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MR Hassuneh, PS Nagarkatti and M Nagarkatti
Department of Biology, Virginia-Maryland Regional College of Veterinary
Medicine, Blacksburg 24061, USA.
In the current study, we investigated the role of interleukin-2 (IL-2) and
IL-4 as autocrine growth factors responsible for autonomous growth of four
murine tumor cell lines: LSA, a radiation leukemia virus- induced T-cell
lymphoma; EL-4, a chemically triggered T-cell lymphoma; PE-3T, a T-cell
line that underwent spontaneous transformation ex vivo; and P815, a
mastocytoma. All tumor cell lines screened constitutively expressed IL-2
receptor (IL-2R) and IL-4R genes. However, only LSA and PE-3T cells
expressed IL-2 and IL-4 genes constitutively, whereas EL-4 and P815 tumor
cells expressed only IL-4 but not IL-2. Monoclonal antibodies (MoAbs)
against IL-2, IL-4, or a combination of these, as well as MoAbs against
IL-2R significantly inhibited the proliferation of LSA but not that of
other tumor cell lines ex vivo. To exclude the possibility that, in other
tumor cell lines, the autocrine growth factor may interact with its
receptor within the cell, the ability of antisense phosphorothioate
oligonucleotides to inhibit the growth of the tumor cells was tested. The
antisense phosphorothioate oligonucleotides specific for IL-2, IL-4, IL-2R
beta, or IL-2R gamma chains, added in culture, could markedly inhibit the
growth of LSA but not that of the other tumor cell lines screened. Inasmuch
as IL-2R beta and IL-2R gamma subunits also serve as a component of the
receptors for IL-4, IL-7, IL-9, and IL-15, the above data suggested that
such cytokine redundancy was not responsible for autonomous growth of the
other tumor cell lines. Addition of exogenous IL-2 or IL-4 to the tumor
cell cultures caused significant enhancement in the proliferation of PE- 3T
cells, whereas other cell lines were either not significantly affected or
slightly inhibited from growing. Interestingly, the LSA tumor growth in
nude mice was significantly inhibited after treatment of these mice with a
combination of MoAbs against IL-2 and IL-4. Together, our studies show for
the first time that IL-2 and IL-4 may serve as autocrine growth factors in
the autonomous proliferation of tumor cells, particularly those that are
retrovirally induced. Second, some tumor cell lines, despite expressing
certain cytokines and their receptors constitutively, may not depend
exclusively on such factors for autocrine growth.
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| Copyright © 1997 by American Society of Hematology Online ISSN: 1528-0020 | |||||||||