In the course of retinoic acid-induced cell differentiation, formation of the complex between NPM1 (nucleophosmin) and TFAP2A (AP-2 alpha) homodimer, bound to the AP-2 alpha response element in the promoter of the NOP2 (p120) gene, represses transcription of the nucleolar protein NOP2. Transcriptional repression probably involves NPM1-mediated recruitment of histone deacetylases HDAC1 and HDAC2 to the NOP2 gene promoter (Liu et al. 2007). NOP2 is a proliferation marker (Valdez et al. 1992).