A Novel Cytoplasmic Dual Specificity Protein Tyrosine Phosphatase Implicated in Muscle and Neuronal Differentiation

Robert J Mourey,Quinn C Vega,Jean S Campbell,Mary Pat Wenderoth,Stephen D Hauschka,Edwin G Krebs,Jack E Dixon

doi:10.1074/jbc.271.7.3795

Abstract

Dual specificity protein tyrosine phosphatases (dsPTPs) are a subfamily of protein tyrosine phosphatases implicated in the regulation of mitogen-activated protein kinase (MAPK). In addition to hydrolyzing phosphotyrosine, dsPTPs can hydrolyze phosphoserine/threonine-containing substrates and have been shown to dephosphorylate activated MAPK. We have identified a novel dsPTP, rVH6, from rat hippocampus. rVH6 contains the conserved dsPTP active site sequence, VXVHCX2GX2RSX5AY(L/I)M, and exhibits phosphatase activity against activated MAPK. In PC12 cells, rVH6 mRNA is induced during nerve growth factor-mediated differentiation but not during insulin or epidermal growth factor mitogenic stimulation. In MM14 muscle cells, rVH6 mRNA is highly expressed in proliferating cells and declines rapidly during differentiation. rVH6 expression correlates with the inability of fibroblast growth factor to stimulate MAPK activity in proliferating but not in differentiating MM14 cells. rVH6 protein localizes to the cytoplasm and is the first dsPTP to be localized outside the nucleus. This novel subcellular localization may expose rVH6 to potential substrates that differ from nuclear dsPTPs substrates.

Highlights

Extracellular signals, such as mitogenic growth factors, bind to specific cell surface receptors that, in turn, initiate intracellular signaling through activation of a series of protein kinases
In COS-1 cells, expressed rVH6 protein localizes to the cytoplasm, and is the first Dual specificity protein tyrosine phosphatases (dsPTPs) to be localized outside the nucleus. rVH6 mRNA is induced in PC12 cells following nerve growth factor (NGF)-mediated differentiation but is not induced following insulin or epidermal growth factor (EGF) mitogenic stimulation
Identification and Cloning of rVH6 cDNA—Degenerate oligonucleotides were used to isolate novel dsPTPs from rat olfactory epithelium cDNA by polymerase chain reaction (PCR)

Summary

A Novel Cytoplasmic Dual Specificity Phosphatase

MAPK activity observed in NGF-mediated neuronal differentiation [23]. In proliferating MM14 myoblasts, rVH6 mRNA levels are expressed at high levels and decline rapidly following commitment to muscle differentiation. The loss of rVH6 message correlates with the ability of basic fibroblast growth factor (bFGF) to stimulate MAPK activity in MM14 muscle cells. The widespread expression of rVH6, as well as its induction by NGF and bFGF, delineates a potential role for rVH6 in regulating proliferation and differentiation

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION