CD38 restrains the activity of extracellular cGAMP in a model of multiple myeloma.

2'3'-cyclic guanosine monophosphate-adenosine monophosphate (cGAMP) is the endogenous agonist of STING; as such, cGAMP has powerful immunostimulatory activity, due to its capacity to stimulate type I interferon-mediated immunity. Recent evidence indicates that cancer cells, under certain conditions, can release cGAMP extracellularly, a phenomenon currently considered important for therapeutic responses and tumor rejection. Nonetheless, the mechanisms that regulate cGAMP activity in the extracellular environment are still largely unexplored. In this work, we collected evidence demonstrating that CD38 glycohydrolase can inhibit extracellular cGAMP activity through its direct binding. We firstly used different cell lines and clinical samples to demonstrate a link between CD38 and extracellular cGAMP activity; we then performed extensive in silico molecular modeling and cell-free biochemical assays to show a direct interaction between the catalytic pocket of CD38 and cGAMP. Altogether, our findings expand the current knowledge about the regulation of cGAMP activity.

The senescence journey in cancer immunoediting.

Cancer progression is continuously controlled by the immune system which can identify and destroy nascent tumor cells or inhibit metastatic spreading. However, the immune system and its deregulated activity in the tumor microenvironment can also promote tumor progression favoring the outgrowth of cancers capable of escaping immune control, in a process termed cancer immunoediting. This process, which has been classified into three phases, i.e. "elimination", "equilibrium" and "escape", is influenced by several cancer- and microenvironment-dependent factors. Senescence is a cellular program primed by cells in response to different pathophysiological stimuli, which is based on long-lasting cell cycle arrest and the secretion of numerous bioactive and inflammatory molecules. Because of this, cellular senescence is a potent immunomodulatory factor promptly recruiting immune cells and actively promoting tissue remodeling. In the context of cancer, these functions can lead to both cancer immunosurveillance and immunosuppression. In this review, the authors will discuss the role of senescence in cancer immunoediting, highlighting its context- and timing-dependent effects on the different three phases, describing how senescent cells promote immune cell recruitment for cancer cell elimination or sustain tumor microenvironment inflammation for immune escape. A potential contribution of senescent cells in cancer dormancy, as a mechanism of therapy resistance and cancer relapse, will be discussed with the final objective to unravel the immunotherapeutic implications of senescence modulation in cancer.

NEDD8-activating enzyme inhibition potentiates the anti-myeloma activity of natural killer cells.

Natural Killer (NK) cells act as important regulators in the development and progression of hematological malignancies and their suppressor activity against Multiple Myeloma (MM) cells has been confirmed in many studies. Significant changes in the distribution of NK cell subsets and dysfunctions of NK cell effector activities were described in MM patients and correlated with disease staging. Thus, restoring or enhancing the functionality of these effectors for the treatment of MM represents a critical need. Neddylation is a post-translational modification that adds a ubiquitin-like molecule, NEDD8, to the substrate protein. One of the outcomes is the activation of the Cullin Ring Ligases (CRLs), a class of ubiquitin-ligases that controls the degradation of about 20% of proteasome-regulated proteins. Overactivation of CRLs has been described in cancer and can lead to tumor growth and progression. Thus, targeting neddylation represents an attractive approach for cancer treatment. Our group has recently described how pharmacologic inhibition of neddylation increases the expression of the NKG2D activating receptor ligands, MICA and MICB, in MM cells, making these cells more susceptible to NK cell degranulation and killing. Here, we extended our investigation to the direct role of neddylation on NK cell effector functions exerted against MM. We observed that inhibition of neddylation enhanced NK cell-mediated degranulation and killing against MM cells and improved Daratumumab/Elotuzumab-mediated response. Mechanistically, inhibition of neddylation increased the expression of Rac1 and RhoA GTPases in NK cells, critical mediators for an efficient degranulation at the immunological synapse of cytotoxic lymphocytes, and augmented the levels of F-actin and perforin polarization in NK cells contacting target cells. Moreover, inhibition of neddylation partially abrogated TGFß-mediated repression of NK cell effector activity. This study describes the role of neddylation on NK cell effector functions and highlights the positive immunomodulatory effects achieved by the inhibition of this pathway in MM.

