Promoter methylation of the DLC‑1 gene and its inhibitory effect on human colon cancer

Upregulation of DLC-1 inhibits pancreatic cancer progression: Studies with clinical samples and a pancreatic cancer model

Deleted in liver cancer 1 (DLC-1) serves a vital role in the progression of multiple cancers, including those of the pancreas. Numerous studies have aimed to reveal the anti-cancer mechanisms of the DLC-1 gene, though few have focused on its impact on the development of pancreatic cancer. Using clinical pancreatic cancer samples and pancreatic cancer cell lines, the present study aimed to reveal the role of DLC-1 in this disease. The expression levels of DLC-1 were determined in pancreatic cancer and adjacent normal tissues from patients with pancreatic cancer, indicating a decreased expression level of DLC-1 in cancerous tissues. Using the pancreatic cancer cell line SW1990, the effect of DLC overexpression on cell proliferation, invasive capacity and the cell cycle and were assessed. Using a mouse tumor model, the tumor-progression capacity of transfected and untransfected SW1990 cells was investigated, indicating that DLC-1 transfection reduced the capacity for tumor progression. Thus, the present study indicated that the overexpression of DLC-1 inhibited the proliferation and reduced the invasive capacity of SW1990 cells both in vitro and in vivo, and that it may have significant inhibitory effects on the development of pancreatic cancer.

Aberrant DNA methylation of alternative promoter of DLC1 isoform 1 in meningiomas

DLC1 encodes GTPase-activating protein with a well-documented tumor suppressor activity. This gene is downregulated in various tumors through aberrant promoter hypermethylation. Five different DLC1 isoforms can be transcribed from alternative promoters. Tumor-related DNA methylation of the DLC1 isoform 1 alternative promoter was identified as being hypermethylated in meningiomas in genome-wide DNA methylation profiling. We determined the methylation pattern of this region in 50 meningioma FFPE samples and sections of 6 normal meninges, with targeted bisulfite sequencing. All histopathological subtypes of meningiomas showed similar and significant increase of DNA methylation levels. High DNA methylation was associated with lack of DLC1 protein expression in meningiomas as determined by immunohistochemistry. mRNA expression levels of 5 isoforms of DLC1 transcript were measured in an additional series of meningiomas and normal meninges. The DLC1 isoform 1 was found as the most expressed in normal control tissue and was significantly downregulated in meningiomas. Transfection of KT21 meningioma cell line with shRNA targeting DLC1 isoform 1 resulted in increased activation of RHO-GTPases assessed with pull-down assay, enhanced cell migration observed in scratch assay as well as slight increase of cell metabolism determind by MTT test. Results indicate that isoform 1 represents the main pool of DLC1 protein in meninges and its downregulation in meningiomas is associated with hypermethylation of CpG dinucleotides within the corresponding promoter region. This isoform is functional GAP protein and tumor suppressor and targeting of its expression results in the increase of DLC1 related cell processes: RHO activation and cell migration.

Mutation of the nm23-H1 gene has a non-dominant role in colorectal adenocarcinoma

Nm23-H1 is a metastasis suppressor gene, which is has a reduced expression in patients with digestive system cancer. However, the mechanistic basis for the genetic instability remains unknown. To study the expression of the nm23-H1 gene in patients with colorectal cancer, polymerase chain reaction-single strand conformation polymorphism was used to analyze any point mutation, and immunohistochemistry was used to detect the expression of nm23-H1. Results revealed that all 63 specimens of Chinese human colorectal cancer tissues exhibit no point mutation. Among those 63 specimens, 19 (30%) exhibited positive immunostaining for the nm23-H1 protein and 44 (70%) exhibited negative immunostaining. These observations suggested that the protein and gene expression levels of nm23-H1 are reduced in colorectal cancer compared with the adjacent normal tissues, and the point mutation in the nm23-H1 gene is not the dominant cause of metastatic colorectal cancer.

The Role of Chromosomal Instability and Epigenetics in Colorectal Cancers Lacking β-Catenin/TCF Regulated Transcription

All colorectal cancer cell lines except RKO displayed active β-catenin/TCF regulated transcription. This feature of RKO was noted in familial colon cancers; hence our aim was to dissect its carcinogenic mechanism. MFISH and CGH revealed distinct instability of chromosome structure in RKO. Gene expression microarray of RKO versus 7 colon cancer lines (with active Wnt signaling) and 3 normal specimens revealed 611 differentially expressed genes. The majority of the tested gene loci were susceptible to LOH in primary tumors with various β-catenin localizations as a surrogate marker for β-catenin activation. The immunohistochemistry of selected genes (IFI16, RGS4, MCTP1, DGKI, OBCAM/OPCML, and GLIPR1) confirmed that they were differentially expressed in clinical specimens. Since epigenetic mechanisms can contribute to expression changes, selected target genes were evaluated for promoter methylation in patient specimens from sporadic and hereditary colorectal cancers. CMTM3, DGKI, and OPCML were frequently hypermethylated in both groups, whereas KLK10, EPCAM, and DLC1 displayed subgroup specificity. The overall fraction of hypermethylated genes was higher in tumors with membranous β-catenin. We identified novel genes in colorectal carcinogenesis that might be useful in personalized tumor profiling. Tumors with inactive Wnt signaling are a heterogeneous group displaying interaction of chromosomal instability, Wnt signaling, and epigenetics.

Selenium-binding protein 1 is associated with the degree of colorectal cancer differentiation and is regulated by histone modification

The aim of the present study was to examine the regulation of selenium binding protein 1 (SELENBP1) expression in colorectal cancer (CRC). Samples of cancer tissue and adjacent normal mucosa were collected from 83 CRC patients, and analyzed for SELENBP1 expression by 2D-DIGE, immunoblotting, RT-PCR and immunostaining. Expression levels of SELENBP1, carcinoembryonic antigen (CEA) and alkaline phosphatase (AKP) were determined in cultures of human colon cancer cell lines (SW480, SW620 and HT29) folllowing treatment with i) sodium butyrate (NaB, 2 mM), a differentiation inducer; ii) Trichostatin A (TSA, 0.3 µM), a histone deacetylase inhibitor; or iii) 5'-aza-2'-deoxycytidine (5-Aza-dC, 5 µM), a DNA methylation inhibitor. SELENBP1 expression was found to be downregulated (2.54-fold) in the CRC samples as determined by 2D-DIGE and confirmed by immunoblotting and RT-PCR. SELENBP1 expression was correlated with the degree of differentiation, but not with TNM stage or lymph node metastasis, and was higher in benign polyps (1.97±0.57) than in CRC tissues (0.96±0.59). In the CRC cell lines, NaB treatment led to the upregulation of SELENBP1, CEA and AKP when compared with the untreated cells (2.24- to 4.82-fold). SELENBP1 was also upregulated in cells treated with TSA alone (1.25- to 3.64-fold), or in combination with 5-Aza-dC (1.32- to 4.13-fold). In CRC, the downregulated SELENBP1 expression was reactivated by inducing differentiation. Therefore, SELENBP1 is a potential pharmacological target for individualized CRC treatment.