SQSTM1/p62 loss reverses the inhibitory effect of sunitinib on autophagy independent of AMPK signaling

Protein kinase CK2 sustains de novo fatty acid synthesis by regulating the expression of SCD-1 in human renal cancer cells

BACKGROUND

Clear cell renal cell carcinoma (ccRCC) is a type of cancer characterized by a vast intracellular accumulation of lipids that are critical to sustain growth and viability of the cells in the tumour microenvironment. Stearoyl-CoA 9-desaturase 1 (SCD-1) is an essential enzyme for the synthesis of monounsaturated fatty acids and consistently overexpressed in all stages of ccRCC growth.

METHODS

Human clear cell renal cell carcinoma lines were treated with small-molecule inhibitors of protein kinase CK2. Effects on the expression levels of SCD-1 were investigated by RNA-sequencing, RT-qPCR, Western blot, and in vivo studies in mice. Phase-contrast microscopy, fluorescence microscopy, flow cytometry, and MALDI-mass spectrometry analysis were carried out to study the effects on endogenous lipid accumulation, induction of endoplasmic reticulum stress, rescue effects induced by exogenous MUFAs, and the identity of lipid populations. Cell proliferation and survival were investigated in real time employing the Incucyte® live-cell analysis system. Statistical significance was determined by applying the two-tailed Student's t test when comparing two groups of data whereas the two-way ANOVA, multiple Tukey's test was employed for multiple comparisons.

RESULTS

Here, we show that protein kinase CK2 is critical for preserving the expression of SCD-1 in ccRCC lines maintained in culture and heterotransplanted into nude mice. Consistent with this, pharmacological inhibition of CK2 leads to induction of endoplasmic reticulum stress linked to unfolded protein response activation and decreased proliferation of the cells. Both effects could be reversed by supplementing the growth medium with oleic acid indicating that these effects are specifically caused by reduced expression of SCD-1. Analysis of lipid composition by MALDI-mass spectrometry revealed that inhibition of CK2 results in a significant accumulation of the saturated palmitic- and stearic acids.

CONCLUSIONS

Collectively, our results revealed a previously unidentified molecular mechanism regulating the synthesis of monounsaturated fatty acids corroborating the notion that novel therapeutic approaches that include CK2 targeting, may offer a greater synergistic anti-tumour effect for cancers that are highly dependent on fatty acid metabolism.

Downregulation of Lnc-ABCA12-3 modulates UBQLN1 expression and protein homeostasis pathways in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by motor neuron degeneration. Dysregulation of long non-coding RNAs (lncRNAs) has been implicated in ALS pathogenesis but their roles remain unclear. Previous studies found lnc-ABCA12-3 was downregulated in ALS patients. We aim to characterize the expression and function of lnc-ABCA12-3 in ALS and explore its mechanisms of action. Lnc-ABCA12-3 expression was analyzed in PBMCs from ALS patients and correlated with clinical outcomes. Effect of modulating lnc-ABCA12-3 expression was assessed in cell models using assays of apoptosis, protein homeostasis and pathway analysis. RNA pull-down and interaction studies were performed to identify lnc-ABCA12-3 binding partners. Lnc-ABCA12-3 was downregulated in ALS patients, correlating with faster progression and shorter survival. Overexpression of lnc-ABAC12-3 conferred protection against oxidative stress-induced apoptosis, while knockdown lnc-ABCA12-3 enhanced cell death. Lnc-ABCA12-3 maintained protein quality control pathways, including ubiquitination, autophagy and stress granule formation, by regulating the ubiquitin shuttle protein UBQLN1. This study identified lnc-ABCA12-3 as a novel regulatory lncRNA implicated in ALS pathogenesis by modulating cellular survival and stress responses through interactions with UBQLN1, influencing disease progression. Lnc-ABCA12-3 may influence ALS through regulating protein homeostasis pathways.

