The retinoblastoma-interacting zinc-finger protein RIZ is a downstream effector of estrogen action

Co-immunoprecipitation experiments in cell extract from cultured cells or t arget tissues indicated that estrogen receptor was complexed with the retin oblastoma binding protein RIZ in a ligand-dependent manner. Mapping of inte raction sites indicated that in bath proteins the same regions and motifs r esponsible for the interaction of transcriptional co-activator and nuclear receptors were involved. In cultured cells, estradiol induced a redistribut ion of RIZ protein within the nucleus and in the cytoplasm. A similar effec t was produced in vivo, in prepuberal rat endometrium, by administration of a physiological dose of estradiol. Therefore, RIZ protein could he a speci fic effector of estrogen action downstream of the hormone-receptor interact ion, presumably involved in proliferation control.