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PMID: 7565795 Published · ppublish English Journal Article Research Support, Non-U.S. Gov't

Conditionally oncogenic forms of the A-Raf and B-Raf protein kinases display different biological and biochemical properties in NIH 3T3 cells.

Molecular and cellular biology ·Vol. 15 ·No. 11 ·1995-11-00 ·Pages 6430-42

Pritchard CA, Samuels ML, Bosch E, McMahon M

Abstract

The protein kinase domains of mouse A-Raf and B-Raf were expressed as fusion proteins with the hormone binding domain of the human estrogen receptor in mammalian cells. In the absence of estradiol, 3T3 and rat1a cells expressing delta A-Raf:ER and delta B-Raf:ER were nontransformed, but upon the addition of estradiol the cells became oncogenically transformed. Morphological oncogenic transformation was more rapid and distinctive in cells expressing delta B-Raf:ER compared with cells expressing delta A-Raf:ER. Biochemical analysis of cells transformed by delta A-Raf:ER and delta B-Raf:ER revealed several interesting differences. The activation of delta B-Raf:ER consistently led to the rapid and robust activation of both MEK and p42/p44 MAP kinases. By contrast, the activation of delta A-Raf:ER led to a weak activation of MEK and the p42/p44 MAP kinases. The extent of activation of MEK in cells correlated with the ability of the different Raf kinases to phosphorylate and activate MEK1 in vitro. delta B-Raf:ER phosphorylated MEK1 approximately 10 times more efficiently than delta Raf-1:ER and at least 500 times more efficiently than delta A-Raf:ER under the conditions of the immune-complex kinase assays. These results were confirmed with epitope-tagged versions of the Raf kinase domains expressed in insect cells. The activation of all three delta Raf:ER proteins in 3T3 cells led to the hyperphosphorylation of the resident p74raf-1 and mSOS1 proteins, suggesting the possibility of "cross-talk" between the different Raf kinases and feedback regulation of intracellular signaling pathways. The activation of either delta B-Raf:ER or delta Raf-1:ER in quiescent 3T3 cells was insufficient to promote the entry of the cells into DNA synthesis. By contrast, the activation of delta A-Raf:ER in quiescent 3T3 cells was sufficient to promote the entry of the cells into S phase after prolonged exposure to beta-estradiol. The delta Raf:ER system has allowed us to reveal significant differences between the biological and biochemical properties of oncogenic forms of the Raf family of protein kinases. We anticipate that cells expressing these proteins and other estradiol-regulated protein kinases will be useful tools in future attempts to unravel the complex web of interactions involved in intracellular signal transduction pathways.

MeSH Terms
3T3 Cells Amino Acid Sequence Animals Base Sequence Calcium-Calmodulin-Dependent Protein Kinases/metabolism Cell Transformation, Neoplastic/drug effects DNA Primers/chemistry Enzyme Activation Estradiol/pharmacology MAP Kinase Kinase 1 Mice Mitogen-Activated Protein Kinase 1 Mitogen-Activated Protein Kinase Kinases Molecular Sequence Data Protein Serine-Threonine Kinases/metabolism Protein-Tyrosine Kinases/metabolism Proto-Oncogene Proteins/metabolism Proto-Oncogene Proteins c-raf Receptors, Estrogen/chemistry Recombinant Fusion Proteins
Chemicals
DNA Primers Proto-Oncogene Proteins Receptors, Estrogen Recombinant Fusion Proteins Estradiol Protein-Tyrosine Kinases Protein Serine-Threonine Kinases Proto-Oncogene Proteins c-raf Calcium-Calmodulin-Dependent Protein Kinases Mitogen-Activated Protein Kinase 1 MAP Kinase Kinase 1 MAP2K1 protein, human Map2k1 protein, mouse Mitogen-Activated Protein Kinase Kinases
Authors & Affiliations
4 authors, click to expand affiliations / ORCID
Pritchard C A
Department of Cell Signaling, DNAX Research Institute of Molecular and Cellular Biology, Palo Alto, California 94304, USA.
Samuels M L
Bosch E
McMahon M
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Article Info
Journal
Molecular and cellular biology
Abbr.
Mol Cell Biol
ISSN
0270-7306
DOI
10.1128/MCB.15.11.6430
Published
1995-11-00
Pages
6430-42
Language
English
Region
United States
NLM ID
8109087
PMCID
PMC230894
Subset
IM
External Links
PubMed source DOI: 10.1128/MCB.15.11.6430 PMC Full Text View journal details
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