Beata Pająk

Calcium Homeostasis and ER Stress in Control of Autophagy in Cancer Cells

Autophagy is a basic catabolic process, serving as an internal engine during responses to various cellular stresses. As regards cancer, autophagy may play a tumor suppressive role by preserving cellular integrity during tumor development and by possible contribution to cell death. However, autophagy may also exert oncogenic effects by promoting tumor cell survival and preventing cell death, for example, upon anticancer treatment. The major factors influencing autophagy are Ca2+ homeostasis perturbation and starvation. Several Ca2+ channels like voltage-gated T- and L-type channels, IP3 receptors, or CRAC are involved in autophagy regulation. Glucose transporters, mainly from GLUT family, which are often upregulated in cancer, are also prominent targets for autophagy induction. Signals from both Ca2+ perturbations and glucose transport blockage might be integrated at UPR and ER stress activation. Molecular pathways such as IRE 1-JNK-Bcl-2, PERK-eIF2α-ATF4, or ATF6-XBP 1-ATG are related to autophagy induced through ER stress. Moreover ER molecular chaperones such as GRP78/BiP and transcription factors like CHOP participate in regulation of ER stress-mediated autophagy. Autophagy modulation might be promising in anticancer therapies; however, it is a context-dependent matter whether inhibition or activation of autophagy leads to tumor cell death.

Organic cation/carnitine transporter OCTN3 is present in astrocytes and is up-regulated by peroxisome proliferators-activator receptor agonist.

In the brain beta-oxidation, which takes place in astrocytes, is not a major process of energy supply. Astrocytes synthesize important lipid metabolites, mainly due to the processes taking place in peroxisomes. One of the compounds necessary in the process of mitochondrial beta-oxidation and export of acyl moieties from peroxisomes is l-carnitine. Two Na-dependent plasma membrane carnitine transporters were shown previously to be present in astrocytes: a low affinity amino acid transporter B(0,+) and a high affinity cation/carnitine transporter OCTN2. The expression of OCTN2 is known to increase in peripheral tissues upon the stimulation of peroxisome proliferators-activator receptor alpha (PPARalpha), a nuclear receptor known to up-regulate several enzymes involved in fatty acid metabolism. The present study was focused on another high affinity carnitine transporter-OCTN3, its presence, regulation and activity in astrocytes. Experiments using the techniques of real-time PCR, Western blot and immunocytochemistry analysis demonstrated the expression of octn3 in rat astrocytes and, out of two rat sequences ascribed as similar to mouse OCTN3, XM_001073573 was found in these cells. PPARalpha activator-2-[4-chloro-6-[(2,3-dimethylphenyl)amino]-2-pyrimidinyl]thio]acetic acid (WY-14,643) stimulated by 50% expression of octn3, while, on the contrary to peripheral tissues, it did not change the expression of octn2. This observation was correlated with an increased Na-independent activity of carnitine transport. Analysis by transmission electron microscopy showed an augmented intracellular localization of OCTN3 upon PPARalpha stimulation, mainly in peroxisomes, indicating a physiological role of OCTN3 as peroxisomal membrane transporter. These observations point to an important role of OCTN3 in peroxisomal fatty acid metabolism in astrocytes.

Extracellular α-Synuclein Leads to Microtubule Destabilization via GSK-3β-Dependent Tau Phosphorylation in PC12 Cells

