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v-mos oncoproteins affect the nuclear retention and reutilization of glucocorticoid receptors
M Qi1, B J Hamilton, D DeFranco
1Department of Biological Sciences, University of Pittsburgh, Pennsylvania 15260.
Abstract:
Expression of the p85gag-mos oncoprotein in temperature sensitive transformed 6m2 cells results in desensitization of glucocorticoid induction of metallothionein-1 mRNA. Indirect immunofluorescence analyses demonstrate that hormone insensitivity in v-mos transformed cells is associated with inefficient nuclear retention of glucocorticoid receptor (GR) protein. Desensitized receptors that accumulate in the cytoplasm of transformed 6m2 cells do not regain the capacity for hormone-dependent nuclear translocation after turnover of the thermo-labile p85gag-mos oncoprotein. Although ligand induced down-regulation of immunoreactive GR protein occurs in transformed 6m2 cells, desensitized receptors appear to retain some capacity to bind hormone in vivo. Thus alterations in the intracellular partitioning of GR protein in v-mos-transformed cells result in the generation of a novel desensitized receptor that is apparently trapped in the cytoplasm and incapable of being reutilized.
Insights
The v-mos oncoprotein desensitizes glucocorticoid receptor (GR) function in cells, trapping it in the cytoplasm. This prevents GR from responding to hormones, even after the oncoprotein is removed.
Area of Science:
- Molecular Biology
- Cell Biology
- Oncology
Background:
- Glucocorticoids regulate gene expression via the glucocorticoid receptor (GR).
- Oncoproteins can disrupt normal cellular signaling pathways.
- Metallothionein-1 (MT-1) gene expression is a known target of glucocorticoid induction.
Purpose of the Study:
- To investigate the mechanism by which the v-mos oncoprotein affects glucocorticoid-induced gene expression.
- To determine the role of glucocorticoid receptor (GR) intracellular localization in v-mos-mediated desensitization.
Main Methods:
- Utilized temperature-sensitive v-mos transformed 6m2 cells.
- Performed indirect immunofluorescence to analyze GR protein localization.
- Assessed metallothionein-1 mRNA levels to measure glucocorticoid response.
Main Results:
- v-mos oncoprotein expression desensitized glucocorticoid induction of MT-1 mRNA.
- Hormone insensitivity correlated with inefficient nuclear retention of GR protein.
- Desensitized GR accumulated in the cytoplasm and could not be reactivated after v-mos removal.
Conclusions:
- v-mos transformation alters GR intracellular partitioning, leading to cytoplasmic trapping.
- This results in a novel desensitized GR phenotype, unresponsive to hormone stimulation.
- The findings highlight GR mislocalization as a mechanism of oncoprotein-induced hormone resistance.