The disulphide cleavage derivative (C42-4) of 11'-deoxyverticillin A (C42) fails to induce apoptosis and genomic instability in HeLa cells

Our previous study revealed 11'-deoxyverticillin A (C42), a natural product isolated from the Ophiocordyceps-associated fungus Clonostachys rogersoniana and a member of the epipolythiodioxopiperazines (ETPs), induced both apoptosis and autophagy in HCT116 cells; however, the role of disulphide/polysulphide bridges of C42 in the regulation of autophagy remains unexplored. Here, we revealed that C42 activated both caspase-dependent apoptosis and autophagy in HeLa cells, whereas its disulphide cleavage derivative C42-4 failed to induce the cleavage of both caspase-3 and PARP-1. In contrast, both C42 and C42-4 increased the formation of autophagosomes, punctate staining of LC3, and the ratio of LC3-II to actin, suggesting that disulphide/polysulphide bridges are dispensable for the induction of the autophagic process. Moreover, we found that C42 but not C42-4 led to nuclear instability by increasing the formation of micronuclei and expression of phosphorylated histone H2AX (γ-H2AX), a widely used marker for DNA double strand breaks (DSBs), while Rad51, a protein pivotal for DNA repair, was decreased upon challenge with C42. These results demonstrate that the disulphide bonds in ETPs play an essential role in the induction of caspase-dependent apoptosis and nuclear stability.

Bromelain activates the AMP-activated protein kinase-autophagy pathway to alleviate hepatic lipid accumulation

Bromelain, a cysteine protease found in pineapple, is known to exert protective effects against non-alcoholic fatty liver disease (NAFLD); however, the underlying mechanism is unclear. In this study, we aimed to investigate the molecular mechanisms underlying the beneficial effects of bromelain using in vivo and in vitro models. C57BL/6 mice were fed a high-fat diet (HFD) with or without bromelain (20 mg/kg/day) for 12 weeks. We found that treatment with bromelain alleviated hepatic lipid accumulation accompanied by the activation of AMP-activated protein kinase (AMPK) and autophagy flux, as evidenced by the elevated levels of phosphorylated AMPK, ATG5, ATG7, LC3-II, and lysosome-associated membrane protein 2 (LAMP2), and the decreased levels of p62 in the liver of HFD-fed mice. In human hepatoma Huh 7 cells, bromelain prevented oleic acid (OA)-induced lipid accumulation and increased the levels of phosphorylated AMPK, ATG5, ATG7, LC3-II, and LAMP2 but decreased the levels of p62. Inhibition of AMPK and autophagy flux by specific inhibitors or small interfering RNAs suppressed bromelain-mediated protective effect on lipid accumulation. Moreover, inhibition of AMPK activity abolished the activation of autophagy flux in OA-treated hepatocytes. Collectively, these findings suggest a new molecular mechanism involving the AMPK-autophagy pathway through which bromelain confers protection against the deregulation of lipid metabolism in the liver.

Grb2 interacts with necrosome components and is involved in rasfonin-induced necroptosis

The underlying mechanism by which growth factor receptor-bound protein 2 (Grb2) regulates necroptosis remains unexplored. In the present study, we found that rasfonin, a fungal natural product and an activator of necroptosis, enhanced Grb2 binding to receptor-interacting serine/threonine kinase 1 (RIP1), which plays a critical role in regulating programmed necrosis. Moreover, we observed that SQSTM/p62 (p62), a protein that can form necrosomes with RIP1, increased its interaction with Grb2 upon rasfonin challenge. Although it has been used as an activator of autophagy in our previous study, here we found that a high dose of rasfonin was able to inhibit autophagic process. Inhibition of RIP1 either chemically or genetically reversed the inhibition of rasfonin on autophagy, whereas knockdown of Grb2 markedly reduced rasfonin-induced necrosis. Additionally, we found that the compound failed to upregulate the expression of RIP1 in Grb2-deprived cells. In summary, our data revealed that Grb2 actively participated in rasfonin-induced necroptosis by interacting with the components of necrosome and mediating their expression.

