Division of Oncology , Children 's Hospital of Philadelphia , Pennsylvania .
Mol Cell Biol 10 : 184-92 ( 1990)
Abstract
Treatment of quiescent MG-63 cells with -O-tetradecanoylphorbol-13-acetate ( TPA ) or platelet-derived growth factor ( PDGF ) stimulates the rapid accumulation of c-myc RNA .
We have now determined that a similar effect can be induced by cAMP .
Treatment with forskolin ( an activator of adenylate cyclase ) , IBMX ( a phosphodiesterase inhibitor ) , PGE1 , and isoproterenol stimulated accumulation of both cAMP and c-myc RNA , but no increase in either cAMP or c-myc RNA was seen with the inactive forskolin analog , 9-dideoxyforskolin .
Forskolin and IBMX acted synergistically in stimulating accumulation of both cAMP and c-myc RNA .
However , three lines of evidence indicated that PDGF action is not mediated by cAMP .
First , PDGF treatment caused no elevation of cAMP within 1 h , even in the presence of IBMX .
Second , the kinetics of c-myc RNA elevation after treatment with PDGF or forskolin were similar , ruling out delayed onset of cAMP stimulation .
Finally , simultaneous treatment with forskolin and the calcium ionophore A23187 enhanced the elevation of c-myc RNA levels ; no such effect was seen with PDGF .
We had previously shown that PDGF action is not affected by prior treatment of MG-63 cells with TPA , a treatment which desensitizes the c-myc response to TPA .
Similarly , TPA pretreatment had minimal effect on forskolin or IBMX-induced c-myc expression .
These data suggest that cAMP , phorbol esters , and PDGF act independently to stimulate c-myc RNA expression in MG-63 cells .
However , nuclear runoff experiments and RNA half-life measurements demonstrated that PDGF , phorbol ester , and cAMP all act to increase the transcription of the MYC gene .