Two physical methods of inducing apoptosis trigger different responses in lymphoma cells
Marcos M. Lee-Hin, Clifford C. Ellingson, Bryron K. Murray and Kim L. O’Neill
Brigham Young University, Provo, UT
Apoptosis or programmed cell death is often a cellular response to physical stress. Apoptotic pathways are diverse and vary according to stress signaling. Inhibition of apoptosis can prevent death, promoting neoplastic transformation and cellular resistance.Additionally, some current cancer regimes try to restore apoptotic balance in the body by inducing apoptosis in carcinomas. Through an enhanced understanding of the pathways that induce apoptosis, more effective cancer treatments could be developed and designed to counter apoptotic resistance in carcinoma cells. In the present study physical stress-induced apoptosis was performed using two different methods: heat shock and UV-radiation. We hypothesized that the two physical methods would induce a similar apoptotic response in each of the five cell lines. Five different lymphoma cell lines (Jurkat, Raji, BW36, Namalwa, and B-JAB) were analyzed using different methods to detect apoptosis including, comet assay and flow cytometry with Annexin V-FITC stain. We established the level of apoptotic induction using both physical agents. From previous experiments with heat shock, it has been established that apoptosis is maximized after one hour at 43 degree Celsius and after a recovery time of 24 hours. For UV-radiation we tested different times of exposures (2, 4, 7, 10, and 14 minutes) using 312nm UV light as well as different incubation times. We found that apoptosis is maximized after 7 minutes of UV-radiation exposure and after a recovery time of 4 hours.(UV照射7分钟后，静置4小时，效果最好） Data from flowcytometry analysis with Annexin-V-FITC showed that lymphoma cell lines responded differently when treated with heat shock than when treated with UV-radiation respectively. Apoptosis with UV-radiation was significantly lower (p<0.05) in all the cell lines than with heat shock. Heat shock induced 71% apoptosis in Jurkat, 68.3% in Raji, 84.3% in BW36, 68% in Namalwa, and 48.1% in B-JAB（热休克诱导凋亡效果最好）. UV-radiation induced 16.75% apoptosis in Jurkats, 17.66% in Raji, 17.59% in BW36, 36.58% in Namalwa,and 11.37% in B-JAB. Data from the flow cytometry and comet assay also confirmed that lymphoma cell lines have a wide spectrum of sensitivity when treated with heat shock. Comet assay data showed similar apoptotic results; in that some cell lines were resistant to heat shock and others were more sensitive to heat shock. We conclude that among the lymphoma cell lines, when apoptosis is induced by different physical agents, the apoptotic response involves alternate pathways. Ongoing research is being performed to assess these pathways and their relationship.