Mouse pro-B Cell Line Research Articles

Detection of CLCF1 protein expression by flow cytometry

Cardiotrophin-like cytokine factor 1 (CLCF1) is an IL-6 family cytokine with neurotrophic and immuno-modulating functions. CLCF1 mRNA has been detected in primary and secondary lymphoid organs, and up-regulation of CLCF1 mRNA levels has been associated with the T helper (Th) 17 polarization. However, information regarding CLCF1 expression by immune cells at the protein level remains scarce. We have developed a methodology that uses a monoclonal antibody (mAb) directed against CLCF1 for the detection of human and mouse CLCF1 by flow cytometry. We have successfully detected CLCF1 protein expression in cells from the mouse pro-B cell line Ba/F3 that were transduced with CLCF1 cDNA. Interestingly, we found that the anti-CLCF1 mAb inhibits CLCF1 biological activity in vitro by binding to an epitope that encompasses site III of the cytokine. Moreover, we have detected CLCF1 expression in mouse splenic T cells, as well as in vitro differentiated Th1 cells. The specificity of the fluorescence signal was demonstrated using Clcf1-deficient lymphocytes generated using a conditional knock-out mouse model. The detection of CLCF1 protein by flow cytometry will be a valuable tool to study CLCF1 expression during normal and pathological immune responses.

Abstract A008: An in vivo screening platform based on Ba/F3 kinase-engineered cell lines for discovering next-generation kinase inhibitors

Abstract Tongtong Liu, Feng He, Xuyang Duan, Shuliang Li, Chang Liu, Jingying Ning, Feng Hao* KYinno Biotechnology (Beijing) Co., Ltd. No.3 Building, Yizhuang Biomedical Park, Beijing, China. Correspondence: Feng.hao@kyinno.com Protein kinases have become very popular targets in the treatment of cancer and other diseases, and since 2001, the FDA has approved more than 70 kinase inhibitor drugs. However, due to innate or acquired resistance in tumors, most of these small molecule inhibitors only delay tumor progression. The development of next-generation kinase inhibitors with better specificity and lower resistance is still ongoing. Ba/F3 is a mouse pro-B cell line whose survival and proliferation depend on IL-3. After transduction with driver genes such as kinase genes or their mutants, Ba/F3 cells switch from IL-3 dependence to driver gene dependence, making Ba/F3 cells a powerful tool for discovering new kinase inhibitors. Our group has constructed over 700 Ba/F3 engineered cell lines stably transfected with kinase gene mutants. These Ba/F3 kinase cell lines have been fully validated by sequencing, western blotting, and inhibitor testing, covering many popular kinases including EGFR (>150 cell lines), RAS (80 cell lines), FGFR (55 cell lines), ERBB2 (49 cell lines), MET (41 cell lines), RET (39 cell lines), BCR-ABL (37 cell lines), EML4-ALK (33 cell lines), and FLT3 (26 cell lines), etc. Most of these transformed Ba/F3 cell lines can be used for xenograft models in immunodeficient mice. Based on these Ba/F3 kinase cell line-derived xenograft models, we have established an in vivo screening platform to evaluate the efficacy and toxicity of candidate drugs against specific kinase mutation types, as well as their comparison with previous generation drugs. Overall, our data suggest that xenograft models derived from Ba/F3 kinase cell lines are powerful models for discovering next-generation kinase inhibitors. Citation Format: Stephanie Wang. An in vivo screening platform based on Ba/F3 kinase-engineered cell lines for discovering next-generation kinase inhibitors [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr A008.

Abstract 28: In vivoscreening platform based on Ba</>F3 kinase engineered cell lines for discovery of next-generation kinase inhibitors

