Priming effects of granulocyte-macrophage colony-stimulating factor are
coupled to cholera toxin-sensitive guanine nucleotide binding protein in
human T lymphocytes
A al-Aoukaty, A Giaid, C Sinoff, AD Ho and AA Maghazachi
Northeastern Ontario Regional Cancer Centre, Sudbury, Ontario, Canada.
In addition to the mobilization of neutrophils and monocytes,
granulocyte-macrophage colony-stimulating factor (GM-CSF) also mobilizes
lymphocytes into peripheral blood. We examined the ability of GM-CSF to
induce the proliferation of purified human T cells (CD3+ CD4+ CD56- CD16-
B1- MO2-) in two major aspects: (1) the mechanisms of GM- CSF interaction
with interleukin-2 (IL-2) causing T-cell proliferation, and (2) the
intracellular signals transmitted by GM-CSF in T lymphocytes. We observed
that concentrations of GM-CSF between 0.01 ng/mL and 10 ng/mL had a
synergistic effect with concentrations of IL-2 between 1 U/mL and 10 U/mL
in stimulating T-cell proliferation. This effect of GM-CSF was maximal when
it was added at the start of the culture. In situ hybridization showed the
presence of mRNA for GM-CSF receptors in T cells. Further analysis showed
that GM-CSF induced the expression of IL-2 receptor (IL-2R) on the surface
of T lymphocytes. These events coincide with the ability of GM-CSF to
increase the intracellular levels of both cyclic 3',5'-adenosine
monophosphate (cAMP) and cyclic 3',5'-guanosine monophosphate (cGMP) in T
cells, to increase the binding of (gamma-35S) GTP to T-cell membranes, and
to enhance GTPase activity as determined by increased hydrolysis of 32P-
GTP. IL-2 also induced IL-2R expression, cyclic nucleotide secretion, and
G-protein activation. However, the presence of IL-2 reduced GM-CSF
induction of these activities. Addition of antibodies to the alpha and beta
subunits of IL-2R permitted the activation of G protein by GM-CSF even when
IL-2 was present. Furthermore, GTP binding and GTPase activity induced by
GM-CSF or IL-2 were inhibited by the addition of cholera toxin (CT), but
not pertussis toxin (PT). Cumulatively, these results suggest that in T
lymphocytes, receptors for GM-CSF or IL-2 may be coupled to the same
CT-sensitive G protein, although other possibilities may exist. The role
that G proteins play in mediating the intracellular signaling pathways
induced by GM-CSF or IL-2 in human T cells is supported by adenosine
diphosphate-ribosylation of a 44-kD or a 39-kD G protein in T-cell
membranes by CT and PT, respectively.
Volume 83,
Issue 5,
pp. 1299-1309,
03/01/1994
Copyright © 1994 by The American Society of Hematology
