MINIREVIEW
Mixed lineage leukemia: roles in human malignancies and
potential therapy
Rolf Marschalek
Biochemistry, Chemistry & Pharmacy, Institute of Pharmaceutical Biology, Goethe-University of Frankfurt ⁄ Main, Germany
Mixed lineage leukemia fusions, acute
leukemia and the HOX signature
Mixed lineage leukemia (MLL) rearrangements define
a small subset of acute leukemia patients, including
those with therapy-induced secondary leukemias. How-
ever, unlike many other types of leukemia, the pres-
ence of distinct MLL rearrangements predicts early
relapse and very poor prognosis [1].
Based on experimental investigations, the ectopic
transcriptional activation of distinct HOXA genes in
conjunction with the MEIS1 gene has been reported
and proposed as a putative cancer mechanism [2–4].
This particular HOXA ⁄ MEIS1 signature was found
to be associated with the ability to show clonal
growth in semi-solid media and confers serial replat-
ing efficiency.
Consistent data, however, have been obtained for
only some tested MLL fusion alleles, most of which
were associated with an acute myeloid leukemia
(AML) disease phenotype. Taking into account that
MLL fusion proteins are associated with acute myeloid
leukemia (AML) and acute lymphoblastic leukemia
(ALL), it argues that other cancer mechanisms may
exist as well. Different committed or permissive cell
types may be malignantly transformed by the huge
number of diverse MLL fusion alleles (see below).

cal functions remain to be elucidated for the other fusion partners. This
minireview tries to sum up some of the available data and mechanisms
identified in leukemic stem and leukemic tumor cells and link this informa-
tion with the known functions of mixed lineage leukemia and certain mixed
lineage leukemia fusion partners.
Abbreviations
ALL, acute lymphoblastic leukemia; AML, acute myeloid leukemia; DSIF, DRB-sensitivity inducing factor; GSK, glycogen synthase kinase;
H3K4, histone H3 lysine 4; HMT, histone methyltransferase; MLL, mixed lineage leukemia; NELF, negative elongation factor; PI3K,
phosphatidylinositol 3 kinase; P-TEFb, positive transcription elongation factor b; SET, su(var)3-9, enhancer-of-zeste, trithorax; TGF,
transforming growth factor.
1822 FEBS Journal 277 (2010) 1822–1831 ª 2010 The Author Journal compilation ª 2010 FEBS
a particular differentiation state in which the
transformed cell has been arrested (e.g. common
myeloid progenitors) [5]. Whether specific HOX
signatures are indeed necessary for leukemogenesis or
are a concomitant phenomenon needs to be answered
on the basis of performed experiments for individual
MLL fusion proteins (see below).
Cellular functions of the MLL protein
The MLL protein has been identified as the mamma-
lian orthologue of the Trithorax protein in inverte-
brates [6]. Disruption of this gene in invertebrates and
vertebrates leads to homeotic transformation and null-
alleles are incompatible with normal embryonic devel-
opment [7,8]. All observed genetic mutations of the
MLL gene (chromosomal translocations, chromosomal
insertions, spliced fusions) seem to occur preferentially
in hematopoietic cells, indicating that this system
imparts unique properties (permissivity, survival and
development of leukemic clones) on a large variety of

open chromatin structures, in particular, to active pro-
moter regions, the MLL complex obviously binds to
different promoters in various tissues. In a recent study,
occupancy of MLL protein was investigated using chro-
matin immunoprecipitation experiments and subsequent
analysis on genome-wide tiling arrays [15]. This study
revealed that MLL was bound to > 2000 different pro-
moter regions within the cell line investigated (U937), of
which 99% were also bound by RNA polymerase II.
However, active transcription can be blocked by associ-
ated Polycomb proteins. Several genes belonging to the
HOXA clusters have been identified (HOXA1, A3, A7,
A9, A10, A11) among these promoters. HOXA genes
are downstream targets of wild-type MLL and of
several tested MLL fusion proteins.
Model systems for the analysis of MLL
fusion proteins and patient analysis
Different MLL fusions have been investigated as a
single transgene using a number of different
approaches. Mouse model systems were based on
transgenic techniques (transgenic mice, knock-in mice,
inverter mice, translocator mice, etc.) [16] or used
retroviral gene transfer [17].
Several laboratories have used retroviral transduc-
tion of murine hematopoietic stem cells to functionally
investigate the oncogenic properties of distinct MLL
fusion alleles. Manipulated hematopoietic stem ⁄ precur-
sor cells were tested in methylcellulose assays for their
clonal growth and replating efficiency, and the result-
ing colonies were transplanted into recipient mice of

