Biopolymers and cell. 2005; 21 (5): 407 - 412

The beta subunit of casein kinase 2 as a novel binding partner of the ribosomal protein S6 kinase 1

G. G. Panasyuk, I. O. Nemzanyy, A. M. Zhyvoloup, V. V. Filonenko, I. T. Gout

Signaling pathways play a major role in regulation and coordination of many cellular processes. The kinases of 40S ribosomal subunit protein, S6K, S6K1 and S6K2, are an important player in signaling network. S6K belongs to and are regulated via PI3-kinase signaling pathway. It is known that S6K1 plays a key role in the regulation of mitogen activated protein biosynthesis facilitated by phosphorylation of ribosomal protein S6 that leads to the translation initiation of mRNA encoding components of the protein synthesis apparatus. Moreover, the participation of S6K1 in the regulation of cell cycle was found. Several protein kinases and phosphatases can use S6K as a substrate in vitro, but only for some of them the functional link to S6K has been demonstrated in vivo that is why molecular mechanisms of regulation of S6K activity in the cell remain unclear. Because of that it is very important to investigate protein targets of S6K in the cell, especially with the use of methodological approaches which would correspond to the conditions in vivo. The yeast-two hybrid system is a modern technique widely used in the world for the identification of protein-protein interactions in vivo. Using activated form of S6K1 as a bait, eight novel binding partners of S6K1 were identified. Among them the interaction between S6K1 and ( regulatory subunit of casein kinase 2 has been discovered. Bioinformatic analysis of the primary structure of S6K1 and S6K2 has shown the presence of several potential CK2 phosphorylation sites, the Ser17 in S6K1 being the most preferential. Further studies have confirmed that S6K1 is phosphorylated at Ser17 by CK2 in the conditions of in vitro kinase reaction. The formation of S6K1/S6K2 beta complex has been proven in vitro as well.