YPI1 and SDS22 Proteins Regulate the Nuclear Localization and Function of Yeast Type 1 Phosphatase Glc7

Abstract

We have recently characterized Ypi1 as an inhibitory subunit of yeast Glc7 PP1 protein phosphatase. In this work we demonstrate that Ypi1 forms a complex with Glc7 and Sds22, another Glc7 regulatory subunit that targets the phosphatase to substrates involved in cell cycle control. Interestingly, the combination of equimolar amounts of Ypi1 and Sds22 leads to an almost full inhibition of Glc7 activity. Because YPI1 is an essential gene, we have constructed conditional mutants that demonstrate that depletion of Ypi1 leads to alteration of nuclear localization of Glc7 and cell growth arrest in mid-mitosis with aberrant mitotic spindle. These phenotypes mimic those produced upon inactivation of Sds22. The fact that progressive depletion of either Ypi1 or Sds22 resulted in similar physiological phenotypes and that both proteins inhibit the phosphatase activity of Glc7 strongly suggest a common role of these two proteins in regulating Glc7 nuclear localization and function.

Plasmodium falciparum Inhibitor-3 Homolog Increases Protein Phosphatase Type 1 Activity and Is Essential for Parasitic Survival

“…These data suggest that PfI3 is essential for blood stage parasites and are in agreement with the in vivo functional studies of I3 in other organisms that demonstrated the indispensable role of I3 in cell survival and division. Studies carried out in yeast showed that the deletion of I3 (Ypi1) is lethal, and its conditional suppression leads to the inhibition of cell growth of mid-mitosis (24,25). More recently, genetic studies in Arabidopsis thaliana revealed that I3 disruption delayed the progression of embryogenesis and arrested the development at an early stage.…”

“…In yeast, it has been shown that the deletion of Inhibitor-3 ortholog (Ypi1) is lethal for Saccharomyces cerevisiae, suggesting an essential function of the gene in the physiology of the yeast, and its depletion (conditional strain) affected the distribution of PP1 and provoked a blockage in anaphase with condensed chromosomes (24). Indirect evidence supporting the idea that Inhibitor-3 inhibits PP1 is the fact that overexpression of this regulator reduces glycogen levels in the yeast because glycogen synthase requires dephosphorylation by PP1 to become active (25).…”

Modulation of Yeast Alkaline Cation Tolerance by Ypi1 Requires Calcineurin

“…As mentioned above, in our initial characterization of Ypi1 functions (Garcia-Gimeno et al 2003) we made the observation that high-copy expression of YPI1 was able to provide a detectable increase in tolerance to alkaline cations, particularly to LiCl, although the basis for this effect was not investigated further. Because Ypi1 is an essential protein, we constructed (Pedelini et al 2007) a strain carrying a conditional allele of YPI1 in which the protein was expressed from a regulatable tetO promoter. To confirm the possible implication of Ypi1 in lithium tolerance, we sought for a specific concentration of doxycycline in which repression of YPI1 expression could lead to lower-than-normal levels of the protein without excessive effect on cell growth and used this condition to test for altered LiCl sensitivity.…”

“…Many of these regulatory proteins have a conserved binding site, with a (R/K)(V/I)X(F/W) consensus sequence, which is necessary for the interaction with an hydrophobic groove in the Glc7 molecule (Bollen et al 2010). Ypi1 is an essential regulatory subunit of Glc7 that plays a role in progression of mitosis; although whether it acts as a positive or negative regulator of the phosphatase, is a matter of controversy (Garcia-Gimeno et al 2003;Pedelini et al 2007;Bharucha et al 2008). Ypi1 has a 48 RHNVRW 53 sequence, which is required for interaction with Glc7 and can be found as a complex with Glc7 and Sds22 (another essential subunit of Glc7) (Pedelini et al 2007).…”

“…Ypi1 is an essential regulatory subunit of Glc7 that plays a role in progression of mitosis; although whether it acts as a positive or negative regulator of the phosphatase, is a matter of controversy (Garcia-Gimeno et al 2003;Pedelini et al 2007;Bharucha et al 2008). Ypi1 has a 48 RHNVRW 53 sequence, which is required for interaction with Glc7 and can be found as a complex with Glc7 and Sds22 (another essential subunit of Glc7) (Pedelini et al 2007). During the course of our initial characterization of this gene product, and due to the essential nature of Ypi1, we performed a number of experiments by overexpressing the protein under different circumstances (Garcia-Gimeno et al 2003).…”