HYPERSENSITIVITY OF HUMAN TESTICULAR-TUMORS TO ETOPOSIDE-INDUCED APOPTOSIS IS ASSOCIATED WITH FUNCTIONAL P53 AND A HIGH BAX-BCL-2 RATIO

Metastatic testicular cancers are curable, whereas bladder cancers and most other solid tumors are not. Cell lines derived from human testic ular (GH, GCT27, and 833K) and bladder (RT4, RT112, and HT1376) tumors retain this differential chemosensitivity in vitro. We have investiga ted the hypothesis that differential sensitivity to chemotherapy is re lated to differences in the threshold of susceptibility to undergoing apoptosis. Sensitivity to etoposide was not directly related to the fr equency of DNA strand breaks. DNA damage was on average 2-fold greater in the testicular than the bladder tumor cell lines; in contrast, the testicular tumor lines were Ii-fold more sensitive to etoposide cytot oxicity than the bladder tumor lines (IC90 values of 19 +/- 6 versus 2 93 +/- 180 mu M, respectively). Using equidamaging (550 rad equivalent s) etoposide treatments, the percentage of cells that underwent drug-i nduced apoptosis was on average higher in the testicular tumor cell li nes than the bladder tumor cell lines. The testicular tumor lines have two characteristics that could confer sensitivity to drug-induced apo ptosis. First, they have functional p53: the product of the p53-depend ent gene waf-1 was increased after etoposide treatment. Second, the te sticular tumor lines expressed relatively high levels of the apoptosis -promoting protein Bar, but there was no expression of the suppressor of apoptosis Bcl-2. In contrast, only one of the three bladder cell li nes (RT4) had functional p53, and all of the bladder lines had readily detectable levels of Bcl-2 and low levels of Bar. In the testicular c ell lines, increases in p53 and p53-transactivated genes were associat ed with apoptosis but not arrest in G(1). In contrast, in the bladder cell line (RT4), increases in p53 and Waf-1 were associated with both arrest in G(1) and apoptosis. The differences in the ratio of Bax:Bcl- 2 could contribute to the differential sensitivity of the two tumor ty pes. However, in contrast to earlier reports, the ratio of Bar and Bcl -2 was not perturbed by DNA damage.