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rgr oncogene: activation by elimination of translational controls and mislocalization
Inmaculada Hernández-Muñoz1, Marta Benet, Miguel Calero
1Department of Pathology, New York University School of Medicine, New York, New York 10016, USA.
Abstract:
Previous studies have identified a novel oncogene, rgr, which has homology to the guanine nucleotide exchange factor (GEF) Ral guanine dissociation stimulator (RALGDS). To determine the mechanism of activation of rgr, the wild-type form was isolated. rgr is expressed physiologically at very low levels, due, at least in part, to a long 5'-untranslated region that contains eight AUGs, which inhibit translation of the main open reading frame. When these regulatory sequences are removed, the wild-type gene is expressed at high levels. An investigation of how this GEF could transform cells showed that RGR interacts with RAS, supporting its involvement as a RAS-GEF. Because RAL is localized mainly to the Golgi, the expression of the RGR protein was identified in RK13 cells, a cell line that expresses endogenous rgr. RGR localizes to endomembranes. To determine its location upon transformation, a green fluorescent protein-RGR fusion protein was used to track the movement of RGR. Increasing amounts of expression result in enhanced localization of RGR to the plasma membrane. These results indicate that rgr is activated when its tight translational controls are eliminated and increased expression allows its relocation to the plasma membrane, where efficient activation of RAS occurs.
Insights
The novel oncogene rgr is activated by removing inhibitory sequences, allowing high expression. This increased expression relocates RGR to the plasma membrane, enabling RAS activation and cell transformation.
Area of Science:
- Molecular Biology
- Cell Biology
- Oncology
Background:
- A novel oncogene, rgr, homologous to guanine nucleotide exchange factor (GEF) Ral guanine dissociation stimulator (RALGDS), has been identified.
- Physiological expression of rgr is typically low due to a long 5'-untranslated region containing multiple AUGs that inhibit translation.
Purpose of the Study:
- To elucidate the activation mechanism of the rgr oncogene.
- To investigate the cellular localization and function of RGR protein.
Main Methods:
- Isolation and manipulation of wild-type rgr gene sequences.
- Expression analysis in RK13 cells.
- Green fluorescent protein (GFP) fusion protein for tracking RGR localization.
- Interaction studies with RAS.
Main Results:
- Removing inhibitory 5'-untranslated region sequences significantly increases wild-type rgr gene expression.
- RGR protein interacts with RAS, confirming its role as a RAS-GEF.
- RGR protein localizes to endomembranes and, upon increased expression, relocates to the plasma membrane.
- Enhanced RGR expression leads to efficient RAS activation.
Conclusions:
- Rgr oncogene activation is regulated by translational control mechanisms.
- Increased RGR expression and subsequent plasma membrane localization are critical for RAS activation and potential cell transformation.