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Thapsigargin and di-tert-butylhydroquinone induce synergistic stimulation of DNA synthesis with phorbol ester and bombesin in Swiss 3T3 cells.

Authors
Type
Published Article
Journal
The Journal of biological chemistry
Publication Date
Volume
269
Issue
51
Pages
32528–32535
Identifiers
PMID: 7798254
Source
Medline
License
Unknown

Abstract

The specific inhibitors of the endoplasmic reticulum Ca2+ pump, thapsigargin and 2,5-di-tert-butylhydroquinone (DBHQ), stimulated reinitiation of DNA synthesis in synergy with either phorbol 12,13-dibutyrate or bombesin in Swiss 3T3 cells. Maximum stimulation was achieved at 0.5 nM thapsigargin and 7.5 microM DBHQ. Kinetics of [3H]thymidine incorporation were consistent with exit from G0 and entry into S phase. Autoradiography of labeled nuclei showed that the increase in [3H]thymidine incorporation was due to an increase in the proportion of cells entering into DNA synthesis. Down-regulation or selective inhibition of protein kinase C abolished this synergistic stimulation of DNA synthesis. Thapsigargin and DBHQ did not potentiate protein kinase C-mediated signals such as direct phosphorylation of myristoylated alanine-rich C-kinase substrate, activation of mitogen-activated protein kinase, and tyrosine phosphorylation of bands 110,000-130,000 and 70,000-80,000. Thapsigargin and DBHQ caused a marked reduction in the ability of bombesin to induce a rapid and transient increase in intracellular Ca2+ via depletion of total cellular Ca2+, measured by 45Ca2+ content. The synergistic stimulation of DNA synthesis by DBHQ and phorbol 12,13-dibutyrate was dependent on a high concentration of extracellular Ca2+ (ED50 = 410 microM) and was preferentially inhibited by the inhibitor of Ca2+ influx econozole. This suggests a role for Ca2+ entry in growth control. This is the first time that either thapsigargin or DBHQ has been shown to stimulate the reinitiation of DNA synthesis in any target cell.

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