Tumor suppressor PNRC1 blocks rRNA maturation by recruiting the decapping complex to the nucleolus.

Focal deletions occur frequently in the cancer genome. However, the putative tumor-suppressive genes residing within these regions have been difficult to pinpoint. To robustly identify these genes, we implemented a computational approach based on non-negative matrix factorization, NMF, and interrogated the TCGA dataset. This analysis revealed a metagene signature including a small subset of genes showing pervasive hemizygous deletions, reduced expression in cancer patient samples, and nucleolar function. Amid the genes belonging to this signature, we have identified PNRC1, a nuclear receptor coactivator. We found that PNRC1 interacts with the cytoplasmic DCP1α/DCP2 decapping machinery and hauls it inside the nucleolus. PNRC1-dependent nucleolar translocation of the decapping complex is associated with a decrease in the 5'-capped U3 and U8 snoRNA fractions, hampering ribosomal RNA maturation. As a result, PNRC1 ablates the enhanced proliferation triggered by established oncogenes such as RAS and MYC These observations uncover a previously undescribed mechanism of tumor suppression, whereby the cytoplasmic decapping machinery is hauled within nucleoli, tightly regulating ribosomal RNA maturation.

ATR addiction in multiple myeloma: synthetic lethal approaches exploiting established therapies.

Therapeutic strategies designed to tinker with cancer cell DNA damage response have led to the widespread use of PARP inhibitors for BRCA1/2-mutated cancers. In the haematological cancer multiple myeloma, we sought to identify analogous synthetic lethality mechanisms that could be leveraged upon established cancer treatments. The combination of ATR inhibition using the compound VX-970 with a drug eliciting interstrand cross-links, melphalan, was tested in in vitro, ex vivo, and most notably in vivo models. Cell proliferation, induction of apoptosis, tumor growth and animal survival were assessed. The combination of ATM inhibition with a drug triggering double strand breaks, doxorucibin, was also probed. We found that ATR inhibition is strongly synergistic with melphalan, even in resistant cells. The combination was dramatically effective in targeting myeloma primary patient cells and cell lines reducing cell proliferation and inducing apoptosis. The combination therapy significantly reduced tumor burden and prolonged survival in animal models. Conversely, ATM inhibition only marginally impacted on myeloma cell survival, even in combination with doxorucibin at high doses. These results indicate that myeloma cells extensively rely on ATR, but not on ATM, for DNA repair. Our findings posit that adding an ATR inhibitor such as VX-970 to established therapeutic regimens may provide a remarkably broad benefit to myeloma patients.

H3K4me3 demethylation by the histone demethylase KDM5C/JARID1C promotes DNA replication origin firing.

DNA replication is a tightly regulated process that initiates from multiple replication origins and leads to the faithful transmission of the genetic material. For proper DNA replication, the chromatin surrounding origins needs to be remodeled. However, remarkably little is known on which epigenetic changes are required to allow the firing of replication origins. Here, we show that the histone demethylase KDM5C/JARID1C is required for proper DNA replication at early origins. JARID1C dictates the assembly of the pre-initiation complex, driving the binding to chromatin of the pre-initiation proteins CDC45 and PCNA, through the demethylation of the histone mark H3K4me3. Fork activation and histone H4 acetylation, additional early events involved in DNA replication, are not affected by JARID1C downregulation. All together, these data point to a prominent role for JARID1C in a specific phase of DNA replication in mammalian cells, through its demethylase activity on H3K4me3.

IκBε deficiency accelerates disease development in chronic lymphocytic leukemia.

The NFKBIE gene, which encodes the NF-κB inhibitor IκBε, is mutated in 3-7% of patients with chronic lymphocytic leukemia (CLL). The most recurrent alteration is a 4-bp frameshift deletion associated with NF-κB activation in leukemic B cells and poor clinical outcome. To study the functional consequences of NFKBIE gene inactivation, both in vitro and in vivo, we engineered CLL B cells and CLL-prone mice to stably down-regulate NFKBIE expression and investigated its role in controlling NF-κB activity and disease expansion. We found that IκBε loss leads to NF-κB pathway activation and promotes both migration and proliferation of CLL cells in a dose-dependent manner. Importantly, NFKBIE inactivation was sufficient to induce a more rapid expansion of the CLL clone in lymphoid organs and contributed to the development of an aggressive disease with a shortened survival in both xenografts and genetically modified mice. IκBε deficiency was associated with an alteration of the MAPK pathway, also confirmed by RNA-sequencing in NFKBIE-mutated patient samples, and resistance to the BTK inhibitor ibrutinib. In summary, our work underscores the multimodal relevance of the NF-κB pathway in CLL and paves the way to translate these findings into novel therapeutic options.

