PA2G4 and gallbladder cancer: circERBB2, containing exons 3 to 7 of ERBB2, bound and promoted nucleolus localization of PA2G4, a modulator of ribosomal DNA (rDNA) transcription, to form a circERBB2-PA2G4-TIFIA complex and increase Pol I activity and rDNA transcription in gallbladder cancer (109).