HSP27 phosphorylation modulates TRAIL-induced activation of Src-Akt/ERK signaling through interaction with β-arrestin2

Functional Diversity of Mammalian Small Heat Shock Proteins: A Review

The small heat shock proteins (sHSPs), whose molecular weight ranges from 12∼43 kDa, are members of the heat shock protein (HSP) family that are widely found in all organisms. As intracellular stress resistance molecules, sHSPs play an important role in maintaining the homeostasis of the intracellular environment under various stressful conditions. A total of 10 sHSPs have been identified in mammals, sharing conserved α-crystal domains combined with variable N-terminal and C-terminal regions. Unlike large-molecular-weight HSP, sHSPs prevent substrate protein aggregation through an ATP-independent mechanism. In addition to chaperone activity, sHSPs were also shown to suppress apoptosis, ferroptosis, and senescence, promote autophagy, regulate cytoskeletal dynamics, maintain membrane stability, control the direction of cellular differentiation, modulate angiogenesis, and spermatogenesis, as well as attenuate the inflammatory response and reduce oxidative damage. Phosphorylation is the most significant post-translational modification of sHSPs and is usually an indicator of their activation. Furthermore, abnormalities in sHSPs often lead to aggregation of substrate proteins and dysfunction of client proteins, resulting in disease. This paper reviews the various biological functions of sHSPs in mammals, emphasizing the roles of different sHSPs in specific cellular activities. In addition, we discuss the effect of phosphorylation on the function of sHSPs and the association between sHSPs and disease.

Alkaloids from Piper longum Exhibit Anti-inflammatory Activity and Synergistic Effects with Chemotherapeutic Agents against Cervical Cancer Cells

Piper longum L. is widely cultivated for food, medicine, and other purposes in tropical and subtropical regions. Sixteen compounds including nine new amide alkaloids were isolated from the roots of P. longum. The structures of these compounds were determined by spectroscopic data. All compounds showed better anti-inflammatory activities (IC₅₀ = 1.90 ± 0.68-40.22 ± 0.45 μM) compared to indomethacin (IC₅₀ = 52.88 ± 3.56 μM). Among the isolated compounds, five dimeric amide alkaloids exhibited synergistic effects with three chemotherapeutic drugs (paclitaxel, adriamycin, or vincristine) against cervical cancer cells. Moreover, these dimeric amide alkaloids also enhanced the efficacy of paclitaxel in paclitaxel-resistant cervical cancer cells. The combination treatment of one of these dimeric amide alkaloids and paclitaxel promoted cancer cell apoptosis, which is related to the Src/ERK/STAT3 signaling pathway.

HSP27 protects against ferroptosis of glioblastoma cells

Ferroptosis, as an new form of non-apoptotic regulated cell death, plays an important role in human cancers. Although it is reported that HSP27 is an novel regulator of ferroptosis in cancer, it remains unknown how HSP27 affects ferroptosis in glioma. In this study, we examined the effect of HSP27 on the ferroptosis of glioblasotma. HSP27 overexpression protects glioblastoma cells from erastin-induced ferroptosis while HSP27 depletion promotes erastin-induced ferroptosis of glioblastoma. Notably, HSP27 phosphorylation is required for the protective function of HSP27 in erastin-induced ferroptosis. Overall, our study reveal novel molecular mechanisms of ferroptosis in glioma and also identify HSP27 as a negative regulator of ferroptosis and a potential target for the treatment of glioma.

Harnessing TRAIL-Induced Apoptosis Pathway for Cancer Immunotherapy and Associated Challenges

The immune cytokine tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has attracted rapidly evolving attention as a cancer treatment modality because of its competence to selectively eliminate tumor cells without instigating toxicity in vivo. TRAIL has revealed encouraging promise in preclinical reports in animal models as a cancer treatment option; however, the foremost constraint of the TRAIL therapy is the advancement of TRAIL resistance through a myriad of mechanisms in tumor cells. Investigations have documented that improvement of the expression of anti-apoptotic proteins and survival or proliferation involved signaling pathways concurrently suppressing the expression of pro-apoptotic proteins along with down-regulation of expression of TRAILR1 and TRAILR2, also known as death receptor 4 and 5 (DR4/5) are reliable for tumor cells resistance to TRAIL. Therefore, it seems that the development of a therapeutic approach for overcoming TRAIL resistance is of paramount importance. Studies currently have shown that combined treatment with anti-tumor agents, ranging from synthetic agents to natural products, and TRAIL could result in induction of apoptosis in TRAIL-resistant cells. Also, human mesenchymal stem/stromal cells (MSCs) engineered to generate and deliver TRAIL can provide both targeted and continued delivery of this apoptosis-inducing cytokine. Similarly, nanoparticle (NPs)-based TRAIL delivery offers novel platforms to defeat barricades to TRAIL therapeutic delivery. In the current review, we will focus on underlying mechanisms contributed to inducing resistance to TRAIL in tumor cells, and also discuss recent findings concerning the therapeutic efficacy of combined treatment of TRAIL with other antitumor compounds, and also TRAIL-delivery using human MSCs and NPs to overcome tumor cells resistance to TRAIL.

