Regulation of human protein kinases and phosphatases by 14-3-3
type: CreativeWork
description: The first part of my thesis shows that a previously-uncharacterised protein FAM122A and its paralogue FAM122C form stable stoichiometric complexes with the protein phosphatase 2A (PP2A) heterotrimer (AαB55αC). Moreover, the FAM122A–PP2A complex is active and contains methylated catalytic C subunit. In contrast, a complex comprising the protein phosphatase methylesterase-1 (PME-1) and the C-subunit of PP2A does not interact with FAM122A. I also identified that FAM122A and its paralogues FAM122B and FAM122C are 14-3-3-binding phosphoproteins. The binding of 14-3-3 to FAM122A is mediated by phosphorylation of Ser37 and Ser62; the latter being a site that is phosphorylated in response to cAMP-elevating agents. Binding of 14-3-3 does not affect the interaction of FAM122A with PP2A. Rather, binding of 14-3-3 promotes localisation of FAM122A to the nucleus, perhaps by masking the nuclear export signal (NES) that I identified. Another possibility is that 14-3-3 binding exposes a nuclear localisation signal (NLS) that was identified on FAM122A, and whose mutation promotes cytoplasmic localisation of the protein. The second part of my thesis stems from my confirmation of bioinformatic predictions that several protein kinases, including MINK1, MAST4, TAOK1, CLK1 and the group II PAK kinases PAK4, PAK6 and PAK7 are novel 14-3-3 binding phosphoproteins. The binding of 14-3-3 to group II PAK kinases is differentially regulated by various signal transduction pathways. The phosphorylation of Ser99 and Ser181 in response to phorbol ester mediates 14-3-3 binding to PAK4. 14-3-3 binding localises PAK4 to the leading edge of the cell. Moreover, Ser/Thr99 is a ‘lynchpin’ site that is conserved across the group II PAK family. In contrast to PAK4, cAMP elevating agents and insulin-like growth factor 1 (IGF1) stimulate phosphorylation of Ser113 that mediates 14-3-3 binding to PAK6. The binding to 14-3-3s retains PAK6 in the cytoplasm, while upon mutation of 14-3-3 binding sites PAK6 is loc…
abstract: The first part of my thesis shows that a previously-uncharacterised protein FAM122A and its paralogue FAM122C form stable stoichiometric complexes with the protein phosphatase 2A (PP2A) heterotrimer (AαB55αC). Moreover, the FAM122A–PP2A complex is active and contains methylated catalytic C subunit. In contrast, a complex comprising the protein phosphatase methylesterase-1 (PME-1) and the C-subunit of PP2A does not interact with FAM122A. I also identified that FAM122A and its paralogues FAM122B and FAM122C are 14-3-3-binding phosphoproteins. The binding of 14-3-3 to FAM122A is mediated by phosphorylation of Ser37 and Ser62; the latter being a site that is phosphorylated in response to cAMP-elevating agents. Binding of 14-3-3 does not affect the interaction of FAM122A with PP2A. Rather, binding of 14-3-3 promotes localisation of FAM122A to the nucleus, perhaps by masking the nuclear export signal (NES) that I identified. Another possibility is that 14-3-3 binding exposes a nuclear localisation signal (NLS) that was identified on FAM122A, and whose mutation promotes cytoplasmic localisation of the protein. The second part of my thesis stems from my confirmation of bioinformatic predictions that several protein kinases, including MINK1, MAST4, TAOK1, CLK1 and the group II PAK kinases PAK4, PAK6 and PAK7 are novel 14-3-3 binding phosphoproteins. The binding of 14-3-3 to group II PAK kinases is differentially regulated by various signal transduction pathways. The phosphorylation of Ser99 and Ser181 in response to phorbol ester mediates 14-3-3 binding to PAK4. 14-3-3 binding localises PAK4 to the leading edge of the cell. Moreover, Ser/Thr99 is a ‘lynchpin’ site that is conserved across the group II PAK family. In contrast to PAK4, cAMP elevating agents and insulin-like growth factor 1 (IGF1) stimulate phosphorylation of Ser113 that mediates 14-3-3 binding to PAK6. The binding to 14-3-3s retains PAK6 in the cytoplasm, while upon mutation of 14-3-3 binding sites PAK6 is loc…
author: Murugesan, Gavuthami
language: eng
date published: 2015
date modified: 2026-07-24T02:08:12Z
provider: University of Dundee
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Dundee