Retraction: DNA-PKCS binding to p53 on the p21WAF1/CIP1 promoter blocks transcription resulting in cell death.

[This retracts the article DOI: 10.18632/oncotarget.378.].

Regulation of Cancer and Cancer-Related Genes via NAD.

SIGNIFICANCE: NAD+ is an essential redox cofactor in cellular metabolism and has emerged as an important regulator of a wide spectrum of disease conditions, most notably, cancers. As such, various strategies targeting NAD+ synthesis in cancers are in clinical trials. Recent Advances: Being a substrate required for the activity of various enzyme families, especially sirtuins and poly(adenosine diphosphate [ADP]-ribose) polymerases, NAD+-mediated signaling plays an important role in gene expression, calcium release, cell cycle progression, DNA repair, and cell proliferation. Many strategies exploring the potential of interfering with NAD+ metabolism to sensitize cancer cells to achieve anticancer benefits are highly promising, and are being pursued. CRITICAL ISSUES: With the multifaceted roles of NAD+ in cancer, it is important to understand how cellular processes are reliant on NAD+. This review summarizes how NAD+ metabolism regulates various pathophysiological processes in cancer, and how this knowledge can be exploited to devise effective anticancer therapies in clinical settings. FUTURE DIRECTIONS: In line with the redundant pathways that facilitate NAD+ metabolism, further studies should comprehensively understand the roles of the various NAD+-synthesizing as well as NAD+-utilizing biomolecules to understand its true potential in cancer treatment.

HDAC6 differentially regulates autophagy in stem-like versus differentiated cancer cells.

Cancer stem-like cells (CSCs), a small population of pluripotent cells residing within heterogeneous tumor mass, remain highly resistant to various chemotherapies as compared to the differentiated cancer cells. It is being postulated that CSCs possess unique molecular mechanisms, such as autophagic homeostasis, that allow CSCs to withstand the therapeutic assaults. Here we demonstrate that HDAC6 inhibition differentially modulates macroautophagy/autophagy in CSCs as compared to that of differentiated cancer cells. Using human and murine CSC models and differentiated cells, we show that the inhibition or knockdown (KD) of HDAC6 decreases CSC pluripotency by downregulating major pluripotency factors POU5F1, NANOG and SOX2. This decreased HDAC6 expression increases ACTB, TUBB3 and CSN2 expression and promotes differentiation in CSCs in an apoptosis-independent manner. Mechanistically, HDAC6 KD in CSCs decreases pluripotency by promoting autophagy, whereas the inhibition of pluripotency via retinoic acid treatment, POU5F1 or autophagy-related gene (ATG7 and ATG12) KD in CSCs decreases HDAC6 expression and promotes differentiation. Interestingly, HDAC6 KD-mediated CSC growth inhibition is further enhanced in the presence of autophagy inducers Tat-Beclin 1 peptide and rapamycin. In contrast to the results observed in CSCs, HDAC6 KD in differentiated breast cancer cells downregulates autophagy and increases apoptosis. Furthermore, the autophagy regulator p-MTOR, upstream negative regulators of p-MTOR (TSC1 and TSC2) and downstream effectors of p-MTOR (p-RPS6KB and p-EIF4EBP1) are differentially regulated in CSCs versus differentiated cancer cells following HDAC6 KD. Overall these data identify the differential regulation of autophagy as a molecular link behind the differing chemo-susceptibility of CSCs and differentiated cancer cells.

Autophagic homeostasis is required for the pluripotency of cancer stem cells.

