Forced expression of the DEK-NUP214 fusion protein promotes proliferation dependent on upregulation of mTOR

BACKGROUND

The t(6;9)(p23;q34) chromosomal translocation is found in 1% of acute myeloid leukemia and encodes the fusion protein DEK-NUP214 (formerly DEK-CAN) with largely uncharacterized functions.

METHODS

We expressed DEK-NUP214 in the myeloid cell lines U937 and PL-21 and studied the effects on cellular functions.

RESULTS

In this study, we demonstrate that expression of DEK-NUP214 increases cellular proliferation. Western blot analysis revealed elevated levels of one of the key proteins regulating proliferation, the mechanistic target of rapamycin, mTOR. This conferred increased mTORC1 but not mTORC2 activity, as determined by the phosphorylation of their substrates, p70 S6 kinase and Akt. The functional importance of the mTOR upregulation was determined by assaying the downstream cellular processes; protein synthesis and glucose metabolism. A global translation assay revealed a substantial increase in the translation rate and a metabolic assay detected a shift from glycolysis to oxidative phosphorylation, as determined by a reduction in lactate production without a concomitant decrease in glucose consumption. Both these effects are in concordance with increased mTORC1 activity. Treatment with the mTORC1 inhibitor everolimus (RAD001) selectively reversed the DEK-NUP214-induced proliferation, demonstrating that the effect is mTOR-dependent.

CONCLUSIONS

Our study shows that the DEK-NUP214 fusion gene increases proliferation by upregulation of mTOR, suggesting that patients with leukemias carrying DEK-NUP214 may benefit from treatment with mTOR inhibitors.

The histone deacetylase inhibitor valproic acid sensitizes diffuse large B-cell lymphoma cell lines to CHOP-induced cell death

Epigenetic code modifications by histone deacetylase inhibitors (HDACis) have recently been proposed as potential new therapies for hematological malignancies. Diffuse large B-cell lymphoma (DLBCL) is the most common form of aggressive lymphoma. At present, standard first line treatment for DLBCL patients is the antracycline-based chemotherapy regimen CHOP (cyclophosphamide, doxorubicin, vincristine and prednisone) combined with the monoclonal anti-CD20 antibody rituximab (R-CHOP). Since only 50-60% of patients reach a long-time cure by this treatment, there is an urgent need for novel treatment strategies to increase the response and long-term remission to initial R-CHOP therapy. In this study, we investigated the effect of the HDAC inhibitor valproic acid (VPA) on DLBCL cell lines. To elucidate the effects of VPA on chemo-sensitivity, we used a cell-line based model of CHOP-refractory DLBCL. All five DLBCL cell lines treated with VPA alone or in combination with CHOP showed decreased viability and proliferation. The VPA-induced sensitization of DLBCL cells to cytotoxic treatment resulted in increased number of apoptotic cell as judged by annexin V-positivity and the presence of cleaved caspase-3. In addition, pretreatment with VPA resulted in a significantly increased DNA-damage as compared to CHOP alone. In summary, HDAC inhibitors such as VPA, are promising therapeutic agents in combination with R-CHOP for patients with DLBCL.

The p53 target gene TRIM22 directly or indirectly interacts with the translation initiation factor eIF4E and inhibits the binding of eIF4E to eIF4G

Background information

The interferon (IFN)‐inducible protein TRIM22 (Staf50) is a member of the tripartite motif protein family and has been suggested a role in the regulation of viral replication as well as of protein ubiquitylation. In addition, we have previously shown that TRIM22 is a direct target gene for the tumour suppressor p53. Consistently, over‐expression of TRIM22 inhibits the clonogenic growth of monoblastic U937 cells, suggesting anti‐proliferative or cell death‐inducing effects.

Results

Here, we demonstrate that TRIM22 directly or indirectly interacts with the eukaryotic translation initiation factor (eIF)4E, and inhibits the binding of eIF4E to eIF4G, thus disturbing the assembly of the eIF4F complex, which is necessary for cap‐dependent translation. Furthermore, TRIM22 exerts a repressive effect on luciferase reporter protein levels and to some extent on radiolabelled methionine incorporation. Even though all nuclear mRNAs are capped, some are more dependent on eIF4F than others for translation. The translation of one of these mRNAs, IRF‐7C, was indeed found to be repressed in the presence of TRIM22.

