Tumor Necrosis Factor Induces Phosphorylation of a 28-kDa mRNA Cap-Binding Protein in Human Cervical Carcinoma Cells

Tumor necrosis factor α (TNF-α ) stimulated the phosphorylation of a 28-kDa protein (p28) in the ME-180 line of human cervical carcinoma cells. The effect of TNF-α on the phosphorylation state of p28 was rapid (4-fold increase within 15 min) and persistent, remaining above the basal level for at least 2 hr. The specific binding of 125I-labeled TNF-α to cell-surface binding sites, the stimulation of p28 phosphorylation by TNF-α , and the inhibition of cell proliferation by TNF-α occurred with nearly identical dose-response relationships. Two-dimensional SDS/PAGE resolved p28 into two isoforms having pI values of 6.2 and 6.1. A phosphorylated cap-binding protein was substantially enriched from lysates of control or TNF-α -treated ME-180 cells by affinity chromatography with 7-methylguanosine 5′-triphosphate-Sepharose. The phosphoprotein recovered from this procedure was the substrate for TNF-α -promoted phosphorylation, p28. Thus, TNF-α stimulates the phosphorylation of this mRNA cap-binding protein, which may be involved in the transduction of TNF-α -receptor binding into cellular responses.