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Cellular transformation by a FERM domain mutant of the Nf2 tumor suppressor gene
Kristen C Johnson1, Joseph L Kissil, Jessica L Fry
1Department of Biology and Center for Cancer Research, Massachusetts Institute of Technology, Cambridge, Massachusetts, MA 02139, USA.
Abstract:
Mutations in the Nf2 tumor suppressor gene lead to tumor formation in humans and mice and cellular overproliferation phenotypes in Drosophila. The Nf2 encoded protein, merlin, shares close sequence similarity in its amino terminus to members of the band 4.1 family of membrane-cytoskeletal linkers. Similarities between merlin and this family suggest a role for merlin in regulating cytoskeletal function. However, the mechanism of the tumor suppressing activity of merlin is not yet understood. Mutational analysis of Nf2 in flies has led to the identification of a dominant-negative allele, which harbors mutations in the amino terminus of the protein. Here, we report that expression of a murine analog of this amino-terminal mutant of Nf2 leads to complete transformation of NIH3T3 fibroblasts in culture. Cells that express this Nf2 mutant allele display disruptions of the actin cytoskeleton, lack of contact inhibition of growth, and anchorage-independent growth. Finally, fibroblasts that express this mutant Nf2 allele form tumors when injected into nude mice.
Insights
Mutations in the Nf2 gene cause tumors by disrupting the merlin protein's function. This study shows a specific Nf2 mutation transforms cells and causes tumor formation in mice.
Area of Science:
- Molecular biology
- Cancer research
- Cell biology
Background:
- Mutations in the Neurofibromatosis type 2 (Nf2) tumor suppressor gene are linked to tumor formation in humans and mice.
- The Nf2 protein, merlin, resembles band 4.1 proteins, suggesting a role in cytoskeletal regulation.
- The precise mechanism of merlin's tumor-suppressive activity remains unclear.
Purpose of the Study:
- To investigate the functional consequences of Nf2 mutations, particularly those affecting the amino terminus.
- To determine if a specific Nf2 mutant can induce cellular transformation and tumor formation.
Main Methods:
- Expression of a murine analog of an amino-terminal mutant Nf2 allele in NIH3T3 fibroblasts.
- Analysis of cellular phenotypes including actin cytoskeleton organization, contact inhibition, and anchorage-independent growth.
- Tumorigenicity assessment by injecting transfected fibroblasts into nude mice.
Main Results:
- Expression of the mutant Nf2 allele induced complete transformation of NIH3T3 fibroblasts.
- Transformed cells exhibited disrupted actin cytoskeleton, loss of contact inhibition, and anchorage-independent growth.
- Fibroblasts expressing the mutant Nf2 allele formed tumors in vivo.
Conclusions:
- Amino-terminal mutations in Nf2 can lead to a dominant-negative effect, causing cellular transformation.
- Merlin's function, particularly its interaction with the cytoskeleton, is critical for its tumor-suppressive activity.
- This study provides insights into the molecular mechanisms underlying Nf2-associated tumorigenesis.