Blood, Vol. 92 No. 10 (November 15), 1998:
pp. 3979-3979
CORRESPONDENCE
Significance of Enhanced Cytokine Receptor Expression by
Glucocorticoids
 |
LETTER |
To the Editor:
As antiproliferative agents, glucocorticoids (GCs) exert their effects
by several mechanisms, the most significant of which being inhibition
of cytokine production and action.1 In addition, GCs
upregulate the expression of select proinflammatory cytokine receptors
directly or indirectly in association with growth factors or other
factors,2,3 thereby augmenting cytokine effects on target
cells. This enhancement of cytokine receptor was specific for the GCs,
required de novo receptor synthesis, and resulted in increased receptor
density but not affinity.4,5 However, the
effect of GCs on interleukin-2 receptor (IL-2R) remain
controversial, because they were shown to either inhibit
IL-2R
6 or enhance high-affinity IL-2R directly or
indirectly in association with IL-2,3 thus raising the
possibility that the reduction in IL-2R expression may be due to
earlier blockade of IL-2 synthesis by GCs. Furthermore, it was reported
that GCs may decrease or increase IL-2R expression and hence the
response to IL-2 stimulation depending on the extent of T-cell
activation.7 The effect of GCs on IL-2R must then be viewed
in the context of direct effect of GCs on IL-2R and the contribution of
IL-2 blockade by GCs on subsequent IL-2R expression.
In light of the reported worsening of the outcome of diseases treated
by GCs, including allograft rejection and autoimmunity, upon
short-term/abrupt GCs withdrawal, which often necessitated brief pulses
of high-dose GCs,8 we assessed the effect of GCs withdrawal
on IL-2R expression and the subsequent response to recombinant IL-2 (rIL-2) stimulation. Our working
hypothesis was that pre-exposure of activated T cells to GCs enhances
cytokine receptor expression, thereby conferring a higher stimulation
index upon restimulation with the respective ligand after GCs are
withdrawn. To mimic GCs withdrawal, human peripheral blood T cells were
treated with the GCs dexamethasone (DEX) or prednisolone (PRED);
preactivated with mitogens (phytohemagglutinin
[PHA] + phorbol myristate acetate [PMA]), receptor cross-linking
antibodies (anti-CD28 Ab + PMA), or the CD3-bypass stimulation
regimen PMA + ionomycin; and cultured for 4 to 48 hours at 37°C.
The cells were then washed (at least 3× with phosphate-buffered
saline [PBS] ) and reactivated with rIL-2. Cytokine receptor
expression was determined by FACS analysis, and T-cell proliferation
was quantitated by measuring the cellular uptake of tritiated
thymidine.
Whereas DEX and PRED directly suppressed IL-1, IL-2, IL-6, and other
cytokine mRNA expression at the transcriptional and posttranscriptional levels,1 pretreatment of activated T cells with DEX (Fig
1) or PRED (data not shown) resulted in
a significant enhancement in (type I) IL-1R, IL-2R (CD25), and IL-6R
(Fig 1). This GCs-induced increase in cytokine receptor expression was
the result of enhanced mRNA expression for the three receptors
(determined by reverse transcription-polymerase chain reaction
[RT-PCR]) and was blocked by the antimetabolites
actinomycin D and cycloheximide, indicating the requirement for de novo
receptor synthesis.
View larger version (38K):
[in this window]
[in a new window]
| Fig 1.
Flow cytometric analysis of (type I) IL-1R, IL-2R
(CD25), and IL-6R expression on T cells pretreated with DEX (0.1 µmol/L; right panels) or a corresponding volume of ethanol (left
panels) and stimulated with PHA (5 µg/mL) + PMA (5 ng/mL; dark
tracings). Light tracings represent cytokine receptor expression by PHA + PMA-stimulated cells; the first (light) tracing represents
background fluorescence. Shown is a representative of three
individually performed experiments.
|
|
GCs enhancement of cytokine receptor expression resulted in augmented
cytokine effect on GCs-pretreated cells. In GCs-pretreated and
mitogen-preactivated T-cell cultures, stimulation with rIL-2 resulted
in a significant concentration-dependent enhancement in proliferation
(P < .05 v ethanol- or medium-pretreated cultures) at all concentrations of GCs (DEX) tested (Fig
2). This enhancement in rIL-2-driven
responses was not specific for the stimulation regimen (PHA + PMA)
used in the preactivation phase, because comparable responses were
obtained using anti-CD28 Ab + PMA or PMA + ionomycin as an alternative
stimulation regimen. Furthermore, the enhancement in IL-2R (CD25)
was not due to possible GCs-induced alteration in cell
viability/apoptosis,9 because the cell viability of GCs-pretreated and PHA + PMA-preactivated cultures was essentially similar to that of ethanol-pretreated and preactivated cultures (Fig
3).
View larger version (12K):
[in this window]
[in a new window]
| Fig 2.
