Suppression of tumorigenicity in simian virus 40-transformed 3T3 cells transfected with alpha-actinin cDNA
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U Glück1, D J Kwiatkowski, A Ben-Ze'ev
1Department of Molecular Genetics and Virology, Weizmann Institute of Science, Rehovot, Israel.
Abstract:
Human cytoskeletal alpha-actinin cDNA was transfected into highly malignant simian virus 40-transformed BALB/c 3T3 (SVT2) cells that express 6-fold lower levels of alpha-actinin than nontransformed BALB/c 3T3 cells. SVT2 clones expressing various levels of alpha-actinin were isolated and their structure and tumorigenic properties were determined. Transfected SVT2 clones expressing alpha-actinin at levels found in nontumorigenic 3T3 cells displayed a flatter phenotype, a decreased ability to grow in suspension culture in soft agar, and a marked reduction in their ability to form tumors in syngeneic BALB/c mice and in athymic nude mice. Clones overexpressing alpha-actinin at the highest level (about 2-fold higher than 3T3 cells) were completely suppressed in their ability to form tumors in syngeneic BALB/c mice. The results suggest that alpha-actinin, an actin-crosslinking protein that is also localized in cell junctions, may have an effective suppressive ability on the transformed phenotype.
Insights
Restoring alpha-actinin levels in malignant cells reduced their tumor-forming ability and altered their structure. This suggests alpha-actinin, an actin-crosslinking protein, may suppress the transformed cell phenotype.
Area of Science:
- Cell Biology
- Molecular Biology
- Cancer Research
Background:
- Simian virus 40-transformed BALB/c 3T3 (SVT2) cells exhibit significantly lower alpha-actinin levels compared to normal cells.
- Alpha-actinin, an actin-crosslinking protein, is also found in cell junctions and plays a role in cytoskeletal organization.
Purpose of the Study:
- To investigate the functional role of alpha-actinin in the malignant transformation of SVT2 cells.
- To determine if restoring alpha-actinin expression can reverse or suppress the transformed phenotype and tumorigenicity.
Main Methods:
- Transfection of human cytoskeletal alpha-actinin cDNA into SVT2 cells.
- Isolation and characterization of SVT2 clones with varying levels of alpha-actinin expression.
- Assessment of cellular phenotype (morphology, growth in soft agar) and tumorigenic potential in vivo (syngeneic and athymic nude mice).
Main Results:
- SVT2 clones expressing alpha-actinin at levels comparable to normal cells showed a flatter morphology and reduced anchorage-independent growth.
- Restored alpha-actinin expression significantly reduced tumor formation in both syngeneic BALB/c and athymic nude mice.
- Highest levels of alpha-actinin expression completely suppressed tumor formation in syngeneic mice.
Conclusions:
- Alpha-actinin expression levels are inversely correlated with the transformed phenotype and tumorigenicity of SVT2 cells.
- Alpha-actinin may function as a tumor suppressor by reversing malignant characteristics.
- The actin-crosslinking and cell junction localization of alpha-actinin are likely important for its tumor-suppressive effects.