Conclusions

Our data suggest TRIM22 to repress protein translation preferably of some specific mRNAs. Taken together, we show that TRIM22 represses translation by inhibiting the binding of eIF4E to eIF4G, suggesting a mechanism for regulation of protein translation, which may be of importance in response to p53 and/or IFN signalling.

Abstract 4005: The leukemia-associated fusion protein DEK-NUP214 induces proliferation through an mTOR-dependent mechanism

Acute myeloid leukemia (AML) is characterized by the dysregulated proliferation and impaired differentiation of myeloid precursor cells. The majority of these leukemias harbor genetic translocations, which determine both the molecular mechanistics and the prognosis of the disease. The t(6;9)(p22;q34) chromosomal translocation is found in 1% of AML, where it is associated with young age and poor prognosis. The translocation occurs between specific introns in the gene DEK on chromosome 6 and the gene NUP214 on chromosome 9, creating the fusion gene DEK-NUP214. The role of DEK-NUP214 in leukemogenesis is still largely uncharacterized. To obtain an experimental model of the disease, we expressed the fusion gene in the myeloid cell line U937 and studied the phenotype of the stable clones. We show that cells expressing DEK-NUP214 proliferate faster and also sustain their proliferative capacity longer in culture than their normal counterparts. Cellular proliferation is regulated by a wide range of signaling pathways, but many converge on the activating phosphorylation of the mechanistic target of rapamycin (mTOR) at Ser2448. Western blot analysis of the clones revealed that cells expressing DEK-NUP214 have higher levels of both phosphorylated and total mTOR protein. To determine the effect on downstream cellular functions, we proceeded to study mTOR-dependent translation and metabolism. We performed a global translation assay where the incorporation of radioactively labeled amino acids into newly synthesized proteins reflects the rate of translation. The results show that cells expressing DEK-NUP214 have a markedly increased translation rate. Cellular metabolism was studied by measuring the consumption of glucose and the production of lactate in cell supernatant. We demonstrate that cells expressing DEK-NUP214 produce less lactate, despite equal glucose consumption and increased proliferation. In concordance with increased mTOR activity, our results suggest that cells expressing DEK-NUP214 shift their metabolism from glycolysis to oxidative phosphorylation. The increased activity of mTOR thus leads to translational and metabolic changes that could play a role in the leukemogenic effect of DEK-NUP214. Interestingly, proliferation induced by DEK-NUP214 is highly dependent on mTOR. Treatment with the mTOR inhibitor everolimus (RAD001) reduces the proliferation of the DEK-NUP214 cells to the level of the control cells, without affecting the control cells. This pivotal role of mTOR suggests that leukemias harboring the t(6;9)(p22;q34) translocation may be susceptible to treatment with either rapamycin or the novel mTOR inhibitors that are approaching the clinic.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4005. doi:10.1158/1538-7445.AM2011-4005

Abstract 3085: The IFN inducible p53 target gene TRIM22 binds to the translation initation factor eIF4E and represses translation through disturbing the assembly of the eIF4F complex

TRIM22 (Staf50) is an interferon (IFN)-inducible protein as well as a p53 target gene. It belongs to the TRIM (TRIpartite Motif) family proteins, characterized of a conserved tripartite motif consisting of a RING finger, B-box and a coiled-coil domain. The TRIM family includes more than 70 proteins, involved in various biological processes; e.g. apoptosis and cell proliferation. Consistently, several TRIM family members are involved in cancer. TRIM22 has been suggested to be an antiviral protein, capable of restricting HIV-, hepatitis B- and encephalomyocarditis replication. The molecular mechanisms for TRIM22 are unclear, but the antiviral activity may be dependent on the ubiquitylation capacity of TRIM22. We have previously shown it to suppress the clonogenic growth of leukemic U-937 cells, suggesting anti-proliferative or cell death-inducing effects. Now, we demonstrate that TRIM22 binds to the translation initiation factor eIF4E, and inhibits the binding of eIF4E to eIF4G, thus disturbing the assembly of the eIF4F complex, vital for cap dependent translation of mRNA. As a consequence, TRIM22 represses translation, as shown by decreased reporter protein levels, as well as global protein synthesis. Pulse-chase and cycloheximide experiments reveal that the repressive effects on the reporter protein is not due to increased protein degradation. Taken together, our data show TRIM22 to repress the binding of eIF4E to eIF4G, suggesting a novel translation regulating mechanism, possibly mediated in response to p53 and/or IFN signaling.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3085. doi:10.1158/1538-7445.AM2011-3085

