CSB428H1F Article #2: Benton et al. Drosophila PAR-1 and 14-3-3 inhibit Baz
PAR-1 phosphorylates Baz on two conserved serines, which is then bound by 14-3-3. This inhibits
the Baz/Par-6/aPKC complex by preventing Baz oligomerization and binding to aPKC. This
excludes Baz complex at lateral sides and also Crb-sdt anchor Baz complex apically.
Baz lacking PAR-1 phosphorylation/14-3-3 binding side for ectopic lateral complex.
Drosophila follicular epithelium surrounds germline and side facing germline is apical.
14-3-3 and PAR-1 is required for epithelial polarization
par-1 null cells display uniform aPKC and other apical protein around the cortex.
14-3-3/leo null cells mostly die. survivors show uniform cortex distribution of apical aPKC, H-
spectrin and basolateral marker-spectrin.
A weaker leo mutant formed multiple layers of abnormal cells that failed to encapsulate germline.
Par-6/aPKC and H-spectrin was diffusely around entire cortex and formed abnormal aggregates.
In a 14-3-3/+;leo/leo double mutant, cells lose cuboidal shape and Baz, Patj, Arm is redistributed
along the lateral and basal membranes.
Show 14-3-3 is required as a cofactor for PAR-1 in epithelial tissue and act downstream of PAR-1.
Baz is a 14-3-3 binding protein
Yeast-two-hybrid show 14-3-3 binds Baz, since presumably yeast kinase phosphorylate Baz.
14-3-3 binding to Baz is not impaired by 14-3-3 mutation that impaired its binding to PAR-1, but
rather is abolished by phosphoserine mutation S151A and S1085A.
Yeast-two-hybrid of smaller fragments show two binding sites at N and C flanking 3 PDZ domains.
Serine is conserved and S950A mutation in C.elegans PAR-3 abolishes interaction with PAR-5.
PAR-1 directly binds and phosphorylate Baz
PAR-1 efficiently phosphorylated 14-3-3 binding sites on Baz in vitro and only C’ S1085 is
phosphorylated but not S1083 or S1084.