FBXO25 Promotes Cutaneous Squamous Cell Carcinoma Growth and Metastasis through Cyclin D1.

FBPs are components of the SCF protein E3 ubiquitin ligase and can specifically bind to substrates and thereby regulate multiple tumor behaviors. However, the role of FBPs, FBXO25 in particular, in cutaneous squamous cell carcinoma (cSCC) has not been explored yet. In this study, we found FBXO25 to be highly expressed in cSCC in mice and in vitro, whereas it was significantly less expressed in normal keratinocytes. Stable silencing of FBXO25 in SCC13 cells led to reduced tumor growth, and the knockdown of FBXO25 was accompanied by downregulation of cyclin D1. Correspondingly, stable overexpression of cyclin D1 in FBXO25-deficient SCC13 tumors increased tumor growth, supporting the hypothesis that FBXO25 promotes cSCC growth and metastasis through cyclin D1. Moreover, we found FBXO25 and cyclin D1 interaction to be facilitated through the repressor (Oct-1) of cyclin D1. Our data indicate that Oct-1 interacts directly with FBXO25 and undergoes downregulation, consequently stabilizing cyclin D1 and promoting tumor growth and metastasis.