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Tumor angiogenesis is essential for malignant growth and metastasis. Bone marrow (BM)-derived endothelial progenitor cells (EPC) contribute to angiogenesis-mediated tumor growth. EPC ablation can reduce tumor growth; however,the lack of a marker that can track EPCs from the BM to tumor neovasculature has impeded progress in understanding the molecular mechanisms underlying EPC biology. Here,we report the use of transgenic mouse and lentiviral models to monitor the BM-derived compartment of the tumor stroma; this approach exploits the selectivity of the transcription factor inhibitor of DNA binding 1 (Id1) for EPCs to track EPCs in the BM,blood,and tumor stroma,as well as mature EPCs. Acute ablation of BM-derived EPCs using Id1-directed delivery of a suicide gene reduced circulating EPCs and yielded significant defects in angiogenesis-mediated tumor growth. Additionally,use of the Id1 proximal promoter to express microRNA-30-based short hairpin RNA inhibited the expression of critical EPC-intrinsic factors,confirming that signaling through vascular endothelial growth factor receptor 2 is required for EPC-mediated tumor biology. By exploiting the selectivity of Id1 gene expression in EPCs,our results establish a strategy to track and target EPCs in vivo,clarifying the significant role that EPCs play in BM-mediated tumor angiogenesis. View Publication

Maintenance of genomic integrity is an essential cellular function. We previously reported that the transcription factor and tumor suppressor CCAAT/enhancer binding protein δ (C/EBPδ,CEBPD; also known as NFIL-6β") promotes genomic stability. However� View Publication

Casitas B-cell lymphoma (Cbl)-family E3 ubiquitin ligases are negative regulators of tyrosine kinase signaling. Recent work has revealed a critical role of Cbl in the maintenance of hematopoietic stem cell (HSC) homeostasis,and mutations in CBL have been identified in myeloid malignancies. Here we show that,in contrast to Cbl or Cbl-b single-deficient mice,concurrent loss of Cbl and Cbl-b in the HSC compartment leads to an early-onset lethal myeloproliferative disease in mice. Cbl,Cbl-b double-deficient bone marrow cells are hypersensitive to cytokines,and show altered biochemical response to thrombopoietin. Thus,Cbl and Cbl-b play redundant but essential roles in HSC regulation,whose breakdown leads to hematological abnormalities that phenocopy crucial aspects of mutant Cbl-driven human myeloid malignancies. View Publication

Chronic myeloid leukemia (CML) is genetically characterized by the Philadelphia (Ph) chromosome,formed through a reciprocal translocation between chromosomes 9 and 22 and giving rise to the constitutively active tyrosine kinase P210 BCR/ABL1. Therapeutic strategies aiming for a cure of CML will require full eradication of Ph chromosome-positive (Ph(+)) CML stem cells. Here we used gene-expression profiling to identify IL-1 receptor accessory protein (IL1RAP) as up-regulated in CML CD34(+) cells and also in cord blood CD34(+) cells as a consequence of retroviral BCR/ABL1 expression. To test whether IL1RAP expression distinguishes normal (Ph(-)) and leukemic (Ph(+)) cells within the CML CD34(+)CD38(-) cell compartment,we established a unique protocol for conducting FISH on small numbers of sorted cells. By using this method,we sorted cells directly into drops on slides to investigate their Ph-chromosome status. Interestingly,we found that the CML CD34(+)CD38(-)IL1RAP(+) cells were Ph(+),whereas CML CD34(+)CD38(-)IL1RAP(-) cells were almost exclusively Ph(-). By performing long-term culture-initiating cell assays on the two cell populations,we found that Ph(+) and Ph(-) candidate CML stem cells could be prospectively separated. In addition,by generating an anti-IL1RAP antibody,we provide proof of concept that IL1RAP can be used as a target on CML CD34(+)CD38(-) cells to induce antibody-dependent cell-mediated cytotoxicity. This study thus identifies IL1RAP as a unique cell surface biomarker distinguishing Ph(+) from Ph(-) candidate CML stem cells and opens up a previously unexplored avenue for therapy of CML. View Publication

Tumor-initiating cells (TICs) are defined by their ability to form tumors after xenotransplantation in immunodeficient mice and appear to be relatively rare in most human cancers. Recent data in melanoma indicate that the frequency of TICs increases dramatically via more permissive xenotransplantation conditions,raising the possibility that the true frequency of TICs has been greatly underestimated in most human tumors. We compared the growth of human pancreatic,non-small cell lung,and head and neck carcinomas in NOD/SCID and NSG mice. Although TIC frequency was detected up to 10-fold higher in NSG mice,it remained low (textless1 in 2500 cells) in all cases. Moreover,aldehyde dehydrogenase-positive (ALDH(+)) and CD44(+)CD24(+) cells,phenotypically distinct cells enriched in TICs,were equally tumorigenic in NOD/SCID and NSG mice. Our findings demonstrate that TICs are rare in these cancers and that the identification of TICs and their frequency in other human malignancies should be validated via primary tumors and highly permissive xenotransplantation conditions. View Publication

