Identification and Functional Characterization of FMN2, a Regulator of the Cyclin-Dependent Kinase Inhibitor p21

The ARF tumor suppressor is a central component of the cellular defense against oncogene activation in mammals. p14ARF activates p53 by binding and inhibiting HDM2, resulting, inter alia, in increased transcription and expression of the cyclin-dependent kinase inhibitor p21 and consequent cell-cycle arrest. We analyzed the effect of p14ARF induction on nucleolar protein dynamics using SILAC mass spectrometry and have identified the human Formin-2 (FMN2) protein as a component of the p14ARF tumor suppressor pathway. We show that FMN2 is increased upon p14ARF induction at both the mRNA and the protein level via a NF-κB-dependent mechanism that is independent of p53. FMN2 enhances expression of the cell-cycle inhibitor p21 by preventing its degradation. FMN2 is also induced by activation of other oncogenes, hypoxia, and DNA damage. These results identify FMN2 as a crucial component in the regulation of p21 and consequent oncogene/stress-induced cell-cycle arrest in human cells. ► Proteomic analysis reveals that ARF induces FMN2 ► ARF, DNA damage, and hypoxia induce FMN2 transcription in a p53-independent manner ► FMN2 promoter is negatively regulated by NF-κB and E2F1 ► FMN2 regulates p21 protein levels by forming a complex and preventing its degradation