PPP4C, also known as PPX, is the catalytic subunit of the PP4 serine/threonine protein phosphatase. PP4 is a holoenzyme that is comprised of the PPP4C catalytic subunit in association with the PP4-R1 or PP4-R2 regulatory subunits. PP4 has been demonstrated to directly interact with and activate NF-kappaB. PP4 also has been demonstrated to interact with histone deacetylase HDAC3 to influence transcription and to serve a role in microtubule organization during mitosis. Signaling through the MAPK and JNK-1 pathway has also been demonstrated to involve PP4.