The human tumor suppressor ARF interacts with spinophilin/neurabin II, a type 1 protein-phosphatase-binding protein

The INK4a gene, one of the most often disrupted loci in human cancer, encod es two unrelated proteins, p16(INK4a) and p14(ARF) (ARF) both capable of in ducing cell cycle arrest. Although it has been clearly demonstrated that AR F inhibits cell cycle via p53 stabilization, very little is known about the involvement of ARF in other cell cycle regulatory pathways, as well as on the mechanisms responsible for activating ARF following onco-proliferative stimuli. In search of factors that might associate with ARF to control its activity or its specificity, we performed a yeast two-hybrid screen. We rep ort here that the human homologue of spinophilin/neurabin II, a regulatory subunit of protein phosphatase 1 catalytic subunit specifically interacts w ith ARF, both in yeast and in mammalian cells. We also show that ectopic ex pression of spinophilin/neurabin II inhibits the formation of G418-resistan t colonies when transfected into human and mouse cell lines, regardless of p53 and ARF status. Moreover, spinophilin/ARF coexpression in Saos-2 cells, where ARF ectopic expression is ineffective, somehow results in a synergic effect. These data demonstrate a role for spinophilin in cell growth and s uggest that ARF and spinophilin could act in partially overlapping pathways .