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  • Title: Kinase suppressor of Ras is ceramide-activated protein kinase.
    Author: Zhang Y, Yao B, Delikat S, Bayoumy S, Lin XH, Basu S, McGinley M, Chan-Hui PY, Lichenstein H, Kolesnick R.
    Journal: Cell; 1997 Apr 04; 89(1):63-72. PubMed ID: 9094715.
    Abstract:
    A proline-directed serine/threonine ceramide-activated protein (CAP) kinase mediates transmembrane signaling through the sphingomyelin pathway. CAP kinase reportedly initiates proinflammatory TNF alpha action by phosphorylating and activating Raf-1. The present studies delineate kinase suppressor of Ras (KSR), identified genetically in Caenorhabditis elegans and Drosophila, as CAP kinase. Mouse KSR, like CAP kinase, renatures and autophosphorylates as a 100-kDa membrane-bound polypeptide. KSR overexpression constitutively activates Raf-1. TNF alpha or ceramide analogs markedly enhance KSR autophosphorylation and its ability to complex with, phosphorylate, and activate Raf-1. In vitro, low nanomolar concentrations of natural ceramide stimulate KSR to autophosphorylate, and transactivate Raf-1. Other lipid second messengers were ineffective. Moreover, Thr269 the Raf-1 site phosphorylated by CAP kinase, is also recognized by KSR. Thus, by previously established criteria, KSR appears to be CAP kinase.
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