Abstract Protein kinases have become very popular targets for cancer and other diseases therapy, with more than 70 kinase inhibitor drugs approved by FDA since 2001. Due to innate or acquired drug resistance of tumors, most of these small-molecule inhibitors can only delay tumor progression. Next-generation kinase inhibitors with better specificity and lower drug resistance remain to be developed. Ba/F3 is a mouse pro-B cell line which is dependent on IL-3 for survival and proliferation. Upon transduction of a driver gene such as kinase genes or their mutants, Ba/F3 cells switch from IL3-dependent to driver gene-dependent, which makes Ba/F3 cells a powerful tool for the discovery of new kinase inhibitors. Our group has constructed more than 500 Ba/F3 engineered cell lines stably transfected with mutants of kinase genes. These Ba/F3 kinase cell lines are well validated by sequencing, western blot and inhibitor test, and cover many hot kinases, including EGFR (151 cell lines), FGFR (45 cell lines), ERBB2 (38 cell lines), KRAS (36 cell lines), BCR-ABL (36 cell lines), EML4-ALK (33 cell lines), KIF5B-RET (30 cell lines), FLT3 (26 cell lines) et.al. Most of these transformed Ba/F3 cell lines can be used in allograft models in immune-deficient mice. Based on these Ba/F3 kinase cell line allograft models, we established an in vivo screening platform to evaluate the efficacy and toxicity of drug candidatestargeting specific mutant types of kinases, as well as comparisons with previous generation drugs. Overall, our data indicate that Ba/F3 kinase cell line-derived allograft models are a powerful model for the discovery of next-generation kinase inhibitors. Citation Format: Tongtong Liu, Feng He, Xuyang Duan, shuliang Li, Chang Liu, Jinying Ning, Feng Hao. In vivoscreening platform based on Ba</>F3 kinase engineered cell lines for discovery of next-generation kinase inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 28.

The DNA binding domain and the C-terminal region of DNA Ligase IV specify its role in V(D)J recombination.

DNA Ligase IV is responsible for the repair of DNA double-strand breaks (DSB), including DSBs that are generated during V(D)J recombination. Like other DNA ligases, Ligase IV contains a catalytic core with three subdomains-the DNA binding (DBD), the nucleotidyltransferase (NTD), and the oligonucleotide/oligosaccharide-fold subdomain (OBD). Ligase IV also has a unique C-terminal region that includes two BRCT domains, a nuclear localization signal sequence and a stretch of amino acid that participate in its interaction with XRCC4. Out of the three mammalian ligases, Ligase IV is the only ligase that participates in and is required for V(D)J recombination. Identification of the minimal domains within DNA Ligase IV that contribute to V(D)J recombination has remained unresolved. The interaction of the Ligase IV DNA binding domain with Artemis, and the interaction of its C-terminal region with XRCC4, suggest that both of these regions that also interact with the Ku70/80 heterodimer are important and might be sufficient for mediating participation of DNA Ligase IV in V(D)J recombination. This hypothesis was investigated by generating chimeric ligase proteins by swapping domains, and testing their ability to rescue V(D)J recombination in Ligase IV-deficient cells. We demonstrate that a fusion protein containing Ligase I NTD and OBDs flanked by DNA Ligase IV DBD and C-terminal region is sufficient to support V(D)J recombination. This chimeric protein, which we named Ligase 37, complemented formation of coding and signal joints. Coding joints generated with Ligase 37 were shorter than those observed with wild type DNA Ligase IV. The shorter length was due to increased nucleotide deletions and decreased nucleotide insertions. Additionally, overexpression of Ligase 37 in a mouse pro-B cell line supported a shift towards shorter coding joints. Our findings demonstrate that the ability of DNA Ligase IV to participate in V(D)J recombination is in large part mediated by its DBD and C-terminal region.

A novel intramolecular negative regulation of mouse Jak3 activity by tyrosine 820.

Jak3, a member of the Janus kinase family, is essential for the cytokine receptor common gamma chain (γc)-mediated signaling. During activation of Jak3, tyrosine residues are phosphorylated and potentially regulate its kinase activity. We identified a novel tyrosine phosphorylation site within mouse Jak3, Y820, which is conserved in human Jak3, Y824. IL-2-induced tyrosine phosphorylation of Jak3 Y824 in human T cell line HuT78 cells was detected by using a phosphospecific, pY824, antibody. Mutation of mouse Jak3 Y820 to alanine (Y820A) showed increased autophosphorylation of Jak3 and enhanced signal transducer and activator of transcription 5 (STAT5) tyrosine phosphorylation and transcriptional activation. Stably expressed Jak3 Y820A in F7 cells, an IL-2 responsive mouse pro-B cell line Ba/F3, exhibited enhanced IL-2-dependent cell growth. Mechanistic studies demonstrated that interaction between Jak3 and STAT5 increased in Jak3 Y820A compared to wild-type Jak3. These data suggest that Jak3 Y820 plays a role in negative regulation of Jak3-mediated STAT5 signaling cascade upon IL-2-stimulation. We speculate that this occurs through an interaction promoted by the tyrosine phosphorylated Y820 or a conformational change by Y820 mutation with either the STAT directly or with the recruitment of molecules such as phosphatases via a SH2 interaction. Additional studies will focus on these interactions as Jak3 plays a crucial role in disease and health.

