In line with observations that SKP2 drives cellular proliferation, cAMP induces proliferation of neuroblastoma cells by upregulating SKP2 (Cho et al., 2007), while growth arrest and differentiation of neuroblastoma cell lines induced by retinoic acid, BMP2, and the HDAC inhibitor Helminthosporium carbonum toxin is accompanied by a decrease in SKP2 levels (Nakamura et al., 2003a,b; Cuende et al., 2008; Deubzer et al., 2008a). Here, HDAC9 is linked to neuroblastoma.