Polycomb repressor complex 2 regulates HOXA9 and HOXA10, activating ID2 in NK/T-cell lines

<p>Abstract</p> <p>Background</p> <p>NK- and T-cells are closely related lymphocytes, originating from the same early progenitor cells during hematopoiesis. In these differentiation processes deregulation of developmental genes may contribute to leukemogenesis. Here, we compared expression profiles of NK- and T-cell lines for identification of aberrantly expressed genes in T-cell acute lymphoblastic leukemia (T-ALL) which physiologically regulate the differentiation program of the NK-cell lineage.</p> <p>Results</p> <p>This analysis showed high expression levels of HOXA9, HOXA10 and ID2 in NK-cell lines in addition to T-cell line LOUCY, suggesting leukemic deregulation therein. Overexpression experiments, chromatin immuno-precipitation and promoter analysis demonstrated that HOXA9 and HOXA10 directly activated expression of ID2. Concomitantly elevated expression levels of HOXA9 and HOXA10 together with ID2 in cell lines containing MLL translocations confirmed this form of regulation in both ALL and acute myeloid leukemia. Overexpression of HOXA9, HOXA10 or ID2 resulted in repressed expression of apoptosis factor BIM. Furthermore, profiling data of genes coding for chromatin regulators of homeobox genes, including components of polycomb repressor complex 2 (PRC2), indicated lacking expression of EZH2 in LOUCY and exclusive expression of HOP in NK-cell lines. Subsequent treatment of T-cell lines JURKAT and LOUCY with DZNep, an inhibitor of EZH2/PRC2, resulted in elevated and unchanged HOXA9/10 expression levels, respectively. Moreover, siRNA-mediated knockdown of EZH2 in JURKAT enhanced HOXA10 expression, confirming HOXA10-repression by EZH2. Additionally, profiling data and overexpression analysis indicated that reduced expression of E2F cofactor TFDP1 contributed to the lack of EZH2 in LOUCY. Forced expression of HOP in JURKAT cells resulted in reduced HOXA10 and ID2 expression levels, suggesting enhancement of PRC2 repression.</p> <p>Conclusions</p> <p>Our results show that major differentiation factors of the NK-cell lineage, including HOXA9, HOXA10 and ID2, were (de)regulated via PRC2 which therefore contributes to T-cell leukemogenesis.</p

SET-NUP214 fusion in acute myeloid leukemia- and T-cell acute lymphoblastic leukemia-derived cell lines

<p>Abstract</p> <p>Background</p> <p><it>SET-NUP214 </it>fusion resulting from a recurrent cryptic deletion, del(9)(q34.11q34.13) has recently been described in T-cell acute lymphoblastic leukemia (T-ALL) and in one case of acute myeloid leukemia (AML). The fusion protein appears to promote elevated expression of <it>HOXA </it>cluster genes in T-ALL and may contribute to the pathogenesis of the disease. We screened a panel of ALL and AML cell lines for <it>SET-NUP214 </it>expression to find model systems that might help to elucidate the cellular function of this fusion gene.</p> <p>Results</p> <p>Of 141 human leukemia/lymphoma cell lines tested, only the T-ALL cell line LOUCY and the AML cell line MEGAL expressed the <it>SET(TAF-</it>Iβ)-<it>NUP214 </it>fusion gene transcript. RT-PCR analysis specifically recognizing the alternative first exons of the two <it>TAF-</it>I isoforms revealed that the cell lines also expressed <it>TAF-</it>Iα-<it>NUP214 </it>mRNA. Results of fluorescence in situ hybridization (FISH) and array-based copy number analysis were both consistent with del(9)(q34.11q34.13) as described. Quantitative genomic PCR also confirmed loss of genomic material between <it>SET </it>and <it>NUP214 </it>in both cell lines. Genomic sequencing localized the breakpoints of the <it>SET </it>gene to regions downstream of the stop codon and to <it>NUP214 </it>intron 17/18 in both LOUCY and MEGAL cells. Both cell lines expressed the 140 kDa SET-NUP214 fusion protein.</p> <p>Conclusion</p> <p>Cell lines LOUCY and MEGAL express the recently described <it>SET-NUP214 </it>fusion gene. Of special note is that the formation of the <it>SET </it>exon 7/<it>NUP214 </it>exon 18 gene transcript requires alternative splicing as the <it>SET </it>breakpoint is located downstream of the stop codon in exon 8. The cell lines are promising model systems for <it>SET-NUP214 </it>studies and should facilitate investigating cellular functions of the the SET-NUP214 protein.</p

