Interplay between endoplasmic reticulum (ER) stress and autophagy induces mutant p53H273 degradation

The unfolded protein response (UPR) is an adaptive response to intrinsic and external stressors, and it is mainly activated by the accumulation of misfolded proteins at the endoplasmic reticulum (ER) lumen producing ER stress. The UPR signaling network is interconnected with autophagy, the proteolytic machinery specifically devoted to clearing misfolded proteins in order to survive bioenergetic stress and/or induce cell death. Oncosuppressor TP53 may undergo inactivation following missense mutations within the DNA-binding domain (DBD), and mutant p53 (mutp53) proteins may acquire a misfolded conformation, often due to the loss of the DBD-bound zinc ion, leading to accumulation of hyperstable mutp53 proteins that correlates with more aggressive tumors, resistance to therapies, and poorer outcomes. We previously showed that zinc supplementation induces mutp53 protein degradation by autophagy. Here, we show that mutp53 (i.e., Arg273) degradation following zinc supplementation is correlated with activation of ER stress and of the IRE1α/XBPI arm of the UPR. ER stress inhibition with chemical chaperone 4-phenyl butyrate (PBA) impaired mutp53 downregulation, which is similar to IRE1α/XBPI specific inhibition, reducing cancer cell death. Knockdown of mutp53 failed to induce UPR/autophagy activation indicating that the effect of zinc on mutp53 folding was likely the key event occurring in ER stress activation. Recently discovered small molecules targeting components of the UPR show promise as a novel anticancer therapeutic intervention. However, our findings showing UPR activation during mutp53 degradation indicate that caution is necessary in the design of therapies that inhibit UPR components

Apigenin, by activating p53 and inhibiting STAT3, modulates the balance between pro-apoptotic and pro-survival pathways to induce PEL cell death

BACKGROUND: Apigenin is a flavonoid widely distributed in plant kingdom that exerts cytotoxic effects against a variety of solid and haematological cancers. In this study, we investigated the effect of apigenin against primary effusion lymphoma (PEL), a KSHV-associated B cell lymphoma characterized by a very aggressive behavior, displaying constitutive activation of STAT3 as well as of other oncogenic pathways and harboring wtp53. METHODS: Cell death was assessed by trypan blue exclusion assay, FACS analysis as well as by biochemical studies. The latter were also utilized to detect the occurrence of autophagy and the molecular mechanisms leading to the activation of both processes by apigenin. FACS analysis was used to measure the intracellular ROS utilizing DCFDA. RESULTS: We show that apigenin induced PEL cell death and autophagy along with reduction of intracellular ROS. Mechanistically, apigenin activated p53 that induced catalase, a ROS scavenger enzyme, and inhibited STAT3, the most important pro-survival pathway in PEL, as assessed by p53 silencing. On the other hand, STAT3 inhibition by apigenin resulted in p53 activation, since STAT3 negatively influences p53 activity, highlighting a regulatory loop between these two pathways that modulates PEL cell death/survival. CONCLUSION: The findings of this study demonstrate that apigenin may modulate pro-apoptotic and pro-survival pathways representing a valid therapeutic strategy against PEL

Cytotoxic drugs activate KSHV lytic cycle in latently infected PEL cells by inducing a moderate ROS increase controlled by HSF1, NRF2 and p62/SQSTM1

Previous studies have indicated that cytotoxic treatments may induce or not activate viral lytic cycle activation in cancer cells latently infected by Kaposi’s sarcoma-associated herpesvirus (KSHV). To investigate the molecular mechanisms responsible for such an effect, we compared two cytotoxic treatments able to induce the viral lytic cycle, named 12-O-tetradecanoylphorbol 13-acetate (TPA) (T) in combination with sodium butyrate (B) and bortezomib (BZ), with two cytotoxic treatments that did not activate this process, named metformin (MET) and quercetin (Q). Our results indicated that TB and bortezomib increased levels of oxygen reactive species (ROS) while metformin and quercetin reduced them. The finding that N-acetylcysteine (NAC), a reactive oxigen species (ROS) scavenger, counteracted K-bZIP expression induced by TB or bortezomib, confirmed that an ROS increase played a role in KSHV lytic cycle activation. Moreover, we found that TB and bortezomib up-regulated p62/Sequestosome1(p62/SQSTM1) protein, while metformin and quercetin down-regulated it. p62/SQSTM1 silencing or the inhibition of NF-E2-related factor 2 (NRF2) or Heat Shock Factor 1 (HSF1), that mediate p62/SQSTM1 transcription, also reduced KSHV lytic antigen expression induced by TB or bortezomib. Interestingly, such combination treatments further increased intracellular ROS and cytotoxicity induced by the single TB or bortezomib treatment, suggesting that NRF2, HSF1 and p62/SQSTM1 keep the ROS level under control, allowing primary effusion lymphoma (PEL) cells to continue to survive and KSHV to replicate

