Towards Selective CK2α and CK2α’ Inhibitors: a Novel Screening Assay by Autodisplay of Heterotetrameric Human Protein Kinase CK2

Bollacke A, Le Borgne M, Jose J

Abstract

Novel inhibitors that target the human protein kinase CK2 are of great interest in the development of new therapeutics for the treatment of cancer. The human protein kinase CK2 commonly occurs as aheterotetrameric enzyme, the so called CK2 holoenzyme, and is composed of two catalytically active α- and/or α’-subunits attached to a dimer of non-catalytically active β-subunits [1]. We recently reported thesuccessful co-expression of CK2 subunits α and β on the cell surface of Escherichia coli via Autodisplay and demonstrated the interaction of the surface presented CK2 subunits, as well as the possibleapplication for the purpose of inhibitor screening by a CE-based assay [2].We herein describe the successful Autodisplay of a paralogous isoform of the catalytically active CK2 subunit, the CK2α’-subunit. Analysis of the kinase activities at different NaCl concentrations for theindividually expressed α’-subunit and for the α’-subunit and the non-catalytically active β-subunit co-expressed, confirms the interaction of the subunits on the cell surface. We further illustrate the potentialapplication of the two surface presented CK2 holoenzymes as a novel inhibition assay by the evaluation of the CK2 inhibitor TMCB which is known to have a different affinity towards the two isoforms [3].Additionally the system was used to screen a small library of CK2 inhibitors with an indeno[1,2-b]indole scaffold [4-6] in order to identify a selective inhibitor of CK2α or CK2α’. Our results demonstrate that thisassay allows the discovery of CK2 inhibitors with a distinct effect on the two different catalytically active CK2 isoforms, thus enabling the identification of inhibitors with a selective affinity towards either CK2α orCK2α’.