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
Istituto Nazionale per la Ricerca sul Cancro, Genova, Italy.
We have analyzed the expression of homeoproteins of the HOX family in
resting and activated lymphoid cells and in neoplastic lymphoid cell lines
by the use of monoclonal antibodies (MoAbs) already shown to react with the
homeoproteins HOXA10, HOXC6, and HOXD4, respectively. Anti-HOXA10 and C6
MoAbs DIDi not show any reactivity with the lymphoid cells tested, whereas
anti-HOXD4 MoAb stained few resting peripheral blood lymphocytes (PBLs) and
most phytohemagglutinin (PHA)-stimulated PBLs as early as 6 hours after
stimulation. The pattern of staining of PHA-activated PBLs is reminiscent
of the stages 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 polyclonal T and natural killer
(NK) cells, with leukemic T- cell lines, and with a Burkitt's lymphoma cell
line. RNAse protection experiments, per formed with probes specific for
HOXD4 or for the highly homologous HOXA4, HOXB4, and HOXC4, belonging to
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 retardation and Southwestern blot assays
showed the presence of a 32-kD homeoprotein with DNA-binding 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.
Volume 85,
Issue 8,
pp. 2084-2090,
04/15/1995
Copyright © 1995 by The American Society of Hematology
