Differences In Apoptosis And Cell Cycle Distribution Between Human Melanoma Cell Lines Uacc903 And Uacc903(+6), Before And After Uv Irradiation

Introduction of human chromosome 6 into malignant melanoma cell line UACC903 resulted in generation of the chromosome mediated suppressed cell subline UACC903(+6) that displays attenuated growth rate, anchorage-dependency, and reduced tumorigenicity. We have showed that overexpression of a chromosome 6-encoded tumor suppressor gene led to partial suppression to UACC903 cell growth. We now describe the differences in apoptosis and cell cycle between UACC903 and UACC903(+6) before and after UV irradiation. MTT assay revealed 86.92 +/- 8.24% of UACC903 cells viable, significantly (p < 0.01) higher than 48.76 +/- 5.31% of UACC903(+6), at 24 hr after 254-nm UV irradiation (40 J/M-2). Before UV treatment, flow cytometry analysis revealed 6.06 +/- 0.20% apoptosis in UACC903, significantly (p = 0.01) lower than 6.67 +/- 0.15% in UACC903(+6). The G0/G1, S and G2/M phase cells of UACC903 were, respectively, 54.10 +/- 0.59%, 22.31 +/- 0.50% and 16.85 +/- 0.25%, all significantly (p < 0.01) different from the corresponding percentages (58.82 +/- 0.35%, 20.48 +/- 0.05%, and 13.17 +/- 0.45%) of UACC903(+6). After the UV treatment, UACC903 cells in apoptosis, G0/G1, S, and G2/M became 12.59 +/- 0.17%, 38.90 +/- 0.67%, 19.74 +/- 0.70%, and 27.01 +/- 0.66%, respectively, while UACC903(+6) cells were 24.16 +/- 0.48%, 37.97 +/- 0.62%, 19.20 +/- 0.52%, and 15.69 +/- 0.14%. TUNEL assay revealed 2.31 +/- 0.62% apoptosis in UACC903, significantly (p < 0.01) lower than 9.60 +/- 1.14% of UACC903(+6), and a linear and exponential increase of apoptosis, respectively, in response to the UV treatment. These results indicate that UACC903(+6) cells have a greater tendency to undergo apoptosis and are thus much more sensitive to UV irradiation. Our findings further suggest a novel mechanism for chromosome 6-mediated suppression of tumorigenesis and metastasis, i. e., through increased cell death.