Fos-related antigen 1 (Fra-1) pairing with and transactivation of JunB in GBM cells

Fos-related antigen 1 (Fra-1) plays an important role in maintenance/progression of various cancers, including glioblastoma multiforme (GBM). In this study, we used both shRNA and siRNA to examine the effect of fra-1 knockdown in GBM cells over-expressing Fra-1. Furthermore, we analyzed both the expression of JunB and its knockdown, a previously identified target for Fra-1, and also examined its potential association with Fra-1. When using fra-1 shRNA and siRNA, we found that GBM cells has Fra-1 levels diminished together with the levels of JunB, but Fra-1 remains unchanged in cells with junB knockdown. This is accompanied by dramatic changes in cell morphology and significant alteration in their migration. We next uncovered that the expression of JunB increased in response to ectopic Fra-1 and also to EGF-induced signaling, similarly to Fra-1. This was associated with an avid pairing between phosphorylated Fra-1 and JunB. Importantly, we found that Fra-1 paired with JunB binds to an AP-1 site in the junB gene promoter. JunB knockdown did not affect Fra-1 and the changes in cell morphology did not fully replicate that seen with Fra-1 knockdown. Thus, Fra-1 takes part in a control of architecture and migratory nature of GBM cells. Moreover, Fra-1 is a phosphorylated factor that transactivates JunB with which it makes effectively AP-1 pairs in GBM cells.