G alpha sub(13) Stimulates Rho-dependent Activation of the Cyclooxygenase-2 Promoter

Cyclooxygenase-2 (COX-2) gene expression is rapidly increased by cytokines, tumor promoters, and growth factors and is markedly enhanced in various cancer cells. Here, we examine the regulation of COX-2 promoter activity by alpha subunits of heterotrimeric G proteins in NIH 3T3 cells. Using a transient transfection assay with a reporter vector in which the murine COX-2 promoter drives the production of luciferase and expression vectors encoding for alpha subunits of G- proteins, we show that overexpression of wild type and constitutively active G alpha sub(13) and G alpha sub(q) induced transcription from the COX-2 promoter. The highest level of induced luciferase activity (5.8-fold) occurred in cells expressing the constitutively active G alpha sub(13)(Q226L). We also show that expression of a constitutively active mutant of Rho (RhoQ63L) also induced transcription from the COX-2 promoter. Co- expression of Clostridium botulinum C3 toxin specifically blocked induction of the COX-2 promoter by either G alpha sub(13)Q226L or RhoQ63L but did not prevent the activation of this promoter by Ras Rac, v-src, or forskolin. We conclude that G alpha sub(13) signals through a Rho-dependent pathway leading to activation of the COX-2 promoter. This pathway is not inhibited by either cytochalasin D, which disrupts actin filament organization, or genistein, a broad spectrum tyrosine kinase inhibitor, indicating a bifurcation of the signaling pathway used by G alpha sub(13)/Rho to induce COX-2 expression from that used to induce stress fiber formation and tyrosine phosphorylation of focal adhesion proteins.