Importance of Bak for celecoxib-induced apoptosis.
The selective cyclooxygenase-2 (COX-2) inhibitor celecoxib constitutes the prototype of pro-apoptotic agents acting through the intrinsic death pathway in a Bcl-2 independent manner. To gain further insight into celecoxib-mediated apoptosis regulation at the level of the mitochondria we tested in how far the crucial pro-apoptotic Bcl-2 proteins Bak and Bax were involved using clones of the Bax-deficient Jurkat T-lymphoma cell model either expressing Bak (Jurkat Bak positive) or being negative for Bak (Jurkat Bak negative), or overexpressing Bcl-2 (Jurkat Bcl-2). Celecoxib induced substantial apoptosis in Jurkat Bak-positive cells. Overexpression of Bcl-2 had only limited protective effects. However, loss of Bak-expression conferred almost complete resistance of Jurkat cells to celecoxib-induced apoptosis. Neither enhanced celecoxib-concentrations nor prolonged incubation times were sufficient to normalize apoptotic rates upon celecoxib-treatment in these Bak/Bax-negative cells. In line with that observation, siRNA-mediated silencing of Bak in the Bak-positive Jurkat cells largely reduced the extent of celecoxib-induced cell death. Interestingly, in celecoxib-sensitive Bak-positive cells, celecoxib-treatment resulted in down-regulation of the anti-apoptotic Bcl-2 protein Mcl-1 which may contribute to celecoxib-mediated activation of Bak-dependent apoptosis. Taken together our data clearly show for the first time the functional relevance of Bak for celecoxib-induced apoptosis in Bax-deficient Jurkat T-lymphoma cells.
Müller
Arndt-Christian
AC
Department of Radiation Oncology, University of Tübingen, Hoppe-Seyler-Strasse 3, D-72076 Tübingen, Germany.
Handrick
René
R
Elsaesser
Simon Johannes
SJ
Rudner
Justine
J
Henke
Guido
G
Ganswindt
Ute
U
Belka
Claus
C
Jendrossek
Verena
V
D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D000068579:Celecoxib; D004305:Dose-Response Relationship, Drug; D006801:Humans; D019169:Jurkat Cells; D024101:Mitochondrial Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D011720:Pyrazoles / Q000633:toxicity*; D013449:Sulfonamides / Q000633:toxicity*; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*
C494772:BAK1 protein, human; D024101:Mitochondrial Proteins; D011720:Pyrazoles; D013449:Sulfonamides; D050998:bcl-2 Homologous Antagonist-Killer Protein; D000068579:Celecoxib