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Expression of c-myc gene in human ovary carcinoma cells treated with vanadate
A V Itkes1, L R Imamova, N M Alexandrova
1Engelhardt Institute of Molecular Biology, USSR Academy of Sciences, Moscow.
Abstract:
The widely accepted hypothesis of vanadate action on cells postulates that this ion inhibits protein phosphatase(s) that dephosphorylates protein phosphotyrosine residues. This inhibition causes tyrosine hyperphosphorylation of cell proteins followed by changes in physiological action of phosphoproteins resulting in stimulation of cell proliferation, expression of protooncogenes, and transient cell transformation. We have found that treatment of human ovary carcinoma (CaOv) cells with vanadate causes the increase in total protein phosphorylation from 1.5- to 2.0-fold whereas the ratio between phosphoserine, phosphothreonine, and phosphotyrosine content remains unchanged. At the same time, enhancement of c-myc gene expression (not c-fos) was observed. Hence, the increase in the ratio of phosphotyrosine to phosphoserine and phosphothreonine is not an obligatory intermediate stage before vanadate-dependent activation of c-myc expression.
Insights
Vanadate treatment increases overall protein phosphorylation in human ovary carcinoma cells. This leads to enhanced c-myc gene expression, challenging the idea that tyrosine hyperphosphorylation is required.
Area of Science:
- Cell Biology
- Biochemistry
- Oncology
Background:
- Vanadate is hypothesized to inhibit protein phosphatases, leading to tyrosine hyperphosphorylation.
- This process is thought to stimulate cell proliferation and protooncogene expression.
Purpose of the Study:
- To investigate the effect of vanadate on protein phosphorylation and gene expression in human ovary carcinoma cells.
- To determine if increased phosphotyrosine levels are necessary for vanadate-induced c-myc expression.
Main Methods:
- Treatment of human ovary carcinoma (CaOv) cells with vanadate.
- Analysis of total protein phosphorylation levels.
- Quantification of phosphoserine, phosphothreonine, and phosphotyrosine content.
- Measurement of c-myc and c-fos gene expression.
Main Results:
- Vanadate treatment increased total protein phosphorylation 1.5- to 2.0-fold in CaOv cells.
- The ratio of phosphoserine, phosphothreonine, and phosphotyrosine remained unchanged.
- Vanadate enhanced c-myc gene expression but not c-fos expression.
Conclusions:
- Increased phosphotyrosine levels are not essential for vanadate-mediated c-myc gene activation.
- Vanadate's effects on gene expression may involve mechanisms beyond simple tyrosine hyperphosphorylation.