Methionine adenosyltransferase 2B-GIT1 complex serves as a scaffold to regulate Ras/Raf/MEK1/2 activity in human liver and colon cancer cells.

Abstract

Methionine adenosyltransferase 2B (MAT2B) encodes for variant proteins V1 and V2 that interact with GIT1 to increase ERK activity and growth in human liver and colon cancer cells. MAT2B or GIT1 overexpression activates MEK. This study explores the mechanism for MEK activation. We examined protein-protein interactions by co-immunoprecipitation and verified by confocal microscopy and pull-down assay using recombinant or in vitro translated proteins. Results were confirmed in an orthotopic liver cancer model. We found that MAT2B and GIT1-mediated MEK1/2 activation was not mediated by PAK1 or Src in HepG2 or RKO cells. Instead, MAT2B and GIT1 interact with B-Raf and c-Raf and enhance recruitment of Raf proteins to MEK1/2. MAT2B-GIT1 activates c-Raf, which is the key mediator for MEK/12 activation, because this still occurred in RKO cells that express constitutively active B-Raf mutant. The mechanism lies with the ability of MAT2B-GIT1 to activate Ras and promote B-Raf/c-Raf heterodimerization. Interestingly, MAT2B but not GIT1 can directly interact with Ras, which increases protein stability. Finally, increased Ras-Raf-MEK signaling occurred in phenotypically more aggressive liver cancers overexpressing MAT2B variants and GIT1. In conclusion, interaction between MAT2B and GIT1 serves as a scaffold and facilitates signaling in multiple steps of the Ras/Raf/MEK/ERK pathway, further emphasizing the importance of MAT2B/GIT1 interaction in cancer growth.

• Authors: Hui Peng, Tony W H Li, Heping Yang, Mary P Moyer, Jose M Mato, Shelly C Lu
• Journal: The American journal of pathology (Am J Pathol) Vol. 185 Issue 4 Pg. 1135-44 (Apr 2015) ISSN: 1525-2191 [Electronic] United States
• PMID: 25794709 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2015 American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.

Chemical References

• Adaptor Proteins, Signal Transducing
• Cell Cycle Proteins
• GIT1 protein, human
• MAT2B protein, human
• Methionine Adenosyltransferase
• src-Family Kinases
• Proto-Oncogene Proteins B-raf
• Proto-Oncogene Proteins c-raf
• p21-Activated Kinases
• Mitogen-Activated Protein Kinase Kinases
• ras Proteins

Topics

• Adaptor Proteins, Signal Transducing (metabolism)
• Cell Cycle Proteins (metabolism)
• Cell Line, Tumor
• Colonic Neoplasms (enzymology, metabolism, pathology)
• Enzyme Activation
• Humans
• Liver Neoplasms (enzymology, metabolism, pathology)
• Methionine Adenosyltransferase (metabolism)
• Mitogen-Activated Protein Kinase Kinases (metabolism)
• Protein Binding
• Protein Multimerization
• Proto-Oncogene Proteins B-raf (metabolism)
• Proto-Oncogene Proteins c-raf (metabolism)
• Up-Regulation
• p21-Activated Kinases (metabolism)
• ras Proteins (metabolism)
• src-Family Kinases (metabolism)