α-Synuclein (ASN) plays an important role in pathogenesis of Parkinsons disease (PD) and other neurodegenerative disorders. Novel and most interesting data showed elevated tauopathy in PD and suggested relationship between ASN and Tau protein. However, the mechanism of ASN-evoked Tau protein modification is not fully elucidated. In this study we investigated the role of extracellular ASN in Tau hyperphosphorylation in rat pheochromocytoma (PC12) cells and the involvement of glycogen synthase kinase-3β (GSK-3β) and cyclin-dependent kinase 5 (CDK5) in ASN-dependent Tau modification. Our results indicated that exogenously added ASN increases Tau phosphorylation at Ser396. Accordingly, the GSK-3β inhibitor (SB-216763) prevented ASN-evoked Tau hyperphosphorylation, but the CDK5 inhibitor had no effect. Moreover, western blot analysis showed that ASN affected GSK-3β via increasing of protein level and activation of this enzyme. GSK-3β activity evaluated by its phosphorylation status assay showed that ASN significantly increased the phosphorylation of this enzyme at Tyr216 with parallel decrease in phosphorylation at Ser9, indicative of stimulation of GSK-3β activity. Moreover, the effect of ASN on microtubule (MT) destabilization and cell death with simultaneous the involvement of GSK-3β in these processes were analyzed. ASN treatment increased the amount of free tubulin and concomitantly reduced the amount of polymerized tubulin and SB-216763 suppressed these ASN-induced changes in tubulin, indicating that GSK-3β is involved in ASN-evoked MT destabilization. ASN-induced apoptotic processes lead to decrease in PC12 cells viability and SB-216763 protected those cells against ASN-evoked cytotoxicity. Concluding, extracellular ASN is involved in GSK-3β-dependent Tau hyperphosphorylation, which leads to microtubule destabilization. GSK-3β inhibition may be an effective strategy for protecting against ASN-induced cytotoxicity.

Verapamil-induced autophagy-like process in colon adenocarcinoma COLO 205 cells; the ultrastructural studies

BACKGROUND Verapamil (Ver) is a well known, worldwide used drug to correct cardiac arrhythmias. The main Ver target is the L-type calcium channel. Modulation of calcium homeostasis vaulted Ver into use in medical applications. METHODS To examine COLO 205 cells morphology after Ver treatment, an electron microscopy technique was used. RESULTS This study shows ultrastructural evidence that Ver initiates autophagy-like process in human colon adenocarcinoma COLO 205 cells. TEM photographs revealed the presence of differently developed autophagic vacuoles in response to Ver administration. Furthermore, extensive ultrastructural cell alterations confirmed that cancer cells died via necrosis or apoptosis, as demonstrated by ruptured plasma membrane or condensed chromatin, respectively. CONCLUSIONS It is the evidence that apoptosis resistant COLO 205 cells are overruled by autophagy-like process. Autophagy-like cell death could be a promising venue to delete cancer cells. Ver appears to be a new potentially effective anticancer compound.

Killing Me Softly: Connotations to Unfolded Protein Response and Oxidative Stress in Alzheimer's Disease.

This review is focused on the possible causes of mitochondrial dysfunction in AD, underlying molecular mechanisms of this malfunction, possible causes and known consequences of APP, Aβ, and hyperphosphorylated tau presence in mitochondria, and the contribution of altered lipid metabolism (nonsterol isoprenoids) to pathological processes leading to increased formation and accumulation of the aforementioned hallmarks of AD. Abnormal protein folding and unfolded protein response seem to be the outcomes of impaired glycosylation due to metabolic disturbances in geranylgeraniol intermediary metabolism. The origin and consecutive fate of APP, Aβ, and tau are emphasized on intracellular trafficking apparently influenced by inaccurate posttranslational modifications. We hypothesize that incorrect intracellular processing of APP determines protein translocation to mitochondria in AD. Similarly, without obvious reasons, the passage of Aβ and tau to mitochondria is observed. APP targeted to mitochondria blocks the activity of protein translocase complex resulting in poor import of proteins central to oxidative phosphorylation. Besides, APP, Aβ, and neurofibrillary tangles of tau directly or indirectly impair mitochondrial biochemistry and bioenergetics, with concomitant generation of oxidative/nitrosative stress. Limited protective mechanisms are inadequate to prevent the free radical-mediated lesions. Finally, neuronal loss is observed in AD-affected brains typically by pathologic apoptosis.