Cross-Dressing of Multiple Myeloma Cells Mediated by Extracellular Vesicles Conveying MIC and ULBP Ligands Promotes NK Cell Killing.

Natural Killer (NK) cells are innate cytotoxic lymphoid cells that play a crucial role in cancer immunosurveillance. NKG2D is an activating receptor that binds to MIC and ULBP molecules typically induced on damaged, transformed, or infected cells. The secretion of NKG2D ligands (NKG2DLs) through protease-mediated cleavage or in an extracellular vesicle (EV) is a mode to control their cell surface expression and a mechanism used by cancer cells to evade NKG2D-mediated immunosurveillance. EVs are emerging as important players in mediating cell-to-cell communication due to their ability to transfer biological material to acceptor cells. Herein, we investigated the spreading of NKG2DLs of both MIC and ULBP molecules through the EV-mediated cross-dressing on multiple myeloma (MM) cells. We focused our attention on two MICA allelic variants, namely MICA*008 and MICA*019, representing the prototype of short and long MICA alleles, respectively, and on ULBP-1, ULBP-2, and ULBP-3. Our findings demonstrate that both ULBP and MICA ligands can be acquired from tumor cells through EVs enhancing NK cell recognition and killing. Moreover, besides MICA, EVs expressing ULBP-1 but not ULBP-2 and 3 were detected in bone marrow aspirates derived from a cohort of MM patients. Our findings shed light on the role of EV-associated MICA allelic variants and ULBP molecules in the modulation of NKG2D-mediated NK cell immunosurveillance in the tumor microenvironment. Moreover, the EV-mediated transfer of NKG2DLs could suggest novel therapeutic approaches based on the usage of engineered nanoparticles aimed at increasing cancer cell immunogenicity.

SUMOylation and related post-translational modifications in natural killer cell anti-cancer responses.

SUMOylation is a reversible modification that involves the covalent attachment of small ubiquitin-like modifier (SUMO) to target proteins, leading to changes in their localization, function, stability, and interactor profile. SUMOylation and additional related post-translational modifications have emerged as important modulators of various biological processes, including regulation of genomic stability and immune responses. Natural killer (NK) cells are innate immune cells that play a critical role in host defense against viral infections and tumors. NK cells can recognize and kill infected or transformed cells without prior sensitization, and their activity is tightly regulated by a balance of activating and inhibitory receptors. Expression of NK cell receptors as well as of their specific ligands on target cells is finely regulated during malignant transformation through the integration of different mechanisms including ubiquitin- and ubiquitin-like post-translational modifications. Our review summarizes the role of SUMOylation and other related pathways in the biology of NK cells with a special emphasis on the regulation of their response against cancer. The development of novel selective inhibitors as useful tools to potentiate NK-cell mediated killing of tumor cells is also briefly discussed.

Doxorubicin-Mediated miR-433 Expression on Exosomes Promotes Bystander Senescence in Multiple Myeloma Cells in a DDR-Independent Manner.

The success of senescence-based anticancer therapies relies on their anti-proliferative power and on their ability to trigger anti-tumor immune responses. Indeed, genotoxic drug-induced senescence increases the expression of NK cell-activating ligands on multiple myeloma (MM) cells, boosting NK cell recognition and effector functions. Senescent cells undergo morphological change and context-dependent functional diversification, acquiring the ability to secrete a vast pool of molecules termed the senescence-associated secretory phenotype (SASP), which affects neighboring cells. Recently, exosomes have been recognized as SASP factors, contributing to modulating a variety of cell functions. In particular, evidence suggests a key role for exosomal microRNAs in influencing many hallmarks of cancer. Herein, we demonstrate that doxorubicin treatment of MM cells leads to the enrichment of miR-433 into exosomes, which in turn induces bystander senescence. Our analysis reveals that the establishment of the senescent phenotype on neighboring MM cells is p53- and p21-independent and is related to CDK-6 down-regulation. Notably, miR-433-dependent senescence does not induce the up-regulation of activating ligands on MM cells. Altogether, our findings highlight the possibility of miR-433-enriched exosomes to reinforce doxorubicin-mediated cellular senescence.

