CASEIN KINASE-II ASSOCIATES WITH EGR-1 AND ACTS AS A NEGATIVE MODULATOR OF ITS DNA-BINDING AND TRANSCRIPTION ACTIVITIES IN NIH 3T3 CELLS

Although the activation domains within early growth response gene prot ein 1 (Egr-1) have been mapped, little is known of the kinases which p hosphorylate Egr-1 and how phosphorylation correlates with the transcr iptional activity of Egr-1. In this study we report that casein kinase II (CKII) co-immunoprecipitates with Egr-1 from NIH 3T3 cell lysates. The association of Egr-1 and CKII requires the C terminus of Egr-1 an d CKII phosphorylates Egr-1 in vitro. The in vitro phosphorylation of Egr-1 by CKII and that induced by serum in vivo was compared by examin ing the CNBr-digested fragments of the phosphorylated Egr-1, CKII stro ngly phosphorylates fragments 7 and 10 which cover part of the activat ion/nuclear localization and DNA binding domains of Egr-1. CKII also p hosphorylates, albeit weakly, fragments 5 and 8 which cover part of ac tivation domain and the entire repression domain of Egr-1, respectivel y. Strong phosphorylation on fragment 10 as well as fragment 5 was als o observed in Egr-1 immunoprecipitated from serum-induced, P-32-labele d cells. CKII phosphorylation of Egr-1 resulted in a decrease of its D NA binding as well as its transcriptional activities.