Despite increasing knowledge regarding melanoma-initiating cells (MICs),questions persist regarding the number and phenotypic nature of cells with tumor-generating capability. Evidence for a phenotypically distinct human MIC has been found in NOD/SCID (non-obese diabetic/severe combined immunodeficiency) mice. However,a phenotypically distinct human MIC was not found in the NOD/SCIDIl2rg(-)/(-) (NSG) mouse model. The demonstration of a distinct population of human melanoma cells responsible for tumorigenesis and tumor cell self-renewal would provide an important target for new melanoma therapies. In this study,we show a 100-fold range in MIC frequency in human melanoma (1 in 18,000 to 1 in 1,851,000 cells) in the NOD/SCID mouse. In this model,human melanoma cells with high aldehyde dehydrogenase (ALDH) activity were enriched 16.8-fold in tumorigenic cells over unfractionated (UNF) cells,such that 1 in 21,000 cells was a MIC. In the NSG mouse,the ALDH expressing cell population was enriched 100-fold in tumorigenic cells over UNF cells,such that one in four cells was a MIC. Xenograft melanomas that developed from ALDH(+) cells displayed robust self-renewal,whereas those from ALDH(-) cells showed minimal self-renewal in vitro. Thus,ALDH(+) melanoma cells have enhanced tumorigenicity over ALDH(-) cells and superior self-renewal ability. View Publication

The chicken anemia virus-derived protein apoptin induces apoptosis in a variety of human malignant and transformed cells but not in normal cells. However,the mechanisms through which apoptin achieves its selective killing effects are not well understood. We developed a lentiviral vector encoding a green fluorescent protein-apoptin fusion gene (LV-GFP-AP) that can efficiently deliver apoptin into hematopoietic cells. Apoptin selectively killed the human multiple myeloma cell lines MM1.R and MM1.S,and the leukemia cell lines K562,HL60,U937,KG1,and NB4. In contrast,normal CD34(+) cells were not killed and maintained their differentiation potential in multilineage colony formation assays. In addition,dexamethasone-resistant MM1.R cells were found to be more susceptible to apoptin-induced cell death than the parental matched MM1.S cells. Death susceptibility correlated with increased phosphorylation and activation of the apoptin protein in MM1.R cells. Expression array profiling identified differential kinase profiles between MM1.R and MM1.S cells. Among these kinases,protein kinase Cβ (PKCβ) was found by immunoprecipitation and in vitro kinase studies to be a candidate kinase responsible for apoptin phosphorylation. Indeed,shRNA knockdown or drug-mediated inhibition of PKCβ significantly reduced apoptin phosphorylation. Furthermore,apoptin-mediated cell death proceeded through the upregulation of PKCβ,activation of caspase-9/3,cleavage of the PKCδ catalytic domain,and downregulation of the MERTK and AKT kinases. Collectively,these results elucidate a novel pathway for apoptin activation involving PKCβ and PKCδ. Further,they highlight the potential of apoptin and its cellular regulators to purge bone marrow used in autologous transplantation for multiple myeloma. View Publication

Here we report the discovery of ON044580,an α-benzoyl styryl benzyl sulfide that possesses potent inhibitory activity against two unrelated kinases,JAK2 and BCR-ABL,and exhibits cytotoxicity to human tumor cells derived from chronic myelogenous leukemia (CML) and myelodysplasia (MDS) patients or cells harboring a mutant JAK2 kinase. This novel spectrum of activity is explained by the non-ATP-competitive inhibition of JAK2 and BCR-ABL kinases. ON044580 inhibits mutant JAK2 kinase and the proliferation of JAK2(V617F)-positive leukemic cells and blocks the IL-3-mediated phosphorylation of JAK2 and STAT5. Interestingly,this compound also directly inhibits the kinase activity of both wild-type and imatinib-resistant (T315I) forms of the BCR-ABL kinase. Finally,ON044580 effectively induces apoptosis of imatinib-resistant CML patient cells. The apparently unrelated JAK2 and BCR-ABL kinases share a common substrate,STAT5,and such substrate competitive inhibitors represent an alternative therapeutic strategy for development of new inhibitors. The novel mechanism of kinase inhibition exhibited by ON044580 renders it effective against mutant forms of kinases such as the BCR-ABL(T315I) and JAK2(V617F). Importantly,ON044580 selectively reduces the number of aneuploid cells in primary bone marrow samples from monosomy 7 MDS patients,suggesting another regulatory cascade amenable to this agent in these aberrant cells. Data presented suggest that this compound could have multiple therapeutic applications including monosomy 7 MDS,imatinib-resistant CML,and myeloproliferative neoplasms that develop resistance to ATP-competitive agents. View Publication

Small populations within an increasing array of solid tumors,labeled cancer stem cells (CSC) or tumor-initiating cells (TIC),have the ability to differentiate,self-renew,and replicate the original tumor in vivo. To date,these cells have been distinguished from the bulk-tumor population by the expression pattern of cell-surface proteins (e.g.,CD24,CD44,CD133) and cellular activities,such as the efflux of Hoechst dye or aldehyde dehydrogenase activity. Recent data have shown that these markers are inducible by exposure to anticancer agents; this finding highlights not only the potential fluidity of the CSC compartment,but also the functionality of these markers. The involvement of CD44 in invasion,adhesion,and metastasis,or the role of CD24 in modulation of src,FAK,and GLI1 are examples of these relevant roles. Instead of looking solely at the marker expression in these populations,we hope to clarify the biologically significant roles these markers and activities play in tumor progression,metastases,and as possible targets for therapy. View Publication

Human solid tumors frequently have pronounced heterogeneity of both neoplastic and normal cells on the histological,genetic,and gene expression levels. While current efforts are focused on understanding heterotypic interactions between tumor cells and surrounding normal cells,much less is known about the interactions between and among heterogeneous tumor cells within a neoplasm. In glioblastoma multiforme (GBM),epidermal growth factor receptor gene (EGFR) amplification and mutation (EGFRvIII/DeltaEGFR) are signature pathogenetic events that are invariably expressed in a heterogeneous manner. Strikingly,despite its greater biological activity than wild-type EGFR (wtEGFR),individual GBM tumors expressing both amplified receptors typically express wtEGFR in far greater abundance than the DeltaEGFR lesion. We hypothesized that the minor DeltaEGFR-expressing subpopulation enhances tumorigenicity of the entire tumor cell population,and thereby maintains heterogeneity of expression of the two receptor forms in different cells. Using mixtures of glioma cells as well as immortalized murine astrocytes,we demonstrate that a paracrine mechanism driven by DeltaEGFR is the primary means for recruiting wtEGFR-expressing cells into accelerated proliferation in vivo. We determined that human glioma tissues,glioma cell lines,glioma stem cells,and immortalized mouse Ink4a/Arf(-/-) astrocytes that express DeltaEGFR each also express IL-6 and/or leukemia inhibitory factor (LIF) cytokines. These cytokines activate gp130,which in turn activates wtEGFR in neighboring cells,leading to enhanced rates of tumor growth. Ablating IL-6,LIF,or gp130 uncouples this cellular cross-talk,and potently attenuates tumor growth enhancement. These findings support the view that a minor tumor cell population can potently drive accelerated growth of the entire tumor mass,and thereby actively maintain tumor cell heterogeneity within a tumor mass. Such interactions between genetically dissimilar cancer cells could provide novel points of therapeutic intervention. View Publication

The importance of cancer metabolism has been appreciated for many years,but the intricacies of how metabolic pathways interconnect with oncogenic signaling are not fully understood. With a clear understanding of how metabolism contributes to tumorigenesis,we will be better able to integrate the targeting of these fundamental biochemical pathways into patient care. The mevalonate (MVA) pathway,paced by its rate-limiting enzyme,hydroxymethylglutaryl coenzyme A reductase (HMGCR),is required for the generation of several fundamental end-products including cholesterol and isoprenoids. Despite years of extensive research from the perspective of cardiovascular disease,the contribution of a dysregulated MVA pathway to human cancer remains largely unexplored. We address this issue directly by showing that dysregulation of the MVA pathway,achieved by ectopic expression of either full-length HMGCR or its novel splice variant,promotes transformation. Ectopic HMGCR accentuates growth of transformed and nontransformed cells under anchorage-independent conditions or as xenografts in immunocompromised mice and,importantly,cooperates with RAS to drive the transformation of primary mouse embryonic fibroblasts cells. We further explore whether the MVA pathway may play a role in the etiology of human cancers and show that high mRNA levels of HMGCR and additional MVA pathway genes correlate with poor prognosis in a meta-analysis of six microarray datasets of primary breast cancer. Taken together,our results suggest that HMGCR is a candidate metabolic oncogene and provide a molecular rationale for further exploring the statin family of HMGCR inhibitors as anticancer agents. View Publication

Killer cell lectin-like receptor F1 (KLRF1) is an activating C-type lectin-like receptor expressed on human NK cells and subsets of T cells. In this study,we show that activation-induced C-type lectin (AICL) is a unique KLRF1 ligand expressed on tumor cell lines of hematopoietic and non-hematopoietic origins. We screened a panel of human tumor cell lines using the KLRF1 reporter cells and found that several tumor lines expressed KLRF1 ligands. We characterized a putative KLRF1 ligand expressed on the U937 cell line. The molecular mass for the deglycosylated ligand was 28 kDa under non-reducing condition and 17 kDa under reducing condition,suggesting that the KLRF1 ligand is a homodimer. By expression cloning from a U937 cDNA library,we identified AICL as a KLRF1 ligand. We generated mAbs against AICL to identify the KLRF1 ligands on non-hematopoietic tumor lines. The anti-AICL mAbs stained the tumor lines that express the KLRF1 ligands and importantly the interaction of KLRF1 with the KLRF1 ligand on non-hematopoietic tumors was completely blocked by the two anti-AICL mAbs. Moreover,NK cell degranulation triggered by AICL-expressing targets was partially inhibited by the anti-AICL mAb. Finally,we demonstrate that AICL is expressed in human primary liver cancers. These results suggest that AICL is expressed on tumor cells of non-hematopoietic origins and raise the possibility that AICL may contribute to NK cell surveillance of tumor cells. View Publication