overexpressed MLL–AF4. Short-term protein expres-
sion of MLL–AF4 in a doxycycline-dependent manner
resulted in the ectopic activation of HoxA7 and HoxA10
(and 560 other genes), whereas the reciprocal
AF4–MLL fusion protein did not activate any Hox gene
(but did activate 660 other genes). Surprisingly, when
both t(4;11) fusion proteins were expressed in the same
cell, not a single HoxA gene was found to be transcrip-
tionally activated (but 800 other genes were). This
indicated that the reciprocal AF4–MLL fusion protein
was dominant over the investigated MLL–AF4 fusion
protein, suppressing the typically observed HOXA
signature [24]. Is this also the case for other genetic rear-
rangements of the MLL gene? With the exception of
t(11;19) translocations, where 50% of all patients carry
only a single MLL–ENL fusion allele [25], most MLL-
rearranged leukemia patients exhibit both MLL fusion
alleles at the genomic DNA level. It is interesting to
note that these reciprocal MLL fusion alleles seem to be
transcribed at lower levels compared with the transcrip-
tional activity of the direct MLL fusion allele
(R. Marschalek, unpublished observation). Therefore,
most investigators tend to analyze transcripts deriving
from the direct MLL fusion allele as diagnostic readout.
This is presumably one reason why reciprocal MLL
fusion alleles have never received much attention. How-
ever, without testing both reciprocal fusion alleles in the
same test system, it is impossible to answer the impor-
tant question about the role of activated HOXA genes
in the leukemogenic transformation process.

argue for the presence of specific mutations in the
cloned constructs, complementing mutations or other
supporting events, for example, the activation of spe-
cific signaling pathways. In order to answer this impor-
tant question, a careful and systematic examination of
available MLL fusion alleles (n > 60) is necessary to
identify and analyze their specific oncogenic potential.
The multitude of MLL fusion partners
A recent study summarized actual knowledge about the
MLL recombinome [31]. This comprehensive study
provided information about  759 analyzed MLL-
mediated leukemia patients and collected a total of 64
different MLL fusion partners. The analyzed MLL
fusion alleles were classified according to their occur-
rence in ALL and AML patients and their putative cel-
lular function. According to this study, 80% of all MLL
rearrangements are caused by AF4 (42%), AF9 (16%),
ENL (11%), AF10 (7%) and ELL (4%). The remaining
20% of MLL-rearranged leukemia patients displayed 59
different fusion partners, most of which were identified
in only single patients. All known MLL fusion partner
genes are categorized in Fig. 1 according to their cellu-
lar localization and their putative function. Twenty-five
of them represent nuclear proteins and 33 represent
cytosolic proteins; one fusion partner could not be clas-
sified. With few exceptions (e.g. the AF4 and SEPTIN
gene family; AF9 and ENL), all these fusion partners
share little or no homology at the protein level, indicat-
ing that different properties are provided by different
fusion proteins. The common denominator in all

promoter regions of active genes. These promoter com-
plexes are arrested and characterized by their association
with the inactive DRB-sensitivity inducing factor (DSIF)
protein and the inhibitory negative elongation factor
(NELF) complex. Initial activation of this complex
results in short transcripts of  50 nucleotides. All
further steps require the presence of P-TEFb kinase
(CDK9 ⁄ CCNT1) and TFIIH (CDK7 ⁄ CCNH): phos-
phorylation of the C-terminal domain-tail of the largest
subunit of RNA polymerase II at serine 2 and 5; phos-
phorylation of DSIF (converts DSIF into an activator);
and phosphorylation of components of the NELF com-
plex, which leads to their dissociation and subsequent
destruction.
However, nuclear P-TEFb complexes are mostly
kept in an inactive state because of an interaction with
a nuclear complex (HEXIM1 ⁄ 7SK ⁄ LARP7 ⁄ MEPCE).
Thus, active P-TEFb kinase is not easily available for
RNA polymerase II. Only a small portion of P-TEFb
kinase is already associated with BRD4, an activator
of P-TEFb kinase which is able to directly bind to his-
tone proteins.
Recently, functional analysis of the above-mentioned
fusion partner proteins – AF4 (family members), AF9,
ENL and AF10 – has shed light on the activation cycle
of P-TEFb kinase. All assemble in a high-molecular
mass complex that binds to DOT1L and P-TEFb kinase
[33]. AF4-bound P-TEFb kinase becomes activated and
interacts with promoter-arrested RNA polymerase.
Activated P-TEFb kinase then phosphorylates DSIF