Pluripotency is an important feature of cancer stem cells (CSCs) that contributes to self-renewal and chemoresistance. The maintenance of pluripotency of CSCs under various pathophysiological conditions requires a complex interaction between various cellular pathways including those involved in homeostasis and energy metabolism. However, the exact mechanisms that maintain the CSC pluripotency remain poorly understood. In this report, using both human and murine models of CSCs, we demonstrate that basal levels of autophagy are required to maintain the pluripotency of CSCs, and that this process is differentially regulated by the rate-limiting enzyme in the NAD+ synthesis pathway NAMPT (nicotinamide phosphoribosyltransferase) and the transcription factor POU5F1/OCT4 (POU class 5 homeobox 1). First, our data show that the pharmacological inhibition and knockdown (KD) of NAMPT or the KD of POU5F1 in human CSCs significantly decreased the expression of pluripotency markers POU5F1, NANOG (Nanog homeobox) and SOX2 (SRY-box 2), and upregulated the differentiation markers TUBB3 (tubulin ß 3 class III), CSN2 (casein ß), SPP1 (secreted phosphoprotein 1), GATA6 (GATA binding protein 6), T (T brachyury transcription factor) and CDX2 (caudal type homeobox 2). Interestingly, these pluripotency-regulating effects of NAMPT and POU5F1 were accompanied by contrasting levels of autophagy, wherein NAMPT KD promoted while POU5F1 KD inhibited the autophagy machinery. Most importantly, any deviation from the basal level of autophagy, either increase (via rapamycin, serum starvation or Tat-beclin 1 [Tat-BECN1] peptide) or decrease (via ATG7 or ATG12 KD), strongly decreased the pluripotency and promoted the differentiation and/or senescence of CSCs. Collectively, these results uncover the link between the NAD+ biosynthesis pathway, CSC transcription factor POU5F1 and pluripotency, and further identify autophagy as a novel regulator of pluripotency of CSCs.

NAD+ salvage pathway in cancer metabolism and therapy.

Nicotinamide adenine dinucleotide (NAD+) is an essential coenzyme for various physiological processes including energy metabolism, DNA repair, cell growth, and cell death. Many of these pathways are typically dysregulated in cancer cells, making NAD+ an intriguing target for cancer therapeutics. NAD+ is mainly synthesized by the NAD+ salvage pathway in cancer cells, and not surprisingly, the pharmacological targeting of the NAD+ salvage pathway causes cancer cell cytotoxicity in vitro and in vivo. Several studies have described the precise consequences of NAD+ depletion on cancer biology, and have demonstrated that NAD+ depletion results in depletion of energy levels through lowered rates of glycolysis, reduced citric acid cycle activity, and decreased oxidative phosphorylation. Additionally, depletion of NAD+ causes sensitization of cancer cells to oxidative damage by disruption of the anti-oxidant defense system, decreased cell proliferation, and initiation of cell death through manipulation of cell signaling pathways (e.g., SIRT1 and p53). Recently, studies have explored the effect of well-known cancer therapeutics in combination with pharmacological depletion of NAD+ levels, and found in many cases a synergistic effect on cancer cell cytotoxicity. In this context, we will discuss the effects of NAD+ salvage pathway inhibition on cancer cell biology and provide insight on this pathway as a novel anti-cancer therapeutic target.

Breast cancer subtype dictates DNA methylation and ALDH1A3-mediated expression of tumor suppressor RARRES1.

Breast cancer subtyping, based on the expression of hormone receptors and other genes, can determine patient prognosis and potential options for targeted therapy. Among breast cancer subtypes, tumors of basal-like and claudin-low subtypes are typically associated with worse patient outcomes, are primarily classified as triple-negative breast cancers (TNBC), and cannot be treated with existing hormone-receptor-targeted therapies. Understanding the molecular basis of these subtypes will lead to the development of more effective treatment options for TNBC. In this study, we focus on retinoic acid receptor responder 1 (RARRES1) as a paradigm to determine if breast cancer subtype dictates protein function and gene expression regulation. Patient tumor dataset analysis and gene expression studies of a 26 cell-line panel, representing the five breast cancer subtypes, demonstrate that RARRES1 expression is greatest in basal-like TNBCs. Cell proliferation and tumor growth assays reveal that RARRES1 is a tumor suppressor in TNBC. Furthermore, gene expression studies, Illumina HumanMethylation450 arrays, and chromatin immunoprecipitation demonstrate that expression of RARRES1 is retained in basal-like breast cancers due to hypomethylation of the promoter. Additionally, expression of the cancer stem cell marker, aldehyde dehydrogenase 1A3, which provides the required ligand (retinoic acid) for RARRES1 transcription, is also specific to the basal-like subtype. We functionally demonstrate that the combination of promoter methylation and retinoic acid signaling dictates expression of tumor suppressor RARRES1 in a subtype-specific manner. These findings provide a precedent for a therapeutically-inducible tumor suppressor and suggest novel avenues of therapeutic intervention for patients with basal-like breast cancer.

