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Morphology of ras-transformed cells becomes apparently normal again with tyrosine kinase inhibitors without a
Abstract:
Radicicol, an inhibitor of protein-tyrosine kinase, was found to cause morphological reversion of v-Ha-ras-transformed NIH3T3 fibroblasts and T24 human urinary bladder carcinoma cells that contain an activated ras mutation. The network of actin stress fibers was restored during the treatment with radicicol. A similar morphological change was observed with another protein-tyrosine kinase inhibitor, herbimycin A. Radicicol did not cause any changes in the proportion of the active GTP binding form of p21ras or its subcellular localization. These results rule out the possibility that the morphological reversion by radicicol is due to direct or indirect inhibition of the p21ras function. Cycloheximide and actinomycin D inhibited the morphological change by radicicol, suggesting that the induced transcription of a gene(s) followed by de novo protein synthesis is required for suppression of the transformed phenotype in ras-transformed cells by tyrosine kinase inhibitors.
Insights
Radicicol, a protein-tyrosine kinase inhibitor, reversed ras-transformed cell morphology by restoring actin stress fibers. This effect requires new gene transcription and protein synthesis, not direct p21ras inhibition.
Area of Science:
- Oncology
- Cell Biology
- Biochemistry
Background:
- Ras-transformed cells exhibit altered morphology and actin cytoskeleton organization.
- Protein-tyrosine kinases play a role in regulating cell growth and transformation.
- Actin stress fiber restoration is a marker for reversion of the transformed phenotype.
Purpose of the Study:
- To investigate the effect of radicicol, a protein-tyrosine kinase inhibitor, on ras-transformed cells.
- To elucidate the mechanism by which radicicol suppresses the transformed phenotype.
- To determine if radicicol's action involves direct inhibition of p21ras function.
Main Methods:
- Treatment of v-Ha-ras-transformed NIH3T3 fibroblasts and T24 human urinary bladder carcinoma cells with radicicol.
- Assessment of cell morphology and actin stress fiber network.
- Analysis of p21ras GTP-binding activity and subcellular localization.
- Inhibition studies using cycloheximide and actinomycin D.
Main Results:
- Radicicol induced morphological reversion in ras-transformed cells, accompanied by restoration of actin stress fibers.
- No changes were observed in the active GTP-binding form or subcellular localization of p21ras.
- Co-treatment with cycloheximide or actinomycin D blocked the morphological reversion induced by radicicol.
- Herbimycin A, another tyrosine kinase inhibitor, produced similar morphological changes.
Conclusions:
- Radicicol suppresses the transformed phenotype in ras-transformed cells through a mechanism independent of direct p21ras inhibition.
- The morphological reversion is dependent on induced gene transcription and de novo protein synthesis.
- Tyrosine kinase inhibitors represent a potential therapeutic strategy for targeting ras-mutated cancers.