NK-like homeodomain proteins activate NOTCH3-signaling in leukemic T-cells

<p>Abstract</p> <p>Background</p> <p>Homeodomain proteins control fundamental cellular processes in development and in cancer if deregulated. Three members of the NK-like subfamily of homeobox genes (NKLs), TLX1, TLX3 and NKX2-5, are implicated in T-cell acute lymphoblastic leukemia (T-ALL). They are activated by particular chromosomal aberrations. However, their precise function in leukemogenesis is still unclear. Here we screened further NKLs in 24 T-ALL cell lines and identified the common expression of MSX2. The subsequent aim of this study was to analyze the role of MSX2 in T-cell differentiation which may be disturbed by oncogenic NKLs.</p> <p>Methods</p> <p>Specific gene activity was examined by quantitative real-time PCR, and globally by expression profiling. Proteins were analyzed by western blot, immuno-cytology and immuno-precipitation. For overexpression studies cell lines were transduced by lentiviruses.</p> <p>Results</p> <p>Quantification of MSX2 mRNA in primary hematopoietic cells demonstrated higher levels in CD34+ stem cells as compared to peripheral blood cells and mature CD3+ T-cells. Furthermore, analysis of MSX2 expression levels in T-cell lines after treatment with core thymic factors confirmed their involvement in regulation. These results indicated that MSX2 represents an hematopoietic NKL family member which is downregulated during T-cell development and may functionally substituted by oncogenic NKLs. For functional analysis JURKAT cells were lentivirally transduced, overexpressing either MSX2 or oncogenic TLX1 and NKX2-5, respectively. These cells displayed transcriptional activation of NOTCH3-signaling, including NOTCH3 and HEY1 as analyzed by gene expression profiling and quantitative RT-PCR, and consistently attenuated sensitivity to gamma-secretase inhibitor as analyzed by MTT-assays. Furthermore, in addition to MSX2, both TLX1 and NKX2-5 proteins interacted with NOTCH-pathway repressors, SPEN/MINT/SHARP and TLE1/GRG1, representing a potential mechanism for (de)regulation. Finally, elevated expression of NOTCH3 and HEY1 was detected in primary TLX1/3 positive T-ALL cells corresponding to the cell line data.</p> <p>Conclusion</p> <p>Identification and analysis of MSX2 in hematopoietic cells implicates a modulatory role via NOTCH3-signaling in early T-cell differentiation. Our data suggest that reduction of NOTCH3-signaling by physiological downregulation of MSX2 expression during T-cell development is abrogated by ectopic expression of oncogenic NKLs, substituting MSX2 function.</p

Subclones in B-lymphoma cell lines: isogenic models for the studyof gene regulation

Genetic heterogeneity though common in tumors has been rarely documented in celllines. To examine how often B-lymphoma cell lines are comprised of subclones, weperformed immunoglobulin (IG) heavy chain hypermutation analysis. Revealing thatsubclones are not rare in B-cell lymphoma cell lines, 6/49 IG hypermutated cell lines(12%) consisted of subclones with individual IG mutations. Subclones were alsoidentified in 2/284 leukemia/lymphoma cell lines exhibiting bimodal CD markerexpression. We successfully isolated 10 subclones from four cell lines (HG3, SUDHL-5, TMD-8, U-2932). Whole exome sequencing was performed to molecularlycharacterize these subclones. We describe in detail the clonal structure of cell lineHG3, derived from chronic lymphocytic leukemia. HG3 consists of three subcloneseach bearing clone-specific aberrations, gene expression and DNA methylationpatterns. While donor patient leukemic cells were CD5+, two of three HG3 subcloneshad independently lost this marker. CD5 on HG3 cells was regulated byepigenetic/transcriptional mechanisms rather than by alternative splicing as reportedhitherto. In conclusion, we show that the presence of subclones in cell lines carryingindividual mutations and characterized by sets of differentially expressed genes is notuncommon. We show also that these subclones can be useful isogenic models forregulatory and functional studies