TNF-α and IFN-s-Dependent Muscle Decay Is Linked to NF-κB- and STAT-1α-Stimulated Atrogin1 and MuRF1 Genes in C2C12 Myotubes

TNF-α was shown to stimulate mitogenicity in C2C12 myoblasts. Selected cytokines TNF-α, IFNα, or IFNγ reduced the expression of myosin heavy chain (MyHC IIa) when given together. Molecular mechanisms of cytokine activities were controlled by NF-κB and JAK/STAT signaling pathways, as metabolic inhibitors, curcumin and AG490, inhibited some of TNF-α and IFNα/IFNγ effects. Insulin was hardly antagonistic to TNF-α- and IFNα/IFNγ-dependent decrease in MyHC IIa protein expression. Cytokines used individually or together also repressed myogenesis of C2C12 cells. Moreover, TNF-α- and IFNα/IFNγ-dependent effects on C2C12 myotubes were associated with increased activity of Atrogin1 and MuRF1 genes, which code ubiquitin ligases. MyHC IIa gene activity was unaltered by cytokines. Inhibition of NF-κB or JAK/STAT with specific metabolic inhibitors decreased activity of Atrogin1 and MuRF1 but not MyHC IIa gene. Overall, these results suggest cooperation between cytokines in the reduction of MyHC IIa protein expression level via NF-κB/JAK/STAT signaling pathways and activation of Atrogin1 and MuRF1 genes as their molecular targets. Insulin cotreatment or pretreatment does not protect against muscle decay induced by examined proinflammatory cytokines.

Preserved cardiomyocyte function and altered desmin pattern in transgenic mouse model of dilated cardiomyopathy

Taking advantage of the unique model of slowly developing dilated cardiomyopathy in mice with cardiomyocyte-specific transgenic overexpression of activated Gαq protein (Tgαq*44 mice) we analyzed the contribution of the cardiomyocyte malfunction, fibrosis and cytoskeleton remodeling to the development of heart failure in this model. Left ventricular (LV) in vivo function, myocardial fibrosis, cytoskeletal proteins expression and distribution, Ca(2+) handling and contractile function of isolated cardiomyocytes were evaluated at the stages of the early, compensated, and late, decompensated heart failure in 4-, 12- and 14-month-old Tgαq*44 mice, respectively, and compared to age-matched wild-type FVB mice. In the 4-month-old Tgαq*44 mice significant myocardial fibrosis, moderate myocyte hypertrophy and increased expression of regularly arranged and homogenously distributed desmin accompanied by increased phosphorylation of desmin chaperone protein, αB-crystallin, were found. Cardiomyocyte shortening, Ca(2+) handling and LV function were not altered. At 12 and 14 months of age, Tgαq*44 mice displayed progressive deterioration of the LV function. The contractile performance of isolated myocytes was still preserved, and the amplitude of Ca(2+) transients was even increased probably due to impairment of Na(+)/Ca(2+) exchanger function, while fibrosis was more extensive than in younger mice. Moreover, substantial disarrangement of desmin distribution accompanied by decreasing phosphorylation of αB-crystallin appeared. In Tgαq*44 mice disarrangement of desmin, at least partly related to inadequate phosphorylation of αB-crystallin seems to be importantly involved in the progressive deterioration of contractile heart function.

FOXO1 and GSK-3β Are Main Targets of Insulin-Mediated Myogenesis in C2C12 Muscle Cells.

Myogenesis and muscle hypertrophy account for muscle growth and adaptation to work overload, respectively. In adults, insulin and insulin-like growth factor 1 stimulate muscle growth, although their links with cellular energy homeostasis are not fully explained. Insulin plays critical role in the control of mitochondrial activity in skeletal muscle cells, and mitochondria are essential for insulin action. The aim of this study was to elucidate molecular mechanism(s) involved in mitochondrial control of insulin-dependent myogenesis. The effects of several metabolic inhibitors (LY294002, PD98059, SB216763, LiCl, rotenone, oligomycin) on the differentiation of C2C12 myoblasts in culture were examined in the short-term (hours) and long-term (days) experiments. Muscle cell viability and mitogenicity were monitored and confronted with the activities of selected genes and proteins expression. These indices focus on the roles of insulin, glycogen synthase kinase 3 beta (GSK-3β) and forkhead box protein O1 (FOXO1) on myogenesis using a combination of treatments and inhibitors. Long-term insulin (10 nM) treatment in “normoglycemic” conditions led to increased myogenin expression and accelerated myogenesis in C2C12 cells. Insulin-dependent myogenesis was accompanied by the rise of mtTFA, MtSSB, Mfn2, and mitochondrially encoded Cox-1 gene expressions and elevated levels of proteins which control functions of mitochondria (kinase—PKB/AKT, mitofusin 2 protein—Mfn-2). Insulin, via the phosphatidylinositol 3-kinase (PI3-K)/AKT-dependent pathway reduced transcription factor FOXO1 activity and altered GSK-3β phosphorylation status. Once FOXO1 and GSK-3β activities were inhibited the rise in Cox-1 gene action and nuclear encoded cytochrome c oxidase subunit IV (COX IV) expressions were observed, even though some mRNA and protein results varied. In contrast to SB216763, LiCl markedly elevated Mfn2 and COX IV protein expression levels when given together with insulin. Thus, inhibition of GSK-3β activity by insulin alone or together with LiCl raised the expression of genes and some proteins central to the metabolic activity of mitochondria resulting in higher ATP synthesis and accelerated myogenesis. The results of this study indicate that there are at least two main targets in insulin-mediated myogenesis: notably FOXO1 and GSK-3β both playing apparent negative role in muscle fiber formation.