Role of NF-κB Signaling in the Interplay between Multiple Myeloma and Mesenchymal Stromal Cells.

Nuclear factor-κB (NF-κB) transcription factors play a key role in the pathogenesis of multiple myeloma (MM). The survival, proliferation and chemoresistance of malignant plasma cells largely rely on the activation of canonical and noncanonical NF-κB pathways. They are triggered by cancer-associated mutations or by the autocrine and paracrine production of cytokines and growth factors as well as direct interaction with cellular and noncellular components of bone marrow microenvironment (BM). In this context, NF-κB also significantly affects the activity of noncancerous cells, including mesenchymal stromal cells (MSCs), which have a critical role in disease progression. Indeed, NF-κB transcription factors are involved in inflammatory signaling that alters the functional properties of these cells to support cancer evolution. Moreover, they act as regulators and/or effectors of pathways involved in the interplay between MSCs and MM cells. The aim of this review is to analyze the role of NF-κB in this hematologic cancer, focusing on NF-κB-dependent mechanisms in tumor cells, MSCs and myeloma-mesenchymal stromal cell crosstalk.

NKG2D engagement on human NK cells leads to DNAM-1 hypo-responsiveness through different converging mechanisms.

Natural killer (NK) cell activation is regulated by activating and inhibitory receptors that facilitate diseased cell recognition. Among activating receptors, NKG2D and DNAM-1 play a pivotal role in anticancer immune responses since they bind ligands upregulated on transformed cells. During tumor progression, however, these receptors are frequently downmodulated and rendered functionally inactive. Of note, NKG2D internalization has been associated with the acquisition of a dysfunctional phenotype characterized by the cross-tolerization of unrelated activating receptors. However, our knowledge of the consequences of NKG2D engagement is still incomplete. Here, by cytotoxicity assays combined with confocal microscopy, we demonstrate that NKG2D engagement on human NK cells impairs DNAM-1-mediated killing through two different converging mechanisms: by the upregulation of the checkpoint inhibitory receptor TIGIT, that in turn suppresses DNAM-1-mediated cytotoxic function, and by direct inhibition of DNAM-1-promoted signaling. Our results highlight a novel interplay between NKG2D and DNAM-1/TIGIT receptors that may facilitate neoplastic cell evasion from NK cell-mediated clearance.

GAS6/TAM signaling pathway controls MICA expression in multiple myeloma cells.

NKG2D ligands play a relevant role in Natural Killer (NK) cell -mediated immune surveillance of multiple myeloma (MM). Different levels of regulation control the expression of these molecules at cell surface. A number of oncogenic proteins and miRNAs act as negative regulators of NKG2D ligand transcription and translation, but the molecular mechanisms sustaining their basal expression in MM cells remain poorly understood. Here, we evaluated the role of the growth arrest specific 6 (GAS6)/TAM signaling pathway in the regulation of NKG2D ligand expression and MM recognition by NK cells. Our data showed that GAS6 as well as MERTK and AXL depletion in MM cells results in MICA downregulation and inhibition of NKG2D-mediated NK cell degranulation. Noteworthy, GAS6 derived from bone marrow stromal cells (BMSCs) also increases MICA expression at both protein and mRNA level in human MM cell lines and in primary malignant plasma cells. NF-kB activation is required for these regulatory mechanisms since deletion of a site responsive for this transcription factor compromises the induction of mica promoter by BMSCs. Accordingly, knockdown of GAS6 reduces the capability of BMSCs to activate NF-kB pathway as well as to enhance MICA expression in MM cells. Taken together, these results shed light on molecular mechanism underlying NKG2D ligand regulation and identify GAS6 protein as a novel autocrine and paracrine regulator of basal expression of MICA in human MM cells.

Impact on NK cell functions of acute versus chronic exposure to extracellular vesicle-associated MICA: Dual role in cancer immunosurveillance.

