May be a allosteric regulator of serine/threonine-protein phosphatase 2A (PP2A). Isoform 1 inhibits catalytic activity of the PP2A(D) core complex in vitro. The PP2A(C):TIPRL complex does not show phosphatase activity. Acts as a negative regulator of serine/threonine-protein phosphatase 4 probably by inhibiting the formation of the active PPP4C:PPP4R2 complex; the function is proposed to implicate it in DNA damage response by promoting H2AX phosphorylated on Ser-140 (gamma-H2AX). May play a role in the regulation of ATM/ATR signaling pathway controlling DNA replication and repair.