In vitro validation study of HER2 and HER4 mutations identified in an ad hoc secondary analysis of the LUX-Lung 8 randomized clinical trial

ObjectivesThe LUX-Lung 8 randomized trial (LL8) demonstrated a prolonged progression-free survival (PFS) in patients with metastatic squamous cell carcinoma (SCC) of the lung after treatment with afatinib compared with erlotinib. A secondary analysis of the LL8 reported that the presence of rare HER2/HER4 mutations may be partly responsible for this result. Patients with HER2 (hazard ratio [HR] 0.06/p-value 0.02) or HER4 (HR 0.21/p-value unreported) mutations had longer PFS after treatment with afatinib. However, the biological function of these mutations is unclear. Materials and MethodsTen HER2 and 13 HER4 point mutations that were detected in the secondary analysis were transduced into the mouse pro-B cell line (Ba/F3) to determine changes in interleukin-3 (IL-3) dependence and sensitivity to six EGFR or pan-HER tyrosine kinase inhibitors (TKIs), including afatinib and erlotinib. The efficacy of the six TKIs was compared using a sensitivity index, defined as the 50% inhibitory concentration divided by trough concentration of each drug at clinically recommended doses. ResultsSeven out of 10 Ba/F3 clones expressing HER2 mutations and all 13 Ba/F3 clones expressing HER4 mutations did not grow in the absence of IL-3, indicating these mutations were non-oncogenic. Three Ba/F3 clones expressing the HER2 mutations E395K, G815R, or R929W acquired IL-3-independent growth. The sensitivity indices for afatinib were ≤ one-fifth of those for erlotinib in all three lines. Other second/third-generation (2G/3G) TKIs showed high efficacy against clones expressing these HER2 mutations. ConclusionsThe majority of HER2/4 mutations detected in lung SCC from LL8 were not oncogenic in the Ba/F3 models, suggesting that the presence of HER2/4 mutations were not responsible for the superior outcomes of afatinib in the LL8 study. However, SCC of the lung in some patients may be driven by rare HER2 mutations, and these patients may benefit from 2G/3G pan-HER-TKI treatment.

The ATP-dependent RNA helicase, DDX42 interacts with paxillin and regulates apoptosis and polarization of Ba/F3 cells

ABSTRACTPaxillin is a focal adhesion adaptor protein, heavily phosphorylated at multiple tyrosine residues, as well as at serine 273 (S273), and is known to be critical for cytoskeleton rearrangement and cell migration. We previously found that paxillin plays a regulatory role in IL-3-dependent survival of Ba/F3 cells, a mouse pro-B cell line. In this study, by using overexpressed His6 tagged-paxillin as a bait, we found that DDX42, a DEAD-box RNA helicase, interacted with paxillin, inhibited apoptosis, and promoted polarization of Ba/F3 cells. His6 tagged-paxillin was stably overexpressed in Ba/F3 cells, pulled-down from cell lysates with Ni+-NTA beads, and analyzed by one-dimensional SDS-PAGE followed by LC–MS. We found that DDX42 co-precipitated with paxillin, as demonstrated by western blotting analysis of His6 tagged-paxillin precipitates with anti-DDX42 antibodies and His6 tagged-DDX42 precipitates with anti-paxillin antibodies. In addition, we observed a preferential interaction of DDX42 with the paxillin mutant, S273A, compared to the S273D mutant. Furthermore, DDX42 overexpression in Ba/F3 cells delayed the apoptosis induced by IL-3 deprivation and promoted restoration of the elongated shape in Ba/F3 cells induced by IL-3 re-supply after a 6 h-deprivation. These results suggested that DDX42 interacts with paxillin and participates in IL-3-dependent cell survival, as well as in the cytoskeletal rearrangements underlying polarization of Ba/F3 cells.

Roles of paxillin phosphorylation in IL-3 withdrawal-induced Ba/F3 cell apoptosis.

