INTRACELLULAR-DISTRIBUTION OF HEAT-INDUCED STRESS GLYCOPROTEINS

Cellular heat stress results in elevated heat-shock protein (HSP) synt hesis and in thermotolerance development. Recently, we demonstrated th at protein glycosylation is also an integral part of the stress respon se with the identification of two major stress glycoproteins, GP50, as sociated with thermotolerance, and P-SG67, the ''prompt'' stress glyco protein induced immediately during acute heat stress. In the present s tudy, we characterized the subcellular location and redistribution of these proteins during the cellular injury and recovery phase. In unhea ted and heated CHO cells, both stress glycoproteins were present in ea ch subcellular fraction isolated by differential centrifugation. Howev er, the subcellular redistribution in the course of cellular recovery after heat stress was specific for each stress glycoprotein. GP50 was present in all subcellular fractions before heat stress, but showed re latively little redistribution after heat stress. By 24 h of recovery following stress, GP50 showed partial depletion from lysosomes and mic rosomes, and was mainly present in the mitochondria. Glycosylated P-SG 67 was redistributed in a more complex fashion. It was seen predominan tly in the lysosomes and microsomes immediately following heat-stress, but after 6 h of recovery following heat stress, it largely disappear ed from the microsomes and was present mainly in the cytosol. By 24 h of recovery following heat stress, it was found predominantly in the n ucleus-rich fraction and mitochondria. The localization of GP50 and P- SG67 by subcellular fractionation is consistent with immunolocalizatio n studies and contrasts with the translocation of HSP70 after heat str ess from cytosol to nuclei and nucleoli. These results reflect a chara cteristic distribution for each stress glycoprotein; their presence in virtually all subcellular fractions suggests multifunctional roles fo r the various stress glycoproteins in the cellular heal stress respons e. (C) 1997 Wiley-Liss, Inc.