No abstract

Stimulation of fibroblasts with serum growth factors results in the rapid activation ofa set of immediate-early genes, among them 3CH134. We have purified a bacterially expressed form of the 3CH134-encoded polypeptide and demonstrated that it has intrinsic protein-tyrosine-phosphatase (PTPase; protein-tyrosine-phosphate phosphohydrolase, EC 3.1.3.48) activity in vitro. This activity is optimal at pH 7.5, is sensitive to vanadate and cysteinyl modifying agents, and is insensitive to a panel of serine/threonine phosphatase inhibitors. Purified 3CH134 protein displays a high degree of selectivity among the tyrosine-phosphorylated polypeptide substrates tested. Under our assay conditions, the rates of dephosphorylation are in the order EDNDYINASL peptide < myelin basic protein < reduced, carboxyamidomethylated, and maleylated lysozyme (RCML) < p42m%*. There is a 200-fold range in rates for these substrates, with p42maPac dephosphorylated 15-fold more rapidly than RCML. Although 3CH134 is most closely related to the tyrosine/serine dual-speciffcity phosphatase VH1, we failed to detect any 3CH134-directed activity on casein or RCML phosphorylated on serine/threonine residues by cAMP-dependent protein kinase. Since 3CH134 expression is controlled transcriptionally and posttranscriptionally, it may represent a class of PTPases whose activity is regulated at the level of protein synthesis and degradation.Serum growth factors stimulate cell proliferation through interactions with their specific cell-surface receptors, activating the intrinsic receptor protein-tyrosine kinases (PTKs; ATP: protein-tyrosine O-phosphotransferase, EC 2.7.1.112). This leads to signal transduction events that include reversible phosphorylation of a number of cellular substrates on tyrosyl residues. Some of these signals are transmitted to the nucleus, where the activation of a set of immediate-early genes occurs. These immediate-early genes encode a diverse array of regulatory proteins including transcription factors and cytokines (1-3). Their expression has been hypothesized to mediate the biological effects of the stimulatory growthfactor.An important feature of these phosphorylation events is their reversibility. The actions of PTKs in conjunction with the activity of a family of protein-tyrosine-phosphatases (PTPases; protein-tyrosine-phosphate phosphohydrolase, EC 3.1.3.48) control the phosphorylation state of tyrosyl residues in signaling proteins. The PTPases include transmembrane, receptor-like, and cytoplasmic enzymes defined by a unique sequence motif, (I/V)HCXAGXXR(S/T)G (4). We have noted that this motif, which contains a cysteinyl residue essential for activity, is present in the predicted sequence of the protein product encoded by the immediateearly gene 3CH134 (5).The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.3CH134 is activated rapidly and transiently in quiesce...

No abstract