Pretreatment with GCs enhances rIL-2-stimulated
proliferation. Proliferation of T cells preactivated and pretreated
with DEX ( ) or a corresponding volume of ethanol ( ) and
reactivated with rIL-2 + PMA. Data points represent the mean ± SEM
of four individually performed experiments. Proliferation of
unstimulated cells (negative control), 1,023 ± 403; rIL-2 ± PMA-stimulated cells (positive control), 27,076 ± 2,944. *P < .05 versus ethanol-pretreated cells.
|
|
View larger version (11K):
[in this window]
[in a new window]
| Fig 3.
Pretreatment with GCs does not alter cell viability. The
percentage of viability (determined by trypan blue exclusion principle)
of T cells activated and treated with DEX ( ) or a corresponding
volume of ethanol ( ). Data points represent the mean of 10 individually performed experiments.
|
|
In essence, GCs upregulation of cytokine receptor expression and the
accompanying enhancement in cytokine-driven response (proliferation)
are not transient events and are distinct from GCs effects on cytokine
gene expression or on cytokine-driven responses, both of which are
profoundly inhibited by GCs treatment. In contrast to suppression of
cytokine expression and cytokine-stimulated responses that require
continued GCs presence, this GCs-induced rebound phenomenon does not
require continued GCs presence. Whereas washing off GCs from
GCs-treated and stimulated cultures followed by resumption of
activation restored cytokine expression at the transcriptional and
posttranscriptional levels, it did not affect enhanced cytokine
receptor expression; in fact, a further increase in receptor densities
were detected in GCs-pretreated cultures. It is tempting to suggest
that this GCs-induced rebound is due to receptor supersensitivity,
where the expression of a specific receptor is upregulated in the face
of lost ligand (cytokine) expression.
Although the conclusion reached here was based on in vitro observation
using well-defined culture conditions; nevertheless, it provides a
plausible explanation for the reported increased morbidity that
frequently accompanies short-term GCs withdrawal. Although the cause of
this GCs-induced rebound phenomenon is not yet completely understood,
our study suggests that enhanced cytokine receptor expression on
activated T cells (and other cell types, most notably macrophages,
fibroblasts, and epithelial cells) by GCs,1 coupled with
sustained cytokine secretion reinstated after removal of GCs, induces
an exaggerated T-cell effector function that ultimately results in
increased morbidity. This also explains the reported efficacy of
high-dose GCs pulse or rapamycin (sirolimus) and other agents that act
by suppressing cytokine-mediated signaling events, but not cyclosporin
A, in controlling this GCs-induced rebound. Collectively, this
underscores the dual nature of GCs in regulating cytokine and cytokine
receptor expression; in essence, GCs suppress cytokine expression while
enhancing the expression of their high-affinity
receptors.
Wassim Y. Almawi
Department of Laboratory
Medicine
St George-Orthodox Hospital
Beirut, Lebanon
David A. Hess
Michael J. Rieder
Department of Pharmacology and
Toxicology
University of Western Ontario
London, Ontario,
Canada
| |
REFERENCES |
1.
Almawi WY, Beyhum HN, Rahme AA, Rieder MJ:
Regulation of cytokine and cytokine receptor by glucocorticoids.
J Leukoc Biol
66:563, 1996
2.
Hawrylowicz C, Guida L, Paleolog E:
Dexamethasone upregulates granulocyte-macrophage colony-stimulating factor receptor expression on human monocytes.
Immunology
83:274, 1994[Medline]
[Order article via Infotrieve]
3.
Lamas M, Sanz E, Martin-Parras L, Espel E, Sperisen P, Collins M, Silva AG:
Glucocorticoid hormones upregulate interleukin-2 receptor alpha gene expression.
Cell Immunol
151:437, 1993[Medline]
[Order article via Infotrieve]
4.
Re F, Muzio M, De Rossi M, Polentaruti N, Giri JG, Mantovani A, Colotta F:
The type II receptor as a decoy target for interleukin 1 in polymorpho-nuclear leukocytes: Characterization of induction by dexamethasone and ligand binding properties of the released decoy receptor.
J Exp Med
179:739, 1994[Abstract/Free Full Text]
5.
Gottschall PE, Koves K, Mizuno K, Tatsuno I, Arimura A:
Glucocorticoid upregulation of interleukin 1 receptor expression in a glioblastoma cell line.
Am J Physiol
261:E362, 1991[Abstract/Free Full Text]
6.
Batuman OA, Ferrero AP, Diaz A, Berger B, Pomerantz RJ:
Glucocorticoid-mediated inhibition of interleukin-2 receptor alpha and beta subunit expression by human T cells.
Immunopharmacology
27:43, 1994[Medline]
[Order article via Infotrieve]
7.
Krouwels FH, van der Heijden JF, Lutter R, van Neerven RJ, Jansen HM, Out TA:
Glucocorticosteroids affect functions of airway- and blood-derived human T cell clones, favoring the Th1 profile through two mechanisms.
Am J Respir Cell Mol Biol
14:388, 1996[Abstract]
8.
Hricik DE, Almawi WY, Strom TB:
Trends in the use of glucocorticoids in renal transplantation.
Transplantation
57:979, 1994[Medline]
[Order article via Infotrieve]
9.
Iseki R, Mukai M, Iwata M:
Regulation of T lymphocyte apoptosis: Signals for the antagonism between activation- and glucococorticoid-induced death.
J Immunol
147:4286, 1991[Abstract]
