Regulation of ribosomal RNA gene transcription during retinoic acid-induced differentiation of mouse teratocarcinoma cells.

We have examined the mechanism of regulation of rRNA synthesis in mouse F9 teratocarcinoma cells that were induced to differentiate by retinoic acid and dibutyryl cAMP. Ribosomal RNA (rRNA) synthesis was significantly reduced during differentiation of F9 cells into parietal endoderm cells. Nuclear run-on assay revealed that the rRNA gene transcription rates were reduced in differentiated cells, and this phenomenon could be mimicked by in vitro transcription assay using nuclear extracts prepared from F9 stem and F9 parietal endoderm cells. Analysis of the DNA-binding activities of two RNA polymerase I (pol I) transcription factors E1BF/Ku and UBF revealed decreased affinity for their cognate recognition sequences. Immunoblot analysis showed a marked reduction in the amounts of E1BF/Ku and UBF in the differentiated cells. Analysis of the steady-state RNA levels for the smaller subunit of E1BF/Ku and for UBF in differentiating F9 cells revealed decreased mRNA synthesis and increase in message level for the differentiation-specific marker laminin B1 with progression of the differentiated status of the cells. This study has demonstrated that differentiation of mouse F9 teratocarcinoma cells into parietal endoderm cells leads to diminished rRNA synthesis, which may be mediated by reduced DNA-binding activities and amounts of at least two pol I transcription factors.