# The TORC2-Dependent Signaling Network in the Yeast _Saccharomyces cerevisiae_
## 6 Structure, Function and Regulation of Pkc1
### Other Potential Targets  
Nem1-Spo7 is not the only phosphoprotein phosphatase reportedly regulated by Pkc1-mediated phosphorylation. The Cdc55-bound form of phosphoprotein phosphatase 2A (PP2A) and its small protein regulators, the so-called \"endosulfins\" (Igo1 and Igo2 in yeast), have important roles in controlling the timing of mitotic entry and exit [275]. The protein kinase Rim15, the yeast ortholog of Drosophila Greatwall and human GWL/MASTL [276], is responsible for installing the phosphorylations of Igo1 and Igo2 that make them inhibitors of Cdc55-PP2A [277], thereby sustaining Cdk1-mediated phosphorylations and promoting mitotic entry. How that inhibition is alleviated to promote mitotic exit has not been completely clear, although in other systems, the Cdc55-PP2A equivalent itself is the enzyme responsible for dephosphorylating the phosphorylated endosulfines during M phase exit [278]. In this context, it was observed that, in yeast cells expressing hyperactive Pkcl1*, they could not hold cell cycle arrest at a mitotic checkpoint. Therefore, Pkcl-dependent modifications in such cells were examined by MS and changes were observed in Cdc55 and Igo2, which seemed to promote dissociation of Igo2, and the putative Pkc1 sites were mapped. However, mutation of the apparent Pkc1-dependent phosphorylation sites on Cdc55 and Igo2, none of which match well with what appears to be the minimal consensus Pkc1 phospho-acceptor motif (Figure 7), did not cause any detectable defects in mitotic progression [239].  
Another reported Pkc1 substrate is the N-terminal F-BAR domain-containing and C-terminal Muniscin/Mu homology domain (MHD)-containing protein Spp1, which was initially reported to localize prominently at the bud neck and was implicated in the processes required for disassembly of the septum ring [279]. Spp1 is a highly phosphorylated protein [280; 281; 282]; eight of the phospho-sites detected in Spp1 fit the minimal -T/S-P- consensus for the major cell cycle driver Cdk1/Cdc28 [136; 283] and five fit the minimal consensus sequence (-R-x-x-S/T-) determined for the bud neck-localized protein kinase Gin4 [136; 284]. However, others find that Spp1 localizes predominantly to cortical puncta and functions as an endocytic adaptor that is involved in cargo selection and negative regulation of Las17 (yeast WASp)-Arp2/3 complex activity [285; 286] during the early stages of actin patch formation for clathrin-dependent endocytosis [287]. Although eukaryotic proteins with such apparently disparate functions certainly exist, it is nonetheless a bit hard to reconcile these two rather distinct roles attributed to Spp1 mechanistically. Also, contrary to the findings implicating Spp1 in septum ring disassembly and in endocytic actin patch function, is a study claiming that Spp1 is phosphorylated in a Rho1- and Pkc1-dependent manner to promote septin collar assembly [242]. The context around only one of the two sites reportedly phosphorylated by Pkc1 in Spp1 resembles well the pseudosubstrate sequence in Pkc1 and other likely Pkc1 sites, whereas a putative Pkc1 site in the cargo-binding clathrin-associated adaptor Apm4 is a better match [237] (Figure 7).  
There is also a report that Pkc1 action is required for processing body (P-body) assembly and for mRNA decay at the step of deadenylation of the 3'-polyA tail under nutrient poor conditions [288]. Unfortunately, in this study, no Pkc1 substrates involved in either of these processes were identified. Finally, despite all of the observations that _PKC1_-regulated processes affect the actin cytoskeleton [67; 193; 214; 289], no direct Pkc1 target intimately associated with the control of actin filament assembly and dynamics per se has yet been reported.