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Abstract. Several years after the isolation of deleted in liver cancer 1 (DLC-1), a gene that encodes a Rho GTPase activating protein, the closely related DLC-2 gene was identified. DLC-1 and DLC-2 are ~50% identical and share the same SAM-RhoGAP-START domain organization. Since DLC-1 and -2 are located at chromosome regions that are commonly deleted in cancer cells and have been found to function as tumor suppressor genes, we sought to compare their expression profiles in several common types of cancer and to determine whether dlc1 and dlc2 proteins cooperate in tumor development. Using cancer-profiling arrays, we detected for the first time down-regulation of DLC-1 expression in renal, uterine and rectal cancers and down-regulation of DLC-2 expression in lung, ovarian, renal, breast, uterine, gastric, colon and rectal tumors. Since DLC-1 also functions as a metastasis suppressor gene in breast cancer, DLC-1 and DLC-2 expression were examined in a series of primary ductal carcinomas derived from patients with regional lymph node metastases. Using quantitative RT-PCR we detected a significantly lower expression of DLC-1 and DLC-2 in high percentage of tumors, suggesting that deficiency of either DLC gene facilitates dissemination of breast carcinoma cells to secondary sites. We examined DLC-2 expression in DLC-1-negative cell lines derived from human breast, non-small cell lung, and hepatocellular carcinomas, that could be rendered less or non-tumorigenic by ectopic expression of DLC-1. DLC-2 transcripts were detected in all cell lines, indicating that none of the cells were deficient in both members of the DLC family. This comparative expression analysis of DLC-1 and -2 identifies down-regulation of the two emerging bona fide tumor suppressor genes in additional types of solid tumors. The large spectrum of cancers with dysregulated DLC genes underlines the involvement of this family of genes in cancer development.

Background-Dietary flavone was previously shown to increase the expression of deleted in liver cancer-1 gene (DLC-1) in HT-29 colon carcinoma cell line (Proteomics 2004;4:2455-64). DLC-1 that encodes a Rho GTPase-activating protein, functions as a tumor suppressor gene and is frequently inactivated or down-regulated in several common cancers. Restoration of DLC-1 expression suppresses in vitro tumor cells proliferation and tumorigenicity in vivo.Methods-Here, the effect of flavone was examined in several DLC-1-deficient cell lines derived from different types human cancer using assays for cell proliferation, gene expression and transfer.Results-We show that exposure to 15μM flavone increased DLC1 expression in breast but not in liver or prostate carcinoma cells or a nonmalignant breast epithelial cell line. Flavone restored the expression of DLC1 in the breast carcinoma cell lines MDA-MB-468, MDA-MB-361, and BT20 as well as in the colon carcinoma cell line HT-29 all of which are DLC-1-negative due to promoter hypermethylation. We further show that flavone inhibited cell proliferation, induced cell cycle arrest at G2-M, increased p21 Waf1 gene expression, and caused apoptosis. Microarray analysis of these aggressive and metastatic breast carcinoma cells revealed 29 flavone-responsive genes, among which the DNA damage-inducible GADD genes were up-regulated and the proto-oncogene STMN1 and IGFBP3 were down-regulated.Conclusions-Flavone-mediated alterations of genes that regulate tumor cell proliferation, cell cycle, and apoptosis contribute to chemopreventive and antitumoral effects of flavone. Alone or in combination with demethylating agents, flavone may be an effective adjunct to chemotherapy in preventing breast cancer metastasis.