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.

p62/SQSTM1 promotes mitophagy and activates the NRF2-mediated antioxidant and anti-inflammatory response restraining EBV-driven B lymphocyte proliferation.

Reactive oxygen species (ROS) and DNA repair, respectively, promote and limit oncogenic transformation of B cells driven by Epstein-Barr virus (EBV). We have previously shown that EBV infection reduced autophagy in primary B lymphocytes and enhanced ROS and interleukin 6 (IL-6) release, promoting B-cell proliferation and immortalization. In this study, we explored the role of p62/SQSTM1, accumulated as a consequence of autophagy reduction in EBV-infected B lymphocytes, and found that it exerted a growth-suppressive effect in these cells. At the molecular level, we found that p62 counteracted IL-6 production and ROS increase by interacting with NRF2 and promoting mitophagy. Moreover, p62/NRF2 axis sustained the expression level of H2AX and ataxia-telangiectasia mutated (ATM), whose activation has been shown to have growth-suppressive effects during the first steps of EBV infection, before latency is established. In conclusion, this study shows for the first time that the accumulation of p62 and the activation of p62/axis counteracted EBV-driven proliferation of primary B lymphocytes.

The impairment of DDR reduces XBP1s, further increasing DNA damage, and triggers autophagy via PERK/eIF2alpha in MM and IRE1alpha/JNK1/2 in PEL cells.

Cancer cells, particularly MM, that are highly secretory cells, and PEL cells that harbor KSHV, are characterized by high level of stress to which they adapt by activating DDR, UPR and autophagy. It is known that UPR sensors may affect DDR, but whether DDR manipulation influences UPR is less known. In this study, we found an intricate interplay between these responses. Indeed, PARP and CHK1 inhibition by AZD2461 and UCN-01, by downregulating c-Myc, reduced the expression of XBP1s, constitutively expressed in these cells, and upregulated CHOP. Interestingly, given the role of XBP1s in regulating DDR, BRCA-1 expression level was reduced, exacerbating DNA damage. Finally, DDR/UPR interplay activated a pro-survival autophagy via PERK/eIF2alpha axis in MM and IRE1alpha/JNK axis in PEL cells, since in the latter case PERK/eIF2alpha activation could be prevented by KSHV that, as other herpesviruses, tries to avoid the blocks of protein translation that this pathway may induce.

Anticancer effect of AZD2461 PARP inhibitor against colon cancer cells carrying wt or dysfunctional p53.

Colon cancer is one of the most common cancers, currently treated with traditional chemotherapies or alternative therapies. However, these treatments are still not enough effective and induce several side effects, so that the search of new therapeutic strategies is needed. The use of Poly-(ADP-ribose)-polymerase (PARP) inhibitors, although originally approved against BRCA-1 or BRCA-2 mutated cancers, has been extended, particularly in combination with other treatments, to cure cancers that do not display defects in DNA repair signaling pathways. The role of p53 oncosuppressor in the regulating the outcome of PARP inhibitor treatment remains an open issue. In this study, we addressed this topic by using a well-tolerated PARP 1/2/3 inhibitor, namely AZD2461, against colon cancer cell lines with different p53 status. We found that AZD2461 reduced cell proliferation in wtp53 and p53-/- cancer cells by increasing ROS and DNA damage, while R273H mutant (mut) p53 counteracted these effects. Moreover, AZD2461 improved the reduction of cell proliferation by low dose radiation (IR) in wtp53 cancer cells, in which a down-regulation of BRCA-1 occurred. AZD2461 did not affect cell proliferation of mutp53 colon cancer cells also in combination with low dose radiation, suggesting that only wt p53 or p53 null colon cancer cells could benefit AZD2461 treatment.

VPA and TSA Interrupt the Interplay between mutp53 and HSP70, Leading to CHK1 and RAD51 Down-Regulation and Sensitizing Pancreatic Cancer Cells to AZD2461 PARP Inhibitor.