Dendritic Cells in Oncolytic Virus-Based Anti-Cancer Therapy.

Dendritic cells (DCs) are specialized antigen-presenting cells that have a notable role in the initiation and regulation of innate and adaptive immune responses. In the context of cancer, appropriately activated DCs can induce anti-tumor immunity by activating innate immune cells and tumor-specific lymphocytes that target cancer cells. However, the tumor microenvironment (TME) imposes different mechanisms that facilitate the impairment of DC functions, such as inefficient antigen presentation or polarization into immunosuppressive DCs. These tumor-associated DCs thus fail to initiate tumor-specific immunity, and indirectly support tumor progression. Hence, there is increasing interest in identifying interventions that can overturn DC impairment within the TME. Many reports thus far have studied oncolytic viruses (OVs), viruses that preferentially target and kill cancer cells, for their capacity to enhance DC-mediated anti-tumor effects. Herein, we describe the general characteristics of DCs, focusing on their role in innate and adaptive immunity in the context of the TME. We also examine how DC-OV interaction affects DC recruitment, OV delivery, and anti-tumor immunity activation. Understanding these roles of DCs in the TME and OV infection is critical in devising strategies to further harness the anti-tumor effects of both DCs and OVs, ultimately enhancing the efficacy of OV-based oncotherapy.

Ras transformation results in cleavage of reticulon protein Nogo-B that is associated with impairment of IFN response.

Dysregulation of Ras signaling is the major cause of various cancers. Aberrant Ras signaling, however, provides a favorable environment for many viruses, making them suitable candidates as cancer-killing therapeutic agents. Susceptibility of cancer cells to such viruses is mainly due to impaired type I interferon (IFN) response, often as a result of activated Ras/ERK signaling in these cells. In this study, we searched for cellular factors modulated by Ras signaling and their potential involvement in promoting viral oncolysis. We found that upon Ras transformation of NIH-3T3 cells, the N-terminus of Nogo-B (reticulon 4) was proteolytically cleaved. Interestingly, Nogo knockdown (KD) in non-transformed and Ras-transformed cells both enhanced virus-induced IFN response, suggesting that both cleaved and uncleaved Nogo can suppress IFN response. However, pharmacological blockade of Nogo cleavage in Ras-transformed cells significantly enhanced virus-induced IFN response, suggesting that cleaved Nogo contributes to enhanced IFN suppression in these cells. We further showed that IFN suppression associated with Ras-induced Nogo-B cleavage was distinct from but synergistic with that associated with an activated Ras/ERK pathway. Our study therefore reveals an important and novel role of Nogo-B and its cleavage in the suppression of anti-viral immune responses by oncogenic Ras transformation.

Newly recruited CD11b+, GR-1+, Ly6C(high) myeloid cells augment tumor-associated immunosuppression immediately following the therapeutic administration of oncolytic reovirus.

Tumor-associated immunosuppression aids cancer cells to escape immune-mediated attack and subsequent elimination. Recently, however, many oncolytic viruses, including reovirus, have been reported to overturn such immunosuppression and promote the development of a clinically desired antitumor immunity, which is known to promote favorable patient outcomes. Contrary to this existing paradigm, in this article we demonstrate that reovirus augments tumor-associated immunosuppression immediately following its therapeutic administration. Our data show that reovirus induces preferential differentiation of highly suppressive CD11b(+), Gr-1(+), Ly6C(high) myeloid cells from bone marrow hematopoietic progenitor cells. Furthermore, reovirus administration in tumor-bearing hosts drives time-dependent recruitment of CD11b(+), Gr-1(+), Ly6C(high) myeloid cells in the tumor milieu, which is further supported by virus-induced increased expression of numerous immune factors involved in myeloid-derived suppressor cell survival and trafficking. Most importantly, CD11b(+), Gr-1(+), Ly6C(high) myeloid cells specifically potentiate the suppression of T cell proliferation and are associated with the absence of IFN-γ response in the tumor microenvironment early during oncotherapy. Considering that the qualitative traits of a specific antitumor immunity are largely dictated by the immunological events that precede its development, our findings are of critical importance and must be considered while devising complementary interventions aimed at promoting the optimum efficacy of oncolytic virus-based anticancer immunotherapies.

