| Research Abstract |
With fluorescently labeled S1-1 isoform specific antibodies and PML isoform specific antibodies, we examined the nuclear bodies of cultured human normal cells (TIG3S), HeLa cells, various normal rat tissues, and various human tumor tissues with the corresponding normal tissues. In young TIG3S cells, S1-1 nuclear bodies were rarely observed, but PML2, 4, 5, 6 nuclear bodies were observed significantly. Furthermore, co-localization of S1-1 and PML6 nuclear bodies was confirmed. In HeLa cells, S1-1 nuclear bodies were hardly observed. In addition, the remarkable cytoplasmic localization of S1-1 and of PML protein, significant nuclear bodies of PML2 and PML6, and rare nuclear bodies of PML4 and PML5 were observed. We confirmed the rare S1-1 nuclear bodies in dividing young TIG3S and HeLa cells. In addition, the S1-1p110 protein levels of young TIG3S and HeLa cells were very low, on the contrary, the S1-1p130 protein was at very high levels. Furthermore, the S1-1p130 level of HeLa cells was 3-fold higher than TIG3S cells. PML and S1-1(RBM10) have many phosphorylation sites by CK2 and PKC, and HeLa cells have significantly higher activity of CK2 than normal cells. Thereby, the PML isoforms which are phosphorylated (S517 of PML) by CK2, degrade in the proteasomes. However, S1-1p130 (RBM10 variant-1) was very stable even in HeLa cells. HeLa and TIG3S cells, which administered with PKC or CK2 inhibitor, significantly developed the S1-1 nuclear bodies. This suggests that the assembly of S1-1 nuclear bodies was suppressed through their phosphorylation by CK2 in the actively dividing cells. In the presence of PKC or CK2 inhibitor, but not CDK2 inhibitor, cell division of HeLa or TIG3S cells was strongly impaired, and the drugs promoted cell death. Our results suggest that S1-1 and PML nuclear bodies regulate the cell growth and promote the cell death pathway
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