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Nuclear import of cubitus interruptus is regulated by hedgehog via a mechanism distinct from Ci stabilization and Ci
1Department of Biochemistry, Molecular Biology and Cell Biology, Robert H. Lurie Comprehensive Cancer Center, Northwestern University, Evanston, Illinois 60208, USA.
Insights
Hedgehog (Hh) signaling regulates Cubitus interruptus (Ci) protein transport into the nucleus, distinct from its stabilization and activation. This study clarifies how Hh controls Ci
Area of Science:
- Developmental Biology
- Cell Signaling
- Molecular Biology
Background:
- The Hedgehog (Hh) pathway is crucial for specifying cell fates in Drosophila wings.
- Cubitus interruptus (Ci) is a key transcription factor in the Hh pathway.
- Hh signaling regulates the processing and activity of Ci, but the precise mechanisms are complex.
Purpose of the Study:
- To investigate the in vivo mechanism of Ci nuclear import.
- To elucidate the relationship between Hh-mediated Ci nuclear import, stabilization, and activation.
- To identify distinct regulatory steps in the Hh signaling pathway.
Main Methods:
- In vivo analysis of Ci protein localization and activity in Drosophila.
- Hedgehog signaling pathway manipulation.
- Assessment of Ci protein stabilization and nuclear translocation.
Main Results:
- Hh signaling is required for rapid Ci nuclear import in cells near the anteroposterior boundary.
- Ci nuclear import is regulated by Hh independently of Ci stabilization.
- Ci stabilization and rapid nuclear import do not guarantee maximal Ci activity, indicating distinct regulatory mechanisms.
- Cos2 and PKA play positive roles in Hh-induced Ci activation.
Conclusions:
- Nuclear import, stabilization, and activation of Ci are regulated by distinct mechanisms.
- Hh signaling controls Ci nuclear import independently of stabilization.
- Cos2 and PKA are positive regulators of Ci activation in response to Hh.
Abstract:
The Hedgehog (Hh) signal is transduced via Cubitus interruptus (Ci) to specify cell fates in the Drosophila wing. In the absence of Hh, the 155 kDa full-length form of Ci is cleaved into a 75 kDa repressor. Hh inhibits the proteolysis of full-length Ci and facilitates its conversion into an activator. Recently, it has been suggested that Hh promotes Ci nuclear import in tissue culture cells. We have studied the mechanism of Ci nuclear import in vivo and the relationship between nuclear import, stabilization and activation. We found that Ci rapidly translocates to the nucleus in cells close to the anteroposterior (AP) boundary and this rapid nuclear import requires Hh signaling. The nuclear import of Ci is regulated by Hh even under conditions in which Ci is fully stabilized. Furthermore, cells that exhibit Ci stabilization and rapid nuclear import do not necessarily exhibit maximal Ci activity. It has been previously shown that stabilization does not suffice for activation. Consistent with this finding, our results suggest that the mechanisms regulating nuclear import, stabilization and activation are distinct from each other. Finally, we show that cos2 and pka, two molecules that have been characterized primarily as negative regulators of Ci activity, also have positive roles in the activation of Ci in response to Hh.