tions provided by the above-mentioned MLL fusion
proteins? A first glimpse came from two recent studies.
Krivtsov et al. [35] demonstrated that expression of a
transgenic Mll–AF4 knockin allele confers ectopic
H3K79 signatures on transcribed regions, thereby
changing the epigenetic code in a genome-wide fash-
ion. This is most likely because the tested Mll–AF4
knockin allele encodes a fusion protein that retains the
ability to bind to AF9, ENL, AF10 and DOT1L, and
thus compete with their binding to the AF4 complex.
An as yet unpublished study has demonstrated that
the reciprocal AF4–MLL fusion protein retains its
H3K4 HMT activity and is able to bind to P-TEFb
kinase and RNA polymerase II (A. Benedikt, unpub-
lished data). The presence of the AF4–MLL fusion
protein seems to enhance transcription via activation
of P-TEFb kinase. In line with this, after 5 days of
induction, ectopic expression of AF4–MLL resulted in
the transcriptional deregulation of 660 genes, of which
580 (88%) were transcriptionally activated, whereas
only 80 were downregulated [24].
From the data presented it is clear that AF4 plays a
central role. AF4 serves as a protein-binding platform
for several other proteins to initiate a fundamental cel-
lular process. P-TEFb binds to the N-terminal portion
of AF4, whereas the C-terminal portion of AF4 con-
fers binding to ENL and ⁄ or AF9 (which in turn binds
to AF10 and DOT1L). Therefore, MLL–AF4, MLL–
AF9, MLL–ENL and MLL–AF10 fusion proteins are
all functionally equivalent as they all bind, directly or

an ‘RNA polymerase II activator complex’. By contrast,
MLL–AF4 binds to pre-assembled ENL ⁄
AF10 ⁄ DOT1L, competing for factors that normally
bind to the AF4 complex. The oncogenic AF4–MLL
fusion protein binds directly to P-TEFb and strongly
activates its kinase function (A. Benedikt, unpublished
data). Activated P-TEFb can be inhibited by the potent
CDK9 inhibitor, flavopiridol, an experimental drug
identified in 1992 as an anticancer drug [37]. Flavopir-
idol has been tested in several clinical trials but was
found to be effective in only few malignacies when
administered in a certain way (e.g. chronic lymphoblas-
tic leukemia). Replication of HIV-1 is also strongly
inhibited by flavopiridol in low nanomolar concentra-
tions, because transcription elongation of HIV-1 is regu-
lated by the TAT ⁄ TAR ⁄ P-TEFb system [38]. Therefore,
CDK9 inhibitors may be a promising tool with which to
gain insight into the molecular mechanisms of MLL-
mediated leukemia. Moreover, many CDK inhibitors
are cross-reactive against glycogen synthase kinase
(GSK) proteins [39]. This may allow specific targeting of
two different mechanisms at the same time (see below:
WNT-signaling pathway; P-TEFb mediated elongation
control of RNA polymerase II), both of which seem to
be crucial for MLL-mediated acute leukemia.
Signaling and MLL-mediated leukemias
Very few studies have tried to experimentally investi-
gate signaling pathways that might be important for
MLL-rearranged cells. As a matter of fact, leukemic
cells obtained from MLL-mediated leukemia patients