Insight into Cisplatin-Resistance Signaling of W1 Ovarian Cancer Cells Emerges mTOR and HSP27 as Targets for Sensitization Strategies

The microenvironment possesses a strong impact on the tumor chemoresistance when cells bind to components of the extracellular matrix. Here we elucidate the signaling pathways of cisplatin resistance in W1 ovarian cancer cells binding to collagen type 1 (COL1) and signaling interference with constitutive cisplatin resistance in W1CR cells to discover the targets for sensitization. Proteome kinase arrays and Western blots were used to identify the signaling components, their impact on cisplatin resistance was evaluated by inhibitory or knockdown approaches. W1 cell binding to COL1 upregulates integrin-associated signals via FAK/PRAS40/mTOR, confirmed by β1-integrin (ITGB1) knockdown. mTOR appears as key for resistance, its blockade reversed COL1 effects on W1 cell resistance completely. W1CR cells compensate ITGB1-knockdown by upregulation of discoidin domain receptor 1 (DDR1) as alternative COL1 sensor. COL1 binding via DDR1 activates the MAPK pathway, of which JNK1/2 appears critical for COL1-mediated resistance. JNK1/2 inhibition inverts COL1 effects in W1CR cells, whereas intrinsic cisplatin resistance remained unaffected. Remarkably, knockdown of HSP27, another downstream MAPK pathway component overcomes intrinsic resistance completely sensitizing W1CR cells to the level of W1 cells for cisplatin cytotoxicity. Our data confirm the independent regulation of matrix-induced and intrinsic chemoresistance in W1 ovarian cancer cells and offer novel targets for sensitization.

Protein Phosphorylation in Serine Residues Correlates with Progression from Precancerous Lesions to Cervical Cancer in Mexican Patients

Protein phosphorylation is a posttranslational modification that is essential for normal cellular processes; however, abnormal phosphorylation is one of the prime causes for alteration of many structural, functional, and regulatory proteins in disease conditions. In cancer, changes in the states of protein phosphorylation in tyrosine residues have been more studied than phosphorylation in threonine or serine residues, which also undergo alterations with greater predominance. In general, serine phosphorylation leads to the formation of multimolecular signaling complexes that regulate diverse biological processes, but in pathological conditions such as tumorigenesis, anomalous phosphorylation may result in the deregulation of some signaling pathways. Cervical cancer (CC), the main neoplasm associated with human papillomavirus (HPV) infection, is the fourth most frequent cancer worldwide. Persistent infection of the cervix with high-risk human papillomaviruses produces precancerous lesions starting with low-grade squamous intraepithelial lesions (LSIL), progressing to high-grade squamous intraepithelial lesions (HSIL) until CC is generated. Here, we compared the proteomic profile of phosphorylated proteins in serine residues from healthy, LSIL, HSIL, and CC samples. Our data show an increase in the number of phosphorylated proteins in serine residues as the grade of injury rises. These results provide a support for future studies focused on phosphorylated proteins and their possible correlation with the progression of cervical lesions.

Phosphorylated Heat Shock Protein 27 Inhibits Lipopolysaccharide-Induced Inflammation in Thp1 Cells by Promoting TLR4 Endocytosis, Ubiquitination, and Degradation

The aims of this study were to investigate the effect of Hsp27 on LPS-induced inflammation and identify the precise mechanisms about how Hsp27 regulates LPS-induced TLR4 signaling in Thp1 cells. Thp1 cells were transfected with Flag-Hsp27 or pcDNA3.1, and then treated with LPS for indicated time. TNF-α, IL-1β, and IL-6 were determined by ELISA. The protein levels of Hsp27, p-Hsp27 (Ser15, Ser78, and Ser82), and TLR4 were measured by Western blotting. In vitro study showed that over-expression of Hsp27 downregulated the release of TNF-α, IL-1β, and IL-6 and suppressed the activation of TLR4 signals after stimulated by LPS. The location of TLR4 and RAB5 was detected by confocal microscopy. Immunoprecipitation was used to determine the ubiquitination and degradation of TLR4 and interaction between Hsp27 and TLR4. Results showed that Hsp27 could promote TLR4 endocytosis and ubiquitination and degradation. Further research revealed that Hsp27 was phosphorylated after LPS, only phosphorylated Hsp27 can interact with TLR4 and inhibit the activation of TLR4 signaling, which was demonstrated by inhibition of Hsp27 phosphorylation with inhibitors or transfection of Hsp27 mutants into Thp1 cells. Phosphorylated Hsp27 reduced the release of TNF-α, IL-1β, and IL-6, and suppressed the activation of TLR4 signaling by promoting TLR4 endocytosis, ubiquitination, and degradation.

