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U0126 reverses Ki-ras-mediated transformation by blocking both mitogen-activated protein kinase and p70 S6 kinase
1Department of Bioactive Molecules, National Institute of Infectious Diseases, Tokyo, Japan.
Abstract:
U0126, a recently introduced mitogen-activated protein kinase [corrected] (MAPK)/extracellular signal-regulated kinase kinase inhibitor reversed morphology and inhibited anchorage-independent growth of Ki-ras-transformed rat fibroblasts. Immunoblot analyses with phosphospecific antibodies indicated that in addition to MAPK, U0126 suppressed activation of p70(S6K), but not Akt, at concentrations at which it normalized the transformed phenotypes. Another MAPK/extracellular signal-regulated kinase kinase inhibitor, PD98059, showed only marginal effects on p70S6K phosphorylation and did not effectively block Ki-ras-induced transformation. However, simultaneous inhibition of the MAPK pathway and the p70S6K pathway by PD98059 in conjunction with the p70S6K inhibitor rapamycin essentially restored the normal phenotype. U0126 or the combination of PD98059 and rapamycin flattened morphology of v-src-transformed cells, but did not reverse anchorage independence, although activation of both MAPK and p706K was blocked. The results suggest that normalization of Ki-ras-induced transformed phenotypes by U0126 is a consequence of concurrent inhibition of the MAPK and p70S6K pathways. Intervention of other pathway(s) appears to be required to completely antagonize transformation by v-src. Simultaneous blockade of more than one signal transduction pathway by combining selective inhibitors might be effective in suppressing uncontrolled tumorigenic growth.
Insights
U0126, a MAPK/ERK kinase inhibitor, normalized Ki-ras-transformed cells by inhibiting both MAPK and p70S6K pathways. Combining inhibitors may effectively suppress tumorigenic growth.
Area of Science:
- Molecular Biology
- Cell Biology
- Cancer Research
Background:
- Ras and Src oncoproteins are key drivers of cellular transformation and tumorigenesis.
- Mitogen-activated protein kinase (MAPK) pathway is frequently activated in cancer.
- Targeting signal transduction pathways offers potential for cancer therapy.
Purpose of the Study:
- To investigate the effects of MAPK/ERK kinase inhibitors on Ki-ras-induced cellular transformation.
- To elucidate the specific signaling pathways involved in U0126-mediated reversal of transformed phenotypes.
- To explore the potential of combined pathway inhibition for cancer treatment.
Main Methods:
- Utilized U0126 and PD98059, MAPK/ERK kinase inhibitors, and rapamycin, a p70S6K inhibitor.
- Assessed cellular morphology and anchorage-independent growth in transformed rat fibroblasts.
- Employed immunoblot analyses with phosphospecific antibodies to detect protein activation.
Main Results:
- U0126 reversed Ki-ras-transformed cell morphology and inhibited growth by suppressing MAPK and p70S6K activation.
- PD98059 showed limited efficacy alone but, combined with rapamycin, restored normal phenotype.
- Combined inhibition of MAPK and p70S6K pathways was crucial for normalizing Ki-ras transformation, but not v-src transformation.
Conclusions:
- U0126 normalizes Ki-ras-induced transformation through concurrent inhibition of MAPK and p70S6K pathways.
- Targeting multiple signal transduction pathways simultaneously may be a viable strategy for suppressing tumorigenic growth.
- Further investigation is needed to identify pathways for complete antagonism of v-src-induced transformation.