therapeutics interfere with DNA synthesis or cause
severe DNA damage.
Two questions related to this topic are: what types
of extracellular signals trigger the switch between the
above-described modes and which signaling pathways
are involved? However, despite the high FLT3 expres-
sion, which might be targeted by the potent inhibitors
PKC412 of CEP-701, very few are currently known.
Therefore, the recently performed study in Michael
Cleary’s laboratory was quite a surprise [41]. Wang
and co-workers demonstrated that active GSK3 is nec-
essary for MLL-mediated leukemia cells to survive.
GSK3 is implicated in different signaling pathways,
for example, protein kinase C, protein kinase A,
RAS ⁄ RAF, WNT-, phosphatidylinositol 3-kinase and
Hedgehog, and thus affects metabolism, the cell cycle,
gene expression, developmental processes and oncogen-
esis. Active GSK3 is indicative of absent WNT-signal-
ing and leads to the proteasomal destruction of
GSK3-phosphorylated b-catenin. Active GSK3 also
phosphorylates members of the MYC family and
inhibits their function, for example, their ability to
transcriptionally activate pro-apoptotic proteins. In the
above-mentioned study, active GSK3 led to a decrease
in p27
Kip1
protein levels. Because p27
Kip1
is a target
for wild-type MLL, active GSK3 seems to prevent the

blocks HH signaling via SMO, and also
blocks apoptosis and MYC-mediated
actions. Moreover, it allows clonal growth
and stabilizes mitochondria. Inhibition of
active GSK3 by lithium or other GSK3
inhibitors leads to cell growth, but may
block differentiation and cause induction of
apoptosis in MLL-rearranged cell lines.
R. Marschalek Role of MLL in human malignancies
FEBS Journal 277 (2010) 1822–1831 ª 2010 The Author Journal compilation ª 2010 FEBS 1827
TNF-ligand [43]. This increases the susceptibility to
pro-apoptotic signals. Moreover, active AXIN ⁄ GSK3
signaling leads to the destruction of SMAD3, and thus
interferes with transforming growth factor (TGF)b sig-
naling [44]. In line with this, GSK3 has recently been
identified in a complex with DDX3 and cellular inhibi-
tor of apoptosis 1 that prevent apoptotic signaling via
competitive binding to death receptors [45]. As men-
tioned above, a second explanation is the inhibitory
effect of mostly all GSK3 inhibitors against certain
CDKs, including CDK9 [39]. As outlined above, inhi-
bition of CDK9 will presumably impair P-TEFb func-
tions associated with several MLL fusion proteins.
This influences cell growth and survival, as recently
demonstrated [46].
Moreover, Fig. 2 summarizes different signaling
pathways that should be strictly controlled or
completely shut-off in MLL-rearranged leukemia cells,
because they would otherwise inactivate GSK3 by
phosphorylation of serine 9. This could be explained

leukemic disease phenotype in secondary recipients.
More importantly, transcriptional activation of p21 was
p53-independent, indicating that leukemic stem cells
may use alternative pathways to activate p21. Activa-
tion of p21 in leukemic stem cells resulted in a quiescent
phenotype, allowing DNA repair processes and mainte-
nance of the leukemic stem compartment [49]. A com-
plex scenario is depicted in Fig. 3 in which active TGFb
signaling, inactive WNT-signaling (= active GSK3)
and several key processes may explain the observed
effects. TGFb signaling led to the formation of a protein
complex that consists of unphosphorylated FOXO
proteins 1, 3a and 4 in conjunction with phosphorylated
SMAD3 and SMAD4. This protein complex can
Fig. 3. The FOXO ⁄ SMAD switch: regulation
of stem cell features. Known pathways
involved in WNT and TGFb signaling, as well
as the ‘FOXO ⁄ SMAD switch’, are depicted.
Regulatory pathways switch between a pro-
liferation state (upper) and a quiescent state
(lower). The p21 protein plays a central role
in the maintenance and quiescence of
leukemic stem cells. MLL FA, MLL fusion
allele. Green arrows, functional ⁄ transcrip-
tional activation; red arrows, inhibitory
function. Tx, act through transcriptional
activation.
Role of MLL in human malignancies R. Marschalek
1828 FEBS Journal 277 (2010) 1822–1831 ª 2010 The Author Journal compilation ª 2010 FEBS
directly activate transcription of the CDKN1a ⁄ p21 gene,

