Restoration of DLC-1 gene expression induces apoptosis and inhibits both cell growth and tumorigenicity in human hepatocellular carcinoma cells

Abstract

The gene deleted in liver cancer-1 (DLC-1) is located on human chromosome 8p21-22, a region thought to harbor tumor suppressor genes on the basis of its frequent deletion or loss of heterozygosity in a variety of human cancers, including hepatocellular carcinoma (HCC). Deletion or altered expression of DLC-1 is common in HCC. In the current study, the subcellular localization of Dlc-1 protein was determined by immunostaining with antibody to DLC-1 and the possible tumor growth suppressor activity of DLC-1 was investigated by examining the effects of of DLC-1 cDNA transfection in two human HCC cell lines lacking expression of the endogenous gene. The results show that Dlc-1protein is localized in the cell cytoplasm, and the restoration of DLC-1 expression in HCC cells resulted in caspase-3-mediated apoptosis, inhibition of cell growth and invasiveness in vitro as well as in reduction of the ability of the cells to form tumors in athymic nude mice. These observations thus support the notion that Dlc-1 protein is involved in hepatocarcinogenesis and has oncosuppressive activity in HCC.

Inhibition of cell proliferation, induction of apoptosis, reactivation of DLC1, and modulation of other gene expression by dietary flavone in breast cancer cell lines

“…Although ectopic expression of DLC-1 in HCC cells was previously shown to induce accumulation of hypodiploid (apoptotic) cells, arrest of the cell cycle at G 2 -M was not observed [8]. The flavone-induced G 2 -M arrest apparent in breast cancer cells in the present study was likely mediated by p21 Waf1 , which induces such arrest in a variety of cell types [33,34,35,36].…”

“…Exposure of HT-29 cells to 150μM flavone for 24 h induced a nearly five fold increase in the amount of DLC-1 mRNA (Fig. 1) We next examined the effect of the same treatment in several other human cancer cell lines that, like HT-29 [13], express DLC1 at a low level [6,8,17]. Among these cell lines, flavone induced up-regulation of DLC-1 mRNA in MDA-MB-468, MDA-MB-361, and BT20 breast carcinoma cell lines but not in the immortal nontumorigenic breast epithelial cell line MCF10F (Fig.…”

“…Given that ectopic expression of DLC-1 in various tumor cell types has been shown to perturb the cell cycle, inhibit cell growth, or induce apoptosis [4,6,7,8], we examined whether flavone exerts similar effects in breast carcinoma or nontumorigenic breast epithelial cell lines. Flavone treatment resulted in inhibition of the proliferation of MDA-MB-468, MDA-MB-361, BT20, and MCF10F cells that was apparent as early as 24 h and increased progressively for up to 4 days (Fig.…”

“…Indeed, DLC1 is emerging as a bona fide tumor suppressor gene, given that ectopic expression of DLC-1 in several common types human cancer cells that do not express the endogenous gene inhibits cell proliferation and induces caspase-3-mediated apoptosis in vitro as well as abolishes or reduces tumorigenicity in vivo [2,3,4,5,6,7,8]. Limited information is available on factors that regulate transcription of endogenous DLC1, however.…”

BNIP-Sα induces cell rounding and apoptosis by displacing p50RhoGAP and facilitating RhoA activation via its unique motifs in the BNIP-2 and Cdc42GAP homology domain

“…For examples, inactivation of RhoA has been reported to cause apoptosis in epithelial cells (Fiorentini et al, 1998a, b), fibroblasts (Bobak et al, 1997) and differentiating myoblasts (Reuveny et al, 2004), while others demonstrated that RhoA activation instead lead to apoptosis in endothelial cells (Bayless and Davis, 2004), neurons and glial cells (Dubreuil et al, 2003), and fibroblast cells (Subauste et al, 2000;Ueda et al, 2004). Similarly, there are studies showing that both restoration (Zhou et al, 2004) and knockout (Wang et al, 2005a, b) of RhoGAP proteins could result in cell death. Taken together, these data demonstrates the importance of maintaining balanced RhoA activity in cell survival.…”