Glucocorticoid modulatory element-binding protein 1 (GMEB1) interacts with the de-ubiquitinase USP40 to stabilize CFLARL and inhibit apoptosis in human non-small cell lung cancer cells

Background

GMEB1 was originally identified via its interaction with GMEB2, which binds to the promoter region of the tyrosine aminotransferase (TAT) gene and modulates transactivation of the glucocorticoid receptor gene. In the cytosol, GMEB1 interacts with and inhibits CASP8, but the molecular mechanism is currently unknown.

Methods

Human non-small cell lung cancer cells and 293FT cells were used to investigate the function of GMEB1/USP40/CFLAR_L complex by WB, GST Pull-Down Assay, Immunoprecipitation, Immunofluorescence and Flow cytometry analysis. A549 cells overexpressing green fluorescent protein and GMEB1 shRNA were used for tumor xenograft using female athymic nu/nu 4-week-old mice.

Results

We found GMEB1 interacted with CFLAR_L (also known as c-FLIP_L) in the cytosol and promoted its stability. USP40 targeted CFLAR_L for K48-linked de-ubiquitination. GMEB1 promoted the binding of USP40 to CFLAR_L. USP40 knockdown did not increase CFLAR_L protein level despite GMEB1 overexpression, suggesting GMEB1 promotes CFLAR_L stability via USP40. Additionally, GMEB1 inhibited the activation of pro-caspase 8 and apoptosis in non-small cell lung cancer (NSCLC) cell via CFLAR_L stabilization. Also, GMEB1 inhibited the formation of DISC upon TRAIL activation. CFLAR_L enhanced the binding of GMEB1 and CASP8. Downregulation of GMEB1 inhibited A549 xenograft tumor growth in vivo.

Conclusions

Our findings show the de-ubiquitinase USP40 regulates the ubiquitination and degradation of CFLAR_L; and GMEB1 acts as a bridge protein for USP40 and CFLAR_L. Mechanistically, we found GMEB1 inhibits the activation of CASP8 by modulating ubiquitination and degradation of CFLAR_L. These findings suggest a novel strategy to induce apoptosis through CFLAR_L targeting in human NSCLC cells.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1182-3) contains supplementary material, which is available to authorized users.

Indispensable role of β-arrestin2 in the protection of remifentanil preconditioning against hepatic ischemic reperfusion injury

Our previous study demonstrated that remifentanil, an opioid agonist, conferred profound liver protection during hepatic ischemia reperfusion injury (HIRI), in which Toll-like receptors (TLRs) played a crucial role in mediating the inflammatory responses. β-arrestin2, a well-known mu opioid receptor desensitizer, is also a negatively regulator of Toll-like receptor 4 (TLR4)-mediated inflammatory reactions in a mitogen-activated protein kinase (MAPK)-dependent manner. Using the rodent models of hepatic ischemia reperfusion injury both in wild type and TLR4 knockout (TLR4 KO) mice, we found that remifentanil preconditioning could inhibit the expression of TLR4 and reduce the inflammatory response induced by HIRI in wild type but not in TLR4 KO mice. For the in-vitro study, LPS was used to treat RAW264.7 macrophage cells to mimic the inflammatory response induced by HIRI. Remifentanil increased β-arrestin2 expression both in vivo and in vitro, while after silencing β-arrestin2 RNA, the effect of remifentanil in reducing cell death and apoptosis, as well as decreasing phosphorylation of ERK and JNK were abolished in RAW264.7 cells. These data suggested that remifentanil could ameliorate mice HIRI through upregulating β-arrestin2 expression, which may function as a key molecule in bridging opioid receptor and TLR4 pathway.

Blocking FSH inhibits hepatic cholesterol biosynthesis and reduces serum cholesterol

Menopause is associated with dyslipidemia and an increased risk of cardio-cerebrovascular disease. The classic view assumes that the underlying mechanism of dyslipidemia is attributed to an insufficiency of estrogen. In addition to a decrease in estrogen, circulating follicle-stimulating hormone (FSH) levels become elevated at menopause. In this study, we find that blocking FSH reduces serum cholesterol via inhibiting hepatic cholesterol biosynthesis. First, epidemiological results show that the serum FSH levels are positively correlated with the serum total cholesterol levels, even after adjustment by considering the effects of serum estrogen. In addition, the prevalence of hypercholesterolemia is significantly higher in peri-menopausal women than that in pre-menopausal women. Furthermore, we generated a mouse model of FSH elevation by intraperitoneally injecting exogenous FSH into ovariectomized (OVX) mice, in which a normal level of estrogen (E2) was maintained by exogenous supplementation. Consistently, the results indicate that FSH, independent of estrogen, increases the serum cholesterol level in this mouse model. Moreover, blocking FSH signaling by anti-FSHβ antibody or ablating the FSH receptor (FSHR) gene could effectively prevent hypercholesterolemia induced by FSH injection or high-cholesterol diet feeding. Mechanistically, FSH, via binding to hepatic FSHRs, activates the Gi2α/β-arrestin-2/Akt pathway and subsequently inhibits the binding of FoxO1 with the SREBP-2 promoter, thus preventing FoxO1 from repressing SREBP-2 gene transcription. This effect, in turn, results in the upregulation of SREBP-2, which drives HMGCR nascent transcription and de novo cholesterol biosynthesis, leading to the increase of cholesterol accumulation. This study uncovers that blocking FSH signaling might be a new strategy for treating hypercholesterolemia during menopause, particularly for women in peri-menopause characterized by FSH elevation only.

