Characterization of a unique factor-independent variant derived from human factor-dependent TF-1 cells: a transformed event

Involvement of pRb-E2F pathway in green tea extract-induced growth inhibition of human myeloid leukemia cells

Both inhibitory and stimulatory effect of EGCG on cancer cells have been reported, which often is linked to receptor tyrosine kinase signaling. In this study, we present evidence that green tea extract and its chemical component, Epigallocatechin-3-gallate (EGCG), inhibit growth of human myeloid leukemia cells through the regulation of pRb synthesis and formation of pRb-E2F complexes. Addition of green tea extract to the culture of TF-1a and MV4-11 myeloid leukemia cells significantly inhibited their proliferation with a substantial portion of cell death being observed. The green tea extract and EGCG had no significant effect on the expression of G1 CDKs and the CDK inhibitors but downregulated the formation of pRb-CDKs. Surprisingly, the expression of pRb was markedly upregulated while the phosphorylation of pRb downregulated. The upregulation of pRb was blocked by pre-treatment with cycloheximide, a protein synthesis inhibitor, suggesting a requirement of protein synthesis. In agreement with these results, pRb-E2F complexes were upregulated and E2F DNA binding activity decreased. Since both TF-1a and MV4-11 are factor-independent cell lines, the upregulation of pRb-E2F complexes and inhibition of DNA binding activity by green tea extract is most likely through a receptor tyrosine kinase-independent pathway. We also found that the stem/progenitor cells derived from these two leukemia cell lines are more sensitive to the inhibitory effect of green tea extract. Our result suggests that concentrated green tea extract and EGCG may have potential for clinical investigation as an inducer of cancer cell death.

PTEN is indispensable for cells to respond to MAPK inhibitors in myeloid leukemia

Constitutively activated MAPK and AKT signaling pathways are often found in solid tumors and leukemias. PTEN is one of the tumor suppressors that are frequently found deficient in patients with late-stage cancers or leukemias. In this study we demonstrate that a MAPK inhibitor, PD98059, inhibits both AKT and ERK phosphorylation in a human myeloid leukemia cell line (TF-1), but not in PTEN-deficient leukemia cells (TF-1a). Ectopic expression of wild-type PTEN in myeloid leukemia cells restored cytokine responsiveness at physiological concentrations of GM-CSF (<0.02 ng/mL) and significantly improved cell sensitivity to MAPK inhibitor. We also found that Early Growth Response 1 (EGR1) was constitutively over-expressed in cytokine-independent TF-1a cells, and ectopic expression of PTEN down-regulated EGR1 expression and restored dynamics of EGR1 expression in response to GM-CSF stimulation. Data from primary bone marrow cells from mice with Pten deletion further supports that PTEN is indispensible for myeloid leukemia cells in response to MAPK inhibitors. Finally, We demonstrate that the absence of EGR1 expression dynamics in response to GM-CSF stimulation is one of the mechanisms underlying drug resistance to MAPK inhibitors in leukemia cells with PTEN deficiency. Our data suggest a novel mechanism of PTEN in regulating expression of EGR1 in hematopoietic cells in response to cytokine stimulation. In conclusion, this study demonstrates that PTEN is dispensable for myeloid leukemia cells in response to MAPK inhibitors, and PTEN regulates EGR1 expression and contributes to the cytokine sensitivity in leukemia cells.

CRISPR/Cas9 knockouts reveal genetic interaction between strain-transcendent erythrocyte determinants of Plasmodium falciparum invasion

