Enhanced expression of the complement regulatory protein, membrane
inhibitor of reactive lysis (CD59), is regulated at the level of
transcription
MH Holguin, CB Martin, JH Weis and CJ Parker
Research Service, Veterans Affairs Medical Center, Salt Lake City, UT
84148.
The membrane inhibitor of reactive lysis (MIRL) is an 18-Kd glycosyl
phosphatidylinositol anchored membrane glycoprotein that inhibits the
cytolytic activity of complement. MIRL is expressed by all hematopoietic
elements and by a wide variety of nonhematopoietic tissues. A deficiency of
MIRL is primarily responsible for the greater sensitivity of the
erythrocytes of paroxysmal nocturnal hemoglobinuria to complement mediated
lysis. Because of its critical role in protecting host cells from injury by
complement, we hypothesized that mechanisms exist that allow MIRL
expression to be regulated. To investigate this hypothesis, both MIRL RNA
and MIRL protein expression were analyzed following exposure of K562
erythroleukemia cells to a variety of potential stimulants. Incubation with
dexamethasone, calcium ionophore, lipopolysaccharide, interleukin 1, tumor
necrosis factor, hemin, and cyclic AMP had no effect on MIRL expression.
However, incubation with phorbol 12-myristate 13 acetate (PMA), induced a
marked increase in MIRL RNA as determined by Northern blot analysis. This
enhanced expression of MIRL RNA was associated with an increase in MIRL
protein expression as determined by immunoprecipitation of metabolically
labeled proteins, Western blot analysis, and immunobinding assay. Enhanced
MIRL RNA expression was first detected after 8 hours and increased through
24 hours of observation. Inhibitors of either protein synthesis or
transcription abrogated the PMA-induced enhancement of MIRL RNA expression.
Together, these results are consistent with a model in which PMA induces
synthesis of a trans acting protein that enhances transcription of the MIRL
gene.
Volume 82,
Issue 3,
pp. 968-977,
08/01/1993
Copyright © 1993 by The American Society of Hematology
