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Rauch, J.* ; Vandamme, D.* ; Mack, B. ; McCann, B.* ; Volinsky, N.* ; Blanco, A.* ; Gires, O. ; Kolch, W.*

Differential localization of A-Raf regulates MST2-mediated apoptosis during epithelial differentiation.

Cell Death Differ. 23, 1283-1295 (2016)
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A-Raf belongs to the family of oncogenic Raf kinases that are involved in mitogenic signaling by activating the MEK-ERK pathway. Low kinase activity of A-Raf toward MEK suggested that A-Raf might have alternative functions. We recently identified A-Raf as a potent inhibitor of the proapoptotic mammalian sterile 20-like kinase (MST2) tumor suppressor pathway in several cancer entities including head and neck, colon, and breast. Independent of kinase activity, A-Raf binds to MST2 thereby efficiently inhibiting apoptosis. Here, we show that the interaction of A-Raf with the MST2 pathway is regulated by subcellular compartmentalization. Although in proliferating normal cells and tumor cells A-Raf localizes to the mitochondria, differentiated non-carcinogenic cells of head and neck epithelia, which express A-Raf at the plasma membrane. The constitutive or induced re-localization of A-Raf to the plasma membrane compromises its ability to efficiently sequester and inactivate MST2, thus rendering cells susceptible to apoptosis. Physiologically, A-Raf re-localizes to the plasma membrane upon epithelial differentiation in vivo. This re-distribution is regulated by the scaffold protein kinase suppressor of Ras 2 (KSR2). Downregulation of KSR2 during mammary epithelial cell differentiation or siRNA-mediated knockdown re-localizes A-Raf to the plasma membrane causing the release of MST2. By using the MCF7 cell differentiation system, we could demonstrate that overexpression of A-Raf in MCF7 cells, which induces differentiation. Our findings offer a new paradigm to understand how differential localization of Raf complexes affects diverse signaling functions in normal cells and carcinomas.
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Publication type Article: Journal article
Document type Scientific Article
Corresponding Author
Keywords Breast-cancer Cells; Protein Phosphatase 2a; Ksr-1 Gene Encodes; Kinase Suppressor; Signal-transduction; Hippo Pathway; C-elegans; Caspase Activation; Pyruvate-kinase; Plasma-membrane
ISSN (print) / ISBN 1350-9047
e-ISSN 1476-5403
Journal Cell Death and Differentiation
Quellenangaben Volume: 23, Issue: 8, Pages: 1283-1295 Article Number: , Supplement: ,
Publisher Nature Publishing Group
Publishing Place London
Non-patent literature Publications
Reviewing status Peer reviewed
Institute(s) CCG Personalized Radiotherapy in Head and Neck Cancer (KKG-KRT)