Modulation of cellular glycosidase activity by hyperthermia

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Abstract
We examined the effect of 45 degrees C hyperthermia on the following glycosidases in CHO cells: beta-galactosidase, beta-hexosaminidase, beta-glucuronidase and alpha-mannosidase. Among these, lysosomal alpha-mannosidase exhibited the most dramatic response to hyperthermia with an increase in activity immediately after 45 degrees C hyperthermia. The increase was linearly dose-dependent with a doubling of activity for every 20 min at 45 degrees C. In contrast to alpha-mannosidase, beta-glucuronidase, beta-galactosidase, and beta-hexosaminidase showed only minor alterations in activity, or none, after hyperthermia of 10 to 60 min at 45 degrees C. Induction of thermotolerance enhanced the heat resistance of beta-galactosidase, but caused increased heat sensitivity for alpha-mannosidase. Intracellular beta-galactosidase, measured by histochemical staining, showed a dramatic redistribution in response to mild hyperthermia (10 min, 45 degrees C); the same effect was not observed for beta-glucuronidase. The data argue against non-specific activation of lysosomes by hyperthermia, and suggest that cells contain lysosomal subpopulations that are characterized by different heat sensitivities and variable glycosidase contents.
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