Heat Shock Protein 27 Phosphorylation Regulates Tumor Cell Migration under Shear Stress

Heat shock protein 27 (HSP27) is a multifunctional protein that undergoes significant changes in its expression and phosphorylation in response to shear stress stimuli, suggesting that it may be involved in mechanotransduction. However, the mechanism of HSP27 affecting tumor cell migration under shear stress is still not clear. In this study, HSP27-enhanced cyan fluorescent protein (ECFP) and HSP27-Ypet plasmids are constructed to visualize the self-polymerization of HSP27 in living cells based on fluorescence resonance energy transfer technology. The results show that shear stress induces polar distribution of HSP27 to regulate the dynamic structure at the cell leading edge. Shear stress also promotes HSP27 depolymerization to small molecules and then regulates polar actin accumulation and focal adhesion kinase (FAK) polar activation, which further promotes tumor cell migration. This study suggests that HSP27 plays an important role in the regulation of shear stress-induced HeLa cell migration, and it also provides a theoretical basis for HSP27 as a potential drug target for metastasis.

Inhibition of ROS-mediated activation Src-MAPK/AKT signaling by orientin alleviates H2O2-induced apoptosis in PC12 cells

Purpose

Reactive oxygen species (ROS) are considered a direct cause of neurodegenerative diseases (NDDs). Drugs developed to target ROS are effective for the treatment of NDDs. Orientin is a pyrone glucoside extracted from Polygonum orientale, and it exhibits many pharmacological activities. In this study, we aimed to determine whether orientin could relieve hydrogen peroxide (H₂O₂)-induced neuronal apoptosis and to investigate the specific target of orientin.

Materials and methods

In this study, the neuroprotective effect and its possible mechanisms of orientin in mouse pheochromocytoma cell line (PC12) cells stimulated by H₂O₂, establishing an oxidative stress model, were investigated. And we further tested the role of ROS in the neuroprotective effects of orientin.

Results

Orientin (5-100 µg/mL) did not cause toxicity in PC12 cells but significantly decreased H₂O₂-induced reduction in PC12 cell viability, cell apoptosis rates, and nuclear condensation. It also inhibited the activation of caspase-3 and degradation of poly(ADP-ribose) polymerase (PARP). Under the stimulation of H₂O₂, MAPKs (ERK, JNK, and p38), AKT, and Src signaling proteins in PC12 cells were activated in a time-dependent manner. The application of inhibitors that were specific for MAPKs, AKT, and Src effectively alleviated H₂O₂-induced cell apoptosis. In addition, the Src inhibitor decreased the activation of MAPKs and AKT signaling. More importantly, orientin effectively decreased H₂O₂-induced phosphorylation of MAPKs, AKT, and Src signaling proteins. Finally, we confirmed that orientin effectively inhibited H₂O₂-induced accumulation of ROS in cells. In addition, ROS inhibitors blocked the Src-MAPKs/AKT signaling pathway-dependent cell apoptosis stimulated by H₂O₂.

Conclusion

These results indicate that alleviation of H₂O₂-induced cell apoptosis by orientin is Src-MAPKs/AKT dependent. Overall, our study confirms that orientin alleviates H₂O₂-induced cell apoptosis by inhibiting the ROS-mediated activation of Src-MAPKs/AKT signaling.

Non-alcoholic fatty liver disease phosphoproteomics: A functional piece of the precision puzzle

BACKGROUND

Molecular signaling events associated with the necroinflammatory changes in nonalcoholic steatohepatitis (NASH) are not well understood.

AIMS

To understand the molecular basis of NASH, we evaluated reversible phosphorylation events in hepatic tissue derived from Class III obese subjects by phosphoproteomic means with the aim of highlighting key regulatory pathways that distinguish NASH from non-alcoholic fatty liver disease (also known as simple steatosis; SS).

MATERIALS & METHODS

Class III obese subjects undergoing bariatric surgery underwent liver biopsy (eight normal patients, eight with simple steatosis, and eight NASH patients). Our strategy was unbiased, comparing global differences in liver protein reversible phosphorylation events across the 24 subjects.

