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Ras-dependent regulation of c-Jun phosphorylation is mediated by the Ral guanine nucleotide exchange factor-Ral
N D de Ruiter1, R M Wolthuis, H van Dam
1Department of Physiological Chemistry and Centre for Biomedical Genetics, University Medical Center Utrecht, 3584 CG Utrecht, The Netherlands.
Abstract:
The transcription factor c-Jun is critically involved in the regulation of proliferation and differentiation as well as cellular transformation induced by oncogenic Ras. The signal transduction pathways that couple Ras activation to c-Jun phosphorylation are still partially elusive. Here we show that an activated version of the Ras effector Rlf, a guanine nucleotide exchange factor (GEF) of the small GTPase Ral, can induce the phosphorylation of serines 63 and 73 of c-Jun. In addition, we show that growth factor-induced, Ras-mediated phosphorylation of c-Jun is abolished by inhibitory mutants of the RalGEF-Ral pathway. These results suggest that the RalGEF-Ral pathway plays a major role in Ras-dependent c-Jun phosphorylation. Ral-dependent regulation of c-Jun phosphorylation includes JNK, a still elusive JNKK, and possibly Src.
Insights
The RalGEF-Ral pathway is crucial for Ras-dependent c-Jun phosphorylation, a key process in cell growth and cancer. This pathway involves JNK and other kinases, impacting cell proliferation and differentiation.
Area of Science:
- Molecular Biology
- Cell Signaling
- Oncology
Background:
- The transcription factor c-Jun regulates cell proliferation, differentiation, and oncogenesis.
- Ras signaling pathways are critical in these cellular processes, but the link to c-Jun phosphorylation is not fully understood.
Purpose of the Study:
- To elucidate the role of the RalGEF-Ral pathway in Ras-mediated c-Jun phosphorylation.
- To identify the specific components involved in this signaling cascade.
Main Methods:
- Utilized activated Ras effector Rlf (a Ral guanine nucleotide exchange factor) to study c-Jun phosphorylation.
- Employed inhibitory mutants of the RalGEF-Ral pathway to assess its necessity in growth factor-induced signaling.
- Investigated the involvement of JNK, JNKK, and Src kinases.
Main Results:
- Activated Rlf induced phosphorylation of c-Jun at serines 63 and 73.
- Inhibitory mutants of the RalGEF-Ral pathway blocked Ras-mediated c-Jun phosphorylation.
- The RalGEF-Ral pathway is essential for Ras-dependent c-Jun phosphorylation, involving JNK, JNKK, and potentially Src.
Conclusions:
- The RalGEF-Ral pathway is a major mediator of Ras-dependent c-Jun phosphorylation.
- This pathway is critical for regulating c-Jun activity in response to growth factors and oncogenic signaling.
- Understanding this pathway offers insights into cancer development and potential therapeutic targets.