AbstractThe cellular heat shock response leads to the enhanced synthesis of a family of heat shock proteins and the development of thermotolerance. In CHO cells, however, heat shock also leads to enhanced synthesis of a 50 kD glycoprotein and elevated activity of N‐acetylgalactosaminyltransferase (GalNAcT). In this study we showed increased GalNAcT activity during thermotolerance expression in all of five mammalian cell lines included in the study. However, there was no simple correlation between cellular heat sensitivity of unheated control cells and basal levels of GalNAcT activity, measured toward the same exogenous acceptor apomucin. Although GalNAcT was elevated in thermotolerant cells, GalNAcT activity itself did not exhibit thermotolerance in terms of reduced sensitivity to heat inactivation. The increase in GalNAcT activity after heating was similar in exponentially growing and plateau‐phase cultures and was inhibited neither by cycloheximide nor actinomycin D. However, the inhibitors by themselves also increased GalNAcT activity in unheated control cells. Chemical inducers of ther‐motolerance (arsenite and diamide) increased GalNAcT activity, but the increase was modest when compared to that following hyperthermia. In addition to GalNAcT, two other glycosyltransferases with specificity for O‐glycans, α1,2‐fuco‐syltransferase and α2,6‐sialyltransferase, also showed increased activity after hyperthermia and during thermotolerance development. Together with previously published data, these results support the hypothesis that heat‐induced activation of O‐glycan‐specific glycosyltransferases plays a physiological role in the cellular heat shock response and in thermo
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