Yet, since both HePTP and Erk are cytosolic enzymes, it is reasonable to conclude that there exists a mechanism for the inhibition of Erk by HePTP to cease in order to allow for the translocation of activated Erk to the nucleus. Indeed, like in many other cases of protein-protein interaction, HePTP appears to be phosphorylated by Erk and p38 at the sites Thr45 and Ser72. Importantly though, a third phosphorylation site in the non-catalytic N terminus (the KIM region) of HePTP has been found—one that is phosphorylated to a much higher stoichiometry by the cAMP pathway, in yet another instance of crosstalk between the cAMP and MAPK pathways.