Heat-stress proteins of rat lung endothelial and mammary adenocarcinoma cells

A rat mammary adenocarcinoma cell clone, MTC, and a rat lung endothelial cell clone, RLE cl.4, both syngeneic to the Fisher 344 rats, were compared for proteins synthesized at 37°C and after a 1-h, 42°C heat dose. The heat stress-induced or -enhanced synthesis of a series of molecular mass groups and isoelectric point species (isomers) was observed in both equilibrium and nonequilibrium two-dimensional gel electrophoresis. Tumor and endothelial cell heat-stress proteins (hsp) were strikingly similar with most hsp in 11 or 13 molecular mass groups having from 1 to 12 major isomers. In comparing the two cell types, 6 of about 23 major hsp isomers appeared different in equilibrium pH gels, with tumor cells seemingly exhibiting less synthesis of these 6 isomers. Four additional endothelial cell hsp isomers were apparent in nonequilibrium pH gels. Since two of these later hsp can be found at higher heat doses in tumor cells, some of these apparent differences between tumor and endothelial cells may be attributable to different dose ranges for induction of hsp. Fluorograms and silver-stained gels showed that several hsp were being synthesized at appreciable levels in unheated cells. However, there were hsp whose synthesis appeared to be de novo rather than representing enhanced synthesis of existing proteins. These last two observations were made in both tumor and normal cells. The constitutive levels of hsp synthesis appeared to be generally similar in unheated tumor and normal cells in vitro with few exceptions. These results indicate the presence of few unique hsp in syngeneic tumor and normal cells in vitro. However, focusing subsequent studies on the few differences may lead to insights concerning hyperthermic biology of tumor and normal cells, phenotypic differences between these cells, and roles of some hsp.