The unique Akt inhibitor SC66 suppressed AMPK activity and abolished autophagy through the EGFR-p62 pathway

Akt is usually considered to be a negative regulator of both autophagy and adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) signaling. In the present study, we found that SC66, a pyridine-based allosteric Akt inhibitor, suppressed basal and H₂ O₂ -induced autophagy concurrent with decreased phosphorylation and activity of AMPK. SC66 treatment led to the formation of a high molecular weight (HMW) form of SQSTM1/p62 (p62), which is an autophagic substrate and is essential for selective autophagy. Moreover, we observed that SC66 inhibited the binding of p62 and microtubule-associated protein light chain 3 (LC3). The immunoprecipitation results revealed the interaction between p62 and epidermal growth factor receptor (EGFR), and knockdown of EGFR reversed SC66-mediated autophagy inhibition without affecting the phosphorylation of acetyl-CoA carboxylase (ACC), a well-known substrate of AMPK. SC66 increased the interaction between EGFR and Beclin 1 and markedly decreased the association of EGFR with VPS34, a critical protein for autophagy induction. Collectively, the data presented here indicate that EGFR-p62 pathway plays a critical role in Akt-mediated positive regulation of autophagy.

A Single, Acute Astragaloside IV Therapy Protects Cardiomyocyte Through Attenuating Superoxide Anion-Mediated Accumulation of Autophagosomes in Myocardial Ischemia-Reperfusion Injury

Myocardial ischemia-reperfusion (I/R) injury, characterized by myocardial cell death (e.g., apoptosis) and generation of reactive oxygen species (ROS) such as superoxide (O2 ·-) and hydrogen peroxide (H2O2), is a serious threat to human health and property. Saponin astragaloside IV (ASIV), extracted from Chinese herbal medicine astragalus, is effective in resolving multiple pathological issues including myocardial I/R injury. Recent studies have shown that autophagy is regulated by ROS and plays an important role in myocardial I/R injury. However, regulation of autophagy by ASIV during myocardial I/R injury and the role of specific ROS involved in the process have been rarely reported. In the present study, we found that SOD2 was downregulated and O2 ·- was upregulated in H2O2-induced H9C2 cardiac myocyte injury in vitro and myocardial I/R injury in vivo, while such alterations were reversed by ASIV. ASIV possessed the ability to alleviate myocardial I/R injury via attenuating I/R-caused autophagosome accumulation. Upregulate of O2 ·- by 2-methoxyestradiol (2-ME) reversed the effect of ASIV-mediated autophagy regulation, which suggested that O2 ·- was vital in this process. In conclusion, our results contribute to understanding the mechanism of ASIV-induced cardioprotective effect.

Sodium-Glucose CoTransporter-2 Inhibitor Empagliflozin Ameliorates Sunitinib-Induced Cardiac Dysfunction via Regulation of AMPK-mTOR Signaling Pathway-Mediated Autophagy

Background: Sodium–glucose cotransporter-2 (SGLT2) inhibitors have been shown to decrease the adverse cardiac events and risks of cardiovascular mortality among patients with or without diabetes, which has made these drugs promising treatment options for patients with chronic heart failure. Cardiac dysfunction is a common and severe side effect induced by cancer chemotherapies, which seriously affects the prognosis and life quality of tumor patients. However, it is not clear whether SGLT2 inhibitors have cardiovascular benefits in patients with cancer chemotherapy–related cardiac dysfunction. We aimed to determine whether empagliflozin (EMPA), an SGLT2 inhibitor, has a protective role against sunitinib (SNT)-induced cardiac dysfunction in a mouse model.

Methods: Male C57BL/6J mice were randomized into control (control, n = 8), empagliflozin (EMPA, n = 8), sunitinib (SNT, n = 12), or sunitinib and empagliflozin coadministration (SNT + EMPA, n = 12) groups. EMPA, SNT, or SNT-combined EMPA was given via oral gavage for consecutive 28 days. Cardiovascular functions and pathological changes were examined, and the underlying mechanisms of EMPA’s effects were investigated in H9c2 cardiomyocytes.

