Distinct protein degradation mechanisms mediated by Cul1 and Cul3 controlling Ci stability in Drosophila eye development

Abstract

The ubiquitin-like protein, Nedd8, covalently modifies members of the Cullin family. Cullins are the major components of a series of ubiquitin ligases that control the degradation of a broad range of proteins. We found that Nedd8 modifies Cul1 in Drosophila. In Drosophila Nedd8 and Cul1 mutants, protein levels of the signal transduction effectors, Cubitus interruptus (Ci) and Armadillo (Arm), and the cell cycle regulator, Cyclin E (CycE), are highly accumulated, suggesting that the Cul1-based SCF complex requires Nedd8 modification for the degradation processes of Ci, Arm, and CycE in vivo. We further show that two distinct degradation mechanisms modulating Ci stability in the developing eye disc are separated by the morphogenetic furrow (MF) in which retinal differentiation is initiated. In cells anterior to the MF, Ci proteolytic processing promoted by PKA requires the activity of the Nedd8-modified Cul1-based SCF Slimb complex. In posterior cells, Ci degradation is controlled by a mechanism that requires the activity of Cul3, another member of the Cullin family. This posterior Ci degradation mechanism, which partially requires Nedd8 modification, is activated by Hedgehog (Hh) signaling and is PKA-independent.

Drosophila homolog of APP-BP1 (dAPP-BP1) interacts antagonistically with APPL during Drosophila development

“…Ci FL accumulation was also observed in some posterior mutant cells. Similar to accumulation previously described for NEDD8 mutant clones, 13 the Ci FL accumulation observed here was in cells located proximal to the MF (Figure 3d-f, arrowheads), but not in cells located distal to it (Figure 3d-f, asterisks). Eye discs were also examined for accumulation of Cul1, since previous investigations 13 have shown that neddylation controls Cul1 stability.…”

“…11,12 In Drosophila NEDD8 mutants, there is an accumulation of protein levels for the cell cycle regulator, Cyclin E (CycE), and for the signal transduction effectors, Cubitus interruptus (Ci), and Armadillo (Arm). 13 Recently, NEDD8 has been shown to be incorporated into a variety of ubiquitinated inclusions, including the neurofibrillary tangles present in AD. 14 APP is the precursor of the amyloid b (Ab) peptide, the main component of senile plaques in AD.…”

“…NEDD8 modification is necessary for SCF slimb -mediated protein degradation in Drosophila wing discs. 13 Thus, protein stability was examined for substrates of Slimb in dAPP-BP1 mutant cells. In developing wing discs, dAPP-BP1 mutant cells accumulated high levels of full-length Ci (Ci FL ) and Arm proteins (Figure 3j-l and m-o).…”

“…These are similar to accumulations previously reported for NEDD8 mutants. 13 In eye discs, Ci FL accumulated in dAPP-BP1 clones located anterior to the morphogenic furrow (MF) (Figure 3d-f, arrows). This is similar to Ci FL accumulation observed in MF cells that transduce the Hh signaling pathway.…”

“…The Cul1 Ex null mutation 13 was used to examine interaction between APPL and SCF ligase. Hé riché et al 29 reported that reduction of Cul1-mediated SCF function causes apoptosis.…”