FOCAL ALTERED COMPARTMENTATION OF REPETITIVE B2 (ALU-LIKE) SEQUENCES IN RAT-LIVER FOLLOWING HEPATOCARCINOGEN EXPOSURE

Rats were treated with low doses of the hepatocarcinogens dimethylnitr osamine or thioacetamide, and livers were examined 48 h later. These t reatments are known to produce altered RNA compartmentation, wherein a class of repetitive RNA sequences normally restricted to the nucleus appears in the cytoplasm. Reverse transcription-PCR amplifications dem onstrated that the sequences showing altered compartmentation consiste d largely of a subfamily of the rodent B2 sequence family, the counter part of human Alu sequences involved in retrotransposition. Northern b lot analyses showed that these B2 sequences were found in cytoplasmic RNA as 170- to 360-nucleotide ''sense'' transcripts, and competition h ybridization experiments established that B2 sequences represented mos t (if not all) of the sequences showing altered compartmentation. The major increase in B2 transcripts in cytoplasmic RNA was not associated with any change in B2 transcription by RNA polymerase III. In situ hy bridizations showed that the altered compartmentation of B2 sequences occurred in well-delineated foci within rat liver; these foci consiste d of a central region containing a prominent infiltrate of macrophages admired with small hepatocytes and a peripheral region of histologica lly normal hepatocytes that showed evidence of oxidative damage. Alter ed compartmentation of B2 sequences may represent an important focal i nitiatory change in a subset of hepatocytes, whereas subsequent retrot ranspositional events (associated with Alu-like sequences) could predi spose initiated cell foci to alterations in promotion/progression phas es.