Expression of Granulocyte Colony Stimulating Factor (G-CSF) and Granulocyte/Macrophage Colony Stimulating Factor (GM-CSF) mRNA upon Stimulation with Phorbol Ester

Stimulated human peripheral blood mononuclear cells (MNC) have been shown to express both G-CSF and GM-CSF. Furthermore, G-CSF is expressed by monocytes but not lymphocytes, whereas GM-CSF is expressed largely by T lymphocytes and at low levels in monocytes/macrophages. Here we present the effect of TPA (12-O-tetradecanoyl phorbol-13-acetate) on G-CSF and GM-CSF expression in stimulated human MNCs and T lymphocytes. We observed that TPA (30nM) decreased G-CSF mRNA levels in MNCs, while ionomycin increased G-CSF in a dose-dependent manner. TPA and ionomycin individually increased GM-CSF mRNA levels in T-lymphocytes and MNCs. Further, GM-CSF was induced synergistically by TPA plus ionomycin, whereas this combination markedly decreased G-CSF mRNA levels in MNCs. These data suggest at least two signaling pathways by which G-CSF and GM-CSF mRNA levels are modulated in a mixed population of monocytes and T lymphocytes, namely protein kinase C (PKC) and calcium. These signals seem to act synergistically in lymphocytes to increase GM-CSF, and not G-CSF mRNA levels specifically. It would also appear these signals act on MNCs in an opposing manner to decrease G-CSF mRNA levels, indicating that activation of PKC and the calcium signaling pathway lead to a cell-type specific modulation of individual cytokines and precise regulation of granulocyte production