Functional expression of c-kit by acute myelogenous leukemia blasts is
enhanced by tumor necrosis factor-alpha through posttranscriptional mRNA
stabilization by a labile protein
MA Brach, HJ Buhring, HJ Gruss, LK Ashman, WD Ludwig, RH Mertelsmann and F Herrmann
Department of Internal Medicine I, University of Freiburg Medical Center,
Germany.
The c-kit proto-oncogene encodes a transmembrane glycoprotein identical to
the receptor for the recently cloned stem cell factor (SCF). The present
study examines constitutive synthesis of transcripts in primary acute
myelogenous leukemia (AML) blasts and the effects of recombinant human
tumor necrosis factor (TNF)-alpha on c-kit mRNA expression in these cells.
The c-kit transcripts were detectable at low levels in 10 of 10 different
AML samples investigated. TNF treatment of AML cells was associated with
enhanced c-kit mRNA expression in all specimens. Nuclear run-on
transcription assays indicated that the c-kit gene was transcriptionally
active in all leukemias examined and the rate of transcription was
unaffected by exposure to TNF, suggesting posttranscriptional control
mechanisms of c-kit mRNA accumulation. In the absence of TNF, the half-life
of c-kit transcripts was 2 to 3 hours, while in TNF-treated AML cells,
c-kit half-life was found to be 5 to 9 hours. Inhibition of protein
synthesis reduced TNF-induced c-kit mRNA expression by Northern blot
analysis, but did not affect the rate of c-kit gene transcription. In the
presence of inhibition of protein synthesis, the half-life of c-kit
transcripts in TNF-induced leukemia cells decreased to 2 to 4 hours. These
findings indicate that levels of c-kit mRNA are controlled by a labile
protein that is involved in TNF- mediated stabilization of c-kit
transcripts. The effects of TNF-alpha also extended to the protein level in
that TNF-alpha treatment of primary AMLs was associated with enhanced
surface expression of the SCF receptor by some of these cells. While
exogenous SCF induced clonogenic growth of all primary AML samples
investigated, TNF-alpha failed to stimulate leukemic cells to proliferate.
However, the combination of SCF and TNF-alpha resulted in synergistic
growth stimulation in seven of nine different AML specimens investigated.
The finding of transmodulation of the SCF receptor through
posttranscriptional modifications might further contribute to our
understanding of the synergistic interplay of TNF-alpha and SCF.
Volume 80,
Issue 5,
pp. 1224-1230,
09/01/1992
Copyright © 1992 by The American Society of Hematology
