Fig. 2.

Several mechanisms for forming chromosomal loops in cancer. Pol II (orange), transcription factors (green) and co-transcription factors (yellow) are always recruited by long-range loop mediators in transcription factories. a Most loops are mediated by CTCF and cohesin, with or without other mediators. b ERα is another common mediator that functions after binding E2 and entering the nucleus. c Pol II can mediate long-range loops between promoters, suggesting that promoters sometimes act as enhancers. d MED1 acts as a chromosomal loop mediator only when it is phosphorylated. e Some lncRNAs can mediate chromosomal loops. f CUX1 is special in that it mediates the binding of two enhancers to one promoter, and when its expression is reduced to 50%, it mediates the binding of one enhancer to one promoter