Platelet-derived growth factor-stimulated c-myc RNA accumulation in MG-63 human osteosarcoma cells is independent of both protein kinase A and protein kinase C.
AUTOR(ES)
Frick, K K
RESUMO
Treatment of quiescent MG-63 cells with 12-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 1,9-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.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=360726Documentos Relacionados
- Modification of the 85-kilodalton subunit of phosphatidylinositol-3 kinase in platelet-derived growth factor-stimulated cells.
- Platelet-Derived Growth Factor-Stimulated Expression of the MCP-1 Immediate-Early Gene Involves an Inhibitory Multiprotein Complex
- P21 v-ras inhibits induction of c-myc and c-fos expression by platelet-derived growth factor.
- Loss of platelet-derived growth factor-stimulated phospholipase activity in NIH-3T3 cells expressing the EJ-ras oncogene.
- Opposing effects of a ras oncogene on growth factor-stimulated phosphoinositide hydrolysis: desensitization to platelet-derived growth factor and enhanced sensitivity to bradykinin.