RESULTS

Of the 3078 phosphorylation sites assigned (2465 phosphoserine, 445 phosphothreonine, 165 phosphotyrosine), 53 were altered by a factor of 2 among cohorts, and of those, 12 were significantly increased or decreased by ANOVA (P < 0.05).

DISCUSSION

Statistical analyses of canonical signaling pathways identified carbohydrate metabolism and RNA post-transcriptional modification among the most over-represented networks.

CONCLUSION

Collectively, these results raise the possibility of abnormalities in carbohydrate metabolism as an important trigger for the development of NASH, in parallel with already established abnormalities in lipid metabolism.

PI3K inhibitor LY294002, as opposed to wortmannin, enhances AKT phosphorylation in gemcitabine-resistant pancreatic cancer cells

LY294002 and wortmannin are chemical compounds that act as potent inhibitors of phosphoinositide 3-kinases (PI3Ks). Both of them are generally used to inhibit cell proliferation as cancer treatment by inhibiting the PI3K/protein kinase B (AKT) signaling pathway. In this study, LY294002 (but not wortmannin) showed an abnormal ability to enhance AKT phosphorylation (at Ser472) specifically in gemcitabine (GEM)-resistant pancreatic cancer (PC) cell lines PK59 and KLM1-R. LY294002 was shown to activate AKT and accumulate phospho-AKT at the intracellular membrane in PK59, which was abolished by treatment with AKTi-1/2 or wortmannin. Inhibiting AKT phosphorylation by treatment with AKTi-1/2 or wortmannin further enhanced LY294002-induced cell death in PK59 and KLM1-R cells. In addition, treatment with wortmannin alone failed to inhibit cell proliferation in both PK59 and KLM1-R cells. Thus, our results reveal that LY294002 displays the opposite effect on PI3K-dependent AKT phosphorylation, which maintains cell survival from the cytotoxicity introduced by LY294002 itself in GEM-resistant pancreatic cancer cells. We suggest that targeting the PI3K/AKT signaling pathway with inhibitors may be counterproductive for patients with PC who have acquired GEM-resistance.

Pro-survival effects by NF-κB, Akt and ERK(1/2) and anti-apoptosis actions by Six1 disrupt apoptotic functions of TRAIL-Dr4/5 pathway in ovarian cancer

Apoptotic signaling provoked by death receptors, DR4 and DR5, are generally considered to promote cell death and chemosensitivity in multiple cancers, but this view is being thrown into doubt with recent findings that up-regulated DR4 and DR5 in advanced stages of ovarian cancer are associated with the poor prognosis. For this conflict, two reasonable explanations have been proposed: one is that DR4 and DR5 not exclusively mediate apoptotic pathway, but also favor survival signal; another is that apoptotic signals by DR4 and DR5 are disrupted by some regulators. This study identified these two speculations in TRAIL-resistant (SKOV-3ip1 and A2780) or sensitive (OVCAR-3) ovarian cancer cells. Activation of DR4 and DR5 using their specific ligand, TRAIL, activated pro-survival factors including NF-κB, Akt and ERK(1/2) in ovarian cancer SKOV-3ip1 and A2780 cells. Pharmacological inhibition of their activities potentiated TRAIL cytotoxicity, reducing cell viability and increasing apoptosis. Six1, a homeobox transcription factor, had higher expression in SKOV-3ip1 and A2780 cells than in OVCAR-3 cells. Silencing Six1 raised levels of apoptotic factors including cleaved Bid, caspase-8 and caspase-3, and overrode the TRAIL-resistance. Co-treatment with Six1 knockdown and peptidyl O-glycosyltransferase 14 overexpression showed additive effects on apoptosis signal, leading to increased apoptosis in SKOV-3ip1 and A2780 cells. This study demonstrated that pro-survival effects by NF-κB, Akt and ERK(1/2) and anti-apoptosis actions by Six1 disrupt apoptotic functions of TRAIL-Dr4/5 pathway in ovarian cancer, which may explain why up-regulated DR4 and DR5 in ovarian cancer are associated with poor prognosis and low survival ratio of the patients.

Phosphorylated heat shock protein 27 promotes lipid clearance in hepatic cells through interacting with STAT3 and activating autophagy

Nonalcoholic fatty liver disease (NAFLD) has become the major liver disease worldwide. Recently, several studies have identified that the activation of autophagy attenuates hepatic steatosis. Heat shock protein 27 (Hsp27) is involved in autophagy in response to various stimuli. In this study, we demonstrate that phosphorylated Hsp27 stimulates autophagy and lipid droplet clearance and interacts with STAT3. In vivo study showed that high fat diet (HFD) feeding increased Hsp25 (mouse orthology of Hsp27) phosphorylation and autophagy in mouse livers. Inhibition of Hsp25 phosphorylation exacerbated HFD-induced hepatic steatosis in mice. In vitro study showed that palmitate-induced lipid overload in hepatic cells was enhanced by Hsp27 knockdown, KRIBB3 treatment and Hsp27-3A (non-phosphorylatable) overexpression but was prevented by Hsp27-WT (wild type) and Hsp27-3D (phosphomimetic) overexpression. Mechanism analysis demonstrated that palmitate could induce Hsp27 phosphorylation which promoted palmitate-induced autophagy. Phosphorylated Hsp27 interacted with STAT3 in response to palmitate treatment, and disrupted the STAT3/PKR complexes, facilitated PKR-dependent eIF2α phosphorylation, and thus stimulated autophagy. To conclude, our study provides a novel mechanism by which the phosphorylated Hsp27 promotes hepatic lipid clearance and suggests a new insight for therapy of steatotic diseases such as nonalcoholic fatty liver disease (NAFLD).