HDAC inhibitors (HDACi) represent promising anti-cancer treatments, as the acetylation of histone and non-histone proteins is often dysregulated in cancer and contributes to cancer onset and progression. HDACi have been also reported to increase the cytotoxicity of DNA-damaging agents, such as radiation or cisplatin. In this study, we found that TSA and, even more effectively, VPA synergized with AZD2461, PARP1, 2 and 3 inhibitor (PARPi) to induce DNA damage and reduce pancreatic cancer cell survival. At a molecular level, VPA and TSA down-regulated CHK1 and RAD51, which is correlated with the interruption of the cross-talk between mutp53 and HSP70. Moreover, VPA and to a lesser extent TSA reactivated wtp53 in these cells, which contributed to CHK1 and RAD51 reduction. These findings suggest that the combination of HDACi and PARPi might improve the treatment of pancreatic cancer, which remains one of the most aggressive and therapy-resistant cancers.

Concomitant Inhibition of IRE1α/XBP1 Axis of UPR and PARP: A Promising Therapeutic Approach against c-Myc and Gammaherpesvirus-Driven B-Cell Lymphomas.

It is emerging that targeting the adaptive functions of Unfolded Protein Response (UPR) may represent a promising anti-cancer therapeutic approach. This is particularly relevant for B-cell lymphomas, characterized by a high level of constitutive stress due to high c-Myc expression. In this study, we found that IRE1α/XBP1 axis inhibition exerted a stronger cytotoxic effect compared to the inhibition of the other two UPR sensors, namely PERK and ATF6, in Burkitt lymphoma (BL) cells, in correlation with c-Myc downregulation. Interestingly, such an effect was more evident in Epstein-Barr virus (EBV)-negative BL cells or those cells expressing type I latency compared to type III latency BL cells. The other interesting finding of this study was that the inhibition of IRE1α/XBP1 downregulated BRCA-1 and RAD51 and potentiated the cytotoxicity of PARP inhibitor AZD2661 against BL cells and also against Primary Effusion Lymphoma (PEL), another aggressive B-cell lymphoma driven by c-Myc and associated with gammaherpesvirus infection. These results suggest that combining the inhibition of UPR sensors, particularly IRE1α/XBP1 axis, and molecules involved in DDR, such as PARP, could offer a new therapeutic opportunity for treating aggressive B-cell lymphomas such as BL and PEL.

Lovastatin reduces PEL cell survival by phosphorylating ERK1/2 that blocks the autophagic flux and engages a cross-talk with p53 to activate p21.

Statins are inhibitors of the mevalonate pathway that besides being cholesterol lowering agents, display anti-cancer properties. This is because cholesterol is an essential component of cell membranes but also because the mevalonate pathway controls protein farnesylation and geranylation, processes essential for the activity of GTPase family proteins. In this study, we found that Lovastatin exerted a dose- and time-dependent cytotoxic effect against PEL cells, an aggressive B cell lymphoma strictly associated with the gammaherpesvirus KSHV and characterized by a poor response to conventional chemotherapies. At molecular level, Lovastatin by dephosphorylating STAT3, induced ERK1/2 activation that inhibited autophagy and phosphorylated p53ser15 that in turn maintained ERK1/2 activated and up-regulated p21. However, p21 played a pro-survival role in this setting, as its inhibition by UC2288 further reduced cell survival in PEL cells undergoing Lovastatin treatment. In conclusion, this study suggests that Lovastatin may represent a valid therapeutic alternative against PEL cells, especially if used in combination with p21 inhibitors.

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. Our 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.

KSHV infection skews macrophage polarisation towards M2-like/TAM and activates Ire1 α-XBP1 axis up-regulating pro-tumorigenic cytokine release and PD-L1 expression.