Iron increases the susceptibility of multiple myeloma cells to bortezomib.

Multiple myeloma is a malignant still incurable plasma cell disorder. Pharmacological treatment based on proteasome inhibition has improved patient outcome; however, bortezomib-resistance remains a major clinical problem. Inhibition of proteasome functionality affects cellular iron homeostasis and iron is a potent inducer of reactive oxygen species and cell death, unless safely stored in ferritin. We explored the potential role of iron in bortezomib-resistance. We analyzed iron proteins, oxidative status and cell viability in 7 multiple myeloma cell lines and in plasma cells from 5 patients. Cells were treated with increasing bortezomib concentrations with or without iron supplementation. We reduced ferritin levels by both shRNA technology and by drug-induced iron starvation. Multiple myeloma cell lines are characterized by distinct ferritin levels, which directly correlate with bortezomib resistance. We observed that iron supplementation upon bortezomib promotes protein oxidation and cell death, and that iron toxicity inversely correlates with basal ferritin levels. Bortezomib prevents ferritin upregulation in response to iron, thus limiting the ability to buffer reactive oxygen species. Consequently, reduction of basal ferritin levels increases both bortezomib sensitivity and iron toxicity. In patients' cells, we confirmed that bortezomib prevents ferritin increase, that iron supplementation upon bortezomib increases cell death and that ferritin reduction overcomes bortezomib resistance. Bortezomib affects iron homeostasis, sensitizing cells to oxidative damage. Modulation of iron status is a strategy worth exploring to improve the efficacy of proteasome inhibition therapies.

MicroRNA and proliferation control in chronic lymphocytic leukemia: functional relationship between miR-221/222 cluster and p27.

We investigated functional relationships between microRNA 221/222 (miR-221/222) cluster and p27, a key regulator of cell cycle, in chronic lymphocytic leukemia (CLL). The enforced expression of miR-221/222 in the CLL cell line MEC1 induced a significant down-regulation of p27 protein and conferred a proliferative advantage to the transduced cells that exhibited faster progression into the S phase of the cell cycle. Accordingly, expression of miR-221/miR-222 and p27 was found to be inversely related in leukemic cells obtained from peripheral blood (PB) of 38 patients with CLL. Interestingly, when miR-221/222 and p27 protein were evaluated in different anatomic compartments (lymph nodes or bone marrow) of the same patients, increased expression of the 2 miRNAs became apparent compared with PB. This finding was paralleled by a low expression of p27. In addition, when CLL cells were induced in vitro to enter cell cycle (eg, with cytosine phosphate guanine oligodeoxynucleotide), a significant increase of miR-221/222 expression and a marked down-regulation of p27 protein were evident. These data indicate that the miR-221/222 cluster modulates the expression of p27 protein in CLL cells and lead to suggest that miR-221/222 and p27 may represent a regulatory loop that helps maintaining CLL cells in a resting condition.

Deletion of a pseudogene within a fragile site triggers the oncogenic expression of the mitotic CCSER1 gene.

The oncogenic role of common fragile sites (CFS), focal and pervasive gaps in the cancer genome arising from replicative stress, remains controversial. Exploiting the TCGA dataset, we found that in most CFS the genes residing within the associated focal deletions are down-regulated, including proteins involved in tumour immune recognition. In a subset of CFS, however, the residing genes are surprisingly overexpressed. Within the most frequent CFS in this group, FRA4F, which is deleted in up to 18% of cancer cases and harbours the CCSER1 gene, we identified a region which includes an intronic, antisense pseudogene, TMSB4XP8. TMSB4XP8 focal ablation or transcriptional silencing elicits the overexpression of CCSER1, through a cis-acting mechanism. CCSER1 overexpression increases proliferation and triggers centrosome amplifications, multinuclearity, and aberrant mitoses. Accordingly, FRA4F is associated in patient samples to mitotic genes deregulation and genomic instability. As a result, cells overexpressing CCSER1 become sensitive to the treatment with aurora kinase inhibitors. Our findings point to a novel tumourigenic mechanism where focal deletions increase the expression of a new class of "dormant" oncogenes.

Constitutive activation of distinct BCR-signaling pathways in a subset of CLL patients: a molecular signature of anergy.

