Induction of protein kinase C mRNA in cultured lymphoblastoid T cells by
iron-transferrin but not by soluble iron
O Alcantara, M Javors and DH Boldt
Audie L. Murphy VA Hospital, San Antonio, TX.
Iron-transferrin (FeTF) is an essential growth factor required for
proliferation of lymphoid cells. FeTF activates protein kinase C (PKC) in
the lymphoblastoid T-cell line, CCRF-CEM. We have treated CEM cells with
human FeTF, then examined levels of PKC mRNA by hybridization analysis
using cDNA probes specific for alpha-, beta-, and gamma-PKC subspecies. CEM
cell mRNA hybridized with the beta-subspecies probe but not with probes for
alpha- or gamma-subspecies. After exposure to FeTF an increase in PKC-beta
mRNA was detectable at 10 minutes, peaked at 12 hours, and was sustained
for 72 hours. Nuclear transcription assays demonstrated that rates of
PKC-beta mRNA transcription were increased in FeTF-treated cells. By
contrast, steady state levels of PKC-beta mRNA did not increase after
treatment of cells with apotransferrin or gallium TF. Similarly, treatment
with soluble iron as ferric ammonium citrate did not increase steady state
levels of PKC-beta mRNA, despite producing a marked increase in cellular
ferritin content. Ferritin increased from a baseline value of 63 ng/10(6)
cells to 98 and 100 ng/10(6) cells in CEM cells treated for 1 hour with
ferric ammonium citrate or FeTF, respectively. FeTF did not increase
cytoplasmic-free calcium in CEM cells loaded with fura-2, indicating that
binding of FeTF to transferrin receptors did not open membrane Ca2+
channels or release intracellular Ca2+. In addition, pretreatment of cells
with desferrioxamine, but not ferrioxamine, blocked the FeTF-induced
increase in PKC-beta transcripts. Therefore, iron as FeTF (not soluble iron
or nonferric TF) stimulates transcription of the CEM cell PKC-beta gene.
Transcriptional rate of the PKC-beta gene does not correlate with cellular
iron content as judged by ferritin measurements. Furthermore, the
requirement for FeTF does not appear to reflect activation of a classic
agonist pathway as judged by stable cellular Ca2+. These data suggest that
delivery of iron by FeTF to one or more specific cellular compartments may
stimulate PKC-beta gene transcription in CEM cells.
Volume 77,
Issue 6,
pp. 1290-1297,
03/15/1991
Copyright © 1991 by The American Society of Hematology