Aldehyde dehydrogenase 1A3 influences breast cancer progression via differential retinoic acid signaling.

Aldehyde dehydrogenase (ALDH) 1A enzymes produce retinoic acid (RA), a transcription induction molecule. To investigate if ALDH1A1 or ALDH1A3-mediated RA signaling has an active role in breast cancer tumorigenesis, we performed gene expression and tumor xenograft studies. Analysis of breast patient tumors revealed that high levels of ALDH1A3 correlated with expression of RA-inducible genes with retinoic acid response elements (RAREs), poorer patient survival and triple-negative breast cancers. This suggests a potential link between ALDH1A3 expression and RA signaling especially in aggressive and/or triple-negative breast cancers. In MDA-MB-231, MDA-MB-468 and MDA-MB-435 cells, ALDH1A3 and RA increased expression of RA-inducible genes. Interestingly, ALDH1A3 had opposing effects in tumor xenografts, increasing tumor growth and metastasis of MDA-MB-231 and MDA-MB-435 cells, but decreasing tumor growth of MDA-MB-468 cells. Exogenous RA replaced ALDH1A3 in inducing the same opposing tumor growth and metastasis effects, suggesting that ALDH1A3 mediates these effects by promoting RA signaling. Genome expression analysis revealed that ALDH1A3 induced largely divergent gene expression in MDA-MB-231 and MDA-MB-468 cells which likely resulted in the opposing tumor growth effects. Treatment with DNA methylation inhibitor 5-aza-2'deoxycytidine restored uniform RA-inducibility of RARE-containing HOXA1 and MUC4 in MDA-MB-231 and MDA-MB-468 cells, suggesting that differences in epigenetic modifications contribute to differential ALDH1A3/RA-induced gene expression in breast cancer. In summary, ALDH1A3 induces differential RA signaling in breast cancer cells which affects the rate of breast cancer progression.

Core needle biopsy of breast cancer tumors increases distant metastases in a mouse model.

INTRODUCTION: Incisional biopsies, including the diagnostic core needle biopsy (CNB), routinely performed before surgical excision of breast cancer tumors are hypothesized to increase the risk of metastatic disease. In this study, we experimentally determined whether CNB of breast cancer tumors results in increased distant metastases and examine important resultant changes in the primary tumor and tumor microenvironment associated with this outcome. METHOD: To evaluate the effect of CNB on metastasis development, we implanted murine mammary 4T1 tumor cells in BALB/c mice and performed CNB on palpable tumors in half the mice. Subsequently, emulating the human scenario, all mice underwent complete tumor excision and were allowed to recover, with attendant metastasis development. Tumor growth, lung metastasis, circulating tumor cell (CTC) levels, variation in gene expression, composition of the tumor microenvironment, and changes in immunologic markers were compared in biopsied and non-biopsied mice. RESULTS: Mice with biopsied tumors developed significantly more lung metastases compared to non-biopsied mice. Tumors from biopsied mice contained a higher frequency of myeloid-derived suppressor cells (MDSCs) accompanied by reduced CD4 + T cells, CD8 + T cells, and macrophages, suggesting biopsy-mediated development of an increasingly immunosuppressive tumor microenvironment. We also observed a CNB-dependent up-regulation in the expression of SOX4, Ezh2, and other key epithelial-mesenchymal transition (EMT) genes, as well as increased CTC levels among the biopsy group. CONCLUSION: CNB creates an immunosuppressive tumor microenvironment, increases EMT, and facilitates release of CTCs, all of which likely contribute to the observed increase in development of distant metastases.

Oncolytic virus-mediated reversal of impaired tumor antigen presentation.