Stimulation through the B-cell antigen receptor (BCR) is believed to be involved in the natural history of chronic lymphocytic leukemia (CLL). Some cases respond to the in vitro cross-linking of surface immunoglobulin (sIg) with effective activation. In contrast, the remaining cases do not respond to such stimulation, thereby resembling B cells anergized after antigen encounter in vivo. However the biochemical differences between the 2 groups are ill defined, and in humans the term B-cell anergy lacks a molecular definition. We examined the expression and activation of key molecules involved in signaling pathways originating from the BCR, and we report that a proportion of CLL patients (a) expresses constitutively phosphorylated extracellular signal-regulated kinase (ERK)1/2 in the absence of AKT activation; (b) displays constitutive phosphorylation of MEK1/2 and increased nuclear factor of activated T cells (NF-AT) transactivation; and (c) is characterized by cellular unresponsiveness to sIg ligation. This molecular profile recapitulates the signaling pattern of anergic murine B cells. Our data indicate that constitutive activation of mitogen activated protein (MAP) kinase signaling pathway along with NF-AT transactivation in the absence of AKT activation may also represent the molecular signature of anergic human B lymphocytes. CLL cases with this signature may be taken as a human model of anergic B cells aberrantly expanded.

WNT Signaling in Hematological Malignancies.

The role of the WNT signaling pathway in key cellular processes, such as cell proliferation, differentiation and migration is well documented. WNT signaling cascade is initiated by the interaction of WNT ligands with receptors belonging to the Frizzled family, and/or the ROR1/ROR2 and RYK families. The downstream signaling cascade results in the activation of the canonical ß-catenin dependent pathway, ultimately leading to transcriptional control of cell proliferation, or the non-canonical pathway, mainly acting on cell migration and cell polarity. The high level of expression of both WNT ligands and WNT receptors in cancer cells and in the surrounding microenvironment suggests that WNT may represent a central conduit of interactions between tumor cells and microenviroment. In this review we will focus on WNT pathways deregulation in hematological cancers, both at the ligand and receptor levels. We will review available literature regarding both the classical ß-catenin dependent pathway as well as the non-canonical pathway, with particular emphasis on the possible exploitation of WNT aberrant activation as a therapeutic target, a notion supported by preclinical data.

Expression and function of toll like receptors in chronic lymphocytic leukaemia cells.

Mature B-cells can recognize microbial antigens via B-cell-receptor (BCR) in a specific way and via Toll-like receptors (TLR) in a costimulatory manner. A wealth of information is gathering on the possible role of antigenic stimulation in the natural history of Chronic Lymphocytic Leukaemia (CLL). However little is known regarding the repertoire and function of TLR in CLL cells. The TLR family includes 10 different transmembrane proteins devoted to recognize specific pathogen-associated molecular patterns and to alarm immunocompetent cells to trigger an immune response. Here, we studied fresh leukaemic cells for the expression pattern of TLR1 to TLR10, NOD1, NOD2 and SIGIRR (also known as TIR8). CLL cells were found to express several pattern recognition receptors including TLR1, TLR2, TLR6, TLR10, NOD1 and NOD2. The specific TLR expressed by CLL cells were functional. Leukaemic cells, upon stimulation with TLR1/2/6 ligands, such as bacterial lipopeptides, activated the nuclear factor-kappaB signalling pathway, expressed CD86 and CD25 activation molecules, and were protected from spontaneous apoptosis. These findings further support the hypothesis that CLL cells resemble antigen-activated B-cells and suggest a potential role of TLR in modulating CLL cell response in the context of specific antigen recognition.

From normal to clonal B cells: Chronic lymphocytic leukemia (CLL) at the crossroad between neoplasia and autoimmunity.

Chronic lymphocytic leukemia (CLL) is a B-cell malignancy endowed with a number of features that recall autoimmune disorders, including the CD5 expression and the development of autoimmune manifestations restricted to self antigens expressed by hematopoietic cells. Several evidences strongly support the possibility that an antigenic stimulation through the B-cell receptor (BCR) is involved in the selection and possibly also the expansion of the malignant clone. Though all evidences suggest specific Ag recognition and possibly stimulation at different time-points, the nature of the Ag(s) is still unknown. It appears likely that CLL cells derive from a pool of auto/polyreactive CD5(+) B cells. Hence CLL appears to be a B-cell malignancy triggered or facilitated in its development and evolution by an auto-Ag. The crucial issues have become to what extent this deleterious binding capacity is central to the natural history of the disease and how it relates to the malignant transformation of the cell.

Human malignant mesothelioma is recapitulated in immunocompetent BALB/c mice injected with murine AB cells.