Natural killer (NK) cells are innate cytotoxic lymphocytes that play a key role in cancer immunosurveillance thanks to their ability to recognize and kill cancer cells. NKG2D is an activating receptor that binds to MIC and ULBP molecules typically induced on damaged, transformed or infected cells. The release of NKG2D ligands (NKG2DLs) in the extracellular milieu through protease-mediated cleavage or by extracellular vesicle (EV) secretion allows cancer cells to evade NKG2D-mediated immunosurveillance. In this work, we investigated the immunomodulatory properties of the NKG2D ligand MICA*008 associated to distinct populations of EVs (i.e., small extracellular vesicles [sEVs] and medium size extracellular vesicles [mEVs]). By using as model a human MICA*008-transfected multiple myeloma (MM) cell line, we found that this ligand is present on both vesicle populations. Interestingly, our findings reveal that NKG2D is specifically involved in the uptake of vesicles expressing its cognate ligand. We provide evidence that MICA*008-expressing sEVs and mEVs are able on one hand to activate NK cells but, following prolonged stimulation induce a sustained NKG2D downmodulation leading to impaired NKG2D-mediated functions. Moreover, our findings show that MICA*008 can be transferred by vesicles to NK cells causing fratricide. Focusing on MM as a clinically and biologically relevant model of tumour-NK cell interactions, we found enrichment of EVs expressing MICA in the bone marrow of a cohort of patients. All together our results suggest that the accumulation of NKG2D ligands associated to vesicles in the tumour microenvironment could favour the suppression of NK cell activity either by NKG2D down-modulation or by fratricide of NK cell dressed with EV-derived NKG2D ligands.

Immunomodulatory effect of NEDD8-activating enzyme inhibition in Multiple Myeloma: upregulation of NKG2D ligands and sensitization to Natural Killer cell recognition.

Multiple Myeloma (MM) is an incurable hematologic malignancy of terminally differentiated plasma cells (PCs), where immune interactions play a key role in the control of cancer cell growth and survival. In particular, MM is characterized by a highly immunosuppressive bone marrow microenvironment where the anticancer/cytotoxic activity of Natural Killer (NK) cells is impaired. This study is focused on understanding whether modulation of neddylation can regulate NK cell-activating ligands expression and sensitize MM to NK cell killing. Neddylation is a post-translational modification that adds a ubiquitin-like protein, NEDD8, to selected substrate proteins, affecting their stability, conformation, subcellular localization, and function. We found that pharmacologic inhibition of neddylation using a small-molecule inhibitor, MLN4924/Pevonedistat, increases the expression of the NK cell-activating receptor NKG2D ligands MICA and MICB on the plasma membrane of different MM cell lines and patient-derived PCs, leading to enhanced NK cell degranulation. Mechanistically, MICA expression is upregulated at mRNA level, and this is the result of an increased promoter activity after the inhibition of IRF4 and IKZF3, two transcriptional repressors of this gene. Differently, MLN4924/Pevonedistat induced accumulation of MICB on the plasma membrane with no change of its mRNA levels, indicating a post-translational regulatory mechanism. Moreover, inhibition of neddylation can cooperate with immunomodulatory drugs (IMiDs) in upregulating MICA surface levels in MM cells due to increased expression of CRBN, the cellular target of these drugs. In summary, MLN4924/Pevonedistat sensitizes MM to NK cell recognition, adding novel information on the anticancer activity of neddylation inhibition.

Cereblon regulates NK cell cytotoxicity and migration via Rac1 activation.

Rearrangement of the actin cytoskeleton is critical for cytotoxic and immunoregulatory functions as well as migration of natural killer (NK) cells. However, dynamic reorganization of actin is a complex process, which remains largely unknown. Here, we investigated the role of the protein Cereblon (CRBN), an E3 ubiquitin ligase complex co-receptor and the primary target of the immunomodulatory drugs, in NK cells. We observed that CRBN partially colocalizes with F-actin in chemokine-treated NK cells and is recruited to the immunological synapse, thus suggesting a role for this protein in cytoskeleton reorganization. Accordingly, silencing of CRBN in NK cells results in a reduced cytotoxicity that correlates with a defect in conjugate and lytic synapse formation. Moreover, CRBN depletion significantly impairs the ability of NK cells to migrate and reduces the enhancing effect of lenalidomide on NK cell migration. Finally, we provided evidence that CRBN is required for activation of the small GTPase Rac1, a critical mediator of cytoskeleton dynamics. Indeed, in CRBN-depleted NK cells, chemokine-mediated or target cell-mediated Rac1 activation is significantly reduced. Altogether our data identify a critical role for CRBN in regulating NK cell functions and suggest that this protein may mediate the stimulatory effect of lenalidomide on NK cells.

