Hyperthermia-induced apoptosis in two rat yolk sac tumor cell lines with different radiothermosensitivity in vitro

We investigated cell susceptibility to hyperthermia-induced apoptosis in tw o rat yolk sac tumor cell lines (RYSTs) and attempted to correlate this wit h the known potentially relevant molecular determinants of apoptosis, p53 p rotein status, Bcl-2 family of proteins and heat shock proteins (Hsp). Pare nt cell line, NMT-1 (carrying wild-type p53 gene) was radiosensitive but th ermoresistant compared to the variant cell line, NMT-1R (mutated type p53), which was isolated from NMT-1 by repeated radiation exposure. Induction of apoptosis by hyperthermia at 43 degreesC was morphologically detected in b oth RYSTs using hematoxylin and eosin, and TUNEL staining and additionally confirmed by DNA ladder formation (the cleavage of DNA into oligonucleosoma l fragments). Western blot analysis showed an increase in expression of p53 , p21(WAF1/CIP1), Hsp70 proteins in both cell lines after heat-shock at 43 degreesC for 30 min. Hsp90 expression increased in NMT-1 but was not affect ed by heating in NMT-1R cells, whereas hyperthermia exerted no effect on th e endogenous expression of Pax. Bcl-2 protein could not be detected in eith er RYST. These results suggest that hyperthermia induced apoptosis in both NMT-1 and NMT-1R and apoptosis in RYSTs may be independent of p53-dependent signaling pathway.