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


RESULTS
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.


CONCLUSIONS
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.
Nagel
Stefan
S
Dept. of Human and Animal Cell Lines, DSMZ - German Collection of Microorganisms and Cell Cultures, Inhoffenstr. 7B, 38124 Braunschweig, Germany. sna@dsmz.de
Venturini
Letizia
L
Marquez
Victor E
VE
Meyer
Corinna
C
Kaufmann
Maren
M
Scherr
Michaela
M
MacLeod
Roderick Af
RA
Drexler
Hans G
HG
D015153:Blotting, Western; D002460:Cell Line; D047369:Chromatin Immunoprecipitation; D015870:Gene Expression; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D000080905:Homeobox A10 Proteins; D018398:Homeodomain Proteins / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D051797:Inhibitor of Differentiation Protein 2 / Q000235:genetics* / Q000378:metabolism; D007694:Killer Cells, Natural / Q000502:physiology*; D020411:Oligonucleotide Array Sequence Analysis; D063146:Polycomb-Group Proteins; D016133:Polymerase Chain Reaction; D054218:Precursor T-Cell Lymphoblastic Leukemia-Lymphoma / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics; D012097:Repressor Proteins / Q000235:genetics* / Q000378:metabolism; D013601:T-Lymphocytes / Q000502:physiology*
D000080905:Homeobox A10 Proteins; D018398:Homeodomain Proteins; C497450:ID2 protein, human; D051797:Inhibitor of Differentiation Protein 2; D063146:Polycomb-Group Proteins; D012097:Repressor Proteins; C097899:homeobox protein HOXA9; C069634:HOXA10 protein, human