Results: Mice in the SNT group exhibited dramatically elevated blood pressure (systolic blood pressure [SBP] 134.30 ± 6.455 mmHg vs. 114.85 ± 6.30 mmHg) and impaired left ventricular function (left ventricular ejection fraction [LVEF] 50.24 ± 3.06% vs. 84.92 ± 2.02%), as compared with those of the control group. However, EMPA could ameliorate SNT-induced cardiotoxicity, both in terms of SBP (117.51 ± 5.28 mmHg vs. 134.30 ± 6.455 mmHg) and LVEF (76.18 ± 5.16% vs. 50.24 ± 3.06 %). In H9c2 cardiomyocytes, SNT-induced cardiomyocyte death and cell viability loss as well as dysfunction of adenosine 5’-monophosphate–activated protein kinase–mammalian target of rapamycin (AMPK-mTOR) signaling–mediated autophagy were restored by EMPA. However, these favorable effects mediated by EMPA were blocked by the inhibition of AMPK or autophagy.

Conclusion: EMPA could ameliorate SNT-induced cardiac dysfunction via regulating cardiomyocyte autophagy, which was mediated by the AMPK-mTOR signaling pathway. These findings supported that SGLT2 inhibitor therapy could be a potential cardioprotective approach for cardiovascular complications among patients receiving SNT. However, these favorable effects still need to be validated in clinical trials.

Fetuin-A exerts a protective effect against experimentally induced intestinal ischemia/reperfusion by suppressing autophagic cell death

Intestinal tissue is highly susceptible to ischemia/reperfusion injury in many hazardous health conditions. The anti-inflammatory and antioxidant glycoprotein fetuin-A showed efficacy in cerebral ischemic injury; however, its protective role against intestinal ischemia/reperfusion remains elusive. Therefore, this study investigated the protective role of fetuin-A supplementation against intestinal structural changes and dysfunction in a rat model of intestinal ischemia/reperfusion. We equally divided 72 male rats into control, sham, ischemia/reperfusion, and fetuin-A-pretreated ischemia/reperfusion (100 mg/kg/day fetuin-A intraperitoneally for three days prior to surgery and a third dose 1 h prior to the experiment) groups. After 2 h of reperfusion, the jejunum was dissected and examined for spontaneous contractility. A jejunal homogenate was used to assess inflammatory and oxidative stress enzymes. Staining of histological sections was carried out with hematoxylin, eosin and Masson's trichrome stain for evaluation. Immunohistochemistry was performed to detect autophagy proteins beclin-1, LC3, and p62. This study found that fetuin-A significantly improved ischemia/reperfusion-induced mucosal injury by reducing the percentage of areas of collagen deposition, increasing the amplitude of spontaneous contraction, decreasing inflammation and oxidative stress, and upregulating p62 expression, which was accompanied by beclin-1 and LC3 downregulation. Our findings suggest that fetuin-A treatment can prevent ischemia/reperfusion-induced jejunal structural and functional changes by increasing antioxidant activity and regulating autophagy disturbances observed in the ischemia/reperfusion rat model. Furthermore, fetuin-A may provide a protective influence against intestinal ischemia/reperfusion complications.

Necrostatin-1 Analog DIMO Exerts Cardioprotective Effect against Ischemia Reperfusion Injury by Suppressing Necroptosis via Autophagic Pathway in Rats

AIM

It has been reported that necrostatin-1 (Nec-1) is a specific necroptosis inhibitor that could attenuate programmed cell death induced by myocardial ischemia/reperfusion (I/R) injury. This study aimed to observe the effect and mechanism of novel Nec-1 analog (Z)-5-(3,5-dimethoxybenzyl)-2-imine-1-methylimidazolin-4-1 (DIMO) on myocardial I/R injury.

METHODS

Male SD rats underwent I/R injury with or without different doses of DIMO (1, 2, or 4 mg/kg) treatment. Isolated neonatal rat cardiomyocytes were subjected to oxygen-glucose deprivation/reoxygenation (OGD/R) treatment with or without DIMO (0.1, 1, 10, or 100 μM). Myocardial infarction was measured by TTC staining. Cardiomyocyte injury was assessed by lactate dehydrogenase assay (LDH) and flow cytometry. Receptor-interacting protein 1 kinase (RIP1K) and autophagic markers were detected by co-immunoprecipitation and Western blotting analysis. Molecular docking of DIMO into the ATP binding site of RIP1K was performed using GLIDE.