vation of NANOG and OCT4 has recently been identi-
fied in an in vitro model system when both t(4;11) fusion
proteins were present. This finding was then validated in
infant and adult t(4;11) leukemia patients [23]. Thus, the
switch between cell growth and quiescence in MLL-
mediated leukemia cells is possibly controlled by a
‘FOXO ⁄ SMAD switch’ which in turn allows re-activa-
tion of embryonic stem cell genes and controls
CDKN1a ⁄ p21 independent of p53. These pathways are
highly attractive for future research and have the poten-
tial for therapeutic intervention. This model would also
explain recent findings in which ‘leukemic stem cells’ –
able to initiate leukemias in a NOD ⁄ SCID mouse model
– have been identified in sorted cells with quite diverse
immunophenotypes (± CD34, ± CD19), indicating
that stem cell characteristics may not be restricted to a
hierarchic stem cell compartment in ALL [55].
Acknowledgements
I thank Geertruy te Kronnie and Theo Dingermann
for critically reading the manuscript. I want to apolo-
gize for not-citing many references due to a citation
limit for this minireview. This work is supported by
research grant 107819 from the Deutsche Krebshilfe
e.V. to RM.
References
1 Holleman A, Cheok MH, den Boer ML, Yang W,
Veerman AJ, Kazemier KM, Pei D, Cheng C, Pui CH,
Relling MV et al. (2004) Gene-expression patterns in
drug-resistant acute lymphoblastic leukemia cells and
response to treatment. N Engl J Med 351, 533–542.

Wnt and the adhesion-dependent signaling pathways
governs the chemosensitivity of acute myeloid leukemia.
Oncogene 25, 3113–3122.
11 Hsieh JJD, Cheng EH & Korsmeyer SJ (2003)
Taspase1: a threonine aspartase required for cleavage
of MLL and proper HOX gene expression. Cell 115,
293–303.
12 Nakamura T, Mori T, Tada S, Krajewski W, Rozovskaia
T, Wassell R, Dubois G, Mazo A, Croce CM & Canaani
E (2002) ALL-1 is a histone methyltransferase that
assembles a supercomplex of proteins involved in
transcriptional regulation. Mol Cell 10, 1119–1128.
R. Marschalek Role of MLL in human malignancies
FEBS Journal 277 (2010) 1822–1831 ª 2010 The Author Journal compilation ª 2010 FEBS 1829
13 Yokoyama A, Wang Z, Wysocka J, Sanyal M, Aufiero
DJ, Kitabayashi I, Herr W & Cleary ML (2004) Leuke-
mia proto-oncoprotein MLL forms a SET1-like histone
methyltransferase complex with menin to regulate Hox
gene expression. Mol Cell Biol 24, 5639–5649.
14 Ruthenburg AJ, Allis CD & Wysocka J (2007) Methyl-
ation of lysine 4 on histone H3: intricacy of writing and
reading a single epigenetic mark. Mol Cell 25, 15–30.
15 Guenther MG, Jenner RG, Chevalier B, Nakamura T,
Croce CM, Canaani E & Young RA (2005) Global and
Hox-specific roles for the MLL1 methyltransferase.
Proc Natl Acad Sci USA 102, 8603–8608.
16 Lobato MN, Metzler M, Drynan L, Forster A, Pannell
R & Rabbitts TH (2008) Modeling chromosomal trans-
locations using conditional alleles to recapitulate initiat-
ing events in human leukemias. J Natl Cancer Inst

S, Herr I, Dingermann T & Marschalek R (2007) The
combined effects of the two reciprocal t(4;11) fusion
proteins, MLL•AF4 and AF4•MLL, confer resistance
to apoptosis, cell cycling capacity and growth transfor-
mation. Oncogene 26, 3352–3363.
25 Meyer C, Burmeister T, Strehl S, Schneider B, Hubert
D, Zach O, Haas O, Klingebiel T, Dingermann T &
Marschalek R (2007) Spliced MLL fusions: a novel
mechanism to generate functional chimeric MLL–
MLLT1 transcripts in t(11;19)(q23;p13.3) leukemia.
Leukemia 21, 588–590.
26 Trentin L, Girodan M, Dingermann T, Basso G, te
Kronnie G & Marschalek R (2009) Two independent
gene signatures in pediatric t(4;11) acute lymphoblastic
leukemia patients. Eur J Haematol 83, 406–419.
27 Stam RW, Schneider P, Hagelstein JA, van der Linden
MH, Stumpel DJ, de Menezes RX, de Lorenzo P,
Valsecchi MG & Pieters R (2009) Gene expression pro-
filing-based dissection of MLL translocated and MLL
germline acute lymphoblastic leukemia in infants. Blood
doi: 10.1182/blood-2009-07-233049.
28 Faber J, Krivtsov AV, Stubbs MC, Wright R, Davis
TN, van den Heuvel-Eibrink M, Zwaan CM, Kung AL
& Armstrong SA (2009) HOXA9 is required for sur-
vival in human MLL-rearranged acute leukemias. Blood
113, 2375–2385.
29 Fuchs U, Rehkamp G, Haas OA, Slany R, Ko
¨
nig M,
Bojesen S, Bohle RM, Damm-Welk C, Ludwig WD,