During malaria blood-stage infections, Plasmodium parasites interact with the RBC surface to enable invasion followed by intracellular proliferation. Critical factors involved in invasion have been identified using biochemical and genetic approaches including specific knockdowns of genes of interest from primary CD34⁺ hematopoietic stem cells (cRBCs). Here we report the development of a robust in vitro culture system to produce RBCs that allow the generation of gene knockouts via CRISPR/Cas9 using the immortal JK-1 erythroleukemia line. JK-1 cells spontaneously differentiate, generating cells at different stages of erythropoiesis, including terminally differentiated nucleated RBCs that we term "jkRBCs." A screen of small-molecule epigenetic regulators identified several bromodomain-specific inhibitors that promote differentiation and enable production of synchronous populations of jkRBCs. Global surface proteomic profiling revealed that jkRBCs express all known Pfalciparum host receptors in a similar fashion to cRBCs and that multiple Pfalciparum strains invade jkRBCs at comparable levels to cRBCs and RBCs. Using CRISPR/Cas9, we deleted two host factors, basigin (BSG) and CD44, for which no natural nulls exist. BSG interacts with the parasite ligand Rh5, a prominent vaccine candidate. A BSG knockout was completely refractory to parasite invasion in a strain-transcendent manner, confirming the essential role for BSG during invasion. CD44 was recently identified in an RNAi screen of blood group genes as a host factor for invasion, and we show that CD44 knockout results in strain-transcendent reduction in invasion. Furthermore, we demonstrate a functional interaction between these two determinants in mediating Pfalciparum erythrocyte invasion.

Inhibition of LIN28B impairs leukemia cell growth and metabolism in acute myeloid leukemia

BACKGROUND

Current conventional chemotherapy for acute myeloid leukemia (AML) can achieve remission in over 70% of patients, but a majority of them will relapse within 5 years despite continued treatment. The relapse is postulated to be due to leukemia stem cells (LSCs), which are different from normal hematopoietic stem cells (HSCs). LIN28B is microRNA regulator and stem cell reprogramming factor. Overexpression of LIN28B has been associated with advance human malignancies and cancer stem cells (CSCs), including AML. However, the molecular mechanism by which LIN28B contributes to the development of AML remains largely elusive.

METHODS

We modulated LIN28B expression in AML and non-leukemic cells and investigated functional consequences in cell proliferation, cell cycle, and colony-forming assays. We performed a microarray-based analysis for LIN28B-silencing cells and interrogated gene expression data with different bioinformatic tools. AML mouse xenograft model was used to examine the in vivo function of LIN28B.

RESULTS

We demonstrated that targeting LIN28B in AML cells resulted in cell cycle arrest, inhibition of cell proliferation and colony formation, which was induced by de-repression of let-7a miRNA. On the other hand, overexpression of LIN28B promoted cell proliferation. Data point to a mechanism where that inhibition of LIN28B induces metabolic changes in AML cells. IGF2BP1 was confirmed to be a novel downstream target of LIN28B via let-7 miRNA in AML. Notably, ectopic expression of LIN28B increased tumorigenicity, while silencing LIN28B led to slow tumor growth in vivo.

CONCLUSIONS

In sum, these results uncover a novel mechanism of an important regulatory signaling, LIN28B/let-7/IGF2BP1, in leukemogenesis and provide a rationale to target this pathway as effective therapeutic strategy.

LIN28B Activation by PRL-3 Promotes Leukemogenesis and a Stem Cell-like Transcriptional Program in AML

PRL-3 (PTP4A3), a metastasis-associated phosphatase, is also upregulated in patients with acute myeloid leukemia (AML) and is associated with poor prognosis, but the underlying molecular mechanism is unknown. Here, constitutive expression of PRL-3 in human AML cells sustains leukemogenesis in vitro and in vivo Furthermore, PRL-3 phosphatase activity dependently upregulates LIN28B, a stem cell reprogramming factor, which in turn represses the let-7 mRNA family, inducing a stem cell-like transcriptional program. Notably, elevated levels of LIN28B protein independently associate with worse survival in AML patients. Thus, these results establish a novel signaling axis involving PRL-3/LIN28B/let-7, which confers stem cell-like properties to leukemia cells that is important for leukemogenesis.Implications: The current study offers a rationale for targeting PRL-3 as a therapeutic approach for a subset of AML patients with poor prognosis. Mol Cancer Res; 15(3); 294-303. ©2016 AACR.

