- Title
- Novel insights into protein phosphatase 2A regulation and function in cell adhesion
- Creator
- Schuhmacher, Diana
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2022
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- The serine/threonine phosphatase family of protein phosphatase 2A (PP2A) enzymes are ubiquitously expressed, universally conserved, and regulate nearly all cellular signal transduction pathways and processes. PP2A dysfunction is linked to numerous human diseases, including neurodegenerative disorders such as Alzheimer’s disease (AD) and cancer. Despite its importance in maintaining cellular homeostasis, much remains to be learned on PP2A regulation and function. In this thesis, we aimed to further clarify the mechanisms by which PP2A substrate specificity is controlled, as well as investigate their effects on selected cellular targets. Of particular interest, the PP2A catalytic subunit (PP2A-C) is methylated by leucine carboxyl methyltransferase 1 (LCMT1) using methyl groups supplied via one-carbon metabolism. PP2A-C methylation regulates PP2A substrate specificity by modulating assembly of specific PP2A heterotrimers. Here, we first demonstrate that PP2A-C methylation state critically regulates the assembly and integrity of tight junctions (TJs) in epithelial MDCK cells. We also show that deregulation of PP2A substrate specificity by expression of SV40 small tumour antigen (small t) induces TJ deficits and F-actin disorganisation in MDCK cells via activation of Src kinase, a tyrosine kinase upregulated in many human cancers. We next provide the first evidence that disturbances in one-carbon metabolism and PP2A-C methylation status in neuronal cells affect the subcellular distribution of Fyn, which plays a central role in the neurodegenerative cascades of AD. Lastly, we challenge a long existing dogma that PP2A is inactivated by Src-mediated tyrosine phosphorylation on Tyr307. We show that Src and Fyn can phosphorylate PP2A-C on two novel tyrosine phosphorylate sites, resulting in changes in PP2A substrate specificity. This mechanism is important for Src/Fyn-mediated activation of ERK, a major growth regulatory kinase involved in cancer, phosphorylation of tau, a pathological hallmark of AD, and regulation of focal adhesion (FA) proteins that control cell adhesion and migration. Our findings unveil novel targets and mechanisms of regulation of PP2A that position this enzyme at the crossroads between tyrosine and serine/threonine signalling, and one-carbon metabolic pathways, that all become dysregulated in cancer and AD.
- Subject
- cell adhesion; PP2A; protein phosphatase 2A; Src family kinases; tight junction
- Identifier
- http://hdl.handle.net/1959.13/1507486
- Identifier
- uon:56025
- Rights
- Copyright 2022 Diana Schuhmacher
- Language
- eng
- Full Text
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | ATTACHMENT01 | Thesis | 16 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 235 KB | Adobe Acrobat PDF | View Details Download |