Cell Systems Biology of Translation Factors and Proteasome-Targeted Protein Complexes Associated with AGC Kinase Sch 9

Abstract

Sch-9 appears to be the Saccharomyces cerevisiae homolog of protein kinase B and S6 kinase and is involved in the control of numerous nutrient-sensitive processes, including regulation of cell size, cell cycle progression, and stress resistance. Sch-9 has also been implicated in the regulation of replicative and chronological life span. The availability of data from global studies of protein-protein interactions now makes it possible to predict and validate functional connections between Sch-9, its putative substrates, and other proteins. Sch-9 appears to be involved in control of biosynthetic and catabolic pathways. Thus, the analysis of Sch-9-associated proteins indicates that this kinase may be involved in regulation of protein synthesis. Sch-9 forms a complex with, and, presumably, phosphorylates starvation- and stress-induced protein kinase GCN2, which, in turn, phosphorylates translation initiation factor eIF2-alpha. Sch-9 also interacts with translation factors Arc1, Pab1 and prion-like protein Sup-35. Thus, Sch-9 may be part of the mechanism that relays availability of nutrients to utilization of glucose and to the rates of protein synthesis. One of the interesting outcomes of the proteome-wide analysis of protein-protein interactions in yeast is the finding that Sch-9 associates with Shp1, Cdc48, and Ufd1, which form a complex responsible for the recognition and targeting of ubiquitinated proteins to the proteasome for degradation. It is unknown and remains to be elucidated, whether mammalian paralogues of Sch-9 are also associated with the proteins involved in translation/protein synthesis and proteasomal degradation.