal of attention as a newly discovered immune checkpoint molecule in recent years. Our results indicate that CD39 not only plays a role in immune regulation, but also enables tumor cells to tolerate hypoxia by inhibiting TCA cycle and reducing cellular oxygen consumption. This study provides evidence that targeting CD39 may be a novel strategy to prevent adaptation of tumor cells in stressed conditions.

PDK4-mediated Nrf2 inactivation contributes to oxidative stress and diabetic kidney injury.

Diabetic kidney disease (DKD) is often featured with redox dyshomeostatis. Pyruvate dehydrogenase kinase 4 (PDK4) is the hub for DKD development. However, the mechanism by which PDK4 mediates DKD is poorly understood. The current work aimed to elucidate the relationship between PDK4 and DKD from the perspective of redox manipulation. Oxidative stress was observed in the human proximal tubular cell line (HK-2 cells) treated with a high concentration of glucose and palmitic acid (HGL). The mechanistic study showed that PDK4 could upregulate Kelch-like ECH-associated protein 1 (Keap1) in HGL-treated HK-2 cells through the suppression of autophagy, resulting in the depletion of nuclear factor erythroid 2-related factor 2 (Nrf2), the master regulator of redox homeostasis. At the cellular level, pharmacological inhibition or genetic knockdown of PDK4 could boost Nrf2, followed by the increase of a plethora of antioxidant enzymes and ferroptosis-suppression enzymes. Meanwhile, the inhibition or knockdown of PDK4 remodeled iron metabolism, further mitigating oxidative stress and lipid peroxidation. The same trend was observed in the DKD mice model. The current work highlighted the role of PDK4 in the development of DKD and suggested that PDK4 might be a promising target for the management of DKD.

Inhibition of the ubiquitin-proteasome system reduces the abundance of pyruvate dehydrogenase kinase 1 in cultured myotubes.

Pyruvate dehydrogenase kinase (PDK), which phosphorylates the pyruvate dehydrogenase complex, regulates glucose metabolism in skeletal muscle. PDK1, an isozyme whose expression is controlled by hypoxia-inducible factor-1α (HIF-1α), is thought to play a role in muscle adaptation to hypoxia. While transcriptional upregulation of PDK1 by HIF-1α is well characterised, mechanisms controlling proteolysis of PDK1 in skeletal muscle have not been thoroughly investigated. Proteasome inhibitor MG132 paradoxically reduced the abundance of PDK1 in human cancer cells and rat L6 myotubes, suggesting that MG132 might direct PDK1 towards autophagic degradation. The objectives of our current study were to determine (1) whether MG132 suppresses PDK1 levels in primary human myotubes, (2) whether chloroquine, an inhibitor of autophagy, prevents MG132-induced suppression of PDK1 in L6 myotubes, and (3) whether PYR-41, an inhibitor of ubiquitination, suppresses PDK1 in L6 myotubes. Using qPCR and/or immunoblotting, we found that despite markedly upregulating HIF-1α protein, MG132 did not alter the PDK1 expression in cultured primary human myotubes, while it suppressed both PDK1 mRNA and protein in L6 myotubes. The PDK1 levels in L6 myotubes were suppressed also during co-treatment with chloroquine and MG132. PYR-41 markedly increased the abundance of HIF-1α in primary human and L6 myotubes, while reducing the abundance of PDK1. In L6 myotubes treated with PYR-41, chloroquine increased the abundance of the epidermal growth factor receptor, but did not prevent the suppression of PDK1. Collectively, our results suggest that cultured myotubes degrade PDK1 via a pathway that cannot be inhibited by MG132, PYR-41, and/or chloroquine.

Unveiling the PDK4-centered rituximab-resistant mechanism in DLBCL: the potential of the "Smart" exosome nanoparticle therapy.

