| Abstract: | High intracellular levels of heat shock proteins and enhanced protein glycosylation are two phenomena closely associated with the cellular stress response. GP50 is the major heat-induced glycoprotein in Chinese hamster ovary (CHO) cells; however, GP50 is not well characterized, and its function is unknown. J6 is a gene originally identified in F9 murine teratocarcinoma cells after exposure to retinoic acid. In this study we show that J6 is heat-inducible and codes for a protein that shares characteristics with GP50. Western blotting of CHO cell homogenates, using a J6 polyclonal antibody, showed a single band with a molecular weight identical to that of GP50. Thermotolerant cells showed increased levels of the J6/GP50 protein. Heat-shocked CHO cells also accumulated transiently high levels of J6 mRNA between 2 and 7 h following 10 rain at 45°C. These induction kinetics are similar to those for GP50 labeling with D-3H]mannose and to the activation of major heat shock genes, e.g., hsp70. Hybrid selection of J6 mRNA from CHO cells, followed by in vitro translation, produced a single band on SDS-PAGE with a molecular weight identical to that of deglycosylated GP50. Neither cellular proliferation (exponential growth versus plateau phase) nor the specific heat shock temperature (41.5°C versus 45°C) had significant effects on J6 induction by heat stress. Stress conditions other than hyperthermia, including ethanol, arsenite, and hypoxia, increased J6 mRNA levels. Conversely, J6 mRNA was reduced by quercetin, brefeldin A, okadaic acid, uv, and hydrogen peroxide. Our data support the hypothesis that J6 is a heat shock gene with a gene product identical to the polypeptide moiety of GP50. |