ChAcNLS, a Novel Modification to Antibody-Conjugates Permitting Target Cell-Specific Endosomal Escape, Localization to the Nucleus, and Enhanced Total Intracellular Accumulation

The design of antibody-conjugates (ACs) for delivering molecules for targeted applications in humans has sufficiently progressed to demonstrate clinical efficacy in certain malignancies and reduced systemic toxicity that occurs with standard nontargeted therapies. One area that can advance clinical success for ACs will be to increase their intracellular accumulation. However, entrapment and degradation in the endosomal-lysosomal pathway, on which ACs are reliant for the depositing of their molecular payload inside target cells, leads to reduced intracellular accumulation. Innovative approaches that can manipulate this pathway may provide a strategy for increasing accumulation. We hypothesized that escape from entrapment inside the endosomal-lysosomal pathway and redirected trafficking to the nucleus could be an effective approach to increase intracellular AC accumulation in target cells. Cholic acid (ChAc) was coupled to the peptide CGYGPKKKRKVGG containing the nuclear localization sequence (NLS) from SV-40 large T-antigen, which is termed ChAcNLS. ChAcNLS was conjugated to the mAb 7G3 (7G3-ChAcNLS), which has nanomolar affinity for the cell-surface leukemic antigen interleukin-3 receptor-α (IL-3Rα). Our aim was to determine whether 7G3-ChAcNLS increased intracellular accumulation while retaining nanomolar affinity and IL-3Rα-positive cell selectivity. Competition ELISA and cell treatment assays were performed. Cell fractionation, confocal microscopy, flow cytometry, and Western blot techniques were used to determine the level of antibody accumulation inside cells and in corresponding nuclei. In addition, the radioisotope copper-64 ((64)Cu) was also utilized as a surrogate molecular cargo to evaluate nuclear and intracellular accumulation by radioactivity counting. 7G3-ChAcNLS effectively escaped endosome entrapment and degradation resulting in a unique intracellular distribution pattern. mAb modification with ChAcNLS maintained 7G3 nM affinity and produced high selectivity for IL-3Rα-positive cells. In contrast, 7G3 ACs with the ability to either escape endosome entrapment or traffic to the nucleus was not superior to 7G3-ChAcNLS for increasing intracellular accumulation. Transportation of (64)Cu when complexed to 7G3-ChAcNLS also resulted in increased nuclear and intracellular radioactivity accumulation. Thus, ChAcNLS is a novel mAb functionalizing technology that demonstrates its ability to increase AC intracellular accumulation in target cells through escaping endosome entrapment coupled to nuclear trafficking.

Functional Characterization of D9, a Novel Deazaneplanocin A (DZNep) Analog, in Targeting Acute Myeloid Leukemia (AML)

Aberrant epigenetic events contribute to tumorigenesis of all human cancers. Significant efforts are underway in developing new generation of epigenetic cancer therapeutics. Although clinical trials for agents targeting DNA hypermethylation and histone deacetylation have yielded promising results, developing agents that target histone methylation remains to be in the early stage. We and others have previously reported that 3-Deazaneplanocin A (DZNep) is a histone methylation inhibitor that has a wide range of anticancer effects in various human cancers. Here, focusing on acute myeloid leukemia (AML) as a model, we reported a less toxic analog of DZNep, named D9, which is shown to be efficacious in AML cell lines and patient-derived samples in vitro, as well as AML tumorigenesis in vivo. Gene expression analysis in a panel of AML cell lines treated with D9 identified a set of genes that is associated with D9 sensitivity and implicated in multiple oncogenic signaling pathways. Moreover, we show that D9 is able to deplete the leukemia stem cells (LSC) and abolish chemotherapy-induced LSC enrichment, leading to dramatic elimination of AML cell survival. Thus, D9 appears to be a robust epigenetic compound that may constitute a potential for AML therapy.

