Identification of glycyrrhizin-binding protein kinase as casein kinase II and characterization of its associated phosphate acceptors in mouse liver

Two forms (G-I and G-II kinases) of casein kinase II (CK-II) in a partially purified CK-II fraction (Mono Q fraction) of mouse liver were separated by means of glycyrrhizin (GL)-affinity column chromatography. Biochemical characterization revealed that these two GL-binding kinases were identical to CK-II. Two phosphate acceptors [p99 (pI 7.0) and p56] copurified with CK-II were identified as ERp99 (Hsp-90 family protein) and calreticulin, respectively. Another protein [p100 (pI 9.0)], which crossreacted with anti-serum against human glucocorticoid receptor (GR). was associated with ERp99, Phosphorylation of p99 [a heterocomplex of p99 (pI 7.0) and p100 (pI 9.0)] and p56 by CK-II in vitro was stimulated significantly by low levels (1-3 mu M) of GL, but inhibited significantly at doses above 20 mu M, However, no effect of GL on autophosphorylation of ERp99 was detected. The data provided here suggest that GL can regulate CK-II-mediated phosphorylation involved in the GL-induced biological effects in mammalian cells. (C) 1996 Academic Press, Inc.