[Transcription Factor Pax5 Promotes B-lymphomagenesis in a Promoter-Independent Manner]

To determine whether B lymphocyte-specific transcription factor Pax5 regulates B-lympho-magenesis without direct binding to promoter.

Mouse B-lymphoma cell line myc3 and 38B9 were infected with GFP^- tagged retrovirus that encodes wide type or various mutant pax5 genes. After viral infection for 48 hours, the percentage of GFP positive lymphoma cells was determined by flow cytomety. The percentage of GFP positive tumor cells was further monitored every 3 days in vitro or once the tumor was formed in vivo. Both cell cycle and apoptic cell number of GFP positive lymphoma cells were analyzed using flow cytometry.

Similar to the infection with wild type Pax5 retrovirus, infection with Pax5 mt 1-357 and Pax5 mt 304-358 that lacks of DNA binding motif can strongly increase the percentage of GFP⁺ B-lymphoma cells both in vitro and in vivo (P<0.01), while infection with empty viral vector migR-GFP and Pax5 mt 1-143 containing only DNA binding motif failed to increase the percentage of GFP positive tumor cells (P>0.05). Moreover, the analysis of flow cytometry demonstrated that more B-lymphoma cells infected with wild type Pax5, Pax5 mt 1-357 and Pax5 mt 304-358 retroviruses entered S and G₂/M phases in comparison with those infected with empty viral vector migR-GFP and Pax5 mt 1-143. Apoptotic rates among different groups were not significantly changed.

Pax5 can promote B-lymphoma cell growth both in vitro and in vivo in a promoter-independent manner. This is mainly due to the accelerating of cell cycle rather than decreasing apoptosis. Our studies provide potential theory for restraing B-lymphomagenesis by targeting the specific Pax5 domains.