Ba/F3, a mouse pro-B cell line, is dependent on IL-3 for its survival and proliferation. IL-3 withdrawal causes cells to round, stop in G1 phase, then undergo apoptosis. Additionally, IL-3 is known to induce tyrosine phosphorylation of paxillin, a scaffold and signaling protein. We previously determined that overexpression of paxillin prohibited Ba/F3 cell apoptosis induced by IL-3 withdrawal. Address whether phosphorylation is essential for the anti-apoptotic effect of overexpressed paxillin. Mutations were introduced into paxillin cDNA at five phosphorylation sites-Y31F, Y40F, Y118F, Y181F, S273A, or S273D. After overexpression of paxillin mutants in Ba/F3 cells, the apoptotic proportions of cell populations were measured by an annexin V conjugation assay while cells were undergoing IL-3 withdrawal. The anti-apoptotic effect of paxillin overexpression was abolished by site-directed mutagenesis replacing Y31, Y40, Y118, and Y181 with phenylalanine, and S273 with aspartic acid. In contrast, the mutation replacing S273 with alanine had no effect on the anti-apoptotic effect. The above results suggest that paxillin-mediated phosphorylation at Y31, Y40, Y118, and Y181 is essential for the anti-apoptotic effect of paxillin overexpression in Ba/F3 cells and contributes to the cell survival signaling pathway triggered by IL-3. Conversely, phosphorylation at S273 is involved in the negative regulation of the anti-apoptotic action of overexpressed paxillin.

Protein Tyrosine Phosphatase SHP-2 Is Involved in the Interleukin-21-Induced Activation of Extracellular Signal-Regulated Kinase 1/2

The cytokine interleukin-21 (IL-21) is mainly produced from activated CD4+ T cells and natural killer T (NKT) cells. IL-21 enhances the proliferation and differentiation of T cells and B cells and also increases cytotoxicity of CD8+ T cells and NK cells through the IL-21 receptor and its downstream signaling molecules such as signal transducers and activator of transcription 3 (STAT3) and extracellular signal-regulated kinase 1/2 (ERK1/2). SH2 domain-containing tyrosine phosphatase (SHP-2) is ubiquitously expressed, including hematopoietic cells. SHP-2 has been implicated in the regulation of IL-6 and IL-3 signaling, but its function in IL-21 signaling has not been investigated. Therefore, we studied the role of SHP-2 in IL-21 signaling by SHP-2 overexpression and knockdown experiments. For the SHP-2 overexpression, we used 293T human embryonic kidney cells, in which the IL-21 receptor system were easily reconstituted and high amounts of exogenous SHP-2 were expressed by vector transfection. In 293T cells, overexpressed SHP-2 caused the increase in the degree of the IL-21-induced ERK1/2 activation. Subsequently, SHP-2 knockdown experiments were performed in the mouse pro-B cell line, BAF21RWT-1, which constitutively expresses human IL-21 receptor and proliferates in an IL-21-dependent manner. SHP-2 knockdown reduced the degree of the IL-21-induced ERK1/2 activation and suppressed cell proliferation. These results suggest that SHP-2 may augment the ERK1/2 activity and cell proliferation activity in IL-21 signaling. We propose that SHP-2 is involved in the IL-21-mediated ERK1/2 activation and cell proliferation.

Abstract 2380: Insertion mutations in the tyrosine kinase domain of FLT3 display a higher oncogenic potential than the D835Y mutation in acute myeloid leukemia

Abstract Acute myeloid leukemia (AML) remains the most common form of acute leukemia among adults and accounts for a large number of deaths. Mutation in FMS-like tyrosine kinase 3 (FLT3) is one of the most prevalent factor in this heterogeneous disease. The major mutations in FLT3 can be categories as internal tandem duplications (ITD) and point mutations. Recent studies suggest that ITDs are subdivided in to two groups depending on their location: the juxtamembrane domain (ITD-JM) and the tyrosine kinase domain (ITD-TDK). Although, ITD-JM has been characterized well the ITD-TKD has not yet been studied well due to its recent discovery. For this reason, we compared ITD mutations in TKD and JM, as well as the most frequently occurring point mutation located in the TKD, D835Y. The purpose of this study was to understand whether it is the mutation’s nature or location that plays the driving role in leukemogenesis. We used a cytokine-dependent mouse pro-B cell line, BaF3, to overexpress different FLT3 mutants. We first examined the colony formation capacity in semisolid cytokine- and serum-free medium. The assay resulted in indistinguishable number and size of colonies for both ITD-JM and ITD-TKD, while D835Y-TKD transfected cells failed to form colonies suggesting that the ITD-TKD mutations have stronger transforming potential than other TKD mutations. In addition to colony formation assays, cell proliferation and survival was significantly higher in ITD-TKD expressing cells compared to cells expressing D835Y-TKD. Finally, we showed that phosphorylation of STAT5 and AKT is increased in ITD-TKD, while other FLT3 downstream signaling remained unaffected. All together, our data suggest that ITD-TKD displays higher oncogenic potential than other TKD mutants. Citation Format: Alissa Marhäll, Thomas Fischer, Florian Heidel, Julhash U. Kazi, Lars Rönnstrand. Insertion mutations in the tyrosine kinase domain of FLT3 display a higher oncogenic potential than the D835Y mutation in acute myeloid leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2380. doi:10.1158/1538-7445.AM2017-2380