Role of Aiolos and Ikaros in the Antitumor and Immunomodulatory Activity of IMiDs in Multiple Myeloma: Better to Lose Than to Find Them.

The Ikaros zing-finger family transcription factors (IKZF TFs) are important regulators of lymphocyte development and differentiation and are also highly expressed in B cell malignancies, including Multiple Myeloma (MM), where they are required for cancer cell growth and survival. Moreover, IKZF TFs negatively control the functional properties of many immune cells. Thus, the targeting of these proteins has relevant therapeutic implications in cancer. Indeed, accumulating evidence demonstrated that downregulation of Ikaros and Aiolos, two members of the IKZF family, in malignant plasma cells as well as in adaptative and innate lymphocytes, is key for the anti-myeloma activity of Immunomodulatory drugs (IMiDs). This review is focused on IKZF TF-related pathways in MM. In particular, we will address how the depletion of IKZF TFs exerts cytotoxic effects on MM cells, by reducing their survival and proliferation, and concomitantly potentiates the antitumor immune response, thus contributing to therapeutic efficacy of IMiDs, a cornerstone in the treatment of this neoplasia.

Liver X Receptors: Regulators of Cholesterol Metabolism, Inflammation, Autoimmunity, and Cancer.

The interplay between cellular stress and immune response can be variable and sometimes contradictory. The mechanisms by which stress-activated pathways regulate the inflammatory response to a pathogen, in autoimmunity or during cancer progression remain unclear in many aspects, despite our recent knowledge of the signalling and transcriptional pathways involved in these diseases. In this context, over the last decade many studies demonstrated that cholesterol metabolism is an important checkpoint for immune homeostasis and cancer progression. Indeed, cholesterol is actively metabolized and can regulate, through its mobilization and/or production of active derivatives, many aspects of immunity and inflammation. Moreover, accumulation of cholesterol has been described in cancer cells, indicating metabolic addiction. The nuclear receptors liver-X-receptors (LXRs) are important regulators of intracellular cholesterol and lipids homeostasis. They have also key regulatory roles in immune response, as they can regulate inflammation, innate and adaptive immunity. Moreover, activation of LXRs has been reported to affect the proliferation and survival of different cancer cell types that show altered metabolic pathways and accumulation of cholesterol. In this minireview we will give an overview of the recent understandings about the mechanisms through which LXRs regulate inflammation, autoimmunity, and cancer, and the therapeutic potential for future treatment of these diseases through modulation of cholesterol metabolism.

Bone Marrow Stromal Cell-Derived IL-8 Upregulates PVR Expression on Multiple Myeloma Cells via NF-kB Transcription Factor.

Bone marrow stromal cells (BMSCs) strongly contribute to multiple myeloma (MM) progression, promoting the survival and growth of malignant plasma cells (PCs). However, the possible impact of these cells on the immune-mediated recognition of MM cells remains largely unknown. DNAM-1 activating receptor plays a prominent role in NK cell anti-MM response engaging the ligands poliovirus receptor (PVR) and nectin-2 on malignant PCs. Here, we analysed the role of MM patient-derived BMSCs in the regulation of PVR expression. We found that BMSCs enhance PVR surface expression on MM cells and promote their NK cell-mediated recognition. PVR upregulation occurs at transcriptional level and involves NF-kB transcription factor activation by BMSC-derived soluble factors. Indeed, overexpression of a dominant-negative mutant of IKBα blocked PVR upregulation. IL-8 plays a prominent role in these mechanisms since blockade of CXCR1/2 receptors as well as depletion of the cytokine via RNA interference prevents the enhancement of PVR expression by BMSC-derived conditioned medium. Interestingly, IL-8 is associated with stromal microvesicles which are also required for PVR upregulation via CXCR1/CXCR2 signaling activation. Our findings identify BMSCs as regulators of NK cell anti-MM response and contribute to define novel molecular pathways involved in the regulation of PVR expression in cancer cells.