Reduced chemotherapeutic sensitivity in high glucose condition: implication of antioxidant response

Resistance to chemotherapy represents a major obstacle to successful treatment. The generation of reactive oxygen species (ROS) has been directly linked to the cytotoxic effects of several antitumor agents, including Adriamycin (ADR), and modulation of the oxidative balance has been implicated in the development and/or regulation of resistance to chemotherapeutic drugs. We recently showed that high glucose (HG) markedly diminished the cancer cell death induced by anticancer agents such as ADR. In the present study we attempted to evaluate the mechanism that impaired the cytotoxic effect of ADR in HG. We found that, in colon cancer cells, HG attenuated ADR-induced ROS production that consequently diminished ADR-induced H2AX phosphorylation and micronuclei (MN) formation. Mechanistically, HG attenuation of ADR-induced ROS production correlated with increased antioxidant response promoted by NRF2 activity. Thus, pharmacologic inhibition of NRF2 pathway by brusatol re-established the ADR cytotoxic effect impaired by HG. Together, the data provide new insights into chemotherapeutic-resistance mechanisms in HG condition dictated by increased NRF2-induced antioxidant response and how they may be overcome in order to restore chemosensitivity and ADR-induced cell death

c-Myc Sustains Pancreatic Cancer Cell Survival and mutp53 Stability through the Mevalonate Pathway

It has been shown that wild-type (wt)p53 inhibits oncogene c-Myc while mutant (mut)p53 may transactivate it, with an opposite behavior that frequently occurs in the crosstalk of wt or mutp53 with molecules/pathways promoting carcinogenesis. Even if it has been reported that mutp53 sustains c-Myc, whether c-Myc could in turn influence mutp53 expression remains to be investigated. In this study, we found that pharmacological or genetic inhibition of c-Myc downregulated mutp53, impaired cell survival and increased DNA damage in pancreatic cancer cells. At the molecular level, we observed that c-Myc inhibition reduced the expression of mevalonate kinase (MVK), a molecule belonging to the mevalonate pathway that-according to previous findings-can control mutp53 stability, and thus contributes to cancer cell survival. In conclusion, this study unveils another criminal alliance between oncogenes, such as c-Myc and mutp53, that plays a key role in oncogenesis

Bortezomib promotes KHSV and EBV lytic cycle by activating JNK and autophagy

KSHV and EBV are gammaherpesviruses strictly linked to human cancers. Even if the majority of cancer cells harbor a latent infection, the few cells that undergo viral replication may contribute to the pathogenesis and maintenance of the virus-associated malignancies. Cytotoxic drugs used for the therapies of cancers harboring virus-infection often have, as side effect, the activation of viral lytic cycle. Therefore it is important to investigate whether they affect viral reactivation and understand the underlying mechanisms involved. In this study, we found that proteasome inhibitor bortezomib, a cytotoxic drug that efficiently target gammaherpesvirus-associated B cell lymphomas, triggered KSHV or EBV viral lytic cycle by activating JNK, in the course of ER stress, and inducing autophagy. These results suggest that the manipulation of these pathways could limit viral spread and improve the outcome of bortezomib treatment in patients affected by gammaherpesvirus-associated lymphomas

ATF6 prevents DNA damage and cell death in colon cancer cells undergoing ER stress

Colon cancer represents one of the most common and aggressive cancers in its advanced state. Among the most innovative anti-cancer approaches, the manipulation of UPR is a promising one, effective also against cancers carrying dysfunctional p53. Interestingly, it is emerging that UPR cross-talks with DDR and that targeting the interplay between these two adaptive responses may be exploited to overcome the resistance to the single DDR- and UPR-targeting treatments. Previous studies have highlighted the role of IRE1 alpha and PERK UPR sensors on DDR, while the impact of ATF6 on this process remains under-investigated. This study shows for the first time that ATF6 sustains the expression level of BRCA-1 and protects colon cancer cells from the cytotoxic effect of ER stressors DPE and Thapsigargin. At molecular level, ATF6 activates mTOR to sustain the expression of HSP90, of which BRCA-1 is a client protein. Therefore, pharmacological or genetic inhibition of ATF6 promoted BRCA-1 degradation and increased DNA damage and cell death, particularly in combination with Adriamycin. All together this study suggests that targeting ATF6 may not only potentiate the cytotoxic effect of drugs triggering ER stress but may render colon cancer cells more sensitive to Adriamycin and possibly to other DNA damaging agents used to treat colon cancer

