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

Abstract

Human cytoskeletal a-actinin cDNA was transfected into highly malignant simian virus 40-transformed BALB/c 3T3 (SVT2) cells that express 6-fold lower levels of a-actinin than nontransformed BALB/c 3T3 cells. SVT2 clones expressing various levels of a-actinin were isolated and their structure and tumorigenic properties were determined. Transfected SVT2 clones expressing a-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 a-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 a-actinin, an actin-crosslinking protein that is also localized in cell junctions, may have an effective suppressive ability on the transformed phenotype.Malignant transformation of cells is characterized by alterations in cell growth, adhesion, motility, and cell shape (1). Among the more conspicuous morphological alterations in transformed cells are a round phenotype and a decrease in the number of microfilament bundles (2, 3). The disorganization of the actin filaments in transformed cells is often associated with a reduced expression of microfilament proteins such as tropomyosin (4), gelsolin (5), and vinculin (6). These changes in microfilaments correlate with the ability of cells to grow in suspension in semisolid medium (7).Previous studies have demonstrated a reversion in the transformed phenotype of cancer cells in the presence of a variety of agents and a return to the original malignant behavior upon their removal (8). This "reverse transformation" includes a reversible modulation in cell shape and the organization of the cytoskeleton (9). However, the relationships between the changes in growth properties and the altered cell structure of transformed cells are still unknown (10). Do the characteristic changes in cell morphology of transformed cells result from alterations in the rate of growth or are changes in cell adhesion and cytostructure responsible for disruption of the adhesion-dependent growth control? In this study we addressed this question directly by modulating the expression ofa single actin-associated protein a-actinin in a tumorigenic cell line and determined the consequences of altered a-actinin expression on the phenotype of the cells. a-Actinin is an abundant cytoplasmic actin-binding protein (11) that crosslinks actin filaments in vitro and is found in both muscle and nonmuscle cells (12,13). In striated muscle cells, a-actinin is localized in Z-disks; in smooth muscle cells, it is in dense plaques; and in nonmuscle cells, a-actinin is found along microfilaments (14) and in adherens junctions (AJs), at sites where actin filaments attach to the membrane (15)(16)(17). The role of a-actinin in mediating actin attachment to the membrane is not completely understood. ...

v-Src suppresses SHPS-1 expression via the Ras-MAP kinase pathway to promote the oncogenic growth of cells

“…Candidate type II tumor suppressor genes such as NO3 (Ozaki and Sakiyama, 1994), maspin (Zou et al, 1994), ela®n (Zhang et al, 1995), a-actinin (Gluck et al, 1993), tropomyosin 1 and 2 (Prasad et al, 1993;Gimona et al, 1996) and SSeCKS (Lin and Gelman, 1997) have been isolated. Although none of their anti-tumor functions has been clari®ed yet, their de®nition as tumor suppressors is strengthened by at least two criteria (Lin and Gelman, 1997).…”

Profilin-1 is a negative regulator of mammary carcinoma aggressiveness

“…Changes in actin cytoskeleton in malignant cells have been found to be correlated with altered expression of various ABPs (Vandekerckhove et al, 1990;Button et al, 1995;Wang et al, 1996;Clark et al, 2000;Pawlak and Helfman, 2001). Experimental manipulations restoring the normal expression levels of several different types of ABPs have been successful in suppressing the phenotype of transformed cells (Gluck et al, 1993;Tanaka et al, 1995;Nikolopoulos et al, 2000), therefore implying that deregulation of ABPs directly contribute to oncogene-induced transformed phenotype of tumour cells. In the emerging story on the role of ABPs in cancer, profilin-1 (Pfn1 -a ubiquitously expressed G-actin-binding protein) is found to be expressed at a significantly low level in both human breast cancer tissue and a variety of breast carcinoma cell lines (Janke et al, 2000), pancreatic (Gronborg et al, 2006) and hepatic (Wu et al, 2006) carcinoma cells compared to their normal counterparts.…”

Suppression of src-induced transformed phenotype by expression of tropomyosin-1

“…Changes in the expression of a number of micro®lament-associated proteins during neoplastic transformation have been well documented (Button et al, 1995;Jammey and Chaponnier, 1995). For example, the expression of gelsolin (Vandekerckhove et al, 1990), vinculin (Ferna ndez et al, 1992), a-actinin (GluÈ ck et al, 1993) and tropomyosins (Leonardi et al, 1982;Cooper et al, 1985;Lin et al, 1985;Matsumura et al, 1983), which bind to and/or modulate the polymerization status of actin, is reported to be down regulated as the cells acquire malignant phenotype.…”