Involvement of glycogen synthase kinase-3beta in arsenic trioxide-induced p21 expression.

摘要

Arsenic trioxide (ATO) has been effectively used as a therapeutic agent to treat acute promyelocytic leukemia and solid tumors, via induction of cell cycle arrest or apoptosis. In our previous studies, we suggest that c-Jun might act as an adapter to regulate p21(WAF1/CIP1) (p21) expression in response to ATO. Therefore, how to regulate the c-Jun to bind to the p21 promoter was further elucidated. It has been reported that glycogen synthase kinase-3beta (GSK-3beta) can phosphorylate the C-terminus (Ser243) of c-Jun to decrease its protein stability and DNA-binding ability and can also increase the degradation of p21 in resting condition or under ultraviolet irradiation. Therefore, we hypothesized that ATO-induced p21 expression might be through the inhibition of GSK-3beta. Using the DNA affinity precipitation assay, ATO could dephosphorylate the C-terminus (Ser243) of c-Jun to enhance its binding to the p21 promoter and resultant p21 expression. ATO, as well as LiCl (GSK-3beta inhibitor), could induce GSK-3beta(Ser9) phosphorylation and p21 expression in a time- and dose-dependent manner. Constitutively active GSK-3beta, FlagGSKCA, and constitutively inactive GSK-3beta, FlagGSKCI, were constructed to further confirm the involvement of GSK-3beta in the ATO-induced p21 expression. However, the stability of p21 protein was increased by ATO, but not LiCl treatment using cycloheximide. Furthermore, ATO-induced GSK-3beta(Ser9) phosphorylation was through the ERK pathway, but not the PI3K/Akt pathway. We suggest that, taken together, ATO-induced ERK phosphorylation could inhibit GSK-3beta activity to dephosphorylate the C-terminus (Ser243) of c-Jun to increase p21 expression and resultant cell death.