Ribosomal Protein Rps8 Protein Translation Mechanism

Cyclin-dependent kinase 11 (CDK11) isoforms are members of the PITSLRE kinase superfamily and closely related to cell cycle regulation, oncogenesis, and apoptosis.During apoptosis, CDK11p110 and CDK11p58 are cleaved by caspases to generate a smaller 46-50 kDa protein which contains the catalytic kinase domain in the C-terminus of CDK11.CDK11p46 was demonstrated to play an important role in cell apoptosis. However, how CDK11p46 exactly promotes apoptosis is unclear.By using His pull-down and mass spectrometry analysis, we identified the ribosomal protein S8 (RPS8), a member of the small subunit ribosome, as an interacting partner of CDKllp46. Further analysis confirmed the association of CDK11p46 and RPS8 in vitro and in vivo, and revealed that RPS8 was not a substrate of CDK11p46. Moreover, RPS8 and CDKllp46 synergize to inhibit the translation process both in cap-and internal ribosomal entry site (IRES)-dependent way, and sensitize cells to Fas ligand-induced apoptosis. Taken together, our results provide evidence for the novel role of CDKllp46 in the regulation of translation and cell apoptosis. It is becoming increasingly evident that the regulation of translation plays a central regulatory role in cell growth, tumorigenesis and cell apoptosis. However the specific mechanism of translation control remains unclear. Ribosome is the component of cell that creates proteins from all amino acids and RNA representing the protein. It is composed of ribosomal proteins and rRNA. Studies have showed that ribosomal proteins and translation factors play a key role in regulation of protein synthesis. More importantly, the phosphorylation of these regulators usually regulates the function of these proteins.In part I, we found that RPS8 inhibited cap-dependent and cap-independent translation. We further predicted the potential phosphorylation sites of RPS8 by using the Scansite online software. Next, we constructed a series of phosphorylation site mutant which mimic the dephosphorylated or phosphorylated form of RPS8. By luciferase reporter gene assay, we found that the phosphorylation of T130 phosphorylation site of RPS8 may contribute to translation. Homology comparison was performed by Genedoc software and showed that T130 site is highly conserved in Mammalia and C. elegans. GPS2.1 software analysis suggested potential kinase of T130 site. Our research helps to further investigate the mechanism of RPS8 in translational regulation.