Leukemic fusion genes MLL/AF4 and AML1/MTG8 support leukemic self-renewal by controlling expression of the telomerase subunit TERT.
MLL/AF4 and AML/MTG8 represent two leukemic fusion genes, which are most frequently found in infant acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML), respectively. We examined the influence of MLL/AF4 and AML1/MTG8 fusion genes on the expression of TERT coding for the telomerase protein subunit, and subsequently telomerase activity in t(4;11)-positive ALL and t(8;21)-positive cell lines, respectively. MLL/AF4 suppression diminished telomerase activity and expression of TERT. Blocking pro-apoptotic caspase activation in conjunction with MLL/AF4 knockdown enhanced the inhibition of TERT gene expression, which suggests that MLL/AF4 depletion does not reduce TERT expression levels by inducing apoptosis. Knockdown of HOXA7, a direct transcriptional target of MLL/AF4 fusion gene, caused a reduction of telomerase and TERT to an extent similar to that observed with MLL/AF4 suppression. Chromatin immunoprecipitation of SEM cells, using ectopically expressed FLAG-tagged Hoxa7, indicates HOXA7 binding site in the TERT promoter region. Furthermore, suppression of the AML1/MTG8 fusion gene was associated with severely reduced clonogenicity, induction of replicative senescence, impaired TERT expression and accelerated telomere shortening. We thus present findings that show a mechanistic link between leukemic fusion proteins, essential for development and maintenance of leukemia, and telomerase, a key element of both normal and malignant self-renewal.
Gessner
A
A
Northern Institute for Cancer Research, Newcastle University, Newcastle upon Tyne, UK.
Thomas
M
M
Castro
P Garrido
PG
Büchler
L
L
Scholz
A
A
Brümmendorf
T H
TH
Soria
N Martinez
NM
Vormoor
J
J
Greil
J
J
Heidenreich
O
O
D017209:Apoptosis; D015153:Blotting, Western; D016922:Cellular Senescence; D047369:Chromatin Immunoprecipitation; D002880:Chromosomes, Human, Pair 11 / Q000235:genetics; D002891:Chromosomes, Human, Pair 21 / Q000235:genetics; D002894:Chromosomes, Human, Pair 4 / Q000235:genetics; D002898:Chromosomes, Human, Pair 8 / Q000235:genetics; D050676:Core Binding Factor Alpha 2 Subunit / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D051788:Myeloid-Lymphoid Leukemia Protein / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D015514:Oncogene Proteins, Fusion / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000235:genetics* / Q000473:pathology*; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000494:pharmacology; D000075142:RUNX1 Translocation Partner 1 Protein; D020133:Reverse Transcriptase Polymerase Chain Reaction; D019098:Telomerase / Q000235:genetics* / Q000378:metabolism; D016615:Telomere / Q000235:genetics; D014178:Translocation, Genetic; D014407:Tumor Cells, Cultured
C107844:AML1-ETO fusion protein, human; D050676:Core Binding Factor Alpha 2 Subunit; C115962:HOXA7 protein, human; D018398:Homeodomain Proteins; C113855:MLL-AF4 fusion protein, human; D015514:Oncogene Proteins, Fusion; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D000075142:RUNX1 Translocation Partner 1 Protein; D051788:Myeloid-Lymphoid Leukemia Protein; C509186:TERT protein, human; D019098:Telomerase