CK2

Casein kinase 2 is exceptional among CMGC kinases in being constitutively active and insensitive to second messengers. Two catalytic genes, CSNK2A1 (alpha) and CSNK2A2 (alpha'), assemble with the CSNK2B regulatory beta subunit into an alpha2beta2 holoenzyme that phosphorylates acidic consensus sequences of the form Ser/Thr-x-x-Asp/Glu. Its substrate list runs into the hundreds and spans NF-kappaB activation, Wnt signaling, circadian timing, DNA repair, suppression of apoptosis and ribosome biogenesis. CK2 is consistently overexpressed or hyperactive in tumors and supports cell survival, which has driven clinical development of ATP-competitive inhibitors including silmitasertib (CX-4945) and the halogenated benzimidazole TBB.