Transforming growth factor-beta1 induced hepatocyte apoptosis--a possible mechanism for growth of colorectal liver metastasis

Copper Alters the Conformation and Transcriptional Activity of the Tumor Suppressor Protein p53 in Human Hep G2 Cells

The tumor suppressor protein p53 plays a role in the molecular response to DNA damage by acting as a DNA-binding transcription factor that regulates specific target genes to arrest the cell cycle, induce repair mechanisms, and initiate apoptotic cell death. To test the effect of copper on the transcriptional activity of p53, Hep G2 cells were transiently transfected with a luciferase reporter gene downstream from multiple p53 response elements. Co-transfection with the p53 gene resulted in a 6-fold increase in luciferase activity, showing that p53 acts as a transcription factor in this system. However, in the presence of copper, luciferase activity was significantly reduced. Oligonucleotide arrays representing 145 known p53-associated genes were hybridized with biotinylated cDNAs from mRNA extracted from control and copper-treated Hep G2 cells. Among the genes that were differentially regulated were fos, RB1, glutathione peroxidase, TGF-β, and 15-lipoxygenase, a gene known to be activated by mutant p53. Although control Hep G2 cells synthesize wild-type p53, immunocytochemistry identified not only wild type, but also mutant p53 in the presence of copper and other agents that induce oxidative damage. Thus, this report not only identifies genes that may play a role in copper-mediated apoptosis, but also suggests that copper-induced oxidative processes result in the synthesis of mutant p53 with altered transcriptional properties.

Portal vein ligation accelerates tumor growth in ligated, but not contralateral lobes

AIM: To investigate the mechanisms of liver growth and atrophy after portal vein ligation (PVL) and its effects on tumor growth.

METHODS: Mice were subjected to PVL, partial hepatectomy, or sham surgery. The morphological alterations, activation of transcription factors, and expression of cytokines and growth factors involved in liver regeneration were evaluated. In a separate set of experiments, murine colorectal carcinoma cells were injected via the portal vein and the effect of each operation on liver tumor growth was studied.

RESULTS: Liver regeneration after PVL and partial hepatectomy were very similar. In ligated lobes, various cytokines, transcription factors and regulatory factors were significantly upregulated compared to non-ligated lobes after PVL. Atrophy in ligated lobes was a result of early necrosis followed by later apoptosis. Tumor growth was significantly accelerated in ligated compared to non-ligated lobes.

CONCLUSION: Tumor growth was accelerated in ligated liver lobes and appeared to be a result of increased growth factor expression.

Relationship between expression of functional Fas ligand in human colon cancer cells and tumor's immune escape

AIM: The evidence has pointed to an abnormal increase in apoptosis among activated Fas-positive lymphocytes, mainly in the periphery of the Fas ligand (FasL)-expressing tumors. On the other hand, to a great extent, the occurrence of tumor is due to the fact that the converted cells cannot undergo a normal process of apoptosis. This study was designed to detect the expression of FasL in human colon carcinoma cells and to determine whether colon cancer cells SW620 could induce apoptosis of lymphocytes by Fas system in vitro.

METHODS: By using immunohistochemical SABC method, the expression of Fas receptor and Fas ligand in SW620 colon carcinoma cell line and Jurkat T cells was observed so as to supply morphological evidence for the functions of Fas receptor and Fas ligand. In an effort to examine the cytotoxicity of effector cells, CytoTox 96â non-radioactive cytotoxicity assay was adopted to measure LDH releasing value after the SW620 cells were co-cultured with the Jurkat T lymphocytes.

RESULTS: It was shown that the Fas ligand of colon carcinoma SW620 cells was positive and the positive substances were distributed in the cell membrane and cytoplasm, and the Fas receptor of colon carcinoma SW620 cells was negative. The Fas receptor and the Fas ligand of Jurkat T lymphocytes turned out to be positive. The positive substances were distributed in the cell membrane. The non-radioactive cytotoxicity assay showed that the apoptotic rate of Jurkat cells remarkably increased with the increase of planting concentration of SW620 and co-cultured time with the Jurkat T lymphocytes. The cytotoxicity was significantly enhanced by PMA and ionomycin.

CONCLUSION: The functional expression of FasL in the colon carcinoma SW620 cells can inversely induce apoptosis of Fas-expressing Jurkat T lymphocytes for immune escape.