Back to Search Start Over

B-Raf protein isoforms interact with and phosphorylate Mek-1 on serine residues 218 and 222.

Authors :
Papin C
Eychène A
Brunet A
Pagès G
Pouysségur J
Calothy G
Barnier JV
Source :
Oncogene [Oncogene] 1995 Apr 20; Vol. 10 (8), pp. 1647-51.
Publication Year :
1995

Abstract

The B-raf/c-Rmil proto-oncogene belongs to the raf/mil family of serine/threonine protein kinases. It encodes multiple protein isoforms resulting from alternative splicing of two exons located upstream of the kinase domain. Recent studies suggested that B-Raf could be the intermediate molecule between Ras and Mek-1 (MAP Kinase Kinase) in signalling pathways specific of neural cells. However, there has been no evidence for a direct interaction between B-Raf and Mek-1. We report here that different B-Raf isoforms can be co-immunoprecipitated with anti-Mek-1 antisera in COS-1 cells and that the kinase activity of B-Raf is not required for its interaction with Mek-1. We also show that all B-Raf isoforms tested phosphorylate Mek-1 in a time-dependent manner, whereas kinase defective mutants fail to do so. Finally, we demonstrate that the constitutively activated S218D, S222D and S218D/S222D mutants of Mek-1 interact similarly with B-Raf. However, only the S218D and S222D mutants, and not the S218D/S222D double mutant, can be phosphorylated by B-Raf isoforms. Therefore, serine residues 218 and 222, previously shown to regulate Mek-1 activity, appear to be the major phosphorylation sites by B-Raf in vitro.

Details

Language :
English
ISSN :
0950-9232
Volume :
10
Issue :
8
Database :
MEDLINE
Journal :
Oncogene
Publication Type :
Academic Journal
Accession number :
7731720