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Regulation of the Ras signalling network
1Ludwig Institute for Cancer Research, Melbourne, Australia.
Abstract:
The mitogenic action of cytokines such as epidermal growth factor (EGF) or platelet derived growth factor (PDGF) involves the stimulation of a signal cascade controlled by a small G protein called Ras. Mutations of Ras can cause its constitutive activation and, as a consequence, bypass the regulation of cell growth by cytokines. Both growth factor-induced and oncogenic activation of Ras involve the conversion of Ras from the GDP-bound (D-Ras) to the GTP-bound (T-Ras) forms. T-Ras activates a network of protein kinases including c-Mos, c-Raf-1 and MAP kinase. Eventually the activation of MAP kinase leads to the activation of the elongation factor 4E and several transcription factors such as c-Jun, c-Myc and c-Fos. There are several modulators of Ras activity, such as the GTPase activating proteins (GAP1 and NF1), which stimulate the conversion of T-Ras to D-Ras. A series of small NF1 fragments, which bind T-Ras, as well as truncated forms of derivatives of c-Raf-1, c-Jun and c-Myc, are capable of blocking the T-Ras-activated mitogenesis in a competitive manner. These agents offer a unique opportunity to control the proliferation of T-Ras-associated tumors, which represent more than 30% of total human carcinomas.
Insights
Mutated Ras proteins drive cancer by constantly signaling cells to grow. Specific molecular fragments can block this Ras signaling, offering a new way to treat Ras-driven tumors, which are common in many cancers.
Area of Science:
- Molecular Biology
- Cell Signaling
- Oncology
Background:
- Cytokines like EGF and PDGF regulate cell growth via Ras signaling.
- Ras mutations lead to constitutive activation, bypassing normal growth control.
- Ras activation involves GDP-bound (D-Ras) to GTP-bound (T-Ras) conversion, initiating downstream kinase cascades.
Purpose of the Study:
- To investigate the mechanism of Ras-mediated mitogenesis.
- To identify potential therapeutic agents targeting Ras activation.
- To explore the role of Ras modulators in controlling tumor proliferation.
Main Methods:
- Studied the signal cascade initiated by Ras activation.
- Investigated the function of Ras modulators like GAP1 and NF1.
- Assessed the inhibitory effects of specific molecular fragments on T-Ras activity.
Main Results:
- Ras activation leads to the formation of T-Ras, which activates kinases like c-Raf-1 and MAP kinase.
- MAP kinase activation results in the upregulation of transcription factors (c-Jun, c-Myc, c-Fos) and elongation factor 4E.
- NF1 fragments and truncated c-Raf-1, c-Jun, c-Myc derivatives competitively inhibit T-Ras-activated mitogenesis.
Conclusions:
- Ras signaling is a critical pathway in cell proliferation and cancer development.
- Targeting T-Ras with specific inhibitors presents a promising therapeutic strategy.
- These findings offer potential for controlling proliferation in over 30% of human carcinomas associated with Ras mutations.