Loss of CCDC6 Affects Cell Cycle through Impaired Intra-S-Phase Checkpoint Control

In most cancers harboring Ccdc6 gene rearrangements, like papillary thyroid tumors or myeloproliferative disorders, the product of the normal allele is supposed to be functionally impaired or absent. To address the consequence of the loss of CCDC6 expression, we applied lentiviral shRNA in several cell lines. Loss of CCDC6 resulted in increased cell death with clear shortening of the S phase transition of the cell cycle. Upon exposure to etoposide, the cells lacking CCDC6 did not achieve S-phase accumulation. In the absence of CCDC6 and in the presence of genotoxic stress, like etoposide treatment or UV irradiation, increased accumulation of DNA damage was observed, as indicated by a significant increase of pH2Ax Ser139. 14-3-3σ, a major cell cycle regulator, was down-regulated in CCDC6 lacking cells, regardless of genotoxic stress. Interestingly, in the absence of CCDC6, the well-known genotoxic stress-induced cytoplasmic sequestration of the S-phase checkpoint CDC25C phosphatase did not occur. These observations suggest that CCDC6 plays a key role in cell cycle control, maintenance of genomic stability and cell survival and provide a rational of how disruption of CCDC6 normal function contributes to malignancy

Transforming activities of the NUP98-KMT2A fusion gene associated with myelodysplasia and acute myeloid leukemia

Inv(11)(p15q23), found in myelodysplastic syndromes and acute myeloid leukemia, leads to expression of a fusion protein consisting of the N-terminal of nucleoporin 98 (NUP98) and the majority of the lysine methyltransferase 2A (KMT2A). To explore the transforming potential of this fusion we established inducible iNUP98-KMT2A transgenic mice. After a median latency of 80 weeks, over 90% of these mice developed signs of disease, with anemia and reduced bone marrow cellularity, increased white blood cell numbers, extramedullary hematopoiesis, and multilineage dysplasia. Additionally, induction of iNUP98-KMT2A led to elevated lineage marker-negative Sca-1+ c-Kit+ cell numbers in the bone marrow, which outcompeted wildtype cells in repopulation assays. Six iNUP98-KMT2A mice developed transplantable acute myeloid leukemia with leukemic blasts infiltrating multiple organs. Notably, as reported for patients, iNUP98-KMT2A leukemic blasts did not express increased levels of the HoxA-B-C gene cluster, and in contrast to KMT2A-AF9 leukemic cells, the cells were resistant to pharmacological targeting of menin and BET family proteins by MI-2-2 or JQ1, respectively. Expression of iNUP98-KMT2A in mouse embryonic fibroblasts led to an accumulation of cells in G1 phase, and abrogated replicative senescence. In bone marrow-derived hematopoietic progenitors, iNUP98-KMT2A expression similarly resulted in increased cell numbers in the G1 phase of the cell cycle, with aberrant gene expression of Sirt1, Tert, Rbl2, Twist1, Vim, and Prkcd, mimicking that seen in mouse embryonic fibroblasts. In summary, we demonstrate that iNUP98-KMT2A has in vivo transforming activity and interferes with cell cycle progression rather than primarily blocking differentiation

2009

The NUP98-NSD1 fusion, product of the t(5;11)(q35;p15.5) chromosomal translocation, is one of the most prevalent genetic alterations in cytogenetically normal pediatric acute myeloid leukemias and is associated with poor prognosis. Co-existence of an FLT3-ITD activating mutation has been found in more than 70% of NUP98-NSD1-positive patients. To address functional synergism, we determined the transforming potential of retrovirally expressed NUP98-NSD1 and FLT3-ITD in the mouse. Expression of NUP98-NSD1 provided mouse strain-dependent, aberrant self-renewal potential to bone marrow progenitor cells. Co-expression of FLT3-ITD increased proliferation and maintained self-renewal in vitro. Transplantation of immortalized progenitors co-expressing NUP98-NSD1 and FLT3-ITD into mice resulted in acute myeloid leukemia after a short latency. In contrast, neither NUP98-NSD1 nor FLT3-ITD single transduced cells were able to initiate leukemia. Interestingly, as reported for patients carrying NUP98-NSD1, an increased Flt3-ITD to wild-type Flt3 mRNA expression ratio with increased FLT3-signaling was associated with rapidly induced disease. In contrast, there was no difference in the expression levels of the NUP98-NSD1 fusion or its proposed targets HoxA5, HoxA7, HoxA9 or HoxA10 between animals with different latencies to develop disease. Finally, leukemic cells co-expressing NUP98-NSD1 and FLT3-ITD were very sensitive to a small molecule FLT3 inhibitor, which underlines the significance of aberrant FLT3 signaling for NUP98-NSD1-positive leukemias and suggests new therapeutic approaches that could potentially improve patient outcome. Potent co-operation between the NUP98-NSD1 fusion and the FLT3-ITD mutation in acute myeloid leukemia inductio

