Abstract

Suramin is a well known antitrypanosomal drug and a novel experimental agent for the treatment of several cancers, yet the molecular mechanisms through which suramin exerts its effects on cell functions are not completely clear. In this study, we investigated the potential of suramin to activate the mitogen-activated protein kinase cascade in cultured Chinese hamster ovary (CHO) cells. The treatment of CHO cells with suramin increased the enzyme activity of extracellular signal-regulated kinases (ERK1/2) approximately 10-fold dose and time dependently. The EC₅₀ value was approximately 2.4 μM. This activation is inhibited by PD98059 and wortmannin/LY294002, indicating a crucial role for mitogen-activated protein kinase kinase (MEK) and phosphatidylinositol 3-kinase (PI3K), respectively. Suramin-mediated stimulation of PI3K was confirmed by the observation that suramin stimulates the phosphorylation of protein kinase B (Akt) in a wortmannin-sensitive manner. Furthermore, cAMP response element-binding protein, a transcription factor, was also activated by suramin in a MEK-dependent manner. The suramin-induced phosphorylation of cGMP-dependent protein kinase was also suggested by a solid-phase kinase assay. The suramin effects on CHO cells were shown to have a concomitant increase in DNA synthesis, which was attenuated by PD98059. Similar activation of ERK1/2 activity by suramin was observed in other cell lines such as Chinese hamster lung or PC12 cells, but not in RBL2H3, ECV304, and OVK18 cells, indicating a cell-type specific mechanism for suramin. These results indicate that suramin induces mitogenic activity in several cell lines through the pathway from PI3K to MEK and ERK.