β-arrestin2 regulates TRAIL-induced HepG2 cell apoptosis via the Src-extracellular signal-regulated signaling pathway

β-arrestins, including β-arrestin1 and β‑arrestin2, two ubiquitously expressed members of the arrestin family in various types of tissue, are adaptor proteins that modulate the desensitization and trafficking of seven membrane‑spanning receptors. Recently, β‑arrestins have been shown to bind to numerous signaling molecules, including c‑Src and mitogen‑activated protein kinase family members. In addition, accumulating evidence has suggested that β‑arrestins are involved in the anti‑apoptosis signaling pathway by associating with kinases, such as Akt and ERK, and altering their activities. However, the role of β‑arrestins in tumor necrosis factor‑related apoptosis‑inducing ligand (TRAIL)‑induced apoptosis remains unclear. In the present study, β‑arrestin2, but not β‑arrestin1, was observed to modulate TRAIL‑triggered HepG2 cell apoptosis by regulating activation of the Src‑extracellular signal‑regulated kinase (ERK) signaling pathway. Using overexpression and RNA interference experiments, β‑arrestin2 was demonstrated to prevent TRAIL‑induced HepG2 cell apoptosis. Additionally, β‑arrestin2 exerted an additive effect on TRAIL‑induced activation of Src and ERK. Furthermore, downregulating β‑arrestin2 expression attenuated the TRAIL‑induced activation of Src and ERK survival signaling and enhanced TRAIL‑induced apoptosis. PP2, a pharmacological inhibitor of Src, reduced activation of the Src‑ERK signaling pathway and enhanced TRAIL‑induced HepG2 cell apoptosis. Co-immunoprecipitation experiments demonstrated a physical association between β‑arrestin2 and Src, and TRAIL stimulation resulted in enhanced quantities of the β‑arrestin2/Src complex. A notable interaction was identified between β‑arrestin2 and death receptors (DR)4 and 5, but only in the presence of TRAIL stimulation. To the best of our knowledge, these findings are the first to demonstrate that β‑arrestin2 mediates TRAIL‑induced apoptosis by combing with DRs and Src, and regulates the activation of Src‑ERK signaling in HepG2 cells. It is hypothesized that the formation of a signaling complex comprising DR, β‑arrestin2 and Src is required for the action of TRAIL on HepG2 cell apoptosis, which provides a novel insight into analyzing the effects of β‑arrestin2 on protecting cells from TRAIL‑induced apoptosis.

Protective Role of β-arrestin2 in Colitis Through Modulation of T-cell Activation

β-arrestin2 (β-arr2), identified as a scaffolding protein in G-protein-coupled receptor desensitization, is a negative regulator of inflammation in polymicrobial sepsis. In this study, we wanted to investigate the role of β-arr2 in intestinal inflammation, a site of persistent microbial stimulation. In the absence of β-arr2, mice exhibited greater extent of mucosal inflammation determined by cellular infiltration and expression of inflammatory mediators even under homeostatic conditions. Furthermore, β-arr2-deficient mice were more susceptible to dextran sulfate sodium-induced colitis as demonstrated by greater body weight loss, higher disease activity index, and shortened colon as compared with wild-type mice. We also show that T cells from β-arr2 knockout mice exhibit altered activation status under both basal and colitic conditions, implicating their involvement in disease induction. Further assessment of the role of β-arr2 in intrinsic T-cell differentiation confirmed its importance in T-cell polarization. Using the T-cell transfer model of colitis, we demonstrate that T-cell-specific β-arr2 is important in limiting colitic inflammation; however, it plays a paradoxical role in concurrent systemic wasting disease. Together, our study highlights a critical negative regulatory role of β-arr2 in intestinal inflammation and demonstrates a distinct role of T-cell-specific β-arr2 in systemic wasting disease.

Multifaceted role of β-arrestins in inflammation and disease

Arrestins are intracellular scaffolding proteins known to regulate a range of biochemical processes including G protein-coupled receptor (GPCR) desensitization, signal attenuation, receptor turnover and downstream signaling cascades. Their roles in regulation of signaling network have lately been extended to receptors outside of the GPCR family, demonstrating their roles as important scaffolding proteins in various physiological processes including proliferation, differentiation and apoptosis. Recent studies have demonstrated a critical role for arrestins in immunological processes including key functions in inflammatory signaling pathways. In this review, we provide a comprehensive analysis of the different functions of the arrestin family of proteins especially related to immunity and inflammatory diseases.