BACKGROUND: Kaposi's Sarcoma Herpesvirus (KSHV) is a gammaherpesvirus strongly linked to human cancer. The virus is also able to induce immune suppression, effect that contributes to onset/progression of the viral-associated malignancies. As KSHV may infect macrophages and these cells abundantly infiltrate Kaposi's sarcoma lesions, in this study we investigated whether KSHV-infection could affect macrophage polarisation to promote tumorigenesis. METHODS: FACS analysis was used to detect macrophage markers and PD-L1 expression. KSHV infection and the molecular pathways activated were investigated by western blot analysis and by qRT-PCR while cytokine release was assessed by Multi-analyte Kit. RESULTS: We found that KSHV infection reduced macrophage survival and skewed their polarisation towards M2 like/TAM cells, based on the expression of CD163, on the activation of STAT3 and STAT6 pathways and the release of pro-tumorigenic cytokines such as IL-10, VEGF, IL-6 and IL-8. We also found that KSHV triggered Ire1 α-XBP1 axis activation in infected macrophages to increase the release of pro-tumorigenic cytokines and to up-regulate PD-L1 surface expression. CONCLUSIONS: The findings that KSHV infection of macrophages skews their polarisation towards M2/TAM and that activate Ire1 α-XBP1 to increase the release of pro-tumorigenic cytokines and the expression of PD-L1, suggest that manipulation of UPR could be exploited to prevent or improve the treatment of KSHV-associated malignancies.

Impact of HHV-6A and HHV-6B lytic infection on autophagy and endoplasmic reticulum stress.

Herpesviruses are known to manipulate autophagy to optimize their replication, counteract immune response and probably to promote tumourigenesis. This study explored, for the first time, the impact of human herpesvirus (HHV)-6 lytic infection on autophagy and demonstrated that HHV-6A and B (viruses sharing more than 80 % homology) differently affected this cellular process. Indeed, while HHV-6A (GS) infection of HSB2 cells promoted autophagy, HHV-6B (Z29) or the virus isolated from the serum of roseola infantum-affected patient-inhibited autophagy in Molt-3 cells or in PBMCs, respectively. Interestingly, the different behaviour of HHV-6A and B on the autophagic process was accompanied by different effects on endoplasmic reticulum stress, unfolded protein response and cell survival that was more strongly reduced by HHV-6B infection. We hypothesize that the ability to inhibit autophagy displayed by HHV-6B could be due to the fact that it contains gene homologues of those encoding for TRS1; the protein responsible for the block of autophagy by human cytomegalovirus. Understanding how HHV-6A/B infection regulates autophagy could be of particular interest, as it has been recently shown that this virus may be involved in Alzheimer's disease in which a dysregulation of autophagy may also play a role.

ATF6 supports lysosomal function in tumor cells to enable ER stress-activated macroautophagy and CMA: impact on mutant TP53 expression.

The inhibition of the unfolded protein response (UPR), which usually protects cancer cells from stress, may be exploited to potentiate the cytotoxic effect of drugs inducing ER stress. However, in this study, we found that ER stress and UPR activation by thapsigargin or tunicamycin promoted the lysosomal degradation of mutant (MUT) TP53 and that the inhibition of the UPR sensor ATF6, but not of ERN1/IRE1 or EIF2AK3/PERK, counteracted such an effect. ATF6 activation was indeed required to sustain the function of lysosomes, enabling the execution of chaperone-mediated autophagy (CMA) as well as of macroautophagy, processes involved in the degradation of MUT TP53 in stressed cancer cells. At the molecular level, by pharmacological and genetic approaches, we demonstrated that the inhibition of ATF6 correlated with the activation of MTOR and with TFEB and LAMP1 downregulation in thapsigargin-treated MUT TP53 carrying cells. We hypothesize that the rescue of MUT TP53 expression by ATF6 inhibition, could further activate MTOR and maintain lysosomal dysfunction, further inhibiting MUT TP53 degradation, in a vicious circle. The findings of this study suggest that the presence of MUT TP53, which often exerts oncogenic properties, should be considered before approaching treatments combining ER stressors with ATF6 inhibitors against cancer cells, while it could represent a promising strategy against cancer cells that harbor WT TP53.

Acetylation increases expression, interaction with TRAPPC4 and surface localization of PD-L1.

