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Expression of HOXC4 Homeoprotein in the Nucleus
of Activated Human Lymphocytes
By Raffaella Meazza, Antonio Faiella, Maria Teresa Corsetti, Irma Airoldi, Silvano Ferrini, Edoardo Boncinelli,
and Giorgio Corte
We have analyzed the expression of homeoproteins of the
HOX family in resting and activated lymphoid cells and in
neoplastic lymphoid cell linesby theuse of monoclonal antibodies (MoAbs) already shown t o react with the homeoproteins HOXA10,HOXC6,
and HOXD4, respectively. AntiHOXAIO and C6 MoAbs DlDi not show any reactivity with
thelymphoid
cells tested, whereas anti-HOXD4 MoAb
stained few resting peripheral blood lymphocytes (PBLs)and
most phytohemagglutinin (PHA)-stimulated PBLs asearly as
6 hours after stimulation. The pattern of staining of PHAactivated PBLs is reminiscent of thestages of nucleolar fragmentation in different phases of the cell cycle. The MoAb
reacted also with activated or Epstein-Barr virus-transformed B cells, with clonal or polyclonalT and natural killer
(NK) cells, with leukemic T-cell lines, and with a Burkii's
lymphoma cell line. RNAse protection experiments, per
formed with probes specific for HOXD4 or for the highly
homologous HOXA4, HOXB4, and HOXC4, belonging t o the
same paralogy group, indicated that only HOXC4 mRNA is
present in resting or activated PBLs. Northern blot analysis
on polyA+ RNA from activated PBLs or Raji cells showed
the presence of two different HOXC4 transcripts of 2.8 and
1.9 kb. Gel retardationandSouthwestern
blot assays
showed the presence of a 32-kD homeoprotein with DNAbinding properties typical of a HOX4 homeoprotein in nucleolar extracts of PHA-activated, but not of resting, lymphocytes. Taken together, these data indicate that the HOXC4
homeoprotein is expressed in activated and/or proliferating
lymphocytes of the T-, B-, or NK-cell lineage, whereas it is
weakly expressed in a minority of resting cells. The early
expression and the nucleolar localization suggest an involvement of HOXC4 in the regulation of genes controlling lymphocyte activation and/or proliferation.
0 1995 by The American Society of Hematology.
H
OMEOBOX GENES (Hox) encode DNA-binding tranB, and C clusters have been found to be expressed during
scription factors,' which are highly conserved
normal hernatop~iesis'~~'~"~
and in leukemia."
Exploiting the availability of monoclonal antibodies
throughout the species. Some of them have been shown to
provide positional information along the antero-posterior
(MoAbs) directed against the recombinant homeoproteins
axis during the embryonic development of Drosophila.','
A10, C6, and D4, we have investigated in detail their expresOutstanding among the vertebrate homeogenes are the class
sion in resting and activated peripheral blood T lymphocytes
I homeogenes that contain a homeobox most closely related
(PBLs).
to archetypal Antennapedia homeobox of the Dr~sophila.'.~
MATERIALS AND METHODS
They are present in four clusters, termed Hox clusters, for
a total of 38 different genes located on different chromoIsolation, Culture, and Staining of Lymphocytes and Cell
s o m e ~and
~ ' ~their role in the control of vertebrate morphoLines
genesis is indicated by several lines of evidence.6However,
Peripheral blood mononuclear cells (PBMCs) from normal volunexpression of Hox genes continues after birth and they may
teers were isolated by Ficoll-Hypaque density gradients. PBMCs
be involved in controlling cellular differentiation processes
wereused either immediately or after stimulation in culture with
also in adulthood. Thus, Hox genes have been found to be
1% (voVvol) phytohemagglutinin (PHA; GIBCO, Grand Island, NY)
or with 1 mg/mL OKT3 MoAb for different time intervals. Culture
expressed in tumor cells and in cultured cell lines of various
medium was RPM1 1640 supplemented with 10% fetal calf serum
origin, including neural, epithelial, myeloid, lymphoid, and
erythoid
but also during normal hematopoie~is.'~.'.'~'~(FCS). B-cell-enriched populations were obtained from tonsillar
mononuclear cells depleted from T cells by rosetting with neuraminiIn particular, mRNAs corresponding to Hox genes of the A,
From the Istituto Nazionale per la Ricerca sul Cancro, Genova;
DIBIT, Istituto Scientijco S. Raffaele, Milano; Centro di Biotecnologie Avanzate, Genova; Centro Infrastrutture Cellulari, C.N.R., Milano; and the Istituto di Chimica Biologica, Universita di Genova,
Genova, Italy.