Ampelopsin induces apoptosis in HepG2 human hepatoma cell line through extrinsic and intrinsic pathways: Involvement of P38 and ERK

Our results showed that ampelopsin significantly inhibited cell viability of hepatoma HepG2 cells using MTT assay. We further investigated the mechanism of anticancer activity by ampelopsin, it showed that ampelopsin induced apoptosis of HepG2 cells using DAPI assay and flow cytometry, which was confirmed by activation of PARP. Next, activation of the caspase cascades were demonstrated, including caspase-8, -9 and -3. We also found that ampelopsin increased the levels of death receptor 4 (DR4), death receptor 5 (DR5) and decreased the expression of Bcl-2 protein, which led to an increase of the Bax/Bcl-2 ratio. Meanwhile, the release of cytochrome c from mitochondria was observed. Ampelopsin decreased the levels of iNOS and COX-2 but had no impact on the level of reactive oxygen species (ROS). In addition, ampelopsin activated ERK1/2 and P38, but little JNK1/2 activation was detected. Further investigation showed that suppression of P38 activation by SB203580 increased the cell viability and also prevented cleavage of caspase-3 and PARP, inhibition of ERK1/2 with U0126 had the opposite action. In conclusion, our results indicated that ampelopsin mainly elicited apoptosis through extrinsic and intrinsic pathway and that ERK1/2 and P38 had opponent effects on the apoptosis.

Ratio of phosphorylated HSP27 to nonphosphorylated HSP27 biphasically acts as a determinant of cellular fate in gemcitabine-resistant pancreatic cancer cells

Gemcitabine has been used most commonly as an anticancer drug to treat advanced pancreatic cancer patients. However, intrinsic or acquired resistance of pancreatic cancer to gemcitabine was also developed, which leads to very low five-year survival rates. Here, we investigated whether cellular levels of HSP27 phosphorylation act as a determinant of cellular fate with gemcitabine. In addition we have demonstrated whether HSP27 downregulation effectively could overcome the acquisition of gemcitabine resistance by using transcriptomic analysis. We observed that gemcitabine induced p38/HSP27 phosphorylation and caused acquired resistance. After acquisition of gemcitabine resistance, cancer cells showed higher activity of NF-κB. NF-κB activity, as well as colony formation in gemcitabine-resistant pancreatic cancer cells, was significantly decreased by HSP27 downregulation and subsequent TRAIL treatment, showing that HSP27 was a common network mediator of gemcitabine/TRAIL-induced cell death. After transcriptomic analysis, gene fluctuation after HSP27 downregulation was very similar to that of pancreatic cancer cells susceptible to gemcitabine, and then in opposite position to that of acquired gemcitabine resistance, which makes it possible to downregulate HSP27 to overcome the acquired gemcitabine resistance to function as an overall survival network inhibitor. Most importantly, we demonstrated that the ratio of phosphorylated HSP27 to nonphosphorylated HSP27 rather than the cellular level of HSP27 itself acts biphasically as a determinant of cellular fate in gemcitabine-resistant pancreatic cancer cells.

Small heat shock proteins: Role in cellular functions and pathology

Small heat shock proteins (sHsps) are conserved across species and are important in stress tolerance. Many sHsps exhibit chaperone-like activity in preventing aggregation of target proteins, keeping them in a folding-competent state and refolding them by themselves or in concert with other ATP-dependent chaperones. Mutations in human sHsps result in myopathies, neuropathies and cataract. Their expression is modulated in diseases such as Alzheimer's, Parkinson's and cancer. Their ability to bind Cu2+, and suppress generation of reactive oxygen species (ROS) may have implications in Cu2+-homeostasis and neurodegenerative diseases. Circulating αB-crystallin and Hsp27 in the plasma may exhibit immunomodulatory and anti-inflammatory functions. αB-crystallin and Hsp20 exhitbit anti-platelet aggregation: these beneficial effects indicate their use as potential therapeutic agents. sHsps have roles in differentiation, proteasomal degradation, autophagy and development. sHsps exhibit a robust anti-apoptotic property, involving several stages of mitochondrial-mediated, extrinsic apoptotic as well as pro-survival pathways. Dynamic N- and C-termini and oligomeric assemblies of αB-crystallin and Hsp27 are important factors for their functions. We propose a "dynamic partitioning hypothesis" for the promiscuous interactions and pleotropic functions exhibited by sHsps. Stress tolerance and anti-apoptotic properties of sHsps have both beneficial and deleterious consequences in human health and diseases. Conditional and targeted modulation of their expression and/or activity could be used as strategies in treating several human disorders. The review attempts to provide a critical overview of sHsps and their divergent roles in cellular processes particularly in the context of human health and disease.

