Differential effects of prenyl pyrophosphates on the phosphatase activity of phosphotyrosyl protein phosphatase

Abstract

AbstractPhosphotyrosyl protein phosphatase (PTPase) 1B was purified from human placenta. Immunoprecipitation analysis revealed that the isolated PTPase 1B appears as a complex with the receptor for protein kinase C (RACK1) and protein kinase C (PKC)δ. The abilities of PTPase 1B and PKCδ to associate with RACK1 were reconfirmed by an in vitro reconstitution experiment. The E. coli expressed and biotinylated mice‐RACK1–encoded fusion protein was capable of recruiting PTPase 1B and PKCδ in the antibiotin immunoprecipitate as a complex of PTPase 1B/RACK1/PKCδ. Thus PTPase 1B enzyme preparation was subjected to further purification by selective binding of PTPase 1B onto PEPTaxol affinity column in the absence of ATP. The purified PTPase 1B enzyme exihibited dose‐dependent phosphatase activity towards [γ–32P]‐ATP labeled mice β‐tubulin‐encoded fusion protein. The dephosphorylation reaction with PTPase 1B was enhanced with geranylgeranyl pyrophosphate, but not with farnesyl pyrophosphate. Interestingly, additional incubation of the purified PTPase 1B enzyme preparation with RACK1, geranylgeranyl pyrophosphate failed to modulate the dephosphorylation activity of PTPase 1B. In contrast, the enhancement effect of farnesyl pyrophosphate on the kinase activity of PKCδ was sustained in the presence of RACK1. That is, farnesyl pyrophosphate may function as a signal to induce the kinase activity of PKCδ in PTPase 1B/RACK1/PKCδ complex but geranylgeranyl pyrophosphate may not for PTPase 1B. J. Exp. Zool. 301A:307–316, 2004. © 2004 Wiley‐Liss, Inc.