Mitogen- and stress-activated kinase 1-mediated histone H3 phosphorylation is crucial for cell transformation

Mitogen- and stress-activated kinase 1 (MSKI) belongs to a family of dual protein kinases that are activated by either extracellular signal-regulated kinase or p38 mitogen-activated protein kinases in response to stress or mitogenic extracellular stimuli. The physiologic role of MSKI in malignant transformation and cancer development is not well understood. Here, we report that MSKI is involved in 12-O-tetradecanoyl-phorbol-13-acetate (TPA)-induced or epidermal growth factor (EGF)-induced neoplastic transformation of JB6 C141 cells. H89, a potent inhibitor of MSKI, strongly suppressed TPA-induced or EGF-induced cell transformation. When cells overexpressing wild-type MSKI were treated with TPA or EGF, colony formation increased substantially compared with untreated cells or cells that did not overexpress MSK1. In contrast, MSK1 COOH terminal or NH2 terminal dead dominant negative mutants dramatically suppressed cell transformation. Introduction of small interfering RNA-MSK1 into JB6 CI41 cells resulted in suppressed TPA-induced or EGF-induced cell transformation. In addition, cell proliferation was inhibited in MSKI knockdown cells compared with MSKI wild-type cells. In wild-type MSKI-overexpressing cells, activator protein (AP-1) activation increased after TPA or EGF stimulation, whereas AP-1 activation decreased in both MSKI dominant-negative mutants and in MSKI knockdown cells. Moreover, TPA-induced or EGF-induced phosphorylation of histone H3 at Ser(10) was increased in wild-type cells but the induced phosphorylation was abolished in MSK1 dominantnegative mutant or MSKI knockdown cells. Thus, MSKI is required for tumor promoter-induced cell transformation through its phosphorylation of histone H3 at Ser(10) and AP-1 activation.