In vitro changes of the nuclear AgNORs pattern induced by RNA inhibitors and 5-fluorouracil in human breast cancer cells, MCF-7 and HBC-4

The morphological changes of argyrophilic nucleolar organizer regions (AgNO Rs) were studied in two human breast cancer cell lines, MCF-7 and HBC-4. Tr eatment with an RNA polymerase inhibitor (actinomycin D) reduced the size o f AgNORs and increased the number of AgNORs. Messenger RNA polymerase inhib itor (alpha-amanitin) also increased the number of AgNORs. However, transla tional blocking agents closely related to ribosomal RNA (cycloheximide and anisomycin) caused a decrease in the number of AgNORs, which seemed to fuse to an aggregate around the nucleolus and formed a single large spherical A gNOR in the final stage. These changes were observed typically when cells w ere treated with 5-fluorouracil or 5-fluorouridine. These morphological cha nges in the AgNORs pattern, AgNORs aggregation, might reflect certain damag e in ribosomal RNA. (C) 1998 Elsevier Science Ireland Ltd. All rights reser ved.