Anti-tumor immunity can eliminate existing cancer cells and also maintain a constant surveillance against possible relapse. Such an antigen-specific adaptive response begins when tumor-specific T cells become activated. T-cell activation requires two signals on antigen presenting cells (APCs): antigen presentation through major histocombatibility complex (MHC) molecules and co-stimulation. In the absence of one or both these signals, T cells remain inactivated or can even become tolerized. Cancer cells and their associated microenvironment strategically hinder the processing and presentation of tumor antigens and consequently prevent the development of anti-tumor immunity. Many studies, however, demonstrate that interventions that over-turn tumor-associated immune evasion mechanisms can establish anti-tumor immune responses of therapeutic potential. One such intervention is oncolytic virus (OV)-based anti-cancer therapy. Here, we discuss how OV-induced immunological events override tumor-associated antigen presentation impairment and promote appropriate T cell-APC interaction. Detailed understanding of this phenomenon is pivotal for devising the strategies that will enhance the efficacy of OV-based anti-cancer therapy by complementing its inherent oncolytic activities with desired anti-tumor immune responses.

The NAD+ synthesizing enzyme nicotinamide mononucleotide adenylyltransferase 2 (NMNAT-2) is a p53 downstream target.

NAD(+) metabolism plays key roles not only in energy production but also in diverse cellular physiology. Aberrant NAD(+) metabolism is considered a hallmark of cancer. Recently, the tumor suppressor p53, a major player in cancer signaling pathways, has been implicated as an important regulator of cellular metabolism. This notion led us to examine whether p53 can regulate NAD(+) biosynthesis in the cell. Our search resulted in the identification of nicotinamide mononucleotide adenylyltransferase 2 (NMNAT-2), a NAD(+) synthetase, as a novel downstream target gene of p53. We show that NMNAT-2 expression is induced upon DNA damage in a p53-dependent manner. Two putative p53 binding sites were identified within the human NMNAT-2 gene, and both were found to be functional in a p53-dependent manner. Furthermore, knockdown of NMNAT-2 significantly reduces cellular NAD(+) levels and protects cells from p53-dependent cell death upon DNA damage, suggesting an important functional role of NMNAT-2 in p53-mediated signaling. Our demonstration that p53 modulates cellular NAD(+) synthesis is congruent with p53's emerging role as a key regulator of metabolism and related cell fate.

Activation of p53 by chemotherapeutic agents enhances reovirus oncolysis.

Mammalian reovirus is a benign virus that possesses the natural ability to preferentially infect and kill cancer cells (reovirus oncolysis). Reovirus exploits aberrant Ras signalling in many human cancers to promote its own replication and spread. In vitro and in vivo studies using reovirus either singly or in combination with anti-cancer drugs have shown very encouraging results. Presently, a number of reovirus combination therapies are undergoing clinical trials for a variety of cancers. Previously we showed that accumulation of the tumor suppressor protein p53 by Nutlin-3a (a specific p53 stabilizer) enhanced reovirus-induced apoptosis, and resulted in significantly higher levels of reovirus dissemination. In this study, we examined the role of p53 in combination therapies involving reovirus and chemotherapeutic drugs. We showed that sub-lethal concentrations of traditional chemotherapy drugs actinomycin D or etoposide, but not doxorubicin, enhanced reovirus-induced apoptosis in a p53-dependent manner. Furthermore, NF-κB activation and expression of p53-target genes (p21 and bax) were important for the p53-dependent enhancement of cell death. Our results show that p53 status affects the efficacy of combination therapy involving reovirus. Choosing the right combination partner for reovirus and a low dosage of the drug may help to both enhance reovirus-induced cancer elimination and reduce drug toxicity.

Multifaceted therapeutic targeting of ovarian peritoneal carcinomatosis through virus-induced immunomodulation.

Immunosuppression associated with ovarian cancer (OC) and resultant peritoneal carcinomatosis (PC) hampers the efficacy of many promising treatment options, including immunotherapies. It is hypothesized that oncolytic virus-based therapies can simultaneously kill OC and mitigate immunosuppression. Currently, reovirus-based anticancer therapy is undergoing phase I/II clinical trials for the treatment of OC. Hence, this study was focused on characterizing the effects of reovirus therapy on OC and associated immune microenvironment. Our data shows that reovirus efficiently killed OC cells and induced higher expression of the molecules involved in antigen presentation including major histocompatibility complex (MHC) class I, ß2-microglobulin (ß2M), TAP-1, and TAP-2. In addition, in the presence of reovirus, dendritic cells (DCs) overcame the OC-mediated phenotypic suppression and successfully stimulated tumor-specific CD8+ T cells. In animal studies, reovirus targeted local and distal OC, alleviated the severity of PC and significantly prolonged survival. These therapeutic effects were accompanied by decreased frequency of suppressive cells, e.g., Gr1.1+, CD11b+ myeloid derived suppressor cells (MDSCs), and CD4+, CD25+, FOXP3+ Tregs, tumor-infiltration of CD3+ cells and higher expression of Th1 cytokines. Finally, reovirus therapy during early stages of OC also resulted in the postponement of PC development. This report elucidates timely information on a therapeutic approach that can target OC through clinically desired multifaceted mechanisms to better the outcomes.

