Phosphotyrosyl phosphatase activator (PTPA) proteins stimulate the phosphotyrosyl phosphatase (PTPase) activity of the dimeric form of protein phosphatase 2A (PP2A). PTPase activity in PP2A (in vitro) is relatively low when compared to the better recognised phosphoserine/ threonine protein phosphorylase activity. The specific biological role of PTPA is unknown, Basal expression of PTPA depends on the activity of a ubiquitous transcription factor, Yin Yang 1 (YY1). The tumour suppressor protein p53 can inhibit PTPA expression through an unknown mechanism that negatively controls YY1 [1].

1: Protein phosphatase 2A: a highly regulated family of serine/threonine phosphatases implicated in cell growth and signalling. Janssens V, Goris J; Biochem J 2001;353:417-439. PMID:11171037