Tc. Cheng et Hp. Benton, THE INTRACELLULAR CA2-PUMP INHIBITORS THAPSIGARGIN AND CYCLOPIAZONIC ACID INDUCE STRESS PROTEINS IN MAMMALIAN CHONDROCYTES(), Biochemical journal, 301, 1994, pp. 563-568
Primary cultures of mammalian articular chondrocytes respond to treatm
ent with the intracellular Ca2+-pump inhibitors thapsigargin (TG) and
cyclopiazonic acid by specific changes in protein synthesis consistent
with a stress response. Two-dimensional gel electrophoresis of newly
synthesized proteins confirmed that the response was consistent with t
he induction of glucose-regulated proteins. The effects of low-dose TG
(10 nM), measured by changes in [S-35]methionine labelling of newly s
ynthesized proteins, can first be observed by 10 h and are maximal by
24 h. The pattern of changes induced by TG is shared with cyclopiazoni
c acid, but effects of both perturbants differ significantly from chan
ges induced by heat shock. Upon removal of TG, normal protein synthesi
s is restored by 48 h. Immunoblots showed increased concentrations of
the stress proteins HSP90, HSP72/73 and HSP60 in chondrocytes treated
with TG, but induction of newly synthesized heat-shock proteins by TG
was not apparent on [S-35]methionine-labelled gels. The alterations in
protein synthesis induced by Ca2+-pump inhibitors were unaffected by
BAPTA-AM loading, which clamped cytosolic Ca2+ at resting levels. We c
onclude that inhibition of intracellular Ca2+-pump activity can elicit
a stress response, which has important implications for the interpret
ation of chronic use of Ca2+-pump inhibitors. In particular, the activ
ation of the cellular shock response should be considered in interpret
ing the regulation of protein synthesis and cell survival by Ca2+-pump
inhibitors such as TG.