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Dissertation
Novel functions of protein phosphatase 2A in Saccharomyces cerevisiae
Doctor of Philosophy (Ph.D.), Drexel University
Apr 2007
DOI:
https://doi.org/10.17918/00007467
Abstract
Protein phosphatase 2A (PP2A) is a major serine/threonine protein phosphatase that plays a role in regulating cell cycle progression, cell growth, cytoskeleton dynamics and multiple signal transduction pathways from yeast to mammals. PP2A is a heterotrimeric protein complex consisting of A and B regulatory subunits and a catalytic C subunit. An additional species of PP2A can be activated by ceramide, and this complex is known as ceramide-activated protein phosphatase (CAPP). The CDC55 gene, in Saccharomyces cerevisiae, encodes for one of two B regulatory subunits of PP2A and the B subunit of CAPP. While identifying novel functions of PP2A, we found cells lacking the amphiphysin-like protein, Rvs161, require Cdc55 for viability under conditions of heat stress, and we linked this lethal genetic interaction to the endocytosis domain of Rvs 161. rvs161[delta] mutants are unable to thrive when stressed by glucose starvation or high salt and mutations in the sphingolipid biosynthetic pathway, including loss of Sur4, the very long chain fatty acid elongase, suppress these phenotypes. Cdc55 is required for sur4-dependent suppression of rvs161[delta] defects, including reinitiation of the endocytosis-dependent degradation of the a-factor receptor, Ste3. Overexpression of CDC55 can also remediate rvs161[delta] growth defects and restore Ste3 degradation or the endocytosis of lucifer yellow in rvs161[delta] cells even under high salt stress, but it can not remediate the actin polarization defects of these cells. Another novel function of PP2A involves Grr1, since cells lacking Grr1, an F-box subunit of the Skp1/Cdc53/F-box (SCF) ubiquitin ligase complex, require Cdc55 for viability. We linked this lethal genetic interaction to the degradation of the G1 cyclin, Cln2, a known substrate of the SCFGrr1 complex. Cln2 is less stable in cdc55[delta] mutants compared to wild type cells, and Cln2 phosphorylation or ubiquitination by the SCF complex are also required for the degradation of Cln2 in cdc55[delta] mutants. Our results suggest that Cln2 is hyperphosphorylated in cells lacking CDC55, causing an increase in its degradation, and cells lacking both CDC55 and GRR1 are inviable due to an accumulation of hyperphosphorylated Cln2. We propose that Cdc55-dependent PP2A regulates the phosphorylation state of Cln2, and, together with Rvs161, regulates a single cellular event, possibly endocytosis.
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Details
- Title
- Novel functions of protein phosphatase 2A in Saccharomyces cerevisiae
- Creators
- Paula Cristina McCourt
- Contributors
- Joseph T. Nickels (Advisor) - Drexel University, Drexel University (1970-)
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Number of pages
- 187 pages
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- Biochemistry and Molecular Biology; College of Medicine; Drexel University
- Other Identifier
- 991021889075504721