The protein kinase activity of the large subunit of herpes simplex virus type 2 ribonucleotide reductase (ICP10) fused to the extracellular domain of the epidermal growth factor receptor is ligand-inducible.
The gene coding for the large subunit of herpes simplex virus type 2 ribonucleotide reductase (RR) (ICP10) has a unique 5' terminal domain the product of which has a serine/threonine (Ser/Thr) protein kinase (PK) catalytic domain preceded by a transmembrane (TM) segment. Because ICP10 localizes on the cell surface and is internalized by the endocytic pathway like an activated growth factor receptor (Hunter et al., 1995, Virology 210, 345-360), we asked whether it is ligand-inducible in order to examine whether it has intrinsic transphosphorylating activity. We constructed a chimeric expression vector that contains the extracellular and TM domains of the epidermal growth factor receptor (EGFR) joined to the intracellular PK and RR domains of ICP10 (pCH5) and established constitutively expressing cell lines in NIH3T3 2.2 cells that do not express EGFR. The chimeric protein, designated p210 CH5, localized to the surface of these cells as determined by immunofluorescent staining with MAb EGFR, and it bound 125I-EGF.p210 CH5 coprecipitated with protein species p170, p120, p88, p60, p44, p34, and p25. EGF treatment activated the PK activity of p210 CH5, resulting in its autophosphorylation and the phosphorylation of the p120, p88, and p34 species. Immunoprecipitation/immunoblotting with anti-ras-GAP antibody and phosphoamino acid analysis indicated that p120 is ras-GAP and it is phosphorylated on Ser/Thr residues. The identities of the phosphorylated p88 and p34 are still unknown. The data indicate that when fused to a ligand-regulated extracellular domain (EGFR), the ICP10 PK auto- and transphosphorylating activities are ligand-inducible. These findings support the interpretation that the ICP10 PK activity is intrinsic and indicate that ras-GAP is one of its phosphorylation substrates.
Smith
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CC
Department of Pharmacology, University of Maryland School of Medicine, Baltimore 21201, USA.
Luo
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JH
Aurelian
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D016475:3T3 Cells; D000818:Animals; D002451:Cell Compartmentation; D002462:Cell Membrane / Q000378:metabolism; D004789:Enzyme Activation; D004815:Epidermal Growth Factor / Q000378:metabolism; D066246:ErbB Receptors / Q000737:chemistry*; D020690:GTPase-Activating Proteins; D018258:Herpesvirus 2, Human / Q000201:enzymology*; D051379:Mice; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry*; D011506:Proteins / Q000378:metabolism; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D012264:Ribonucleotide Reductases / Q000737:chemistry*; D015398:Signal Transduction; D020703:ras GTPase-Activating Proteins
D020690:GTPase-Activating Proteins; D011506:Proteins; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D020703:ras GTPase-Activating Proteins; D004815:Epidermal Growth Factor; D012264:Ribonucleotide Reductases; D066246:ErbB Receptors; D017346:Protein Serine-Threonine Kinases