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Mas oncogene signaling and transformation require the small GTP-binding protein Rac
I E Zohn1, M Symons, M Chrzanowska-Wodnicka
1Department of Pharmacology, Lineberger Comprehensive Cancer Center, University of North Carolina School of Medicine, Chapel Hill 27599-7038, USA.
Abstract:
The Mas oncogene encodes a novel G-protein-coupled receptor that was identified originally as a transforming protein when overexpressed in NIH 3T3 cells. The mechanism and signaling pathways that mediate Mas transformation have not been determined. We observed that the foci of transformed NIH 3T3 cells caused by Mas were similar to those caused by activated Rho and Rac proteins. Therefore, we determined if Mas signaling and transformation are mediated through activation of a specific Rho family protein. First, we observed that, like activated Rac1, Mas cooperated with activated Raf and caused synergistic transformation of NIH 3T3 cells. Second, both Mas- and Rac1-transformed NIH 3T3 cells retained actin stress fibers and showed enhanced membrane ruffling. Third, like Rac, Mas induced lamellipodium formation in porcine aortic endothelial cells. Fourth, Mas and Rac1 strongly activated the JNK and p38, but not ERK, mitogen-activated protein kinases. Fifth, Mas and Rac1 stimulated transcription from common DNA promoter elements: NF-kappaB, serum response factor (SRF), Jun/ATF-2, and the cyclin D1 promoter. Finally, Mas transformation and some of Mas signaling (SRF and cyclin D1 but not NF-kappaB activation) were blocked by dominant negative Rac1. Taken together, these observations suggest that Mas transformation is mediated in part by activation of Rac-dependent signaling pathways. Thus, Rho family proteins are common mediators of transformation by a diverse variety of oncogene proteins that include Ras, Dbl family, and G-protein-coupled oncogene proteins.
Insights
The Mas oncogene activates Rac-dependent signaling pathways, contributing to cell transformation. This study reveals Rho family proteins as common mediators in oncogene-induced cell transformation.
Area of Science:
- Oncogene signaling
- Cellular transformation mechanisms
- G-protein-coupled receptors
Background:
- The Mas oncogene encodes a G-protein-coupled receptor involved in cell transformation.
- The specific signaling pathways mediating Mas-induced transformation remain unclear.
Purpose of the Study:
- To investigate whether Mas signaling and transformation involve the activation of Rho family proteins, particularly Rac.
- To elucidate the signaling pathways downstream of Mas activation.
Main Methods:
- Comparative analysis of Mas and activated Rac1 in NIH 3T3 cell transformation.
- Assessment of actin cytoskeleton organization (stress fibers, membrane ruffling, lamellipodium formation).
- Evaluation of mitogen-activated protein kinase (MAPK) activation (JNK, p38, ERK).
- Analysis of transcriptional activation of key promoter elements (NF-kappaB, SRF, Jun/ATF-2, Cyclin D1).
- Inhibition studies using dominant-negative Rac1.
Main Results:
- Mas-transformed cells exhibited phenotypes similar to those transformed by activated Rac1, including retained actin stress fibers and enhanced membrane ruffling.
- Mas and Rac1 synergistically transformed NIH 3T3 cells with activated Raf and activated common MAPK pathways (JNK, p38).
- Mas-mediated transformation and specific signaling events (SRF, Cyclin D1 activation) were partially blocked by dominant-negative Rac1, implicating Rac in Mas signaling.
Conclusions:
- Mas-induced cell transformation is, in part, mediated by Rac-dependent signaling pathways.
- Rho family proteins, including Rac, are identified as common mediators of transformation across diverse oncogene types.
- This research clarifies the mechanism of Mas oncogene action and highlights the role of Rho GTPases in oncogenesis.