Hyperthermic induction of apoptosis in malignant fibrous histiocytoma cells: possible involvement of a p53-independent pathway in the induction of bax gene.

We have previously reported the unique heat sensitivity of a cell line of malignant fibrous histiocytoma cells, the MFH-2NR cell line. In the present study, treatment of MFH-2NR cells, at 43 degrees C for 1 h evoked typical apoptosis in these cells, which showed characteristic morphological changes, such as internucleosomal DNA fragmentation (DNA ladders), cell shrinkage, and chromatin condensation. Under these conditions, we examined p53 and bax protein levels, and p53 and bax mRNA expression to assess the potential relationship between these two proteins for the induction of apoptosis. The p53 protein, which is usually detected in trace amounts in normal cells, was highly expressed in untreated MFH-2NR cells, and the level did not increase after heat treatment, whereas the bax protein level increased from 30 min after the treatment. No change in p53 mRNA was found, but a transient increase in bax mRNA, peaking at 30 min, was detected by Northern blotting. DNA sequence analysis of the p53 gene from MFH-2NR cells demonstrated a GGG right arrow GAG homozygous point mutation in codon 242 of exon 6. These results suggest that the expression of bax protein and mRNA was augmented by a p53-independent pathway in the hyperthermia-induced apoptosis of MFH-2NR cells.