Abstract
To clarify the status of tax gene, we analyzed human Tβcell leukemia virus typeβI (HTLVβI) associated cell lines and fresh adult Tβcell leukemia (ATL) cells. We compared 2 types of HTLVβI associated cell lines: one was derived from leukemic cells (leukemic cell line) and the other from nonleukemic cells (nonleukemic cell line). Although all nonleukemic cell lines expressed Tax, it could not be detected in 3 of 5 leukemic cell lines, in which nonsense mutation or deletion (60 bp) of tax genes, and DNA methylation in 5β²βLTR were identified as the responsible changes. We found such genetic changes of the tax gene in 5 of 47 fresh ATL cases (11%). The tax gene transcripts could be detected in 14 of 41 fresh ATL cases (34%) by RTβPCR. In ATL cases with genetic changes that could not produce Tax protein, the tax gene was frequently transcribed, suggesting that such cells do not need the transcriptional silencing. Although DNA methylation of 5β²βLTR was detected in the fresh ATL cases (19 of 28 cases; 68%), the complete methylation associated with transcriptional silencing was observed only in 4 cases. Since partial methylation could not silence the transcription, and the tax gene transcription was not detected in 27 of 41 cases (66%), the epigenetic change(s) other than DNA methylation is considered to play an important role in the silencing. Β© 2004 WileyβLiss, Inc.