Suppression of tumorigenicity in simian virus 40-transformed 3T3 cells transfected with alpha-actinin cDNA.

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.