Interaction between Protein Phosphatase 5 and the A subunit of Protein Phosphatase 2A

Abstract

Members of the phosphoprotein phosphatase family of serine/threonine phosphatases are thought to exist in different native oligomeric complexes. Protein phosphatase 2A (PP2A) is composed of a catalytic subunit (PP2Ac) that complexes with an A subunit, which in turn also interacts with one of many B subunits that regulate substrate specificity and/or (sub)cellular localization of the enzyme. Another family member, protein phosphatase 5 (PP5), contains a tetratricopeptide repeat domain at its N terminus, which has been suggested to mediate interactions with other proteins. PP5 was not thought to interact with partners homologous to the A or B subunits that exist within PP2A. However, our results indicate that this may not be the case. A yeast two-hybrid screen revealed an interaction between PP5 and the A subunit of PP2A. This interaction was confirmed for endogenous proteins in vivo using immunoprecipitation analysis and for recombinant proteins by in vitro binding experiments. Our results also indicate that the tetratricopeptide repeat domain of PP5 is required and sufficient for this interaction. In addition, immunoprecipitated PP5 contains associated B subunits. Thus, our results suggest that PP5 can exist in a PP2A-like heterotrimeric form containing both A and B subunits.The reversible phosphorylation of proteins, catalyzed by protein kinases and phosphatases, is a major mechanism for regulating many cellular processes, including intermediary metabolism, cell cycle progression, DNA replication, transcription, and protein translation (1-3). It is estimated that one-third of all cellular proteins undergo reversible phosphorylation, which cells utilize to regulate the functional properties of key regulatory proteins involved in specific pathways (4).Based on homology of amino acid sequences and the similarity of three-dimensional structures, phosphoprotein phosphatases (PPPs) 1 are divided into three families designated PPP, PPM, and PTP (5, 6). The PPP and PPM families are comprised of phosphoserine-and phosphothreonine-specific enzymes, whereas the PTP family is comprised of phosphotyrosine-specific and/or dual specificity phosphatases. As suggested by the name, dual specificity phosphatases can dephosphorylate all three phosphoresidues (7). Protein phosphatase 2A (PP2A) together with PP1, PP2B (calcineurin), PP4, PP5, PP6, and PP7 are classified in the PPP family (4). PP2A exists as a heterotrimer composed of a catalytic subunit (PP2Ac), an A subunit (also known as PR65), and a B subunit. There are three major families of B subunits, PR55/B, PR61/BЈ, PR72/BЉ, with multiple isoforms within each family (4 -6, 8). The association of PP2Ac with different B subunits modulates the activity, substrate specificity, and/or (sub)cellular location of the holoenzymes, enabling them to control numerous cellular functions (3, 4, 9, 10).Protein phosphatase 5 (PP5), another member of the PPP family of phosphatases, differs from the other serine/threonine phosphatases in that it contains regulatory and (sub)cellular targetin...

Disruption of Serine/Threonine Protein Phosphatase 5 (PP5:PPP5c) in Mice Reveals a Novel Role for PP5 in the Regulation of Ultraviolet Light-induced Phosphorylation of Serine/Threonine Protein Kinase Chk1 (CHEK1)

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Heat Shock Protein gp96 Interacts with Protein Phosphatase 5 and Controls Toll-like Receptor 2 (TLR2)-mediated Activation of Extracellular Signal-regulated Kinase (ERK) 1/2 in Post-hypoxic Kidney Cells

“…Protein phosphatase PP5 is implicated in a variety of cellular processes and associates with many proteins involved in cellular signaling, such as the glucocorticoid receptor-Hsp90 complex (45,51), DNA-dependent protein kinase (52), G ␣12 /G␣ 13 subunits of the heteromeric G proteins (53), human blue-light photoreceptor cryptochrome 2 (54), Hsp90-dependent heme-regulated eukaryotic initiation factor 2␣ kinase (55), ASK1 (19,21), or A-regulatory subunit of protein phosphatase 2A (21,56). These studies have provided lines of evidence that PP5 plays important role in the regulation of the cellular responses to stress.…”

Activation and regulation of ATM kinase activity in response to DNA double-strand breaks

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