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The mdm-2 oncogene is translocated and overexpressed in a murine plasmacytoma cell line expressing wild-type p53
1Department of Biochemistry and Molecular Biology, Wright State University, Dayton, Ohio.
Abstract:
The cellular p53 protein has been demonstrated to possess growth-inhibitory activity. Recent work suggests that the murine double minute gene (mdm-2) encodes a protein that may function as a cellular regulator or mediator of p53 function. We were interested in determining if the mdm-2 gene was overexpressed in mouse tumor cells, in particular mouse plasmacytomas that harbor wild type-p53 protein. A novel chromosomal translocation of the mdm-2 gene was detected in the SP2 cell line, that is derived from plasmacytoma MOPC21. The translocation results in a head-to-head arrangement of the mdm-2 gene (chromosome 10) with the immunoglobulin C kappa gene (chromosome 6), analogous to the translocations that activate the c-myc gene in murine plasmacytomas. Based on Northern blot analysis, the translocation induces a 10-fold elevation of mdm-2 RNA. Primer extension assays demonstrate that the 5' end of the mdm-2 RNA from the translocated gene is colinear with the 5' mdm-2 mRNA from an unrearranged gene, suggesting that the mRNA and encoded protein are unaltered. This chromosomal translocation represents the first example in which mdm-2 overexpression is activated by a genetic alteration other than gene amplification.
Insights
A novel chromosomal translocation activates the murine double minute gene (mdm-2) in mouse plasmacytoma cells. This genetic alteration leads to a 10-fold increase in mdm-2 RNA, representing a new mechanism for gene overexpression.
Area of Science:
- Molecular Biology
- Cancer Genetics
- Cellular Regulation
Background:
- The p53 protein exhibits growth-inhibitory properties.
- The murine double minute gene (mdm-2) encodes a protein potentially regulating p53 function.
- Investigating mdm-2 gene expression in wild-type p53 mouse tumor cells is crucial.
Purpose of the Study:
- To determine if the mdm-2 gene is overexpressed in mouse tumor cells, specifically plasmacytomas.
- To identify the mechanism of mdm-2 overexpression in these tumor cells.
Main Methods:
- Detection of chromosomal translocations in the SP2 plasmacytoma cell line.
- Northern blot analysis to quantify mdm-2 RNA levels.
- Primer extension assays to analyze mdm-2 mRNA structure.
Main Results:
- A novel head-to-head translocation between the mdm-2 gene (chromosome 10) and the immunoglobulin C kappa gene (chromosome 6) was identified in the SP2 cell line.
- Northern blot analysis revealed a 10-fold elevation in mdm-2 RNA levels due to the translocation.
- Primer extension assays confirmed that the translocated mdm-2 mRNA and its encoded protein remain unaltered.
Conclusions:
- This chromosomal translocation is the first identified mechanism activating mdm-2 overexpression independent of gene amplification.
- The findings provide new insights into the regulation of mdm-2 in cancer development.
- This study establishes a novel genetic alteration leading to mdm-2 overexpression in murine plasmacytomas.