L. Comai et al., Inhibition of RNA polymerase I transcription in differentiated myeloid leukemia cells by inactivation of selectivity factor 1, CELL GROWTH, 11(1), 2000, pp. 63-70
Transcription by RNA polymerase I (pol I) regulates the rate of ribosome bi
ogenesis and the biosynthetic potential of the cell; therefore, it plays an
important role in the control of cell growth. Differentiation of the human
promyelocytic leukemic cell line U937 is accompanied by drastic decreases
in pol I transcriptional activity. We have used cell-free extracts prepared
from undifferentiated and differentiated U937 cells to investigate the mol
ecular mechanisms responsible for this inhibitory process. Our analysis ind
icates that the activity of the TATA binding protein (TBP)/TBP-associated f
actor (TAF) complex selectivity factor 1 (SL1), one of the factors required
for accurate and promoter-specific transcription by RNA pol I, is severely
repressed in differentiated U937 cells. Moreover, the reduction in SL1 act
ivity is not a consequence of a decrease in SL1, because there is no detect
able difference in the abundance of TBP or TAFs before and after U937 cell
differentiation. In conclusion, our results indicate that the selectivity f
actor SL1 is an important target for the regulation of pol I transcription
during cell differentiation.