Eliminating malignant contamination from therapeutic human spermatogonial stem cells

Spermatogonial stem cell (SSC) transplantation has been shown to restore fertility in several species and may have application for treating some cases of male infertility (e.g., secondary to gonadotoxic therapy for cancer). To ensure safety of this fertility preservation strategy, methods are needed to isolate and enrich SSCs from human testis cell suspensions and also remove malignant contamination. We used flow cytometry to characterize cell surface antigen expression on human testicular cells and leukemic cells (MOLT-4 and TF-1a). We demonstrated via FACS that EpCAM is expressed by human spermatogonia but not MOLT-4 cells. In contrast, HLA-ABC and CD49e marked >95% of MOLT-4 cells but were not expressed on human spermatogonia. A multiparameter sort of MOLT-4-contaminated human testicular cell suspensions was performed to isolate EpCAM+/HLA-ABC-/CD49e- (putative spermatogonia) and EpCAM-/HLA-ABC+/CD49e+ (putative MOLT-4) cell fractions. The EpCAM+/HLA-ABC-/CD49e- fraction was enriched for spermatogonial colonizing activity and did not form tumors following human-to-nude mouse xenotransplantation. The EpCAM-/HLA-ABC+/CD49e+ fraction produced tumors following xenotransplantation. This approach could be generalized with slight modification to also remove contaminating TF-1a leukemia cells. Thus, FACS provides a method to isolate and enrich human spermatogonia and remove malignant contamination by exploiting differences in cell surface antigen expression.

TGFbeta inhibits GM-CSF-induced phosphorylation of ERK and MEK in human myeloid leukaemia cell lines via inhibition of phosphatidylinositol 3-kinase (PI3-k)

OBJECTIVES

Activation of SMAD-independent p44/42 MAPK (ERK1/2) signalling by TGFbeta has been recently reported in various cell types. However, the mechanisms for the linkage between the SMAD-dependent and -independent pathways are poorly understood. In this study, we investigated whether TGF-beta activates the ERK pathway and how TGFbeta communicates with the MAP kinase signals induced by a mitogen, in human myeloid leukaemia cells.

MATERIALS AND METHODS AND RESULTS

TGFbeta dramatically suppressed proliferation of MV4-11 and TF-1 cells without detectable phosphorylation of ERK1/2 and MEK1/2 for the duration of 48 h, as detected by MTT assay and Western blot analysis, respectively. In contrast, GM-CSF induced rapid and transient phosphorylation of MEK1/2 and ERK1/2 and up-regulated cell proliferation. Both GM-CSF-induced ERK1/2 activation and cell proliferation were significantly inhibited by TGFbeta. GM-CSF also induced transient phosphorylation of the p85 subunit of PI3-kinase. Corresponding to this change, phosphorylated p85 was found to bind to the GM-CSF receptor-alpha subunit, as detected by immunoprecipitation and Western blot analysis. PD98059, a selective inhibitor of MEK, blocked GM-CSF-induced phosphorylation of MEK and ERK but not p85. However, TGFbeta and LY294002, a potent inhibitor of PI3-kinase, significantly inhibited phosphorylation of both p85 and ERK1/2.

CONCLUSIONS

These studies thus indicate that TGFbeta does not activate the ERK pathway but turns off the GM-CSF-induced ERK signal via inhibition of the PI3-kinase-Akt pathway, in these human leukaemia cells.

Quiescent subpopulations of human CD34-positive hematopoietic stem cells are preferred targets for stable recombinant adeno-associated virus type 2 transduction

We have previously demonstrated recombinant adeno-associated viral (rAAV) transduction of human CD34(+) hematopoietic stem cells (HSCs) capable of serial engraftment in vivo. Here we evaluated the capacity of rAAV2 to mediate gene transfer into nondividing, quiescent, primitive CD34(+) cells subdivided on the basis of metabolic, mitotic, and phenotypic properties. Results revealed that CD34(+)CD38() marrow cells are the most quiescent, exist primarily in G(0) at isolation and are the only population to remain nondividing during the entire exposure to free rAAV. Despite significant differences in the extended clonogenic capacities of CD34(+) subsets in stromal cultures, the frequency of rAAV marking of colonies derived from primitive progenitors was similar in all three populations, suggesting that both primitive and more differentiated progenitors were initially transduced at equal levels. After transduction, episomal and integrated rAAV genomes were detected in all CD34(+) subsets. However, the more quiescent cells displayed higher levels of integrated rAAV than did rapidly dividing cells. Importantly, stable long-term integration was observed only in the most primitive, quiescent CD34(+)CD38(-) subset, indicating that this HSC compartment comprises the preferred substrate for stable rAAV2 transduction. Previously described rate limitations to transgene expression were observed in transduced CD34(+) cells and could be overcome by tyrphostin pretreatment, which resulted in augmented second-strand synthesis. These results represent the first demonstration of rAAV-mediated gene transfer to primitive, quiescent human CD34(+)CD38(-) stem cells and reveal that nondividing CD34(+)CD38(-) HSCs are the optimal CD34(+) targets for rAAV transduction.