Genotoxic agents promote the nuclear accumulation of annexin A2: role of annexin A2 in mitigating DNA damage.

Annexin A2 is an abundant cellular protein that is mainly localized in the cytoplasm and plasma membrane, however a small population has been found in the nucleus, suggesting a nuclear function for the protein. Annexin A2 possesses a nuclear export sequence (NES) and inhibition of the NES is sufficient to cause nuclear accumulation. Here we show that annexin A2 accumulates in the nucleus in response to genotoxic agents including gamma-radiation, UV radiation, etoposide and chromium VI and that this event is mediated by the nuclear export sequence of annexin A2. Nuclear accumulation of annexin A2 is blocked by the antioxidant agent N-acetyl cysteine (NAC) and stimulated by hydrogen peroxide (H2O2), suggesting that this is a reactive oxygen species dependent event. In response to genotoxic agents, cells depleted of annexin A2 show enhanced phospho-histone H2AX and p53 levels, increased numbers of p53-binding protein 1 nuclear foci and increased levels of nuclear 8-oxo-2'-deoxyguanine, suggesting that annexin A2 plays a role in protecting DNA from damage. This is the first report showing the nuclear translocation of annexin A2 in response to genotoxic agents and its role in mitigating DNA damage.

Viral subversion of autophagy impairs oncogene-induced senescence.

Many viruses have evolved elegant strategies to co-opt cellular autophagic responses to facilitate viral propagation and evasion of immune surveillance. Kaposi's sarcoma-associated herpesvirus (KSHV) establishes a life-long persistent infection in its human host, and is etiologically linked to several cancers. KSHV gene products have been shown to modulate autophagy but their contribution to pathogenesis remains unclear. Our recent study demonstrated that KSHV subversion of autophagy promotes bypass of oncogene-induced senescence (OIS), an important host barrier to tumor initiation. These findings suggest that KSHV has evolved to subvert autophagy, at least in part, to establish an optimal niche for infection, concurrently dampening host antiviral defenses and allowing the ongoing proliferation of infected cells.

Reovirus variants with mutations in genome segments S1 and L2 exhibit enhanced virion infectivity and superior oncolysis.

Reovirus preferentially replicates in transformed cells and is being explored as a cancer therapy. Immunological and physical barriers to virotherapy inspired a quest for reovirus variants with enhanced oncolytic potency. Using a classical genetics approach, we isolated two reovirus variants (T3v1 and T3v2) with superior replication relative to wild-type reovirus serotype 3 Dearing (T3wt) on various human and mouse tumorigenic cell lines. Unique mutations in reovirus λ2 vertex protein and σ1 cell attachment protein were associated with the large plaque-forming phenotype of T3v1 and T3v2, respectively. Both T3v1 and T3v2 exhibited higher infectivity (i.e., a higher PFU-to-particle ratio) than T3wt. A detailed analysis of virus replication revealed that virus cell binding and uncoating were equivalent for variant and wild-type reoviruses. However, T3v1 and T3v2 were significantly more efficient than T3wt in initiating productive infection. Thus, when cells were infected with equivalent input virus particles, T3v1 and T3v2 produced significantly higher levels of early viral RNAs relative to T3wt. Subsequent steps of virus replication (viral RNA and protein synthesis, virus assembly, and cell death) were equivalent for all three viruses. In a syngeneic mouse model of melanoma, both T3v1 and T3v2 prolonged mouse survival compared to wild-type reovirus. Our studies reveal that oncolytic potency of reovirus can be improved through distinct mutations that increase the infectivity of reovirus particles.