92–106.
35 Krivtsov AV, Feng Z, Lemieux ME, Faber J, Vempati
S, Sinha AU, Xia X, Jesneck J, Bracken AP, Silverman
LB et al. (2008) H3K79 methylation profiles define mur-
ine and human MLL–AF4 leukemias. Cancer Cell 14,
355–368.
36 Bursen A, Schwabe K, Ru
¨
ster B, Henschler R,
Ruthardt M, Dingermann T & Marschalek R (2009)
The AF4•MLL fusion protein is capable of inducing
ALL in mice without requirement of MLL AF4. Blood.
37 Kaur G, Stetler-Stevenson M, Sebers S, Worland P,
Sedlacek H, Myers C, Czech J, Naik R & Sausville E
Role of MLL in human malignancies R. Marschalek
1830 FEBS Journal 277 (2010) 1822–1831 ª 2010 The Author Journal compilation ª 2010 FEBS
(1992) Growth inhibition with reversible cell cycle arrest
of carcinoma cells by flavone L86-8275. J Natl Cancer
Inst 84, 1736–1740.
38 Chao SH, Fujinaga K, Marion JE, Taube R, Sausville
EA, Senderowicz AM, Peterlin BM & Price DH (2000)
Flavopiridol inhibits P-TEFb and blocks HIV-1 replica-
tion. J Biol Chem 275, 28345–28348.
39 Knockaert M, Greengard P & Meijer L (2002) Pharma-
cological inhibitors of cyclin-dependent kinases. Trends
Pharmacol Sci 23, 417–425.
40 Tothova Z, Kollipara R, Huntly BJ, Lee BH, Castrillon
DH, Cullen DE, McDowell EP, Lazo-Kallanian S,
Williams IR, Sears C et al. (2007) FoxOs are critical
mediators of hematopoietic stem cell resistance to physi-

llar MP, Bach C, Buhl S,
Maethner E & Slany RK (2009) Misguided transcrip-
tional elongation causes mixed lineage leukemia. PLoS
Biol 7, e1000249, doi: 10.1371/journal.pbio.1000249.
47 Adler HT, Nallaseth FS, Walter G & Tkachuk DC
(1997) HRX leukemic fusion proteins form a hetero-
complex with the leukemia-associated protein SET and
protein phosphatase 2A. J Biol Chem 272, 28407–28414.
48 Viale A, De Franco F, Orleth A, Cambiaghi V, Giuliani
V, Bossi D, Ronchini C, Ronzoni S, Muradore I,
Monestiroli S et al. (2009) Cell-cycle restriction limits
DNA damage and maintains self-renewal of leukaemia
stem cells. Nature 457, 51–56.
49 Seoane J, Le HV, Shen L, Anderson SA & Massague
´
J
(2004) Integration of Smad and forkhead pathways in
the control of neuroepithelial and glioblastoma cell pro-
liferation. Cell 117, 211–223.
50 Barreto G, Scha
¨
fer A, Marhold J, Stach D, Swamina-
than SK, Handa V, Do
¨
derlein G, Maltry N, Wu W,
Lyko F et al.
(2007) Gadd45a promotes epigenetic gene
activation by repair-mediated DNA demethylation.
Nature 445, 671–675.
51 Kuroda T, Tada M, Kubota H, Kimura H, Hatano

rangements; underlined: interacting proteins found to be
twice or more as binding partner for different MLL
fusion partner proteins.
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R. Marschalek Role of MLL in human malignancies
FEBS Journal 277 (2010) 1822–1831 ª 2010 The Author Journal compilation ª 2010 FEBS 1831