In eukaryotes, the phosphorylation and dephosphorylation of proteins on serine and threonine residues is an essential means of regulating a broad range of cellular functions including division, homeostasis and apoptosis. A group of proteins that are intimately involved in this process are the protein phosphatases. In general, the protein phosphatase (PP) holoenzyme is a trimeric complex composed of a regulatory subunit, a variable subunit and a catalytic subunit. Four major families of protein phosphatase catalytic subunit have been identified, designated PP1, PP2A, PP2B and PP2C. An additional protein phosphatase catalytic subunit, PPX, is a putative member of a novel PP family. PP6, also known as PPP6C, is a 305 amino acid cytoplasmic protein that belongs to the PPP phosphatase family. Ubiquitously expressed, PP6 is component of a signaling pathway regulating cell cycle progression in response to IL-2 receptor stimulation and is involved in suppressing inflammatory responses by specifically down-regulating TR4.