PD-L1 is an immune checkpoint inhibitor, whose surface expression may be exploited by cancer cells to escape T cell-mediated immune recognition. PD-L1 expression and nuclear localization can be affected by epigenetic modifications, such as acetylation. In this study, we showed that VPA, a class I/IIa HDAC inhibitor, upregulated PD-L1 expression on the surface of pancreatic cancer cells. To this effect contributed the increased transcription, in correlation with histone acetylation of the PD-L1 gene and the acetylation of PD-L1 protein, which led to an increased interaction with TRAPPC4, molecule involved in PD-L1 recycling to the cell membrane. Interestingly, the BRD4 inhibitor JQ-1, counteracted PD-L1 transcription and reduced its surface expression, suggesting that such a combination could improve the outcome of VPA treatment, also because it increased the cytotoxic effect of VPA. Also considering that this HDACi did not upregulate PD-L2 and that the supernatant of VPA-treated cancer cells did not increase PD-L1 expression on the surface of macrophages exposed to it.

HHV-6A Infection of Papillary Thyroid Cancer Cells Induces Several Effects Related to Cancer Progression.

Recent studies have shown that thyrocytes are permissive to HHV-6A infection and that the virus may contribute to the pathogenesis of autoimmune thyroiditis. Thyroid autoimmune diseases increase the risk of papillary cancer, which is not surprising considering that chronic inflammation activates pathways that are also pro-oncogenic. Moreover, in this condition, cell proliferation is stimulated as an attempt to repair tissue damage caused by the inflammatory process. Interestingly, it has been reported that the well-differentiated papillary thyroid carcinoma (PTC), the less aggressive form of thyroid tumor, may progress to the more aggressive follicular thyroid carcinoma (FTC) and eventually to the anaplastic thyroid carcinoma (ATC), and that to such progression contributes the presence of an inflammatory/immune suppressive tumor microenvironment. In this study, we investigated whether papillary tumor cells (BCPAP) could be infected by human herpes virus-6A (HHV-6A), and if viral infection could induce effects related to cancer progression. We found that the virus dysregulated the expression of several microRNAs, such as miR-155, miR-9, and the miR-221/222 cluster, which are involved in different steps of carcinogenesis, and increased the secretion of pro-inflammatory cytokines, particularly IL-6, which may also sustain thyroid tumor cell growth and promote cancer progression. Genomic instability and the expression of PTEN, reported to act as an oncogene in mutp53-carrying cells such as BCPAP, also increased following HHV-6A-infection. These findings suggest that a ubiquitous herpesvirus such as HHV-6A, which displays a marked tropism for thyrocytes, could be involved in the progression of PTC towards more aggressive forms of thyroid tumor.

JQ-1/bortezomib combination strongly impairs MM and PEL survival by inhibiting c-Myc and mTOR despite the activation of prosurvival mechanisms.

Multiple myeloma (MM) and primary effusion lymphoma (PEL) are two aggressive hematologic cancers against which bortezomib and JQ-1, proteasome and bromodomain and extraterminal domain (BET) inhibitors, respectively, have been shown to have a certain success. However, the combination of both seems to be more promising than the single treatments against several cancers, including MM. Indeed, in the latter, proteasome inhibition upregulated nuclear respiratory factor 1 (NRF1), and such a prosurvival effect was counteracted by BET inhibitors. In the present study, we found that JQ-1/bortezomib induced a strong cytotoxic effect against PEL and discovered new insights into the cytotoxic mechanisms induced by such a drug combination in PEL and MM cells. In particular, a stronger c-Myc downregulation, leading to increased DNA damage, was observed in these cells after treatment with JQ-1/bortezomib than after treatment with the single drugs. Such an effect contributed to mechanistic target of rapamycin (mTOR)-phosphorylated eukaryotic translation initiation factor 4E-binding protein 1 (p-4EBP1) axis inhibition, also occurring through c-Myc downregulation. However, besides the prodeath effects, JQ-1/bortezomib activated unfolded protein response (UPR) and autophagy as prosurvival mechanisms. In conclusion, this study demonstrated that JQ-1/bortezomib combination could be a promising treatment for MM and PEL, unveiling new molecular mechanisms underlying its cytotoxic effect, and suggested that UPR and autophagy inhibition could be exploited to further potentiate the cytotoxicity of JQ-1/bortezomib.