Submitted May 31, 1994; accepted November 18, 1994.
Supported by grants from Progetti Finalizzati CNR Ingegneria
Genetica and APRO. the VII AIDS Project and by a grant to G.C.
from the Minister0 della Sanita, the Italian Association f o r Cancer
Research(AIRC) and MURST. LA. isthe recipient of anAIRC
fellowship.
Address reprint requests to Giorgio Corte, MD, Advanced Biotechnology Center, CBA, V.le Benedetto XV, 10, 16132 Genova,
Italy.
The publication costsof this article were defrayed in part by page
chargepayment. This article must therefore be hereby marked
"advertisement" in accordance with 18 U.S.C. section 1734 solely to
indicate this fact.
0 1995 by The American Society of Hematology.
0006-497I/95/8508-0011$3.00/0
2084
dase-treated sheep red blood cells (SRBCs). These B-cell-enriched
populations were activated in culture withan optimal dilution of
Staphylococcus aureus Cowan strain-I (SAC) andwith 100 UlmL
of human recombinant interleukin-2 (IL-2) for 72 hours.
T- and natural killer (NK)-cell clones and polyclonal lines used
in this study were obtained from purified T- or NK-cell populations
by the use of a PHA-dependent microculture system, as previously
described." They were expanded in IL-2-containing medium and
characterized for their surface markers expression by indirect immunofluorescence and cytofluorimetric analysis, using commercially
available MoAbs, as previously described."
MoAbs to HOXAIO and HOXD4 were produced and characterized as previously described.IxFor the assessment of reactivity with
anti-HOX MoAbs, cells werewashed in mediumwithout FCS,
attached to poly-L-lysine-coated multitest slides (ICN Biomedicals,
San Francisco, CA), and fixed in cold methanouacetone (501.50v011
vol). After drying, slides were saturated with phosphate-buffered
saline (PBS) containing 10% FCS and then stained overnight at 4°C
withthe appropriate dilution of 4C5, 3B2, or D7.87 anti-HOX
MoAbs or with UCHT-I (anti-CD3 MoAb, kindly provided byDr
Peter Beverley, ICRF, London, UK) or with an irrelevant MoAb
as controls. After five washings, fluorescein isothiocyanate (FITC)Blood, Vol 85, No 8 (April 15). 1995: pp 2084-2090
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2085
EXPRESSION OF HOXC4 IN ACTIVATED HUMAN LYMPHOCYTES
Fig 1. Staining of human
4C5 (antiPBLs with
MoAb
HOXD4 [A through F]), MoAb
D7.87 (anti-HOXAlO [GI), MoAb
382 (anti-HOXCG[HI), or an irrelevant MoAb (11. (AI Resting PBLs;
(B through F1 PBLs at 3,6,12,48,
or 72 hours, respectively, after
stimulation with PHA; (G, H, and
I) PBLs 72 hours after stimulation with PHA. Cells were
attached to poly-L-lysin-coated
slides, fixed in methanollacetone, and stained by indirect
immunofluorescence. Original
magnification x630.
conjugate goat antimouse Ig was added for 2 hours. The slides were
washed extensively and scored for positivity.
For immunoprecipitation. Sf9 cells were labelled for I hour with
1 0 0 pCi of "S-methionine 2 days after infection with the relevant
recombinant Baculovirus. The nuclear extract, obtained as previously described," was incubated for I hour with the 4C5 antibody
and rotated for 3 hours with 50 pL of Sepharose-bound protein A.
After washing three times with PBS, the Sepharose beads were
boiled in gel loading buffer and loaded onto a 12% polyacrylamide
gel.
RNA Analysis
RNase profection. Cytoplasmic RNA was extracted and hybridized overnight in 40-pp aliquots to radiolabeled RNA probes corresponding to the analyzed HOX genes or actin RNA probe at 55°C.
Mixtures were then digested with RNase A and TI ( I hour at 32°C)
and proteinase K, extracted with phenol-chlorophorm. and precipitated in ethanol. Electrophoresis was performed on a 6% polyacrylamide sequencing gel, which was then dried and exposed for 24 to
48 hours at -70°C to Kodak XAR5 film (Eastman Kodak, Rochester,
NY). Quantitation of the relative amounts of protected mRNA was
performed by standard densitometry.
