Figure 1.

Regulation of early transcriptional steps of ribosome biogenesis in CRC. MYC is overexpressed in colorectal tumor cells, binds to rDNA sequences, and in cooperation with UBF and SL1 factors, leads to the hyperactivation of RNA pol I-mediated synthesis of the 47S rRNA precursor [84]. MYC, in cooperation with RPF2 and RRS1, activates RNA pol II-mediated transcription of genes coding for ribosomal assembly factors and RPs, as well as RNA pol III-mediated synthesis of 5S rRNA [57]. Overexpression of the three rRNA polymerases and the associated factors is frequent in CRC [80,81,82,83]. Together with RPF2 (protein ribosome production factor 2 homolog), RRS1 cooperates with POL III and drives 5S rRNA synthesis, while POL II activates ribosomal proteins and assembly factors mRNAs and snoRNAs synthesis.