PSMC4 and neoplasm: The 26S proteasome is also dynamically phosphorylated during the cell cycle at the Thr25 of the 19S subunit Rpt3 mediated by dual-specificity tyrosine-regulated kinase 2 (DYRK2), whereas blocking Rpt3-Thr25 phosphorylation markedly impairs proteasome activity (as confirmed by decreased peptidase activities and degradation of the total proteins, GFP-degron fusion proteins targeted to Ub-dependent or independent degradation, and ATPase activity), promotes the accumulation of cell cycle inhibitors p21Cip1 and p27Kip1, and hampers cell proliferation and tumor growth [151].