Potent co-operation between the NUP98-NSD1 fusion and the FLT3-ITD mutation in acute myeloid leukemia induction

The NUP98-NSD1 fusion, product of the t(5;11)(q35;p15.5) chromosomal translocation, is one of the most prevalent genetic alterations in cytogenetically normal pediatric acute myeloid leukemias and is associated with poor prognosis. Co-existence of an FLT3-ITD activating mutation has been found in more than 70% of NUP98-NSD1-positive patients. To address functional synergism, we determined the transforming potential of retrovirally expressed NUP98-NSD1 and FLT3-ITD in the mouse. Expression of NUP98-NSD1 provided mouse strain-dependent, aberrant self-renewal potential to bone marrow progenitor cells. Co-expression of FLT3-ITD increased proliferation and maintained self-renewal in vitro. Transplantation of immortalized progenitors co-expressing NUP98-NSD1 and FLT3-ITD into mice resulted in acute myeloid leukemia after a short latency. In contrast, neither NUP98-NSD1 nor FLT3-ITD single transduced cells were able to initiate leukemia. Interestingly, as reported for patients carrying NUP98-NSD1, an increased Flt3-ITD to wild-type Flt3 mRNA expression ratio with increased FLT3-signaling was associated with rapidly induced disease. In contrast, there was no difference in the expression levels of the NUP98-NSD1 fusion or its proposed targets HoxA5, HoxA7, HoxA9 or HoxA10 between animals with different latencies to develop disease. Finally, leukemic cells co-expressing NUP98-NSD1 and FLT3-ITD were very sensitive to a small molecule FLT3 inhibitor, which underlines the significance of aberrant FLT3 signaling for NUP98-NSD1-positive leukemias and suggests new therapeutic approaches that could potentially improve patient outcome

CCDC6 knock down results in altered cellular localization of CDC25C and accelerated G₂/S transition upon etoposide-mediated genotoxic stress.

<p>Control and CCDC6 knock down HCT116 cells were treated with etoposide (20 µM). (<b>A</b>) Cell lysates of HCT116 cells treated with etoposide (20 µM) for 2, 4, 8, 12 and 24 hours and mock control treated with DMSO vehicle were resolved on a SDS-PAGE and probed for 14-3-3σ and CDC25C. 14-3-3σ protein levels were down-regulated in the absence of CCDC6 protein expression and the CDC25C protein level regulation was altered. (<b>B</b>) Cells grown on cover slips were exposed to etoposide for 4, 8, 12, 24 hours, fixed and stained for CDC25C. In mock cells, CDC25C is kept in the cytosol upon etoposide treatment at 8 and 12 hours but is localized in the nucleus in the absence of CCDC6. (<b>C</b>) Cells exposed to etoposide for 12 hours were co-stained for CDC25C and 14-3-3σ. CDC25C is kept in the cytosol upon etoposide treatment and exhibits co-localization with 14-3-3σ (seen in yellow) but enters the nucleus in the absence of CCDC6.</p

Normal Cell cycle progression is altered upon CCDC6 knock down.