BACKGROUND: Diffuse large B-cell lymphoma (DLBCL) represents a prevalent malignant tumor, with approximately 40% of patients encountering treatment challenges or relapse attributed to rituximab resistance, primarily due to diminished or absent CD20 expression. Our prior research identified PDK4 as a key driver of rituximab resistance through its negative regulation of CD20 expression. Further investigation into PDK4's resistance mechanism and the development of advanced exosome nanoparticle complexes may unveil novel resistance targets and pave the way for innovative, effective treatment modalities for DLBCL. METHODS: We utilized a DLBCL-resistant cell line with high PDK4 expression (SU-DHL-2/R). We infected it with short hairpin RNA (shRNA) lentivirus for RNA sequencing, aiming to identify significantly downregulated mRNA in resistant cells. Techniques including immunofluorescence, immunohistochemistry, and Western blotting were employed to determine PDK4's localization and expression in resistant cells and its regulatory role in phosphorylation of Histone deacetylase 8 (HDAC8). Furthermore, we engineered advanced exosome nanoparticle complexes, aCD20@ExoCTX/siPDK4, through cellular, genetic, and chemical engineering methods. These nanoparticles underwent characterization via Dynamic Light Scattering (DLS) and Transmission Electron Microscopy (TEM), and their cellular uptake was assessed through flow cytometry. We evaluated the nanoparticles' effects on apoptosis in DLBCL-resistant cells and immune cells using CCK-8 assays and flow cytometry. Additionally, their capacity to counteract resistance and exert anti-tumor effects was tested in a resistant DLBCL mouse model. RESULTS: We found that PDK4 initiates HDAC8 activation by phosphorylating the Ser-39 site, suppressing CD20 protein expression through deacetylation. The aCD20@ExoCTX/siPDK4 nanoparticles served as effective intracellular delivery mechanisms for gene therapy and monoclonal antibodies, simultaneously inducing apoptosis in resistant DLBCL cells and triggering immunogenic cell death in tumor cells. This dual action effectively reversed the immunosuppressive tumor microenvironment, showcasing a synergistic therapeutic effect in a subcutaneous mouse tumor resistance model. CONCLUSIONS: This study demonstrates that PDK4 contributes to rituximab resistance in DLBCL by modulating CD20 expression via HDAC8 phosphorylation. The designed exosome nanoparticles effectively overcome this resistance by targeting the PDK4/HDAC8/CD20 pathway, representing a promising approach for drug delivery and treating patients with Rituximab-resistant DLBCL.

PER2 binding to PDK1 enhances the cisplatin sensitivity of oral squamous cell carcinoma through inhibition of the AKT/mTOR pathway.

Cisplatin (CDDP) is a cornerstone chemotherapeutic agent used to treat oral squamous cell carcinoma (OSCC) and many solid cancers. However, the mechanisms underlying tumor resistance to CDDP obscure the enhancement of its therapeutic efficacy. In this study, we unveil diminished expression of the biological clock gene PER2 in OSCC, negatively correlated with the expression of multidrug resistance protein 1 (MDR1) and multidrug resistance-associated protein 1 (MRP1). The overexpression of PER2 suppressed MDR1 and MRP1 expression and increased intracellular CDDP levels and DNA damage, thereby bolstering OSCC cell sensitivity to CDDP. In vivo tumorigenic assays corroborated that PER2 overexpression notably increased OSCC sensitivity to CDDP, augmenting the suppression of OSCC tumorigenesis. Co-immunoprecipitation, GST pull-down, and cycloheximide tracking assays revealed that PER2, via its C-terminal domain, bound to and diminishes PDK1 stability. The degradation of PDK1 was further dependent on the suppression of the AKT/mTOR pathway to enhance the sensitivity of OSCC cells to CDDP. Our study supports PER2 as a target for improving CDDP sensitivity in OSCC, and the combination of PER2 and CDDP is a novel strategy with potential clinical therapeutic value.

Molecular insights into the regulatory landscape of PKC-related kinase-2 (PRK2/PKN2) using targeted small compounds.

The PKC-related kinases (PRKs, also termed PKNs) are important in cell migration, cancer, hepatitis C infection, and nutrient sensing. They belong to a group of protein kinases called AGC kinases that share common features like a C-terminal extension to the catalytic domain comprising a hydrophobic motif. PRKs are regulated by N-terminal domains, a pseudosubstrate sequence, Rho-binding domains, and a C2 domain involved in inhibition and dimerization, while Rho and lipids are activators. We investigated the allosteric regulation of PRK2 and its interaction with its upstream kinase PDK1 using a chemical biology approach. We confirmed the phosphoinositide-dependent protein kinase 1 (PDK1)-interacting fragment (PIF)-mediated docking interaction of PRK2 with PDK1 and showed that this interaction can be modulated allosterically. We showed that the polypeptide PIFtide and a small compound binding to the PIF-pocket of PRK2 were allosteric activators, by displacing the pseudosubstrate PKL region from the active site. In addition, a small compound binding to the PIF-pocket allosterically inhibited the catalytic activity of PRK2. Together, we confirmed the docking interaction and allostery between PRK2 and PDK1 and described an allosteric communication between the PIF-pocket and the active site of PRK2, both modulating the conformation of the ATP-binding site and the pseudosubstrate PKL-binding site. Our study highlights the allosteric modulation of the activity and the conformation of PRK2 in addition to the existence of at least two different complexes between PRK2 and its upstream kinase PDK1. Finally, the study highlights the potential for developing allosteric drugs to modulate PRK2 kinase conformations and catalytic activity.