1141636674 Differential serine and tyrosine phosphorylation of Signal Transducer and Activator of Transcription 3 (STAT3) in Jeg‐3 choriocarcinoma cell lines

Abstract

Background: Signal Transducer and Activator of Transcription 3 (STAT3) is an intracellular signalling molecule, which is used by several cytokines, including leukemia inhibitory factor (LIF), epithelial growth factor (EGF), and interleukin‐6 (IL‐6). It induces a variety of gene transcripts and cell functions. In trophoblast cells and in tumor cells, its tyrosine phosphorylation is directly linked to their invasiveness. The regulation and function of STAT3 serine phosphorylation is still widely unclear.Material and Methods: Jeg‐3 choriocarcinoma cells were stimulated with different concentrations of EGF, IL‐6 and LIF. STAT3 serine (727) and tyrosine (705) phosphorylation were analyzed 5–60 min after stimulation by SDS‐PAGE electrophoresis followed by Western blotting.Results: Jeg‐3 cells display spontaneous STAT3 serine phosphorylation. 100 ng/mL EGF induces a time‐dependent reduction starting 15 min after stimulation. Tyrosine phosphorylation does not occur spontaneously, but is strongly induced by EGF at all analyzed time points. LIF induces tyrosine phosphorylation, but affects serine phosphorylation only very slightly. IL‐6 did not influence neither serine phosphorylation nor tyrosine phosphorylation.Discussion: The EGF induced STAT3 tyrosine phosphorylation may be responsible for its invasion triggering capacities. The parallel reduction of serine phosphorylation may enhance this effect. LIF was formerly shown to enhance trophoblast invasion via STAT3 tyrosine phosphorylation. IL‐6 displays very little effects on STAT3 and seems to use other pathways for signalling.