Screening for genes involved in tissue invasion based on placenta formation and cancer cell lines with low and high metastatic potential

Suppression of B3GNT7 gene expression in colon adenocarcinoma and its potential effect in the metastasis of colon cancer cells

The cell surface sialyl Lewis a (sLe(a)) and sialyl Lewis x (sLe(x)) antigens, which are built on the terminals of glyco-structures called poly-N-acetyllactosamine (LacNAc) chains, have been shown to play a critical role in the metastasis of colon cancer. In the present investigation, expression of the B3GNT7 gene, which encodes a β-1,3-N-acetylglucosaminyltransferase that mainly acts on and extends sulfated poly-LacNAc chains, was found to be markedly suppressed during the oncogenetic processes associated with colon cancer. DNA methylation in the promoter region of the B3GNT7 gene was found to play a significant role in the suppression of the B3GNT7 gene in colon cancer cells. The results obtained from Transwell experiments and the nude mice xenograft model demonstrated that ectopic expression of the B3GNT7 gene in colon cancer cells diminished the migration capability and the liver-metastasis potential, respectively, of colon cancer cells. Flow cytometric analysis showed that expression of cell surface sLe(a) and sLe(x) antigens was decreased in colon cancer cells when the B3GNT7 gene was ectopically expressed. Taken together, the results of the present investigation suggest a link between suppression of B3GNT7 gene expression and elevation of sLe(a)/sLe(x) antigen expressions on the surface of cells and that this consequently promotes the metastasis potential of cancer cells as part of the colon cancer oncogenetic process.

Identification of differentially expressed genes in isogenic highly metastatic and poorly metastatic cell lines of R3230AC rat mammary adenocarcinoma

Tumour metastasis occurs as a result of a cascade of events including alterations in the expression of various genes. The identification of such genes is essential to understanding formation of metastasis. In a previous study, highly metastatic (LN4.D6) and poorly metastatic (CAb.D5) cell lines were obtained from the rat mammary adenocarcinoma cell line R3230AC. Subtractive hybridization was used to identify differentially expressed genes between these two cell lines. We identified eight cDNA clones in CAb.D5 and six cDNA clones in LN4.D6 that were differentially expressed. One of the cDNA clones in each cell line had no homology with known sequences. Expression patterns of these differentially expressed genes were examined in a pair of rat mammary and prostate adenocarcinoma cell lines. Compared with cell lines examined, cDNA FF-10 was only expressed in CAb.D5; however, cDNA RB-8, RE-1, RF-5 were only expressed in the highly metastatic LN4.D6. No correlation was observed between expression patterns of the differentially expressed genes and metastatic potential of these cells. However, differential expression of genes, especially cytokeratins (CK8 and CK5) and collagens (III and IV) between highly metastatic and low metastatic rat mammary adenocarcinoma cell lines might initiate further investigation of these genes in metastatic process.

BRPK, a novel protein kinase showing increased expression in mouse cancer cell lines with higher metastatic potential

A novel protein kinase named BRPK was isolated and partially characterized. BRPK was expressed at a higher level in three carcinoma cell lines with higher metastatic potential. Mouse and human BRPK cDNAs are well conserved and encode 580 and 581 amino acids, respectively. BRPK has a serine/threonine-type protein kinase domain, and the recombinant proteins of BRPK were capable of autophosphorylation. The results of a comparative sequence analysis indicated a possible link of BRPK to BRAP2. BRAP2 is known to bind the nuclear localization signal of BRCA1. We cloned mouse BRAP2 cDNA and showed the presence of isoforms.

A novel beta1,3-N-acetylglucosaminyltransferase involved in invasion of cancer cells as assayed in vitro

Using a two-step screening system for genes involved in tissue invasion [Kataoka et al., Cancer Lett. 163(2) (2001) 213], we identified a cDNA whose expression level was higher in mouse placenta at later stages of gestation and in sublines of cancer cells with low degrees of invasiveness. The deduced amino acid sequence showed relatively high similarity with beta1,3-N-acetylglucosaminyltransferase2 approximately 5 (beta3GnT2 approximately 5), and the protein was therefore named beta3GnT7. A possible human ortholog was identified and its chromosomal locus was determined to be 2q37.1. In the mouse, beta3GnT7 was most strongly expressed in the placenta and colon. Moderate amounts of mRNA were detected in the lung, stomach, small intestine, and kidney. The expression of beta3GnT7 was very weak in the cerebrum, cerebellum, heart, and testis. Transfection of the antisense oligonucleotide significantly enhanced the motility of a lung cancer cell line (KLN205-MUC1) in a monolayer compared to the controls. Furthermore, the antisense oligonucleotide increased the number of cells that invaded the matrix-coated membrane in an in vitro invasion model. These results indicate that beta3GnT7 may play a role in preventing cells from migrating out of the original tissues and invading surrounding tissues.