12 stimulates apoptosis in epithelial cells through JNK1-mediated Bcl-2 degradation and up-regulation of IκBα

Vijay Yanamadala, Hideyuki Negoro, Lakshman Gunaratnam, Tianqing Kong, Bradley M. Denker

Research output: Contribution to journalArticlepeer-review

32 Scopus citations

Abstract

Apoptosis is an essential mechanism for the maintenance of somatic tissues, and when dysregulated can lead to numerous pathological conditions. G proteins regulate apoptosis in addition to other cellular functions, but the roles of specific G proteins in apoptosis signaling are not well characterized. Gα12 stimulates protein phosphatase 2A (PP2A), a serine/threonine phosphatase that modulates essential signaling pathways, including apoptosis. Herein, we examined whether Gα12 regulates apoptosis in epithelial cells. Inducible expression of Gα12 or constitutively active (QL)α12 in Madin-Darby canine kidney cells led to increased apoptosis with expression of QLα12, but not Gα12. Inducing QLα12 led to degradation of the anti-apoptotic protein Bcl-2 (via the proteasome pathway), increased JNK activity, and up-regulated IκBα protein levels, a potent stimulator of apoptosis. Furthermore, the QLα12-stimulated activation of JNK was blocked by inhibiting PP2A. To characterize endogenous Gα12 signaling pathways, non-transfected MDCK-II and HEK293 cells were stimulated with thrombin. Thrombin activated endogenous Gα12 (confirmed by GST-tetratricopeptide repeat (TPR) pull-downs) and stimulated apoptosis in both cell types. The mechanisms of thrombin-stimulated apoptosis through endogenous Gα12 were nearly identical to the mechanisms identified in QLα12-MDCK cells and included loss of Bcl-2, JNK activation, and up-regulation of IκBα. Knockdown of the PP2A catalytic subunit in HEK293 cells inhibited thrombin-stimulated apoptosis, prevented JNK activation, and blocked Bcl-2 degradation. In summary, Gα12 has a major role in regulating epithelial cell apoptosis through PP2A and JNK activation leading to loss of Bcl-2 protein expression. Targeting these pathways in vivo may lead to new therapeutic strategies for a variety of disease processes.

Original languageEnglish (US)
Pages (from-to)24352-24363
Number of pages12
JournalJournal of Biological Chemistry
Volume282
Issue number33
DOIs
StatePublished - Aug 17 2007

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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