Induction of Protein Kinase C mRNA in Cultured Lymphoblastoid T Cells by Iron-Transferrin But Not by Soluble Iron

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 a-, p-, and yPKC subspecies. CEM cell mRNA hybridized with the p-subspecies probe but not with probes for aor y-subspecies. After exposure to FeTF an increase in PKC-p mRNA was detectable at 10 minutes, peaked at 12 hours, and was sustained for 72 hours. Nuclear transcription assays demonstrated that rates of PKC-p mRNA transcription were increased in FeTF-treated cells. By contrast, steady state levels of PKC-p 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-p mRNA, despite producing a marked increase in cellular ferritin content. Ferritin increased from a baseline value of 63 ng/106 cells to 98 and 100 ng/lO“ cells in CEM cells treated for 1 hour