Growth control of genetically modified cells using an antibody/c-Kit chimera

Gene therapy has been regarded as an innovative potential treatment against serious congenital diseases. However, applications of gene therapy remain limited, partly because its clinical success depends on therapeutic gene-transduced cells acquiring a proliferative advantage. To address this problem, we have developed the antigen-mediated genetically modified cell amplification (AMEGA) system, which uses chimeric receptors to enable the selective proliferation of gene-transduced cells. In this report, we describe mimicry of c-Kit signaling and its application to the AMEGA system. We created an antibody/c-Kit chimera in which the extracellular domain of c-Kit is replaced with an anti-fluorescein single-chain Fv antibody fragment and the extracellular D2 domain of the erythropoietin receptor. A genetically modified mouse pro-B cell line carrying this chimera showed selective expansion in the presence of fluorescein-conjugated BSA (BSA-FL) as a growth inducer. By further engineering the transmembrane domain of the chimera to reduce interchain interaction we attained stricter ligand-dependency. Since c-Kit is an important molecule in the expansion of hematopoietic stem cells (HSCs), this antibody/c-Kit chimera could be a promising tool for gene therapy targeting HSCs.

Two-Step Engulfment of Apoptotic Cells

Apoptotic cells expose phosphatidylserine on their surface as an "eat me" signal, and macrophages respond by engulfing them. Although several molecules that specifically bind phosphatidylserine have been identified, the molecular mechanism that triggers engulfment remains elusive. Here, using a mouse pro-B cell line, Ba/F3, that grows in suspension, we reconstituted the engulfment of apoptotic cells. The parental Ba/F3 cells did not engulf apoptotic cells. Ba/F3 transformants expressing T cell immunoglobulin- and mucin-domain-containing molecule 4 (Tim4), a type I membrane protein that specifically binds phosphatidylserine, efficiently bound apoptotic cells in a phosphatidylserine-dependent manner but did not engulf them. However, Ba/F3 transformants expressing both Tim4 and the integrin α(v)β(3) complex bound to and engulfed apoptotic cells in the presence of milk fat globule epidermal growth factor factor VIII (MFG-E8), a secreted protein that can bind phosphatidylserine and integrin α(v)β(3). These results indicate that the engulfment of apoptotic cells proceeds in two steps: Tim4 tethers apoptotic cells, and the integrin α(v)β(3) complex mediates engulfment in coordination with MFG-E8. A similar two-step engulfment of apoptotic cells was observed with mouse resident peritoneal macrophages. Furthermore, the Tim4/integrin-mediated engulfment by the Ba/F3 cells was enhanced in cells expressing Rac1 and Rab5, suggesting that this system well reproduces the engulfment of apoptotic cells by macrophages.

Abstract LB-189: Fbxo7 functions in the proliferation and maturation of hematopoietic cells

