CHARACTERIZATION OF HUMAN PROXIMAL TUBULAR CELLS AFTER HYPOXIC PRECONDITIONING - CONSTITUTIVE AND HYPOXIA-INDUCED EXPRESSION OF HEAT-SHOCK-PROTEINS HSP70(A,-B,-AND-C), HSC70, AND HSP90

In animal models of cardiac or cerebral ischemic preconditioning, indu ction of heat shock proteins (HSPs), especially HSP70, correlates with protection from subsequent injury. The extent of HSP70 induction afte r stress correlates inversely with initial HSP70 levels. Primate cells , unlike nonprimate cells, express high basal levels of HSP70; thus, p rimate cells may respond differently to preconditioning than nonprimat e cells. We have demonstrated that exposing cultured human proximal tu bular epithelial cells (PTEC) to 12 h of hypoxia followed by a 24-h re covery period (hypoxic preconditioning) induces resistance to subseque nt hypoxic injury. Herein, we characterize the expression of HSP70, HS P90, and heat shock cognate-70 (HSC70) in PTEC under basal conditions and after hypoxic preconditioning. By Northern blot analysis, we demon strate that hypoxic preconditioning of PTEC increases mRNA for HSP70 > HSP90 > HSC70. With reverse transcription and polymerase chain reacti on, mRNA transcripts from three different HSP70 genes (HSP70 A, B, and C) were detected in unstressed PTEC. Transcripts hom these genes were also detected in freshly isolated human renal cortex, indicating that all three genes are expressed in vivo. By Western blot analysis, we d emonstrate that PTEC express high basal levels of HSP70, HSC70, and HS P90. Hypoxic preconditioning did not lead to a significant increase in protein content of any of these HSPs, despite increased mRNA levels. This suggests that HSP accumulation cannot account for the development of cytoresistance after hypoxic preconditioning in PTEC. However, hig h basal expression of HSP70 in human PTEC may contribute to their inna te resistance for hypoxia. (C) 1997 Academic Press.