Constitutive interplay of BCl-2, GSH and NF-?B in the modulation of the resistibility against UV-A-induced oxidative damage and cell death in human hepatocellular carcinoma cells

MK Shih, ^a CL Chern, ^a TZ Liu ^b

AIM: (1) To clarify if the expressions of BCl-2, GSH and NF-?B are differentiation status regulated in human hepatocellular carcinoma (HCC) cell lines. (2)To establish the relationship between the capability to resist UV-A-induced oxidative damage and cell death and the interplay of BCl-2, GSH and NF-?B. METHODS: Two types of HCC cell lines with distinct differentiation status, namely: Hep G2 (well differentiated) and SK-Hep-1 (poorly-differentiated) were used. Both cell lines were exposed to various fluences of UV-A irradiation (50-150 KJ/m2). Measurement of MDA (as index of lipid peroxidation) and Trypan Blue Exclusion (as index of cell viability) were carried out by the conventional methods. BCl-2 protein was assayed by the ELISA technique. GSH content was determined fluorometrically. NF-?B was evaluated using EMSA technique. RESULTS: (1) After exposed to a fluence of UV-A irradiation (144 KJ/m2), SK-Hep-1 cells had a 27-fold increases in MDA production as compared to Hep G2 cells (1773ñ114 vs 65ñ1 nmole/106 cells). This is accompanied with a drastic reduction of cell viability in SK-Hep-1 cells, but not in Hep G2 cells. (2) Hep G2 cell was found to express much higher levels of anti-apoptotic BCl-2 protein when compared to SK-Hep-1 cells (204ñ4 vs 58ñ3 Unit/mg protein). (3) A distinct disparity in GSH contents of both types of HCC cells was found (Hep G2: 247ñ3.3 vs SK-Hep-1: 74ñ1.3 õmole/mg protein) and differences in the constitutive expression of ?-glutamylcysteine synthetase heavy subunit (?-GCSh) was found to be associated with this observed phenomenon. (4) Constitutive expression of NF-?B was found to be highly activated in SK-Hep-1, but not in Hep G2 cells. CONCLUSION: Based on these data, we suggest that high BCl-2 and GSH expressions of a HCC cell can bestow excellent resistibility to UV-A-induced oxidative damage and cell death. Conversely, high NF-?B expression may weaken its resistibility toward UV-A irradiation.

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Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Paris, France; February 9 - 12, 2002; in the section on Gene Expression, Part 1.

http://www.cancerprev.org/Journal/Issues/26/101/993/4236