Inhibition of geranylgeranylation mediates sensitivity to CHOP-induced cell death of DLBCL cell lines

Prenylation is a post-translational hydrophobic modification of proteins, important for their membrane localization and biological function. The use of inhibitors of prenylation has proven to be a useful tool in the activation of apoptotic pathways in tumor cell lines. Rab geranylgeranyl transferase (Rab GGT) is responsible for the prenylation of the Rab family. Overexpression of Rab GGTbeta has been identified in CHOP refractory diffuse large B cell lymphoma (DLBCL). Using a cell line-based model for CHOP resistant DLBCL, we show that treatment with simvastatin, which inhibits protein farnesylation and geranylgeranylation, sensitizes DLBCL cells to cytotoxic treatment. Treatment with the farnesyl transferase inhibitor FTI-277 or the geranylgeranyl transferase I inhibitor GGTI-298 indicates that the reduction in cell viability was restricted to inhibition of geranylgeranylation. In addition, treatment with BMS1, a combined inhibitor of farnesyl transferase and Rab GGT, resulted in a high cytostatic effect in WSU-NHL cells, demonstrated by reduced cell viability and decreased proliferation. Co-treatment of BMS1 or GGTI-298 with CHOP showed synergistic effects with regard to markers of apoptosis. We propose that inhibition of protein geranylgeranylation together with conventional cytostatic therapy is a potential novel strategy for treating patients with CHOP refractory DLBCL.

The involvement of cellular proliferation status in the expression of the human proto-oncogene DEK

The role of the DEK protein, involved in the leukemia-associated fusion protein DEK-CAN, is not yet known. In this study, we show a higher expression of DEK mRNA in immature cells than in mature cells. Furthermore, a correlation between DEK expression and cell proliferation was demonstrated, suggesting that DEK plays a role in the proliferation of hematopoietic cells and raising the question of whether the DEK-CAN fusion protein might perturb regulation of proliferation in leukemic cells.

Characterisation of the biosynthesis and processing of the neutrophil granule membrane protein CD63 in myeloid cells

The biosynthesis and processing of the neutrophil granule membrane protein CD63, present in azurophil granules, was investigated in four myeloid cell lines. The amount of CD63 synthesised differed, so did the amount of protein processed to high molecular weight forms, with the demonstration of a more prominent synthesis of CD63 in K562 cells. Newly synthesised CD63 was initially detected as two precursor forms with molecular weight of 32 and 35 kDa, respectively. These two initial forms were processed further to yield high molecular weight forms of CD63 with a mean molecular weight of 50 kDa. Treatment with endoglycosidase H or N-glycosidase F revealed a protein core, free from asparagine-linked carbohydrates, with a molecular weight of 23 kDa. Newly synthesised CD63 was susceptible to digestion with endoglycosidase H, and the protein was not completely resistant to endoglycosidase H until after 4 h of chase, indicating that transport through the medial and trans-Golgi complex with conversion of high-mannose carbohydrates to complex oligosaccharide side chains had occurred. This finding indicates a relatively long processing time for CD63 compared to that of soluble azurophil granule proteins. By digestion with O-glycanase, the existence of O-linked oligosaccharides on CD63 could not be demonstrated. Biosynthetic labelling of cells in the presence of brefeldin A showed the importance of a functional Golgi apparatus for processing of the protein to its high molecular weight forms.

Distribution of diplococcus pneumoniae types in acute otitis media in children and influence of the types on the clinical course in penicillin v therapy

Abstract Pneumococci isolated from the ear exudate in 245 children under 10 years of age afflicted with acute otitis media were typed. Types 3, 6, 14, 18, 19 and 23 were found in 80% of the cases. In the remaining cases, 15 other types were found. Five strains were not typable with the antisera used. Types 14 and 23 were found twice as often in the age group 0-3 years as in the higher age groups, whereas the opposite was true for type 3. The relapse frequency was highest after types 14 and 19 infections. The frequency of residual secretory otitis was highest after type 14 infections. Types 19 and 23 were never found in infections followed by secretory otitis. Patients with type 14 infections, healed or unhealed, showed the same blood group distribution within the ABO and Lewis systems as a normal Swedish population. Penicillin V therapy failed to eliminate the pneumococcal strain from the nasopharynx in 40% of consecutive cases of otitis media. Relapse after penicillin-treated pneumococcal otitis is to be regarded as a new complication of the primary infection and not as a reinfection from the environment.