The C-terminal Kinase and ERK-binding Domains of Drosophila S6KII (RSK) Are Required for Phosphorylation of the Protein and Modulation of Circadian Behavior

• Published in: The Journal of biological chemistry 2012-05, Vol.287 (20), p.16748-16758
• Main Authors: Tangredi, Michelle M., Ng, Fanny S., Jackson, F. Rob
• Format: Article
• Language: English
• Subjects: Animals; Behavior, Animal - physiology; Circadian; Circadian Clocks - physiology; Drosophila melanogaster; Drosophila Proteins - genetics; Drosophila Proteins - metabolism; ERK; Mutagenesis, Site-Directed; Mutation; Neurobiology; p90 Ribosomal S6 Kinase; Phosphorylation - genetics; Protein Structure, Tertiary; Ribosomal Protein S6 Kinases, 90-kDa - genetics; Ribosomal Protein S6 Kinases, 90-kDa - metabolism; Rsk; S6 Kinase; Signal Transduction
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M111.315929

A detailed structure/function analysis of Drosophila p90 ribosomal S6 kinase (S6KII) or its mammalian homolog RSK has not been performed in the context of neuronal plasticity or behavior. We previously reported that S6KII is required for normal circadian periodicity. Here we report a site-directed mutagenesis of S6KII and analysis of mutants, in vivo, that identifies functional domains and phosphorylation sites critical for the regulation of circadian period. We demonstrate, for the first time, a role for the S6KII C-terminal kinase that is independent of its known role in activation of the N-terminal kinase. Both S6KII C-terminal kinase activity and its ERK-binding domain are required for wild-type circadian period and normal phosphorylation status of the protein. In contrast, the N-terminal kinase of S6KII is dispensable for modulation of circadian period and normal phosphorylation of the protein. We also show that particular sites of S6KII phosphorylation, Ser-515 and Thr-732, are essential for normal circadian behavior. Surprisingly, the phosphorylation of S6KII residues, in vivo, does not follow a strict sequential pattern, as implied by certain cell-based studies of mammalian RSK protein. S6KII (RSK) kinase is important for neuronal plasticity and behavior. Using genetic approaches, we identified functional S6KII domains relevant for circadian behavior. ERK binding to S6KII and activation of its C-terminal kinase modulate circadian period whereas the N-terminal kinase is dispensable for circadian function. This is the first in vivo structure/function analysis of S6KII (RSK) in the context of behavior.