A gradient of cactus protein degradation establishes dorsoventral polarity in the Drosophila embryo.
Dorsoventral polarity in the Drosophila embryo is established by a signaling pathway active on the ventral and ventrolateral surfaces of the embryo. Signal transduction via the protein kinase Pelle frees the Rel-related protein Dorsal from its cytoplasmic inhibitor Cactus, allowing Dorsal to translocate into ventral and ventrolateral nuclei and direct gene expression. Here, we show by immunochemical analyses that Pelle-mediated signaling induces the spatially graded degradation of Cactus. Using a tissue culture system which reconstitutes Pelle-dependent Cactus degradation, we show that a motif in Cactus resembling the sites of signal-dependent phosphorylation in the vertebrate homologs IkappaB-alpha and IkappaB-beta is essential for Pelle-induced Cactus degradation. Substitution of four serines within this motif with nonphosphorylatable alanine residues generated a mutant Cactus that still functions as a Dorsal inhibitor but is resistant to induced degradation. Injection of RNA encoding this altered form of Cactus has a dominant negative effect on establishment of dorsoventral polarity in the embryo. We conclude that dorsoventral signaling results in a Cactus concentration gradient and propose that signal-dependent phosphorylation directs the spatially regulated proteolysis of Cactus protein.
Reach
M
M
Department of Pharmacology, School of Medicine, The University of California at San Diego, La Jolla 92093-0636, USA.
Galindo
R L
RL
Towb
P
P
Allen
J L
JL
Karin
M
M
Wasserman
S A
SA
D000595:Amino Acid Sequence; D000818:Animals; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D029721:Drosophila Proteins; D004331:Drosophila melanogaster / Q000196:embryology*; D004625:Embryo, Nonmammalian / Q000166:cytology / Q000502:physiology*; D007150:Immunohistochemistry; D008969:Molecular Sequence Data; D010750:Phosphoproteins / Q000737:chemistry / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction
D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D010750:Phosphoproteins; D011994:Recombinant Proteins; C077938:cact protein, Drosophila; C079896:pll protein, Drosophila; D017346:Protein Serine-Threonine Kinases