<p>Cell cycle analysis was performed using propidium iodide (PI) staining and measuring the DNA content, at the indicated time points, starting 48 hours after transduction. Cell cycle was analyzed with FlowJo software and Jean-Fox algorithm. In all time points both in HCT116 (<b>A</b>), (<b>B</b>) and HeLa (<b>C</b>), (<b>D</b>) the percentage of cells in the S phase is reduced upon knock down of CCDC6 in comparison to the control (mock). One, out of three, representative experiment is shown. (<b>E</b>) HCT116 cells were synchronized by serum starvation for 48 hours followed by restimulation with 5% of FCS. CCDC6 knock down resulted in incomplete arrest at G₁ and not total synchronization, as the control cells. 14 hours after serum stimulation the majority of the control cells are in S phase while CCDC6 knock down cells demonstrated a delay in S phase entering. 4 hours later, control and CCDC6 knock down cells showed the same profile, suggesting shorter duration of S upon CCDC6 knock down. 24 hours later, control cells were cycling normally and CCDC6 knock down cells exhibited a delay in completing G₂ phase and re-entering G₁.</p

CCDC6 knock down alters proliferation rate and increases cell death <i>in vitro</i>.

<p>Cells were transduced using lentivirus, expressing two different small hairpins for CCDC6, labeled as sh1 and sh2 and cultured for 48 hours. The same viral vector was applied as control (mock: mock transduced). (<b>A</b>) Western blot analysis using anti-CCDC6 mouse monoclonal antibody demonstrated the efficient knock down of CCDC6 protein expression. Growth curves were performed in triplicates using trypan blue dye exclusion for counting the alive (<b>B</b>) and the dead cells (<b>C</b>). Decreased proliferation rate and increased cell death was observed in the absence of CCDC6. (<b>D</b>) The subG₀/G₁ population, as measured by flow cytometry, is indicative of apoptosis and is significantly increased following CCDC6 knock down. The percentage of survival was calculated for each time point by excluding both early apoptotic and dead cells. (<b>E</b>) Apoptotic cell death was analyzed by Po-PRO and 7-ADD staining. The Po-PRO single-positive cells are early apoptotic while the double positive stained cells for Po-PRO and 7-AAD are late apoptotic and dead cells. All assays were performed in three independent experiments.</p

Deficient S phase checkpoint regulation upon etoposide treatment in the absence of CCDC6.

<p>(<b>A</b>) HCT116 cells were treated with 20 µM etoposide and cells were harvested at predetermined time points for cell cycle analysis. In the absence of CCDC6, no S phase accumulation is observed and the transition to G₂ phase is accelerated. One representative experiment is shown, out of three performed. (<b>B</b>) Concomitant apoptotic cell death was quantified by measuring the subG₀/G₁ DNA content. CCDC6 knock down cells showed higher levels of apoptosis, at earlier time point, in comparison to the control, in response to genotoxic stress upon etoposide treatment. (<b>C</b>) The percentage of cell survival was assessed by gating for PoPRO and 7-AAD negative cells. CCDC6 knock down resulted in lower cell survival upon etoposide induced genotoxic stress. The assays were performed in triplicates.</p

PFI-1, a highly selective protein interaction inhibitor, targeting BET Bromodomains

Bromo and extra terminal (BET) proteins (BRD2, BRD3, BRD4, and BRDT) are transcriptional regulators required for efficient expression of several growth promoting and antiapoptotic genes as well as for cell-cycle progression. BET proteins are recruited on transcriptionally active chromatin via their two N-terminal bromodomains (BRD), a protein interaction module that specifically recognizes acetylated lysine residues in histones H3 and H4. Inhibition of the BET-histone interaction results in transcriptional downregulation of a number of oncogenes, providing a novel pharmacologic strategy for the treatment of cancer. Here, we present a potent and highly selective dihydroquinazoline-2-one inhibitor, PFI-1, which efficiently blocks the interaction of BET BRDs with acetylated histone tails. Cocrystal structures showed that PFI-1 acts as an acetyl-lysine (Kac) mimetic inhibitor efficiently occupying the Kac binding site in BRD4 and BRD2. PFI-1 has antiproliferative effects on leukemic cell lines and efficiently abrogates their clonogenic growth. Exposure of sensitive cell lines with PFI-1 results in G1 cell-cycle arrest, downregulation of MYC expression, as well as induction of apoptosis and induces differentiation of primary leukemic blasts. Intriguingly, cells exposed to PFI-1 showed significant downregulation of Aurora B kinase, thus attenuating phosphorylation of the Aurora substrate H3S10, providing an alternative strategy for the specific inhibition of this well-established oncology target