Northern blot. Total RNA was extracted by the guanidine thiocyanate technique. Poly(A)' was selected by one passage on oligo
(dT) cellulose column, run in 25 pg on 1 .0% agarose-formaldehyde
gel, and transferred to nylon membrane by Northern capillary blot-
ting. Filters were hybridized to IO7 cpm of HOXC4 probe labeled
bynick translation to a specific activity of 3.6 X 10' dpmlmg,
washed at high stringency (final wash. 0. I % sodium dodecyl sulfate
[SDS]. 0.1X SSC at60°C).and exposed for 72 hours toKodak
XAR5 film. HOXC4 probe was a 250-bp EcoRIIHindlll clone.
Gel Retardation and Southwestern Blot Analysis
Mobility shift experiments were performed with the blunt-ended
double-stranded oligonucleotide 4B-26 (S'GCCAAGCCCAITobtained
AGGCTACCTGAACT3') as described." Nucleiwere
from resting and from 24-hour PHA-activated PRLs by centrifugation at 1 0 0 g of cells lysed in PBS containing 0.5% NP40 and 10
mmol/L MgClz through a cushion of 0.25 mol/L sucrose containing
I O mmolIL MgCI2. After two washings in 0.25 moln sucrose, the
nuclear extract was obtained resuspending the nuclear pellet in 2
v01 of 25 mmollL HEPES, pH 7.9, 620 mmol/LNaCI, I mmol/L
DIT, and I mmol/L MgClz (buffer HS). Purifiednucleoliwere
preparedfromthenuclei
by successive cycles of sonication and
centrifugation through a cushion of 0.88 mol/L sucrose. "Core"
nucleoli were prepared by digestion with 25 mglmL of DNase I for
30 minutes at room temperature. Nucleolar extracts were obtained
by resuspending the nucleolar pellet in 2 v01 of buffer HS.
For Southwestern blot analysis, a nucleolar extract from resting
or PHA-activated lymphocytes was subjected to SDS-polyacrylamide gel electrophoresis (SDS-PAGE) in a 12% polyacrylamide
gel and transferred to nitrocellulose according to standard proce-
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MEAZZA ET AL
2086
Table 1. Reactivity of Normal andNeoplastic Lymphoid
Cells With Anti-HOX MoAbs
Reactivity With MoAb
Anti-HOXt
Cells
Lineage (phenotype).
Polyclonal line
Polyclonal line
Clone G1.MV
Clone DM 2.6
Clone DM4.8
Polyclonal line
Clone
Line 82
Line 51
Jurkat
MOLT 13
MOLT 4
H9
CEM
RAJ1
T(CD3'4'8-TCRdfl')
T(CD3'4-8'TCRdfl')
T(CD3'4TTCRylb')
T(CD3'4%TCRa/@')
T(CD3'4-8+TCRa/fl')
NK(CD3-16')
NK(CD3-16')
EBV-transformed B cell
EBV-transformed B cell
T-ALL
T-ALL
T-ALL
T-ALL
T-ALL
Burkitt's lymphoma
A10
C6
D4
-
-
++
NT
NT
NT
-
-
-
the nucleolus, which displays characteristic morphologic
changes along the replicative cellcycle.*" Thus, a single
bright spot was evident at 6 to 24 hours after PHA stimulation, corresponding to the single large nucleolus typical of
the GI phase of the cell cycle, whereas, at 48 to 72 hours,
several spots were observed, in accordance with the nucleo-
++
++
++
2!F:
++
++
++
m
++
++
++
z
'$ A
a
a
v)
I
W I
0,
a n
+
+
-l -l
W
++
X
g
n
2
m m m
n n n a
a
=
4
B
i
m
+
++
++
+++
Abbreviation: NT, not tested.
Surface antigens of clones and polyclonal T o r NK cell lines were
studied by indirect immunofluorescence and cytofluorimetric analysis.
t Reactivity of anti-HOX MoAbs was evaluated by indirect immunofluorescence on fixed cells and scored by fluorescence microscope
examination.
HOXC4
&
cr
a
YI
.&
_
dures. The blot was then denaturatedrenaturated, incubated with the
radioactive oligonucleotide, and washed as previously described."