RESULTS

DIMO at doses of 1 or 2 mg/kg improved myocardial infarct size. However, the DIMO 4 mg/kg dose was ineffective. DIMO at the dose of 0.1 μM decreased LDH leakage and the ratio of PI-positive cells followed by OGD/R treatment. I/R or OGD/R increased RIP1K expression and in its interaction with RIP3K, as well as impaired myocardial autophagic flux evidenced by an increase in LC3-II/I ratio, upregulated P62 and Beclin-1, and activated cathepsin B and L. In contrast, DIMO treatment reduced myocardial cell death and reversed the above mentioned changes in RIP1K and autophagic flux caused by I/R and OGD/R. DIMO binds to RIP1K and inhibits RIP1K expression in a homology modeling and ligand docking.

CONCLUSION

DIMO exerts cardioprotection against I/R- or OGD/R-induced injury, and its mechanisms may be associated with the reduction in RIP1K activation and restoration impaired autophagic flux.

Inhibition of Ref(2)P, the Drosophila homologue of the p62/SQSTM1 gene, increases lifespan and leads to a decline in motor function

Objective

Sequestosome 1 (p62/SQSTM1) is a multifunctional scaffold/adaptor protein encoded by the p62/SQSTM1 gene with function in cellular homeostasis. Mutations in the p62/SQSTM1 gene have been known to be associated with patients with amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), and Parkinson disease (PD). The aim of the present study was to create a novel model of human neurogenerative disease in Drosophila melanogaster by altering the expression of Ref(2)P, the Drosophila orthologue of the human p62/SQSTM1 gene. Ref(2)P expression was altered in all neurons, the dopaminergic neurons and in the motor neurons, with longevity and locomotor function assessed over time.

Results

Inhibition of Ref(2)P resulted in a significantly increased median lifespan in the motor neurons, followed by a severe decline in motor skills. Inhibition of Ref(2)P in the dopaminergic neurons resulted in a significant, but minimal increase in median lifespan, accompanied by a drastic decline in locomotor function. Inhibition of Ref(2)P in the ddc-Gal4-expressing neurons resulted in a significant increase in median lifespan, while dramatically reducing motor function.

Different Role of Raptor and Rictor in Regulating Rasfonin-Induced Autophagy and Apoptosis in Renal Carcinoma Cells

Both Raptor and Rictor are the key components in the complexes of mammalian target of rapamycin (mTOR), which play a vital role in mediating autophagy. Unlike mTOR, the regulatory role of either Raptor or Rictor in the regulation of autophagic process is relatively less explored. In present study, we found that rasfonin, which isolated from Talaromyces sp. 3656-A1 and was a fungal natural product, activated both caspase-dependent apoptosis and autophagy in ACHN, a renal carcinoma cell line. Knockdown of Raptor decreased both rasfonin-induced autophagic flux and PARP-1 cleavage, and in contrast, Rictor silencing increased apoptosis concomitantly enhancing rasfonin-induced autophagy. Unexpectedly, API-2, which was widely used as an inhibitor of Akt, promoted rasfonin-dependent autophagy in Raptor-depleted but not Rictor-deprived cells. Collectively, these results demonstrated that Raptor and Rictor could play a distinctly regulatory role in rasfonin-enhanced autophagy and apoptosis.

Estradiol modulated colorectal cancer stem cells bioactivity and interaction with endothelial cells