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

IMPORTANCE: The 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.

mTORC1/ERK1/2 Interplay Regulates Protein Synthesis and Survival in Acute Myeloid Leukemia Cell Lines.

mTOR is constitutively activated in acute myeloid leukemia (AML) cells, as indicated by the phosphorylation of its substrates, 4EBP1 and P70S6K. Here, we found that quercetin (Q) and rapamycin (Rap) inhibited P70S6K phosphorylation, partially dephosphorylated 4EBP1, and activated ERK1/2 in U937 and THP1, two leukemia cell lines. ERK1/2 inhibition by U0126 induced a stronger dephosphorylation of mTORC1 substrates and activated AKT. The concomitant inhibition of ERK1/2 and AKT further dephosphorylated 4EBP1 and further increased Q- or Rap-mediated cytotoxicity, compared to the single ERK1/2 or AKT inhibition in cells undergoing Q- or Rap-treatments. Moreover, quercetin or rapamycin reduced autophagy, particularly when used in combination with the ERK1/2 inhibitor, U0126. This effect was not dependent on TFEB localization in nuclei or cytoplasm or on the transcription of different autophagy genes, but did correlate with the reduction in protein translation due to a strong eIF2α-Ser51 phosphorylation. Thus, ERK1/2, by limiting 4EBP1 de-phosphorylation and eIF2α phosphorylation, behaves as a paladin of protein synthesis. Based on these findings, the combined inhibition of mTORC1, ERK1/2, and AKT should be considered in treatment of AML.

NRF2 and STAT3: friends or foes in carcinogenesis?

NRF2 is a transcription factor that plays a pivotal role in carcinogenesis, also through the interaction with several pro-survival pathways. NRF2 controls the transcription of detoxification enzymes and a variety of other molecules impinging in several key biological processes. This perspective will focus on the complex interplay of NRF2 with STAT3, another transcription factor often aberrantly activated in cancer and driving tumorigenesis as well as immune suppression. Both NRF2 and STAT3 can be regulated by ER stress/UPR activation and their cross-talk influences and is influenced by autophagy and cytokines, contributing to shape the microenvironment, and both control the execution of DDR, also by regulating the expression of HSPs. Given the importance of these transcription factors, more investigations aimed at better elucidating the outcome of their networking could help to discover new and more efficacious strategies to fight cancer.

Targeting c-Myc Unbalances UPR towards Cell Death and Impairs DDR in Lymphoma and Multiple Myeloma Cells.

Multiple myeloma (MM) and primary effusion lymphoma (PEL) are aggressive hematological cancers, for which the search for new and more effective therapies is needed. Both cancers overexpress c-Myc and are highly dependent on this proto-oncogene for their survival. Although c-Myc inhibition has been shown to reduce PEL and MM survival, the underlying mechanisms leading to such an effect are not completely clarified. In this study, by pharmacologic inhibition and silencing, we show that c-Myc stands at the cross-road between UPR and DDR. Indeed, it plays a key role in maintaining the pro-survival function of UPR, through the IRE1α/XBP1 axis, and sustains the expression level of DDR molecules such as RAD51 and BRCA1 in MM and PEL cells. Moreover, we found that c-Myc establishes an interplay with the IRE1α/XBP1 axis whose inhibition downregulated c-Myc, skewed UPR towards cell death and enhanced DNA damage. In conclusion, this study unveils new insights into the molecular mechanisms leading to the cytotoxic effects of c-Myc inhibition and reinforces the idea that its targeting may be a promising therapeutic approach against MM and PEL that, although different cancers, share some similarities, including c-Myc overexpression, constitutive ER stress and poor response to current chemotherapies.