Display Settings:

Format

Send to:

Choose Destination
J Biol Chem. 2008 Oct 24;283(43):29273-84. doi: 10.1074/jbc.M803443200. Epub 2008 Aug 20.

PP4R4/KIAA1622 forms a novel stable cytosolic complex with phosphoprotein phosphatase 4.

Author information

  • 1Samuel Lunenfeld Research Institute at Mount Sinai Hospital, Toronto, Ontario M4M 2Y8, Canada.

Abstract

Protein serine/threonine phosphatase 4 (PP4c) is an essential polypeptide involved in critical cellular processes such as microtubule growth and organization, DNA damage checkpoint recovery, apoptosis, and tumor necrosis factor alpha signaling. Like other phosphatases of the PP2A family, PP4c interacts with regulatory proteins, which specify substrate targeting and intracellular localization. The identification of these regulatory proteins is, therefore, key to fully understanding the function of this enzyme class. Here, using a sensitive affinity purification/mass spectrometry approach, we identify a novel, stable cytosolic PP4c interacting partner, KIAA1622, which we have renamed PP4R4. PP4R4 displays weak sequence homology with the A (scaffolding) subunit of the PP2A holoenzyme and specifically associates with PP4c (and not with the related PP2Ac or PP6c phosphatases). The PP4c.PP4R4 interaction is disrupted by mutations analogous to those abrogating the association of PP2Ac with PP2A A subunit. However, unlike the PP2A A subunit, which plays a scaffolding role, PP4R4 does not bridge PP4c with previously characterized PP4 regulatory subunits. PP4c.PP4R4 complexes exhibit phosphatase activity toward a fluorogenic substrate and gammaH2AX, but this activity is lower than that associated with the PP4c.PP4R2.PP4R3 complex, which itself is less active than the free PP4c catalytic subunit. Our data demonstrate that PP4R4 forms a novel cytosolic complex with PP4c, independent from the complexes containing PP4R1, PP4R2.PP4R3, and alpha4, and that the regulatory subunits of PP4c have evolved different modes of interaction with the catalytic subunit.

PMID:
18715871
[PubMed - indexed for MEDLINE]
PMCID:
PMC2662017
Free PMC Article

Images from this publication.See all images (6)Free text

FIGURE 1.
FIGURE 2.
FIGURE 3.
FIGURE 4.
FIGURE 5.
FIGURE 6.
PubMed Commons home

PubMed Commons

0 comments
How to join PubMed Commons

    Supplemental Content

    Icon for HighWire Icon for PubMed Central
    Loading ...
    Write to the Help Desk