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Cactus protein degradation mediates Drosophila dorsal-ventral signaling
M P Belvin1, Y Jin, K V Anderson
1Department of Molecular and Cell Biology, University of California at Berkeley 94720, USA.
Abstract:
Dorsal-ventral patterning in the Drosophila embryo relies on a signal transduction pathway that is similar to a signaling pathway leading to the activation of the mammalian transcription factor NF-kappa B. Stimulation of this Drosophila pathway on the ventral side of the embryo causes the nuclear translocation of Dorsal, the Drosophila NF-kappa B homolog. Cactus, like its mammalian homolog I kappa B, inhibits nuclear translocation by binding Dorsal and retaining it in the cytoplasm. We show that Cactus, like I kappa B, is rapidly degraded in response to signaling. More importantly, signal-dependent degradation of Cactus does not require the presence of Dorsal, indicating that Cactus degradation is a direct response to signaling, and that disruption of the Dorsal/Cactus complex is a secondary result of Cactus degradation. Mutant alleles of cactus that encode more stable forms of the protein block signaling, showing that efficient degradation is necessary for signaling. We find that Cactus protein stability is regulated by two independent processes that rely on different regions within the protein: signal-dependent degradation requires sequences in the amino terminus or ankyrin repeats, whereas signal-independent degradation of free Cactus requires the carboxy-terminal region of the protein that includes a PEST sequence.
Insights
Drosophila Cactus protein degradation is essential for signaling, independent of Dorsal. This process requires specific protein regions for signal-dependent and signal-independent degradation.
Area of Science:
- Developmental Biology
- Molecular Biology
- Cell Signaling
Background:
- Dorsal-ventral patterning in Drosophila embryos involves a pathway analogous to the mammalian NF-kappa B signaling pathway.
- The Drosophila Dorsal protein, a homolog of NF-kappa B, translocates to the nucleus upon ventral stimulation.
- Cactus, the Drosophila I kappa B homolog, sequesters Dorsal in the cytoplasm.
Purpose of the Study:
- To investigate the role of Cactus degradation in the Drosophila signaling pathway.
- To determine if Cactus degradation is a direct response to signaling.
- To identify the protein regions responsible for Cactus stability regulation.
Main Methods:
- Analysis of Cactus protein degradation in response to signaling.
- Use of mutant cactus alleles with altered protein stability.
- Mapping of protein domains involved in signal-dependent and signal-independent degradation.
Main Results:
- Cactus undergoes rapid degradation upon pathway stimulation, similar to I kappa B.
- Cactus degradation is a direct response to signaling and does not require Dorsal.
- Mutant Cactus proteins with increased stability inhibit signaling, highlighting the necessity of degradation.
- Distinct protein regions regulate signal-dependent (N-terminus/ankyrin repeats) and signal-independent (C-terminus/PEST sequence) degradation.
Conclusions:
- Efficient Cactus degradation is crucial for signal transduction in Drosophila development.
- Cactus degradation is a primary event, preceding the disruption of the Dorsal/Cactus complex.
- Protein stability of Cactus is finely tuned by distinct regulatory mechanisms involving specific protein domains.