Article

Mitogen-activated 70K S6 kinase. Identification of in vitro 40 S ribosomal S6 phosphorylation sites.

Friedrich Miescher Institute, Basel, Switzerland.
Journal of Biological Chemistry (Impact Factor: 4.6). 12/1991; 266(33):22770-5.
Source: PubMed

ABSTRACT Recently we purified and cloned the mitogen/oncogene-activated Mr 70,000 (70K) S6 kinase from the livers of rats treated with cycloheximide (Kozma, S. C., Lane, H. A., Ferrari, S., Luther, H., Siegmann, M., and Thomas, G. (1989) EMBO J. 8, 4125-4132; Kozma, S. C., Ferrari, S., Bassand, P., Siegmann, M., Totty, N., and Thomas, G. (1990) Proc. Natl. Acad. Sci. U. S. A. 87, 7365-7369). Prior to determining the ability of this kinase to phosphorylate the same sites observed in S6 in vivo, we established the effects of different cations and autophosphorylation on kinase activity. The results show that the 70K S6 kinase is dependent on Mg2+ for activity and that this requirement cannot be substituted for by Mn2+. Furthermore, 50-fold lower concentrations of Mn2+ block the effect of Mg2+ on the kinase. This effect is not limited to Mn2+ but can be substituted for by a number of cations, with Zn2+ being the most potent inhibitor, IC50 approximately 2 microM. In the presence of optimum Mg2+ concentrations the enzyme incorporates an average of 1.2 mol of phosphate/mol of kinase and an average of 3.7 mol of phosphate/mol of S6. The autophosphorylation reaction appears to be intramolecular and leads to a 25% reduction in kinase activity toward S6. In the case of S6 all of the sites of phosphorylation are found to reside in a 19-amino acid peptide at the carboxyl end of the protein. Four of these sites have been identified as Ser235, Ser236, Ser240, and Ser244, equivalent to four of the five sites previously observed in vivo (Krieg, J., Hofsteenge, J., and Thomas, G. (1988) J. Biol. Chem. 263, 11473-11477). A fifth mole of phosphate is incorporated at low stoichiometry into the peptide, but the amino acid which is phosphorylated cannot be unequivocally assigned. The low level of phosphorylation of the fifth site in vitro is discussed with regard to known results and to a potential three-dimensional model for the carboxyl terminus of S6.

0 Followers
 · 
62 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Successful myelin repair in the adult CNS requires the robust and timely production of myelin proteins to generate new myelin sheaths. The underlying regulatory mechanisms and complex molecular basis of myelin regeneration, however, remain poorly understood. Here, we investigate the role of ERK MAP kinase signaling in this process. Conditional deletion of Erk2 from cells of the oligodendrocyte lineage resulted in delayed remyelination following demyelinating injury to the adult mouse corpus callosum. The delayed repair occurred as a result of a specific deficit in the translation of the major myelin protein, MBP. In the absence of ERK2, activation of the ribosomal protein S6 kinase (p70S6K) and its downstream target, ribosomal protein S6 (S6RP), was impaired at a critical time when premyelinating oligodendrocytes were transitioning to mature cells capable of generating new myelin sheaths. Thus, we have described an important link between the ERK MAP kinase signaling cascade and the translational machinery specifically in remyelinating oligodendrocytes in vivo. These results suggest an important role for ERK2 in the translational control of MBP, a myelin protein that appears critical for ensuring the timely generation of new myelin sheaths following demyelinating injury in the adult CNS. Copyright © 2015 the authors 0270-6474/15/357850-16$15.00/0.
    The Journal of Neuroscience : The Official Journal of the Society for Neuroscience 05/2015; 35(20):7850-65. DOI:10.1523/JNEUROSCI.4380-14.2015 · 6.75 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Neural progenitor cells (NPCs) have distinct proliferation capacities at different stages of brain development. Lin28 is an RNA-binding protein with two homologs in mice: Lin28a and Lin28b. Here we show that Lin28a/b are enriched in early NPCs and their expression declines during neural differentiation. Lin28a single-knockout mice show reduced NPC proliferation, enhanced cell cycle exit and a smaller brain, whereas mice lacking both Lin28a alleles and one Lin28b allele display similar but more severe phenotypes. Ectopic expression of Lin28a in mice results in increased NPC proliferation, NPC numbers and brain size. Mechanistically, Lin28a physically and functionally interacts with Imp1 (Igf2bp1) and regulates Igf2-mTOR signaling. The function of Lin28a/b in NPCs could be attributed, at least in part, to the regulation of their mRNA targets that encode Igf1r and Hmga2. Thus, Lin28a and Lin28b have overlapping functions in temporally regulating NPC proliferation during early brain development. © 2015. Published by The Company of Biologists Ltd.
    Development 05/2015; 142(9):1616-27. DOI:10.1242/dev.120543 · 6.27 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: mTOR is a central nutrient sensor that signals a cell to grow and proliferate. Through distinct protein complexes it regulates different levels of available cellular energy substrates required for cell growth. One of the important functions of the complex is to maintain available amino acid pool by regulating protein translation. Dysregulation of mTOR pathway leads to aberrant protein translation which manifests into various pathological states. Our review focuses on the role mTOR signaling plays in protein translation and its physiological role. It also throws some light on available data that show translation dysregulation as a cause of pathological complexities like cancer and the available drugs that target the pathway for cancer treatment.
    01/2014; 2014:686984. DOI:10.1155/2014/686984