Differential regulation of stress proteins by high hydrostatic pressure, heat shock, and unbalanced calcium homeostasis in chondrocytic cells

High hydrostatic pressure (HP) has recently been shown to increase cellular heat shock protein 70 (Hsp70) level in a specific way that does not involv e transcriptional activation of the gene, but rather the stabilisation of t he mRNA for Hsp70. in this study, we investigated whether there are other o bservable changes caused by HP stress, and compared them with those induced by certain other forms of stressors. A chondrocytic cell line T/C28a4 was exposed to 30 MPa continuous HP, heat shock at 43 degreesC, and increased c ytosolic calcium concentration by the addition of sarco-endoplasmic reticul um Ca2+ ATPase inhibitor thapsigargin (25 nM) or calcium ionophore A23187 ( 1 muM) in the cultures. The protein synthesis was studied by in vitro metab olic labelling followed by one- and two-dimensional polyacrylamide gel elec trophoresis, and mass spectrometry was utilized to confirm the identity of the protein spots on two-dimensional gels. Continuous 30 MPa HP increased r emarkably the relative labelling of Hsp70. labelling of Hsp90 was also incr eased by 15-20%, although no clear change was evident at the protein level in Western blots. Elevated intracellular Ca2+ concentration induced by thap sigargin and calcium ionophore A23187 increased mainly the synthesis of glu cose-regulated protein 78 (Crp78/BiP), whereas Hsp70 and Hsp90 were decreas ed by the treatment. Heat shock was the strongest inducer of Hsp70 and Hsp9 0. This study further confirmed the induction of Hsp70 in chondrocytic cell s exposed to high HP, but it also showed that calcium-mediated responses ar e unlikely to cause the stress response observed in the hydrostatically pre ssurized cells. (C) 2000 Wiley-Liss. Inc.