Cancer Research Center , Boston University School of Medicine , Massachusetts 02118 .
J Biol Chem 270 : 3100-6 ( 1995)
Abstract
The interferon-inducible , double-stranded RNA ( dsRNA)-dependent eukaryotic initiation factor-2 alpha kinase PKR has primarily been characterized as a component of the interferon-mediated cellular antiviral response .
Several lines of evidence now exist that suggest that PKR plays a role in the regulation of growth in uninfected cells .
The most direct examples are the finding of an oncogenic variant of PKR and the effects of activators and inhibitors of PKR phosphorylation on the expression of platelet-derived growth factor ( PDGF)-inducible genes .
Previous reports have shown that 1 ) dsRNA , a direct activator of PKR , induces the genes c-myc , c-fos , and JE ; 2 ) 2-aminopurine , a chemical inhibitor of PKR , blocks the induction of these genes by serum ; and 3 ) activated p21ras induces a cellular inhibitor of PKR .
We report here that activation of PKR was correlated with the induction of the immediate early genes c-fos , c-myc , and JE by PDGF in the following situations : 1 ) PDGF induction of these genes , also inducible by dsRNA , was blocked by two inhibitors of PKR activation : 2-aminopurine and v-ras ; 2 ) PDGF induction of another immediate early gene , egr-1 , which could not be induced by dsRNA , was not blocked by 2-aminopurine or v-ras ; 3 ) agents that reverse v-ras inhibition of PKR activation also reversed the v-ras block of PDGF induction of c-myc , c-fos , and JE ; 4 ) down-regulation of PKR protein levels by antisense inhibition of translation blocked the induction of c-myc , c-fos , and JE by PDGF , but had no effect on egr-1 induction ; and finally , 5 ) PKR was autophosphorylated in vivo in response to PDGF .
These results provide direct evidence that PKR activation functions as a second messenger in a growth factor signal transduction pathway .
Thus , PKR may serve as a common mediator of growth-promoting and growth inhibitory signals .
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Chemical Identifiers ( Names)
Department of Biochemistry , Gifu University School of Medicine , Japan .
Biochem Biophys Res Commun 207 : 460-6 ( 1995)
Abstract
Platelet-derived growth factor ( PDGF ) , a potent mitogen for fibroblasts and many other cell types , was used to examine phosphatidylcholine-specific phospholipase D ( PLD ) , phosphoinositide-specific phospholipase C ( PI-PLC ) and tyrosine phosphorylation in NIH3T3 fibroblast and its Ki-ras-transformed derivative , DT .
When cells prelabeled with [ 3H ] myristic acid were stimulated by 10 and 50 ng/ml of PDGF in presence of 0.3% butanol , formation of phosphatidylbutanol ( PtdBut ) was increased three to six fold in NIH3T3 fibroblasts whereas it was marginal in DT cells .
Myo-[3H]inositol-labeled cells showed higher inositol phosphate production in nontransformed control fibroblasts , indicating higher phospholipase C activity compared to the transformed DT cells .
PDGF caused increase in tyrosine phosphorylation of a group of proteins with -130 kDa , PLC-gamma 1 and PDGF receptor in NIH3T3 cells .
There was no significant increase in tyrosine phosphorylation in both PDGF receptor and PLC-gamma 1 in DT cells .
These results suggest that PLD acts as a downstream effector molecule of PLC-gamma 1 in the PDGF-mediated signal transduction pathway .
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Chemical Identifiers ( Names)
Max-Planck Society , Research Group Growth Factor Signal Transduction , Medical Faculty , Friedrich-Schiller University , Jena , Germany .
Cancer Res 54 : 6106-14 ( 1994)
Abstract
A novel class of tyrosine kinase blockers represented by the tyrphostins AG1295 and AG1296 is described .
These compounds inhibit selectively the platelet-derived growth factor ( PDGF ) receptor kinase and the PDGF-dependent DNA synthesis in Swiss 3T3 cells and in porcine aorta endothelial cells with 50% inhibitory concentrations below 5 and 1 microM , respectively .
The PDGF receptor blockers have not effect on epidermal growth factor receptor autophosphorylation ; weak effects on DNA synthesis stimulated by insulin , by epidermal growth factor , or by a combination of both ; and over an order of magnitude weaker blocking effect on fibroblast growth factor-dependent DNA synthesis .
AG1296 potently inhibits signaling of human PDGF alpha- and beta-receptors as well as of the related stem cell factor receptor ( c-Kit ) but has no effect on autophosphorylation of the vascular endothelial growth factor receptor KDR or on DNA synthesis induced by vascular endothelial growth factor in porcine aortic endothelial cells .
Treatment by AG1296 reverses the transformed phenotype of sis-transfected NIH 3T3 cells but has no effect on src-transformed NIH 3T3 cells or on the activity of the kinase p60c-src(F527 ) immunoprecipitated from these cells .
These potent and selective compounds represent leads for the development of novel agents to combat tumors driven by PDGF or to inhibit PDGF action in other diseases in which PDGF plays a key role , such as restenosis .