Abstract The F-box protein Fbxo7 specifically enhances the levels of cyclin D-Cdk6 complexes, the predominant G1 kinase active in hematopoietic cells, which is a commonly activated oncogenic pathway in lymphoid neoplasms. In addition, Fbxo7 is itself abundantly expressed in high-grade B and T cell malignancies. Previously we have tested the ability of Fbxo7 to act as an oncogene in the hematopoietic compartment in adoptive transfer experiments using p53 null hematopoietic stem cells over expressing Fbxo7. Animals reconstituted with these cells develop T cell lymphoma, supporting the idea that Fbxo7 can have tumor promoting activity in vivo. However, in experiments presented here, to investigate the transforming capacity of Fbxo7 in B lymphocytes, we found that overexpression of Fbxo7 in the mouse pro-B cell line Ba/F3 did not transform cells nor enhance their proliferation. Instead, the stable reduction of Fbxo7 expression increased proliferation and decreased cell size, which were attributable to shortening of G1 phase, decreased p27 levels and increased Cdk2 activity. These results suggest that Fbxo7 normally restrains proliferation in pro-B cells. Reducing Fbxo7 expression also changed the cell surface marker phenotype to resemble a more immature state of B cell maturation. To investigate the activities of Fbxo7 in hematopoietic cells in a more physiological setting, we have generated an in vivo model of reduced Fbxo7 expression by engineering a mouse with an insertional mutation of the LacZ gene into the FBXO7 locus. Phenotypic characterization of these mice will also be presented, and these data support the idea that Fbxo7 regulates the proliferation and the maturation of different precursor cell populations, including pro-B cells and pro-erythroblasts. We propose that Fbxo7 has the capacity to function as a tumor suppressor and also as an oncogene depending on the cell type and its stage of differentiation. 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 LB-189. doi:10.1158/1538-7445.AM2011-LB-189

MOHITO, a novel mouse cytokine-dependent T-cell line, enables studies of oncogenic signaling in the T-cell context

The mouse pro-B cell line Ba/F3 has gained major interest as a model system to investigate oncogenic tyrosine kinases and to determine the efficacy of kinase inhibitors. While Ba/F3 cells are suitable to study oncogenic kinases derived from various cell types, the signaling networks in Ba/F3 cells are B-cell specific. We have established a mouse CD4+CD8+ double positive T-cell line (named MOHITO, for MOuse Hematopoietic Interleukin-dependent cell line of T-cell Origin) that has many features of human T-cell acute lymphoblastic leukemia (Notch1 and Jak1 mutation, TCR rearrangement) and is dependent on interleukin-7. The MOHITO cell line can be transformed to cytokine independent proliferation by BCR-ABL1 or mutant JAK1. This mouse T-cell line is a novel model system to investigate protein signaling and inhibition in a T-cell specific context and is a valuable tool to study and verify oncogenic capacity of mutations in the kinome and phosphatome in T-cell malignancies.

Transferrin Receptor 1: A Ferritin Receptor as Well?

Transferrin Receptor 1: A Ferritin Receptor as Well?

Abstract LB-24: Nuclear localization of PDC-E2, a mitochondrial enzyme, and its role in STAT5-dependent gene transcription

Abstract STAT (signal transducer and activator of transcription) proteins play a critical role in cellular response to a wide variety of cytokine and growth factors by regulating specific nuclear genes. Many STAT-target genes are involved in cell proliferation, resistance to apoptosis, angiogenesis, and immune evasion. As a result, numerous cancer cells exhibit constitutive activation of STAT proteins. Among seven STAT family members, STAT3, STAT5a and STAT5b are most widely implicated in tumorigenesis. STAT-dependent gene transcription can be finely tuned through the association with co-factors in the nucleus. Therefore, detailed understanding of how different STAT family member acts in concert with distinct co-factor in the nucleus is essential in elucidating the mechanisms underlying STAT-dependent oncogenesis. We showed previously that STAT5 (including 5a and 5b), but not STAT3, specifically interacts with PDC-E2 (E2 subunit of pyruvate dehydrogenase complex), which is a nuclearly encoded mitochondrial enzyme. However, the functional significance of this novel association remains unknown. Here we report that PDC-E2 may function as a co-activator in STAT5-dependent gene transcription. Our earlier studies indicated that interleukin-3 (IL-3) induced mitochondrial translocation of STAT5 in BaF3, an IL-3-dependent mouse pro-B cell line. Further subcellular fractionation analysis revealed that a substantial amount of PDC-E2 could be detected in the nucleus in addition to mitochondrion. In contrast to IL-3-induced STAT5 nuclear translocation, the nuclear presence of PDC-E2 was constitutive and independent of IL-3 stimulation. This finding was confirmed by immunofluoresence analysis showing nuclear localization of PDC-E2 and its co-localization with STAT5 after IL-3 stimulation. Overexpression of PDC-E2 in BaF3 cells augmented IL-3-induced STAT5 activity as measured by reporter assay with consensus STAT5-binding sites. Consistent with the reporter data, PDC-E2 overexpression in BaF3 cells led to elevated mRNA levels of endogenous SOCS3 (suppressor of cytokine signaling 3) gene, a known STAT5 target. We further identified two functional STAT5-binding sites in the SOCS3 gene promoter important for its IL-3-inducibility. The observation that both cis-acting elements were essential for PDC-E2's synergistic effect strongly supports the role of PDC-E2 in up-regulating the transactivating ability of STAT5. All together, our results clearly demonstrate a unique function of PDC-E2 in the nucleus through STAT5. Functional interaction between STAT5 and PDC-E2 in the nucleus, therefore, may represent a novel molecular target in modulating STAT5 activity in tumor cells and shed new light on targeted cancer therapy. Furthermore, these findings will provide important insights into dysregulated nuclear-mitochondrial crosstalk in human cancers. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-24.

