Expression profile of the tumor suppressor genes DLC-1 and DLC-2 in solid tumors

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.