PMA-induced differentiation of a bone marrow progenitor cell line activates HIV-1 LTR-driven transcription

Cells of the monocyte-macrophage lineage play an important role in human immunodeficiency virus type 1 (HIV-1)-associated disease. Infected myeloid precursor cells of the bone marrow are thought to be a viral reservoir that may repopulate the peripheral blood, central nervous system (CNS), and other organ systems throughout the course of disease. To model select aspects of HIV-1 infection of the bone marrow compartment in vitro, the erythro-myeloid precursor cell line, TF-1, was used. Phorbol 12-myristate 13-acetate (PMA) was found to induce the TF-1 cell line to differentiate through the myeloid lineage and become activated, as demonstrated by cellular morphologic changes and surface expression of differentiation and activation markers. Herein we demonstrate that HIV-1 long terminal repeats (LTRs) from T-, M-, and dual-tropic molecular clones have similar basal LTR activity in TF-1 cells and that differentiation of these cells by PMA resulted in increased LTR activity. Examination of specific cis-acting elements involved in basal and PMA-induced LTR activity demonstrated that the transcription factor families nuclear factor-kappa B (NF-kappaB) and specificity protein (Sp) contributed to the LTR activity of TF-1 cells, the Sp family being the most critical. These studies elucidate the impact of infected bone marrow monocytic cell differentiation on LTR activity and its potential impact on HIV-1-associated disease.

Cancer-selective induction of cytotoxicity by tissue-specific expression of targetedtrans-splicing ribozyme

For suicide gene therapy to be successfully applied for clinical settings, cancer-restricted expression of such suicide gene should be required. We previously showed that group I intron from Tetrahymena can induce new RNA that exerts anti-cancer activity through RNA replacement by trans-splicing reaction with high fidelity and specificity onto targeted human telomerase reverse transcriptase (hTERT) RNA in cancer cells, and hence the ribozyme can selectively retard growth of the cells in vivo as well as in vitro. However, the shortage of complete tumor-selectivity due to telomerase expression of highly proliferating normal cells can limit therapeutic applicability of the hTERT-targeting approach. In this study, to explore the possibility of improving specificity of cancer therapy, we have attempted to stimulate anticancer gene activity specifically in liver cancer cells by tissue-specific expression of the hTERT-targeting trans-splicing ribozyme using liver-specific promoters. Transient transfection experiments demonstrated that the expression of transgene such as luciferase gene was specifically and highly triggered from hTERT-expressing liver cancer cells transfected with the ribozyme. Moreover, liver-specific expression of the ribozyme with diphtheria toxin A or herpes simplex virus thymidine kinase gene as 3' exon could specifically and highly retard the growth of the hTERT-expressing liver cancer cells. In conclusion, we can greatly improve specificity of cancer cytotoxicity by combination of transcriptional targeting for tissue-specific transgene expression with RNA replacement for cancer-specific anticancer gene induction.

Specific Regression of Human Cancer Cells by Ribozyme-Mediated Targeted Replacement of Tumor-Specific Transcript