The mitochondrial serine protease HtrA2/Omi cleaves RIP1 during apoptosis of Ba/F3 cells induced by growth factor withdrawal

Interleukin-3 (IL-3) deprivation of the mouse pro-B cell line Ba/F3 induces cell death that is abrogated by B-cell lymphoma 2 (Bcl-2) overexpression, but remains unaffected by the pan-caspase inhibitor carbobenzoxy-valyl-analyl-aspartyl-[O-methyl]-fluoromethylketone (zVAD-fmk). IL-3 withdrawal causes receptor-interacting protein (RIP)1 cleavage into C-terminal fragments of 30 and 25 kDa, and only cleavage leading to the former was prevented by zVAD-fmk. siRNA experiments demonstrated that generation of the 25-kDa fragment was due to a Bcl-2-modulated release of the mitochondrial serine protease high temperature requirement protein A2 (HtrA2)/Omi. Accordingly, recombinant HtrA2/Omi efficiently cleaved mouse RIP1 in vitro, generating fragments matching those observed in IL-3-deprived Ba/F3 cells. The HtrA2/Omi cleavage site in mouse RIP1 was mapped to the intermediate domain and the corresponding N- and C-terminal fragments were impaired in their ability to activate nuclear factor-kappaB, c-Jun N-terminal kinase and p38 mitogen-activated protein kinase. Interestingly, knockdown of HtrA2/Omi afforded protection against IL-3 withdrawal-induced death in the presence of zVAD-fmk, demonstrating a role for HtrA2/Omi in caspase-independent cell death during growth factor withdrawal by cleaving RIP1.

Inhibition of G1 to S Phase Progression by a Novel Zinc Finger Protein P58TFL at P-bodies

We recently reported the translocation of the immunoglobulin (Ig) light chain kappa locus gene with a possible tumor suppressor gene, TFL, in transformed follicular lymphoma. However, the functional significance in cell transformation remains to be elucidated. Here, we first identified two gene products, P58(TFL) and P36(TFL), derived by alternative splicing. The expression was prominent in normal human lymphocytes but defective in some leukemia/lymphoma cell lines. Overexpression of either protein in a mouse pro-B cell line, Ba/F3, and a human leukemia cell line, Jurkat, inhibited G(1) to S phase progression through suppression of retinoblastoma protein (Rb) phosphorylation. The dominant gene product, P58(TFL), colocalized with mRNA-processing body markers, eukaryotic translation initiation factor 2C and DCP1 decapping-enzyme homolog A, but not with a stress granule maker, T-cell intracellular antigen 1, in the cytoplasm. Taken together with the unique CCCH-type zinc finger motif, the present study suggests that P58(TFL) could play an important role in the regulation of cell growth through posttranscriptional modification of cell cycle regulators, at least partially, upstream of Rb.

Multi-Targeted Receptor Tyrosine Kinase Inhibitor, ABT-869, Induces Apoptosis and Suppresses Proliferation of Ba/F3 FLT-3 ITD Mutant Cells in Vitro and in Vivo through Inhibition of FLT3 and AKT.