CD155: A Multi-Functional Molecule in Tumor Progression.

CD155 is an adhesion molecule belonging to the Nectin/Nectin-like family often overexpressed on tumor cells and involved in many different processes such as cell adhesion, migration and proliferation. In contrast to these pro-tumorigenic functions, CD155 is also a ligand for the activating receptor DNAM-1 expressed on cytotoxic lymphocytes including Natural Killer (NK) cells and involved in anti-tumor immune response. However, during tumor progression inhibitory receptors for CD155 are up-regulated on the surface of effector cells, contributing to an impairment of their cytotoxic capacity. In this review we will focus on the roles of CD155 as a ligand for the activating receptor DNAM-1 regulating immune surveillance against cancer and as pro-oncogenic molecule favoring tumor proliferation, invasion and immune evasion. A deeper understanding of the multiple roles played by CD155 in cancer development contributes to improving anti-tumor strategies aimed to potentiate immune response against cancer.

Hitting More Birds with a Stone: Impact of TGF-ß on ILC Activity in Cancer.

Transforming growth factor (TGF)-ß is a central immunosuppressive cytokine within tumor microenvironment inhibiting the expansion and function of major cellular components of adaptive and innate immune system. Among them, compelling evidence has demonstrated that TGF-ß is a key regulator of natural killer (NK) cells, innate lymphoid cells (ILCs) with a critical role in immunosurveillance against different kinds of cancer cells. A TGF-ß rich tumor microenvironment blocks NK cell activity at multiple levels. This immunosuppressive factor exerts direct regulatory effects on NK cells including inhibition of cytokine production, alteration of activating/inhibitory receptor expression, and promotion of the conversion into non cytotoxic group I ILC (ILC1). Concomitantly, TGF-ß can render tumor cells less susceptible to NK cell-mediated recognition and lysis. Indeed, accumulating evidence suggest that changes in levels of NKG2D ligands, mainly MICA, as well as an increase of immune checkpoint inhibitors (e.g., PD-L1) and other inhibitory ligands on cancer cells significantly contribute to TGF-ß-mediated suppression of NK cell activity. Here, we will take into consideration two major mechanisms underlying the negative regulation of ILC function by TGF-ß in cancer. First, we will address how TGF-ß impacts the balance of signals governing NK cell activity. Second, we will review recent advances on the role of this cytokine in driving ILC plasticity in cancer. Finally, we will discuss how the development of therapeutic approaches blocking TGF-ß may reverse the suppression of host immune surveillance and improve anti-tumor NK cell response in the clinic.

Innate Immune Response Regulation by the Human RNASET2 Tumor Suppressor Gene.

The link between cancer development or progression and immune system dysregulation has long been established. Virtually every cell type belonging to both the innate and adaptive immune system has been reported to be involved in a complex interplay that might culminate into either a pro- or anti-tumorigenic response. Among the cellular components of the innate immune system, cells belonging to the monocyte/macrophage lineage have been consistently shown to play a key role in the tumorigenic process. The most advanced human tumors are reported to be strongly infiltrated with Tumor-Associated Macrophages (TAMs) endowed with the ability to contribute to tumor growth and dissemination. However, given their widely acknowledged functional plasticity, macrophages can display anti-tumor properties as well. Based on these premises, experimental approaches to promote the in vivo macrophage shift from pro-tumor to anti-tumor phenotype represent one of the most promising research field aimed at developing immune system-mediated tumor suppressive therapies. In this context, the human RNASET2 oncosuppressor gene has emerged as a potential tool for macrophage-mediated tumor suppression. A growing body of experimental evidence has been reported to suggest a role for this gene in the regulation of macrophage activity in both in vitro and in vivo experimental models. Moreover, several recent reports suggest a role for this gene in a broad range of cell types involved in immune response, pointing at RNASET2 as a putative regulator of several functional features within the immune system.