In this study, we describe a novel approach to human cancer therapy that is based upon trans-splicing ribozyme-mediated replacement of cancer-specific RNAs with new transcripts that exert therapeutic activities. We have developed a specific ribozyme that can reprogram human telomerase reverse transcriptase (hTERT) RNA to induce transgene activity selectively in cancer cells that express the RNA. The ribozyme-mediated triggering of the transgene expression was accomplished via a high-fidelity trans-splicing reaction with the targeted residue in the hTERT-expressing cells. The ribozyme also induced cytotoxic activity in various hTERT-expressing cancer cells, hence selectively retarding the growth of those cells. Efficient and specific cell regression was also detected with ganciclovir (GCV) treatment only in hTERT-positive cancer cells, which were established to express stably the specific ribozyme that contains the herpes simplex virus thymidine kinase (HSV-tk) gene. Tissue-specific expression of the ribozyme could further augment the target specificity of the ribozyme. Importantly, we observed efficient regression of tumors with GCV treatment in mice that had been inoculated subcutaneously with hTERT-positive cancer cells that stably expressed the specific ribozyme that contains HSV-tk. These results suggest that the hTERT RNA-targeting trans-splicing ribozyme could be a powerful agent for tumor-targeted specific gene therapy.

TNF-α-Induced Growth Suppression of CD34+ Myeloid Leukemic Cell Lines Signals Through TNF Receptor Type I and Is Associated with NF-κB Activation

Conflicting results have been reported regarding the effect of TNF-α on the growth of human primitive hemopoietic cells. In this study, we have examined the effect of TNF-α on the proliferation of several CD34+/CD38+ (KG-1, TF-1) and CD34+/CD38− (KG-1a, TF-1a) myeloid leukemic progenitor cell lines. Our data show that TNF-α markedly inhibits the growth of these cells in both liquid and soft agar cultures. Addition of GM-CSF or IL-3 does not prevent TNF-α-induced growth inhibition. Flow cytometry analyses of propidium iodide-stained cells demonstrated cell death of all four cell lines, as judged by the presence of cells with hypodiploid DNA content after exposure of cells to TNF-α for 4 days. Annexin V assays detected apoptosis in TF-1, but not in TF-1a, KG-1, and KG-1a cells in terms of translocation of phosphatidylserine shortly after TNF-α treatment. Neutralizing anti-TNF receptor type I (TNFR-I; p55) Ab almost completely reversed TNF-α-induced growth inhibition in both liquid and soft agar cultures, whereas anti-TNFR-II (p75) Ab had only a marginal effect. TNF-α rapidly induced marked activation of nuclear transcription factor NF-κB in all 4 cell lines. The majority of this effect was abolished by the type I receptor Ab, whereas the type II receptor neutralizing Ab had no effect. Our data also show that TNF-α is incapable of inducing activation of the mitogen-activated protein kinase pathway in these leukemic cell lines.

Transforming growth factor beta inhibits growth of more differentiated myeloid leukemia cells and retinoblastoma protein phosphorylation at serine 795

Transforming growth factor beta (TGF-beta) has been shown to be a specific inhibitor of early human myeloid progenitors. We show here that TGF-beta1 potentially inhibited not only the growth of primitive but also more mature myeloid leukemic cells. Surprisingly, those apparently more mature progenitor cells, such as MV4-11 and Mo7e cells, are very sensitive to the action of TGF-beta. The addition of TGF-beta1 to liquid cultures of these cells significantly inhibited their proliferation, with as much as 72% inhibition of growth of MV4-11 cells. The suppressive effect by TGF-beta1 was not reversed or prevented by granulocyte-macrophage colony-stimulating factor or interleukin 3 used to promote cell growth in TF-1a and MV4-11 cells. TGF-beta1 completely abolished the clonal growth of MV4-11 cells in soft agar and inhibited Mo7e, KG-1, K562, TF-1, and TF-1a colony growth by 99%, 90%, 63%, 53%, and 43%, respectively. The cells treated with TGF-beta1 showed progressive accumulation in the G1 phase of cell cycle. Maximal G1 arrest (93%) was observed in MV4-11 cells. Using anti-retinoblastoma protein (pRb) and anti-specific phosphorylated-pRb antibodies, we demonstrated that TGF-beta1 greatly inhibited pRb phosphorylation at serine 795 in MV4-11 and Mo7e cells. Taken together, our data suggest that the sensitivity of myeloid leukemic progenitor cells to growth inhibition by TGF-beta may not be inversely correlated with their maturation stage, and the inhibition of the cells appeared to be linked to the suppression of pRb phosphorylation at serine 795.