This study aimed to evaluate the modulatory role of sex-related hormone estradiol on cancer stem cells with the origin of colorectal adenocarcinoma in vitro. Cancer stem cells were incubated with 100 nM estradiol for 48 h. The cell survival rate was analyzed using the MTT assay. Immunocytochemistry staining of Ki-67 and Inhibin and Apoptosis PCR array were done to measure proliferation/apoptosis. Cell migration was monitored via the Transwell Migration assay. The expression of exosome biogenesis genes was measured using a real-time PCR assay. The fatty acid profile was monitored using gas chromatography. The level of FAK, SQSTM1, ER, and SIRT1 was examined using Western blotting. Cancer stem-endothelial cell interaction was investigated using Surface Plasmon Resonance assay. Data showed no significant differences in cancer stem cell viability and proliferation between control and estradiol-treated groups (p>0.05). PCR array highlighted the up-regulation of both pro- and anti-apoptosis effectors in the treatment group compared to the control cells (p<0.05). Cell migration capacity was increased after treatment with estradiol (p<0.001). Both exocytosis and exosome biogenesis were decreased in cancer stem cells exposed to estradiol (p<0.05). Data showed the reduction of palmitic acid, and increase of Palmitoleic and Linolenic acids in estradiol-treated cells. Estrogen induced estrogen receptor, SQSTM1 proteins and decreased SIRT1 factor after 48 h. Surface Plasmon Resonance revealed the suppression of cancer stem-endothelial cell interaction and affinity. Estradiol could change the migration, juxtacrine and paracrine activities of cancer stem cells, showing the importance of sex-related hormones in the dynamic of cancer development.

The central regulator p62 between ubiquitin proteasome system and autophagy and its role in the mitophagy and Parkinson's disease

The ubiquitin-proteasome system (UPS) and autophagy are two major degradative pathways of proteins in eukaryotic cells. As about 30% of newly synthesized proteins are known to be misfolded under normal cell conditions, the precise and timely operation of the UPS and autophagy to remove them as well as their tightly controlled regulation, is so important for proper cell function and survival. In the UPS, target proteins are labeled by small proteins called ubiquitin, which are then transported to the proteasome complex for degradation. Alternatively, many greatly damaged proteins are believed to be delivered to the lysosome for autophagic degradation. Although these autophagy and UPS pathways have not been considered to be directly related, many recent studies proposed their close link and dynamic interconversion. In this review, we’ll focus on the several regulatory molecules that function in both UPS and autophagy and their crosstalk. Among the proposed multiple modulators, we will take a closer look at the so-called main connector of UPS-autophagy regulation, p62. Last, the functional role of p62 in the mitophagy and its implication for the pathogenesis of Parkinson’s disease, one of the major neurodegenerative diseases, will be briefly reviewed.

The interrupted effect of autophagic flux and lysosomal function induced by graphene oxide in p62-dependent apoptosis of F98 cells

BACKGROUND

Graphene oxide (GO) nanoparticles (NPs) have been widely applied in various fields, especially in biomedical applications. Extensive studies have suggested that GO can pass through the blood-brain barrier (BBB) and induce abnormal autophagy and cytotoxicity in the central nervous system (CNS). However, the effect and specific mechanism of GO on astrocytes, the most abundant cells in the brain still has not been extensively investigated.

RESULTS

In this study, we systematically explored the toxicity and mechanism of GO exposure in the rat astroglioma-derived F98 cell line using molecular biological techniques (immunofluorescence staining, flow cytometry and Western blot) at the subcellular level and the signaling pathway level. Cells exposed to GO exhibited decreased cell viability and increased lactate dehydrogenase (LDH) release in a concentration- and time-dependent manner. GO-induced autophagy was evidenced by transmission electron microscopy (TEM) and immunofluorescence staining. Western blots showed that LC3II/I and p62 were upregulated and PI3K/Akt/mTOR was downregulated. Detection of lysosomal acidity and cathepsin B activity assay indicated the impairment of lysosomal function. Annexin V-FITC-PI detection showed the occurrence of apoptosis after GO exposure. The decrease in mitochondrial membrane potential (MMP) with an accompanying upregulation of cleaved caspase-3 and Bax/Bcl-2 further suggested that endogenous signaling pathways were involved in GO-induced apoptosis.

CONCLUSION

The exposure of F98 cells to GO can elicit concentration- and time-dependent toxicological effects. Additionally, increased autophagic response can be triggered after GO treatment and that the blocking of autophagy flux plays a vital role in GO cytotoxicity, which was determined to be related to dysfunction of lysosomal degradation. Importantly, the abnormal accumulation of autophagic substrate p62 protein can induce capase-3-mediated apoptosis. Inhibition of abnormal accumulation of autophagic cargo could alleviate the occurrence of GO-induced apoptosis in F98 cells.