| Ribosomal S6 kinase 2 (S6K2) is a serine/threonine protein kinase in the AGC family of kinases. It was discovered after p70S6K (S6K1-S6 kinase 1) was thought to be the sole kinase involved with 40S ribosomal protein S6 phosphorylation. S6K2 is highly homologous to ribosomal S6 kinase 1 in the catalytic domains but differs from S6KI in the N- and C-terminal ends with nuclear localization signals, having a unique proline-rich region in the carboxyl terminal tail, and reacting differently when knocked-out in mammalian studies, amongst others. Since S6K2 is a more recent discovery, most published reports have focused on characterizing the protein itself and the events leading to and affecting S6K2 activation. We attempt here to find novel substrates for S6K2 that can potentially shed light on S6K2 function. To do this, new protein substrate search techniques are utilized including protein microarray, Pro-Q Diamond phosphoprotein staining, and MALDI-TOF-MS. We found three potential S6K2 substrate proteins via microarray screening: Protein Kinase C zeta (PKCzeta), Casine Kinase 1 gamma 1 (CK1gammal), and Casein Kinase 1 gamma 2 (CKl2gamma). PKCzeta and CKlgammal were proven to not be actual S6K2 substrates in live HEK293 cells. We observed that CK1gamma2 was phosphorylated in vitro, but whether CKIgamma2 is an in vivo substrate of S6K2 remains to be seen. |
