1Laboratory of Cancer Research, Department of Biomedical Research, National Institute of Health, Seoul, Korea. 2Department of Biology, Sangmyung University, Seoul, Korea.
ABSTRACT
PURPOSE: Apoptosis is a physiological mechanism for deleting cells from the body for development and homeostasis.
Exogenous cytokines such as tumor necrosis factor alpha (TNFalpha) and transforming growth factor beta (TGF beta) are known to modulate apoptosis, thus can provide a new therapeutic modality for various malignancies. We studied whether TNFalpha or TGFbeta can induce apoptosis or exert antiproliferative effect on human gastric cancer cell line (AGS) and which genes are involved in the cytokine-induced apoptotic pathway.
MATERIALS AND METHODS: To examine the effect of TNFalpha or TGF beta on AGS cell line (human gastric adenocarcimoma), we performed following tests; MTT test, trypan blue dye exclusion assay and colony forming efficiency. Total DNA was extracted from the TNFalpha-treated AGS cells and DNA ladder was detected as the hallmark of apoptosis, and flow cytometry analysis was performed for another apoptotic index. The effects of TNFalpha on c-myc expression was observed using RT-PCR.
RESULTS: TNFalpha suppressed AGS cell growth, in a time- and dose-dependent manner, but TGFbeta had no effect on AGS cell growth. Electrophoretic analysis of total cellular DNA revealed the pattern of internucleosomal DNA cleavage, which is specific for apoptosis and the effect was observed from 24 to 72 hrs after 50 ng/ml TNFalpha treatment.
Time-dependent increse of apoptotic cells by TNFalpha was detected by flow cytometry analysis. Morphological changes such as cell to cell contacts and extension of cell processes were observed in TNFalpha-treated AGS cells.
RT-PCR using c-myc primers showed thatthe mRNA levels were increased 6 hrs after TNFalpha treatment and persisted for 72 hrs.
CONCLUSION: It is suggested that TNFalpha, but not TGF beta, functions as an important inducer of apoptosis in AGS cell line, and c-myc may function as a critical endogenous activator of the pathway leading to cell death of AGS cells.
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