KSHV dysregulates bulk macroautophagy, mitophagy and UPR to promote endothelial to mesenchymal transition and CCL2 release, key events in viral-driven sarcomagenesis

Kaposi's Sarcoma-associated Herpesvirus (KSHV) is the causative agent of KS, an aggressive neoplasm that mainly occurs in immune-compromised patients. Spindle cells represent the main feature of this aggressive malignancy and arise from KSHV-infected endothelial cells undergoing endothelial to mesenchymal transition (EndMT), which changes their cytoskeletal composition and organization. As in epithelial to mesenchymal transition (EMT), EndMT is driven by transcription factors such as SNAI1 and ZEB1 and implies a cellular reprogramming mechanism regulated by several molecular pathways, particularly PI3K/AKT/MTOR. Here we found that KSHV activated MTOR and its targets 4EBP1 and ULK1 and reduced bulk macroautophagy and mitophagy to promote EndMT, activate ER stress/ Unfolded Protein Response (UPR), and increase the release of the pro-angiogenic and pro-inflammatory chemokine CCL2 by HUVEC cells. This study suggests that the manipulation of macroautophagy, mitophagy, and UPR and the interplay between the three could be a promising strategy to counteract EndMT, angiogenesis, and inflammation, the key events of KSHV-driven sarcomagenesis

NFE2L2 and STAT3 converge on common targets to promote survival of primary lymphoma cells

NFE2L2 and STAT3 are key pro-survival molecules, and thus, their targeting may represent a promising anti-cancer strategy. In this study, we found that a positive feedback loop occurred between them and provided evidence that their concomitant inhibition efficiently impaired the survival of PEL cells, a rare, aggressive B cell lymphoma associated with the gammaherpesvirus KSHV and often also EBV. At the molecular level, we found that NFE2L2 and STAT3 converged in the regulation of several pro-survival molecules and in the activation of processes essential for the adaption of lymphoma cells to stress. Among those, STAT3 and NFE2L2 promoted the activation of pathways such as MAPK3/1 and MTOR that positively regulate protein synthesis, sustained the antioxidant response, expression of molecules such as MYC, BIRC5, CCND1, and HSP, and allowed DDR execution. The findings of this study suggest that the concomitant inhibition of NFE2L2 and STAT3 may be considered a therapeutic option for the treatment of this lymphoma that poorly responds to chemotherapies

The inhibition of IRE1alpha/XBP1 axis prevents EBV-driven lymphomagenesis in NSG mice

Post-transplant lymphoproliferative disorders (PTLD) are a group of heterogeneous diseases originating in conditions of immune deficiency, whose main driver is considered to be Epstein-Barr virus (EBV). Here, we explored the role of IRE1alpha/XBP1s axis in EBV-driven lymphomagenesis in an NOD SCID gamma mouse model, as these animals develop malignancies that closely resemble PTLD when engrafted with EBV-positive peripheral blood momonuclear cells (PBMC). This study evidences for the first time that 4μ8C IRE1 alpha endoribonuclease inhibitor prevented lymphomagenesis in vivo and B-cell immortalization in vitro driven by the virus. At the molecular level, 4μ8C reduced the expression of EBV antigens such as ZEBRA and LMP1, downregulated c-Myc and cyclin D1, and prevented the activation of STAT3, molecules known to be involved in viral lymphomagenesis. The results obtained in this study suggest that the inhibition of IRE1 alpha endoribonuclease may represent a promising therapeutic strategy to prevent EBV-associated PTLD that arise in immune-deficient patients.IMPORTANCEThe novelty of this study lies in the fact that it shows that IRE1 alpha endoribonuclease inhibition by 4μ8C was able to counteract Epstein-Barr virus-driven lymphomagenesis in NOD SCID gamma mice and prevent B-cell immortalization in vitro, unveiling that this drug may be a promising therapeutic approach to reduce the risk of post-transplant lymphoproliferative disorders (PTLD) onset in immune-deficient patients. This hypothesis is further supported by the fact that 4μ8C impaired the survival of PTLD-like cells derived from mice, meaning that it could be helpful also in the case in which there is the possibility that these malignancies have begun to arise