The POU-Domain Transcription Factor Oct-6/POU3F1 as a Regulator of Cellular Response to Genotoxic Stress.

DNA damage and the generation of reactive oxygen species (ROS) are key mechanisms of apoptotic cell death by commonly used genotoxic drugs. However, the complex cellular response to these pharmacologic agents remains yet to be fully characterized. Several studies have described the role of transcription factor octamer-1 (Oct-1)/Pit-1, Oct-1/2, and Unc-86 shared domain class 2 homeobox 1 (POU2F1) in the regulation of the genes important for cellular response to genotoxic stress. Evaluating the possible involvement of other POU family transcription factors in these pathways, we revealed the inducible expression of Oct-6/POU3F1, a regulator of neural morphogenesis and epidermal differentiation, in cancer cells by genotoxic drugs. The induction of Oct-6 occurs at the transcriptional level via reactive oxygen species (ROS) and ataxia telangiectasia mutated- and Rad3-related (ATR)-dependent mechanisms, but in a p53 independent manner. Moreover, we provide evidence that Oct-6 may play a role in the regulation of cellular response to DNA damaging agents. Indeed, by using the shRNA approach, we demonstrate that in doxorubicin-treated H460 non-small-cell lung carcinoma (NSCLC) cells, Oct-6 depletion leads to a reduced G2-cell cycle arrest and senescence, but also to increased levels of intracellular ROS and DNA damage. In addition, we could identify p21 and catalase as Oct-6 target genes possibly mediating these effects. These results demonstrate that Oct-6 is expressed in cancer cells after genotoxic stress, and suggests its possible role in the control of ROS, DNA damage response (DDR), and senescence.

Activation of liver X receptor up-regulates the expression of the NKG2D ligands MICA and MICB in multiple myeloma through different molecular mechanisms.

NK cells have an important role in immunosurveillance of multiple myeloma (MM) progression, and their activity is enhanced by combination therapies able to regulate the expression of specific activating ligands. Liver X receptors (LXRs) are nuclear receptors and important regulators of intracellular cholesterol and lipid homeostasis. Moreover, they have regulatory roles in both cancer and immune response. Indeed, they can regulate inflammation and innate and acquired immunity. Furthermore, LXR activation directly acts in cancer cells (e.g., prostate, breast, melanoma, colon cancer, hepatocarcinoma, glioblastoma, and MM) that show an accumulation of cholesterol and alteration of LXR-mediated metabolic pathways. Here, we investigated the role of LXR and cholesterol on the expression of the NK cell-activating ligands major histocompatibility complex class I chain-related molecule A and B (MICA and MICB) in MM cells. The results shown in this work indicate that MM cells are responsive to LXR activation, which induces changes in the intracellular cholesterol content. These changes correlate with an enhanced expression of MICA and MICB in human MM cell lines and in primary malignant plasma cells, 2 ligands of the NK group 2D receptor (NKG2D)/CD314 activating receptor expressed in cytotoxic lymphocytes, rendering MM cells more sensitive to recognition, degranulation, and killing by NK cells. Mechanistically, we observed that LXR activation regulates MICA and MICB expression at different levels: MICA at the transcriptional level, enhancing mica promoter activity, and MICB by inhibiting its degradation in lysosomes. The present study provides evidence that activation of LXR, by enhancing NKG2D ligand expression, can promote NK cell-mediated cytotoxicity and suggests a novel immune-mediated mechanism involving modulation of intracellular cholesterol levels in cancer cells.-Bilotta, M. T., Abruzzese, M. P., Molfetta, R., Scarno, G., Fionda, C., Zingoni, A., Soriani, A., Garofalo, T., Petrucci, M. T., Ricciardi, M. R., Paolini, R., Santoni, A., Cippitelli, M. Activation of liver X receptor up-regulates the expression of the NKG2D ligands MICA and MICB in multiple myeloma through different molecular mechanisms.