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Inhibition of Fos- and Ras-induced transformation by mutant Fos proteins with structural alterations in functionally
M Wick1, F C Lucibello, R Müller
1Institut für Molekularbiologie und Tumorforschung (IMT), Phillips-Universität Marburg, Germany.
Abstract:
We show that transformation-defective Fos proteins lacking either a functional leucine zipper (mutants L345 and J/R510s) or the 110 amino-terminal amino acids (mutant BR800) inhibit the induction of morphological transformation by v-Fos. Both types of mutants specifically repress transformation without any significant effect on cell proliferation. In contrast, several transformation-defective Fos mutants with structural alterations in the acidic region or the right half of the adjacent basic DNA contact site do not show any inhibition of transformation. This result, taken together with the repression of transformation by the leucine zipper-deficient mutants L345 and J/R510s, indicates that the interaction of Fos with proteins other than Jun is necessary for transformation. The leucine zipper-deficient mutants also inhibit Fos-mediated activation of AP-1-dependent transcription. This suggests that their inhibitory effect on transformation may at least in part be the result of the squelching of proteins other than Jun family members that are required for Fos-mediated transactivation. All three mutants were also found to inhibit transformation by the point-mutated H-ras oncogene from EJ carcinoma cells and to trigger a partial reversion of the transformed phenotype of Ras-transformed fibroblasts. These findings support the conclusion that Ras-induced transformation involves signal transduction pathways inducing the c-fos gene.
Insights
Transformation-defective Fos proteins lacking leucine zippers or N-terminal domains inhibit v-Fos-induced cell transformation. This suggests Fos interacts with non-Jun proteins for transformation and Ras signaling pathways activate c-fos.
Area of Science:
- Oncogenic transformation
- Cell signaling pathways
- Protein-protein interactions
Background:
- The Fos oncoprotein plays a critical role in cellular transformation and gene regulation.
- Understanding Fos protein interactions is crucial for deciphering oncogenic signaling pathways.
- Specific domains of Fos are essential for its transforming activity and transcriptional regulation.
Purpose of the Study:
- To investigate the role of specific Fos protein domains in v-Fos-induced cellular transformation.
- To determine whether Fos interaction with non-Jun proteins is required for transformation.
- To elucidate the mechanism by which Fos regulates transformation and its relationship with Ras signaling.
Main Methods:
- Generation and characterization of transformation-defective Fos mutants (L345, J/R510s, BR800).
- Assays for morphological transformation induction by v-Fos and inhibition by Fos mutants.
- Analysis of cell proliferation and AP-1-dependent transcriptional activation.
- Investigation of inhibition of H-ras oncogene-induced transformation and reversion of Ras-transformed phenotype.
Main Results:
- Fos mutants lacking functional leucine zippers or N-terminal domains inhibit v-Fos-induced transformation without affecting cell proliferation.
- Mutants altering acidic or DNA-binding regions do not inhibit transformation.
- Leucine zipper-deficient mutants inhibit AP-1 transcriptional activation, suggesting squelching of non-Jun proteins.
- These mutants also inhibit H-ras-induced transformation and partially revert Ras-transformed cells.
Conclusions:
- Fos interaction with proteins other than Jun is necessary for cellular transformation.
- The inhibitory effects of leucine zipper mutants may involve squelching of essential non-Jun cofactors.
- Ras-induced transformation involves signal transduction pathways that activate the c-fos gene.