Abstract
Two human lymphoblast cell lines, TK6 and WTK1, were derived from the same cell line (WI-L2) originally isolated from a male human spleen, these two cell lines have very similar cytological and growth characteristics but differ in p53 status; while the TK6 cell line expresses wild-type p53, and mutant-type p53 in WTK1 cell line. After treated with sodium arsenite, apoptosis was found on both of the cells, and TK6 cells were more sensitive than WTK1 cells. Treatment with 40μM sodium arsenite for 4 h and a post-incubation for 24 h in TK6 cells induced obvious sub-G1 apoptosis (60%). Only some sub-G1 cells were found in WTK1 cells after the same treatment (10%). WTK1 cells with normal p53 transfection (WTK1-p53) in same treatment appeared a similar result as that in TK6 cells, 60% sub-G1 apoptosis was found. Also, the survival fractions after arsenite treatment were similar in TK6 and WTK1-p53 cells. In contrast, WTK1 cells were more resistant to sodium arsenite. This indicated that sodium arsenite-induced apoptosis was p53-dependent. On the other hand, more sensitive to sodium arsenite in TK6 and WTK1-p53 cells (normal P53) is not due to more sodium arseinte accumulation or less excretion in these cells. The results show that there was no difference in sodium arsenite accumulation and excretion after treatment for 4 h and in excretion after post-incubation for 2 h among TK6, WTK1-p53 and WTK1 cells. Western blot analysis showed that P53 expression was found in both TK6 and WTK1-p53 cells after x-ray or 40mM sodium arsenite treatment. The highest level (3.9-fold) of untreated control sample on P53 expression appeared in TK6 cells after treatment with sodium arsenite for 4 h plus a post-incubation for 2 h. In WTK1-p53 cells, after the same treatment for 4 h, only 1.2-fold of P53 expression was showed. However, 4.2-fold of P53 expression was found from cells after a further post-incubation for 4 h. There was only 1.5-fold of P53 expression in WTK1 cells after treatment with 80mM sodium arsenite for 4 h, and 2.4-fold of P53 expression in treated cells after 4 h post-incubation. Egr-1 expression (2.1-fold) of untreated control sample was found in WTK1 cells after treatment with 80mM sodium arsenite for 4 h. And, after a post-incubation for 3 h, 2.5-fold Egr-1 expression remained in cells. There was no obvious Egr-1 induction in TK6 and WTK1-p53 cells after 40mM sodium arsenite treatment for 4 h or post-incubation for another 4 h. According to these results, it concluded that Egr-1 may play a relatively important role in mediating arsenic-induced p53-independent apoptosis in WTK1 cells.