FLT3 is a receptor tyrosine kinase of the subclass III family that plays a vital role in the regulation of differentiation, proliferation and survival of normal hematopoietic cells. FLT3 mutations are often found in patients with acute myelogenous leukemia (AML) and confer a poor prognosis. Of these mutations, 15–35% are FLT3 ITD (internal tandem duplication) mutations and 5–7% are point mutations in the FLT3 kinase activation loop, e.g. D835V. We are studying the signaling pathways associated with a small molecule multi-targeted receptor tyrosine kinase inhibitor (RTKI), ABT-869. To determine the effects of ABT-869 in vitro and in vivo, a Ba/F3 mouse pro-B lymphocytic cell line harboring the FLT-3 ITD or FLT-3 D835V mutation was used as an isolated FLT-3 mutant model system. In vitro, ABT-869 is effective in inhibiting the proliferation of Ba/F3 Flt-3 ITD mutant cells (IC50 value of 1 nM) when compared to Ba/F3 Flt-3 D835V mutant (IC50 value between 1 and 10 μM) and Ba/F3 Flt-3 wildtype (WT) cells (IC50 value of 10 μM). Annexin V and propidium iodide staining of cells revealed that an increase in apoptosis occurred in Ba/F3 Flt-3 ITD mutant cells treated with 1μM ABT-869 for 24 hours (42.8%) when compared to untreated (4.7%) or vehicle control (4.0%) cells. Ba/F3 Flt-3 D835V mutant cell lines demonstrated a 12.5% rate of apoptosis at 1μM, compared to untreated (1.99%) and vehicle control (2.1%) cell lines. Propidium iodide staining of treated Ba/F3 Flt-3 WT cell lines revealed no difference in apoptosis when compared to untreated Ba/F3 Flt-3 WT cells or DMSO controls. PARP cleavage was observed in Ba/F3 FLT-3 ITD mutant cells, following 6 hours of treatment with 1 to 100 nM ABT-869, whereas no cleavage was observed in Ba/F3 WT cells treated with ABT-869. To study the effects of ABT-869 in vivo, we treated SCID mice injected with Ba/F3 Flt-3 ITD, Ba/F3 Flt-3 D835V, or Ba/F3 Flt-3 WT cells and monitored disease progression using bioluminescence imaging. The mice injected with the Ba/F3 FLT-3 ITD mutant cells and treated with vehicle control developed metastases and had a median survival time of 2 weeks. In contrast, the ABT-869 treated group had slower disease progression with median survival of 6.2 weeks (P<0.008). Both control and treated mice injected with Ba/F3 FLT-3 D835V mutant cell lines developed metastases and had similar survival (median 1.7 and 1.9 weeks, respectively). Survival times of control and treated mice injected with Ba/F3 FLT-3 WT cells were also similar (median 8.4 and 8.1 weeks, respectively). Previous work identified that ABT-869 induced apoptosis of acute myeloid leukemia cells through inhibition of FLT-3 reception phosphorylation, which is observed as early as 3 hours after treatment. In Ba/F3 cells expressing FLT-3 ITD, ABT-869 also inhibited phosphorylation of AKT, which is upstream of the pro-apoptotic protein Bad. Therefore, our preclinical data suggest that ABT-869 induces apoptosis of FLT-3 ITD mutant cells both in vitro and in vivo. These studies provide rationale for the treatment of acute leukemia patients harboring the FLT3-ITD mutation with ABT-869 and the potential benefit of combining small molecule inhibitors that target both RTKs and AKT.

Characterization of the Effects of Pim Kinase Inhibition on Multiple Oncogene-Driven Cell Lines

We report here the biological effects of inhibiting Pim-1, -2 and -3 serine/threonine protein kinases in cells and in vivo using a novel, potent and selective small molecule inhibitor directed against these kinases. In vitro enzyme assays revealed potent inhibition of all three Pim kinase isoforms while maintaining selectivity against more than 220 other protein kinases. In cells, compound treatment produced biological effects consistent with Pim inhibition, including a reduction in BAD protein phosphorylation. Moreover, this biological activity corresponds well with the compound's anti-proliferative and pro-apoptotic activity in the IL-3 dependent mouse pro-B cell line Ba/F3 and in factor-indpendent Ba/F3 cell lines dependent upon the expression of BCR-Abl or TEL-JAK2 for growth and survival. Importantly, compared to the BCR-Abl driven Ba/F3 cell line, this compound was equally effective at blocking the growth of an Imatinib-resistant BCR-Abl[ T315I]-driven Ba/F3 cell line. Finally, this compound possesses pharmacokinetic properties that predict the potential for in vivo activity. Therefore, we assessed the effect of Pim kinase inhibition on tumor growth in a mouse subcutaneous tumor xenograft model employing a cell line driven by the TEL-JAK2 oncogene. Results demonstrated that the compound significantly inhibited tumor growth in a dose-dependent manner. In terms of potential clinical utility, these data show that Pim kinase inhibition could be an effective therapeutic strategy for numerous hematologic malignancies including chronic and acute myelogenous leukemias, particularly in those patients that have become resistant to existing therapies such as Imatinib.