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Increased G1 cyclin/cdk activity in cells overexpressing the candidate oncogene, MCT-1
J Dierov1, M Prosniak, G Gallia
1Center for NeuroVirology and NeuroOncology, MCP Hanhemann School of Medicine, Philadelphia, Pennsylvania 19102, USA.
Abstract:
We have recently identified a novel candidate oncogene, MCT-1, in the HUT 78 T-cell line. When overexpressed in NIH3T3 fibroblasts, the MCT-1 gene shortens the G1 phase of the cell cycle and promotes anchorage-independent growth. Progression of cells through a late G1 phase restriction point is regulated by G1 cyclins whose phosphorylation of the retinoblastoma gene product facilitates entry into S phase. Deregulated expression of G1 cyclins and their cognate cdk partners is often found in human tumor cells. In order to address the potential relationship of MCT-1 to cell cycle regulatory molecules, we analyzed the ability of MCT-1 overexpression to modulate cdk4 and cdk6 kinase activity in NIH3T3 fibroblasts constitutively overexpressing MCT-1. We observed an increase in the kinase activity of both cdk4 and cdk6 in asynchronously growing transformed cells compared with the parent cells. This increased kinase activity was accompanied by an elevated level of cyclin D1 protein and increased G1 cyclin/cdk complex formation. We also observed a correlation between increased protein levels of MCT-1 with cyclin D1 expression in a panel of lymphoid cell lines derived from T-cell malignancies. These results demonstrate that constitutive expression of MCT-1 is associated with deregulation of protein kinase-mediated G1 phase checkpoints.
Insights
The novel oncogene MCT-1 shortens the G1 cell cycle phase and promotes growth. MCT-1 overexpression increases cyclin D1 and cdk4/cdk6 kinase activity, suggesting a role in T-cell malignancies.
Area of Science:
- Oncology
- Molecular Biology
- Cell Cycle Regulation
Background:
- A novel candidate oncogene, MCT-1, was identified in the HUT 78 T-cell line.
- Overexpression of MCT-1 in NIH3T3 fibroblasts shortens the G1 phase and promotes anchorage-independent growth.
- Progression through the G1 restriction point is regulated by G1 cyclins and retinoblastoma protein phosphorylation, crucial for S phase entry.
Purpose of the Study:
- To investigate the relationship between MCT-1 and cell cycle regulatory molecules.
- To analyze the effect of MCT-1 overexpression on cdk4 and cdk6 kinase activity in NIH3T3 fibroblasts.
- To determine the correlation between MCT-1 levels and cyclin D1 expression in T-cell malignancies.
Main Methods:
- Overexpression of MCT-1 in NIH3T3 fibroblasts.
- Assay of cdk4 and cdk6 kinase activity in asynchronously growing cells.
- Western blot analysis of cyclin D1 protein levels.
- Analysis of MCT-1 and cyclin D1 expression in lymphoid cell lines.
Main Results:
- MCT-1 overexpression increased cdk4 and cdk6 kinase activity in NIH3T3 fibroblasts.
- Elevated cyclin D1 protein levels and increased G1 cyclin/cdk complex formation were observed.
- A correlation was found between increased MCT-1 protein levels and cyclin D1 expression in T-cell malignancy cell lines.
Conclusions:
- Constitutive MCT-1 expression is associated with deregulation of protein kinase-mediated G1 phase checkpoints.
- MCT-1 may play a significant role in the pathogenesis of T-cell malignancies through cell cycle dysregulation.