Gα12 Specifically Regulates COX-2 Induction by Sphingosine 1-Phosphate

Abstract

Sphingosine 1‐phosphate (S1P), a sphingolipid released from activated platelets, stimulates COX‐2 induction. S1P activates GPCRs coupled to Gα family members. This study investigated whether Gα12 family regulates COX‐2 induction by S1P and if so, what the molecular basis is for its COX‐2 regulation. Gene knockout or chemical inhibitor experiments revealed that S1P induction of COX‐2 requires Gα12, but not Gα13, Gαq or Gαi/o. The specific role of Gα12 in COX‐2 induction by S1P was verified by promoter luciferase assay, Gα12 transfection and siRNA experiments. Absence of Gα12 inhibited NF‐κB DNA binding activity. Immunocytochemistry, ChIP and NF‐κB site mutation analyses confirmed the functional role of NF‐κB in COX‐2 gene transcription by S1P. Gα12 deficiency unaffected S1P‐mediated IκBα phosphorylation, but abrogated its ubiquitinylation and degradation, thereby abolishing p65 nuclear translocation. Chemical inhibition of S1P‐activated JNK abolished IκBα ubiquitinylation by S1P. Consistently, JNK transfection caused S1P to degrade IκBα during Gα12 deficiency. S1P injection induced COX‐2 in the lungs and livers of mice with an increase in the plasma PGE2, which was prevented by Gα12 gene knockout. Of the Gα proteins coupled to S1P receptors, Gα12 specifically regulates NF‐κB‐mediated COX‐2 induction by S1P, which is mediated by ubiquitinylation and degradation, but not phosphorylation, of IκBα.

S1P/S1P 2 Signaling Induces Cyclooxygenase-2 Expression in Wilms Tumor

“…10 However, in mouse embryonic fibroblast cells, S1P-induced COX-2 expression was specifically regulated by Gα 12 . 9 These findings indicated that S1P-induced COX-2 expression might be cell type-specific.…”

Gα12 Stimulates Apoptosis in Epithelial Cells through JNK1-mediated Bcl-2 Degradation and Up-regulation of IκBα

“…Recently, G␣ 12 -mediated activation of JNK was reported to induce proteasomal degradation of IB␣, leading to the activation of NF-B in the regulation of cyclooxygenase transcription. However, this study did not examine apoptosis (64). Here, we reveal novel suppression of NF-B activity by G␣ 12 through the targeted up-regulation of IB␣ expression.…”

The Role of Sphingolipids in Arachidonic Acid Metabolism

“…Davaille et al (17) have reported that S1P treatment causes strong induction of COX-2, which peaks after 3 h and remains elevated for at least 8 h. In contrast, COX-1 expression is not affected by S1P. Subsequently, Ki et al (18) have reported that Ga 12 specifically regulates nuclear factorkB-mediated COX-2 induction by S1P downstream of S1P 1 , S1P 3 , and S1P 5 , in a process mediated by the c-jun N-terminal kinase-dependent ubiquitination and degradation of IkBa. Although they showed that S1P-induced COX-2 induction was not attenuated by RNA interference of S1P 2 , another group has shown that S1P 2 activation induces COX-2 expression (19).…”