Pharmaceutical Sciences Faculty Publications

Regulation of Raf-1 by Direct Feedback Phosphorylation

Document Type

Article

Publication Date

1-21-2005

Journal Title

Molecular Cell

ISSN

1097-2765

Volume

17

Issue

2

First Page

215

Last Page

224

DOI

10.1016/j.molcel.2004.11.055

PubMed ID

15664191

Abstract

The Raf-1 kinase is an important signaling molecule, functioning in the Ras pathway to transmit mitogenic, differentiative, and oncogenic signals to the downstream kinases MEK and ERK. Because of its integral role in cell signaling, Raf-1 activity must be precisely controlled. Previous studies have shown that phosphorylation is required for Raf-1 activation, and here, we identify six phosphorylation sites that contribute to the downregulation of Raf-1 after mitogen stimulation. Five of the identified sites are proline-directed targets of activated ERK, and phosphorylation of all six sites requires MEK signaling, indicating a negative feedback mechanism. Hyperphosphorylation of these six sites inhibits the Ras/Raf-1 interaction and desensitizes Raf-1 to additional stimuli. The hyperphosphorylated/desensitized Raf-1 is subsequently dephosphorylated and returned to a signaling-competent state through interactions with the protein phosphatase PP2A and the prolyl isomerase Pin1. These findings elucidate a critical Raf-1 regulatory mechanism that contributes to the sensitive, temporal modulation of Ras signaling.

Keywords

Cell line, down-regulation, enzyme activation, feedback, physiological, isoenzymes, mutagenesis, peptides, peptidylprolyl isomerase, phosphoprotein phosphatases, phosphorylation, platelet-derived growth factor, proteins

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