Abstract
Activated ras is known to dysregulate TGF-beta signaling by altering the expression of TGF-beta type II receptor (RII). It is well documented that tumor cells harboring mutant ras are more resistant to radiation than cells with wild-type ras. In this study, we hypothesized that the use of farnesyltransferase inhibitor (FTI, L-744,832) may directly restore TGF-beta signaling through RII expression via ras dependent or independent pathway leading to induction of radiation sensitivity. Two pancreatic cancer cell lines, BxPC-3 and MIA PaCa-2 were used in this study. FTI inhibited farnesylation of Ras protein more significantly in MIA PaCa-2 than BxPC-3 cells. In contrast, MIA PaCa-2 cells were resistant to radiation when compared to BxPC-3 cells. BxPC-3 cells were more resistant to FTI than MIA PaCa-2 cells. In combination treatment, no significant radiosensitizing effect of FTI was observed in BxPC-3 cells at 5 or 10 microM. However, in MIA PaCa-2 cells, a significant radiosensitizing effect was observed at both 5 and 10 microM concentrations (P>0.004). The TGF-beta effector gene p21(waf1/cip1) was elevated in combination treatment in MIA PaCa-2 but not in BxPC-3 cells. In MIA PaCa-2 cells, FTI induced TGF-beta responsive promoter activity as assessed by 3TP-luciferase activity. A further induction of luciferase activity was observed in MIA PaCa-2 cells treated with radiation and FTI. Induction of TGF-beta signaling by FTI was mediated through restoration of the RII expression, as demonstrated by RT-PCR analysis. In addition, re-expression of RII by FTI was associated with a decrease in DNA methyltransferase 1 (DNMT1) levels. Thus, these findings suggest that the L-744,832 treatment restores the RII expression through inhibition of DNMT1 levels causing induction of TGF-beta signaling by radiation and this forms a novel molecular mechanism of radiosensitization by FTI.
Publication types
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Comparative Study
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Adenocarcinoma / metabolism
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Adenocarcinoma / pathology*
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Alkyl and Aryl Transferases / antagonists & inhibitors*
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Alkyl and Aryl Transferases / physiology
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Apoptosis / drug effects
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Apoptosis / radiation effects
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Cyclin-Dependent Kinase Inhibitor p21
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Cyclins / biosynthesis
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Cyclins / genetics
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DNA (Cytosine-5-)-Methyltransferase 1
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DNA (Cytosine-5-)-Methyltransferases / antagonists & inhibitors
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DNA (Cytosine-5-)-Methyltransferases / metabolism
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DNA Methylation / drug effects
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Enzyme Induction / drug effects
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Enzyme Inhibitors / pharmacology*
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Farnesyltranstransferase
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Gene Expression Regulation, Neoplastic / drug effects*
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Genes, ras*
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Humans
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Methionine / analogs & derivatives*
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Methionine / pharmacology*
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Neoplasm Proteins / antagonists & inhibitors
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Neoplasm Proteins / deficiency
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Neoplasm Proteins / genetics
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Neoplasm Proteins / physiology*
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Pancreatic Neoplasms / metabolism
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Pancreatic Neoplasms / pathology*
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Protein Prenylation / drug effects
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Protein Processing, Post-Translational / drug effects
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Protein Processing, Post-Translational / physiology
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Protein Serine-Threonine Kinases
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Proto-Oncogene Proteins p21(ras) / deficiency
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Proto-Oncogene Proteins p21(ras) / physiology*
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Radiation Tolerance / drug effects
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Radiation-Sensitizing Agents / pharmacology
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Receptor, Transforming Growth Factor-beta Type II
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Receptors, Transforming Growth Factor beta / biosynthesis*
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Receptors, Transforming Growth Factor beta / genetics
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Recombinant Fusion Proteins / physiology
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Regulatory Sequences, Nucleic Acid
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Signal Transduction / drug effects*
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Signal Transduction / physiology
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Transforming Growth Factor beta / immunology
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Transforming Growth Factor beta / pharmacology
Substances
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CDKN1A protein, human
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Cyclin-Dependent Kinase Inhibitor p21
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Cyclins
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Enzyme Inhibitors
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L 744832
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Neoplasm Proteins
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Radiation-Sensitizing Agents
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Receptors, Transforming Growth Factor beta
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Recombinant Fusion Proteins
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Transforming Growth Factor beta
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Methionine
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DNA (Cytosine-5-)-Methyltransferase 1
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DNA (Cytosine-5-)-Methyltransferases
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DNMT1 protein, human
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Alkyl and Aryl Transferases
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Farnesyltranstransferase
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Protein Serine-Threonine Kinases
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Receptor, Transforming Growth Factor-beta Type II
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Proto-Oncogene Proteins p21(ras)