SDS-22 stabilizes the PP1 catalytic subunits GSP-1/-2 contributing to polarity establishment in C. elegans embryos

In many cells, cell polarity depends on the asymmetric distribution of the conserved PAR proteins, maintained by a balanced activity between kinases and phosphatases. The C. elegans one-cell embryo is polarized along the anterior-posterior axis, with the atypical protein kinase C PKC-3 enriched in the anterior, and the ring finger protein PAR-2 in the posterior. PAR-2 localization is regulated by PKC-3 and the PP1 phosphatases GSP-1/-2. Here, we find that, like GSP-2 depletion, depletion of the conserved PP1 interactor SDS-22 results in the rescue of the polarity defects of a pkc-3 temperature-sensitive mutant. Consistent with the rescue, SDS-22 depletion or mutation results in reduced GSP - 1/ - 2 protein levels and activity. The decreased levels of GSP-1/-2 can be rescued by reducing proteasomal activity. Our data suggest that SDS-22 regulates polarity not by directly regulating the localization or activity of GSP-1/-2, but by protecting these PP1 catalytic subunits from proteasome-mediated degradation, supporting recent data in human cells showing the SDS22 is required to stabilize nascent PP1.