RESULTS
Reactivity of Resting and Activated Lymphocytes With
Antihomeoprotein MoAbs
We have analyzed the expression of three different human
HOX proteins in resting and activated lymphocytes by means
of the MoAbs D7.87, 3B2, and 4C5, which react with the
homeoproteins HOXAIO, HOXC6 and HOXD4, respectively. These MoAbs were raised against recombinant proteins produced in insect cells using the baculovirus expression system" and specifically reacted with nuclear extracts
of infected cells expressing the respective immunizing homeoprotein. Indirect immunofluorescence onfixed
cells
showedthat a small proportion of resting PBLs (ranging
from 3% to 15% in 5 different donors) was weakly stained
by 4C5 (anti-HOXD4) MoAb (Fig 1A). Conversely, most of
the PHA-stimulated PBLs displayed a bright nuclear staining
with this MoAb (Fig IB through F). Similar data were obtained when anti-CD3 MoAb was used as mitogenic stimulus
(data not shown). In timekourse experiments, the staining
pattern changed significantly after PHA stimulation. A significant nuclear staining was observed as soon as 3 hours
after stimulation, was distinctly visible after 6 hours, and
reachedmaximal intensity at 24 hours. The staining was
concentrated in a single bright spot in each nucleus from 6
to 24 hours after stimulation, whereas several (up to 5 ) nuclear spots were observed at 72 hours. This pattern of nuclear
staining mayreflect a localization of immunoreactivity in
*
yl
ACTlh
Fig 2. (Left) RNase protection analysis of total RNA (40 mg) from
Jurkat, resting PBLs, PHA-activated PBLs, cycloheximide-treated
PHA-activated PBLs, and Raji cells hybridized t o HOXC4 probe (250bp €coRI/Hindlll clone). Expression of human p-actin is shown
as an
internal control. (Right) Northernblot analysis of the HOXC4 mRNAs
in poly (AI' RNA from PHA-activated PBL. Twenty-five micrograms
of poly (A)' RNa was loaded in each lane.
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2087
EXPRESSION OF HOXC4 IN ACTIVATED HUMAN LYMPHOCYTES
Table 2. Expression of HOXA4, B4. C4. and D4 Genes
in Lymphoid Cells by RNAse Protection Assay
1
HOX Gene
PBLs Resting
PHA-Activated PELS
Raji
Jurkat
A4
B4
c4
D4
-
-
+l-
NT
-
+++
-
+++ ++++
-
+++
++++
-
2
3
-
-
Abbreviation: NT, not tested.
lar fragmentation occurring in the progression of the cell
cycle. Parallel .'H-thymidine uptake experiments confirmed
that DNA synthesis started after 48 hours of stimulation
(data not shown). No immunoreactivity was observed using
3B2 and D7.87 MoAbs in both resting (Fig IC and H) and
activated PBLs (data not shown). We further investigated
the reactivity of these MoAbs in cultured human T-cell
clones and polyclonal lines mantained in culture with recombinant 1L-2 (rIL-2) for different time intervals ( I to 4 weeks).
As shown in Table I , this analysis showed that 4C5 MoAb
reacted with all the T cells analyzed, independently of the
CD4/CD8 surface phenotype and of the T-cell receptor
(TCR) molecules (either cd,O or ylb) expressed. Also, in
these cells, 3B2 and D7.87 MoAbs displayed no immunoreactivity. In addition, the human T-cell leukemia lines Jurkat,
Molt4, Moltl3, CEM, and H9 were stained by 4C5 MoAb
(Table l ) . We next investigated the reactivity of the antibody
in activated B- and NK-lymphoid cells. As shown in Table
I , resting tonsilar B-cell populations displayed little or no
reactivitywith4CSMoAb,
whereas B-cell blasts induced
by SAC + rIL-2, Epstein-Barr virus (EBV)-transformed Bcell lines, the Raji Burkitt's lymphoma cell line, and IL-2cultured polyclonal CD3-16+ NK-cell lines were brightly
36 KD
+
29 KD
Fig 4. SDS-PAGE analysis of the material immunoprecipitatedby
4C5 antibody from nuclear extracts of Sf9 cells labeled with 35S-methionine. Lane 1, HOXCG-transfected Sf9 cells; lane 2, HOXD4transfected Sf9 cells; lane 3, HOXC4-transfectedSf9 cells. The arrows
indicate the position of the molecular weight markers (Glyceraldehyde-3-phosphatedehydrogenase and carbonic anhydrase).
stained by 4C5 MoAb. All these cells displayed a similar
pattern of immunoreactivity consisting of single or multiple
nuclear spots. Therefore, a nuclear immunoreactivity with
4C5 MoAb is characteristic of activated and/or proliferating
lymphocytes, independently of their B-, T-, or NK-cell lineage.
