GSK3β-Dependent Phosphorylation Alters DNA Binding, Transactivity and Half-Life of the Transcription Factor USF2

The upstream stimulatory factor 2 (USF2) is a regulator of important cellular processes and is supposed to have also a role during tumor development. However, the knowledge about the mechanisms that control the function of USF2 is limited. The data of the current study show that USF2 function is regulated by phosphorylation and identified GSK3 beta as an USF2-phosphorylating kinase. The phosphorylation sites within USF2 could be mapped to serine 155 and threonine 230. In silico analyses of the 3-dimensional structure revealed that phosphorylation of USF2 by GSK3 beta converts it to a more open conformation which may influence transactivity, DNA binding and target gene expression. Indeed, experiments with GSK3 beta- deficient cells revealed that USF2 transactivity, DNA binding and target gene expression were reduced upon lack of GSK3 beta. Further, experiments with USF2 variants mimicking GSK3 beta phosphorylated USF2 in GSK3 beta-deficient cells showed that phosphorylation of USF2 by GSK3 beta did not affect cell proliferation but increased cell migration. Together, this study reports a new mechanism by which USF2 may contribute to cancerogenesis.