Human ARF protein interacts with Topoisomerase I and stimulates its activity

The ARF gene (p19(ARF) in mouse and p14(ARF) in man) has become a central a ctor of the cell cycle regulation process as it participates to the ARF-MDM 2-p53 pathway and the Rh-E2F-1 pathway. By use of immunoprecipitation and W estern blotting (IP/WB), we now show that ARF physically associates with To poisomerase I(Topo I), ARF-Topo I immune complexes were detected in SF9 ins ect cells infected with recombinant baculoviruses encoding the two genes as well as in 293 cells that express endogeneously these proteins. Preparatio ns of a GST-ARF recombinant protein stimulated the DNA relaxation activity of Topo I but, in contrast, had no effect an the decatenation activity of T opo TT, The Topo I stimulation was also detected in cell extracts of SF9 ce lls expressing both proteins, A confocal microscopy study indicated that pa rt of ARF and Topo I colocalized in the granular component structure of the nucleolus. As a whole, our data indicate that Topo I is a new partner of A RF and suggest that ARF is involved in cell reactions that require Topo I.