Resting and PHA-Activated Normal T Lymphocytes and
Jurkat and Raji Cell Lines Express HOXC4 But Not
HOXD4 mRNA
Fig 3. Staining of Sf9 cells with MoAb 4C5 (anti-HOXD4). (A) Cells
expressing the HOXD4 protein; (B) cells expressing the HOXC4 protein; (Cl cells expresingthe HOXCG protein; and (D) uninfected cells.
It is known that HOX genes are organized in four clusters
on different chromosomes. These clusters can be aligned so
that the genes are grouped into 13 vertical groups on the
basis of their position in the chromosomes. The vertically
aligned genes are referred to as paralogs and display a very
high degree of homology.'" Therefore, there is a high probability that a MoAb raised against a particular homeoprotein
encoded by an HOX gene displays cross-reactivity with the
homeoproteins encoded by the paralog genes. To test
whether the reactivity to 4C5 MoAb in lymphocytes was
related to HOXD4 gene expression or to the expression of the
paralog genes HOXA4, HOXB4, or HOXC4, we performed
RNase protection experiments using probes specific for the
four different paralogs. As shown inFig 2 and Table 2,
resting PBLs, PHA-activated PBLs, and Raji and Jurkat cells
expressed mRNA specific for the HOXC4 gene, in accordance to previous reports,'3 whereas HOXD4 mRNAwas
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MEAZZA ET AL
2088
Fig 5. Effectof cycloheximide and actinomycin D treatment on
the expression of HOXC4 by human PHA-activated PBLs. (A) PBLs 8
hours after stimulation; (B) PBLs 8 hours after stimulation treated
with cycloheximide; (D) PBLs 8 hours after stimulation treated with
actinomycin D; and (C) unstimulated untreated control PBLs. Cells
were fixed and stained with 4C5 MoAb as in Fig l.
undetectable in all cells tested. HOXA4 and HOXB4
mRNAs were also undetectable in resting and PHA-stimulated normal lymphocytes and in Jurkat cells. However, Raji
cells expressed both HOXA4 andHOXB4. Therefore, the
only HOX4 paralog expressed in activated T lymphocytes
isHOXC4. These data wereconfirmed by Northernblot
analysis performed on poly-A’ RNA extracted from PHAactivated PBLs and Raji cells with a HOXC4-specific cDNA
probe. Two transcripts of 2.8 and 1.9 kb, corresponding to
different forms of HOXC4 mRNA, were detected in activated PBLs (Fig 2) and Raji cells (data not shown). Therefore, it is evident that only HOXC4 could represent the homeoprotein identified by4CS MoAb in lymphoid cells. In
this context, it was important to assess whether the antiHOXD4 MoAb 4C5 could also react with the HOXC4 protein. We then analyzed the reactivity of this MoAb on Sf-9
cells expressing HOXC4, using the baculovirus expression
system. As shown in Fig 3, the anti-HOXD4 MoAb reacted
in a similar manner, with Sf9 cells expressing either HOXD4
(A) or HOXC4 (B). whereas no reactivity was detected in
uninfected cells (D) or in Sf9 cells expressing HOXC6 (Fig
3C). EVX I , HOXA 10, HOXB7, EMX l , EMX2, or OTX2
homeoproteins (data not shown). The reactivity of the antibody was also assessed by immunoprecipitation analysis of
25S-methionine-labeled protein extracts from HOXDC,
HOXCC, and HOXC6-transfected Sf9 cells, respectively.
The antibody recognizes in the first two extracts a protein
with the correct molecular weight (“kD), whereas no bands
are visible in the immunoprecipitate from the extract from
HOXC6-transfected cells (Fig 4).
The presence of HOXC4 mRNA also in resting lymphocytes, in which only a weak staining with 4CS MoAb was
observed in a small proportion of cells, maybe explained
in different ways. The expression of HOXC4 protein may
be regulated at the posttranscriptional level so that very low
amounts or no HOXC4 protein is present in resting lymphocytes. Alternatively, the HOXC4 protein maybe diffusely
present in the cytoplasm, in which it may fail to react with
4C5 MoAb. Cell activation would result in the entrance of
the HOXC4 protein in the nucleus and the subsequent concentration of this protein in the nucleolus would allow its
detection by MoAb 4C5. To test these hypotheses, we studied the immunoreactivity with 4C5 MoAb in lymphocytes
that had been stimulated with PHA for 8 hours in the presence of either actinomycin D (0.5 mg/mL) or cycloheximide
(50 mmol/L). Actinomycin D,which blocks transcription,
only partially inhibited immunoreactivity, whereas a complete inhibition was observed in the presence of cycloheximide, which blocks mRNA translation into proteins (Fig 5).
