aPKC-mediated phosphorylation regulates asymmetric membrane localization of the cell fate determinant Numb.
In Drosophila, the partition defective (Par) complex containing Par3, Par6 and atypical protein kinase C (aPKC) directs the polarized distribution and unequal segregation of the cell fate determinant Numb during asymmetric cell divisions. Unequal segregation of mammalian Numb has also been observed, but the factors involved are unknown. Here, we identify in vivo phosphorylation sites of mammalian Numb and show that both mammalian and Drosophila Numb interact with, and are substrates for aPKC in vitro. A form of mammalian Numb lacking two protein kinase C (PKC) phosphorylation sites (Numb2A) accumulates at the cell membrane and is refractory to PKC activation. In epithelial cells, mammalian Numb localizes to the basolateral membrane and is excluded from the apical domain, which accumulates aPKC. In contrast, Numb2A is distributed uniformly around the cell cortex. Mutational analysis of conserved aPKC phosphorylation sites in Drosophila Numb suggests that phosphorylation contributes to asymmetric localization of Numb, opposite to aPKC in dividing sensory organ precursor cells. These results suggest a model in which phosphorylation of Numb by aPKC regulates its polarized distribution in epithelial cells as well as during asymmetric cell divisions.
Smith
Christian A
CA
Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada.
Lau
Kimberly M
KM
Rahmani
Zohra
Z
Dho
Sascha E
SE
Brothers
Greg
G
She
Ye Min
YM
Berry
Donna M
DM
Bonneil
Eric
E
Thibault
Pierre
P
Schweisguth
François
F
Le Borgne
Roland
R
McGlade
C Jane
CJ
D000595:Amino Acid Sequence; D000818:Animals; D001485:Basement Membrane / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D016764:Cell Polarity; D002478:Cells, Cultured; D004285:Dogs; D004330:Drosophila; D029721:Drosophila Proteins / Q000737:chemistry / Q000378:metabolism*; D004847:Epithelial Cells / Q000378:metabolism / Q000648:ultrastructure; D007605:Juvenile Hormones / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism* / Q000502:physiology; D014018:Tissue Distribution
D029721:Drosophila Proteins; D007605:Juvenile Hormones; C060606:numb protein, Drosophila; C115015:PKC-3 protein; D011493:Protein Kinase C