Heat shock protein 27 phosphorylation in the proliferation and apoptosis of human umbilical vein endothelial cells induced by high glucose through the phosphoinositide 3‑kinase/Akt and extracellular signal‑regulated kinase 1/2 pathways

In the present study, the effect of the heat shock protein 27 (HSP27) signaling pathway on the proliferation and apoptosis of human umbilical vein endothelial cells (HUVECs) induced by high glucose (HG) was investigated. HUVEC proliferation in the indicated conditions was measured by the alamarBlue® assay. Apoptosis in HUVECs cultured with HG was analyzed by an Annexin V‑fluorescein isothiocyanate/propidium iodide apoptosis detection kit. HSP27 activity was evaluated by western blotting with specific phospho‑HSP27 antibody. HUVEC proliferation induced by HG was observed to be reduced by the HSP27 inhibitor quercetin in a concentration‑dependent manner, with a concomitant increase in apoptosis. The phosphorylation of HSP27 induced by HG was blocked by the specific phosphoinositide 3‑kinase (PI3K) inhibitor LY294002 and the specific extracellular signal‑regulated kinase (ERK) 1/2 inhibitor U0126 in a concentration‑dependent manner, with peak inhibition rates of 62.6 and 56.1%, respectively. LY294002 and U0126 also reduced HUVEC proliferation with a concomitant increase in apoptotic rate. In conclusion, HSP27 phosphorylation is important in mediating the proliferation and apoptosis of HUVECs induced by high glucose, and PI3K/Akt and ERK1/2 are important signaling pathways that contribute to HSP27 phosphorylation.

The multiple facets of drug resistance: one history, different approaches

Some cancers like melanoma and pancreatic and ovarian cancers, for example, commonly display resistance to chemotherapy, and this is the major obstacle to a better prognosis of patients. Frequently, literature presents studies in monolayer cell cultures, 3D cell cultures or in vivo studies, but rarely the same work compares results of drug resistance in different models. Several of these works are presented in this review and show that usually cells in 3D culture are more resistant to drugs than monolayer cultured cells due to different mechanisms. Searching for new strategies to sensitize different tumors to chemotherapy, many methods have been studied to understand the mechanisms whereby cancer cells acquire drug resistance. These methods have been strongly advanced along the years and therapies using different drugs have been increasingly proposed to induce cell death in resistant cells of different cancers. Recently, cancer stem cells (CSCs) have been extensively studied because they would be the only cells capable of sustaining tumorigenesis. It is believed that the resistance of CSCs to currently used chemotherapeutics is a major contributing factor in cancer recurrence and later metastasis development. This review aims to appraise the experimental progress in the study of acquired drug resistance of cancer cells in different models as well as to understand the role of CSCs as the major contributing factor in cancer recurrence and metastasis development, describing how CSCs can be identified and isolated.

Phosphorylation of heat shock protein 27 antagonizes TNF-α induced HeLa cell apoptosis via regulating TAK1 ubiquitination and activation of p38 and ERK signaling

Tumor necrosis factor (TNF)-α is a potent cytokine that regulates critical cellular processes including apoptosis. TNF-α usually triggers both survival and apoptotic signals in various cell types. Heat shock protein 27 (HSP27), an important cellular chaperone, is believed to protect cells from apoptosis. HSP27 can be phosphorylated and changed its cellular function according to different stimuli. However, available reports on the role of HSP27 phosphorylation in apoptosis remain elusive. In this study, we investigated the role of HSP27 phosphorylation in TNF-α induced apoptosis in human cervical carcinoma (HeLa) cells. We found that TNF-α induced apoptosis was enhanced if we suppressed the TNF-α induced HSP27 phosphorylation by specific inhibitor CMPD1 or MAPKAPK2 (MK2) knockdown or by overexpression of non-phosphorylatable mutant HSP27-3A. Through co-immunoprecipitation and confocal microscopy, we observed that HSP27 associated with transforming growth factor-β (TGF-β)-activated kinase 1 (TAK1) in response to TNF-α stimulation. By blocking MK2 activity or overexpressing phospho-mimetic mutant Hsp27-3D, we further showed that HSP27 phosphorylation facilitated the TNF-α induced ubiquitination and phosphorylation of TAK1 and the activations of p38 MAPK and ERK, the TAK1 downstream pro-survival signaling. In addition, we also found that increased HSP27 phosphorylation inhibited TRADD ubiquitination but did not influence the binding between TRADD and FADD in a pro-apoptotic complex. Taken together, our data indicated that HSP27 phosphorylation was involved in modulating the TNF-α induced apoptosis via interacting with TAK1 and regulating TAK1 post-translational modifications in HeLa cells. This study demonstrates that HSP27 phosphorylation serves as a novel regulator in TNF-α-induced apoptosis, and provides a new insight into the cytoprotective role of HSP27 phosphorylation.