Malignant Mesothelioma is a highly aggressive cancer, which is difficult to diagnose and treat. Here we describe the molecular, cellular and morphological characterization of a syngeneic system consisting of murine AB1, AB12 and AB22 mesothelioma cells injected in immunocompetent BALB/c mice, which allows the study of the interplay of tumor cells with the immune system. Murine mesothelioma cells, like human ones, respond to exogenous High Mobility Group Box 1 protein, a Damage-Associated Molecular Pattern that acts as a chemoattractant for leukocytes and as a proinflammatory mediator. The tumors derived from AB cells are morphologically and histologically similar to human MM tumors, and respond to treatments used for MM patients. Our system largely recapitulates human mesothelioma, and we advocate its use for the study of MM development and treatment.

Histone demethylase JARID1C inactivation triggers genomic instability in sporadic renal cancer.

Mutations in genes encoding chromatin-remodeling proteins are often identified in a variety of cancers. For example, the histone demethylase JARID1C is frequently inactivated in patients with clear cell renal cell carcinoma (ccRCC); however, it is largely unknown how JARID1C dysfunction promotes cancer. Here, we determined that JARID1C binds broadly to chromatin domains characterized by the trimethylation of lysine 9 (H3K9me3), which is a histone mark enriched in heterochromatin. Moreover, we found that JARID1C localizes on heterochromatin, is required for heterochromatin replication, and forms a complex with established players of heterochromatin assembly, including SUV39H1 and HP1α, as well as with proteins not previously associated with heterochromatin assembly, such as the cullin 4 (CUL4) complex adaptor protein DDB1. Transcription on heterochromatin is tightly suppressed to safeguard the genome, and in ccRCC cells, JARID1C inactivation led to the unrestrained expression of heterochromatic noncoding RNAs (ncRNAs) that in turn triggered genomic instability. Moreover, ccRCC patients harboring JARID1C mutations exhibited aberrant ncRNA expression and increased genomic rearrangements compared with ccRCC patients with tumors endowed with other genetic lesions. Together, these data suggest that inactivation of JARID1C in renal cancer leads to heterochromatin disruption, genomic rearrangement, and aggressive ccRCCs. Moreover, our results shed light on a mechanism that underlies genomic instability in sporadic cancers.

Developmental expression of the cell cycle and apoptosis controlling gene, Lot1, in the rat cerebellum and in cultures of cerebellar granule cells.

The Lot1 gene encodes a zinc finger protein that, in vitro, concurrently regulates apoptosis and cell cycle arrest and belongs to a recently identified family of proteins with oncogenic and tumor-supressor functions. The present study, based on the development of the first antibody reportedly produced against rat Lot1, examines protein expression during normal development of the rat cerebellum and following methylazoxymethanol (MAM) administration, which results in hypoplasia of the cerebellar granule cell population. Using light microscopic immunocytochemistry, specific immunostaining for the Lot1 protein was observed at postnatal days 2 to 7 in the superficial external granule layer composed primarily of proliferating neuronal precursor cells. Purkinje cells showed distinct nuclear labeling at P7. In the adult cerebellum, the overall low Lot1 level was essentially associated with Purkinje cells. Experimentally altered developmental conditions, such as those obtained through MAM-induced microencephaly, did not drastically affect the pattern of Lot1 expression. In particular, Purkinje cells continued to show normal levels of immunoreactivity notwithstanding the altered cerebellar architecture. Primary cultures of cerebellar granule cells showed a temporal pattern of Lot1 expression resembling that of in vivo development, with mRNA and protein levels progressively decreasing with differentiation. When cerebellar granule cells were exposed to different neurotoxic challenges, Lot1 appeared not affected by purely apoptotic cell death, while transitorily induced by mixed necrotic-apoptotic cell death.

The role of toll-like receptors in chronic B-cell malignancies.

Toll-like receptors (TLR) are key players in host defence from infection. They recognize a specific set of molecular patterns of microbial origin, immediately trigger an innate immune response, and bridge innate and adaptive immunity. TLR have also been shown to play a role in tumor development. In this context, chronic B-cell malignancies are an interesting example as clonal B lymphocytes remain responsive to and dependent on stimuli originating from the microenvironment which then become crucial for maintaining and propagating the disease. Emerging evidences suggest that, among other microenvironmental elements, TLR ligands may play a role in the pathogenesis of chronic B-cell lymphoid malignancies. Conceivably, their manipulation may find a place in specific settings of treatment of these tumors.