Narrow time window of metabolic changes associated with transition to overt heart failure in Tgaq*44 mice

BACKGROUND The timing and consequences of alternations in substrate utilization in heart failure (HF) and their relationship with structural changes remain unclear. This study aimed to analyze metabolic changes associated with transition to overt heart failure in transgenic mouse model of HF resulting from cardiac-specific overexpression of constitutively active Gαq*. METHODS Structural changes quantified by morphometry, relative cardiac mRNA and protein expression of PPARα, FAT/CD36, CPT-1, GLUT-4 and glycolytic efficiency following administration of 1-(13)C glucose were investigated in 4-14-month-old Tgαq*44 mice (TG), compared with age-matched FVB wild type mice (WT). RESULTS Initial hypertrophy in TG (4-10-month of age) was featured by an accelerated glycolytic pathway that was not accompanied by structural changes in cardiomyocytes. In 10-month-old TG, cardiomyocyte elongation and hypertrophic remodeling and increased glycolytic flux was accompanied by relatively low expression of FAT/CD36, CPT-1 and PPARα. During the transition phase (12-month-old TG), a pronounced increase in PPARα with an increase in relative fatty acid (FA) flux was associated with anomalies of cardiomyocytes with accumulation of lipid droplets and glycogen as well as cell death. At the stage of overt heart failure (14-month-old TG), an accelerated glycolytic pathway with a decline in FA oxidation was accompanied by further structural changes. CONCLUSION Tgαq*44 mice display three distinct phases of metabolic/structural changes during hypertrophy and progression to HF, with relatively short period of increase in FA metabolism, highlighting a narrow metabolic changes associated with transition to overt heart failure in Tgaq*44 mice that have therapeutic significance.

Verapamil treatment induces cytoprotective autophagy by modulating cellular metabolism

Verapamil, an L‐type calcium channel blocker, has been used successfully to treat cardiovascular diseases. Interestingly, we have recently shown that treatment of cancer cells with verapamil causes an effect on autophagy. As autophagy is known to modulate chemotherapy responses, this prompted us to explore the impact of verapamil on autophagy and cell viability in greater detail. We report here that verapamil causes an induction of autophagic flux in a number or tumor cells and immortalized normal cells. Moreover, we found that inhibition of autophagy in COLO 205 cells, via treatment with the chloroquine (CQ) or by CRISPR/Cas9‐mediated disruption of the autophagy genes Atg7 and Atg5, causes an upregulation of apoptotic markers in response to verapamil. In search of a mechanism for this effect and because autophagy can often mitigate metabolic stress, we examined the impact of verapamil on cellular metabolism. This revealed that in normal prostate cells, verapamil diminishes glucose and glycolytic intermediate levels leading to adenosine 5′‐triphosphate (ATP) depletion. In contrast, in COLO 205 cells it enhances aerobic glycolysis and maintains ATP. Importantly, we found that the autophagic response in these cells is related to the activity of l‐lactate dehydrogenase A (LDHA, EC 1.1.1.27), as inhibition of LDHA reduces both basal and verapamil‐induced autophagy and consequently decreases cell viability. In summary, these findings not only identify a novel mechanism of cytoprotective autophagy induction but they also highlight the potential of using verapamil together with inhibitors of autophagy for the treatment of malignant disease.