These data indicate that HOXC4 protein is indeed rapidly
synthesised after PHA activation and, together with the finding that HOXC4 mRNA is present also in resting lymphocytes, suggest that the expression of HOXC4 in activated
lymphocytes is regulated at the posttranscriptional level.
Evidence for a 32-kD DNA-Binding Homeoprotein in the
Nucleoli of Activated Lvmphocytes
Because further characterization of the HOX protein identified in activated lymphocytes could not be performed by
Western blotting because the 4C5 MoAb does not recognize
the denaturated protein or by immunoprecipitation because
of the very small amount of protein, we performed gel retardation assays on nucleolar extracts fromresting or PHAactivated lymphocytes. These assays were performed using
the synthetic oligonucleotide 4B-26, known to bindwith
l
2
A
BOUND
1
2
B
*
4-45
-36
-29
4-24
FREE -b
n
Fig 6.Presence
of a 32-kD DNA-binding homeoprotein inthe
nucleoli of activated lymphocytes. (A) Gel retardation assay with the
radiolabeled oligonucleotide 48-26. Lane 1, nucleolar extract from
PBLs 24 hours after stimulation with PHA; lane 2, unstimulated PBLs.
(B) Southwestern analysis with the oligonucleotide 48-26. Lane 1,
unstimulated PBLs; lane 2, PBLs 24 hours after PHA stimulation.
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EXPRESSION OF HOXC4 IN ACTIVATED HUMAN LYMPHOCYTES
2089
high affinity to HOXD419 and to other homeoproteins belonging to the same paralogy group, which share the same
homeodomain. As shown in Fig 6A, nucleolar extracts of
activated lymphocytes contained a DNA-binding protein capable of binding to 4B-26, whereas no DNA-binding activity
was observed in the nucleoli of resting PBLs.
The molecular characteristics of the DNA-binding protein
present in the nucleoli of activated PBLs were analyzed by
Southwestern blot. Nucleolar extracts were size-fractionated
by SDS-PAGE, blotted, and probed with radiolabeled 4B26 in the presence of an excess of unlabeled poly(d1-dC)(dIdC). As shown in Fig 6B, a single band of approximately
32 kD was detected only in the nucleolar extracts of activated
lymphocytes; this molecular weight is comparable to that of
the recombinant HOXC4 protein produced in Sf9 cells.
tion may indicate a regulatory role on genes present in the
nucleolus, such as those encoding for ribosomal RNA and
other unknown genes. In this context it is well known that
resting lymphocytes display a relatively low number of ribosomes and a low level of protein synthesis that sharply increase during the blastic transformation. On the other hand,
these results do not imply that the HOXC4 homeoprotein
localizes exclusively in the nucleolus. The homeoprotein
could be present elsewhere in the nucleus at a concentration
below the sensitivity of immunofluorescence and yet high
enough to exert its regulatory activity on genes involved in
the activation and/or proliferation of lymphoid cells. Resting
T lymphocytes have an amount of HOXC4 mRNA comparable to that of activated T lymphocytes, but the homeoprotein
is synthesized only after stimulation. This finding indicates
that its synthesis is regulated at the translational level. The
existence of this type of regulation notonly implies the
need for an immediate synthesis of HOXC4 upon activation,
suggesting a regulatory role of the early stages of lymphocyte
stimulation, but also that the presence of a Hox protein
should not be inferred on the basis of the expression of its
mRNA alone and should be confirmed either by immunologic or functional evidence.
DISCUSSION
Taken together, these data indicate that the HOXC4 homeoprotein is expressed in the nucleus of proliferating lymphocytes of the T, B, and NK lineages. The synthesis of
HOXC4 in T cells starts immediately after mitogen stimulation and the homeoprotein accumulates in the nucleus several
hours before the onset of DNA replication and cell proliferation. The localization of the immunoreactivity, together with
the changes in the number of nuclear spots along the proliferREFERENCES
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1995 85: 2084-2090
Expression of HOXC4 homeoprotein in the nucleus of activated
human lymphocytes
R Meazza, A Faiella, MT Corsetti, I Airoldi, S Ferrini, E Boncinelli and G Corte
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